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RFC 3868 - Signalling Connection Control Part User Adaptation La


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Network Working Group                                   J. Loughney, Ed.
Request for Comments: 3868                                         Nokia
Category: Standards Track                                  G. Sidebottom
                                                   Signatus Technologies
                                                                L. Coene
                                                              G. Verwimp
                                                            Siemens n.v.
                                                               J. Keller
                                                                 Tekelec
                                                             B. Bidulock
                                                     OpenSS7 Corporation
                                                            October 2004

    Signalling Connection Control Part User Adaptation Layer (SUA)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document defines a protocol for the transport of any Signalling
   Connection Control Part-User signalling over IP using the Stream
   Control Transmission Protocol.  The protocol is designed to be
   modular and symmetric, to allow it to work in diverse architectures,
   such as a Signalling Gateway to IP Signalling Endpoint architecture
   as well as a peer-to-peer IP Signalling Endpoint architecture.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.  Scope. . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.2.  Abbreviations and Terminology. . . . . . . . . . . . . .  4
       1.3.  Signalling Transport Architecture. . . . . . . . . . . .  6
       1.4.  Services Provided by the SUA Layer . . . . . . . . . . .  9
       1.5.  Internal Functions Provided in the SUA Layer . . . . . . 11
       1.6.  Definition of SUA Boundaries . . . . . . . . . . . . . . 14
   2.  Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . 19
   3.  Protocol Elements. . . . . . . . . . . . . . . . . . . . . . . 19
       3.1.  Common Message Header. . . . . . . . . . . . . . . . . . 20
       3.2.  SUA Connectionless Messages. . . . . . . . . . . . . . . 24
       3.3.  Connection Oriented Messages . . . . . . . . . . . . . . 27
       3.4.  Signalling Network Management (SNM) Messages . . . . . . 42
       3.5.  Application Server Process State Maintenance Messages. . 49
       3.6.  ASP Traffic Maintenance Messages . . . . . . . . . . . . 53
       3.7.  SUA Management Messages. . . . . . . . . . . . . . . . . 56
       3.8.  Routing Key Management (RKM) Messages. . . . . . . . . . 58
       3.9.  Common Parameters. . . . . . . . . . . . . . . . . . . . 61
       3.10. SUA-Specific parameters. . . . . . . . . . . . . . . . . 74
   4.  Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 92
       4.1.  Procedures to Support the SUA-User Layer . . . . . . . . 92
       4.2.  Receipt of Primitives from the Layer Management. . . . . 93
       4.3.  AS and ASP State Maintenance . . . . . . . . . . . . . . 95
       4.4.  Routing Key Management Procedures. . . . . . . . . . . .109
       4.5.  Availability and/or Congestion Status of SS7
             Destination Support101 . . . . . . . . . . . . . . . . .112
       4.6.  MTP3 Restart . . . . . . . . . . . . . . . . . . . . . .115
       4.7.  SCCP - SUA Interworking at the SG. . . . . . . . . . . .115
   5.  Examples of SUA Procedures . . . . . . . . . . . . . . . . . .117
       5.1.  SG Architecture. . . . . . . . . . . . . . . . . . . . .117
       5.2   IPSP Examples. . . . . . . . . . . . . . . . . . . . . .119
   6.  Security Considerations. . . . . . . . . . . . . . . . . . . .121
   7.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .121
       7.1.  SCTP Payload Protocol ID . . . . . . . . . . . . . . . .121
       7.2.  Port Number. . . . . . . . . . . . . . . . . . . . . . .121
       7.3.  Protocol Extensions. . . . . . . . . . . . . . . . . . .121
   8.  Timer Values . . . . . . . . . . . . . . . . . . . . . . . . .123
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .123
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .123
       10.1. Normative References . . . . . . . . . . . . . . . . . .123
       10.2. Informative References . . . . . . . . . . . . . . . . .124

   Appendix A.  Signalling Network Architecture . . . . . . . . . . .125
       A.1.  Generalized Peer-to-Peer Network Architecture. . . . . .125
       A.2.  Signalling Gateway Network Architecture. . . . . . . . .126
       A.3.  Signalling Gateway Message Distribution
             Recommendations. . . . . . . . . . . . . . . . . . . . .128
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .129
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . .131

1.  Introduction

   There is ongoing integration of switched circuit networks and IP
   networks.  Network service providers are designing IP-based
   signalling architectures that need support for SS7 and SS7-like
   signalling protocols.  IP provides an effective way to transport user
   data and for operators to expand their networks and build new
   services.  In these networks, there is need for interworking between
   the SS7 and IP domains [2719].

   This document defines a protocol for the transport SS7 SCCP-User
   protocols [ANSI SCCP] [ITU SCCP], such as TCAP and RANAP, over IP
   using the Stream Control Transmission Protocol (SCTP) [2960].

1.1.  Scope

   This document details the delivery of SCCP-user messages (MAP & CAP
   over TCAP [ANSI TCAP] [ITU TCAP], RANAP [RANAP], etc.) messages over
   IP between two signalling endpoints.  Consideration is given for the
   transport from a signalling gateway to an IP signalling node (such as
   an IP-resident Database) as described in the Framework Architecture
   for Signalling Transport [2719].  This protocol can also support
   transport of SCCP-user messages between two endpoints wholly
   contained within an IP network.

   The delivery mechanism addresses the following criteria:

   *  Support for transfer of SCCP-User Part messages
   *  Support for SCCP connectionless service.
   *  Support for SCCP connection oriented service.
   *  Support for the operation of SCCP-User protocol peers.
   *  Support for the management of SCTP transport associations between
      signalling gateways and IP-based signalling nodes.
   *  Support for distributed IP-based signalling nodes.
   *  Support for the asynchronous reporting of status changes to
      management functions.

