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RFC 7058 - Media Control Channel Framework (CFW) Call Flow Examp


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Internet Engineering Task Force (IETF)                       A. Amirante
Request for Comments: 7058                          University of Napoli
Category: Informational                                      T. Castaldi
ISSN: 2070-1721                                               L. Miniero
                                                                Meetecho
                                                             S P. Romano
                                                    University of Napoli
                                                           November 2013

        Media Control Channel Framework (CFW) Call Flow Examples

Abstract

   This document provides a list of typical Media Control Channel
   Framework call flows.  It aims at being a simple guide to the use of
   the interface between Application Servers and MEDIACTRL-based Media
   Servers, as well as a base reference document for both implementors
   and protocol researchers.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7058.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................4
   2. Conventions .....................................................5
   3. Terminology .....................................................5
   4. A Practical Approach ............................................6
      4.1. State Diagrams .............................................6
   5. Control Channel Establishment ..................................10
      5.1. COMEDIA Negotiation .......................................11
      5.2. SYNC ......................................................14
      5.3. K-ALIVE ...................................................15
      5.4. Wrong Behavior ............................................17
   6. Use-Case Scenarios and Examples ................................20
      6.1. Echo Test .................................................27
           6.1.1. Direct Echo Test ...................................28
           6.1.2. Echo Test Based on Recording .......................30
      6.2. Phone Call ................................................39
           6.2.1. Direct Connection ..................................42
           6.2.2. Conference-Based Approach ..........................44
           6.2.3. Recording a Conversation ...........................51
      6.3. Conferencing ..............................................57
           6.3.1. Simple Bridging ....................................62
           6.3.2. Rich Conference Scenario ...........................66
           6.3.3. Coaching Scenario ..................................75
           6.3.4. Sidebars ...........................................83
           6.3.5. Floor Control ......................................93
      6.4. Additional Scenarios ......................................99
           6.4.1. Voice Mail ........................................100
           6.4.2. Current Time ......................................107
           6.4.3. DTMF-Driven Conference Manipulation ...............112
   7. Media Resource Brokering ......................................126
      7.1. Publishing Interface .....................................127
      7.2. Consumer Interface .......................................136
           7.2.1. Query Mode ........................................137
           7.2.2. Inline-Aware Mode .................................140
           7.2.3. Inline-Unaware Mode ...............................155
      7.3. Handling Media Dialogs ...................................157
           7.3.1. Query and Inline-Aware Mode .......................157
           7.3.2. Inline-Unaware Mode ...............................160
           7.3.3. CFW Protocol Behavior .............................167
   8. Security Considerations .......................................170
   9. Acknowledgments ...............................................180
   10. References ...................................................180
      10.1. Normative References ....................................180
      10.2. Informative References ..................................181

1.  Introduction

   This document provides a list of typical MEDIACTRL Media Control
   Channel Framework [RFC6230] call flows.  The motivation for this
   comes from our implementation experience with the framework and its
   protocol.  This drove us to write a simple guide to the use of the
   several interfaces between Application Servers and MEDIACTRL-based
   Media Servers, and a base reference document for other implementors
   and protocol researchers.

   Following this spirit, this document covers several aspects of the
   interaction between Application Servers and Media Servers.  However,
   in the context of this document, the call flows almost always depict
   the interaction between a single Application Server (which, for the
   sake of conciseness, is called the AS from now on) and a single Media
   Server (MS).  In Section 7, some flows involving more entities by
   means of a Media Resource Broker compliant with [RFC6917] are
   presented.  To help readers understand all the flows (as related to
   both SIP dialogs and Media Control Channel Framework (CFW)
   transactions), the domains hosting the AS and the MS in all the
   scenarios are called 'as.example.com' and 'ms.example.net',
   respectively, per [RFC2606].  The flows will often focus more on the
   CFW [RFC6230] interaction, rather than on the other involved
   protocols, e.g., SIP [RFC3261], the Session Description Protocol
   (SDP) [RFC3264], or RTP [RFC3550].

   In the next paragraphs, a brief overview of our implementation
   approach is described, with particular focus on protocol-related
   aspects.  This involves state diagrams that depict both the client
   side (the AS) and the server side (the MS).  Of course, this section
   is not at all to be considered a mandatory approach to the
   implementation of the framework.  It is only meant to help readers
   understand how the framework works from a practical point of view.

   Once done with these preliminary considerations, in the subsequent
   sections real-life scenarios are addressed.  In this context, first
   of all, the establishment of the Control Channel is dealt with.
   After that, some use-case scenarios involving the most typical
   multimedia applications are depicted and described.

   It is worth pointing out that this document is not meant in any way
   to be a self-contained guide to implementing a MEDIACTRL-compliant
   framework.  The specifications are a mandatory read for all
   implementors, especially because this document follows their
   guidelines but does not delve into the details of every aspect of the
   protocol.

2.  Conventions

   Note that due to RFC formatting conventions, SIP/SDP and CFW lines
   whose content exceeds 72 characters are split across lines.  This
   line folding is marked by a backslash at the end of the first line.
   This backslash, the preceding whitespace, the following CRLF, and the
   whitespace beginning the next line would not appear in the actual
   protocol contents.  Note also that the indentation of the XML content
   is only provided for readability.  Actual messages will follow strict
   XML syntax, which allows, but does not require, indentation.  Due to
   the same limit of 72 characters per line, this document also
   sometimes splits the content of XML elements across lines.  Please be
   aware that when this happens, no whitespace is actually meant to be
   at either the beginning or the end of the element content.

   Note also that a few diagrams show arrows that go from a network
   entity to itself.  It's worth pointing out that such arrows do not
   represent any transaction message but are rather meant as an
   indication to the reader that the involved network entity made a
   decision, within its application logic, according to the input it
   previously received.

3.  Terminology

   This document uses the same terminology as [RFC6230], [RFC6231],
   [RFC6505], and [RFC6917].  The following terms are only a
   summarization of the terms most commonly used in this context and are
   mostly derived from the terminology used in the related documents:

   COMEDIA:  connection-oriented media (i.e., TCP and Transport Layer
      Security (TLS)).  Also used to signify the support in SDP for
      connection-oriented media and the RFCs that define that support
      ([RFC4145] and [RFC4572]).

   Application Server:  an entity that requests media processing and
      manipulation from a Media Server; typical examples are Back-to-
      Back User Agents (B2BUAs) and endpoints requesting manipulation of
      a third party's media stream.

   Media Server:  an entity that performs a service, such as media
      processing, on behalf of an Application Server; typical provided
      functions are mixing, announcement, tone detection and generation,
      and play and record services.

   Control Channel:  a reliable connection between an Application Server
      and a Media Server that is used to exchange framework messages.

   VCR controls:  runtime control of aspects of an audio playback like
      speed and volume, via dual-tone multi-frequency (DTMF) signals
      sent by the user, in a manner that resembles the functions of a
      VCR (video cassette recorder) controller.

4.  A Practical Approach

   In this document, we embrace an engineering approach to the
   description of a number of interesting scenarios that can be realized
   through the careful orchestration of the Media Control Channel
   Framework entities, namely the Application Server and the Media
   Server.  We will demonstrate, through detailed call flows, how a
   variegated bouquet of services (ranging from very simple scenarios to
   much more complicated examples) can be implemented with the
   functionality currently offered, within the main MEDIACTRL framework,
   by the Control Packages that have been made available to date.  The
   document aims at being a useful guide for those interested in
   investigating the inter-operation among MEDIACTRL components, as well
   as being a base reference document for application developers willing
   to build advanced services on top of the base infrastructure made
   available by the framework.

4.1.  State Diagrams

   In this section, we present an "informal" view of the main MEDIACTRL
   protocol interactions, in the form of state diagrams.  Each diagram
   is indeed a classical representation of a Mealy automaton, comprising
   a number of possible protocol states, indicated with rectangular
   boxes.  Transitions between states are indicated through edges, with
   each edge labeled with a slash-separated pair representing a specific
   input together with the associated output (a dash in the output
   position means that, for that particular input, no output is
   generated from the automaton).  Some of the inputs are associated
   with MEDIACTRL protocol messages arriving at a MEDIACTRL component
   while it is in a certain state.  This is the case for 'CONTROL',
   'REPORT' (in its various "flavors" -- pending, terminate, etc.),
   '200', '202', and 'Error' (error messages correspond to specific
   numeric codes).  Further inputs represent triggers arriving at the
   MEDIACTRL automaton from the upper layer, namely the Application
   Programming Interface used by programmers while implementing
   MEDIACTRL-enabled services.  Such inputs have been indicated with the
   term 'API' followed by the message that the API itself is triggering
   (as an example, 'API terminate' is a request to send a 'REPORT'
   message with a status of 'terminate' to the peering component).

   Four diagrams are provided.  Two of them (Figures 1 and 2) describe
   normal operation of the framework.  Figure 3 contains two diagrams
   describing asynchronous event notifications.  Figure 1 embraces the
   MS perspective, whereas Figure 2 shows the AS side.  The upper part
   of Figure 3 shows how events are generated, on the MS side, by
   issuing a CONTROL message addressed to the AS; events are
   acknowledged by the AS through standard 200 responses.  Hence, the
   behavior of the AS, which mirrors that of the MS, is depicted in the
   lower part of the figure.

   Coming back to Figure 1, the diagram shows that the MS activates upon
   reception of CONTROL messages coming from the AS.  The CONTROL
   messages instruct the MS regarding the execution of a specific
   command that belongs to one of the available Control Packages.  The
   execution of the received command can either be quick or require some
   time.  In the former case, right after completing its operation, the
   MS sends back to the AS a 200 message, which basically acknowledges
   correct termination of the invoked task.  In the latter case, the MS
   first sends back an interlocutory 202 message containing a 'Timeout'
   value, which lets it enter a different state ('202' sent).  While in
   the new state, the MS keeps on performing the invoked task.  If the
   task does not complete in the provided timeout, the server will
   update the AS on the other side of the Control Channel by
   periodically issuing 'REPORT update' messages; each such message has
   to be acknowledged by the AS (through a '200' response).  Eventually,
   when the MS is done with the required service, it sends to the AS a
   'REPORT terminate' message.  The transaction is concluded when the AS
   acknowledges receipt of the message.  It is worth pointing out that
   the MS may send a 202 response after it determines that the request
   does not contain any errors that cannot be reported in a later REPORT
   terminate request instead.  After the MS sends a 202 response, any
   error that it (or the API) finds in the request is reported in the
   final REPORT terminate request.  Again, the behavior of the AS, as
   depicted in Figure 2, mirrors the above-described actions undertaken
   at the MS side.  The figures also show the cases in which
   transactions cannot be successfully completed due to abnormal
   conditions; such conditions always trigger the creation and
   transmission of a specific 'Error' message that, as mentioned
   previously, is reported as a numeric error code.

   +------------------+  CONTROL/-  +------------------+ API 202/202
   | Idle/'terminate' |------------>| CONTROL received |---------+
   +------------------+             +------------------+         |
     ^          ^   ^   API 200/200    |     |                   |
     |          |   |                  |     |                   |
     |          |   +------------------+     |                   |
     | 200/-    |      API Error/Error       |                   |
     |          +----------------------------+                   |
     |                                                           |
   +-------------+                                               |
   | Waiting for |                                               v
   |  last 200   |<------------------------+             +------------+
   +-------------+                         |             | '202' sent |
        ^                                  |             +------------+
        |                                  |               |     |
        |                                  +---------------+     |
        | API terminate/                     API terminate/      |
        | REPORT terminate                   REPORT terminate    |
        |                                                        |
      +--------------------+                                     |
      | 'update' confirmed |------+                  API update/ |
      +--------------------+      |                REPORT update |
                ^                 | API update/                  |
                |                 | REPORT update                |
                |                 v                              |
                |   200/-      +---------------+                 |
                +--------------| 'update' sent |<----------------+
                               +---------------+

                 Figure 1: Media Server CFW State Diagram

                 +--------------+   202/-   +--------------+
             +-->| CONTROL sent |---------->| 202 received |
             |   +--------------+           +--------------+
             |        |       |                 |     |
             |        |       |                 |     |
API CONTROL/ |        | 200/- |                 |     |
send CONTROL |        |       |                 |     |
             |        |       | Error/          |     |
+------------------+  |       | Error           |     |
| Idle/'terminate' |<-+       |                 |     |
+------------------+<---------+                 |     |
    ^          ^                                |     |
    |          |            REPORT 'terminate'/ |     |
    |          |                       send 200 |     |
    |          +--------------------------------+     | REPORT 'update'/
    |                                                 | send 200
    | REPORT 'terminate'/                             |
    | send 200                                        |
    |                     +-----------+               |
    +---------------------| 'update ' |<--------------+
                          +-----------+
                            ^      |
                            |      | REPORT 'update'/
                            +------+ send 200

              Figure 2: Application Server CFW State Diagram

                                    +--------------+
                                +-->| CONTROL sent |
                                |   +--------------+
                                |           |
                                |           |
                   API CONTROL/ |           | 200/-
                   send CONTROL |           |
                                |           |
                   +------------------+     |
                   | Idle/'terminate' |<----+
                   +------------------+

                          (Media Server perspective)

           +------------------+  CONTROL/-  +------------------+
           | Idle/'terminate' |------------>| CONTROL received |
           +------------------+             +------------------+
                        ^       API 200/200          |
                        |                            |
                        +----------------------------+

                       (Application Server perspective)

                       Figure 3: Event Notifications

5.  Control Channel Establishment

   As specified in [RFC6230], the preliminary step to any interaction
   between an AS and an MS is the establishment of a Control Channel
   between the two.  As explained in the next subsection, this is
   accomplished by means of a connection-oriented media (COMEDIA)
   [RFC4145] [RFC4572] negotiation.  This negotiation allows a reliable
   connection to be created between the AS and the MS.  It is here that
   the AS and the MS agree on the transport-level protocol to use (TCP /
   Stream Control Transmission Protocol (SCTP)) and whether any
   application-level security is needed or not (e.g., TLS).  For the
   sake of simplicity, we assume that an unencrypted TCP connection is
   negotiated between the two involved entities.  Once they have
   connected, a SYNC message sent by the AS to the MS consolidates the
   Control Channel.  An example of how a keep-alive message is triggered
   is also presented in the following paragraphs.  For the sake of
   completeness, this section also includes a couple of common mistakes
   that can occur when dealing with the Control Channel establishment.

               AS                              MS
               |                               |
               | INVITE (COMEDIA)              |
               |------------------------------>|
               |                  100 (Trying) |
               |<------------------------------|
               |              200 OK (COMEDIA) |
               |<------------------------------|
               | ACK                           |
               |------------------------------>|
               |                               |
               |==============================>|
               | TCP CONNECT (CTRL CHANNEL)    |
               |==============================>|
               |                               |
               | SYNC (Dialog-ID, etc.)        |
               |+++++++++++++++++++++++++++++>>|
               |                               |--+
               |                               |  | Check SYNC
               |                               |<-+
               |                        200 OK |
               |<<+++++++++++++++++++++++++++++|
               |                               |
               .                               .
               .                               .

                  Figure 4: Control Channel Establishment

5.1.  COMEDIA Negotiation

   As a first step, the AS and the MS establish a Control SIP dialog.
   This is usually originated by the AS itself.  The AS generates a SIP
   INVITE message containing in its SDP body information about the TCP
   connection it wants to establish with the MS.  In the provided
   example (see Figure 5 and the attached call flow), the AS wants to
   actively open a new TCP connection, which on its side will be bound
   to port 5757.  If the request is fine, the MS answers by
   communicating to the AS the transport address to connect to in order
   to establish the TCP connection.  In the provided example, the MS
   will listen on port 7575.  Once this negotiation is over, the AS can
   effectively connect to the MS.

   The negotiation includes additional attributes.  The 'cfw-id'
   attribute is the most important, since it specifies the Dialog-ID,
   which in turn will be subsequently referred to by both the AS and the
   MS as specified in [RFC6230].

                     AS                              MS
                     |                               |
                     | 1. INVITE (COMEDIA)           |
                     |------------------------------>|
                     |               2. 100 (Trying) |
                     |<------------------------------|
                     |           3. 200 OK (COMEDIA) |
                     |<------------------------------|
                     | 4. ACK                        |
                     |------------------------------>|
                     |                               |
                     |==============================>|
                     | TCP CONNECT (CTRL CHANNEL)    |
                     |==============================>|
                     |                               |
                     .                               .
                     .                               .

              Figure 5: COMEDIA Negotiation: Sequence Diagram

1. AS -> MS (SIP INVITE)
------------------------
   INVITE sip:MediaServer@ms.example.net:5060 SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.1:5060;\
           branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060
   Max-Forwards: 70
   Contact: <sip:ApplicationServer@203.0.113.1:5060>
   To: <sip:MediaServer@ms.example.net:5060>
   From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
   Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
   CSeq: 1 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
   Content-Type: application/sdp
   Content-Length: 203

   v=0
   o=lminiero 2890844526 2890842807 IN IP4 as.example.com
   s=MediaCtrl
   c=IN IP4 as.example.com
   t=0 0
   m=application 5757 TCP cfw
   a=connection:new
   a=setup:active
   a=cfw-id:5feb6486792a

2. AS <- MS (SIP 100 Trying)
----------------------------
   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
           branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060
   To: <sip:MediaServer@ms.example.net:5060>;tag=499a5b74
   From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
   Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
   CSeq: 1 INVITE
   Content-Length: 0

3. AS <- MS (SIP 200 OK)
------------------------
   SIP/2.0 200 OK
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
           branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060
   Contact: <sip:MediaServer@ms.example.net:5060>
   To: <sip:MediaServer@ms.example.net:5060>;tag=499a5b74
   From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
   Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
   CSeq: 1 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
   Content-Type: application/sdp
   Content-Length: 199

   v=0
   o=lminiero 2890844526 2890842808 IN IP4 ms.example.net
   s=MediaCtrl
   c=IN IP4 ms.example.net
   t=0 0
   m=application 7575 TCP cfw
   a=connection:new
   a=setup:passive
   a=cfw-id:5feb6486792a

4. AS -> MS (SIP ACK)
---------------------
   ACK sip:MediaServer@ms.example.net:5060 SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
                branch=z9hG4bK-d8754z-22940f5f4589701b-1---d8754z-;rport
   Max-Forwards: 70
   Contact: <sip:ApplicationServer@203.0.113.1:5060>
   To: <sip:MediaServer@ms.example.net:5060>;tag=499a5b74
   From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
   Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
   CSeq: 1 ACK
   Content-Length: 0

5.2.  SYNC

   Once the AS and the MS have successfully established a TCP
   connection, an additional step is needed before the Control Channel
   can be used.  In fact, as seen in the previous subsection, the first
   interaction between the AS and the MS happens by means of a SIP
   dialog, which in turn allows the creation of the TCP connection.
   This introduces the need for a proper correlation between the above-
   mentioned entities (SIP dialog and TCP connection), so that the MS
   can be sure that the connection came from the AS that requested it.
   This is accomplished by means of a dedicated framework message called
   a SYNC message.  This SYNC message uses a unique identifier called
   the Dialog-ID to validate the Control Channel.  This identifier, as
   introduced previously, is meant to be globally unique and as such is
   properly generated by the caller (the AS in the call flow) and added
   as an SDP media attribute (cfw-id) to the COMEDIA negotiation in
   order to make both entities aware of its value:

                       a=cfw-id:5feb6486792a
                                ^^^^^^^^^^^^
   It also offers an additional negotiation mechanism.  In fact, the AS
   uses the SYNC to not only properly correlate, as explained before,
   but also negotiate with the MS the Control Packages in which it is
   interested, as well as agree on a 'Keep-Alive' timer needed by both
   the AS and the MS so that they will know if problems on the
   connection occur.  In the provided example (see Figure 6 and the
   related call flow), the AS sends a SYNC with a Dialog-ID constructed
   as needed (using the 'cfw-id' attribute from the SIP dialog) and
   requests access to two Control Packages: specifically, the
   Interactive Voice Response (IVR) package and the Mixer package.  The
   AS also instructs the MS that a 100-second timeout is to be used for
   keep-alive messages.  The MS validates the request by matching the
   received Dialog-ID with the SIP dialog values, and, assuming that it
   supports the Control Packages the AS requested access to (and for the
   sake of this document we assume that it does), it answers with a

   200 message.  Additionally, the MS provides the AS with a list of
   other unrequested packages it supports (in this case just a dummy
   package providing testing functionality).

             AS                              MS
             .                               .
             .                               .
             |                               |
             | 1. SYNC (Dialog-ID, etc.)     |
             |+++++++++++++++++++++++++++++>>|
             |                               |--+
             |                               |  | Check SYNC
             |                               |<-+
             |                     2. 200 OK |
             |<<+++++++++++++++++++++++++++++|
             |                               |
             .                               .
             .                               .

                     Figure 6: SYNC: Sequence Diagram

   1. AS -> MS (CFW SYNC)
   ----------------------
      CFW 6e5e86f95609 SYNC
      Dialog-ID: 5feb6486792a
      Keep-Alive: 100
      Packages: msc-ivr/1.0,msc-mixer/1.0

   2. AS <- MS (CFW 200)
   ---------------------
      CFW 6e5e86f95609 200
      Keep-Alive: 100
      Packages: msc-ivr/1.0,msc-mixer/1.0
      Supported: msc-example-pkg/1.0

   The framework-level transaction identifier is obviously the same in
   both the request and the response (6e5e86f95609), since the AS needs
   to be able to match the response to the original request.  At this
   point, the Control Channel is finally established, and it can be used
   by the AS to request services from the MS.

5.3.  K-ALIVE

   [RFC6230] provides a mechanism for implementing a keep-alive
   functionality.  Such a mechanism is especially useful whenever any
   NAT or firewall sits in the path between an AS and an MS.  In fact,
   NATs and firewalls may have timeout values for the TCP connections

   they handle, which means that if no traffic is detected on these
   connections within a specific time they could be shut down.  This
   could be the case for a Control Channel established between an AS and
   an MS but not used for some time.  For this reason, [RFC6230]
   specifies a dedicated framework message (K-ALIVE) that the AS and MS
   can use in order to generate traffic on the TCP connection and keep
   it alive.

   As discussed in Section 5.2, the timeout value for the keep-alive
   mechanism is set by the SYNC request.  Specifically, in the example,
   the AS specified a value of 100 seconds.  In fact, the timeout value
   is not actually negotiated between the AS and MS, as it is simply
   specified by whichever endpoint takes the active role.  The
   100-second value is compliant with how NATs and firewalls are usually
   implemented, since in most cases the timeout value they use before
   shutting TCP connections down is around 2 minutes.  Such a value has
   a strong meaning within the context of this mechanism.  In fact, it
   means that the active role (the AS, in this case) has to send a
   K-ALIVE message before those 100 seconds pass; otherwise, the passive
   role (the MS) will tear down the connection, treating it like a
   timeout.  [RFC6230] suggests a more conservative approach towards
   handling this timeout value, suggesting that the K-ALIVE message be
   triggered before 80% of the negotiated time passes (80 seconds, in
   this case).  This is exactly the case presented in Figure 7.

                   AS                              MS
                   .                               .
                   .                               .
                   |                               |
     ~80 s have +--|                               |
   passed since |  |                               |
   last K-ALIVE +->|                               |
                   | 1. K-ALIVE                    |
                   |+++++++++++++++++++++++++++++>>|
                   |                               |--+ Reset the local
                   |                               |  | 'Keep-Alive'
                   |                               |<-+ timer
                   |                     2. 200 OK |
                   |<<+++++++++++++++++++++++++++++|
      Reset the +--|                               |
          local |  |                               |
   'Keep-Alive' +->|                               |
          timer    |                               |
                   .                               .
                   .                               .

                    Figure 7: K-ALIVE: Sequence Diagram

   After the Control Channel has been established (COMEDIA+SYNC), both
   the AS and the MS start local 'Keep-Alive' timers mapped to the
   negotiated keep-alive timeout value (100 seconds).  When about
   80 seconds have passed since the start of the timer (80% of
   100 seconds), the AS sends a framework-level K-ALIVE message to the
   MS.  The message as seen in the protocol message dump is very
   lightweight, since it only includes a single line with no additional
   header.  When the MS receives the K-ALIVE message, it resets its
   local 'Keep-Alive' timer and sends a 200 message back as
   confirmation.  As soon as the AS receives the 200 message, it resets
   its local 'Keep-Alive' timer as well, and the mechanism starts over
   again.

   The actual transaction steps are presented below.

   1. AS -> MS (K-ALIVE)
   ---------------------
      CFW 518ba6047880 K-ALIVE

   2. AS <- MS (CFW 200)
   ---------------------
      CFW 518ba6047880 200

   If the timer expired in either the AS or the MS (i.e., the K-ALIVE or
   the 200 arrived after the 100 seconds), the connection and the
   associated SIP control dialog would be torn down by the entity
   detecting the timeout, thus ending the interaction between the AS and
   the MS.

5.4.  Wrong Behavior

   This section will briefly address some types of behavior that could
   represent the most common mistakes when dealing with the
   establishment of a Control Channel between an AS and an MS.  These
   scenarios are obviously of interest, since they result in the AS and
   the MS being unable to interact with each other.  Specifically, these
   simple scenarios will be described:

   1.  an AS providing the MS with a wrong Dialog-ID in the initial
       SYNC.

   2.  an AS sending a generic CONTROL message instead of SYNC as a
       first transaction.

   The first scenario is depicted in Figure 8.

             AS                              MS
             .                               .
             .                               .
             |                               |
             | 1. SYNC (Dialog-ID, etc.)     |
             |+++++++++++++++++++++++++++++>>|
             |                               |--+
             |                               |  | Check SYNC (wrong!)
             |                               |<-+
             |                        2. 481 |
             |<<+++++++++++++++++++++++++++++|
             |                               |
             |<-XX- CLOSE TCP CONNECTION -XX-|
             |                               |
             | SIP BYE                       |
             |------------------------------>|
             |                               |
             .                               .
             .                               .

           Figure 8: SYNC with Wrong Dialog-ID: Sequence Diagram

   This scenario is similar to the scenario presented in Section 5.2,
   but with a difference: instead of using the correct, expected
   Dialog-ID in the SYNC message (5feb6486792a, the one negotiated via
   COMEDIA), the AS uses a wrong value (4hrn7490012c).  This causes the
   SYNC transaction to fail.  First of all, the MS sends a framework-
   level 481 message.  This response, when given in reply to a SYNC
   message, means that the SIP dialog associated with the provided
   Dialog-ID (the wrong identifier) does not exist.  The Control Channel
   must be torn down as a consequence, and so the MS also closes the TCP
   connection it received the SYNC message from.  The AS at this point
   is supposed to tear down its SIP control dialog as well, and so it
   sends a SIP BYE to the MS.

   The actual transaction is presented below.

   1. AS -> MS (CFW SYNC with wrong Dialog-ID)
   -------------------------------------------
      CFW 2b4dd8724f27 SYNC
      Dialog-ID: 4hrn7490012c
      Keep-Alive: 100
      Packages: msc-ivr/1.0,msc-mixer/1.0

   2. AS <- MS (CFW 481)
   ---------------------
      CFW 2b4dd8724f27 481

   The second scenario is depicted in Figure 9.

             AS                              MS
             .                               .
             .                               .
             |                               |
             | 1. CONTROL                    |
             |+++++++++++++++++++++++++++++>>|
             |                               |--+ First transaction
             |                               |  | is not a SYNC
             |                               |<-+
             |                        2. 403 |
             |<<+++++++++++++++++++++++++++++|
             |                               |
             |<-XX- CLOSE TCP CONNECTION -XX-|
             |                               |
             | SIP BYE                       |
             |------------------------------>|
             |                               |
             .                               .
             .                               .

          Figure 9: Incorrect First Transaction: Sequence Diagram

   This scenario demonstrates another common mistake that could occur
   when trying to set up a Control Channel.  In fact, [RFC6230] mandates
   that the first transaction after the COMEDIA negotiation be a SYNC to
   conclude the setup.  If the AS, instead of triggering a SYNC message
   as expected, sends a different message to the MS (in the example
   below, it tries to send an <audit> message addressed to the IVR
   Control Package), the MS treats it like an error.  As a consequence,
   the MS replies with a framework-level 403 message (Forbidden) and,
   just as before, closes the TCP connection and waits for the related
   SIP control dialog to be torn down.

   The actual transaction is presented below.

   1. AS -> MS (CFW CONTROL instead of SYNC)
   -----------------------------------------
      CFW 101fbbd62c35 CONTROL
      Control-Package: msc-ivr/1.0
      Content-Type: application/msc-ivr+xml
      Content-Length: 78

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
         <audit/>
      </mscivr>

   2. AS <- MS (CFW 403 Forbidden)
   -------------------------------
      CFW 101fbbd62c35 403

6.  Use-Case Scenarios and Examples

   The following scenarios have been chosen for their common presence in
   many rich real-time multimedia applications.  Each scenario is
   depicted as a set of call flows involving both the SIP/SDP signaling
   (UACs<->AS<->MS) and the Control Channel communication (AS<->MS).

   All the examples assume that a Control Channel has already been
   correctly established and SYNCed between the reference AS and MS.
   Also, unless stated otherwise, the same User Agent Client (UAC)
   session is referenced in all the examples that will be presented in
   this document.  The UAC session is assumed to have been created as
   described in Figure 10:

   UAC                  AS                          MS
    |                   |                           |
    | INVITE (X)        |                           |
    |------------------>|                           |
    |     180 (Ringing) |                           |
    |<------------------|                           |
    |                   |--+                        |
    |                   |  | Handle app(X)          |
    |                   |<-+                        |
    |                   | INVITE (Y) as 3PCC        |
    |                   |-------------------------->|
    |                   |              100 (Trying) |
    |                   |<--------------------------|
    |                   |                           |--+ Negotiate media
    |                   |                           |  | with UAC; map
    |                   |                           |<-+ tags and labels
    |                   |                    200 OK |
    |                   |<--------------------------|
    |            200 OK |                           |
    |<------------------|                           |
    | ACK               |                           |
    |------------------>|                           |
    |                   | ACK                       |
    |                   |-------------------------->|
    |                   |                           |
    |<<###########################################>>|
    |         RTP Media Stream(s) flowing           |
    |<<###########################################>>|
    |                   |                           |
    .                   .                           .
    .                   .                           .

                     Figure 10: 3PCC Sequence Diagram

   Note well: This is only an example of a possible approach involving a
   Third-Party Call Control (3PCC) negotiation among the UAC, the AS,
   and the MS, and as such is not at all to be considered the mandatory
   way, nor best common practice, in the presented scenario.  [RFC3725]
   provides several different solutions and many details about how 3PCC

   can be realized, with pros and cons.  It is also worth pointing out
   that the two INVITEs displayed in the figure are different SIP
   dialogs.

   The UAC first places a call to a SIP URI for which the AS is
   responsible.  The specific URI is not relevant to the examples, since
   the application logic behind the mapping between a URI and the
   service it provides is a matter that is important only to the AS.
   So, a generic 'sip:mediactrlDemo@as.example.com' is used in all the
   examples, whereas the service this URI is associated with in the AS
   logic is mapped scenario by scenario to the case under examination.
   The UAC INVITE is treated as envisaged in [RFC5567].  The INVITE is
   forwarded by the AS to the MS via a third party (e.g., the 3PCC
   approach), without the SDP provided by the UAC being touched, in
   order to have the session fully negotiated by the MS according to its
   description.  The MS matches the UAC's offer with its own
   capabilities and provides its answer in a 200 OK.  This answer is
   then forwarded, again without the SDP contents being touched, by the
   AS to the target UAC.  This way, while the SIP signaling from the UAC
   is terminated in the AS, all the media would start flowing directly
   between the UAC and the MS.

   As a consequence of this negotiation, one or more media connections
   are created between the MS and the UAC.  They are then addressed,
   when needed, by the AS and the MS by means of the concatenation of
   tags, as specified in [RFC6230].  How the identifiers are created and
   addressed is explained by using the sample signaling provided in the
   following lines.

1. UAC -> AS (SIP INVITE)
-------------------------
   INVITE sip:mediactrlDemo@as.example.com SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.2:5063;rport;branch=z9hG4bK1396873708
   From: <sip:lminiero@users.example.com>;tag=1153573888
   To: <sip:mediactrlDemo@as.example.com>
   Call-ID: 1355333098
   CSeq: 20 INVITE
   Contact: <sip:lminiero@203.0.113.2:5063>
   Content-Type: application/sdp
   Max-Forwards: 70
   User-Agent: Linphone/2.1.1 (eXosip2/3.0.3)
   Subject: Phone call
   Expires: 120
   Content-Length: 330

   v=0
   o=lminiero 123456 654321 IN IP4 203.0.113.2
   s=A conversation
   c=IN IP4 203.0.113.2
   t=0 0
   m=audio 7078 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000/1
   a=rtpmap:3 GSM/8000/1
   a=rtpmap:8 PCMA/8000/1
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-11
   m=video 9078 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=1;QCIF=1

2. UAC <- AS (SIP 180 Ringing)
------------------------------
   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP 203.0.113.2:5063;rport=5063; \
                                                branch=z9hG4bK1396873708
   Contact: <sip:mediactrlDemo@as.example.com>
   To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
   From: <sip:lminiero@users.example.com>;tag=1153573888
   Call-ID: 1355333098
   CSeq: 20 INVITE
   Content-Length: 0

3. AS -> MS (SIP INVITE)
------------------------
   INVITE sip:MediaServer@ms.example.net:5060;transport=UDP SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
                branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport
   Max-Forwards: 70
   Contact: <sip:ApplicationServer@203.0.113.1:5060>
   To: <sip:MediaServer@ms.example.net:5060>
   From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
   Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
   CSeq: 1 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
   Content-Type: application/sdp
   Content-Length: 330

   v=0
   o=lminiero 123456 654321 IN IP4 203.0.113.2
   s=A conversation
   c=IN IP4 203.0.113.2
   t=0 0
   m=audio 7078 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000/1
   a=rtpmap:3 GSM/8000/1
   a=rtpmap:8 PCMA/8000/1
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-11
   m=video 9078 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=1;QCIF=1

4. AS <- MS (SIP 100 Trying)
----------------------------
   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
           branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport=5060
   To: <sip:MediaServer@ms.example.net:5060>;tag=6a900179
   From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
   Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
   CSeq: 1 INVITE
   Content-Length: 0

5. AS <- MS (SIP 200 OK)
------------------------
   SIP/2.0 200 OK
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
           branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport=5060
   Contact: <sip:MediaServer@ms.example.net:5060>
   To: <sip:MediaServer@ms.example.net:5060>;tag=6a900179
   From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
   Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
   CSeq: 1 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
   Content-Type: application/sdp
   Content-Length: 374

   v=0
   o=lminiero 123456 654322 IN IP4 ms.example.net
   s=MediaCtrl
   c=IN IP4 ms.example.net
   t=0 0
   m=audio 63442 RTP/AVP 0 3 8 101

   a=rtpmap:0 PCMU/8000
   a=rtpmap:3 GSM/8000
   a=rtpmap:8 PCMA/8000
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-15
   a=ptime:20
   a=label:7eda834
   m=video 33468 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=2
   a=label:0132ca2

6. UAC <- AS (SIP 200 OK)
-------------------------
   SIP/2.0 200 OK
   Via: SIP/2.0/UDP 203.0.113.2:5063;rport=5063; \
                                                branch=z9hG4bK1396873708
   Contact: <sip:mediactrlDemo@as.example.com>
   To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
   From: <sip:lminiero@users.example.com>;tag=1153573888
   Call-ID: 1355333098
   CSeq: 20 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
   Content-Type: application/sdp
   Content-Length: 374

   v=0
   o=lminiero 123456 654322 IN IP4 ms.example.net
   s=MediaCtrl
   c=IN IP4 ms.example.net
   t=0 0
   m=audio 63442 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000
   a=rtpmap:3 GSM/8000
   a=rtpmap:8 PCMA/8000
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-15
   a=ptime:20
   a=label:7eda834
   m=video 33468 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=2
   a=label:0132ca2

7. UAC -> AS (SIP ACK)
----------------------
   ACK sip:mediactrlDemo@as.example.com SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.2:5063;rport;branch=z9hG4bK1113338059
   From: <sip:lminiero@users.example.com>;tag=1153573888
   To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
   Call-ID: 1355333098
   CSeq: 20 ACK
   Contact: <sip:lminiero@203.0.113.2:5063>
   Max-Forwards: 70
   User-Agent: Linphone/2.1.1 (eXosip2/3.0.3)
   Content-Length: 0

8. AS -> MS (SIP ACK)
---------------------
   ACK sip:MediaServer@ms.example.net:5060;transport=UDP SIP/2.0
   Via: SIP/2.0/UDP 203.0.113.1:5060; \
                branch=z9hG4bK-d8754z-5246003419ccd662-1---d8754z-;rport
   Max-Forwards: 70
   Contact: <sip:ApplicationServer@203.0.113.1:5060>
   To: <sip:MediaServer@ms.example.net:5060;tag=6a900179
   From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
   Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
   CSeq: 1 ACK
   Content-Length: 0

   As a result of the 3PCC negotiation just presented, the following
   relevant information is retrieved:

   1.  The 'From' and 'To' tags (10514b7f and 6a900179, respectively) of
       the AS<->MS session:

     From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
                                                           ^^^^^^^^
     To: <sip:MediaServer@ms.example.net:5060>;tag=6a900179
                                                   ^^^^^^^^

   2.  The labels [RFC4574] associated with the negotiated media
       connections, in this case an audio stream (7eda834) and a video
       stream (0132ca2):

      m=audio 63442 RTP/AVP 0 3 8 101
      [..]
      a=label:7eda834
              ^^^^^^^

      m=video 33468 RTP/AVP 98
      [..]
      a=label:0132ca2
              ^^^^^^^
   These four identifiers allow the AS and MS to univocally and
   unambiguously address to each other the connections associated with
   the related UAC.  Specifically:

   1.  10514b7f:6a900179, the concatenation of the 'From' and 'To' tags
       through a colon (':') token, addresses all the media connections
       between the MS and the UAC.

   2.  10514b7f:6a900179 <-> 7eda834, the association of the previous
       value with the label attribute, addresses only one of the media
       connections of the UAC session (in this case, the audio stream).
       Since, as will be made clearer in the example scenarios, the
       explicit identifiers in requests can only address 'from:tag'
       connections, an additional mechanism will be required to have a
       finer control of individual media streams (i.e., by means of the
       <stream> element in package-level requests).

   The mapping that the AS makes between the UACs<->AS and the AS<->MS
   SIP dialogs is out of scope for this document.  We just assume that
   the AS knows how to address the right connection according to the
   related session it has with a UAC (e.g., to play an announcement to a
   specific UAC).  This is obviously very important, since the AS is
   responsible for all the business logic of the multimedia application
   it provides.

6.1.  Echo Test

   The echo test is the simplest example scenario that can be achieved
   by means of an MS.  It basically consists of a UAC directly or
   indirectly "talking" to itself.  A media perspective of such a
   scenario is depicted in Figure 11.

              +-------+  A (RTP)                 +--------+
              |  UAC  |=========================>| Media  |
              |   A   |<=========================| Server |
              +-------+                 A (RTP)  +--------+

                  Figure 11: Echo Test: Media Perspective

   From the framework point of view, when the UAC's leg is not attached
   to anything yet, what appears is shown in Figure 12: since there's no
   connection involving the UAC yet, the frames it might be sending are
   discarded, and nothing is sent to it (except for silence, if its
   transmission is requested).

                                           MS
                                        +------+
                           UAC          |      |
                            o----->>-------x   |
                            o.....<<.......x   |
                                        |      |
                                        +------+

             Figure 12: Echo Test: UAC Media Leg Not Attached

   Starting from these considerations, two different approaches to the
   Echo Test scenario are explored in this document:

   1.  a Direct Echo Test approach, where the UAC directly talks to
       itself.

   2.  a Recording-based Echo Test approach, where the UAC indirectly
       talks to itself.

6.1.1.  Direct Echo Test

   In the Direct Echo Test approach, the UAC is directly connected to
   itself.  This means that, as depicted in Figure 13, each frame the MS
   receives from the UAC is sent back to it in real time.

                                           MS
                                        +------+
                           UAC          |      |
                            o----->>-------@   |
                            o-----<<-------@   |
                                        |      |
                                        +------+

            Figure 13: Echo Test: Direct Echo (Self-Connection)

   In the framework, this can be achieved by means of the Mixer Control
   Package [RFC6505], which is in charge of joining connections and
   conferences.

   A sequence diagram of a potential transaction is depicted in
   Figure 14:

  UAC                      AS                                 MS
   |                       |                                  |
   |                       | 1. CONTROL (join UAC to itself)  |
   |                       |++++++++++++++++++++++++++++++++>>|
   |                       |                                  |--+ self-
   |                       |                                  |  | join
   |                       |                        2. 200 OK |<-+ UAC
   |                       |<<++++++++++++++++++++++++++++++++|
   |                       |                                  |
   |<<######################################################>>|
   |         Everything is now echoed back to the UAC         |
   |<<######################################################>>|
   |                       |                                  |
   .                       .                                  .
   .                       .                                  .

             Figure 14: Self-Connection: Framework Transaction

   The transaction steps have been numbered and are explained below:

   o  The AS requests the joining of the connection to itself by sending
      to the MS a CONTROL request (1) that is specifically meant for the
      conferencing Control Package (msc-mixer/1.0).  A <join> request is
      used for this purpose, and since the connection must be attached
      to itself, both id1 and id2 attributes are set to the same value,
      i.e., the connectionid.

   o  The MS, having checked the validity of the request, enforces the
      joining of the connection to itself.  This means that all the
      frames sent by the UAC are sent back to it.  To report the result
      of the operation, the MS sends a 200 OK (2) in reply to the AS,
      thus ending the transaction.  The transaction ended successfully,
      as indicated by the body of the message (the 200 status code in
      the <response> tag).

   The complete transaction -- that is, the full bodies of the exchanged
   messages -- is provided in the following lines:

   1. AS -> MS (CFW CONTROL)
   -------------------------
      CFW 4fed9bf147e2 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 130

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="10514b7f:6a900179" id2="10514b7f:6a900179"/>
      </mscmixer>

   2. AS <- MS (CFW 200 OK)
   ------------------------
      CFW 4fed9bf147e2 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

6.1.2.  Echo Test Based on Recording

   In the Recording-based Echo Test approach, the UAC is NOT directly
   connected to itself, but rather indirectly.  This means that, as
   depicted in Figure 15, each frame the MS receives from the UAC is
   first recorded; then, when the recording process is ended, the whole
   recorded frames are played back to the UAC as an announcement.

                                MS
                             +------+
                UAC          |      |
                 o----->>-------+~~~~~> (recording.wav) ~~+
                 o-----<<-------+   |                     |
                             |  ^   |                     v
                             +--|---+                     |
                                +~~~~~~~~~~~<<~~~~~~~~~~~~+

                 Figure 15: Echo Test: Recording Involved

   In the framework, this can be achieved by means of the IVR Control
   Package [RFC6231], which is in charge of both the recording and the
   playout phases.  However, the whole scenario cannot be accomplished
   in a single transaction; at least two steps, in fact, need to be
   performed:

   1.  First, a recording (preceded by an announcement, if requested)
       must take place.

   2.  Then, a playout of the previously recorded media must occur.

   This means that two separate transactions need to be invoked.  A
   sequence diagram of a potential multiple transaction is depicted in
   Figure 16:

 UAC                      AS                                 MS
  |                       |                                  |
  |                       | A1. CONTROL (record for 10s)     |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                          A2. 202 |
  |                       |<<++++++++++++++++++++++++++++++++| prepare &
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |           A3. REPORT (terminate) |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | A4. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  |<<########################################################|
  |           "This is an echo test: say something"          |
  |<<########################################################|
  |                       |                                  |
  |########################################################>>|
  |          10 s of audio from the UAC are recorded         |--+ save
  |########################################################>>|  | in a
  |                       |                                  |<-+ file
  |                       |       B1. CONTROL (<recordinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |       Use recorded +--| B2. 200 OK                       |
  |       file to play |  |++++++++++++++++++++++++++++++++>>|
  |       announcement +->|                                  |
  |                       | C1. CONTROL (play recorded)      |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                          C2. 202 |
  |                       |<<++++++++++++++++++++++++++++++++| prepare &
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |           C3. REPORT (terminate) |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | C4. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  |<<########################################################|
  |         "Can you hear me? It's me, UAC, talking"         |
  |<<########################################################|
  |                       |                                  |
  |                       |       D1. CONTROL (<promptinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | D2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  .                       .                                  .
  .                       .                                  .

        Figure 16: Recording-Based Echo: Two Framework Transactions

   The first obvious difference that stands out when looking at the
   diagram is that, unlike the Direct Echo scenario, the MS does not
   reply with a 200 message to the CONTROL request originated by the AS.
   Instead, a 202 provisional message is sent first, followed by a
   REPORT message.  The 202+REPORT(s) mechanism is used whenever the MS
   wants to tell the AS that the requested operation might take more
   time than the limit specified in the definition of the Control
   Package.  So, while the <join> operation in the Direct Echo scenario
   was expected to be fulfilled in a very short time, the IVR request
   was assumed to last longer.  A 202 message provides a timeout value
   and tells the AS to wait a bit, since the preparation of the dialog
   might not happen immediately.  In this example, the preparation ends
   before the timeout, and so the transaction is concluded with a
   'REPORT terminate', which reports the end of the transaction (as did
   the 200 message in the previous example).  If the preparation took
   longer than the timeout, an additional 'REPORT update' would have
   been sent with a new timeout value, and so on, until completion by
   means of a 'REPORT terminate'.

   Note that the REPORT mechanism depicted is only shown to clarify its
   behavior.  In fact, the 202+REPORT mechanism is assumed to be
   involved only when the requested transaction is expected to take a
   long time (e.g., retrieving a large media file for a prompt from an
   external server).  In this scenario, the transaction would be
   prepared in much less time and as a consequence would very likely be
   completed within the context of a simple CONTROL+200 request/
   response.  The following scenarios will only involve 202+REPORTs when
   they are strictly necessary.

   Regarding the dialog itself, note how the AS-originated CONTROL
   transactions are terminated as soon as the requested dialogs start.
   As specified in [RFC6231], the MS uses a framework CONTROL message to
   report the result of the dialog and how it has proceeded.  The two
   transactions (the AS-generated CONTROL request and the MS-generated
   CONTROL event) are correlated by means of the associated dialog
   identifier, as explained below.  As before, the transaction steps
   have been numbered.  The two transactions are distinguished by the
   preceding letter (A,B=recording, C,D=playout).

   o  The AS, as a first transaction, invokes a recording on the UAC
      connection by means of a CONTROL request (A1).  The body is for
      the IVR package (msc-ivr/1.0) and requests the start
      (<dialogstart>) of a new recording context (<record>).  The
      recording must be preceded by an announcement (<prompt>), must not
      last longer than 10 s (maxtime), and cannot be interrupted by a
      DTMF tone (dtmfterm=false).  This is only done once (the missing

      repeatCount attribute is 1 by default for a <dialog>), which means
      that if the recording does not succeed the first time, the
      transaction must fail.  A video recording is requested
      (considering that the associated connection includes both audio
      and video and no restriction is enforced on streams to record),
      which is to be fed by both of the negotiated media streams.  A
      beep has to be played (beep=true) right before the recording
      starts, to notify the UAC.

   o  As seen before, the MS sends a provisional 202 response to let the
      AS know that the operation might need some time.

   o  In the meantime, the MS prepares the dialog (e.g., by retrieving
      the announcement file, for which an HTTP URL is provided, and by
      checking that the request is well formed) and if all is fine it
      starts it, notifying the AS with a new REPORT (A3) with a
      terminated status.  As explained previously, interlocutory REPORT
      messages with an update status would have been sent if the
      preparation took longer than the timeout provided in the 202
      message (e.g., if retrieving the resource via HTTP took longer
      than expected).  Once the dialog has been prepared and started,
      the UAC connection is then passed to the IVR package, which first
      plays the announcement on the connection, followed by a beep, and
      then records all the incoming frames to a buffer.  The MS also
      provides the AS with a unique dialog identifier (dialogid) that
      will be used in all subsequent event notifications concerning the
      dialog it refers to.

   o  The AS acks the latest REPORT (A4), thus terminating this
      transaction, and waits for the results.

   o  Once the recording is over, the MS prepares a notification CONTROL
      (B1).  The <event> body is prepared with an explicit reference to
      the previously provided dialog identifier, in order to make the AS
      aware of the fact that the notification is related to that
      specific dialog.  The event body is then completed with the
      recording-related information (<recordinfo>), in this case the
      path to the recorded file (here, an HTTP URL) that can be used by
      the AS for anything it needs.  The payload also contains
      information about the prompt (<promptinfo>), which is, however,
      not relevant to the scenario.

   o  The AS concludes this first recording transaction by acking the
      CONTROL event (B2).

   Now that the first transaction has ended, the AS has the 10-s
   recording of the UAC talking and can let the UAC hear it by having
   the MS play it for the UAC as an announcement:

   o  In the second transaction, the AS invokes a playout on the UAC
      connection by means of a new CONTROL request (C1).  The body is
      once again for the IVR package (msc-ivr/1.0), but this time it
      requests the start (<dialogstart>) of a new announcement context
      (<prompt>).  The file to be played is the file that was recorded
      before (<media>).

   o  Again, the usual provisional 202 (C2) takes place.

   o  In the meantime, the MS prepares and starts the new dialog, and
      notifies the AS with a new REPORT (C3) with a terminated status.
      The connection is then passed to the IVR package, which plays the
      file on it.

   o  The AS acks the terminating REPORT (C4), now waiting for the
      announcement to end.

   o  Once the playout is over, the MS sends a CONTROL event (D1) that
      contains in its body (<promptinfo>) information about the just-
      concluded announcement.  As before, the proper dialogid is used as
      a reference to the correct dialog.

   o  The AS concludes this second and last transaction by acking the
      CONTROL event (D2).

   As in the previous paragraph, the whole CFW interaction is provided
   for a more in-depth evaluation of the protocol interaction.

   A1. AS -> MS (CFW CONTROL, record)
   ----------------------------------
      CFW 796d83aa1ce4 CONTROL
      Control-Package: msc-ivr/1.0
      Content-Type: application/msc-ivr+xml
      Content-Length: 265

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <dialogstart connectionid="10514b7f:6a900179">
          <dialog>
            <prompt>
              <media
                loc="http://www.example.com/demo/echorecord.mpg"/>
            </prompt>
            <record beep="true" maxtime="10s"/>
          </dialog>
        </dialogstart>
      </mscivr>

   A2. AS <- MS (CFW 202)
   ----------------------
      CFW 796d83aa1ce4 202
      Timeout: 5

   A3. AS <- MS (CFW REPORT terminate)
   -----------------------------------
      CFW 796d83aa1ce4 REPORT
      Seq: 1
      Status: terminate
      Timeout: 25
      Content-Type: application/msc-ivr+xml
      Content-Length: 137

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
         <response status="200" reason="Dialog started"
                   dialogid="68d6569"/>
      </mscivr>

   A4. AS -> MS (CFW 200, ACK to 'REPORT terminate')
   -------------------------------------------------
      CFW 796d83aa1ce4 200
      Seq: 1

   B1. AS <- MS (CFW CONTROL event)
   --------------------------------
      CFW 0eb1678c0bfc CONTROL
      Control-Package: msc-ivr/1.0
      Content-Type: application/msc-ivr+xml
      Content-Length: 403

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <event dialogid="68d6569">
          <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="9987" termmode="completed"/>
            <recordinfo duration="10017" termmode="maxtime">
              <mediainfo
     loc="http://www.example.net/recordings/recording-68d6569.mpg"
     type="video/mpeg" size="591872"/>
            </recordinfo>
          </dialogexit>
        </event>
      </mscivr>

   B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
   ----------------------------------------------
      CFW 0eb1678c0bfc 200

   C1. AS -> MS (CFW CONTROL, play)
   --------------------------------
      CFW 1632eead7e3b CONTROL
      Control-Package: msc-ivr/1.0
      Content-Type: application/msc-ivr+xml
      Content-Length: 241

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <dialogstart connectionid="10514b7f:6a900179">
          <dialog>
            <prompt>
              <media
     loc="http://www.example.net/recordings/recording-68d6569.mpg"/>
            </prompt>
          </dialog>
        </dialogstart>
      </mscivr>

   C2. AS <- MS (CFW 202)
   ----------------------
      CFW 1632eead7e3b 202
      Timeout: 5

   C3. AS <- MS (CFW REPORT terminate)
   -----------------------------------
      CFW 1632eead7e3b REPORT
      Seq: 1
      Status: terminate
      Timeout: 25
      Content-Type: application/msc-ivr+xml
      Content-Length: 137

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
         <response status="200" reason="Dialog started"
                   dialogid="5f5cb45"/>
      </mscivr>

   C4. AS -> MS (CFW 200, ACK to 'REPORT terminate')
   -------------------------------------------------
      CFW 1632eead7e3b 200
      Seq: 1

   D1. AS <- MS (CFW CONTROL event)
   --------------------------------
      CFW 502a5fd83db8 CONTROL
      Control-Package: msc-ivr/1.0
      Content-Type: application/msc-ivr+xml
      Content-Length: 230

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <event dialogid="5f5cb45">
          <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="10366" termmode="completed"/>
          </dialogexit>
        </event>
      </mscivr>

   D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
   ----------------------------------------------
      CFW 502a5fd83db8 200

6.2.  Phone Call

   Another scenario that might involve the interaction between an AS and
   an MS is the classic phone call between two UACs.  In fact, even
   though the most straightforward way to achieve this would be to let
   the UACs negotiate the session and the media to be used between them,
   there are cases when the services provided by an MS might also prove
   useful for such phone calls.

   One of these cases is when the two UACs have no common supported
   codecs: having the two UACs directly negotiate the session would
   result in a session with no available media.  Involving the MS as a
   transcoder would in this case still allow the two UACs to
   communicate.  Another interesting case is when the AS (or any other
   entity on whose behalf the AS is working) is interested in
   manipulating or monitoring the media session between the UACs, e.g.,
   to record the conversation.  A similar scenario will be dealt with in
   Section 6.2.2.

   Before looking at how such a scenario might be accomplished by means
   of the Media Control Channel Framework, it is worth mentioning what
   the SIP signaling involving all the interested parties might look
   like.  In fact, in such a scenario, a 3PCC approach is absolutely
   needed.  An example is provided in Figure 17.  Again, the presented
   example is not at all to be considered best common practice when 3PCC
   is needed in a MEDIACTRL-based framework.  It is only described in
   order to help the reader more easily understand what the requirements
   are on the MS side, and as a consequence what information might be
   required.  [RFC3725] provides a much more detailed overview on 3PCC
   patterns in several use cases.  Only an explanatory sequence diagram
   is provided, without delving into the details of the exchanged SIP
   messages.

   UAC(1)        UAC(2)                  AS                          MS
     |             |                     |                           |
     | INVITE (offer A)                  |                           |
     | Call-Id: A  |                     |                           |
     |---------------------------------->|                           |
     |             |          100 Trying |                           |
     |             |          Call-Id: A |                           |
     |<----------------------------------|                           |
     |             |   INVITE (no offer) |                           |
     |             |   Call-Id: B        |                           |
     |             |<--------------------|                           |
     |             | 180 Ringing         |                           |
     |             | Call-Id: B          |                           |
     |             |-------------------->|                           |
     |             |         180 Ringing |                           |
     |             |          Call-Id: A |                           |
     |<----------------------------------|                           |
     |             |                     | INVITE (offer A)          |
     |             |                     | Call-Id: C                |
     |             |                     |-------------------------->|
     |             |                     |         200 OK (offer A') |
     |             |                     |         Call-Id: C        |
     |             |                     |<--------------------------|
     |             |                     | ACK                       |
     |             |                     | Call-Id: C                |
     |             |                     |-------------------------->|
     |             | 200 OK (offer B)    |                           |
     |             | Call-Id: B          |                           |
     |             |-------------------->|                           |
     |             |                     | INVITE (offer B)          |
     |             |                     | Call-Id: D                |
     |             |                     |-------------------------->|
     |             |                     |         200 OK (offer B') |
     |             |                     |         Call-Id: D        |
     |             |                     |<--------------------------|
     |             |                     | ACK                       |
     |             |                     | Call-Id: D                |
     |             |                     |-------------------------->|
     |             |      ACK (offer B') |                           |
     |             |      Call-Id: B     |                           |

     |             |<--------------------|                           |
     |             |   200 OK (offer A') |                           |
     |             |   Call-Id: A        |                           |
     |<----------------------------------|                           |
     | ACK         |                     |                           |
     | Call-Id: A  |                     |                           |
     |---------------------------------->|                           |
     |             |                     |                           |
     .             .                     .                           .
     .             .                     .                           .

                  Figure 17: Phone Call: Example of 3PCC

   In this example, UAC1 wants to place a phone call to UAC2.  To do so,
   it sends an INVITE to the AS with its offer A.  The AS sends an
   offerless INVITE to UAC2.  When UAC2 responds with a 180, the same
   message is forwarded by the AS to UAC1 to notify it that the callee
   is ringing.  In the meantime, the AS also adds a leg to the MS for
   UAC1, as explained at the beginning of Section 6.  To do so, it of
   course uses the offer A that UAC1 made.  Once UAC2 accepts the call
   by providing its own offer B in the 200, the AS also adds a leg for
   offer B to the MS.  At this point, the negotiation can be completed
   by providing the two UACs with the SDP answer negotiated by the MS
   with them (A' and B', respectively).

   Of course, this is only one way to deal with the signaling and shall
   not be considered an absolutely mandatory approach.

   Once the negotiation is over, the two UACs are not in communication
   yet.  In fact, it's up to the AS now to actively trigger the MS to
   somehow attach their media streams to each other, by referring to the
   connection identifiers associated with the UACs as explained
   previously.  This document presents two different approaches that
   might be followed, according to what needs to be accomplished.  A
   generic media perspective of the phone call scenario is depicted in
   Figure 18.  The MS is basically in the media path between the
   two UACs.

   +-------+  UAC1 (RTP)        +--------+  UAC1 (RTP)        +-------+
   |  UAC  |===================>| Media  |===================>|  UAC  |
   |   1   |<===================| Server |<===================|   2   |
   +-------+        UAC2 (RTP)  +--------+        UAC2 (RTP)  +-------+

                 Figure 18: Phone Call: Media Perspective

   From the framework point of view, when the UACs' legs are not
   attached to anything yet, what appears is shown in Figure 19: since
   there are no connections involving the UACs yet, the frames they
   might be sending are discarded, and nothing is sent to them (except
   for silence, if its transmission is requested).

                                     MS
                              +--------------+
                UAC 1         |              |         UAC 2
                  o----->>-------x        x.......>>.....o
                  o.....<<.......x        x-------<<-----o
                              |              |
                              +--------------+

             Figure 19: Phone Call: UAC Media Leg Not Attached

6.2.1.  Direct Connection

   The Direct Connection approach is the easiest, and a more
   straightforward, approach to get the phone call between the two UACs
   to work.  The idea is basically the same as that of the Direct Echo
   approach.  A <join> directive is used to directly attach one UAC to
   the other, by exploiting the MS to only deal with the transcoding/
   adaption of the flowing frames, if needed.

   This approach is depicted in Figure 20.

                                     MS
                              +--------------+
                UAC 1         |              |         UAC 2
                  o----->>-------+~~~>>~~~+------->>-----o
                  o-----<<-------+~~~<<~~~+-------<<-----o
                              |              |
                              +--------------+

                 Figure 20: Phone Call: Direct Connection

  UAC1       UAC2         AS                                   MS
   |           |          |                                    |
   |           |          | 1. CONTROL (join UAC1 to UAC2)     |
   |           |          |++++++++++++++++++++++++++++++++++>>|
   |           |          |                                    |--+ join
   |           |          |                                    |  | UAC1
   |           |          |                          2. 200 OK |<-+ UAC2
   |           |          |<<++++++++++++++++++++++++++++++++++|
   |           |          |                                    |
   |<<#######################################################>>|
   |                UAC1 can hear UAC2 talking                 |
   |<<#######################################################>>|
   |           |          |                                    |
   |           |<<###########################################>>|
   |           |          UAC2 can hear UAC1 talking           |
   |           |<<###########################################>>|
   |           |          |                                    |
   |<*talking*>|          |                                    |
   .           .          .                                    .
   .           .          .                                    .

           Figure 21: Direct Connection: Framework Transactions

   The framework transactions needed to accomplish this scenario are
   very trivial and easy to understand.  They are basically the same as
   those presented in the Direct Echo Test scenario; the only difference
   is in the provided identifiers.  In fact, this time the MS is not
   supposed to attach the UACs' media connections to themselves but has
   to join the media connections of two different UACs, i.e., UAC1 and
   UAC2.  This means that in this transaction, id1 and i2 will have to
   address the media connections of UAC1 and UAC2.  In the case of a
   successful transaction, the MS takes care of forwarding all media
   coming from UAC1 to UAC2 and vice versa, transparently taking care of
   any required transcoding steps, if necessary.

   1. AS -> MS (CFW CONTROL)
   -------------------------
      CFW 0600855d24c8 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 130

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="10514b7f:6a900179" id2="e1e1427c:1c998d22"/>
      </mscmixer>

   2. AS <- MS (CFW 200 OK)
   ------------------------
      CFW 0600855d24c8 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   Such a simple approach has its drawbacks.  For instance, with such an
   approach, recording a conversation between two users might be tricky
   to accomplish.  In fact, since no mixing would be involved, only the
   single connections (UAC1<->MS and UAC2<->MS) could be recorded.  If
   the AS wants a conversation-recording service to be provided anyway,
   it needs additional business logic on its side.  An example of such a
   use case is provided in Section 6.2.3.

6.2.2.  Conference-Based Approach

   The approach described in Section 6.2.1 surely works for a basic
   phone call but, as explained previously, might have some drawbacks
   whenever more advanced features are needed.  For instance, one can't
   record the whole conversation -- only the single connections -- since
   no mixing is involved.  Additionally, even the single task of playing
   an announcement over the conversation could be complex, especially if
   the MS does not support implicit mixing over media connections.  For
   this reason, in more advanced cases a different approach might be
   taken, like the conference-based approach described in this section.

   The idea is to use a mixing entity in the MS that acts as a bridge
   between the two UACs.  The presence of this entity allows more
   customization of what needs to be done with the conversation, like
   the recording of the conversation that has been provided as an
   example.  The approach is depicted in Figure 22.  The mixing
   functionality in the MS will be described in more detail in the
   following section (which deals with many conference-related
   scenarios), so only some hints will be provided here for basic
   comprehension of the approach.

                                      MS
                              +---------------+
                UAC A         |               |         UAC B
                  o----->>-------+~~>{#}::>+:::::::>>:::::o
                  o:::::<<:::::::+<::{#}<~~+-------<<-----o
                              |       :       |
                              |       :       |
                              +-------:-------+
                                      :
                                      +::::> (conversation.wav)

             Figure 22: Phone Call: Conference-Based Approach

   To identify a single sample scenario, let's consider a phone call
   that the AS wants to record.

   Figure 23 shows how this could be accomplished in the Media Control
   Channel Framework.  This example, as usual, hides the previous
   interaction between the UACs and the AS and instead focuses on the
   Control Channel operations and what follows.

 UAC1        UAC2       AS                                 MS
  |           |         |                                  |
  |           |         | A1. CONTROL (create conference)  |
  |           |         |++++++++++++++++++++++++++++++++>>|
  |           |         |                                  |--+ create
  |           |         |                                  |  | conf and
  |           |         |      A2. 200 OK (conferenceid=Y) |<-+ its ID
  |           |         |<<++++++++++++++++++++++++++++++++|
  |           |         |                                  |
  |           |         | B1. CONTROL (record for 10800 s) |
  |           |         |++++++++++++++++++++++++++++++++>>|
  |           |         |                                  |--+ start
  |           |         |                                  |  | the
  |           |         |                       B2. 200 OK |<-+ dialog
  |           |         |<<++++++++++++++++++++++++++++++++|
  |        Recording +--|                                  |
  |       of the mix |  |                                  |
  |      has started +->|                                  |
  |           |         | C1. CONTROL (join UAC1<->confY)  |
  |           |         |++++++++++++++++++++++++++++++++>>|
  |           |         |                                  |--+  join
  |           |         |                                  |  | UAC1 &
  |           |         |                       C2. 200 OK |<-+ confY
  |           |         |<<++++++++++++++++++++++++++++++++|
  |           |         |                                  |
  |<<####################################################>>|
  |           Now UAC1 is mixed in the conference          |
  |<<####################################################>>|
  |           |         |                                  |
  |           |         | D1. CONTROL (join UAC2<->confY)  |
  |           |         |++++++++++++++++++++++++++++++++>>|
  |           |         |                                  |--+  join
  |           |         |                                  |  | UAC2 &
  |           |         |                       D2. 200 OK |<-+ confY
  |           |         |<<++++++++++++++++++++++++++++++++|
  |           |         |                                  |
  |           |<<########################################>>|
  |           |            Now UAC2 is mixed too           |
  |           |<#########################################>>|
  |           |         |                                  |
  |<*talking*>|         |                                  |
  |           |         |                                  |
  .           .         .                                  .
  .           .         .                                  .