1.2.  Abbreviations and Terminology

1.2.1.  Abbreviations

   CAP - CAMEL Application Protocol.

   GTT - Global Title Translation.

   MAP - Mobile Application Protocol.

   PC - Signalling System no. 7 Point Code.

   RANAP - Radio Access Network Application Protocol.

   SCTP - Stream Control Transmission Protocol.

   SS7 - Signalling System no. 7.

   TCAP - Transaction Capabilities Application Protocol.

1.2.2.  Terminology

   Signalling Gateway (SG) - Network element that terminates switched
   circuit networks and transports SCCP-User signalling over IP to an IP
   signalling endpoint.  A Signalling Gateway could be modeled as one or
   more Signalling Gateway Processes, which are located at the border of
   the SS7 and IP networks.  Where an SG contains more than one SGP, the
   SG is a logical entity and the contained SGPs are assumed to be
   coordinated into a single management view to the SS7 network and to
   the supported Application Servers.

   Application Server (AS) - A logical entity serving a specific Routing
   Key.  An example of an Application Server is a virtual IP database
   element handling all requests for an SCCP-user.  The AS contains a
   set of one or more unique Application Server Processes, of which one
   or more is normally actively processing traffic.

   Application Server Process (ASP) - An Application Server Process
   serves as an active or backup process of an Application Server (e.g.,
   part of a distributed signalling node or database element). Examples
   of ASPs are MGCs, IP SCPs, or IP-based HLRs.  An ASP contains an SCTP
   endpoint and may be configured to process traffic within more than
   one Application Server.

   IP Server Process (IPSP) - A process instance of an IP-based
   application.  An IPSP is essentially the same as an ASP, except that
   it uses SUA in a peer-to-peer fashion.  Conceptually, an IPSP does
   not use the services of a Signalling Gateway.

   Signalling Gateway Process (SGP) - A process instance of a Signalling
   Gateway.  It serves as an active, load-sharing or broadcast process
   of a Signalling Gateway.

   Signalling Process - A process instance that uses SUA to communicate
   with other signalling process.  An ASP, a SGP and an IPSP are all
   signalling processes.

   Association - An association refers to an SCTP association.  The
   association provides the transport for the delivery of SCCP-User
   protocol data units and SUA layer peer messages.

   Routing Key - The Routing Key describes a set of SS7 parameters
   and/or parameter ranges that uniquely defines the range of signalling
   traffic configured to be handled by a particular Application Server.
   An example would be where a Routing Key consists of a particular SS7
   SCCP SSN plus an identifier to uniquely mark the network that the SSN
   belongs to, for which all traffic would be directed to a particular
   Application Server.  Routing Keys are mutually exclusive in the sense
   that a received SS7 signalling message cannot be directed to more
   than one Routing Key.  Routing Keys can be provisioned, for example,
   by a MIB or registered using SUA's dynamic registration procedures.
   Routing keys MUST NOT span multiple network appearances.

   Routing Context - An Application Server Process may be configured to
   process traffic within more than one Application Server.  In this
   case, the Routing Context parameter is exchanged between the SGP and
   the ASP (or between two ASPs), identifying the relevant Application
   Server.  From the perspective of an SGP/ASP, the Routing Context
   uniquely identifies the range of traffic associated with a particular
   Application Server, which the ASP is configured to receive.  There is
   a 1:1 relationship between a Routing Context value and a Routing Key
   within an AS.  Therefore the Routing Context can be viewed as an
   index into an AS Table containing the AS Routing Keys.

   Address Mapping Function (AMF) - The AMF is an implementation
   dependent function that is responsible for resolving the address
   presented in the incoming SCCP/SUA message to correct SCTP
   association for the desired endpoint.  The AMF MAY use routing
   context / routing key information as selection criteria for the
   appropriate SCTP association.

   Fail-over - The capability to reroute signalling traffic as required
   to an alternate Application Server Process, or group of ASPs, within
   an Application Server in the event of failure or unavailability of a
   currently used Application Server Process. Fail-over may apply upon
   the return to service of a previously unavailable Application Server
   Process.

   Host - The computing platform that the SGP or ASP process is running
   on.

   Layer Management - Layer Management is a nodal function that handles
   the inputs and outputs between the SUA layer and a local management
   entity.

   Network Appearance - The Network Appearance is an SUA local reference
   (typically an integer) shared by SG and AS that together with a
   Signalling Point Code uniquely identifies an SS7 node by indicating
   the specific SS7 network it belongs to.

   Network Byte Order - Most significant byte first, a.k.a. Big Endian.

   Stream - A stream refers to an SCTP stream; a unidirectional logical
   channel established from one SCTP endpoint to another associated SCTP
   endpoint, within which all user messages are delivered sequenced
   except for those submitted to the unordered delivery service.

   Transport address - an address that serves as a source or destination
   for the unreliable packet transport service used by SCTP.  In IP
   networks, a transport address is defined by the combination of an IP
   address and an SCTP port number.  Note, only one SCTP port may be
   defined for each endpoint, but each SCTP endpoint may have multiple
   IP addresses.

1.3.  Signalling Transport Architecture

   The framework architecture that has been defined for switched circuit
   networks signalling transport over IP [2719] uses multiple
   components, including an IP transport protocol, a signalling common
   transport protocol and an adaptation module to support the services
   expected by a particular switched circuit networks signalling
   protocol from its underlying protocol layer.

   In general terms, the SUA architecture can be modeled as a peer-to-
   peer architecture.  The first section considers the SS7 to IP
   interworking architectures for connectionless and connection-oriented
   transport.  For this case, it is assumed that the ASP initiates the
   establishment of the SCTP association with SG.

1.3.1.  Protocol Architecture for Connectionless Transport

   In this architecture, the SCCP and SUA layers interface in the SG.
   Interworking between the SCCP and SUA layers is needed to provide for
   the transfer of the user messages as well as the management messages.