       Figure 23: Conference-Based Approach: Framework Transactions

   The AS uses two different packages to accomplish this scenario: the
   Mixer package (to create the mixing entity and join the UACs) and the
   IVR package (to record what happens in the conference).  The
   framework transaction steps can be described as follows:

   o  First of all, the AS creates a new hidden conference by means of a
      <createconference> request (A1).  This conference is properly
      configured according to the use it is assigned to.  In fact, since
      only two participants will be joined to it, both
      'reserved-talkers' and 'reserved-listeners' are set to 2, just as
      the 'n' value for the N-best audio mixing algorithm.  The video
      layout is also set accordingly (<single-view>/<dual-view>).

   o  The MS sends notification of the successful creation of the new
      conference in a 200 framework message (A2).  The identifier
      assigned to the conference, which will be used in subsequent
      requests addressed to it, is 6013f1e.

   o  The AS requests a new recording for the newly created conference.
      To do so, it places a proper request to the IVR package (B1).  The
      AS is interested in a video recording (type=video/mpeg), which
      must not last longer than 3 hours (maxtime=10800s), after which
      the recording must end.  Additionally, no beep must be played on
      the conference (beep=false), and the recording must start
      immediately whether or not any audio activity has been reported
      (vadinitial=false is the default value for <record>).

   o  The transaction is handled by the MS, and when the dialog has been
      successfully started, a 200 OK is issued to the AS (B2).  The
      message contains the dialogid associated with the dialog
      (00b29fb), which the AS must refer to for later notifications.

   o  At this point, the AS attaches both UACs to the conference with
      two separate <join> directives (C1/D1).  When the MS confirms the
      success of both operations (C2/D2), the two UACs are actually in
      contact with each other (even though indirectly, since a hidden
      conference they're unaware of is on their path), and their media
      contribution is recorded.

A1. AS -> MS (CFW CONTROL, createconference)
--------------------------------------------
   CFW 238e1f2946e8 CONTROL
   Control-Package: msc-mixer
   Content-Type: application/msc-mixer+xml
   Content-Length: 395

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <createconference reserved-talkers="2" reserved-listeners="2">
         <audio-mixing type="nbest" n="2"/>
         <video-layouts>
            <video-layout min-participants='1'>
               <single-view/>
            </video-layout>
            <video-layout min-participants='2'>
               <dual-view/>
            </video-layout>
         </video-layouts>
         <video-switch>
            <controller/>
         </video-switch>
      </createconference>
   </mscmixer>

A2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 238e1f2946e8 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 151

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <response status="200" reason="Conference created"
                conferenceid="6013f1e"/>
   </mscmixer>

B1. AS -> MS (CFW CONTROL, record)
----------------------------------
   CFW 515f007c5bd0 CONTROL
   Control-Package: msc-ivr
   Content-Type: application/msc-ivr+xml
   Content-Length: 226

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <dialogstart conferenceid="6013f1e">
         <dialog>
            <record beep="false" type="video/mpeg" maxtime="10800s"/>
         </dialog>
      </dialogstart>
   </mscivr>

B2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 515f007c5bd0 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="00b29fb"/>
   </mscivr>

C1. AS -> MS (CFW CONTROL, join)
--------------------------------
   CFW 0216231b1f16 CONTROL
   Control-Package: msc-mixer
   Content-Type: application/msc-mixer+xml
   Content-Length: 123

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <join id1="10514b7f:6a900179" id2="6013f1e"/>
   </mscmixer>

C2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 0216231b1f16 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 125

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <response status="200" reason="Join successful"/>
   </mscmixer>

D1. AS -> MS (CFW CONTROL, join)
--------------------------------
   CFW 140e0f763352 CONTROL
   Control-Package: msc-mixer
   Content-Type: application/msc-mixer+xml
   Content-Length: 124

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <join id1="219782951:0b9d3347" id2="6013f1e"/>
   </mscmixer>

D2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 140e0f763352 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 125

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <response status="200" reason="Join successful"/>
   </mscmixer>

   The recording of the conversation can subsequently be accessed by the
   AS by waiting for an event notification from the MS.  This event,
   which will be associated with the previously started recording
   dialog, will contain the URI of the recorded file.  Such an event may
   be triggered by either a natural completion of the dialog (e.g., the
   dialog has reached its programmed 3 hours) or any interruption of the
   dialog itself (e.g., the AS actively requests that the recording be
   interrupted, since the call between the UACs ended).

6.2.3.  Recording a Conversation

   The previous section described how to take advantage of the
   conferencing functionality of the Mixer package in order to allow the
   recording of phone calls in a simple way.  However, using a dedicated
   mixer just for a phone call might be considered overkill.  This
   section shows how recording a conversation and subsequently playing
   it out can be accomplished without a mixing entity involved in the
   call, i.e., by using the Direct Connection approach as described in
   Section 6.2.1.

   As explained previously, if the AS wants to record a phone call
   between two UACs, the use of just the <join> directive without a
   mixer forces the AS to just rely on separate recording commands.
   That is, the AS can only instruct the MS to separately record the
   media flowing on each media leg: a recording for all the data coming
   from UAC1, and a different recording for all the data coming from
   UAC2.  If someone subsequently wants to access the whole
   conversation, the AS may take at least two different approaches:

   1.  It may mix the two recordings itself (e.g., by delegating it to
       an offline mixing entity) in order to obtain a single file
       containing the combination of the two recordings.  This way, a
       simple playout as described in Section 6.1.2 would suffice.

   2.  Alternatively, it may take advantage of the mixing functionality
       provided by the MS itself.  One way to do this is to create a
       hidden conference on the MS, attach the UAC as a passive
       participant to it, and play the separate recordings on the
       conference as announcements.  This way, the UAC accessing
       the recording would experience both of the recordings at the
       same time.

   The second approach is considered in this section.  The framework
   transaction as described in Figure 24 assumes that a recording has
   already been requested for both UAC1 and UAC2, that the phone call
   has ended, and that the AS has successfully received the URIs to both
   of the recordings from the MS.  Such steps are not described again,
   since they would be quite similar to the steps described in
   Section 6.1.2.  As mentioned previously, the idea is to use a
   properly constructed hidden conference to mix the two separate
   recordings on the fly and present them to the UAC.  It is, of course,
   up to the AS to subsequently unjoin the user from the conference and
   destroy the conference itself once the playout of the recordings ends
   for any reason.

 UAC3                     AS                                 MS
  |                       |                                  |
  | (UAC1 and UAC2 have previously been recorded; the AS has |
  |  the two different recordings available for playout.)    |
  |                       |                                  |
  |                       | A1. CONTROL (create conference)  |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ create
  |                       |                                  |  | conf &
  |                       |      A2. 200 OK (conferenceid=Y) |<-+ its ID
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |                       | B1. CONTROL (join UAC3 & confY)  |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ join
  |                       |                                  |  | UAC &
  |                       |                       B2. 200 OK |<-+ confY
  |                       |<+++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<######################################################>>|
  |   UAC3 is now a passive participant in the conference    |
  |<<######################################################>>|
  |                       |                                  |
  |                       | C1. CONTROL (play REC1 on confY) |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       | D1. CONTROL (play REC2 on confY) |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ Start
  |                       |                                  |  | both
  |                       |                                  |  | of the
  |                       |                                  |  |dialogs
  |                       |                       C2. 200 OK |<-+
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                       D2. 200 OK |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<########################################################|
  |  The two recordings are mixed and played together to UAC |
  |<<########################################################|
  |                       |                                  |
  |                       |       E1. CONTROL (<promptinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | E2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |       F1. CONTROL (<promptinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|

  |                       | F2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  .                       .                                  .
  .                       .                                  .

         Figure 24: Phone Call: Playout of a Recorded Conversation

   The diagram above assumes that a recording of both of the channels
   (UAC1 and UAC2) has already taken place.  Later, when we desire to
   play the whole conversation to a new user, UAC3, the AS may take care
   of the presented transactions.  The framework transaction steps are
   only apparently more complicated than those presented so far.  The
   only difference, in fact, is that transactions C and D are
   concurrent, since the recordings must be played together.

   o  First of all, the AS creates a new conference to act as a mixing
      entity (A1).  The settings for the conference are chosen according
      to the use case, e.g., the video layout, which is fixed to
      <dual-view>, and the switching type to <controller>.  When the
      conference has been successfully created (A2), the AS takes note
      of the conference identifier.

   o  At this point, UAC3 is attached to the conference as a passive
      user (B1).  There would be no point in letting the user contribute
      to the conference mix, since he will only need to watch a
      recording.  In order to specify his passive status, both the audio
      and video streams for the user are set to 'recvonly'.  If the
      transaction succeeds, the MS notifies the AS (B2).

   o  Once the conference has been created and UAC3 has been attached to
      it, the AS can request the playout of the recordings; in order to
      do so, it requests two concurrent <prompt> directives (C1 and D1),
      addressing the recording of UAC1 (REC1) and UAC2 (REC2),
      respectively.  Both of the prompts must be played on the
      previously created conference and not to UAC3 directly, as can be
      deduced from the 'conferenceid' attribute of the <dialog> element.

   o  The transactions "live their lives" exactly as explained for
      previous <prompt> examples.  The originating transactions are
      first prepared and started (C2, D2), and then, as soon as the
      playout ends, a related CONTROL message is triggered by the MS
      (E1, F1).  This notification may contain a <promptinfo> element
      with information about how the playout proceeded (e.g., whether
      the playout completed normally or was interrupted by a DTMF
      tone, etc.).

 A1. AS -> MS (CFW CONTROL, createconference)
 --------------------------------------------
    CFW 506e039f65bd CONTROL
    Control-Package: msc-mixer/1.0
    Content-Type: application/msc-mixer+xml
    Content-Length: 312

    <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
       <createconference reserved-talkers="0" reserved-listeners="1">
          <audio-mixing type="controller"/>
          <video-layouts>
             <video-layout min-participants='1'>
                <dual-view/>
             </video-layout>
          </video-layouts>
          <video-switch>
             <controller/>
          </video-switch>
       </createconference>
    </mscmixer>

 A2. AS <- MS (CFW 200 OK)
 -------------------------
    CFW 506e039f65bd 200
    Timeout: 10
    Content-Type: application/msc-mixer+xml
    Content-Length: 151

    <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
       <response status="200" reason="Conference created"
                 conferenceid="2625069"/>
    </mscmixer>

 B1. AS -> MS (CFW CONTROL, join)
 --------------------------------
    CFW 09202baf0c81 CONTROL
    Control-Package: msc-mixer/1.0
    Content-Type: application/msc-mixer+xml
    Content-Length: 214

    <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
       <join id1="aafaf62d:0eac5236" id2="2625069">
          <stream media="audio" direction="recvonly"/>
          <stream media="video" direction="recvonly"/>
       </join>
    </mscmixer>

 B2. AS <- MS (CFW 200 OK)
 -------------------------
    CFW 09202baf0c81 200
    Timeout: 10
    Content-Type: application/msc-mixer+xml
    Content-Length: 125

    <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
       <response status="200" reason="Join successful"/>
    </mscmixer>

 C1. AS -> MS (CFW CONTROL, play recording from UAC1)
 ----------------------------------------------------
    CFW 3c2a08be4562 CONTROL
    Control-Package: msc-ivr/1.0
    Content-Type: application/msc-ivr+xml
    Content-Length: 229

    <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
       <dialogstart conferenceid="2625069">
          <dialog>
             <prompt>
                <media
   loc="http://www.example.net/recordings/recording-4ca9fc2.mpg"/>
             </prompt>
          </dialog>
       </dialogstart>
    </mscivr>

 D1. AS -> MS (CFW CONTROL, play recording from UAC2)
 ----------------------------------------------------
    CFW 1c268d810baa CONTROL
    Control-Package: msc-ivr/1.0
    Content-Type: application/msc-ivr+xml
    Content-Length: 229

    <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
       <dialogstart conferenceid="2625069">
          <dialog>
             <prompt>
                <media
   loc="http://www.example.net/recordings/recording-39dfef4.mpg"/>
             </prompt>
          </dialog>
       </dialogstart>
    </mscivr>

 C2. AS <- MS (CFW 200 OK)
 -------------------------
    CFW 1c268d810baa 200
    Timeout: 10
    Content-Type: application/msc-ivr+xml
    Content-Length: 137

    <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
       <response status="200" reason="Dialog started"
                 dialogid="7a457cc"/>
    </mscivr>

 D2. AS <- MS (CFW 200 OK)
 -------------------------
    CFW 3c2a08be4562 200
    Timeout: 10
    Content-Type: application/msc-ivr+xml
    Content-Length: 137

    <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
       <response status="200" reason="Dialog started"
                 dialogid="1a0c7cf"/>
    </mscivr>

 E1. AS <- MS (CFW CONTROL event, playout of recorded UAC1 ended)
 ----------------------------------------------------------------
    CFW 77aec0735922 CONTROL
    Control-Package: msc-ivr/1.0
    Content-Type: application/msc-ivr+xml
    Content-Length: 230

    <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
       <event dialogid="7a457cc">
          <dialogexit status="1" reason="Dialog successfully completed">
             <promptinfo duration="10339" termmode="completed"/>
          </dialogexit>
       </event>
    </mscivr>

 E2. AS -> MS (CFW 200, ACK to 'CONTROL event')
 ----------------------------------------------
    CFW 77aec0735922 200

 F1. AS <- MS (CFW CONTROL event, playout of recorded UAC2 ended)
 ----------------------------------------------------------------
    CFW 62726ace1660 CONTROL
    Control-Package: msc-ivr/1.0
    Content-Type: application/msc-ivr+xml
    Content-Length: 230

    <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
       <event dialogid="1a0c7cf">
          <dialogexit status="1" reason="Dialog successfully completed">
             <promptinfo duration="10342" termmode="completed"/>
          </dialogexit>
       </event>
    </mscivr>

 F2. AS -> MS (CFW 200, ACK to 'CONTROL event')
 ----------------------------------------------
    CFW 62726ace1660 200

6.3.  Conferencing

   One of the most important services the MS must be able to provide is
   mixing.  This involves mixing media streams from different sources
   and delivering the resulting mix(es) to each interested party, often
   according to per-user policies, settings, and encoding.  A typical
   scenario involving mixing is, of course, media conferencing.  In such
   a scenario, the media sent by each participant is mixed, and each
   participant typically receives the overall mix, excluding its own
   contribution and encoded in the format it negotiated.  This example
   points out in a quite clear way how mixing must take care of the
   profile of each involved entity.

   A media perspective of such a scenario is depicted in Figure 25.

                                +-------+
                                |  UAC  |
                                |   C   |
                                +-------+
                                   " ^
                           C (RTP) " "
                                   " "
                                   " " A+B (RTP)
                                   v "
   +-------+  A (RTP)           +--------+  A+C (RTP)         +-------+
   |  UAC  |===================>| Media  |===================>|  UAC  |
   |   A   |<===================| Server |<===================|   B   |
   +-------+         B+C (RTP)  +--------+           B (RTP)  +-------+

                 Figure 25: Conference: Media Perspective

   From the framework point of view, when the UACs' legs are not
   attached to anything yet, what appears is shown in Figure 26: since
   there are no connections involving the UACs yet, the frames they
   might be sending are discarded, and nothing is sent back to them
   (except for silence, if its transmission is requested).

                                     MS
                             +----------------+
               UAC A         |                |         UAC B
                 o----->>-------x          x.......>>.....o
                 o.....<<.......x          x-------<<-----o
                             |                |
                             |                |
                             |       xx       |
                             |       |.       |
                             +-------|.-------+
                                     |.
                                     ^v
                                     ^v
                                     |.
                                     oo
                                   UAC C

               Figure 26: Conference: UAC Legs Not Attached

   The next subsections will cover several typical scenarios involving
   mixing and conferencing as a whole, specifically:

   1.  Simple Bridging scenario, which is a very basic (i.e., no
       "special effects"; just mixing involved) conference involving one
       or more participants.

   2.  Rich Conference scenario, which enriches the Simple Bridging
       scenario by adding additional features typically found in
       conferencing systems (e.g., DTMF collection for PIN-based
       conference access, private and global announcements, recordings,
       and so on).

   3.  Coaching scenario, which is a more complex scenario that involves
       per-user mixing (customers, agents, and coaches don't all get the
       same mixes).

   4.  Sidebars scenario, which adds more complexity to the previous
       conferencing scenarios by involving sidebars (i.e., separate
       conference instances that only exist within the context of a
       parent conference instance) and the custom media delivery that
       follows.

   5.  Floor Control scenario, which provides some guidance on how floor
       control could be involved in a MEDIACTRL-based media conference.

   All of the above-mentioned scenarios depend on the availability of a
   mixing entity.  Such an entity is provided in the Media Control
   Channel Framework by the conferencing package.  Besides allowing for
   the interconnection of media sources as seen in the Direct Echo Test
   section, this package enables the creation of abstract connections
   that can be joined to multiple connections.  These abstract
   connections, called conferences, mix the contribution of each
   attached connection and feed them accordingly (e.g., a connection
   with a 'sendrecv' property would be able to contribute to the mix and
   listen to it, while a connection with a 'recvonly' property would
   only be able to listen to the overall mix but not actively contribute
   to it).

   That said, each of the above-mentioned scenarios will start more or
   less in the same way: by the creation of a conference connection (or
   more than one, as needed in some cases) to be subsequently referred
   to when it comes to mixing.  A typical framework transaction to
   create a new conference instance in the Media Control Channel
   Framework is depicted in Figure 27:

                    AS                                 MS
                    |                                  |
                    | 1. CONTROL (create conference)   |
                    |++++++++++++++++++++++++++++++++>>|
                    |                                  |--+ create
                    |                                  |  | conf and
                    |       2. 200 OK (conferenceid=Y) |<-+ its ID
                    |<<++++++++++++++++++++++++++++++++|
         map URI +--|                                  |
          X with |  |                                  |
           confY +->|                                  |
                    |                                  |
                    .                                  .
                    .                                  .

               Figure 27: Conference: Framework Transactions

   The call flow is quite straightforward and can typically be
   summarized in the following steps:

   o  The AS invokes the creation of a new conference instance by means
      of a CONTROL request (1); this request is addressed to the
      conferencing package (msc-mixer/1.0) and contains in the body the
      directive (<createconference>) with all the desired settings for
      the new conference instance.  In the example below, the mixing
      policy is to mix the five ('reserved-talkers') loudest speakers
      (nbest), while ten listeners at maximum are allowed.  Video
      settings are configured, including the mechanism used to select
      active video sources (<controller>, meaning the AS will explicitly
      instruct the MS about it) and details about the video layouts to
      make available.  In this example, the AS is instructing the MS to
      use a <single-view> layout when only one video source is active,
      to pass to a <quad-view> layout when at least two video sources
      are active, and to use a <multiple-5x1> layout whenever the number
      of sources is at least five.  Finally, the AS also subscribes to
      the "active-talkers" event, which means it wants to be informed
      (at a rate of 4 seconds) whenever an active participant is
      speaking.

   o  The MS creates the conference instance, assigns a unique
      identifier to it (6146dd5), and completes the transaction with a
      200 response (2).

   o  At this point, the requested conference instance is active and
      ready to be used by the AS.  It is then up to the AS to integrate
      the use of this identifier in its application logic.

   1. AS -> MS (CFW CONTROL)
   -------------------------
      CFW 3032e5fb79a1 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 489

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
        <createconference reserved-talkers="5" reserved-listeners="10">
           <audio-mixing type="nbest"/>
           <video-layouts>
             <video-layout min-participants='1'>
                <single-view/>
             </video-layout>
             <video-layout min-participants='2'>
                <quad-view/>
             </video-layout>
             <video-layout min-participants='5'>
                <multiple-5x1/>
             </video-layout>
           </video-layouts>
           <video-switch>
              <controller/>
           </video-switch>
           <subscribe>
              <active-talkers-sub interval="4"/>
           </subscribe>
        </createconference>
      </mscmixer>

   2. AS <- MS (CFW 200)
   ---------------------
      CFW 3032e5fb79a1 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 151

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Conference created"
                   conferenceid="6146dd5"/>
      </mscmixer>

6.3.1.  Simple Bridging

   As mentioned previously, the simplest way that an AS can use a
   conference instance is simple bridging.  In this scenario, the
   conference instance just acts as a bridge for all the participants
   that are attached to it.  The bridge takes care of transcoding, if
   needed (in general, different participants may use different codecs
   for their streams), echo cancellation (each participant will receive
   the overall mix, excluding its own contribution) and per-participant
   mixing (each participant may receive different mixed streams,
   according to what it needs/is allowed to send/receive).  This
   assumes, of course, that each interested participant must be somehow
   joined to the bridge in order to indirectly communicate with the
   other participants.  From the media perspective, the scenario can be
   seen as depicted in Figure 28.

                                      MS
                             +-----------------+
               UAC A         |                 |         UAC B
                 o----->>-------+~~~>{##}:::>+:::::::>>:::::o
                 o:::::<<:::::::+<:::{##}<~~~+-------<<-----o
                             |        ^:       |
                             |        |v       |
                             |        ++       |
                             |        |:       |
                             +--------|:-------+
                                      |:
                                      ^v
                                      ^v
                                      |:
                                      oo
                                    UAC C

                  Figure 28: Conference: Simple Bridging

   In the framework, the first step is obviously to create a new
   conference instance as seen in the introductory section (Figure 27).
   Assuming that a conference instance has already been created,
   bridging participants to it is quite straightforward and can be
   accomplished as seen in the Direct Echo Test scenario.  The only
   difference here is that each participant is not directly connected to
   itself (Direct Echo) or another UAC (Direct Connection) but to the
   bridge instead.  Figure 29 shows the example of two different UACs
   joining the same conference.  The example, as usual, hides the
   previous interaction between each of the two UACs and the AS, and
   instead focuses on what the AS does in order to actually join the
   participants to the bridge so that they can interact in a conference.
   Please note also that to make the diagram more readable, two
   different identifiers (UAC1 and UAC2) are used in place of the
   identifiers previously employed to introduce the scenario (UAC A,
   B, C).

 UAC1      UAC2         AS                                   MS
  |          |          |                                    |
  |          |          | A1. CONTROL (join UAC1 and confY)  |
  |          |          |++++++++++++++++++++++++++++++++++>>|
  |          |          |                                    |--+  join
  |          |          |                                    |  | UAC1 &
  |          |          |                         A2. 200 OK |<-+ confY
  |          |          |<<++++++++++++++++++++++++++++++++++|
  |          |          |                                    |
  |<<######################################################>>|
  |            Now UAC1 is mixed in the conference           |
  |<<######################################################>>|
  |          |          |                                    |
  |          |          | B1. CONTROL (join UAC2 and confY)  |
  |          |          |++++++++++++++++++++++++++++++++++>>|
  |          |          |                                    |--+  join
  |          |          |                                    |  | UAC2 &
  |          |          |                         B2. 200 OK |<-+ confY
  |          |          |<<++++++++++++++++++++++++++++++++++|
  |          |          |                                    |
  |          |<<###########################################>>|
  |          |    Now UAC2 too is mixed in the conference    |
  |          |<<###########################################>>|
  |          |          |                                    |
  .          .          .                                    .
  .          .          .                                    .

          Figure 29: Simple Bridging: Framework Transactions (1)

   The framework transaction steps are actually quite trivial and easy
   to understand, since they're very similar to some previously
   described scenarios.  The AS joins both UAC1 (id1 in A1) and UAC2
   (id1 in B1) to the conference (id2 in both transactions).  As a
   result of these two operations, both UACs are mixed in the
   conference.  Since no <stream> is explicitly provided in any of the
   transactions, all the media from the UACs (audio/video) are attached
   to the conference (as long as the conference has been properly
   configured to support both, of course).

   A1. AS -> MS (CFW CONTROL)
   --------------------------
      CFW 434a95786df8 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 120

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="e1e1427c:1c998d22" id2="6146dd5"/>
      </mscmixer>

   A2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 434a95786df8 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   B1. AS -> MS (CFW CONTROL)
   --------------------------
      CFW 5c0cbd372046 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 120

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="10514b7f:6a900179" id2="6146dd5"/>
      </mscmixer>

   B2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 5c0cbd372046 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   Once one or more participants have been attached to the bridge, their
   connections and how their media are handled by the bridge can be
   dynamically manipulated by means of another directive, called
   <modifyjoin>.  A typical use case for this directive is the change of
   direction of an existing media (e.g., a previously speaking
   participant is muted, which means its media direction changes from
   'sendrecv' to 'recvonly').  Figure 30 shows how a framework
   transaction requesting such a directive might appear.

 UAC1      UAC2         AS                                 MS
  |          |          |                                  |
  |          |          | 1. CONTROL (modifyjoin UAC1)     |
  |          |          |++++++++++++++++++++++++++++++++>>|
  |          |          |                                  |--+ modify
  |          |          |                                  |  | join
  |          |          |                        2. 200 OK |<-+ settings
  |          |          |<<++++++++++++++++++++++++++++++++|
  |          |          |                                  |
  |<<######################################################|
  |      Now UAC1 can receive but not send (recvonly)      |
  |<<######################################################|
  |          |          |                                  |
  .          .          .                                  .
  .          .          .                                  .

          Figure 30: Simple Bridging: Framework Transactions (2)

   The directive used to modify an existing join configuration is
   <modifyjoin>, and its syntax is exactly the same as the syntax
   required in <join> instructions.  In fact, the same syntax is used
   for identifiers (id1/id2).  Whenever a <modifyjoin> is requested and
   id1 and id2 address one or more joined connections, the AS is
   requesting a change of the join configuration.  In this case, the AS
   instructs the MS to mute (<stream> media=audio, direction=recvonly)
   UAC1 (id1=UAC1) in the conference (id2) it has been attached to
   previously.  Any other connection existing between them is left
   untouched.

   It is worth noting that the <stream> settings are enforced according
   to both the provided direction AND the id1 and id2 identifiers.  For
   instance, in this example id1 refers to UAC1, while id2 refers to the
   conference in the MS.  This means that the required modifications
   have to be applied to the stream specified in the <stream> element of
   the message, along the direction that goes from 'id1' to 'id2' (as
   specified in the <modifyjoin> element of the message).  In the
   provided example, the AS wants to mute UAC1 with respect to the
   conference.  To do so, the direction is set to 'recvonly', meaning
   that, for what affects id1, the media stream is only to be received.
   If id1 referred to the conference and id2 to UAC1, to achieve the
   same result the direction would have to be set to 'sendonly', meaning
   "id1 (the conference) can only send to id2 (UAC1), and no media
   stream must be received".  Additional settings for a <stream> (e.g.,
   audio volume, region assignments, and so on) follow the same
   approach, as discussed in subsequent sections.

   1. AS -> MS (CFW CONTROL)
   -------------------------
      CFW 57f2195875c9 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 182

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <modifyjoin id1="e1e1427c:1c998d22" id2="6146dd5">
            <stream media="audio" direction="recvonly"/>
         </modifyjoin>
      </mscmixer>

   2. AS <- MS (CFW 200 OK)
   ------------------------
      CFW 57f2195875c9 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 123

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join modified"/>
      </mscmixer>

6.3.2.  Rich Conference Scenario

   The previous scenario can be enriched with additional features often
   found in existing conferencing systems.  Typical examples include
   IVR-based menus (e.g., the DTMF collection for PIN-based conference
   access), partial and complete recordings in the conference (e.g., for

   the "state your name" functionality and recording of the whole
   conference), private and global announcements, and so on.  All of
   this can be achieved by means of the functionality provided by the
   MS.  In fact, even if the conferencing and IVR features come from
   different packages, the AS can interact with both of them and achieve
   complex results by correlating the effects of different transactions
   in its application logic.

   From the media and framework perspective, a typical Rich Conference
   scenario can be seen as depicted in Figure 31.

                                      MS
                                       +-------- (announcement.wav)
     (conference_recording.wav) <:::::+|
                                      :|
                             +--------:|--------+
               UAC A         |        :v        |         UAC B
                 o----->>-------+~~~>{##}:::>+:::::::>>:::::o
                 o:::::<<:::::::+<:::{##}<~~~+-------<<-----o
                             |        ^:     |  |
                             |        |v     v  |
                             |        ++     * (collect DTMF, get name)
                             |        |:        |
                             +--------|:--------+
                                      |:
                                      ^v
                                      ^v
                                      |:
                                      oo
                                    UAC C

              Figure 31: Conference: Rich Conference Scenario

   To identify a single sample scenario, let's consider this sequence
   for a participant joining a conference (which again we assume has
   already been created):

   1.  The UAC as usual INVITEs a URI associated with a conference, and
       the AS follows the previously explained procedure to have the UAC
       negotiate a new media session with the MS.

   2.  The UAC is presented with an IVR menu, in which it is requested
       to input a PIN code to access the conference.

   3.  If the PIN is correct, the UAC is asked to state its name so that
       it can be recorded.

   4.  The UAC is attached to the conference, and the previously
       recorded name is announced globally to the conference to
       advertise its arrival.

   Figure 32 shows a single UAC joining a conference.  The example, as
   usual, hides the previous interaction between the UAC and the AS, and
   instead focuses on what the AS does to actually interact with the
   participant and join it to the conference bridge.

 UAC                      AS                                 MS
  |                       |                                  |
  |                       | A1. CONTROL (request DTMF PIN)   |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |                       A2. 200 OK |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<########################################################|
  |   "Please input the PIN number to join the conference"   |
  |<<########################################################|
  |                       |                                  |
  |########################################################>>|
  |                   DTMF digits are collected              |--+ get
  |########################################################>>|  | DTMF
  |                       |                                  |<-+ digits
  |                       |      B1. CONTROL (<collectinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |       Compare DTMF +--| B2. 200 OK                       |
  |        digits with |  |++++++++++++++++++++++++++++++++>>|
  |     the PIN number +->|                                  |
  |                       | C1. CONTROL (record name)        |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |                       C2. 200 OK |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<########################################################|
  |          "Please state your name after the beep"         |
  |<<########################################################|
  |                       |                                  |
  |########################################################>>|
  |  Audio from the UAC is recorded (until timeout or DTMF)  |--+ save
  |########################################################>>|  | in a
  |                       |                                  |<-+ file
  |                       |       D1. CONTROL (<recordinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|

  |     Store recorded +--| D2. 200 OK                       |
  |       file to play |  |++++++++++++++++++++++++++++++++>>|
  |    announcement in +->|                                  |
  |   conference later    |                                  |
  |                       | E1. CONTROL (join UAC & confY)   |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ join
  |                       |                                  |  | UAC &
  |                       |                       E2. 200 OK |<-+ confY
  |                       |<+++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<######################################################>>|
  |     UAC is now included in the mix of the conference     |
  |<<######################################################>>|
  |                       |                                  |
  |                       | F1. CONTROL (play name on confY) |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |                       F2. 200 OK |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<########################################################|
  |  Global announcement: "Simon has joined the conference"  |
  |<<########################################################|
  |                       |                                  |
  |                       |       G1. CONTROL (<promptinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | G2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  .                       .                                  .
  .                       .                                  .