      ********   SS7   ***************   IP   ********
      * SEP  *---------*             *--------*      *
      *  or  *         *      SG     *        * ASP  *
      * STP  *         *             *        *      *
      ********         ***************        ********

      +------+                                +------+
      | SUAP |                                | SUAP |
      +------+         +------+------+        +------+
      | SCCP |         | SCCP | SUA  |        | SUA  |
      +------+         +------+------+        +------+
      | MTP3 |         | MTP3 |      |        |      |
      +------+         +------+ SCTP |        | SCTP |
      | MTP2 |         | MTP2 |      |        |      |
      +------+         +------+------+        +------+
      |  L1  |         |  L1  |  IP  |        |  IP  |
      +------+         +------+------+        +------+
          |               |         |            |
          +---------------+         +------------+

        SUAP - SCCP/SUA User Protocol (TCAP, for example)
        STP  - SS7 Signalling Transfer Point

   See Appendix A.3.1 for operation recommendations.

1.3.1.1.  SG as endpoint

   In this case, the connectionless SCCP messages are routed on point
   code (PC) and subsystem number (SSN).  The subsystem identified by
   SSN and Routing Context is regarded as local to the SG.  This means
   from SS7 point of view, the SCCP-user is located at the SG.

1.3.1.2.  Signalling Gateway as relay-point

   A Global Title translation is executed at the signalling gateway,
   before the destination of the message can be determined.  The actual
   location of the SCCP-user is irrelevant to the SS7 network.  GT
   Translation yields an "SCCP entity set", from which an Application
   Server can be derived.  Selection of the Application Server is based
   on the SCCP called party address (and possibly other SS7 parameters
   depending on the implementation).

1.3.2.  Protocol Architecture for Connection-Oriented Transport

   In this architecture, the SCCP and SUA layers share an interface in
   the signalling gateway process to associate the two connection
   sections needed for the connection-oriented data transfer between SEP
   and ASP.  Both connection sections are setup when routing the Connect
   Request messages from the signalling end point via signalling gateway
   process to ASP and visa versa.  The routing of the Connect Request
   message is performed in the same way as described in 1.3.1.

      ********   SS7   ***************   IP   ********
      * SEP/ *---------*      SG     *--------* ASP  *
      * STP  *         *             *        *      *
      ********         ***************        ********

      +------+                                +------+
      | SUAP |                                | SUAP |
      +------+         +------+------+        +------+
      | SCCP |         | SCCP | SUA  |        | SUA  |
      +------+         +------+------+        +------+
      | MTP3 |         | MTP3 |      |        |      |
      +------|         +------+ SCTP |        | SCTP |
      | MTP2 |         | MTP2 |      |        |      |
      +------+         +------+------+        +------+
      |  L1  |         |  L1  |  IP  |        |  IP  |
      +------+         +------+------+        +------+
          |               |         |            |
          +---------------+         +------------+

        SUAP - SCCP/SUA Application Protocol (e.g., - RANAP/RNSAP)
        STP  - SS7 Signalling Transfer Point

   See Appendix A.3.2 for operation recommendations.

1.3.3.  All IP Architecture

   This architecture can be used to carry a protocol that uses the
   transport services of SCCP within an IP network.  This allows
   flexibility in developing networks, especially when interaction
   between legacy signalling is not needed.  The architecture removes
   the need for signalling gateway functionality.

      ********   IP   ********
      * IPSP *--------* IPSP *
      ********        ********

      +------+        +------+
      | SUAP |        | SUAP |
      +------+        +------+
      | SUA  |        | SUA  |
      +------+        +------+
      | SCTP |        | SCTP |
      +------+        +------+
      |  IP  |        |  IP  |
      +------+        +------+
         |                |
         +----------------+

      SUAP - SCCP/SUA Application Protocol (e.g., - RANAP/RNSAP)

1.3.4.  ASP Fail-over Model and Terminology

   The SUA protocol supports ASP fail-over functions to support a high
   availability of transaction processing capability.

   An Application Server can be considered as a list of all ASPs
   configured/registered to handle SCCP-user messages within a certain
   range of routing information, known as a Routing Key.  One or more
   ASPs in the list may normally be active to handle traffic, while
   others may be inactive but available in the event of failure or
   unavailability of the active ASP(s).

   For operation recommendations, see Appendix A.

1.4.  Services Provided by the SUA Layer

1.4.1.  Support for the transport of SCCP-User Messages

   The SUA supports the transfer of SCCP-user messages.  The SUA layer
   at the signalling gateway and at the ASP support the seamless
   transport of user messages between the signalling gateway and the
   ASP.

1.4.2.  SCCP Protocol Class Support

   Depending upon the SCCP-users supported, the SUA supports the 4
   possible SCCP protocol classes transparently.  The SCCP protocol
   classes are defined as follows:

   *  Protocol class 0 provides unordered transfer of SCCP-user messages
      in a connectionless manner.

   *  Protocol class 1 allows the SCCP-user to select the sequenced
      delivery of SCCP-user messages in a connectionless manner.

   *  Protocol class 2 allows the bidirectional transfer of SCCP-user
      messages by setting up a temporary or permanent signalling
      connection.

   *  Protocol class 3 allows the features of protocol class 2 with the
      inclusion of flow control.  Detection of message loss or mis-
      sequencing is included.

   Protocol classes 0 and 1 make up the SCCP connectionless service.
   Protocol classes 2 and 3 make up the SCCP connection-oriented
   service.

1.4.3.  Native Management Functions

   The SUA layer provides the capability to indicate errors associated
   with the SUA-protocol messages and to provide notification to local
   management and the remote peer as is necessary.

1.4.4.  Interworking with SCCP Network Management Functions

   SUA uses the existing ASP management messages for ASP status
   handling.  The interworking with SCCP management messages consists of
   DUNA, DAVA, DAUD, DRST, DUPU or SCON messages (defined in section 3)
   on receipt of SSP, SSA, SST or SSC (defined by SCCP) to the
   appropriate ASPs.  See also chapter 1.4.5.  The primitives below are
   sent between the SCCP and SUA management functions in the SG to
   trigger events in the IP and SS7 domain.

   Generic   |Specific   |
   Name      |Name       |ANSI/ITU Reference
   ----------+-----------+---------------------------------------------
   N-State   |Request    |ITU-Q.711   Chap 6.3.2.3.2 (Tab 16/Q.711)
             |Indication |ANSI-T1.112 Chap 2.3.2.3.2 (Tab 8E/T1.112.1)
   ----------+-----------+---------------------------------------------
   N-PCstate |Indication |ITU-Q.711   Chap 6.3.2.3.3 (Tab 1/Q.711)
             |           |ANSI-T1.112 Chap 2.3.2.3.4 (Tab 8G/T1.112.1)
   ----------+-----------+---------------------------------------------
   N-Coord   |Request    |ITU-Q.711   Chap 6.3.2.3.1 (Tab 15/Q.711)
             |Indication |ANSI-T1.112 Chap 2.3.2.3.3 (Tab 8F/T1.112.1)
             |Response   |
             |Confirm    |

1.4.5.  Support for the management between the SGP and ASP.

   The SUA layer provides interworking with SCCP management functions at
   the SG for operation between the switched circuit networks and the IP
   network.  It should:

   *  Provide an indication to the SCCP-user at an ASP that a SS7
      endpoint/peer is unreachable.
   *  Provide an indication to the SCCP-user at an ASP that a SS7
      endpoint/peer is reachable.
   *  Provide congestion indication to SCCP-user at an ASP.
   *  Provide the initiation of an audit of SS7 endpoints at the SG.

1.4.6.  Relay function

   For network scalability purposes, the SUA may be enhanced with a
   relay functionality to determine the next hop SCTP association toward
   the destination SUA endpoint.

   The determination of the next hop may be based on Global Title
   information (e.g., E.164 number), in analogy with SCCP GTT in SS7
   networks, modeled in [ITU-T Q.714].  It may also be based on Hostname
   information, IP address or pointcode contained in the called party
   address.

   This allows for greater scalability, reliability and flexibility in
   wide-scale deployments of SUA.  The usage of a relay function is a
   deployment decision.

1.5.  Internal Functions Provided in the SUA Layer

   To perform its addressing and relaying capabilities, the SUA makes
   use of an Address Mapping Function (AMF).  This function is
   considered part of SUA, but the way it is realized is left
   implementation / deployment dependent (local tables, DNS [3761],
   LDAP, etc.)

   The AMF is invoked when a message is received at the incoming
   interface.  The AMF is responsible for resolving the address
   presented in the incoming SCCP/SUA message to SCTP associations to
   destinations within the IP network.  The AMF will select the
   appropriate SCTP association based upon routing context / routing key
   information available.  The destination might be the end SUA node or
   a SUA relay node.  The Routing Keys reference an Application Server,
   which will have one or more ASPs processing traffic for the AS.  The
   availability and status of the ASPs is handled by SUA ASP management
   messages.

   Possible SS7 address/routing information that comprise a Routing Key
   entry includes, for example, OPC, DPC, SIO found in the MTP3 routing
   label, SCCP subsystem number, or Transaction ID.  IP addresses and
   hostnames can also be used as Routing Key Information.

   It is expected that the routing keys be provisioned via a MIB,
   dynamic registration or external process, such as a database.

1.5.1.  Address Mapping at the SG

   Normally, one or more ASPs are active in the AS (i.e., currently
   processing traffic) but in certain failure and transition cases it is
   possible that there may not be an active ASP available.  The SGP will
   buffer the message destined for this AS for a time T(r) or until an
   ASP becomes available.  When no ASP becomes available before expiry
   of T(r), the SGP will flush the buffered messages and initiate the
   appropriate return or refusal procedures.

   If there is no address mapping match for an incoming message, a
   default treatment MAY be specified.  Possible solutions are to
   provide a default Application Server to direct all unallocated
   traffic to a (set of) default ASP(s), or to drop the messages and
   provide a notification to management.  The treatment of unallocated
   traffic is implementation dependent.

1.5.2.  Address Mapping at the ASP

   To direct messages to the SS7 network, the ASP MAY perform an address
   mapping to choose the proper SGP for a given message.  This is
   accomplished by observing the Destination Point Code and other
   elements of the outgoing message, SS7 network status, SGP
   availability, and Routing Context configuration tables.

   A Signalling Gateway may be composed of one or more SGPs.  There is,
   however, no SUA messaging to manage the status of an SGP.  Whenever
   an SCTP association to an SGP exists, it is assumed to be available.
   Also, every SGP of one SG communicating with one ASP regarding one AS
   provides identical SS7 connectivity to this ASP.

   An ASP routes responses to the SGP that it received messages from;
   within the routing context which it is currently active and receiving
   traffic.

1.5.3.  Address Mapping Function at a Relay Node

   The relay function is invoked when:

   -  Routing is on Global Title

   -  Routing is on Hostname
   -  Routing is on SSN and PC or SSN and IP Address and the address
      presented is not the one of the relay node

   Translation/resolution of the above address information yields one of
   the following:

   -  Route on SSN: SCTP association ID toward the destination node, SSN
      and optionally Routing Context and/or IP address.
   -  Route on GT: SCTP association ID toward next relay node, (new) GT
      and optionally SSN and/or Routing Context.
   -  Routing on Hostname: SCTP association ID toward next relay node,
      (new) Hostname and optionally SSN and/or Routing Context.
   -  A local SUA-user (combined relay/end node)

   To prevent looping, an SS7 hop counter is used.  The originating end
   node (be it an SS7 or an IP node) sets the value of the SS7 hop
   counter to the maximum value (15 or less).  Each time the relay
   function is invoked within an intermediate (relay) node, the SS7 hop
   counter is decremented.  When the value reaches zero, the return or
   refusal procedures are invoked with reason "Hop counter violation".