        Figure 32: Rich Conference Scenario: Framework Transactions

   As can be deduced from the sequence diagram above, the AS, in its
   business logic, correlates the results of different transactions,
   addressed to different packages, to implement a conferencing scenario
   more complex than the Simple Bridging scenario previously described.
   The framework transaction steps are as follows:

   o  Since this is a private conference, the UAC is to be presented
      with a request for a password, in this case a PIN number.  To do
      so, the AS instructs the MS (A1) to collect a series of DTMF
      digits from the specified UAC (connectionid=UAC).  The request
      includes both a voice message (<prompt>) and the described digit
      collection context (<collect>).  The PIN is assumed to be a

      4-digit number, and so the MS has to collect 4 digits maximum
      (maxdigits=4).  The DTMF digit buffer must be cleared before
      collecting (cleardigitbuffer=true), and the UAC can use the star
      key to restart the collection (escapekey=*), e.g., if the UAC is
      aware that he mistyped any of the digits and wants to start again.

   o  The transaction goes on as usual (A2), with the transaction being
      handled and notification of the dialog start being sent in a 200
      OK.  After that, the UAC is actually presented with the voice
      message and is subsequently requested to input the required PIN
      number.

   o  We assume that the UAC typed the correct PIN number (1234), which
      is reported by the MS to the AS by means of the usual MS-generated
      CONTROL event (B1).  The AS correlates this event to the
      previously started dialog by checking the referenced dialogid
      (06d1bac) and acks the event (B2).  It then extracts the
      information it needs from the event (in this case, the digits
      provided by the MS) from the <controlinfo> container (dtmf=1234)
      and verifies that it is correct.

   o  Since the PIN is correct, the AS can proceed to the next step,
      i.e., asking the UAC to state his name, in order to subsequently
      play the recording on the conference to report the new
      participant.  Again, this is done with a request to the IVR
      package (C1).  The AS instructs the MS to play a voice message
      ("state your name after the beep"), to be followed by a recording
      of only the audio from the UAC (in stream, media=audio/sendonly,
      while media=video/inactive).  A beep must be played right before
      the recording starts (beep=true), and the recording must only last
      3 seconds (maxtime=3s), since it is only needed as a brief
      announcement.

   o  Without delving again into the details of a recording-related
      transaction (C2), the AS finally gets the URI of the requested
      recording (D1, acked in D2).

   o  At this point, the AS attaches the UAC (id1) to the conference
      (id2), just as explained for the Simple Bridging scenario (E1/E2).

   o  Finally, to notify the other participants that a new participant
      has arrived, the AS requests a global announcement on the
      conference.  This is a simple <prompt> request to the IVR package
      (F1), as explained in previous sections (e.g., Section 6.1.2,
      among others), but with a slight difference: the target of the
      prompt is not a connectionid (a media connection) but the
      conference itself (conferenceid=6146dd5).  As a result of this
      transaction, the announcement would be played on all the media

      connections attached to the conference that are allowed to receive
      media from it.  The AS specifically requests that two media files
      be played:

      1.  the media file containing the recorded name of the new user as
          retrieved in D1 ("Simon...").

      2.  a pre-recorded media file explaining what happened ("... has
          joined the conference").

      The transaction then follows its usual flow (F2), and the event
      that sends notification regarding the end of the announcement (G1,
      acked in G2) concludes the scenario.

A1. AS -> MS (CFW CONTROL, collect)
-----------------------------------
   CFW 50e56b8d65f9 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 311

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <dialogstart connectionid="10514b7f:6a900179">
        <dialog>
          <prompt>
              <media
           loc="http://www.example.net/prompts/conf-getpin.wav"
           type="audio/x-wav"/>
          </prompt>
          <collect maxdigits="4" escapekey="*" cleardigitbuffer="true"/>
        </dialog>
     </dialogstart>
   </mscivr>

A2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 50e56b8d65f9 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="06d1bac"/>
   </mscivr>

B1. AS <- MS (CFW CONTROL event)
--------------------------------
   CFW 166d68a76659 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 272

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <event dialogid="06d1bac">
         <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="2312" termmode="completed"/>
            <collectinfo dtmf="1234" termmode="match"/>
         </dialogexit>
      </event>
   </mscivr>

B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 166d68a76659 200

C1. AS -> MS (CFW CONTROL, record)
----------------------------------
   CFW 61fd484f196e CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 373

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <dialogstart connectionid="10514b7f:6a900179">
         <dialog>
            <prompt>
               <media
         loc="http://www.example.net/prompts/conf-rec-name.wav"
         type="audio/x-wav"/>
            </prompt>
            <record beep="true" maxtime="3s"/>
         </dialog>
         <stream media="audio" direction="sendonly"/>
         <stream media="video" direction="inactive"/>
      </dialogstart>
   </mscivr>

C2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 61fd484f196e 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="1cf0549"/>
   </mscivr>

D1. AS <- MS (CFW CONTROL event)
--------------------------------
   CFW 3ec13ab96224 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 402

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <event dialogid="1cf0549">
       <dialogexit status="1" reason="Dialog successfully completed">
         <promptinfo duration="4988" termmode="completed"/>
         <recordinfo duration="3000" termmode="maxtime">
           <mediainfo
  loc="http://www.example.net/recordings/recording-1cf0549.wav"
  type="audio/x-wav" size="48044"/>
         </recordinfo>
       </dialogexit>
     </event>
   </mscivr>

D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 3ec13ab96224 200

E1. AS -> MS (CFW CONTROL, join)
--------------------------------
   CFW 261d188b63b7 CONTROL
   Control-Package: msc-mixer/1.0
   Content-Type: application/msc-mixer+xml
   Content-Length: 120

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <join id1="10514b7f:6a900179" id2="6146dd5"/>
   </mscmixer>

E2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 261d188b63b7 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 125

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
      <response status="200" reason="Join successful"/>
   </mscmixer>

F1. AS -> MS (CFW CONTROL, play)
--------------------------------
   CFW 718c30836f38 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 334

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <dialogstart conferenceid="6146dd5">
       <dialog>
         <prompt>
           <media
  loc="http://www.example.net/recordings/recording-1cf0549.wav"
  type="audio/x-wav"/>
               <media
  loc="http://www.example.net/prompts/conf-hasjoin.wav"
  type="audio/x-wav"/>
         </prompt>
       </dialog>
     </dialogstart>
   </mscivr>

F2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 718c30836f38 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="5f4bc7e"/>
   </mscivr>

G1. AS <- MS (CFW CONTROL event)
--------------------------------
   CFW 6485194f622f CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 229

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <event dialogid="5f4bc7e">
         <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="1838" termmode="completed"/>
         </dialogexit>
      </event>
   </mscivr>

G2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 6485194f622f 200

6.3.3.  Coaching Scenario

   Another typical conference-based use case is the so-called Coaching
   scenario.  In such a scenario, a customer (called "A" in the
   following example) places a call to a business call center.  An agent
   (B) is assigned to the customer.  A coach (C), who cannot be heard by
   the customer, provides the agent with whispered suggestions about
   what to say.  This scenario is also described in [RFC4597].

   As can be deduced from the scenario description, per-user policies
   for media mixing and delivery, i.e., who can hear what, are very
   important.  The MS must make sure that only the agent can hear the
   coach's suggestions.  Since this is basically a multiparty call
   (despite what the customer might be thinking), a mixing entity is
   needed in order to accomplish the scenario requirements.  To
   summarize:

   o  The customer (A) must only hear what the agent (B) says.

   o  The agent (B) must be able to hear both A and the coach (C).

   o  C must be able to hear both A and B in order to give B the right
      suggestions and also be aware of the whole conversation.

   From the media and framework perspective, such a scenario can be seen
   as depicted in Figure 33.

    **************              +-------+
    * A=Customer *              |  UAC  |
    * B=Agent    *              |   C   |
    * C=Coach    *              +-------+
    **************                 " ^
                           C (RTP) " "
                                   " "
                                   " " A+B (RTP)
                                   v "
   +-------+  A (RTP)           +--------+  A+C (RTP)         +-------+
   |  UAC  |===================>| Media  |===================>|  UAC  |
   |   A   |<===================| Server |<===================|   B   |
   +-------+           B (RTP)  +--------+           B (RTP)  +-------+

              Figure 33: Coaching Scenario: Media Perspective

   From the framework point of view, when the previously mentioned legs
   are not attached to anything yet, what appears is shown in Figure 34.

                                    MS
                      +---------------------------+
                      |                           |
        UAC A         |                           |         UAC B
          o.....<<.......x                     x-------<<-----o
          o----->>-------x                     x.......>>.....o
                      |                           |
                      |                           |
                      |                           |
                      |                           |
                      |            xx             |
                      |            .|             +
                      +------------v^-------------+
                                   v^
                                   .|
                                   .|
                                   oo
                                  UAC C

            Figure 34: Coaching Scenario: UAC Legs Not Attached

   By contrast, what the scenario should look like is depicted in
   Figure 35.  The customer receives media directly from the agent
   ('recvonly'), while all of the three involved participants contribute
   to a hidden conference.  Of course, the customer is not allowed to

   receive the mixed flows from the conference ('sendonly'), unlike the
   agent and the coach, who must both be aware of the whole conversation
   ('sendrecv').

                                    MS
                      +---------------------------+
                      |                           |
        UAC A         |                           |         UAC B
          o-----<<-------+----<<----+----<<----+-------<<-----o
          o----->>-------+          |          +------->>-----o
                      |  |          v          ^  |
                      |  +~~~~~~~>[##]::::>::::+  |
                      |            v^             |
                      |            ||             |
                      |            ++             |
                      |            :|             +
                      +------------v^-------------+
                                   v^
                                   :|
                                   :|
                                   oo
                                  UAC C

         Figure 35: Coaching Scenario: UAC Legs Mixed and Attached

   In the framework, this can be achieved by means of the Mixer Control
   Package, which, as demonstrated in the previous conferencing
   examples, can be exploited whenever mixing and joining entities are
   needed.  The needed steps can be summarized in the following list:

   1.  First of all, a hidden conference is created.

   2.  Then, the three participants are all attached to it, each with a
       custom mixing policy, specifically:

       *  the customer (A) as 'sendonly'.

       *  the agent (B) as 'sendrecv'.

       *  the coach (C) as 'sendrecv' and with a gain of -3 dB to halve
          the volume of its own contribution (so that the agent actually
          hears the customer at a louder volume and hears the coach
          whispering).

   3.  Finally, the customer is joined to the agent as a passive
       receiver ('recvonly').

   A diagram of such a sequence of transactions is depicted in
   Figure 36:

  A      B      C       AS                                 MS
  |      |      |       |                                  |
  |      |      |       | A1. CONTROL (create conference)  |
  |      |      |       |++++++++++++++++++++++++++++++++>>|
  |      |      |       |                                  |--+ create
  |      |      |       |                                  |  | conf and
  |      |      |       |      A2. 200 OK (conferenceid=Y) |<-+ its ID
  |      |      |       |<<++++++++++++++++++++++++++++++++|
  |      |      |       |                                  |
  |      |      |       | B1. CONTROL (join A-->confY)     |
  |      |      |       |++++++++++++++++++++++++++++++++>>|
  |      |      |       |                                  |--+ join A
  |      |      |       |                                  |  | & confY
  |      |      |       |                       B2. 200 OK |<-+ sendonly
  |      |      |       |<<++++++++++++++++++++++++++++++++|
  |      |      |       |                                  |
  |######################################################>>|
  |   Customer (A) is mixed (sendonly) in the conference   |
  |######################################################>>|
  |      |      |       |                                  |
  |      |      |       | C1. CONTROL (join B<->confY)     |
  |      |      |       |++++++++++++++++++++++++++++++++>>|
  |      |      |       |                                  |--+ join B
  |      |      |       |                                  |  | & confY
  |      |      |       |                       C2. 200 OK |<-+ sendrecv
  |      |      |       |<<++++++++++++++++++++++++++++++++|
  |      |      |       |                                  |
  |      |<<#############################################>>|
  |      | Agent (B) is mixed (sendrecv) in the conference |
  |      |<##############################################>>|
  |      |      |       |                                  |
  |      |      |       | D1. CONTROL (join C<->confY)     |
  |      |      |       |++++++++++++++++++++++++++++++++>>|
  |      |      |       |                                  |--+ join C
  |      |      |       |                                  |  | & confY
  |      |      |       |                       D2. 200 OK |<-+ sendrecv
  |      |      |       |<<++++++++++++++++++++++++++++++++|
  |      |      |       |                                  |
  |      |      |<<######################################>>|
  |      |      |  Coach (C) is mixed (sendrecv) as well   |
  |      |      |<<######################################>>|
  |      |      |       |                                  |

  |      |      |       | E1. CONTROL (join A<--B)         |
  |      |      |       |++++++++++++++++++++++++++++++++>>|
  |      |      |       |                                  |--+ join
  |      |      |       |                                  |  | A & B
  |      |      |       |                       E2. 200 OK |<-+ recvonly
  |      |      |       |<<++++++++++++++++++++++++++++++++|
  |      |      |       |                                  |
  |<<######################################################|
  | Finally, Customer (A) is joined (recvonly) to Agent (B)|
  |<<######################################################|
  |      |      |       |                                  |
  .      .      .       .                                  .
  .      .      .       .                                  .

           Figure 36: Coaching Scenario: Framework Transactions

   o  First of all, the AS creates a new hidden conference by means of a
      <createconference> request (A1).  This conference is properly
      configured according to the use it is assigned to, i.e., to mix
      all the involved parties accordingly.  Since only three
      participants will be joined to it, 'reserved-talkers' is set to 3.
      'reserved-listeners', on the other hand, is set to 2, since only
      the agent and the coach must receive a mix, while the customer
      must be unaware of the coach.  Finally, the video layout is set to
      <dual-view> for the same reason, since only the customer and the
      agent must appear in the mix.

   o  The MS sends notification of the successful creation of the new
      conference in a 200 framework message (A2).  The identifier
      assigned to the conference, which will be used in subsequent
      requests addressed to it, is 1df080e.

   o  Now that the conference has been created, the AS joins the three
      actors to it with different policies, namely (i) the customer (A)
      is joined as 'sendonly' to the conference (B1), (ii) the agent (B)
      is joined as 'sendrecv' to the conference (C1), and (iii) the
      coach (C) is joined as 'sendrecv' (but audio only) to the
      conference and with a lower volume (D1).  The custom policies are
      enforced by means of properly constructed <stream> elements.

   o  The MS takes care of the requests and acks them (B2, C2, D2).  At
      this point, the conference will receive media from all the actors
      but only provide the agent and the coach with the resulting mix.

   o  To complete the scenario, the AS joins A with B directly as
      'recvonly' (E1).  The aim of this request is to provide A with
      media too, namely the media contributed by B.  This way, A is
      unaware of the fact that its media are accessed by C by means of
      the hidden mixer.

   o  The MS takes care of this request too and acks it (E2), concluding
      the scenario.

   A1. AS -> MS (CFW CONTROL, createconference)
   --------------------------------------------
      CFW 238e1f2946e8 CONTROL
      Control-Package: msc-mixer
      Content-Type: application/msc-mixer+xml
      Content-Length: 329

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <createconference reserved-talkers="3" reserved-listeners="2">
            <audio-mixing type="nbest"/>
            <video-layouts>
               <video-layout min-participants='1'>
                  <dual-view/>
               </video-layout>
            </video-layouts>
            <video-switch>
               <controller/>
            </video-switch>
         </createconference>
      </mscmixer>

   A2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 238e1f2946e8 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 151

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Conference created"
                   conferenceid="1df080e"/>
      </mscmixer>

   B1. AS -> MS (CFW CONTROL, join)
   --------------------------------
      CFW 2eb141f241b7 CONTROL
      Control-Package: msc-mixer
      Content-Type: application/msc-mixer+xml
      Content-Length: 226

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="10514b7f:6a900179" id2="1df080e">
            <stream media="audio" direction="sendonly"/>
            <stream media="video" direction="sendonly"/>
         </join>
      </mscmixer>

   B2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 2eb141f241b7 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   C1. AS -> MS (CFW CONTROL, join)
   --------------------------------
      CFW 515f007c5bd0 CONTROL
      Control-Package: msc-mixer
      Content-Type: application/msc-mixer+xml
      Content-Length: 122

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="756471213:c52ebf1b" id2="1df080e"/>
      </mscmixer>

   C2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 515f007c5bd0 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   D1. AS -> MS (CFW CONTROL, join)
   --------------------------------
      CFW 0216231b1f16 CONTROL
      Control-Package: msc-mixer
      Content-Type: application/msc-mixer+xml
      Content-Length: 221

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="z9hG4bK19461552:1353807a" id2="1df080e">
            <stream media="audio">
               <volume controltype="setgain" value="-3"/>
            </stream>
         </join>
      </mscmixer>

   D2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 0216231b1f16 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   E1. AS -> MS (CFW CONTROL, join)
   --------------------------------
      CFW 140e0f763352 CONTROL
      Control-Package: msc-mixer
      Content-Type: application/msc-mixer+xml
      Content-Length: 236

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="10514b7f:6a900179" id2="756471213:c52ebf1b">
            <stream media="audio" direction="recvonly"/>
            <stream media="video" direction="recvonly"/>
         </join>
      </mscmixer>

   E2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 140e0f763352 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

6.3.4.  Sidebars

   Within the context of conferencing, there could be a need for
   so-called sidebars, or side conferences.  This would be the case, for
   instance, if two or more participants of a conference were willing to
   create a side conference among each other while still receiving part
   of the original conference mix in the background.  Motivations for
   such a use case can be found in both [RFC4597] and [RFC5239].  It is
   clear that in such a case the side conference is actually a separate
   conference but must also somehow be related to the original
   conference.  Although the application-level relationship is out of
   scope for this document (this "belongs" to Centralized Conferencing
   (XCON)), the media stream relationship is more relevant here, because
   there is a stronger relationship at the media level from the
   MEDIACTRL point of view.  Consequently, it is interesting to analyze
   how sidebars could be used to construct the conference mixes
   according to the MEDIACTRL specification.

   The scenario presented in this section is a conference hosting four
   different participants: A, B, C, and D.  All these participants are
   attached to the conference as active senders and receivers of the
   existing media streams.  At a certain point in time, two participants

   (B and D) decide to create a sidebar just for them.  The sidebar they
   want to create is constructed so that only audio is involved.  The
   audio mix of the sidebar must not be made available to the main
   conference.  The mix of the conference must be attached to the
   sidebar, but with a lower volume (30%), because it is just background
   to the actual conversation.  This would allow both B and D to talk to
   each other without A and C listening to them, while B and D could
   still have an overview of what's happening in the main conference.

   From the media and framework perspective, such a scenario can be seen
   as depicted in Figure 37.

                                 +-------+
                                 |  UAC  |
                                 |   C   |
                                 +-------+
                                    " ^
                            C (RTP) " "
                                    " "
                                    " " A (RTP)
                                    v "
    +-------+  A (RTP)           +--------+  D+[a+c] (RTP)     +-------+
    |  UAC  |===================>| Media  |===================>|  UAC  |
    |   A   |<===================| Server |<===================|   B   |
    +-------+           C (RTP)  +--------+           B (RTP)  +-------+
                                    ^ "
                                    " " B+[a+c] (RTP)
                                    " "
                            D (RTP) " "
                                    " v
                                 +-------+
                                 |  UAC  |
                                 |   D   |
                                 +-------+

                  Figure 37: Sidebars: Media Perspective

   From the framework point of view, when all the participants are
   attached to the main conference, what appears is shown in Figure 38.

                                    UAC C
                                      oo
                                      :|
                                      ^v
                                      ^v
                                      :|
                             +--------:|-------+
                             |        :|       |
                             |        ++       |
               UAC A         |        ^|       |         UAC B
                 o----->>-------+~~~>{##}:::>+:::::::>>:::::o
                 o:::::<<:::::::+<:::{##}<~~~+-------<<-----o
                             |        ^:       |
                             |        |v       |
                             |        ++       |
                             |        |:       |
                             +--------|:-------+
                                      |:
                                      ^v
                                      ^v
                                      |:
                                      oo
                                    UAC D

             Figure 38: Sidebars: UAC Legs in Main Conference

   By contrast, what the scenario should look like is depicted in
   Figure 39.  A new mixer is created to host the sidebar.  The main mix
   is then attached as 'sendonly' to the sidebar mix at a lower volume
   (in order to provide the sidebar users with a background of the main
   conference).  The two interested participants (B and D) have their
   audio leg detached from the main conference and attached to the
   sidebar.  This detachment can be achieved by either actually
   detaching the leg or just modifying the status of the leg to
   'inactive'.  Note that this only affects the audio stream: the video
   of the two users is still attached to the main conference, and what
   happens at the application level may or may not have been changed
   accordingly (e.g., XCON protocol interactions).

   Please note that the main conference is assumed to be in place and
   the involved participants (A, B, C, and D) attached ('sendrecv')
   to it.

                                 UAC C
                                   oo
                                   :|
                                   ^v
                                   ^v
                                   :|
                          +--------:|----------------+
                          |        :|                |
                          |        ++                |
            UAC A         |        ^|                |          UAC B
              o----->>-------+~~~>{##}:::>{##}:::>+:::::::>>:::::o
              o:::::<<:::::::+<:::{##}    {##}<~~~+-------<<-----o
                          |                ^:        |
                          |                ++        |
                          |                |v        |
                          +----------------|:--------+
                                           |:
                                           ^v
                                           ^v
                                           |:
                                           oo
                                          UAC D

             Figure 39: Sidebars: UAC Legs Mixed and Attached

   The situation may subsequently be reverted (e.g., destroying the
   sidebar conference and reattaching B and D to the main conference
   mix) in the same way.  The AS would just need to unjoin B and D from
   the hidden conference and change their connection with the main
   conference back to 'sendrecv'.  After unjoining the main mix and the
   sidebar mix, the sidebar conference could then be destroyed.  For
   brevity, and because similar transactions have already been
   presented, these steps are not described here.

   In the framework, just as in the previous section, the presented
   scenario can again be achieved by means of the Mixer Control Package.
   The needed steps can be summarized in the following list:

   1.  First of all, a hidden conference is created (the sidebar mix).

   2.  Then, the main conference mix is attached to it as 'sendonly' and
       with a gain of -5 dB to limit the volume of its own contribution
       to 30% (so that B and D can hear each other at a louder volume
       while still listening to what's happening in the main conference
       in the background).

   3.  B and D are detached from the main mix for audio (<modifyjoin>
       with 'inactive' status).

   4.  B and D are attached to the hidden sidebar mix for audio.

   Note that for detaching B and D from the main mix, a <modifyjoin>
   with an 'inactive' status is used, instead of an <unjoin>.  The
   motivation for this is related to how a subsequent rejoining of B and
   D to the main mix could take place.  In fact, by using <modifyjoin>
   the resources created when first joining B and D to the main mix
   remain in place, even if marked as unused at the moment.  An
   <unjoin>, on the other hand, would actually free those resources,
   which in turn could be granted to other participants joining the
   conference in the meantime.  This means that when needing to reattach
   B and D to the main mix, the MS may not have the resources to do so,
   resulting in an undesired failure.

   A diagram of such a sequence of transactions (where confX is the
   identifier of the pre-existing main conference mix) is depicted in
   Figure 40:

  B         D         AS                                 MS
  |         |         |                                  |
  |         |         | A1. CONTROL (create conference)  |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ create
  |         |         |                                  |  | conf and
  |         |         |      A2. 200 OK (conferenceid=Y) |<-+ its ID
  |         |         |<<++++++++++++++++++++++++++++++++|
  |         |         |                                  |
  |         |         | B1. CONTROL (join confX-->confY) |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ join confX
  |         |         |                                  |  | & confY
  |         |         |                       B2. 200 OK |<-+ sendonly
  |         |         |<<++++++++++++++++++++++++++++++++|    (30% vol)
  |         |         |                                  |
  |         |         | C1. CONTROL (modjoin B---confX)  |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ modjoin B
  |         |         |                                  |  | & confX
  |         |         |                       C2. 200 OK |<-+ (inactive)
  |         |         |<<++++++++++++++++++++++++++++++++|
  |         |         |                                  |

  |         |         | D1. CONTROL (join B<-->confY)    |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ join B
  |         |         |                                  |  | & confY
  |         |         |                       D2. 200 OK |<-+ sendrecv
  |         |         |<<++++++++++++++++++++++++++++++++|    (audio)
  |         |         |                                  |
  |<<##################################################>>|
  |   Participant B is mixed (sendrecv) in the sidebar   |
  |     (A, C, and D can't listen to her/him anymore)    |
  |<<##################################################>>|
  |         |         |                                  |
  |         |         | E1. CONTROL (modjoin D---confX)  |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ modjoin D
  |         |         |                                  |  | & confX
  |         |         |                       E2. 200 OK |<-+ (inactive)
  |         |         |<<++++++++++++++++++++++++++++++++|
  |         |         |                                  |
  |         |         | F1. CONTROL (join D<-->confY)    |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ join D
  |         |         |                                  |  | & confY
  |         |         |                       F2. 200 OK |<-+ sendrecv
  |         |         |<<++++++++++++++++++++++++++++++++|    (audio)
  |         |         |                                  |
  |         |<<########################################>>|
  |         |  D is mixed (sendrecv) in the sidebar too  |
  |         |  (A and C can't listen to her/him anymore) |
  |         |<<########################################>>|
  |         |                                            |
  .         .                                            .
  .         .                                            .

                Figure 40: Sidebars: Framework Transactions

   o  First of all, the hidden conference mix is created (A1).  The
      request is basically the same as that presented in previous
      sections, i.e., a <createconference> request addressed to the
      Mixer package.  The request is very lightweight and asks the MS to
      only reserve two listener seats ('reserved-listeners', since only
      B and D have to hear something) and three talker seats
      ('reserved-listeners', because in addition to B and D the main mix
      is also an active contributor to the sidebar).  The mixing will be
      driven by directives from the AS (mix-type=controller).  When the
      mix is successfully created, the MS provides the AS with its
      identifier (519c1b9).

   o  As a first transaction after that, the AS joins the audio from the
      main conference and the newly created sidebar conference mix (B1).
      Only audio needs to be joined (media=audio), with a 'sendonly'
      direction (i.e., only flowing from the main conference to the
      sidebar and not vice versa) and at 30% volume with respect to the
      original stream (setgain=-5 dB).  A successful completion of the
      transaction is reported to the AS (B2).

   o  At this point, the AS makes the connection of B (2133178233:
      18294826) and the main conference (2f5ad43) inactive by means of a
      <modifyjoin> directive (C1).  The request is taken care of by the
      MS (C2), and B is actually excluded from the mix for sending as
      well as receiving.

   o  After that, the AS (D1) joins B (2133178233:18294826) to the
      sidebar mix created previously (519c1b9).  The MS attaches the
      requested connections and sends confirmation to the AS (D2).

   o  The same transactions already done for B are done for D as well
      (id1=1264755310:2beeae5b), i.e., the <modifyjoin> to make the
      connection in the main conference inactive (E1-2) and the <join>
      to attach D to the sidebar mix (F1-2).  At the end of these
      transactions, A and C will only listen to each other, while B and
      D will listen to each other and to the conference mix as a
      comfortable background.

   A1. AS -> MS (CFW CONTROL, createconference)
   --------------------------------------------
      CFW 7fdcc2331bef CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 198

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <createconference reserved-talkers="3" reserved-listeners="2">
            <audio-mixing type="controller"/>
         </createconference>
      </mscmixer>

   A2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 7fdcc2331bef 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 151

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Conference created"
                   conferenceid="519c1b9"/>
      </mscmixer>

   B1. AS -> MS (CFW CONTROL, join with setgain)
   ---------------------------------------------
      CFW 4e6afb6625e4 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 226

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="2f5ad43" id2="519c1b9">
            <stream media="audio" direction="sendonly">
               <volume controltype="setgain" value="-5"/>
            </stream>
         </join>
      </mscmixer>

   B2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 4e6afb6625e4 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   C1. AS -> MS (CFW CONTROL, modifyjoin with 'inactive' status)
   -----------------------------------------------------------
      CFW 3f2dba317c83 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 193

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <modifyjoin id1="2133178233:18294826" id2="2f5ad43">
            <stream media="audio" direction="inactive"/>
         </modifyjoin>
      </mscmixer>

   C2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 3f2dba317c83 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 123

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join modified"/>
      </mscmixer>

   D1. AS -> MS (CFW CONTROL, join to sidebar)
   -------------------------------------------
      CFW 2443a8582d1d CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 181

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="2133178233:18294826" id2="519c1b9">
            <stream media="audio" direction="sendrecv"/>
         </join>
      </mscmixer>

   D2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 2443a8582d1d 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

   E1. AS -> MS (CFW CONTROL, modifyjoin with 'inactive' status)
   -----------------------------------------------------------
      CFW 436c6125628c CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 193

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <modifyjoin id1="1264755310:2beeae5b" id2="2f5ad43">
            <stream media="audio" direction="inactive"/>
         </modifyjoin>
      </mscmixer>

   E2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 436c6125628c 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 123

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join modified"/>
      </mscmixer>

   F1. AS -> MS (CFW CONTROL, join to sidebar)
   -------------------------------------------
      CFW 7b7ed00665dd CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 181

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <join id1="1264755310:2beeae5b" id2="519c1b9">
            <stream media="audio" direction="sendrecv"/>
         </join>
      </mscmixer>

   F2. AS <- MS (CFW 200 OK)
   -------------------------
      CFW 7b7ed00665dd 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 125

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join successful"/>
      </mscmixer>

6.3.5.  Floor Control

   As described in [RFC4597], floor control is a feature typically
   needed and employed in most conference scenarios.  In fact, while not
   a mandatory feature to implement when realizing a conferencing
   application, it provides additional control of the media streams
   contributed by participants, thus allowing for moderation of the
   available resources.  The Centralized Conferencing (XCON) framework
   [RFC5239] suggests the use of the Binary Floor Control Protocol
   (BFCP) [RFC4582] to achieve the aforementioned functionality.  That
   said, a combined use of floor control functionality and the tools
   made available by the MEDIACTRL specification for conferencing would
   definitely be interesting to investigate.  [RFC5567] introduces two
   different approaches to integrating floor control with the MEDIACTRL
   architecture: (i) a topology where the floor control server is
   co-located with the AS and (ii) a topology where the floor control
   server is co-located with the MS.  The two approaches are obviously
   different with respect to the amount of information the AS and the MS
   have to deal with, especially when thinking about the logic behind
   the floor queues and automated decisions.  Nevertheless, considering
   how the Media Control Channel Framework is conceived, approach (ii)
   would need a dedicated package (be it an extension or a totally new
   package) in order to make the MS aware of floor control and allow the

   MS to interact with the interested UAC accordingly.  At the time of
   writing, such a package doesn't exist yet, and as a consequence only
   approach (i) will be dealt with in the presented scenario.

   The scenario will then assume that the Floor Control Server (FCS) is
   co-located with the AS.  This means that all the BFCP requests will
   be sent by Floor Control Participants (FCPs) to the FCS, which will
   make the AS directly aware of the floor statuses.  For the sake of
   simplicity, the scenario assumes that the involved participants are
   already aware of all the identifiers needed in order to make BFCP
   requests for a specific conference.  Such information may have been
   carried according to the COMEDIA negotiation as specified in
   [RFC4583].  It is important to note that such information must not
   reach the MS.  This means that within the context of the 3PCC
   mechanism that may have been used in order to attach a UAC to the MS,
   all the BFCP-related information negotiated by the AS and the UAC
   must be removed before making the negotiation available to the MS,
   which may be unable to understand the specification.  A simplified
   example of how this could be achieved is presented in Figure 41.
   Please note that within the context of this example scenario,
   different identifiers may be used to address the same entity.
   Specifically, in this case the UAC (the endpoint sending and
   receiving media) is also a FCP, as it negotiates a BFCP channel too.

  UAC                               AS
 (FCP)                             (FCS)                              MS
  |                                 |                                 |
  | INVITE (SDP: RTP+BFCP)          |                                 |
  |-------------------------------->|                                 |
  |                                 | INVITE (SDP: RTP)               |
  |                                 |-------------------------------->|
  |                                 |          200 (SDP: RTP'+labels) |
  |                                 |<--------------------------------|
  |                        match +--|                                 |
  |                       floors |  |                                 |
  |                     & labels +->|                                 |
  |                                 |                                 |
  |    200 (SDP: RTP'+BFCP'+labels) |                                 |
  |<--------------------------------|                                 |
  | ACK                             |                                 |
  |-------------------------------->|                                 |
  |                                 | ACK                             |
  |                                 |-------------------------------->|
  |                                 |                                 |
  |<<###################### RTP MEDIA STREAMS ######################>>|
  |                                 |                                 |
  |<<******** BFCP CHANNEL *******>>|                                 |
  |                                 |                                 |
  .                                 .                                 .
  .                                 .                                 .

             Figure 41: Floor Control: Example of Negotiation

   From the media and framework perspective, such a scenario doesn't
   differ much from the conferencing scenarios presented earlier.  It is
   more interesting to focus on the chosen topology for the scenario, as
   depicted in Figure 42.