1.5.4.  SCTP Stream Mapping

   The SUA supports SCTP streams.  Signalling Gateway SG and Application
   Servers need to maintain a list of SCTP and SUA-users for mapping
   purposes.  SCCP-users requiring sequenced message transfer need to be
   sent over a stream with sequenced delivery.

   SUA uses stream 0 for SUA management messages.  It is OPTIONAL that
   sequenced delivery be used to preserve the order of management
   message delivery.

   Stream selection based on protocol class:

   -  Protocol class 0: SUA MAY select unordered delivery.  The stream
      selected is based on traffic information available to the SGP or
      ASP.

   -  Protocol class 1: SUA MUST select ordered delivery.  The stream
      selected is based upon the sequence parameter given by the upper
      layer over the primitive interface and other traffic information
      available to the SGP or ASP

   -  Protocol classes 2 and 3: SUA MUST select ordered delivery. The
      stream selected is based upon the source local reference of the
      connection and other traffic information available to the SGP or
      ASP.

1.5.5.  Flow Control

   Local Management at an ASP may wish to stop traffic across an SCTP
   association to temporarily remove the association from service or to
   perform testing and maintenance activity.  The function could
   optionally be used to control the start of traffic on to a newly
   available SCTP association.

1.5.6.  Congestion Management

   The SUA layer is informed of local and IP network congestion by means
   of an implementation-dependent function (e.g., an implementation-
   dependent indication from the SCTP of IP network congestion).

   At an ASP or IPSP, the SUA layer indicates congestion to local SCCP-
   Users by means of an appropriate SCCP primitive (e.g., N-INFORM, N-
   NOTICE), as per current SCCP procedures, to invoke appropriate upper
   layer responses.  When an SG determines that the transport of SS7
   messages is encountering congestion, the SG MAY trigger SS7 SCCP
   Congestion messages to originating SS7 nodes, per the congestion
   procedures of the relevant SCCP standard.  The triggering of SS7 SCCP
   Management messages from an SG is an implementation-dependent
   function.

   The SUA layer at an ASP or IPSP MAY indicate local congestion to an
   SUA peer with an SCON message.  When an SG receives a congestion
   message (SCON) from an ASP, and the SG determines that an endpoint is
   now encountering congestion, it MAY trigger congestion procedures of
   the relevant SCCP standard.

1.6.  Definition of SUA Boundaries

1.6.1.  Definition of the upper boundary

   The following primitives are supported between the SUA and an SCCP-
   user (a reference to ITU and ANSI sections where these primitives and
   corresponding parameters are described, is also given):

   Generic     |Specific  |
   Name        |Name      |ANSI/ITU Reference
   ------------+----------+-------------------------------------------
   N-CONNECT   |Request   |ITU-Q.711   Chap 6.1.1.2.2 (Tab 2/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.2 (Tab 2/T1.112.1)
               |Response  |
               |Confirm   |
   ------------+----------+-------------------------------------------
   N-DATA      |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 3/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 3/T1.112.1)

   ------------+----------+-------------------------------------------
   N-EXPEDITED |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 4/Q.711)
   DATA        |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 4/T1.112.1)
   ------------+----------+-------------------------------------------
   N-RESET     |Request   |ITU-Q.711   Chap 6.1.1.2.3 (Tab 5/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.3 (Tab 5/T1.112.1)
               |Response  |
               |Confirm   |
   ------------+----------+-------------------------------------------
   N-DISCONNECT|Request   |ITU-Q.711   Chap 6.1.1.2.4 (Tab 6/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.4 (Tab 6/T1.112.1)
   ------------+----------+-------------------------------------------
   N-INFORM    |Request   |ITU-Q.711   Chap 6.1.1.3.2 (Tab 8/Q.711)
               |Indication|ANSI-T1.112 Chap 2.1.1.2.5 (Tab 6A/T1.112.1)
   ------------+----------+-------------------------------------------
   N-UNITDATA  |Request   |ITU-Q.711   Chap 6.2.2.3.1 (Tab 12/Q.711)
               |Indication|ANSI-T1.112 Chap 2.2.2.3.1 (Tab 8A/T1.112.1)
   ------------+----------+-------------------------------------------
   N-NOTICE    |Indication|ITU-Q.711   Chap 6.2.2.3.2 (Tab 13/Q.711)
               |          |ANSI-T1.112 Chap 2.2.2.3.2 (Tab 8B/T1.112.1)
   ------------+----------+--------------------------------------------
   N-STATE     |Request   |ITU-Q.711   Chap 6.3.2.3.2 (Tab 16/Q.711)
               |Indication|ANSI-T1.112 Chap 2.3.2.3.2 (Tab 8E/T1.112.1)
   ------------+----------+--------------------------------------------
   N-PCSTATE   |Indication|ITU-Q.711   Chap 6.3.2.3.3 (Tab 17/Q.711)
               |          |ANSI-T1.112 Chap 2.3.2.3.4 (Tab 8G/T1.112.1)
   ------------+----------+--------------------------------------------
   N-COORD     |Request   |ITU-Q.711   Chap 6.3.2.3.1 (Tab 15/Q.711)
               |Indication|ANSI-T1.112 Chap 2.3.2.3.3 (Tab 8F/T1.112.1)
               |Response  |
               |Confirm   |

1.6.2.  Definition of the lower boundary

   The upper layer primitives provided by the SCTP are provided in
   [SCTP].

1.6.3.  Definition of the Boundary between SUA and Layer Management

   M-SCTP_ESTABLISH request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to establish an SCTP association with its
             peer.

   M-SCTP_ESTABLISH confirm
   Direction: SUA -> LM
   Purpose:  ASP confirms to LM that it has established an SCTP
             association with its peer.

   M-SCTP_ESTABLISH indication
   Direction: SUA -> LM
   Purpose:  SUA informs LM that a remote ASP has established an SCTP
             association.

   M-SCTP_RELEASE request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to release an SCTP association with its
             peer.

   M-SCTP_RELEASE confirm
   Direction: SUA -> LM
   Purpose:  ASP confirms to LM that it has released SCTP association
             with its peer.

   M-SCTP_RELEASE indication
   Direction: SUA -> LM
   Purpose:  SUA informs LM that a remote ASP has released an SCTP
             Association or the SCTP association has failed.

   M-SCTP RESTART indication
   Direction: SUA -> LM
   Purpose:  SUA informs LM that an SCTP restart indication has been
             received.

   M-SCTP_STATUS request
   Direction: LM -> SUA
   Purpose:  LM requests SUA to report the status of an SCTP
             association.

   M-SCTP_STATUS confirm
   Direction: SUA -> LM
   Purpose:  SUA responds with the status of an SCTP association.

   M-SCTP STATUS indication
   Direction: SUA -> LM
   Purpose:  SUA reports the status of an SCTP association.

   M-ASP_STATUS request
   Direction: LM -> SUA
   Purpose:  LM requests SUA to report the status of a local or remote
               ASP.

   M-ASP_STATUS confirm
   Direction: SUA -> LM
   Purpose:  SUA reports status of local or remote ASP.

   M-AS_STATUS request
   Direction: LM -> SUA
   Purpose:  LM requests SUA to report the status of an AS.

   M-AS_STATUS confirm
   Direction: SUA -> LM
   Purpose:  SUA reports the status of an AS.

   M-NOTIFY indication
   Direction: SUA -> LM
   Purpose:  SUA reports that it has received a Notify message from its
             peer.

   M-ERROR indication
   Direction: SUA -> LM
   Purpose:  SUA reports that it has received an Error message from its
             peer or that a local operation has been unsuccessful.

   M-ASP_UP request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to start its operation and send an ASP Up
             message to its peer.

   M-ASP_UP confirm
   Direction: SUA -> LM
   Purpose:  ASP reports that is has received an ASP UP Ack message
             from its peer.

   M-ASP_UP indication
   Direction: SUA -> LM
   Purpose:  SUA reports it has successfully processed an incoming ASP
             Up message from its peer.

   M-ASP_DOWN request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to stop its operation and send an ASP Down
             message to its peer.

   M-ASP_DOWN confirm
   Direction: SUA -> LM
   Purpose:  ASP reports that is has received an ASP Down Ack message
             from its peer.

   M-ASP_DOWN indication
   Direction: SUA -> LM
   Purpose:  SUA reports it has successfully processed an incoming ASP
             Down message from its peer, or the SCTP association has
             been lost/reset.

   M-ASP_ACTIVE request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to send an ASP Active message to its peer.

   M-ASP_ACTIVE confirm
   Direction: SUA -> LM
   Purpose:  ASP reports that is has received an ASP Active Ack message
             from its peer.

   M-ASP_ACTIVE indication
   Direction: SUA -> LM
   Purpose:  SUA reports it has successfully processed an incoming ASP
             Active message from its peer.

   M-ASP_INACTIVE request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to send an ASP Inactive message to its
             peer.

   M-ASP_INACTIVE confirm
   Direction: LM -> SUA
   Purpose:  ASP reports that is has received an ASP Inactive
             Ack message from its peer.

   M-ASP_INACTIVE indication
   Direction: SUA -> LM
   Purpose:  SUA reports it has successfully processed an incoming ASP
             Inactive message from its peer.

   M-AS_ACTIVE indication
   Direction: SUA -> LM
   Purpose:  SUA reports that an AS has moved to the AS-ACTIVE state.

   M-AS_INACTIVE indication
   Direction: SUA -> LM
   Purpose: SUA reports that an AS has moved to the AS-INACTIVE state.

   M-AS_DOWN indication
   Direction: SUA -> LM
   Purpose: SUA reports that an AS has moved to the AS-DOWN state.

   If the SUA layer supports dynamic registration of Routing Key, the
   layer MAY support the following additional primitives:

   M-RK_REG request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to register RK(s) with its peer by sending
             REG REQ message.

   M-RK_REG confirm
   Direction: SUA -> LM
   Purpose:  ASP reports that it has received REG RSP message with
             registration status as successful from its peer.

   M-RK_REG indication
   Direction: SUA -> LM
   Purpose:  SUA informs LM that it has successfully processed an
             incoming REG REQ message.

   M-RK_DEREG request
   Direction: LM -> SUA
   Purpose:  LM requests ASP to deregister RK(s) with its peer by
             sending DEREG REQ message.

   M-RK_DEREG confirm
   Direction: SUA -> LM
   Purpose:  ASP reports that it has received DEREG RESP message with
             deregistration status as successful from its peer.

   M-RK_DEREG indication
   Direction: SUA -> LM
   Purpose:  SUA informs LM that it has successfully processed an
             incoming DEREG REQ from its peer.

2.  Conventions

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
   they appear in this document, are to be interpreted as described in
   BCP 14, RFC 2119 [2119].

3.  Protocol Elements

   The general message format includes a Common Message Header together
   with a list of zero or more parameters as defined by the Message
   Type.

   For forward compatibility, all Message Types may have attached
   parameters even if none are specified in this version.

   The Reserved field is set to 0 in messages sent and is not to be
   examined in messages received.