   +-------+                    +--------+
   |  UAC  |                    |   AS   |                     +-------+
   | (FCP) |<****** BFCP ******>|  (FCS) |<****** BFCP *******>| (FCC) |
   +-------+                    +--------+                     +-------+
       ^                             ^
       |                             |
       |                         CFW |
       |                             |
       |                             v
       |                        +--------+
       +----------RTP---------->|   MS   |
                                +--------+

               Figure 42: Floor Control: Overall Perspective

   The AS, besides maintaining the already-known SIP signaling among the
   involved parties, also acts as the FCS for the participants in the
   conferences for which it is responsible.  In the scenario, two Floor
   Control Participants are involved: a basic Participant (FCP) and a
   Chair (FCC).

   As in all of the previously described conferencing examples, in the
   framework this can be achieved by means of the Mixer Control Package.
   Assuming that the conference has been created, the participant has
   been attached ('recvonly') to it, and the participant is aware of the
   involved BFCP identifiers, the needed steps can be summarized in the
   following list:

   1.  The assigned chair, FCC, sends a subscription for events related
       to the floor for which it is responsible (FloorQuery).

   2.  The FCP sends a BFCP request (FloorRequest) to access the audio
       resource ("I want to speak").

   3.  The FCS (AS) sends a provisional response to the FCP
       (FloorRequestStatus PENDING) and handles the request in its
       queue.  Since a chair is assigned to this floor, the request is
       forwarded to the FCC for a decision (FloorStatus).

   4.  The FCC makes a decision and sends it to the FCS (ChairAction
       ACCEPTED).

   5.  The FCS takes note of the decision and updates the queue
       accordingly.  The decision is sent to the FCP (FloorRequestStatus
       ACCEPTED).  The floor has not been granted yet.

   6.  As soon as the queue allows it, the floor is actually granted to
       the FCP.  The AS, which is co-located with the FCS, understands
       in its business logic that such an event is associated with the
       audio resource being granted to the FCP.  As a consequence, a
       <modifyjoin> ('sendrecv') is sent through the Control Channel to
       the MS in order to unmute the FCP UAC in the conference.

   7.  The FCP is notified of this event (FloorRequestStatus GRANTED),
       thus ending the scenario.

   A diagram of such a sequence of transactions (also involving the BFCP
   message flow at a higher level) is depicted in Figure 43:

 UAC1      UAC2       AS
 (FCP)     (FCC)     (FCS)                               MS
  |         |         |                                  |
  |<<####################################################|
  |   UAC1 is muted (recvonly stream) in the conference  |
  |<<####################################################|
  |         |         |                                  |
  |         | FloorQuery                                 |
  |         |*******>>|                                  |
  |         |         |--+ handle                        |
  |         |         |  | subscription                  |
  |         |         |<-+                               |
  |         | FloorStatus                                |
  |         |<<*******|                                  |
  |         |         |                                  |
  | FloorRequest      |                                  |
  |*****************>>|                                  |
  |         |         |--+ handle                        |
  |         |         |  | request                       |
  |           Pending |<-+ (queue)                       |
  |<<*****************|                                  |
  |         |         |                                  |
  |         | FloorStatus                                |
  |         |<<*******|                                  |
  |         |         |                                  |
  |         | ChairAction (ACCEPT)                       |

  |         |*******>>|                                  |
  |         | ChairActionAck                             |
  |         |<<*******|                                  |
  |         |         |--+ handle                        |
  |         |         |  | decision                      |
  |         |         |<-+ (queue)                       |
  |          Accepted |                                  |
  |<<*****************|                                  |
  |         | FloorStatus                                |
  |         |<<*******|                                  |
  |         |         |                                  |
  |         |         |--+ queue                         |
  |         |         |  | grants                        |
  |         |         |<-+ floor                         |
  |         |         |                                  |
  |         |         | 1. CONTROL (modjoin UAC<->conf)  |
  |         |         |++++++++++++++++++++++++++++++++>>|
  |         |         |                                  |--+ modjoin
  |         |         |                                  |  | UAC & conf
  |         |         |                        2. 200 OK |<-+ (sendrecv)
  |         |         |<<++++++++++++++++++++++++++++++++|
  |         |         |                                  |
  |<<##################################################>>|
  |   UAC1 is now unmuted (sendrecv) in the conference   |
  |        and can speak, contributing to the mix        |
  |<<##################################################>>|
  |         |         |                                  |
  |           Granted |                                  |
  |<<*****************|                                  |
  |         | FloorStatus                                |
  |         |<<*******|                                  |
  |         |         |                                  |
  .         .                                            .
  .         .                                            .

             Figure 43: Floor Control: Framework Transactions

   As can easily be deduced from the above diagram, the complex
   interaction at the BFCP level only results in a single transaction at
   the MEDIACTRL level.  In fact, the purpose of the BFCP transactions
   is to moderate access to the audio resource, which means providing
   the event trigger to MEDIACTRL-based conference manipulation

   transactions.  Before being granted the floor, the FCP UAC is
   excluded from the conference mix at the MEDIACTRL level ('recvonly').
   As soon as the floor has been granted, the FCP UAC is included in the
   mix.  In MEDIACTRL words:

   o  Since the FCP UAC must be included in the audio mix, a
      <modifyjoin> is sent to the MS in a CONTROL directive.  The
      <modifyjoin> has as identifiers the connectionid associated with
      the FCP UAC (e1e1427c:1c998d22) and the conferenceid of the mix
      (cf45ee2).  The <stream> element tells the MS that the audio media
      stream between the two must become bidirectional ('sendrecv'),
      changing the previous status ('recvonly').  Please note that in
      this case only audio was involved in the conference; if video were
      involved as well, and video had to be unchanged, a <stream>
      directive for video had to be placed in the request as well in
      order to maintain its current status.

   1. AS -> MS (CFW CONTROL)
   -------------------------
      CFW gh67ffg56w21 CONTROL
      Control-Package: msc-mixer/1.0
      Content-Type: application/msc-mixer+xml
      Content-Length: 182

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <modifyjoin id1="e1e1427c:1c998d22" id2="cf45ee2">
            <stream media="audio" direction="sendrecv"/>
         </modifyjoin>
      </mscmixer>

   2. AS <- MS (CFW 200 OK)
   ------------------------
      CFW gh67ffg56w21 200
      Timeout: 10
      Content-Type: application/msc-mixer+xml
      Content-Length: 123

      <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
         <response status="200" reason="Join modified"/>
      </mscmixer>

6.4.  Additional Scenarios

   This section includes additional scenarios that can be of interest
   when dealing with AS<->MS flows.  The aim of the following
   subsections is to present the use of features peculiar to the IVR
   package: specifically, variable announcements, VCR (video cassette

   recorder) prompts, parallel playback, recurring dialogs, and custom
   grammars.  To describe how call flows involving such features might
   happen, three sample scenarios have been chosen:

   1.  Voice Mail (variable announcements for digits, VCR controls).

   2.  Current Time (variable announcements for date and time, parallel
       playback).

   3.  DTMF-driven Conference Manipulation (recurring dialogs, custom
       grammars).

6.4.1.  Voice Mail

   An application that typically uses the services an MS can provide is
   Voice Mail.  In fact, while it is clear that many of its features are
   part of the application logic (e.g., the mapping of a URI with a
   specific user's voice mailbox, the list of messages and their
   properties, and so on), the actual media work is accomplished through
   the MS.  Features needed by a Voice Mail application include the
   ability to record a stream and play it back at a later time, give
   verbose announcements regarding the status of the application,
   control the playout of recorded messages by means of VCR controls,
   and so on.  These features are all supported by the MS through the
   IVR package.

   Without delving into the details of a full Voice Mail application and
   all its possible use cases, this section will cover a specific
   scenario and try to deal with as many interactions as possible that
   may happen between the AS and the MS in such a context.  This
   scenario, depicted as a sequence diagram in Figure 44, will be as
   follows:

   1.  The UAC INVITEs a URI associated with his mailbox, and the AS
       follows the previously explained procedure to have the UAC
       negotiate a new media session with the MS.

   2.  The UAC is first prompted with an announcement giving him the
       amount of available new messages in the mailbox.  After that, the
       UAC can choose which message to access by sending a DTMF tone.

   3.  The UAC is then presented with a VCR-controlled announcement, in
       which the chosen received mail is played back to him.  VCR
       controls allow him to navigate through the prompt.

   This is a quite oversimplified scenario, considering that it doesn't
   even allow the UAC to delete old messages or organize them but just
   to choose which received message to play.  Nevertheless, it gives us

   the chance to deal with variable announcements and VCR controls --
   two typical features that a Voice Mail application would almost
   always take advantage of.  Other features that a Voice Mail
   application would rely upon (e.g., recording streams, event-driven
   IVR menus, and so on) have been introduced in previous sections, and
   so representing them would be redundant.  This means that the
   presented call flows assume that some messages have already been
   recorded and are available at reachable locations.  The example also
   assumes that the AS has placed the recordings in its own storage
   facilities, since it is not safe to rely upon the internal MS
   storage, which is likely to be temporary.

 UAC                      AS                                 MS
  |                       |                                  |
  |                       | A1. CONTROL (play variables and  |
  |                       |      collect the user's choice)  |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  | prepare &
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |                       A2. 200 OK |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<########################################################|
  |                "You have five messages ..."              |
  |<<########################################################|
  |                       |                                  |
  |                       |      B1. CONTROL (<collectinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | B2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  |                       | C1. CONTROL (VCR for chosen msg) |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  | prepare &
  |                       |                                  |--+ start
  |                       |                                  |  | the
  |                       |                       C2. 200 OK |<-+ dialog
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       |                                  |
  |<<########################################################|
  |          "Hi there, I tried to call you but..."          |--+
  |<<########################################################|  | handle
  |                       |                                  |  | VCR-
  |########################################################>>|  | driven
  |        The UAC controls the playout using DTMF           |  | (DTMF)
  |########################################################>>|  |playout
  |                       |                                  |<-+

  |                       |       D1. CONTROL (<dtmfnotify>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | D2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  .                       .                                  .
  .       (other events are received in the meantime)        |
  .                       .                                  .
  |                       |      E1. CONTROL (<controlinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | E2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  .                       .                                  .
  .                       .                                  .

               Figure 44: Voice Mail: Framework Transactions

   The framework transaction steps are as follows:

   o  The first transaction (A1) is addressed to the IVR package (msc-
      ivr).  It is basically an [RFC6231] 'promptandcollect' dialog, but
      with a slight difference: some of the prompts to play are actual
      audio files, for which a URI is provided (media loc="xxx"), while
      others are so-called <variable> prompts; these <variable> prompts
      are actually constructed by the MS itself according to the
      directives provided by the AS.  In this example, the sequence of
      prompts requested by the AS is as follows:

      1.  play a wav file ("you have...").

      2.  play a digit ("five...") by building it (variable: digit=5).

      3.  play a wav file ("messages...").

      A DTMF collection is requested as well (<collect>) to be taken
      after the prompts have been played.  The AS is only interested in
      a single digit (maxdigits=1).

   o  The transaction is handled by the MS, and if everything works fine
      (i.e., the MS retrieved all the audio files and successfully built
      the variable announcements), the dialog is started; its start is
      reported, together with the associated identifier (5db01f4) to the
      AS in a terminating 200 OK message (A2).

   o  The AS then waits for the dialog to end in order to retrieve the
      results in which it is interested (in this case, the DTMF tone the
      UAC chooses, since it will affect which message will have to be
      played subsequently).

   o  The UAC hears the prompts and chooses a message to play.  In this
      example, he wants to listen to the first message and so inputs
      "1".  The MS intercepts this tone and notifies the AS of it in a
      newly created CONTROL event message (B1); this CONTROL includes
      information about how each single requested operation ended
      (<promptinfo> and <collectinfo>).  Specifically, the event states
      that the prompt ended normally (termmode=completed) and that the
      subsequently collected tone is 1 (dtmf=1).  The AS acks the event
      (B2), since the dialogid provided in the message is the same as
      that of the previously started dialog.

   o  At this point, the AS uses the value retrieved from the event to
      proceed with its business logic.  It decides to present the UAC
      with a VCR-controllable playout of the requested message.  This is
      done with a new request to the IVR package (C1), which contains
      two operations: <prompt> to address the media file to play (an old
      recording) and <control> to instruct the MS about how the playout
      of this media file shall be controlled via DTMF tones provided by
      the UAC (in this example, different DTMF digits are associated
      with different actions, e.g., pause/resume, fast forward, rewind,
      and so on).  The AS also subscribes to DTMF events related to this
      control operation (matchmode=control), which means that the MS is
      to trigger an event any time that a DTMF associated with a control
      operation (e.g., 7=pause) is intercepted.

   o  The MS prepares the dialog and, when the playout starts, sends
      notification in a terminating 200 OK message (C2).  At this point,
      the UAC is presented with the prompt and can use DTMF digits to
      control the playback.

   o  As explained previously, any DTMF associated with a VCR operation
      is then reported to the AS, together with a timestamp stating when
      the event happened.  An example is provided (D1) in which the UAC
      pressed the fast-forward key (6) at a specific time.  Of course,
      as for any other MS-generated event, the AS acks it (D2).

   o  When the playback ends (whether because the media reached its
      termination or because any other interruption occurred), the MS
      triggers a concluding event with information about the whole
      dialog (E1).  This event, besides including information about the
      prompt itself (<promptinfo>), also includes information related to
      the VCR operations (<controlinfo>), that is, all the VCR controls

      the UAC used (fast forward/rewind/pause/resume in this example)
      and when it happened.  The final ack by the AS (E2) concludes the
      scenario.

A1. AS -> MS (CFW CONTROL, play and collect)
--------------------------------------------
   CFW 2f931de22820 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 429

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <dialogstart connectionid="10514b7f:6a900179">
         <dialog>
            <prompt>
               <media
            loc="http://www.example.net/prompts/vm-youhave.wav"
            type="audio/x-wav"/>
               <variable value="5" type="digits"/>
               <media
           loc="http://www.example.net/prompts/vm-messages.wav"
           type="audio/x-wav"/>
            </prompt>
            <collect maxdigits="1" escapekey="*"
                     cleardigitbuffer="true"/>
         </dialog>
      </dialogstart>
   </mscivr>

A2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 2f931de22820 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="5db01f4"/>
   </mscivr>

B1. AS <- MS (CFW CONTROL event)
--------------------------------
   CFW 7c97adc41b3e CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 270

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <event dialogid="5db01f4">
         <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="11713" termmode="completed"/>
            <collectinfo dtmf="1" termmode="match"/>
         </dialogexit>
      </event>
   </mscivr>

B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 7c97adc41b3e 200

C1. AS -> MS (CFW CONTROL, VCR)
-------------------------------
   CFW 3140c24614bb CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 423

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <dialogstart connectionid="10514b7f:6a900179">
         <dialog>
            <prompt bargein="false">
               <media
  loc="http://www.example.com/messages/recording-4ca9fc2.mpg"/>
            </prompt>
            <control gotostartkey="1" gotoendkey="3"
                     ffkey="6" rwkey="4" pausekey="7" resumekey="9"
                     volupkey="#" voldnkey="*"/>
            </dialog>
         <subscribe>
            <dtmfsub matchmode="control"/>
         </subscribe>
      </dialogstart>
   </mscivr>

C2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 3140c24614bb 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="3e936e0"/>
   </mscivr>

D1. AS <- MS (CFW CONTROL event, dtmfnotify)
--------------------------------------------
   CFW 361840da0581 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 179

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <event dialogid="3e936e0">
         <dtmfnotify matchmode="control" dtmf="6"
                     timestamp="2008-12-16T12:58:36Z"/>
      </event>
   </mscivr>

D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 361840da0581 200

      [..] The other VCR DTMF notifications are skipped for brevity [..]

E1. AS <- MS (CFW CONTROL event, dialogexit)
--------------------------------------------
   CFW 3ffab81c21e9 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 485

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <event dialogid="3e936e0">
         <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="10270" termmode="completed"/>
            <controlinfo>
               <controlmatch dtmf="6" timestamp="2008-12-16T12:58:36Z"/>
               <controlmatch dtmf="4" timestamp="2008-12-16T12:58:37Z"/>
               <controlmatch dtmf="7" timestamp="2008-12-16T12:58:38Z"/>
               <controlmatch dtmf="9" timestamp="2008-12-16T12:58:40Z"/>
            </controlinfo>
         </dialogexit>
      </event>
   </mscivr>

E2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 3ffab81c21e9 200

6.4.2.  Current Time

   An interesting scenario to create with the help of features provided
   by the MS is what is typically called 'Current Time'.  A UAC calls a
   URI, which presents the caller with the current date and time.  As
   can easily be deduced by the very nature of the application, variable
   announcements play an important role in this scenario.  In fact,
   rather than having the AS build an announcement according to the
   current time using different framework messages, it is much easier to
   rely upon the "variable announcements" mechanism provided by the IVR
   package, as variable announcements provide several ways to deal with
   dates and times.

   To make the scenario more interesting and have it cover more
   functionality, the application is also assumed to have background
   music played during the announcement.  Because most of the
   announcements will be variable, a means is needed to have more
   streams played in parallel on the same connection.  This can be
   achieved in two different ways:

   1.  two separate and different dialogs, playing the variable
       announcements and the background track, respectively.

   2.  a single dialog implementing a parallel playback.

   The first approach assumes that the available MS implements implicit
   mixing, which may or may not be supported since it's a recommended
   feature but not mandatory.  The second approach assumes that the MS
   implements support for more streams of the same media type (in this
   case audio) in the same dialog, which, exactly as for the case of
   implicit mixing, is not to be taken for granted.  Because the first
   approach is quite straightforward and easy to understand, the
   following scenario uses the second approach and assumes that the
   available MS supports parallel playback of more audio tracks within
   the context of the same dialog.

   That said, the covered scenario, depicted as a sequence diagram in
   Figure 45, will be as follows:

   1.  The UAC INVITEs a URI associated with the Current Time
       application, and the AS follows the previously explained
       procedure to have the UAC negotiate a new media session with the
       MS.

   2.  The UAC is presented with an announcement including (i) a voice
       stating the current date and time; (ii) a background music track;
       and (iii) a mute background video track.

 UAC                      AS                                 MS
  |                       |                                  |
  |                       | A1. CONTROL (play variables)     |
  |                       |++++++++++++++++++++++++++++++++>>| prepare
  |                       |                                  |--+ and
  |                       |                          A2. 202 |  | start
  |                       |<<++++++++++++++++++++++++++++++++|  | the
  |                       |                                  |  | dialog
  |                       |                                  |  | (takes
  |                       |           A3. REPORT (terminate) |<-+ time)
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | A4. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  |<<########################################################|
  |            "16th of december 2008, 5:31 PM..."           |
  |<<########################################################|
  |                       |                                  |
  |                       |       B1. CONTROL (<promptinfo>) |
  |                       |<<++++++++++++++++++++++++++++++++|
  |                       | B2. 200 OK                       |
  |                       |++++++++++++++++++++++++++++++++>>|
  |                       |                                  |
  .                       .                                  .
  .                       .                                  .
  .                       .                                  .

              Figure 45: Current Time: Framework Transactions

   The framework transaction steps are as follows:

   o  The first transaction (A1) is addressed to the IVR package (msc-
      ivr); it is basically an [RFC6231] 'playannouncements' dialog,
      but, unlike all the scenarios presented so far, it includes
      directives for a parallel playback, as indicated by the <par>
      element.  There are three flows to play in parallel:

      *  a sequence (<seq>) of variable and static announcements (the
         actual time and date).

      *  a music track ('media=music.wav') to be played in the
         background at a lower volume (soundLevel=50%).

      *  a mute background video track (media=clock.mpg).

      The global announcement ends when the longest of the three
      parallel steps ends (endsync=last).  This means that if one of the
      steps ends before the others, the step is muted for the rest of
      the playback.  In this example, the series of static and
      <variable> announcements is requested by the AS:

      *  play a wav file ("Tuesday...").

      *  play a date ("16th of december 2008...") by building it
         (variable: date with a ymd=year/month/day format).

      *  play a time ("5:31 PM...") by building it (variable: time with
         a t12=12 hour day format, am/pm).

   o  The transaction is extended by the MS (A2) with a new timeout, as
      in this case the MS needs some more time to retrieve all the
      needed media files.  Should the new timeout expire as well, the MS
      would send a further message to extend it again (a REPORT update),
      but for the sake of simplicity we assume that in this scenario it
      is not needed.  If everything went fine (i.e., the MS retrieved
      all the audio files and successfully built the variable
      announcements, and it supports parallel playback as requested),
      the dialog is started.  Its start is reported, together with the
      associated identifier (415719e), to the AS in a terminating REPORT
      message (A3).

   o  The AS acks the REPORT (A4) and waits for the dialog to end in
      order to either conclude the application or proceed to further
      steps if required by the application itself.

   o  When the last of the three parallel announcements ends, the dialog
      terminates, and an event (B1) is triggered to the AS with the
      relevant information (promptinfo).  The AS acks (B2) and
      terminates the scenario.

A1. AS -> MS (CFW CONTROL, play)
--------------------------------
   CFW 0c7680191bd2 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 506

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <dialogstart connectionid="21c8e07b:055a893f">
       <dialog>
         <prompt bargein="true">
           <par endsync="last">
             <seq>
               <media loc="http://www.example.com/day-2.wav"/>
               <variable value="2008-12-16" type="date" format="ymd"/>
               <variable value="17:31" type="time" format="t12"/>
             </seq>
             <media loc="http://www.example.com/music.wav"
                    soundLevel="50%"/>
             <media loc="http://www.example.com/clock.mpg"/>
           </par>
         </prompt>
       </dialog>
     </dialogstart>
   </mscivr>

A2. AS <- MS (CFW 202)
----------------------
   CFW 0c7680191bd2 202
   Timeout: 5

A3. AS <- MS (CFW REPORT terminate)
-----------------------------------
   CFW 0c7680191bd2 REPORT
   Seq: 1
   Status: terminate
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="415719e"/>
   </mscivr>

A4. AS -> MS (CFW 200, ACK to 'REPORT terminate')
-------------------------------------------------
   CFW 0c7680191bd2 200
   Seq: 1

B1. AS <- MS (CFW CONTROL event)
--------------------------------
   CFW 4481ca0c4fca CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 229

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
      <event dialogid="415719e">
         <dialogexit status="1" reason="Dialog successfully completed">
            <promptinfo duration="8046" termmode="completed"/>
         </dialogexit>
      </event>
   </mscivr>

B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 4481ca0c4fca 200

6.4.3.  DTMF-Driven Conference Manipulation

   To complete the scenarios presented in Section 6.3, this section
   deals with how the AS can use the MS to detect DTMF tones from
   conference participants and take actions on the conference
   accordingly.  A typical example is when participants in a conference
   are provided with specific codes to:

   o  mute/unmute themselves in the conference;

   o  change their volume in the conference, or the volume of the
      conference itself;

   o  change the video layout in the conference, if allowed;

   o  kick abusive users out of the conference;

   and so on.  To achieve all this, the simplest thing an AS can do is
   to prepare a recurring DTMF collection for each participant with
   specific grammars to match.  If the collected tones match the
   grammar, the MS would notify the AS of the tones and start the
   collection again.  Upon receipt of <collectinfo> events, the AS would

   in turn originate the proper related request, e.g., a <modifyjoin> on
   the participant's stream with the conference.  This is made possible
   by three features provided by the IVR package:

   1.  the 'repeatCount' attribute.

   2.  the subscription mechanism.

   3.  the Speech Recognition Grammar Specification (SRGS) [SRGS].

   The first feature allows recurring instances of the same dialog
   without the need for additional requests upon completion of the
   dialog itself.  In fact, the 'repeatCount' attribute indicates how
   many times the dialog has to be repeated.  When the attribute has the
   value 0, it means that the dialog has to be repeated indefinitely,
   meaning that it's up to the AS to destroy it by means of a
   <dialogterminate> request when the dialog is no longer needed.  The
   second feature allows the AS to subscribe to events related to the
   IVR package without waiting for the dialog to end, e.g., matching
   DTMF collections in this case.  Finally, the last feature allows
   custom matching grammars to be specified.  This way, only a subset of
   the possible DTMF strings can be specified, so that only those
   matches in which the AS is interested are reported.  Grammars other
   than SRGS may be supported by the MS and will achieve the same
   result.  This document will only describe the use of an SRGS grammar,
   since support for SRGS is mandated in [RFC6231].

   To identify a single sample scenario, we assume that a participant
   has successfully joined a conference, e.g., as detailed in Figure 32.
   We also assume that the following codes are to be provided within the
   conference to participants in order to let them take advantage of
   advanced features:

   1.  *6 to mute/unmute themselves (on/off trigger).

   2.  *1 to lower their own volume in the conference and *3 to raise
       it.

   3.  *7 to lower the volume of the conference stream they are
       receiving and *9 to raise it.

   4.  *0 to leave the conference.

   This means that six different codes are supported and are to be
   matched in the requested DTMF collection.  All other codes are
   collected by the MS but discarded, and no event is triggered to the
   AS.  Because all the codes have the '*' (star) DTMF code in common,
   the following is an example of an SRGS grammar that may be used in
   the request by the AS:

     <grammar mode="dtmf" version="1.0"
              xmlns="http://www.w3.org/2001/06/grammar">
       <rule id="digit">
         <one-of>
           <item>0</item>
           <item>1</item>
           <item>3</item>
           <item>6</item>
           <item>7</item>
           <item>9</item>
         </one-of>
       </rule>
       <rule id="action" scope="public">
         <item>
           *
           <item><ruleref uri="#digit"/></item>
         </item>
       </rule>
     </grammar>

   As can be deduced by looking at the grammar, the presented SRGS XML
   code specifies exactly the requirements for the collections to match.
   The rule is to match any string that has a star ('*') followed by a
   single supported digit (0, 1, 3, 6, 7, or 9).  Such grammar, as
   stated in [RFC6231], may be either provided inline in the request
   itself or referenced externally by means of the 'src' attribute.  In
   the example scenario, we'll put it inline, but an external reference
   to the same document would achieve exactly the same result.

   Figure 46 shows how the AS might request the recurring collection for
   a UAC.  As before, the example assumes that the UAC is already a
   participant in the conference.

 UAC                  AS                                     MS
  |                   |                                      |
  |                   | A1. CONTROL (recurring collection)   |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |--+ start
  |                   |                                      |  | the
  |                   |                           A2. 200 OK |<-+ dialog
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   |                                      |
  |########################################################>>|
  |          Recurring DTMF digit collection starts          |--+ get
  |########################################################>>|  | DTMF
  |                   |                                      |<-+ digits
  |                   |            B1. CONTROL (dtmfinfo=*1) |
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   | B2. 200 OK                           |--+ get
  |                   |++++++++++++++++++++++++++++++++++++>>|  | DTMF
  |                   |                                      |<-+ digits
  |                   | C1. CONTROL (modifyjoin UAC1-->conf) |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |--+ modify
  |                   |                                      |  | UAC
  |                   |                           C2. 200 OK |<-+ volume
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   |                                      |
  |########################################################>>|
  |          Volume of UAC in conference is lowered          |
  |########################################################>>|
  |                   |                                      |
  |                   |            D1. CONTROL (dtmfinfo=*9) |
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   | D2. 200 OK                           |--+ get
  |                   |++++++++++++++++++++++++++++++++++++>>|  | DTMF
  |                   |                                      |<-+ digits
  |                   | E1. CONTROL (modifyjoin UAC1<--conf) |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |--+ modify
  |                   |                                      |  | conf
  |                   |                           E2. 200 OK |<-+ volume
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   |                                      |
  |<<########################################################|
  |  Now UAC can hear the conference mix at a higher volume  |
  |<<########################################################|

  |                   |                                      |
  |                   |            F1. CONTROL (dtmfinfo=*6) |
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   | F2. 200 OK                           |--+ get
  |                   |++++++++++++++++++++++++++++++++++++>>|  | DTMF
  |                   |                                      |<-+ digits
  |                   | G1. CONTROL (modifyjoin UAC1-->conf) |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |--+ mute
  |                   |                                      |  | UAC in
  |                   |                           G2. 200 OK |<-+ conf
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   |                                      |
  |########################################################>>|
  |             UAC is now muted in the conference           |
  |########################################################>>|
  |                   |                                      |
  |                   |            H1. CONTROL (dtmfinfo=*0) |
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   | H2. 200 OK                           |--+ get
  |                   |++++++++++++++++++++++++++++++++++++>>|  | DTMF
  |                   |                                      |<-+ digits
  |                   | I1. CONTROL (destroy DTMF dialog)    |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |--+ delete
  |                   |                                      |  | the
  |                   |                           I2. 200 OK |<-+ dialog
  |                   |<<++++++++++++++++++++++++++++++++++++|    (DTMF
  |                   |                                      |collection
  |                   |                                      |    stops)
  |                   |             J1. CONTROL (dialogexit) |
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   | J2. 200 OK                           |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |
  |########################################################>>|
  |           No more tones from UAC are collected           |
  |########################################################>>|
  |                   |                                      |
  |                   | K1. CONTROL (unjoin UAC1<-X->conf)   |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |--+ unjoin
  |                   |                                      |  | UAC &
  |                   |                           K2. 200 OK |<-+ conf
  |                   |<<++++++++++++++++++++++++++++++++++++|
  |                   |                                      |
  |                   |          L1. CONTROL (unjoin-notify) |
  |                   |<<++++++++++++++++++++++++++++++++++++|

  |                   | L2. 200 OK                           |
  |                   |++++++++++++++++++++++++++++++++++++>>|
  |                   |                                      |
  .                   .                                      .
  .                   .                                      .

              Figure 46: DTMF-Driven Conference Manipulation:
                          Framework Transactions

   As can be deduced from the sequence diagram above, the AS, in its
   business logic, correlates the results of different transactions,
   addressed to different packages, to implement a more complex
   conferencing scenario.  In fact, <dtmfnotify> events are used to take
   actions according to the functions of the DTMF codes.  The framework
   transaction steps are as follows:

   o  The UAC is already in the conference, and so the AS starts a
      recurring collect with a grammar to match.  This is done by
      placing a CONTROL request addressed to the IVR package (A1).  The
      operation to implement is a <collect>, and we are only interested
      in two-digit DTMF strings (maxdigits).  The AS is not interested
      in a DTMF terminator (termchar is set to a non-conventional DTMF
      character), and the DTMF escape key is set to '#' (the default is
      '*', which would conflict with the code syntax for the conference
      and so needs to be changed).  A custom SRGS grammar is provided
      inline (<grammar> with mode=dtmf).  The whole dialog is to be
      repeated indefinitely (dialog has repeatCount=0), and the AS wants
      to be notified when matching collections occur (dtmfsub with
      matchmode=collect).

   o  The request is handled by the MS (A2) and then successfully
      started (dialogid=01d1b38).  This means that the MS has started
      collecting DTMF tones from the UAC.

   o  The MS collects a matching DTMF string from the UAC (*1).  Since
      the AS subscribed to this kind of event, a CONTROL event
      notification (dtmfnotify) is triggered by the MS (B1), including
      the collected tones.  Since the dialog is recurring, the MS
      immediately restarts the collection.

   o  The AS acks the event (B2) and in its business logic understands
      that the code '*1' means that the UAC wants its own volume to be
      lowered in the conference mix.  The AS is able to associate the
      event with the right UAC by referring to the attached dialogid
      (01d1b38).  It then acts accordingly by sending a <modifyjoin>
      (C1) that does exactly this: the provided <stream> child element
      instructs the MS to modify the volume of the UAC-->conference
      audio flow (setgain=-5 dB 'sendonly').  Note that the "setgain"

      value is the absolute volume level.  If the user's request is to
      lower the volume level, the AS must remember the previously set
      volume level and from it calculate the new volume level.  Note how
      the request also includes directives for the inverse direction.
      This verbose approach is needed; otherwise, the MS would not only
      change the volume in the requested direction but would also
      disable the media flow in the other direction.  Having a proper
      <stream> addressing the UAC<--conf media flow as well ensures that
      this doesn't happen.

   o  The MS successfully enforces the requested operation (C2),
      changing the volume.

   o  A new matching DTMF string from the UAC is collected (*9).  As
      before, an event is triggered to the AS (D1).

   o  The AS acks the event (D2) and matches the new code ('*9') with
      its related operation (raise the volume of the conference mix for
      the UAC), taking the proper action.  A different <modifyjoin> is
      sent (E1) with the new instructions (setgain=+3 dB 'recvonly').
      The same considerations regarding how the incremental operation
      should be mapped to the command apply here as well.  Note also how
      a <stream> for the inverse direction ('sendonly') is again
      provided just as a placeholder, which basically instructs the MS
      that the settings for that direction are not to be changed,
      maintaining the previous directives of (C1).

   o  The MS successfully enforces this requested operation as well
      (E2), changing the volume in the specified direction.

   o  At this point, a further matching DTMF string from the UAC is
      collected (*6) and sent to the AS (F1).

   o  After the required ack (F2), the AS reacts by implementing the
      action associated with the new code ('*6'), by which the UAC
      requested that it be muted within the conference.  A new
      <modifyjoin> is sent (G1) with a properly constructed payload
      (setstate=mute 'sendonly'), and the MS enforces it (G2).

   o  A last (in this scenario) matching DTMF string is collected by the
      MS (*0).  As with all the previous codes, notification of this
      string is sent to the AS (H1).

   o  The AS acks the event (H2) and understands that the UAC wants to
      leave the conference now (since the code is *0).  This means that
      a series of actions must be taken:

      *  The recurring collection is stopped, since it's no longer
         needed.