3.1.  Common Message Header

   The protocol messages for the SCCP-User Adaptation Protocol requires
   a message structure which contains a version, message class, message
   type, message length and message contents.  This message header is
   common among all signalling protocol adaptation layers:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Version    |   Reserved    | Message Class | Message Type  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Message Length                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Message Data                          |

   Note that the 'data' portion of SUA messages SHALL contain SCCP-User
   data, not the encapsulated SCCP message.

   Optional parameters can only occur at most once in an SUA message.

3.1.1.  SUA Protocol Version

   The version field (ver) contains the version of the SUA adaptation
   layer.  The supported versions are:

      1   SUA version 1.0

3.1.2.  Message Classes

   Message Classes

      0         SUA Management (MGMT) Message
      1         Reserved
      2         Signalling Network Management (SNM) Messages
      3         ASP State Maintenance (ASPSM) Messages
      4         ASP Traffic Maintenance (ASPTM) Messages
      5         Reserved
      6         Reserved
      7         Connectionless Messages
      8         Connection-Oriented Messages
      9         Routing Key Management (RKM) Messages.
      10 - 127  Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

3.1.3.  Message Types

   SUA Management Messages

      0         Error (ERR)
      1         Notify (NTFY)
      2 - 127   Reserved by the IETF
      128- 255  Reserved for IETF-Defined Message Class Extensions

   Signalling Network Management (SNM) Messages

      0         Reserved
      1         Destination Unavailable (DUNA)
      2         Destination Available (DAVA)
      3         Destination State Audit (DAUD)
      4         Signalling Congestion (SCON)
      5         Destination User Part Unavailable (DUPU)
      6         Destination Restricted (DRST)
      7 - 127   Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

   Application Server Process State Maintenance (ASPSM) Messages

      0         Reserved
      1         ASP Up (UP)
      2         ASP Down (DOWN)
      3         Heartbeat (BEAT)
      4         ASP Up Ack (UP ACK)
      5         ASP Down Ack (DOWN ACK)
      6         Heartbeat Ack (BEAT ACK)
      7 - 127   Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

   ASP Traffic Maintenance (ASPTM) Messages

      0         Reserved
      1         ASP Active (ACTIVE)
      2         ASP Inactive (INACTIVE)
      3         ASP Active Ack (ACTIVE ACK)
      4         ASP Inactive Ack (INACTIVE ACK)
      5 - 127   Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

   Routing Key Management (RKM) Messages

      0         Reserved
      1         Registration Request (REG REQ)
      2         Registration Response (REG RSP)
      3         Deregistration Request (DEREG REQ)
      4         Deregistration Response (DEREG RSP)
      5 - 127   Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

   Connectionless (CL) Messages

      0         Reserved
      1         Connectionless Data Transfer (CLDT)
      2         Connectionless Data Response (CLDR)
      3 - 127   Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

   Connection-Oriented (CO) Messages

      0         Reserved
      1         Connection Request (CORE)
      2         Connection Acknowledge (COAK)
      3         Connection Refused (COREF)
      4         Release Request (RELRE)
      5         Release Complete (RELCO)
      6         Reset Confirm (RESCO)
      7         Reset Request (RESRE)
      8         Connection Oriented Data Transfer (CODT)
      9         Connection Oriented Data Acknowledge (CODA)
      10        Connection Oriented Error (COERR)
      11        Inactivity Test (COIT)
      12 - 127  Reserved by the IETF
      128 - 255 Reserved for IETF-Defined Message Class Extensions

3.1.4.  Message Length

   The Message Length defines the length of the message in octets,
   including the header and including all padding bytes.  Message Length
   is a 32-bit identifier.

3.1.5.  Tag-Length-Value Format

   SUA messages consist of a Common Header followed by zero or more
   parameters, as defined by the message type.  The Tag-Length-Value
   (TLV) parameters contained in a message are defined in a Tag-Length-
   Value format as shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Parameter Tag        |       Parameter Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                       Parameter Value                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameter Tag: 16 bits (unsigned integer)

      Tag field is a 16-bit identifier of the type of parameter.  It
      takes a value of 0 to 65535.

   Parameter Length: 16 bits (unsigned integer)

      The Parameter Length field contains the size of the parameter in
      bytes, including the Parameter Tag, Parameter Length, and
      Parameter Value fields.  The Parameter Length does not include any
      padding bytes.  However, composite parameters will contain all
      padding bytes, since all parameters contained within this
      composite parameter will be considered multiples of 4 bytes.

   Parameter Value: variable-length.

      The Parameter Value field contains the actual information to be
      transfered in the parameter.

      The total length of a parameter (including Tag, Parameter Length
      and Value fields) MUST be a multiple of 4 bytes.  If the length of
      the parameter is not a multiple of 4 bytes, the sender pads the
      parameter at the end (i.e., after the Parameter Value field) with
      all zero bytes.  The length of the padding is NOT included in the
      parameter length field.  A sender SHOULD NOT pad with more than 3
      bytes.  The receiver MUST ignore the padding bytes.

   Implementation note: The use of TLV in principle allows the
   parameters to be placed in a random order in the message.  However,
   some guidelines should be considered for easy processing in the
   following order:

   -  Parameters needed to correctly process other message parameters,
      preferably should precede these parameters (such as Routing
      Context).
   -  Mandatory parameters preferably SHOULD precede any optional
      parameters.
   -  The data parameter will normally be the final one in the message.

   -  The receiver SHOULD accept parameters in any order, except where
      explicitly mandated.

3.2.  SUA Connectionless Messages

   The following section describes the SUA Connectionless transfer
   messages and parameter contents.  The general message format includes
   a Common Message Header together with a list of zero or more
   parameters as defined by the Message Type.  All Message Types can
   have attached parameters.