      *  The UAC is unjoined from the conference it is in.

      *  Additional operations might be considered, e.g., a global
         announcement stating that the UAC is leaving, but for the sake
         of conciseness such operations are not listed here.

      The former is accomplished by means of a <dialogterminate> request
      (I1) to the IVR package (dialogid=01d1b38) and the latter by means
      of an <unjoin> request (K1) to the Mixer package.

   o  The <dialogterminate> request is handled by the MS (I2), and the
      dialog is terminated successfully.  As soon as the dialog has
      actually been terminated, a <dialogexit> event is triggered as
      well to the AS (J1).  This event has no report of the result of
      the last iteration (since the dialog was terminated abruptly with
      an immediate=true) and is acked by the AS (J2) to finally complete
      the dialog lifetime.

   o  The <unjoin> request is immediately enforced (K2).  As a
      consequence of the unjoin operation, an <unjoin-notify> event
      notification is triggered by the MS (L1) to confirm to the AS that
      the requested entities are no longer attached to each other.  The
      status in the event is set to 0, which, as stated in the
      specification, means that the join has been terminated by an
      <unjoin> request.  The ack from the AS (L2) concludes this
      scenario.

A1. AS -> MS (CFW CONTROL, recurring collect with grammar)
----------------------------------------------------------
   CFW 238e1f2946e8 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 809

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <dialogstart connectionid="14849028:37fc2523">
       <dialog repeatCount="0">
         <collect maxdigits="2" termchar="A" escapekey="#">
           <grammar>
             <grammar version="1.0" mode="dtmf"
                      xmlns="http://www.w3.org/2001/06/grammar">
               <rule id="digit">
                 <one-of>
                   <item>0</item>
                   <item>1</item>
                   <item>3</item>
                   <item>6</item>
                   <item>7</item>
                   <item>9</item>
                 </one-of>
               </rule>
               <rule id="action" scope="public">
                 <example>*3</example>
                 <one-of>
                   <item>
                     *
                     <ruleref uri="#digit"/>
                   </item>
                 </one-of>
               </rule>
             </grammar>
           </grammar>
         </collect>
       </dialog>
       <subscribe>
         <dtmfsub matchmode="collect"/>
       </subscribe>
     </dialogstart>
   </mscivr>

A2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 238e1f2946e8 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 137

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog started" dialogid="01d1b38"/>
   </mscivr>

B1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
   CFW 1dd62e043c00 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 180

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <event dialogid="01d1b38">
       <dtmfnotify matchmode="collect" dtmf="*1"
                   timestamp="2008-12-17T17:20:53Z"/>
     </event>
   </mscivr>

B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 1dd62e043c00 200

C1. AS -> MS (CFW CONTROL, modifyjoin with setgain)
---------------------------------------------------
   CFW 0216231b1f16 CONTROL
   Control-Package: msc-mixer/1.0
   Content-Type: application/msc-mixer+xml
   Content-Length: 290

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <modifyjoin id1="873975758:a5105056" id2="54b4ab3">
       <stream media="audio" direction="sendonly">
         <volume controltype="setgain" value="-5"/>
       </stream>
       <stream media="audio" direction="recvonly"/>
     </modifyjoin>
   </mscmixer>

C2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 0216231b1f16 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 123

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <response status="200" reason="Join modified"/>
   </mscmixer>

D1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
   CFW 4d674b3e0862 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 180

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <event dialogid="01d1b38">
       <dtmfnotify matchmode="collect" dtmf="*9"
                   timestamp="2008-12-17T17:20:57Z"/>
     </event>
   </mscivr>

D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 4d674b3e0862 200

E1. AS -> MS (CFW CONTROL, modifyjoin with setgain)
---------------------------------------------------
   CFW 140e0f763352 CONTROL
   Control-Package: msc-mixer/1.0
   Content-Type: application/msc-mixer+xml
   Content-Length: 292

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <modifyjoin id1="873975758:a5105056" id2="54b4ab3">
       <stream media="audio" direction="recvonly">
         <volume controltype="setgain" value="+3"/>
       </stream>
       <stream media="audio" direction="sendonly"/>
     </modifyjoin>
   </mscmixer>

E2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 140e0f763352 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 123

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <response status="200" reason="Join modified"/>
   </mscmixer>

F1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
   CFW 478ed6f1775b CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 180

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <event dialogid="01d1b38">
       <dtmfnotify matchmode="collect" dtmf="*6"
                   timestamp="2008-12-17T17:21:02Z"/>
     </event>
   </mscivr>

F2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 478ed6f1775b 200

G1. AS -> MS (CFW CONTROL, modifyjoin with setstate)
----------------------------------------------------
   CFW 7fdcc2331bef CONTROL
   Control-Package: msc-mixer/1.0
   Content-Type: application/msc-mixer+xml
   Content-Length: 295

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <modifyjoin id1="873975758:a5105056" id2="54b4ab3">
       <stream media="audio" direction="sendonly">
         <volume controltype="setstate" value="mute"/>
       </stream>
       <stream media="audio" direction="recvonly"/>
     </modifyjoin>
   </mscmixer>

G2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 7fdcc2331bef 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 123

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <response status="200" reason="Join modified"/>
   </mscmixer>

H1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
   CFW 750b917a5d4a CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 180

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <event dialogid="01d1b38">
       <dtmfnotify matchmode="collect" dtmf="*0"
                   timestamp="2008-12-17T17:21:05Z"/>
     </event>
   </mscivr>

H2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 750b917a5d4a 200

I1. AS -> MS (CFW CONTROL, dialogterminate)
-------------------------------------------
   CFW 515f007c5bd0 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 128

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <dialogterminate dialogid="01d1b38" immediate="true"/>
   </mscivr>

I2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 515f007c5bd0 200
   Timeout: 10
   Content-Type: application/msc-ivr+xml
   Content-Length: 140

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <response status="200" reason="Dialog terminated"
               dialogid="01d1b38"/>
   </mscivr>

J1. AS <- MS (CFW CONTROL dialogexit event)
-------------------------------------------
   CFW 76adc41122c1 CONTROL
   Control-Package: msc-ivr/1.0
   Content-Type: application/msc-ivr+xml
   Content-Length: 155

   <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <event dialogid="01d1b38">
       <dialogexit status="0" reason="Dialog terminated"/>
     </event>
   </mscivr>

J2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 76adc41122c1 200

K1. AS -> MS (CFW CONTROL, unjoin)
----------------------------------
   CFW 4e6afb6625e4 CONTROL
   Control-Package: msc-mixer/1.0
   Content-Type: application/msc-mixer+xml
   Content-Length: 127

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <unjoin id1="873975758:a5105056" id2="54b4ab3"/>
   </mscmixer>

K2. AS <- MS (CFW 200 OK)
-------------------------
   CFW 4e6afb6625e4 200
   Timeout: 10
   Content-Type: application/msc-mixer+xml
   Content-Length: 122

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <response status="200" reason="Join removed"/>
   </mscmixer>

L1. AS <- MS (CFW CONTROL unjoin-notify event)
----------------------------------------------
   CFW 577696293504 CONTROL
   Control-Package: msc-mixer/1.0
   Content-Type: application/msc-mixer+xml
   Content-Length: 157

   <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <event>
       <unjoin-notify status="0"
                      id1="873975758:a5105056" id2="54b4ab3"/>
     </event>
   </mscmixer>

L2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
   CFW 577696293504 200

7.  Media Resource Brokering

   All the flows presented so far describe the interaction between a
   single AS and a single MS.  This is the simplest topology that can be
   envisaged in a MEDIACTRL-compliant architecture, but it's not the
   only topology that is allowed.  [RFC5567] presents several possible
   topologies that potentially involve several AS and several MS as
   well.  To properly allow for such topologies, an additional element
   called the Media Resource Broker (MRB) has been introduced in the
   MEDIACTRL architecture.  Such an entity, and the protocols needed to
   interact with it, has been standardized in [RFC6917].

   An MRB is basically a locator that is aware of a pool of MS and makes
   them available to interested AS according to their requirements.  For
   this reason, two different interfaces have been introduced:

   o  the Publishing interface (Section 7.1), which allows an MRB to
      subscribe for notifications at the MS it is handling (e.g.,
      available and occupied resources, current state, etc.).

   o  the Consumer interface (Section 7.2), which allows an interested
      AS to query an MRB for an MS capable of fulfilling its
      requirements.

   The flows in the following sections will present some typical
   use-case scenarios involving an MRB and the different topologies in
   which it has been conceived to work.

   Additionally, a few considerations on the handling of media dialogs
   whenever an MRB is involved are presented in Section 7.3.

7.1.  Publishing Interface

   An MRB uses the MS's Publishing interface to acquire relevant
   information.  This Publishing interface, as specified in [RFC6917],
   is made available as a Control Package for the Media Control Channel
   Framework.  This means that in order to receive information from an
   MS, an MRB must negotiate a Control Channel as explained in
   Section 5.  This package allows an MRB to either request information
   in the form of a direct request/answer from an MS or subscribe for
   events.

   Of course, since the MRB is interested in the Publishing interface,
   the previously mentioned negotiation must be changed in order to take
   into account the need for the MRB Control Package.  The name of this
   package is 'mrb-publish/1.0', which means that the SYNC might look
   like the following:

   1. MRB -> MS (CFW SYNC)
   -----------------------
      CFW 6b8b4567327b SYNC
      Dialog-ID: z9hG4bK-4542-1-0
      Keep-Alive: 100
      Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0

   2. MRB <- MS (CFW 200)
   ----------------------
      CFW 6b8b4567327b 200
      Keep-Alive: 100
      Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0
      Supported: msc-example-pkg/1.0

   The meaning of this negotiation was presented previously.  It is
   enough to point out that the MRB in this case adds a new item to the
   'Packages' it needs support for (mrb-publish/1.0).  In this case, the
   MS supports it, and in fact it is added to the negotiated packages in
   the reply:

           Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0
                                               ^^^^^^^^^^^^^^^

   The MS as described in Section 5, on the other hand, did not have
   support for that package, since only 'msc-example-pkg/1.0' was part
   of the 'Supported' list.

   Figure 47 presents a ladder diagram of a typical interaction based on
   the MRB Control Package.

         MRB                                            MS
          |                                              |
          | A1. CONTROL (MRB subscription)               |
          |--------------------------------------------->|
          |                                   A2. 200 OK |
          |<---------------------------------------------|
          |                                              |--+ collect
          |                                              |  | requested
          |                                              |<-+ info
          |               B1. CONTROL (MRB notification) |
          |<---------------------------------------------|
          | B2. 200 OK                                   |
          |--------------------------------------------->|
          |                                              |
          .                                              .
          .                                              .
          |                                              |
          |                                              |--+ collect
          |                                              |  | up-to-date
          |                                              |<-+ info
          |               C1. CONTROL (MRB notification) |
          |<---------------------------------------------|
          | C2. 200 OK                                   |
          |--------------------------------------------->|
          |                                              |
          .                                              .
          .                                              .
          |                                              |
          | D1. CONTROL (Update MRB subscription)        |
          |--------------------------------------------->|
          |                                   D2. 200 OK |
          |<---------------------------------------------|
          |                                              |
          .                                              .
          .                                              .

    Figure 47: Media Resource Brokering: Subscription and Notification

   In this example, the MRB subscribes for information at the specified
   MS, and events are triggered on a regular, negotiated basis.  All of
   these messages flow through the Control Channel, as do all of the
   messages discussed in this document.  The framework transaction steps
   are as follows:

   o  The MRB sends a new CONTROL message (A1) addressed to the MRB
      package (mrb-publish/1.0); it is a subscription for information
      (<subscription>), and the MRB is asking to be notified at least
      every 10 minutes (<minfrequency>) or, if required, every 30
      seconds at maximum.  The subscription must last 30 minutes
      (<expires>), after which no additional notifications must be sent.

   o  The MS acknowledges the request (A2) and sends notification of the
      success of the request in a 200 OK message (<mrbresponse>).

   o  The MS prepares and sends the first notification to the MRB (B1).
      As has been done with other packages, the notification has been
      sent as an MS-generated CONTROL message; it is a notification
      related to the request in the first message, because the 'id'
      (p0T65U) matches that request.  All of the information that the
      MRB subscribed for is provided in the payload.

   o  The MRB acknowledges the notification (B2) and uses the retrieved
      information to update its own information as part of its business
      logic.

   o  The previous step (the MRB acknowledges notifications and uses the
      retrieved information) repeats at the required frequency, with
      up-to-date information.

   o  After a while, the MRB updates its subscription (D1) to get more
      frequent updates (minfrequency=1, an update every second at
      least).  The MS accepts the update (D2), although it may adjust
      the frequency in the reply according to its policies (e.g., a
      lower rate, such as minfrequency=30).  The notifications continue,
      but at the newer rate; the expiration is also updated accordingly
      (600 seconds again, since the update refreshes it).

A1. MRB -> MS (CONTROL, publish request)
----------------------------------------
   CFW lidc30BZObiC CONTROL
   Control-Package: mrb-publish/1.0
   Content-Type: application/mrb-publish+xml
   Content-Length: 337

   <mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
      <mrbrequest>
         <subscription action="create" seqnumber="1" id="p0T65U">
            <expires>60</expires>
            <minfrequency>600</minfrequency>
            <maxfrequency>30</maxfrequency>
         </subscription>
      </mrbrequest>
   </mrbpublish>

A2. MRB <- MS (200 to CONTROL, request accepted)
------------------------------------------------
   CFW lidc30BZObiC 200
   Timeout: 10
   Content-Type: application/mrb-publish+xml
   Content-Length: 139

   <mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
           <mrbresponse status="200" reason="OK: Request accepted"/>
   </mrbpublish>

B1. MRB <- MS (CONTROL, event notification from MS)
---------------------------------------------------
   CFW 03fff52e7b7a CONTROL
   Control-Package: mrb-publish/1.0
   Content-Type: application/mrb-publish+xml
   Content-Length: 4157

   <mrbpublish version="1.0"
             xmlns="urn:ietf:params:xml:ns:mrb-publish">
    <mrbnotification seqnumber="1" id="p0T65U">
        <media-server-id>a1b2c3d4</media-server-id>
        <supported-packages>
            <package name="msc-ivr/1.0"/>
            <package name="msc-mixer/1.0"/>
            <package name="mrb-publish/1.0"/>
            <package name="msc-example-pkg/1.0"/>
        </supported-packages>

        <active-rtp-sessions>
            <rtp-codec name="audio/basic">
                <decoding>10</decoding>
                <encoding>20</encoding>
            </rtp-codec>
        </active-rtp-sessions>
        <active-mixer-sessions>
            <active-mix conferenceid="7cfgs43">
                <rtp-codec name="audio/basic">
                    <decoding>3</decoding>
                    <encoding>3</encoding>
                </rtp-codec>
            </active-mix>
        </active-mixer-sessions>
        <non-active-rtp-sessions>
            <rtp-codec name="audio/basic">
                <decoding>50</decoding>
                <encoding>40</encoding>
            </rtp-codec>
        </non-active-rtp-sessions>
        <non-active-mixer-sessions>
            <non-active-mix available="15">
                <rtp-codec name="audio/basic">
                    <decoding>15</decoding>
                    <encoding>15</encoding>
                </rtp-codec>
            </non-active-mix>
        </non-active-mixer-sessions>
        <media-server-status>active</media-server-status>
        <supported-codecs>
            <supported-codec name="audio/basic">
                <supported-codec-package name="msc-ivr/1.0">
                    <supported-action>encoding</supported-action>
                    <supported-action>decoding</supported-action>
                </supported-codec-package>
                <supported-codec-package name="msc-mixer/1.0">
                    <supported-action>encoding</supported-action>
                    <supported-action>decoding</supported-action>
                </supported-codec-package>
            </supported-codec>
        </supported-codecs>

        <application-data>TestbedPrototype</application-data>
        <file-formats>
            <supported-format name="audio/x-wav">
                <supported-file-package>
                    msc-ivr/1.0
                </supported-file-package>
            </supported-format>
        </file-formats>
        <max-prepared-duration>
            <max-time max-time-seconds="3600">
                <max-time-package>msc-ivr/1.0</max-time-package>
            </max-time>
        </max-prepared-duration>
        <dtmf-support>
            <detect>
                <dtmf-type package="msc-ivr/1.0" name="RFC4733"/>
                <dtmf-type package="msc-mixer/1.0" name="RFC4733"/>
            </detect>
            <generate>
                <dtmf-type package="msc-ivr/1.0" name="RFC4733"/>
                <dtmf-type package="msc-mixer/1.0" name="RFC4733"/>
            </generate>
            <passthrough>
                <dtmf-type package="msc-ivr/1.0" name="RFC4733"/>
                <dtmf-type package="msc-mixer/1.0" name="RFC4733"/>
            </passthrough>
        </dtmf-support>
        <mixing-modes>
            <audio-mixing-modes>
                <audio-mixing-mode package="msc-ivr/1.0"> \
                     nbest \
                </audio-mixing-mode>
            </audio-mixing-modes>
            <video-mixing-modes activespeakermix="true" vas="true">
                <video-mixing-mode package="msc-mixer/1.0"> \
                     single-view \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     dual-view \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     dual-view-crop \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     dual-view-2x1 \
                </video-mixing-mode>

                <video-mixing-mode package="msc-mixer/1.0"> \
                     dual-view-2x1-crop \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     quad-view \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     multiple-5x1 \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     multiple-3x3 \
                </video-mixing-mode>
                <video-mixing-mode package="msc-mixer/1.0"> \
                     multiple-4x4 \
                </video-mixing-mode>
            </video-mixing-modes>
        </mixing-modes>
        <supported-tones>
            <supported-country-codes>
                <country-code package="msc-ivr/1.0">GB</country-code>
                <country-code package="msc-ivr/1.0">IT</country-code>
                <country-code package="msc-ivr/1.0">US</country-code>
            </supported-country-codes>
            <supported-h248-codes>
                <h248-code package="msc-ivr/1.0">cg/*</h248-code>
                <h248-code package="msc-ivr/1.0">biztn/ofque</h248-code>
                <h248-code package="msc-ivr/1.0">biztn/erwt</h248-code>
                <h248-code package="msc-mixer/1.0">conftn/*</h248-code>
            </supported-h248-codes>
        </supported-tones>
        <file-transfer-modes>
            <file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
        </file-transfer-modes>
        <asr-tts-support>
            <asr-support>
                <language xml:lang="en"/>
            </asr-support>
            <tts-support>
                <language xml:lang="en"/>
            </tts-support>
        </asr-tts-support>
        <vxml-support>
            <vxml-mode package="msc-ivr/1.0" support="rfc6231"/>
        </vxml-support>

        <media-server-location>
            <civicAddress xml:lang="it">
                <country>IT</country>
                <A1>Campania</A1>
                <A3>Napoli</A3>
                <A6>Via Claudio</A6>
                <HNO>21</HNO>
                <LMK>University of Napoli Federico II</LMK>
                <NAM>Dipartimento di Informatica e Sistemistica</NAM>
                <PC>80210</PC>
            </civicAddress>
        </media-server-location>
        <label>TestbedPrototype-01</label>
        <media-server-address>
            sip:MediaServer@ms.example.net
        </media-server-address>
        <encryption/>
    </mrbnotification>
   </mrbpublish>

B2. MRB -> MS (200 to CONTROL)
------------------------------
   CFW 03fff52e7b7a 200

(C1 and C2 omitted for brevity)

D1. MRB -> MS (CONTROL, publish request)
----------------------------------------
CFW pyu788fc32wa CONTROL
Control-Package: mrb-publish/1.0
Content-Type: application/mrb-publish+xml
Content-Length: 342

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
    <mrbrequest>
        <subscription action="update" seqnumber="2" id="p0T65U">
            <expires>600</expires>
            <minfrequency>1</minfrequency>
        </subscription>
    </mrbrequest>
</mrbpublish>

D2. MRB <- MS (200 to CONTROL, request accepted)
------------------------------------------------
CFW pyu788fc32wa 200
Timeout: 10
Content-Type: application/mrb-publish+xml
Content-Length: 332

<mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
    <mrbresponse status="200" reason="OK: Request accepted">
        <subscription action="create" seqnumber="2" id="p0T65U">
            <expires>600</expires>
            <minfrequency>30</minfrequency>
        </subscription>
    </mrbresponse>
</mrbpublish>

7.2.  Consumer Interface

   Whereas the Publishing interface is used by an MS to publish its
   functionality and up-to-date information to an MRB, the Consumer
   interface is used by an interested AS to access a resource.  An AS
   can use the Consumer interface to contact an MRB and describe the
   resources it needs.  The MRB then replies with the needed
   information: specifically, the address of an MS that is capable of
   meeting the requirements.

   However, unlike the Publishing interface, the Consumer interface is
   not specified as a Control Package.  Rather, it is conceived as an
   XML-based protocol that can be transported by means of either HTTP or
   SIP, as will be shown in the following sections.

   As specified in [RFC6917], the Consumer interface can be involved in
   two topologies: Query mode and Inline mode.  In the Query mode
   (Section 7.2.1), the Consumer requests and responses are conveyed by
   means of HTTP.  Once the AS gets the answer, the usual MEDIACTRL
   interactions occur between the AS and the MS chosen by the MRB.  By
   contrast, in the Inline mode, the MRB is in the path between the AS
   and the pool of MS it is handling.  In this case, an AS can place
   Consumer requests using SIP as a transport, by means of a multipart
   payload (Section 7.2.2) containing the Consumer request itself and an
   SDP related either to the creation of a Control Channel or to a UAC
   media dialog.  This is called Inline-aware mode, since it assumes
   that the interested AS knows that an MRB is in place and knows how to
   talk to it.  The MRB is also conceived to work with AS that are
   unaware of its functionality, i.e., unaware of the Consumer
   interface.  In this kind of scenario, the Inline mode is still used,
   but with the AS thinking the MRB it is talking to is actually an MS.
   This approach is called Inline-unaware mode (Section 7.2.3).

7.2.1.  Query Mode

   As discussed in the previous section, in the Query mode the AS sends
   Consumer requests by means of HTTP.  Specifically, an HTTP POST is
   used to convey the request.  The MRB is assumed to send its response
   by means of an HTTP 200 OK reply.  Since a successful Consumer
   response contains information to contact a specific MS (the MS the
   MRB has deemed most capable of fulfilling the AS's requirements), an
   AS can subsequently directly contact the MS, as described in
   Section 5.  This means that in the Query mode the MRB acts purely as
   a locator, and then the AS and the MS can talk 1:1.

   Figure 48 presents a ladder diagram of a typical Consumer request in
   the Query topology:

     AS                                             MRB
      |                                              |
      | 1. HTTP POST (Consumer request)              |
      |--------------------------------------------->|
      |                                              |
      |                                              |
      |                                              |--+ Parse request
      |                                              |  | and see if any
      |                                              |<-+ MS applies
      |                                              |
      |                2. 200 OK (Consumer response) |
      |<---------------------------------------------|
      |                                              |
      |--+ Parse response and                        |
      |  | start session (SIP/COMEDIA/CFW)           |
      |<-+ with MS reported by MRB                   |
      |                                              |
      .                                              .
      .                                              .

              Figure 48: Media Resource Brokering: Query Mode

   In this example, the AS is interested in an MS meeting a defined set
   of requirements.  The MS must:

   1.  support both the IVR and Mixer packages.

   2.  provide at least 10 G.711 encoding/decoding RTP sessions for IVR
       purposes.

   3.  support HTTP-based streaming and support for the audio/x-wav file
       format in the IVR package.

   These requirements are properly formatted according to the MRB
   Consumer syntax.  The framework transaction steps are as follows:

   o  The AS sends an HTTP POST message to the MRB (1).  The payload is,
      of course, the Consumer request, which is reflected by the
      Content-Type header (application/mrb-consumer+xml).  The Consumer
      request (<mediaResourceRequest>, uniquely identified by its 'id'
      attribute set to the random value 'n3un93wd'), includes some
      general requirements (<generalInfo>) and some IVR-specific
      requirements (<ivrInfo>).  The general part of the requests
      contains the set of required packages (<packages>).  The
      IVR-specific section contains requirements concerning the number
      of required IVR sessions (<ivr-sessions>), the file formats that
      are to be supported (<file-formats>), and the required file
      transfer capabilities (<file-transfer-modes>).

   o  The MRB gets the request and parses it.  Then, according to its
      business logic, it realizes it can't find a single MS capable of
      targeting the request and as a consequence picks two MS instances
      that can handle 60 and 40 of the requested sessions, respectively.
      It prepares a Consumer response (2) to provide the AS with the
      requested information.  The response (<mediaResourceResponse>,
      which includes the same 'id' attribute as the request) indicates
      success (status=200) and includes the relevant information
      (<response-session-info>).  Specifically, the response includes
      transaction-related information (the same session-id and seq
      provided by the AS in its request, to allow proper request/
      response matching) together with information on the duration of
      the reservation (expires=3600, i.e., after an hour the request
      will expire) and the SIP addresses of the chosen MS.

   Note how the sequence number the MRB returned is not 1.  According to
   the MRB specification, this is the starting value to increment for
   the sequence number to be used in subsequent requests.  This means
   that should the AS want to update or remove the session it should use
   10 as a value for the sequence number in the related request.
   According to Section 12 of [RFC6917], this random value for the first
   sequence number is also a way to help prevent a malicious entity from
   messing with or disrupting another AS session with the MRB.  In fact,
   sequence numbers in requests and responses have to match, and failure
   to provide the correct sequence number would result in session
   failure and a 405 error message.

1. AS -> MRB (HTTP POST, Consumer request)
------------------------------------------
 POST /Mrb/Consumer HTTP/1.1
 Content-Length: 893
 Content-Type: application/mrb-consumer+xml
 Host: mrb.example.com:8080
 Connection: Keep-Alive
 User-Agent: Apache-HttpClient/4.0.1 (java 1.5)

 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <mrbconsumer version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-consumer">
    <mediaResourceRequest id="n3un93wd">
        <generalInfo>
            <packages>
                <package>msc-ivr/1.0</package>
                <package>msc-mixer/1.0</package>
            </packages>
        </generalInfo>
        <ivrInfo>
            <ivr-sessions>
                <rtp-codec name="audio/basic">
                    <decoding>100</decoding>
                    <encoding>100</encoding>
                </rtp-codec>
            </ivr-sessions>
            <file-formats>
                <required-format name="audio/x-wav"/>
            </file-formats>
            <file-transfer-modes>
                <file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
            </file-transfer-modes>
        </ivrInfo>
    </mediaResourceRequest>
 </mrbconsumer>

2. AS <- MRB (200 to POST, Consumer response)
---------------------------------------------
 HTTP/1.1 200 OK
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 Date: Thu, 28 Jul 2011 10:34:45 GMT

 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <mrbconsumer version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-consumer">
    <mediaResourceResponse reason="Resource found" status="200"
                           id="n3un93wd">
        <response-session-info>
            <session-id>z603G3yaUzM8</session-id>
            <seq>9</seq>
            <expires>3600</expires>
            <media-server-address
                              uri="sip:MediaServer@ms.example.com:5080">
                <ivr-sessions>
                    <rtp-codec name="audio/basic">
                        <decoding>60</decoding>
                        <encoding>60</encoding>
                    </rtp-codec>
                </ivr-sessions>
            </media-server-address>
            <media-server-address
                       uri="sip:OtherMediaServer@pool.example.net:5080">
                <ivr-sessions>
                    <rtp-codec name="audio/basic">
                        <decoding>40</decoding>
                        <encoding>40</encoding>
                    </rtp-codec>
                </ivr-sessions>
            </media-server-address>
        </response-session-info>
    </mediaResourceResponse>
 </mrbconsumer>

   For the sake of conciseness, the subsequent steps are not presented.
   They are very trivial, since they basically consist of the AS issuing
   a COMEDIA negotiation with either of the obtained MS, as already
   presented in Section 5.  The same can be said with respect to
   attaching UAC media dialogs.  In fact, since after the Query the
   AS<->MS interaction becomes 1:1, UAC media dialogs can be redirected
   directly to the proper MS using the 3PCC approach, e.g., as shown in
   Figure 10.

7.2.2.  Inline-Aware Mode

   Unlike the Query mode, in the Inline-Aware MRB Mode (IAMM) the AS
   sends Consumer requests by means of SIP.  Of course, saying that the
   transport changes from HTTP to SIP is not as trivial as it seems.  In
   fact, HTTP and SIP behave in very different ways, and this is
   reflected in the way the Inline-aware mode is conceived.

   An AS willing to issue a Consumer request by means of SIP has to do
   so by means of an INVITE.  As specified in [RFC6917], the payload of
   the INVITE can't contain only the Consumer request itself.  In fact,
   the Consumer request is assumed to be carried within a SIP
   transaction.  A Consumer session is not strictly associated with the
   lifetime of any SIP transaction, meaning that Consumer requests
   belonging to the same session may be transported over different SIP
   messages; therefore, a hangup on any of these SIP dialogs would not
   affect a Consumer session.

   That said, as documented in [RFC6230], [RFC6917] envisages two kinds
   of SIP dialogs over which a Consumer request may be sent: a SIP
   control dialog (a SIP dialog sent by the AS in order to set up a
   Control Channel) and a UAC media dialog (a SIP dialog sent by the AS
   in order to attach a UAC to an MS).  In both cases, the AS would
   prepare a multipart/mixed payload to achieve both ends, i.e.,
   receiving a reply to its Consumer request and effectively carrying on
   the negotiation described in the SDP payload.

   The behaviors in the two cases, which are called the CFW-based
   approach and the media dialog-based approach, respectively, are only
   slightly different, but both will be presented to clarify how they
   could be exploited.  To make things clearer for the reader, the same
   Consumer request as the Consumer request presented in the Query mode
   will be sent, in order to clarify how the behavior of the involved
   parties may differ.

7.2.2.1.  Inline-Aware Mode: CFW-Based Approach

   Figure 49 presents a ladder diagram of a typical Consumer request in
   the CFW-based Inline-aware topology:

   AS                      MRB                          MS
    |                       |                           |
    | 1. INVITE             |                           |
    | (multipart/mixed:     |                           |
    |  application/cfw,     |                           |
    |  application/mrb-consumer+xml)                    |
    |---------------------->|                           |
    |       2. 100 (Trying) |                           |
    |<----------------------|                           |
    |                       |--+ Extract SDP and        |
    |                       |  | MRB payloads; handle   |
    |                       |<-+ Consumer request to    |
    |                       |    pick MS                |
    |                       |                           |

    |                       | 3. INVITE                 |
    |                       | (application/cfw from 1.) |
    |                       |-------------------------->|
    |                       |           4. 100 (Trying) |
    |                       |<--------------------------|
    |                       |                           |--+ Negotiate
    |                       |                           |  | CFW Control
    |                       |                           |<-+ Channel
    |                       |                 5. 200 OK |
    |                       | (application/cfw from MS) |
    |                       |<--------------------------|
    |                       | 6. ACK                    |
    |                       |-------------------------->|
    |        Prepare new +--|                           |
    |       payload with |  |                           |
    |    SDP from MS and +->|                           |
    |     Consumer reply    |                           |
    |                       |                           |
    |             7. 200 OK |                           |
    |     (multipart/mixed: |                           |
    |      application/cfw from MS,                     |
    |      application/mrb-consumer+xml)                |
    |<----------------------|                           |
    | 8. ACK                |                           |
    |---------------------->|                           |
    |                       |                           |
    |--+ Read Consumer      |                           |
    |  | reply and use SDP  |                           |
    |<-+ to create CFW Chn. |                           |
    |                       |                           |
    |                                                   |
    |<<############## TCP CONNECTION #################>>|
    |                                                   |
    | CFW SYNC                                          |
    |++++++++++++++++++++++++++++++++++++++++++++++++++>|
    |                                                   |
    .                       .                           .
    .                       .                           .

     Figure 49: Media Resource Brokering: CFW-Based Inline-Aware Mode

   To make the scenario easier to understand, we assume that the AS is
   interested in exactly the same set of requirements as those presented
   in Section 7.2.1.  This means that the Consumer request originated by
   the AS will be the same as before, with only the transport/topology
   changing.

   Please note that to make the protocol contents easier to read, a
   simple 'Part' is used whenever a boundary for a multipart/mixed
   payload is provided, instead of the actual boundary that would be
   inserted in the SIP messages.

   The framework transaction steps (for simplicity's sake, only the
   payloads, and not the complete SIP transactions, are reported) are as
   follows:

1. AS -> MRB (INVITE multipart/mixed)
-------------------------------------
   [..]
   Content-Type: multipart/mixed;boundary="Part"

   --Part
   Content-Type: application/sdp

   v=0
   o=- 2890844526 2890842807 IN IP4 as.example.com
   s=MediaCtrl
   c=IN IP4 as.example.com
   t=0 0
   m=application 48035 TCP cfw
   a=connection:new
   a=setup:active
   a=cfw-id:vF0zD4xzUAW9

   --Part
   Content-Type: application/mrb-consumer+xml

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <mrbconsumer version="1.0"
                xmlns="urn:ietf:params:xml:ns:mrb-consumer">
     <mediaResourceRequest id="fr34asx1">
        <generalInfo>
            <packages>
                <package>msc-ivr/1.0</package>
                <package>msc-mixer/1.0</package>
            </packages>
        </generalInfo>
        <ivrInfo>
            <ivr-sessions>
                <rtp-codec name="audio/basic">
                    <decoding>100</decoding>
                    <encoding>100</encoding>
                </rtp-codec>
            </ivr-sessions>

            <file-formats>
                <required-format name="audio/x-wav"/>
            </file-formats>
            <file-transfer-modes>
                <file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
            </file-transfer-modes>
        </ivrInfo>
     </mediaResourceRequest>
   </mrbconsumer>

   --Part

3. MRB -> MS (INVITE SDP only)
------------------------------
   [..]
   Content-Type: application/sdp

   v=0
   o=- 2890844526 2890842807 IN IP4 as.example.com
   s=MediaCtrl
   c=IN IP4 as.example.com
   t=0 0
   m=application 48035 TCP cfw
   a=connection:new
   a=setup:active
   a=cfw-id:vF0zD4xzUAW9

5. MRB <- MS (200 OK SDP)
-------------------------
   [..]
   Content-Type: application/sdp

   v=0
   o=lminiero 2890844526 2890842808 IN IP4 ms.example.net
   s=MediaCtrl
   c=IN IP4 ms.example.net
   t=0 0
   m=application 7575 TCP cfw
   a=connection:new
   a=setup:passive
   a=cfw-id:vF0zD4xzUAW9

7. AS <- MRB (200 OK multipart/mixed)
-------------------------------------
   [..]
   Content-Type: multipart/mixed;boundary="Part"

   --Part
   Content-Type: application/sdp

   v=0
   o=lminiero 2890844526 2890842808 IN IP4 ms.example.net
   s=MediaCtrl
   c=IN IP4 ms.example.net
   t=0 0
   m=application 7575 TCP cfw
   a=connection:new
   a=setup:passive
   a=cfw-id:vF0zD4xzUAW9

   --Part
   Content-Type: application/mrb-consumer+xml

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <mrbconsumer version="1.0"
                xmlns="urn:ietf:params:xml:ns:mrb-consumer">
     <mediaResourceResponse reason="Resource found" status="200"
                            id="fr34asx1">
        <response-session-info>
            <session-id>z603G3yaUzM8</session-id>
            <seq>9</seq>
            <expires>3600</expires>
            <media-server-address
                              uri="sip:MediaServer@ms.example.com:5080">
                <connection-id>32pbdxZ8:KQw677BF</connection-id>
                <ivr-sessions>
                    <rtp-codec name="audio/basic">
                        <decoding>60</decoding>
                        <encoding>60</encoding>
                    </rtp-codec>
                </ivr-sessions>
            </media-server-address>

            <media-server-address
                       uri="sip:OtherMediaServer@pool.example.net:5080">
                <ivr-sessions>
                    <rtp-codec name="audio/basic">
                        <decoding>40</decoding>
                        <encoding>40</encoding>
                    </rtp-codec>
                </ivr-sessions>
            </media-server-address>
        </response-session-info>
     </mediaResourceResponse>
   </mrbconsumer>

   --Part

   The sequence diagram and the dumps effectively show the different
   approach with respect to the Query mode.  The SIP INVITE sent by the
   AS (1.) includes both a Consumer request (the same as before) and an
   SDP to negotiate a CFW channel with an MS.  The MRB takes care of the
   request exactly as before (provisioning two MS instances) but with a
   remarkable difference: first of all, it picks one of the two MS
   instances on behalf of the AS (negotiating the Control Channel in
   steps 3 to 6) and only then replies to the AS with both the MS side
   of the SDP negotiation (with information on how to set up the Control
   Channel) and the Consumer response itself.

   The Consumer response is also slightly different in the first place.
   In fact, as can be seen in 7., there's an additional element
   (<connection-id>) that the MRB has added to the message.  This
   element contains the 'connection-id' that the AS and MS would have
   built out of the 'From' and 'To' tags as explained in Section 6, had
   the AS contacted the MS directly.  Since the MRB has actually done
   the negotiation on behalf of the AS, without this information the AS
   and MS would refer to different connectionid attributes to target the
   same dialog, thus causing the CFW protocol not to behave as expected.
   This aspect will be more carefully described in the next section (for
   the media dialog-based approach), since the 'connection-id' attribute
   is strictly related to media sessions.

   As before, for the sake of conciseness the subsequent steps of the
   previous transaction are quite trivial and therefore are not
   presented.  In fact, as shown in the flow, the SIP negotiation has
   resulted in both the AS and the chosen MS negotiating a Control
   Channel.  This means that the AS is only left to instantiate the
   Control Channel and send CFW requests according to its application
   logic.

   It is worthwhile to highlight the fact that, as in the Query example,
   the AS gets the addresses of both of the chosen MS in this example as
   well, since a Consumer transaction has taken place.  This means that,
   just as in the Query case, any UAC media dialog can be redirected
   directly to the proper MS using the 3PCC approach, e.g., as shown in
   Figure 10, rather than again using the MRB as a Proxy/B2BUA.  Of
   course, a separate SIP control dialog would be needed before
   attempting to use the second MS instance.

7.2.2.2.  Inline-Aware Mode: Media Dialog-Based Approach

   There's a second way to take advantage of the IAMM mode, i.e.,
   exploiting SIP dialogs related to UAC media dialogs as 'vessels' for
   Consumer messages.  As will be made clearer in the following sequence
   diagram and protocol dumps, this scenario does not differ much from
   the scenario presented in Section 7.2.2.1 with respect to the
   Consumer request/response, but it may be useful to compare these two
   scenarios and show how they may differ with respect to the management
   of the media dialog itself and any CFW Control Channel that may be
   involved.

   Figure 50 presents a ladder diagram of a typical Consumer request in
   the media dialog-based Inline-aware topology:

   UAC              AS                     MRB                        MS
    |               |                       |                          |
    | 1. INVITE     |                       |                          |
    | (audio/video) |                       |                          |
    |-------------->|                       |                          |
    | 2. 100 Trying |                       |                          |
    |<--------------|                       |                          |
    |               | 3. INVITE             |                          |
    |               | (multipart/mixed:     |                          |
    |               |  audio/video from 1., |                          |
    |               |  application/mrb-consumer+xml)                   |
    |               |---------------------->|                          |
    |               |       4. 100 (Trying) |                          |
    |               |<----------------------|                          |
    |               |                       |--+ Extract SDP and       |
    |               |                       |  | MRB payloads; handle  |
    |               |                       |<-+ Consumer request to   |
    |               |                       |    pick Media Servers    |
    |               |                       |                          |
    |               |                       | 5. INVITE                |
    |               |                       | (audio/video from 3.)    |
    |               |                       |------------------------->|

    |               |                       |          6. 100 (Trying) |
    |               |                       |<-------------------------|
    |               |                       |                       +--|
    |               |                       |   Handle media dialog |  |
    |               |                       |       (connection-id) +->|
    |               |                       |                          |
    |               |                       |                7. 200 OK |
    |               |                       |    (audio/video from MS) |
    |               |                       |<-------------------------|
    |               |                       | 8. ACK                   |
    |               |                       |------------------------->|
    |               |        Prepare new +--|                          |
    |               |       payload with |  |                          |
    |               |    SDP from MS and +->|                          |
    |               |     Consumer reply    |                          |
    |               |                       |                          |
    |               |             9. 200 OK |                          |
    |               |     (multipart/mixed: |                          |
    |               |      audio/video from MS,                        |
    |               |      application/mrb-consumer+xml)               |
    |               |<----------------------|                          |
    |               | 10. ACK               |                          |
    |               |---------------------->|                          |
    |               |                       |                          |
    |               |--+ Read Consumer      |                          |
    |               |  | reply and send     |                          |
    |               |<-+ SDP back to UAC    |                          |
    |    11. 200 OK |                       |                          |
    |(audio/video from MS)                  |                          |
    |<--------------|                       |                          |
    | 12. ACK       |                       |                          |
    |-------------->|                       |                          |
    |               |                       |                          |
    |<<*************************** RTP ******************************>>|
    |               |                       |                          |
    |               |--+ Negotiate          |                          |
    |               |  | CFW channel        |                          |
    |               |<-+ towards MS         |                          |
    |               |    (if needed)        |                          |
    .               .                       .                          .
    .               .                       .                          .
    |               |                       |                          |
    |               |<<############## TCP CONNECTION ################>>|
    |               |                                                  |

    |               | CFW SYNC                                         |
    |               |+++++++++++++++++++++++++++++++++++++++++++++++++>|
    |               |                                                  |
    .               .                       .                          .
    .               .                       .                          .

          Figure 50: Media Resource Brokering: Media Dialog-Based
                             Inline-Aware Mode

   To make the scenario easier to understand, we assume that the AS is
   interested in exactly the same set of requirements as those presented
   in Section 7.2.1.  This means that the Consumer request originated by
   the AS will be the same as before, with only the transport/topology
   changing.

   Again, please note that to make the protocol contents easier to read,
   a simple 'Part' is used whenever a boundary for a multipart/mixed
   payload is provided, instead of the actual boundary that would be
   inserted in the SIP messages.

   The framework transaction steps (for simplicity's sake, only the
   relevant headers and payloads, and not the complete SIP transactions,
   are reported) are as follows:

1. UAC -> AS (INVITE with media SDP)
------------------------------------
   [..]
   From: <sip:lminiero@users.example.com>;tag=1153573888
   To: <sip:mediactrlDemo@as.example.com>
   [..]
   Content-Type: application/sdp

   v=0
   o=lminiero 123456 654321 IN IP4 203.0.113.2
   s=A conversation
   c=IN IP4 203.0.113.2
   t=0 0
   m=audio 7078 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000/1
   a=rtpmap:3 GSM/8000/1
   a=rtpmap:8 PCMA/8000/1
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-11
   m=video 9078 RTP/AVP 98

3. AS -> MRB (INVITE multipart/mixed)
-------------------------------------
   [..]
   From: <sip:ApplicationServer@as.example.com>;tag=fd4fush5
   To: <sip:Mrb@mrb.example.org>
   [..]
   Content-Type: multipart/mixed;boundary="Part"

   --Part
   Content-Type: application/sdp

   v=0
   o=lminiero 123456 654321 IN IP4 203.0.113.2
   s=A conversation
   c=IN IP4 203.0.113.2
   t=0 0
   m=audio 7078 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000/1
   a=rtpmap:3 GSM/8000/1
   a=rtpmap:8 PCMA/8000/1
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-11
   m=video 9078 RTP/AVP 98

   --Part
   Content-Type: application/mrb-consumer+xml

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <mrbconsumer version="1.0"
                xmlns="urn:ietf:params:xml:ns:mrb-consumer">
    <mediaResourceRequest id="bnv3xc45">
        <generalInfo>
            <packages>
                <package>msc-ivr/1.0</package>
                <package>msc-mixer/1.0</package>
            </packages>
        </generalInfo>
        <ivrInfo>
            <ivr-sessions>
                <rtp-codec name="audio/basic">
                    <decoding>100</decoding>
                    <encoding>100</encoding>
                </rtp-codec>
            </ivr-sessions>
            <file-formats>
                <required-format name="audio/x-wav"/>
            </file-formats>

            <file-transfer-modes>
                <file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
            </file-transfer-modes>
        </ivrInfo>
    </mediaResourceRequest>
   </mrbconsumer>

   --Part

5. MRB -> MS (INVITE SDP only)
------------------------------
   [..]
   From: <sip:Mrb@mrb.example.org:5060>;tag=32pbdxZ8
   To: <sip:MediaServer@ms.example.com:5080>
   [..]
   Content-Type: application/sdp

   v=0
   o=lminiero 123456 654321 IN IP4 203.0.113.2
   s=A conversation
   c=IN IP4 203.0.113.2
   t=0 0
   m=audio 7078 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000/1
   a=rtpmap:3 GSM/8000/1
   a=rtpmap:8 PCMA/8000/1
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-11
   m=video 9078 RTP/AVP 98

7. MRB <- MS (200 OK SDP)
-------------------------
   [..]
   From: <sip:Mrb@mrb.example.org:5060>;tag=32pbdxZ8
   To: <sip:MediaServer@ms.example.com:5080>;tag=KQw677BF
   [..]
   Content-Type: application/sdp

   v=0
   o=lminiero 123456 654322 IN IP4 203.0.113.1
   s=MediaCtrl
   c=IN IP4 203.0.113.1
   t=0 0
   m=audio 63442 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000
   a=rtpmap:3 GSM/8000

   a=rtpmap:8 PCMA/8000
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-15
   a=ptime:20
   a=label:7eda834
   m=video 33468 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=2
   a=label:0132ca2

9. AS <- MRB (200 OK multipart/mixed)
-------------------------------------
   [..]
   From: <sip:ApplicationServer@as.example.com>;tag=fd4fush5
   To: <sip:Mrb@mrb.example.org>;tag=117652221
   [..]
   Content-Type: multipart/mixed;boundary="Part"

   --Part
   Content-Type: application/sdp

   v=0
   o=lminiero 123456 654322 IN IP4 203.0.113.1
   s=MediaCtrl
   c=IN IP4 203.0.113.1
   t=0 0
   m=audio 63442 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000
   a=rtpmap:3 GSM/8000
   a=rtpmap:8 PCMA/8000
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-15
   a=ptime:20
   a=label:7eda834
   m=video 33468 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=2
   a=label:0132ca2

   --Part
   Content-Type: application/mrb-consumer+xml

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <mrbconsumer version="1.0"
                xmlns="urn:ietf:params:xml:ns:mrb-consumer" >
    <mediaResourceResponse reason="Resource found" status="200"
                           id="bnv3xc45">
        <response-session-info>
            <session-id>z1skKYZQ3eFu</session-id>
            <seq>9</seq>
            <expires>3600</expires>
            <media-server-address
                              uri="sip:MediaServer@ms.example.com:5080">
                <connection-id>32pbdxZ8:KQw677BF</connection-id>
                <ivr-sessions>
                    <rtp-codec name="audio/basic">
                        <decoding>60</decoding>
                        <encoding>60</encoding>
                    </rtp-codec>
                </ivr-sessions>
            </media-server-address>
            <media-server-address
                       uri="sip:OtherMediaServer@pool.example.net:5080">
                <ivr-sessions>
                    <rtp-codec name="audio/basic">
                        <decoding>40</decoding>
                        <encoding>40</encoding>
                    </rtp-codec>
                </ivr-sessions>
            </media-server-address>
        </response-session-info>
    </mediaResourceResponse>
   </mrbconsumer>

   --Part

11. UAC <- AS (200 OK SDP)
--------------------------
   [..]
   From: <sip:lminiero@users.example.com>;tag=1153573888
   To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
   [..]
   Content-Type: application/sdp

   v=0
   o=lminiero 123456 654322 IN IP4 203.0.113.1
   s=MediaCtrl
   c=IN IP4 203.0.113.1
   t=0 0

   m=audio 63442 RTP/AVP 0 3 8 101
   a=rtpmap:0 PCMU/8000
   a=rtpmap:3 GSM/8000
   a=rtpmap:8 PCMA/8000
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-15
   a=ptime:20
   a=label:7eda834
   m=video 33468 RTP/AVP 98
   a=rtpmap:98 H263-1998/90000
   a=fmtp:98 CIF=2
   a=label:0132ca2

   The first obvious difference is that the first INVITE (1.) is not
   originated by the AS itself (the AS was willing to set up a Control
   Channel in the previous example) but by an authorized UAC (e.g., to
   take advantage of a media service provided by the AS).  As such, the
   first INVITE only contains an SDP to negotiate an audio and video
   channel.  The AS in its business logic needs to attach this UAC to an
   MS according to some specific requirements (e.g., the called URI is
   associated to a specific service) and as such prepares a Consumer
   request to be sent to the MRB in order to obtain a valid MS for that
   purpose.  As before, the Consumer request is sent together with the
   SDP to the MRB (3.).  The MRB extracts the Consumer payload and takes
   care of it as usual; it picks two MS instances and attaches the UAC
   to the first MS instance (5.).  Once the MS has successfully
   negotiated the audio and video streams (7.), the MRB takes note of
   the 'connection-id' associated with this call (which will be needed
   afterwards in order to manipulate the audio and video streams for
   this user) and sends back to the AS both the SDP returned by the MS
   and the Consumer response (9.).  The AS extracts the Consumer
   response and takes note of both the MS instances it has been given
   and the connection-id information.  It then completes the scenario by
   sending back to the UAC the SDP returned by the MS (11.).

   At this point, the UAC has successfully been attached to an MS.  The
   AS only needs to set up a Control Channel to that MS, if needed.
   This step may not be required, especially if the Consumer request is
   an update to an existing session rather than the preparation of a new
   session.  Assuming that a Control Channel towards that MS doesn't
   exist yet, the AS creates it as usual by sending an INVITE directly
   to the MS for which it has an address.  Once done with that, it can
   start manipulating the audio and video streams of the UAC.  To do so,
   it refers to the <connection-id> element as reported by the MRB,
   rather than relying on the <connection-id> element that it is aware
   of.  In fact, the AS is aware of a connection-id value (fd4fush5:
   117652221, built out of the messages exchanged with the MRB), while
   the MS is aware of another (32pbdxZ8:KQw677BF, built out of the

   MRB-MS interaction).  The right connection-id is of course the one
   the MS is aware of, and as such the AS refers to that connection-id,
   which the MRB added to the Consumer response just for that purpose.

7.2.3.  Inline-Unaware Mode

   Whereas in the Inline-aware mode the AS knows it is sending an INVITE
   to an MRB and not to an MS, and acts accordingly (using the
   multipart/mixed payload to query for an MS able to fulfill its
   requirements), in the Inline-Unaware MRB Mode (IUMM) the AS does not
   distinguish an MRB from an MS.  This means that an MRB-unaware AS
   having access to an MRB talks to it as if it were a generic MEDIACTRL
   MS: i.e., the AS negotiates a Control Channel directly with the MRB
   and attaches its media dialogs there as well.  Of course, since the
   MRB doesn't provide any MS functionality by itself, it must act as a
   Proxy/B2BUA between the AS and an MS for both the Control Channel
   dialog and the media dialogs.  According to implementation or
   deployment choices, simple redirects could also be exploited for that
   purpose.

   The problem is that without any Consumer request being placed by the
   MRB-unaware AS the MRB can't rely on AS-originated directives to pick
   one MS rather than another.  In fact, the MRB can't know what the AS
   is looking for.  The MRB is then assumed to pick one according to its
   logic, which is implementation specific.

   Figure 51 presents a ladder diagram of a typical Consumer request in
   the Inline-unaware topology:

   AS                      MRB                          MS
    |                       |                           |
    | 1. INVITE             |                           |
    | (application/cfw)     |                           |
    |---------------------->|                           |
    |       2. 100 (Trying) |                           |
    |<----------------------|                           |
    |                       |--+ Pick an MS             |
    |                       |  | and redirect           |
    |                       |<-+ INVITE there           |
    |                       |                           |
    |                       | 3. INVITE                 |
    |                       | (application/cfw from 1.) |
    |                       |-------------------------->|
    |                       |           4. 100 (Trying) |
    |                       |<--------------------------|
    |                       |                           |--+ Negotiate
    |                       |                           |  | CFW Control
    |                       |                           |<-+ Channel
    |                       |                 5. 200 OK |
    |                       | (application/cfw from MS) |
    |                       |<--------------------------|
    |                       | 6. ACK                    |
    |                       |-------------------------->|
    |                       |                           |
    |             7. 200 OK |                           |
    |(application/cfw from MS)                          |
    |<----------------------|                           |
    | 8. ACK                |                           |
    |---------------------->|                           |
    |                       |                           |
    |                                                   |
    |<<############## TCP CONNECTION #################>>|
    |                                                   |
    | CFW SYNC                                          |
    |++++++++++++++++++++++++++++++++++++++++++++++++++>|
    |                                                   |
    .                       .                           .
    .                       .                           .

         Figure 51: Media Resource Brokering: Inline-Unaware Mode

   As can be seen in the diagram, in this topology the MRB basically
   acts as a 3PCC between the AS and the chosen MS.

   The same can be said with respect to attaching UAC media dialogs.
   The MRB remembers the MS it has chosen for the AS, and for every UAC
   media dialog the AS tries to attach to the MRB, it makes sure that it
   is somehow actually redirected to the MS.

   No content for the presented messages is provided in this section, as
   in the IUMM mode no Consumer transaction is involved.  In this
   example, a simple [RFC6230] Control Channel negotiation occurs where
   the MRB acts as an intermediary, that is, picking an MS for the AS
   according to some logic.  In this case, in fact, the AS does not
   support the MRB specification and so just tries to set up a Control
   Channel according to its own logic.

   It is worth pointing out that the MRB may actually enforce its
   decision about the MS to grant to the AS in different ways.
   Specifically, the sentence "redirect the INVITE" that is used in
   Figure 51 does not necessarily mean that a SIP 302 message should be
   used for that purpose.  A simple way to achieve this may be
   provisioning the unaware AS with different URIs, all actually
   transparently handled by the MRB itself; this would allow the MRB to
   simply map those URIs to different MS instances.  The SIP 'Contact'
   header may also be used by the MRB in a reply to an INVITE coming
   from an AS to provide the actual URI on which the chosen MS might be
   reached.  A motivation for such a discussion, and more details on
   this topic, are provided in Section 7.3.2.

7.3.  Handling Media Dialogs

   It is worthwhile to briefly address how media dialogs would be
   managed whenever an MRB is involved in the following scenarios.  In
   fact, the presence of an MRB may introduce an additional complexity
   compared to the quite straightforward 1:1 AS-MS topology.

7.3.1.  Query and Inline-Aware Mode

   Normally, especially in the Query and IAMM case, the MRB would only
   handle Consumer requests by an AS, and after that the AS and the MS
   picked by the MRB for a specific request would talk directly to each
   other by means of SIP.  This is made possible by the fact that the AS
   gets the MS SIP URI in reply to its request.  In this case, an AS can
   simply relay media dialogs associated with that session to the right
   MS to have them handled accordingly.  Of course, in order for this to
   work it is assumed that the AS creates a Control Channel to a chosen
   MS before it has any requests to service.

   An example of such a scenario is presented in Figure 52.  Please note
   that this diagram and subsequent diagrams in this section are
   simplified with respect to the actual protocol interactions.  For

   instance, the whole SIP transactions are not presented, and only the
   originating messages are presented in order to clarify the scenario
   in a simple way.

UAC              AS                           MRB                     MS
 |                |                            |                      |
 |                | 1. Consumer request        |                      |
 |                |--------------------------->|                      |
 |                |                            |                      |
 |                |       2. Consumer response |                      |
 |                |<---------------------------|                      |
 |                |                            |                      |
 |                | 3. COMEDIA negotiation to create CFW channel      |
 |                |-------------------------------------------------->|
 |                |                            |                      |
 |                |<<############## CFW CONNECTION #################>>|
 | 4. INVITE xyz  |                            |                      |
 |--------------->|                            |                      |
 |                | 5. Attach UAC to MS (3PCC)                        |
 |                |-------------------------------------------------->|
 |                |                            |                      |
 |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
 |                |                            |                      |
 .                .                            .                      .
 .                .                            .                      .

              Figure 52: Handling Media Dialogs in Query/IAMM

   As can be deduced from the diagram, the interactions among the
   components are quite straightforward.  The AS knows which MS it has
   been assigned to (as a consequence of the MRB Consumer request,
   whether it has been achieved by means of HTTP or SIP), and so it can
   easily attach any UAC accessing its functionality to the MS itself
   and manipulate its media connections by using the CFW Control Channel
   as usual.

   In such a scenario, the MRB is only involved as a locator.  Once the
   MRB provides the AS with the URI of the required resource, it doesn't
   interfere with subsequent interactions unless it wants to perform
   monitoring (e.g., by exploiting the Publishing information reported
   by the MS).  As a consequence, the scenario basically becomes 1:1
   between the AS and the MS again.

   Nevertheless, there are cases when having an MRB in the SIP signaling
   path as well might be a desired feature, e.g., for more control over
   the use of the resources.  Considering how the Consumer interface has
   been envisaged, this feature is easily achievable, with no change to
   the protocol required at all.  Specifically, in order to achieve such

   functionality, the MRB may reply to a Consumer request with a URI for
   which the MRB is responsible (rather than the MS SIP URI as discussed
   previously) and map this URI to the actual MS URI in its business
   logic; this would be transparent to the AS.  This way, the AS would
   interact with the MRB as if it were the MS itself.

   Figure 53 shows how the scenario would change in this case.

 UAC              AS                           MRB                    MS
  |                |                            |                      |
  |                | 1. Consumer request        |                      |
  |                |--------------------------->|                      |
  |                |                            |                      |
  |                |       2. Consumer response |                      |
  |                |<---------------------------|                      |
  |                |                            |                      |
  |                | 3. COMEDIA negotiation     |                      |
  |                |--------------------------->|                      |
  |                |                            | 4. COMEDIA neg.      |
  |                |                            |--------------------->|
  |                |                            |                      |
  |                |<<############## CFW CONNECTION #################>>|
  | 5. INVITE xyz  |                            |                      |
  |--------------->|                            |                      |
  |                | 6. Attach UAC to MS (3PCC) |                      |
  |                |--------------------------->|                      |
  |                |                            | 7. Attach UAC (3PCC) |
  |                |                            |--------------------->|
  |                |                            |                      |
  |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
  |                |                            |                      |
  .                .                            .                      .
  .                .                            .                      .

             Figure 53: Handling Media Dialogs in Query/IAMM:
                         MRB in the Signaling Path

   This time, even though the MRB has picked a specific MS after a
   request from an AS, it replies with another SIP URI, a URI it would
   reply to itself.  The AS would contact that URI in order to negotiate
   the Control Channel, and the MRB would proxy/forward the request to
   the actual MS transparently.  Eventually, the Control Channel would
   be instantiated between the AS and the MS.  The same happens for UACs
   handled by the AS; the AS would forward the calls to the URI provided
   to it, the one handled by the MRB, which would in turn relay the call
   to the MS in order to have the proper RTP channels created between
   the UAC and the MS.

   This scenario is not very different from the previous scenario,
   except that the MRB is now on the signaling path for both the SIP
   control dialog and the SIP media dialogs, allowing it to have more
   control of the resources (e.g., triggering a BYE if a resource has
   expired).  There are several possible approaches an MRB might take to
   allocate URIs to map to a requested MS.  For example, an MRB might
   use SIP URI parameters to generate multiple SIP URIs that are unique
   but that all route to the same host and port, e.g.,
   sip:MrbToMs@mrb.example.com:5080;p=1234567890.  Alternatively, the
   MRB might simply allocate a pool of URIs for which it would be
   responsible and manage the associations with the requested MS
   services accordingly.

7.3.2.  Inline-Unaware Mode

   As mentioned previously, in the IUMM case the AS would interact with
   the MRB as if it were the MS itself.  One might argue that this would
   make the AS act as it would in the IAMM case.  This is not the case,
   however, since the AS actually provided the MRB with information
   about the resources it required, leading to the selection of a proper
   MS, while in the IUMM case the MRB would have to pick an MS with no
   help from the AS at all.

   That said, the IUMM case is also very interesting with respect to
   media dialog management.  In fact, in the MRB-unaware mode, there
   would be no Consumer request, and an AS would actually see the MRB as
   an MS.  Unlike the previous scenarios, because there is no AS<->MRB
   interaction and as such no MS selection process, the MRB would likely
   be in the signaling path anyway, at least when the AS first shows up.
   The MRB could either redirect the AS to an MS directly or
   transparently act as a Proxy/B2BUA and contact an MS (according to
   implementation-specific policies) on behalf of the unaware AS.

   While apparently not a problem, this raises an issue when the same
   unaware AS has several sessions with different MS.  The AS would only
   see one "virtual" MS (the MRB), and so it would relay all calls
   there, making it hard for the MRB to understand where these media
   dialogs should belong: specifically, whether the UAC calling belongs
   to the AS application logic leading to MS1 or MS2, or somewhere else.

   One possible, and very simple, approach to take care of this issue is
   to always relay the SIP dialogs from the same unaware AS to the same
   MS, as depicted in Figure 54.

UAC1  UAC2       AS                           MRB                     MS
 |     |          |                            |                      |
 |     |          | 1. COMEDIA negotiation (A) |                      |
 |     |          |--------------------------->|                      |
 |     |          |                            | 2. COMEDIA neg. (A)  |
 |     |          |                            |--------------------->|
 |     |          |                            |                      |
 |     |          |<<############## CFW CONNECTION #################>>|
 |     |          |                            |                      |
 |     |          | 3. COMEDIA negotiation (B) |                      |
 |     |          |--------------------------->|                      |
 |     |          |                            | 4. COMEDIA neg. (B)  |
 |     |          |                            |--------------------->|
 |     |          |                            |                      |
 |     |          |<<############## CFW CONNECTION #################>>|
 | 5. INVITE xyz  |                            |                      |
 |--------------->|                            |                      |
 |     |          | 6. Attach UAC1 to MS (3PCC)|                      |
 |     |          |--------------------------->|                      |
 |     |          |                            | 7. Attach UAC (3PCC) |
 |     |          |                            |--------------------->|
 |     |          |                            |                      |
 |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
 |     |          |                            |                      |
 |     | 8. INVITE|                            |                      |
 |     |    jkl   |                            |                      |
 |     |--------->|                            |                      |
 |     |          | 9. Attach UAC2 to MS (3PCC)|                      |
 |     |          |--------------------------->|                      |
 |     |          |                            | 10. Attach UAC (3PCC)|
 |     |          |                            |--------------------->|
 |     |          |                            |                      |
 |     |<<++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
 |     |          |                            |                      |
 .     .          .                            .                      .
 .     .          .                            .                      .

       Figure 54: Handling Media Dialogs in IUMM: Always the Same MS

   In this example, the AS creates two different Control Channel
   sessions (A and B) to address two different business logic
   implementations; e.g., the AS SIP URI 'xyz' (associated with CFW
   session A) may be an IVR pizza-ordering application, while the AS SIP
   URI 'jkl' (associated with CFW session B) may be associated with a

   conference room.  It's quite clear, then, that if the MRB forwarded
   the two CFW sessions to two different MS, the handling of UAC media
   dialogs would prove troublesome, because the MRB would have
   difficulty figuring out whether UAC1 should be attached to the MS
   managing CFW session A or the MS managing CFW session B.  In this
   example, forwarding all CFW sessions and UAC media dialogs coming
   from the same MRB-unaware AS to the same MS would work as expected.
   The MRB would in fact leave the mapping of media dialogs and CFW
   sessions up to the AS.

   This approach, while very simple and indeed not very scalable, would
   actually help take care of the issue.  In fact, no matter how many
   separate Control Channels the AS might have with the MRB/MS (in this
   example, Control Channel A would be mapped to application xyz and
   Control Channel B to application jkl), the termination point would
   still always be the same MS, which would consequently be the
   destination for all media dialogs as well.

   To overcome the scalability limitations of such an approach, at least
   in regard to the MRB being in the SIP signaling path for all calls, a
   different approach needs to be exploited.  In fact, especially in the
   case of different applications handled by the same unaware AS, it
   makes sense to try to exploit different MS for that purpose and to
   correctly track media dialogs being forwarded accordingly.  This
   means that the MRB must find a way to somehow redirect the unaware AS
   to different MS when it predicts or realizes that a different
   application logic is involved.

   To do so, the MRB might use different approaches.  One approach would
   use redirection, e.g., by means of a SIP 302 message in reply to a
   Control Channel negotiation originated by an unaware AS.  Such an
   approach is depicted in Figure 55.

UAC1             AS                           MRB                     MS
 |                |                            |                      |
 |                | 1. COMEDIA negotiation     |                      |
 |                |--------------------------->|                      |
 |                |                            |                      |
 |                |          2. 302 Moved (MS) |                      |
 |                |<---------------------------|                      |
 |                |                            |                      |
 |                | 3. COMEDIA negotiation     |                      |
 |                |-------------------------------------------------->|
 |                |                            |                      |
 |                |<<############## CFW CONNECTION #################>>|
 |                |                            |                      |
 | 4. INVITE xyz  |                            |                      |
 |--------------->|                            |                      |
 |                | 5. Attach UAC1 to MS (3PCC)|                      |
 |                |-------------------------------------------------->|
 |                |                            |                      |
 |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
 |                |                            |                      |
 .                .                            .                      .
 .                .                            .                      .

          Figure 55: Handling Media Dialogs in IUMM: Redirection

   With this approach, the MRB might redirect the AS to a specific MS
   whenever a new Control Channel is to be created, and as a consequence
   the AS would redirect the related calls there.  This is similar to
   the first approach of the Query/IAMM case, with the difference that
   no Consumer request would be involved.  The scenario would again fall
   back to a 1:1 topology between the AS and the MS, making the
   interactions quite simple.

   Just as before, the MRB might be interested in being in the signaling
   path for the SIP dialogs, instead of just acting as a locator.  A
   third potential approach could be implementing the "virtual" URIs
   handled by the MRB, as described in the previous section.  Rather
   than resorting to explicit redirection or always using the same MS,

   the MRB may redirect new SIP control dialogs to one of its own URIs,
   using the same approach previously presented in Figure 53.  Such an
   approach, as applied to the IUMM case, is depicted in Figure 56.

UAC1             AS                              MRB                  MS
 |                |                               |                   |
 |                | 1. COMEDIA negotiation (MRB)  |                   |
 |                |------------------------------>|                   |
 |                |                               |                   |
 |                |           2. 302 Moved (MRB') |                   |
 |                |<------------------------------|                   |
 |                |                               |                   |
 |                | 3. COMEDIA negotiation (MRB') |                   |
 |                |------------------------------>|                   |
 |                |                               | 4. COMEDIA neg.   |
 |                |                               |------------------>
 |                |                               |                   |
 |                |<<############## CFW CONNECTION #################>>|
 |                |                               |                   |
 | 5. INVITE xyz  |                               |                   |
 |--------------->|                               |                   |
 |                | 6. Attach UAC1 to MRB' (3PCC) |                   |
 |                |------------------------------>|                   |
 |                |                               | 7 Attach UAC (3PCC)
 |                |                               |------------------>
 |                |                               |                   |
 |<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
 |                |                               |                   |
 .                .                               .                   .
 .                .                               .                   .

   Figure 56: Handling Media Dialogs in IUMM: MRB in the Signaling Path

   It is worth pointing out, though, that in both cases there are
   scenarios where there could be no assurance that the 302 sent by the
   MRB would be seen by the AS.  In fact, should a proxy be between the
   AS and the MRB, such a proxy could itself act on the 302.  To
   properly cope with such an issue, the MRB might also use the
   'Contact' header in the SIP responses to the INVITE to address the
   right MS.  Although the AS is not required to use the information in
   such a header to reach the MS, it could be reasonable to exploit it
   for that purpose, as it would take care of the proxy scenario
   mentioned above.

   To conclude, there is a further approach an MRB might try to exploit
   to take care of the IUMM case.  Since, as explained before, the
   issues related to the IUMM case mostly relate to the fact that the
   MRB is seen as a single MS instance by the AS, a simple way to
   overcome this might be to make the MRB look like a set of different
   MS right away; this can be done by simply provisioning the unaware AS
   with a series of different URIs, all handled by the MRB itself acting
   as a pool of "virtual" MS.  This way, the AS may be designed to use
   different MS for different classes of calls, e.g., for different
   applications it is managing (two in the example presented in this
   section), and as such would contact two different provisioned URIs to
   create two distinct Control Channels towards two different MS.  Since
   both of the URIs would be handled by the MRB, the MRB can use them to
   determine to which MS each call should be directed.  Expanding on
   Figure 54 by removing the constraint to always use the same MS, this
   new scenario might look like that depicted in Figure 57.

 UAC1  UAC2       AS                           MRB              MS1  MS2
  |     |          |                            |                 |    |
  |     |          | 1. COMEDIA negotiation (A) |                 |    |
  |     |          |    INVITE fake-ms1         |                 |    |
  |     |          |--------------------------->|                 |    |
  |     |          |                            | 2. COMEDIA (A)  |    |
  |     |          |                            |---------------->|    |
  |     |          |                            |                 |    |
  |     |          |<<############## CFW CONNECTION 1 ##########>>|    |
  |     |          |                            |                 |    |
  |     |          | 3. COMEDIA negotiation (B) |                 |    |
  |     |          |    INVITE fake-ms2         |                 |    |
  |     |          |--------------------------->|                 |    |
  |     |          |                            | 4. COMEDIA neg. (B)  |
  |     |          |                            |--------------------->|
  |     |          |                            |                 |    |
  |     |          |<<############## CFW CONNECTION 2 ###############>>|
  |     |          |                            |                 |    |
  | 5. INVITE xyz  |                            |                 |    |
  |--------------->|                            |                 |    |
  |     |          | 6. Attach UAC1 to fake-ms1 (3PCC)            |    |
  |     |          |--------------------------->|                 |    |
  |     |          |                            | 7. Attach UAC   |    |
  |     |          |                            |---------------->|    |
  |     |          |                            |                 |    |
  |<<++++++++++++++++++++++ RTP channels +++++++++++++++++++++++>>|    |
  |     |          |                            |                 |    |
  | 8. INVITE jkl  |                            |                 |    |
  |--------------->|                            |                 |    |
  |     |          | 9. Attach UAC2 to fake-ms2 (3PCC)            |    |
  |     |          |--------------------------->|                 |    |
  |     |          |                            | 10. Attach UAC  |    |
  |     |          |                            |--------------------->|
  |     |          |                            |                 |    |
  |<<+++++++++++++++++++++++++ RTP channels +++++++++++++++++++++++++>>|
  |     |          |                            |                 |    |
  .     .          .                            .                 .    .
  .     .          .                            .                 .    .

        Figure 57: Handling Media Dialogs in IUMM: Provisioned URIs

   In this new example, we still assume that the same unaware AS is
   handling two different applications, still associated with the same
   URIs as before.  This time, though, we also assume that the AS has
   been designed to try to use different MS instances to handle the two
   very different applications for which it is responsible.  We also
   assume that it has been configured to be able to use two different MS
   instances, reachable at SIP URI 'fake-ms1' and 'fake-ms2',

   respectively, and both actually handled by the MRB transparently.
   This results, just as before, in two different Control Channels (A
   and B) being created, but this time towards two different MS.
   Specifically, the MRB makes sure that for this AS the Control Channel
   negotiation towards 'fake-ms1' is actually redirected to MS1.  At the
   same time, 'fake-ms2' is associated with MS2.  Once the AS has set up
   the Control Channels with both of the MS, it is ready to handle media
   dialogs.  UAC1 calls the SIP URI 'xyz' on the AS to order a pizza.
   The AS attaches the media dialog to the MS it knows is responsible
   for that branch of application logic, i.e., 'fake-ms1'.  The MRB in
   turn makes sure that it reaches the right MS instance, MS1.  Later
   on, a different user, UAC2, calls SIP URI 'jkl' to join a conference
   room.  This time, the AS attaches this new media dialog to the MS
   instance handling the conference application, i.e., 'fake-ms2'.
   Again, the MRB makes sure that it is actually MS2 that receives the
   dialog.

   Again, this diagram is only meant to describe how the MRB might
   enforce its decisions.  Just as described in the previous examples,
   the MRB may choose to either act as a Proxy/B2BUA between the AS and
   the MS instances or redirect the AS to the right MS instances when
   they're first contacted (e.g., by means of the Contact header and/or
   a SIP redirect, as explained before) and let the AS attach the media
   dialogs by itself.

7.3.3.  CFW Protocol Behavior

   As shown in the previous diagrams, no matter what the topology, the
   AS and MS usually end up with a direct connection with respect to the
   CFW Control Channel.  As such, it can be expected that the CFW
   protocol continue to work as it should, and as a consequence all the
   call flows presented in this document can easily be reproduced in
   those circumstances as well.

   Nevertheless, one aspect needs to be considered very carefully.  It's
   worthwhile to remind readers that both the AS and the MS use some
   SIP-related information to address the entities they manipulate.
   This is the case, for instance, for the <connectionid> element to
   which both the AS and the MS refer when addressing a specific UAC.
   As explained in Section 6, this 'connectionid' identifier is
   constructed by concatenating the 'From' and 'To' tags extracted from
   a SIP header: specifically, from the headers of the AS<->MS leg that
   allows a UAC to be attached to the MS.  The presence of an additional
   component in the path between the AS and the MS, the MRB, might alter
   these tags, thus causing the AS to use tags (AS<->MRB) different than
   those used by the MS (MRB<->MS).  This would result in the AS and MS
   using different 'connectionid' identifiers to address the same UAC,
   thus preventing the protocol from working as expected.  As a

   consequence, it's very important that any MRB implementation take
   very good care to preserve the integrity of the involved SIP headers
   when proxying/forwarding SIP dialogs between the AS and MS, in order
   not to "break" the behavior of the protocol.

   Let's take, for instance, the scenario depicted in Figure 53,
   especially steps 6 and 7, which specifically address a UAC being
   attached by an AS to an MS via the MRB.  Let's assume that Figure 58
   shows what happens to the 'From' and 'To' headers in that scenario,
   when dealing with the 3PCC approach to attach a specific UAC to
   the MS.

UAC              AS                         MRB                       MS
 |                |                          |                        |
 | INVITE xyz     |                          |                        |
 |--------------->|                          |                        |
 |                | SIP [..]                 |                        |
 |                | From: <..>;tag=a1b2c3    |                        |
 |                | To: <..>;tag=d4e5f6      |                        |
 |                |<------------------------>|                        |
 |                |                          | SIP [..]               |
 |                |                          | From: <..>;tag=aaabbb  |
 |                |                          | To: <..>;tag=cccddd    |
 |                |                          |<---------------------->|
 |                |                          |                        |
 |                | 1. CONTROL (play announcement to UAC)             |
 |                |-------------------------------------------------->|
 |                |                               2. 200 (IVR Error!) |
 |                |<--------------------------------------------------|
 |                |                          |                        |
 .                .                          .                        .
 .                .                          .                        .

     Figure 58: CFW Protocol Behavior in the Case of Manipulated Tags

   In this example, once done with the 3PCC, and now that the UAC is
   attached to the MS, the AS and the MS end up with different
   interpretations of what the 'connectionid' for the UAC should be.  In
   fact, the AS builds a 'connectionid' using the tags it is aware of
   (a1b2c3:d4e5f6), while the MS builds a different identifier after
   receiving different information from the MRB (aaabbb:cccddd).

   As a consequence, when the AS tries to play an announcement to the
   UAC using the connectionid it correctly constructed, the MS just as
   correctly replies with an error, since it doesn't know that
   identifier.  This is correct protocol behavior, because in this case
   it was caused by misuse of the information needed for it to work as
   expected.

   1. AS -> MS (CFW CONTROL, play)
   -------------------------------
      CFW ffhg45dzf123 CONTROL
      Control-Package: msc-ivr/1.0
      Content-Type: application/msc-ivr+xml
      Content-Length: 284

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <dialogstart connectionid="a1b2c3:d4e5f6">
          <dialog>
            <prompt>
              <media loc="http://www.example.net/hello.wav"/>
            </prompt>
          </dialog>
        </dialogstart>
      </mscivr>

   2. AS <- MS (CFW 200 OK)
   ------------------------
      CFW ffhg45dzf123 200
      Timeout: 10
      Content-Type: application/msc-ivr+xml
      Content-Length: 148

      <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <response status="407" reason="connectionid does not exist"
                  dialogid=""/>
      </mscivr>

   In an even worse scenario, the connectionid might actually exist but
   might be mapped to a different UAC.  In such a case, the transaction
   would succeed, but a completely different UAC would be involved, thus
   causing a silent failure that neither the AS nor the MS would be
   aware of.

   That said, proper management of these sensitive pieces of information
   by the MRB would prevent such failure scenarios from happening.  How
   this issue is taken care of in the IAMM case (both CFW-based and
   media dialog-based) has already been described.  Addressing this
   issue for the IUMM case is not documented in [RFC6917] as explicitly
   out of scope and as such may be implementation specific.

   The same applies to SDP fields as well.  In fact, the AS and MS use
   ad hoc SDP attributes to instantiate a Control Channel, as they use
   SDP labels to address specific media connections of a UAC media
   dialog when a fine-grained approach is needed.  As a consequence, any

   MRB implementation should limit any SDP manipulation as much as
   possible or at least take very good care not to cause changes that
   could "break" the expected behavior of the CFW protocol.

8.  Security Considerations

   All the MEDIACTRL documents have strong statements regarding security
   considerations within the context of the interactions occurring at
   all levels among the involved parties.  Considering the sensitive
   nature of the interaction between AS and MS, particular efforts have
   been devoted to providing guidance on how to secure what flows
   through a Control Channel.  In fact, transactions concerning dialogs,
   connections, and mixes are quite strongly related to resources
   actually being deployed and used in the MS.  This means that it is in
   the interest of both AS and MS that resources created and handled by
   an entity are not manipulated by a potentially malicious third party
   if permission was not granted.

   Because strong statements are provided in the aforementioned
   documents and these documents provide good guidance to implementors
   with respect to these issues, this section will only provide the
   reader with some MEDIACTRL call flows that show how a single secured
   MS is assumed to reply to different AS when receiving requests that
   may cross the bounds within which each AS is constrained.  This would
   be the case, for instance, for generic auditing requests, or explicit
   conference manipulation requests where the involved identifiers are
   not part of the context of the originating AS.

   To address a very specific scenario, let's assume that two different
   AS, AS1 and AS2, have established a Control Channel with the same MS.
   Considering the SYNC transaction that an AS and an MS use to set up a
   Control Channel, the MS is able to discern the requests coming from
   AS1 from the requests coming from AS2.  In fact, as explained in
   Sections 5.1 and 5.2, an AS and an MS negotiate a cfw-id attribute in
   the SDP, and the same value is subsequently used in the SYNC message
   on the Control Channel that is created after the negotiation, thus
   reassuring both the AS and the MS that the Control Channel they share
   is in fact the channel they negotiated in the first place.

   Let's also assume that AS1 has created a conference mix
   (confid=74b6d62) to which it has attached some participants within
   the context of its business logic, while AS2 has created a currently
   active IVR dialog (dialogid=dfg3252) with a user agent it is handling
   (237430727:a338e95f).  AS2 has also joined two connections to each
   other (1:75d4dd0d and 1:b9e6a659).  Clearly, it is highly desirable
   that AS1 not be aware of what AS2 is doing with the MS and vice
   versa, and that they not be allowed to manipulate each other's
   resources.  The following transactions will occur:

   1.  AS1 places a generic audit request to both the Mixer and IVR
       packages.

   2.  AS2 places a generic audit request to both the Mixer and IVR
       packages.

   3.  AS1 tries to terminate the dialog created by AS2 (6791fee).

   4.  AS2 tries to join a user agent it handles (1:272e9c05) to the
       conference mix created by AS1 (74b6d62).

   A sequence diagram of the above-mentioned transactions is depicted in
   Figure 59, which shows how the MS is assumed to reply in all cases,
   in order to avoid security issues:

      AS1                     AS2                                 MS
       |                       |                                  |
       | A1. CONTROL (IVR audit)                                  |
       |++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>|
       |                       |                       A2. 200 OK |
       |<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
       |                       |                                  |
       | B1. CONTROL (Mixer audit)                                |
       |++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>|
       |                       |                       B2. 200 OK |
       |<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
       |                       |                                  |
       |                       | C1. CONTROL (IVR audit)          |
       |                       |++++++++++++++++++++++++++++++++>>|
       |                       |                       C2. 200 OK |
       |                       |<<++++++++++++++++++++++++++++++++|
       |                       |                                  |
       |                       | D1. CONTROL (Mixer audit)        |
       |                       |++++++++++++++++++++++++++++++++>>|
       |                       |                       D2. 200 OK |
       |                       |<<++++++++++++++++++++++++++++++++|
       |                       |                                  |
       | E1. CONTROL (dialogterminate)                            |
       |++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>|
       |                       |                E2. 403 Forbidden |
       |<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
       |                       |                                  |
       |                       | F1. CONTROL (join UAC&conf[AS1]) |
       |                       |++++++++++++++++++++++++++++++++>>|
       |                       |                F2. 403 Forbidden |
       |                       |<<++++++++++++++++++++++++++++++++|
       |                       |                                  |
       .                       .                                  .
       .                       .                                  .

         Figure 59: Security Considerations: Framework Transaction

   The expected outcome of the transaction is that the MS partially
   "lies" to both AS1 and AS2 when replying to the audit requests (not
   all of the identifiers are reported, but only those identifiers with
   which each AS is directly involved), and the MS denies the requests
   for the unauthorized operations (403).  Looking at each transaction
   separately:

   o  In the first transaction (A1), AS1 places a generic <audit>
      request to the IVR package.  The request is generic, since no
      attributes are passed as part of the request, meaning that AS1 is
      interested in the MS capabilities as well as all of the dialogs
      that the MS is currently handling.  As can be seen in the reply
      (A2), the MS only reports in the <auditresponse> the package
      capabilities, while the <dialogs> element is empty; this is
      because the only dialog the MS is handling has actually been
      created by AS2, which causes the MS not to report the related
      identifier (6791fee) to AS1.  In fact, AS1 could use that
      identifier to manipulate the dialog, e.g., by tearing it down and
      thus causing the service to be interrupted without AS2's
      intervention.

   o  In the second transaction (B1), AS1 places an identical <audit>
      request to the Mixer package.  The request is again generic,
      meaning that AS1 is interested in the package capabilities as well
      as all the mixers and connections that the package is handling at
      the moment.  This time, the MS reports not only capabilities (B2)
      but information about mixers and connections as well.  However,
      this information is not complete; in fact, only information about
      mixers and connections originated by AS1 is reported (mixer
      74b6d62 and its participants), while the information originated by
      AS2 is omitted in the report.  The motivation is the same as
      before.

   o  In the third and fourth transactions (C1 and D1), it's AS2 that
      places an <audit> request to both the IVR and Mixer packages.  As
      with the previous transactions, the audit requests are generic.
      Looking at the replies (C2 and D2), it's obvious that the
      capabilities section is identical to the replies given to AS1.  In
      fact, the MS has no reason to "lie" about what it can do.  The
      <dialogs> and <mixers> sections are totally different.  AS2 in
      fact receives information about its own IVR dialog (6791fee),
      which was omitted in the reply to AS1, while it only receives
      information about the only connection it created (1:75d4dd0d and
      1:b9e6a659) without any details related to the mixers and
      connections originated by AS1.

   o  In the fifth transaction (E1), AS1, instead of just auditing the
      packages, tries to terminate (<dialogterminate>) the dialog
      created by AS2 (6791fee).  Since the identifier has not been
      reported by the MS in the reply to the previous audit request, we
      assume that AS1 accessed it via a different out-of-band mechanism.
      This is assumed to be an unauthorized operation, because the
      above-mentioned dialog is outside the bounds of AS1; therefore,
      the MS, instead of handling the syntactically correct request,
      replies (E2) with a framework-level 403 message (Forbidden),
      leaving the dialog untouched.

   o  Similarly, in the sixth and last transaction (F1), AS2 tries to
      attach (<join>) one of the UACs it is handling to the conference
      mix created by AS1 (74b6d62).  Just as in the previous
      transaction, the identifier is assumed to have been accessed by
      AS2 via some out-of-band mechanism, since the MS didn't report it
      in the reply to the previous audit request.  While one of the
      identifiers (the UAC) is actually handled by AS2, the other (the
      conference mix) is not; therefore, as with the fifth transaction,
      this last transaction is regarded by the MS as outside the bounds
      of AS2.  For the same reason as before, the MS replies (F2) with a
      framework-level 403 message (Forbidden), leaving the mix and the
      UAC unjoined.

  A1. AS1 -> MS (CFW CONTROL, audit IVR)
  --------------------------------------
     CFW 140e0f763352 CONTROL
     Control-Package: msc-ivr/1.0
     Content-Type: application/msc-ivr+xml
     Content-Length: 81

     <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <audit/>
     </mscivr>

  A2. AS1 <- MS (CFW 200, auditresponse)
  --------------------------------------
     CFW 140e0f763352 200
     Timeout: 10
     Content-Type: application/msc-ivr+xml
     Content-Length: 1419

     <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <auditresponse status="200">
        <capabilities>
           <dialoglanguages/>
           <grammartypes/>
           <recordtypes>
              <mimetype>audio/x-wav</mimetype>
              <mimetype>video/mpeg</mimetype>
           </recordtypes>
           <prompttypes>
              <mimetype>audio/x-wav</mimetype>
              <mimetype>video/mpeg</mimetype>
           </prompttypes>
           <variables>
              <variabletype type="date"
                            desc="value formatted as YYYY-MM-DD">
                 <format desc="month day year">mdy</format>
                 <format desc="year month day">ymd</format>
                 <format desc="day month year">dmy</format>
                 <format desc="day month">dm</format>
              </variabletype>
              <variabletype type="time" desc="value formatted as HH:MM">
                 <format desc="24 hour format">t24</format>
                 <format desc="12 hour format with am/pm">t12</format>
              </variabletype>
              <variabletype type="digits" desc="value formatted as D+">
                 <format desc="general digit string">gen</format>
                 <format desc="cardinal">crn</format>
                 <format desc="ordinal">ord</format>
              </variabletype>
           </variables>
           <maxpreparedduration>60s</maxpreparedduration>
           <maxrecordduration>1800s</maxrecordduration>
           <codecs>
              <codec name="audio"><subtype>basic</subtype></codec>
              <codec name="audio"><subtype>gsm</subtype></codec>
              <codec name="video"><subtype>h261</subtype></codec>
              <codec name="video"><subtype>h263</subtype></codec>
              <codec name="video"><subtype>h263-1998</subtype></codec>
              <codec name="video"><subtype>h264</subtype></codec>
           </codecs>

        </capabilities>
        <dialogs>
        </dialogs>
     </auditresponse>
     </mscivr>

  B1. AS1 -> MS (CFW CONTROL, audit mixer)
  ----------------------------------------
     CFW 0216231b1f16 CONTROL
     Control-Package: msc-mixer/1.0
     Content-Type: application/msc-mixer+xml
     Content-Length: 87

     <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
        <audit/>
     </mscmixer>

  B2. AS1 <- MS (CFW 200, auditresponse)
  --------------------------------------
     CFW 0216231b1f16 200
     Timeout: 10
     Content-Type: application/msc-mixer+xml
     Content-Length: 903

     <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <auditresponse status="200">
       <capabilities>
          <codecs>
             <codec name="audio"><subtype>basic</subtype></codec>
             <codec name="audio"><subtype>gsm</subtype></codec>
             <codec name="video"><subtype>h261</subtype></codec>
             <codec name="video"><subtype>h263</subtype></codec>
             <codec name="video"><subtype>h263-1998</subtype></codec>
             <codec name="video"><subtype>h264</subtype></codec>
          </codecs>
       </capabilities>
       <mixers>
         <conferenceaudit conferenceid="74b6d62">
           <participants>
             <participant id="1864574426:e2192766"/>
             <participant id="1:5a97fd79"/>
           </participants>
           <video-layout min-participants="1">
             <quad-view/>
           </video-layout>
         </conferenceaudit>

         <joinaudit id1="1864574426:e2192766" id2="74b6d62"/>
         <joinaudit id1="1:5a97fd79" id2="74b6d62"/>
       </mixers>
     </auditresponse>
     </mscmixer>

  C1. AS2 -> MS (CFW CONTROL, audit IVR)
  --------------------------------------
     CFW 0216231b1f16 CONTROL
     Control-Package: msc-ivr/1.0
     Content-Type: application/msc-ivr+xml
     Content-Length: 81

     <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <audit/>
     </mscivr>

  C2. AS2 <- MS (CFW 200, auditresponse)
  --------------------------------------
     CFW 0216231b1f16 200
     Timeout: 10
     Content-Type: application/msc-ivr+xml
     Content-Length: 1502

     <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
     <auditresponse status="200">
        <capabilities>
           <dialoglanguages/>
           <grammartypes/>
           <recordtypes>
              <mimetype>audio/wav</mimetype>
              <mimetype>video/mpeg</mimetype>
           </recordtypes>
           <prompttypes>
              <mimetype>audio/wav</mimetype>
              <mimetype>video/mpeg</mimetype>
           </prompttypes>
           <variables>
              <variabletype type="date"
                            desc="value formatted as YYYY-MM-DD">
                 <format desc="month day year">mdy</format>
                 <format desc="year month day">ymd</format>
                 <format desc="day month year">dmy</format>
                 <format desc="day month">dm</format>
              </variabletype>

              <variabletype type="time" desc="value formatted as HH:MM">
                 <format desc="24 hour format">t24</format>
                 <format desc="12 hour format with am/pm">t12</format>
              </variabletype>
              <variabletype type="digits" desc="value formatted as D+">
                 <format desc="general digit string">gen</format>
                 <format desc="cardinal">crn</format>
                 <format desc="ordinal">ord</format>
              </variabletype>
           </variables>
           <maxpreparedduration>60s</maxpreparedduration>
           <maxrecordduration>1800s</maxrecordduration>
           <codecs>
              <codec name="audio"><subtype>basic</subtype></codec>
              <codec name="audio"><subtype>gsm</subtype></codec>
              <codec name="video"><subtype>h261</subtype></codec>
              <codec name="video"><subtype>h263</subtype></codec>
              <codec name="video"><subtype>h263-1998</subtype></codec>
              <codec name="video"><subtype>h264</subtype></codec>
           </codecs>
        </capabilities>
        <dialogs>
           <dialogaudit dialogid="6791fee" state="started"
                        connectionid="237430727:a338e95f"/>
        </dialogs>
     </auditresponse>
     </mscivr>

  D1. AS2 -> MS (CFW CONTROL, audit mixer)
  ----------------------------------------
     CFW 515f007c5bd0 CONTROL
     Control-Package: msc-mixer/1.0
     Content-Type: application/msc-mixer+xml
     Content-Length: 87

     <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
        <audit/>
     </mscmixer>

  D2. AS2 <- MS (CFW 200, auditresponse)
  --------------------------------------
     CFW 515f007c5bd0 200
     Timeout: 10
     Content-Type: application/msc-mixer+xml
     Content-Length: 548

     <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
     <auditresponse status="200">
        <capabilities>
           <codecs>
              <codec name="audio"><subtype>basic</subtype></codec>
              <codec name="audio"><subtype>gsm</subtype></codec>
              <codec name="video"><subtype>h261</subtype></codec>
              <codec name="video"><subtype>h263</subtype></codec>
              <codec name="video"><subtype>h263-1998</subtype></codec>
              <codec name="video"><subtype>h264</subtype></codec>
           </codecs>
        </capabilities>
        <mixers>
           <joinaudit id1="1:75d4dd0d" id2="1:b9e6a659"/>
        </mixers>
     </auditresponse>
     </mscmixer>

  E1. AS1 -> MS (CFW CONTROL, dialogterminate)
  --------------------------------------------
     CFW 7fdcc2331bef CONTROL
     Control-Package: msc-ivr/1.0
     Content-Type: application/msc-ivr+xml
     Content-Length: 127

     <mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
        <dialogterminate dialogid="6791fee" immediate="true"/>
     </mscivr>

  E2. AS1 <- MS (CFW 403 Forbidden)
  ---------------------------------
     CFW 7fdcc2331bef 403

  F1. AS2 -> MS (CFW CONTROL, join to conference)
  -----------------------------------------------
     CFW 140e0f763352 CONTROL
     Control-Package: msc-mixer/1.0
     Content-Type: application/msc-mixer+xml
     Content-Length: 117

     <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
        <join id1="1:272e9c05" id2="74b6d62"/>
     </mscmixer>

  F2. AS2 <- MS (CFW 403 Forbidden)
  ---------------------------------
     CFW 140e0f763352 403

9.  Acknowledgments

   The authors would like to thank Dale Worley for the thorough review
   of the whole document and for contributing text to make the document
   easier to read.

10.  References

10.1.  Normative References

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4574]  Levin, O. and G. Camarillo, "The Session Description
              Protocol (SDP) Label Attribute", RFC 4574, August 2006.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572, July 2006.

   [RFC6230]  Boulton, C., Melanchuk, T., and S. McGlashan, "Media
              Control Channel Framework", RFC 6230, May 2011.

   [RFC6231]  McGlashan, S., Melanchuk, T., and C. Boulton, "An
              Interactive Voice Response (IVR) Control Package for the
              Media Control Channel Framework", RFC 6231, May 2011.

   [RFC6505]  McGlashan, S., Melanchuk, T., and C. Boulton, "A Mixer
              Control Package for the Media Control Channel Framework",
              RFC 6505, March 2012.

   [RFC6917]  Boulton, C., Miniero, L., and G. Munson, "Media Resource
              Brokering", RFC 6917, April 2013.

   [RFC5239]  Barnes, M., Boulton, C., and O. Levin, "A Framework for
              Centralized Conferencing", RFC 5239, June 2008.

   [RFC4582]  Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
              Control Protocol (BFCP)", RFC 4582, November 2006.

   [RFC4583]  Camarillo, G., "Session Description Protocol (SDP) Format
              for Binary Floor Control Protocol (BFCP) Streams",
              RFC 4583, November 2006.

10.2.  Informative References

   [RFC2606]  Eastlake, D. and A. Panitz, "Reserved Top Level DNS
              Names", BCP 32, RFC 2606, June 1999.

   [RFC3725]  Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
              Camarillo, "Best Current Practices for Third Party Call
              Control (3pcc) in the Session Initiation Protocol (SIP)",
              BCP 85, RFC 3725, April 2004.

   [SRGS]     Hunt, A. and S. McGlashan, "Speech Recognition Grammar
              Specification Version 1.0", W3C Recommendation,
              March 2004.

   [RFC4597]  Even, R. and N. Ismail, "Conferencing Scenarios",
              RFC 4597, August 2006.

   [RFC5567]  Melanchuk, T., "An Architectural Framework for Media
              Server Control", RFC 5567, June 2009.

Authors' Addresses

   Alessandro Amirante
   University of Napoli
   Via Claudio 21
   Napoli  80125
   Italy

   EMail: alessandro.amirante@unina.it

   Tobia Castaldi
   Meetecho
   Via Carlo Poerio 89
   Napoli  80100
   Italy

   EMail: tcastaldi@meetecho.com

   Lorenzo Miniero
   Meetecho
   Via Carlo Poerio 89
   Napoli  80100
   Italy

   EMail: lorenzo@meetecho.com

   Simon Pietro Romano
   University of Napoli
   Via Claudio 21
   Napoli  80125
   Italy

   EMail: spromano@unina.it

 

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