3.2.1.  Connectionless Data Transfer (CLDT)

   This message transfers data between one SUA to another.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0115          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Protocol Class                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0102          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Source Address                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0103          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                     Destination Address                       /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0116         |             Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Control                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0101          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SS7 Hop Count                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Importance                           |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0114          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Priority                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0013          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Correlation ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0117          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Segmentation                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010B          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Protocol Class                Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     Sequence Control              Mandatory
     SS7 Hop Count                 Optional
     Importance                    Optional
     Message Priority              Optional
     Correlation ID                Optional
     Segmentation                  Optional
     Data                          Mandatory

   Implementation note: This message covers the following SCCP messages:
   unitdata (UDT), extended unitdata (XUDT), long unitdata (LUDT).

3.2.2.  Connectionless Data Response (CLDR)

   This message is used as a response message by the peer to report
   errors in the received CLDT message, when the return on error option
   is set.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0106          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           SCCP Cause                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0102          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Source Address                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0103          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                     Destination Address                       /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0101          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SS7 Hop Count                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Importance                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0114          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Priority                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0013          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Correlation ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0117          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Segmentation                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010b          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     SCCP Cause                    Mandatory
     Source Address                Mandatory
     Destination Address           Mandatory
     SS7 Hop Count                 Optional
     Importance                    Optional
     Message Priority              Optional
     Correlation ID                Optional
     Segmentation                  Optional
     Data                          Optional

   Implementation note: This message covers the following SCCP messages:
   unitdata service (UDTS), extended unitdata service (XUDTS) and long
   unitdata service (LUDTS).

3.3.  Connection Oriented Messages

3.3.1.  Connection Oriented Data Transfer (CODT)

   This message transfers data between one SUA to another for
   connection-oriented service.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0107          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0114          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Priority                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0013          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Correlation ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010b          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Sequence Number               Optional *1
     Destination Reference Number  Mandatory
     Message Priority              Optional
     Correlation ID                Optional
     Data                          Mandatory

   NOTE *1:   This parameter is not present in case of Expedited Data
              (ED).

   Implementation note: For the CODT to represent DT1, DT2 and ED
   messages, the following conditions MUST be met:

   DT1 is represented by a CODT when:
     Sequence Number parameter is present (contains "more" indicator).

   DT2 is represented by a CODT when:
     Sequence Number parameter is present (contains P(S), P(R) and more
     indicator)

   ED is represented by a CODT with:
     Sequence Number parameter is not present

3.3.2.  Connection Oriented Data Acknowledge (CODA)

   The peer uses this message to acknowledge receipt of data.  This
   message is used only with protocol class 3.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0108          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Receive Sequence Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010A          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Credit                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     Receive Sequence Number       Optional *1
     Credit                        Mandatory *1

   NOTE *1:    Mandatory when representing Data Acknowledgement (AK).

   Implementation note: For the CODA to represent DA and EA messages,
   the following conditions MUST be met:

   DA is represented by a CODA when:
     Receive Sequence Number parameter is present (contains P(S), P(R)
     and more indicator)

   EA is represented by a CODA when:
     Receive Sequence Number parameter is not present

3.3.3.  Connection Request (CORE)

   This message is used for establishing a signalling connection between
   two peer endpoints.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0115          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Protocol Class                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0103          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                     Destination Address                       /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0116          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Control                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0107          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0102          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Source Address                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0101          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SS7 Hop Count                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                          Importance                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0114          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Priority                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010A          |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Credit                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010b          |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Protocol Class                Mandatory
     Source Reference Number       Mandatory
     Destination Address           Mandatory
     Sequence Control              Mandatory
     Sequence Number               Optional *1
     Source Address                Optional
     SS7 Hop Count                 Optional
     Importance                    Optional
     Message Priority              Optional
     Credit                        Optional *1
     Data                          Optional

   NOTE *1:    Mandatory for protocol class 3 only.

   Implementation note: This message covers the following SCCP message:
   Connection Request (CR).

3.3.4.  Connection Acknowledge (COAK)

   This message is used to acknowledge a connection request from the
   peer endpoint.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0115          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Protocol Class                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x01116          |            Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Control                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010A          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Credit                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0102          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Source Address                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Importance                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0114          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Message Priority                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0103          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   /                     Destination Address                       /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010b          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Protocol Class                Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     Sequence Control              Mandatory
     Credit                        Mandatory *2
     Source Address                Optional
     Importance                    Optional
     Message Priority              Optional
     Destination Address           Optional *1
     Data                          Optional

   NOTE *1:    Destination Address parameter will be present in case
               that the received CORE message conveys the Source
               Address parameter.

   NOTE *2:    Only applicable for protocol class 3.

   Implementation note: This message covers the following SCCP message:
   Connection Confirm (CC).

3.3.5.  Connection Refused (COREF)

   This message is used to refuse a connection request between two peer
   endpoints.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0106          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           SCCP Cause                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0102          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Source Address                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0103          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                     Destination Address                       /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Importance                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010B          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context                    Mandatory
     Destination Reference Number       Mandatory
     SCCP Cause                         Mandatory
     Source Address                     Optional
     Destination Address                Optional *1
     Importance                         Optional
     Data                               Optional

   Note *1:    Destination Address parameter will be present in case
               that the received CORE message conveys the Source Address
               parameter.

   Implementation note: This message covers the following SCCP message:
   Connection REFused (CREF).

3.3.6.  Release Request (RELRE)

   This message is used to request a signalling connection between two
   peer endpoints be released.  All associated resources can then be
   released.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0106          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          SCCP Cause                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Importance                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010b          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     SCCP Cause                    Mandatory
     Importance                    Optional
     Data                          Optional

   Implementation note: This message covers the following SCCP message:
   connection ReLeaSeD (RLSD).

3.3.7.  Release Complete (RELCO)

   This message is used to acknowledge the release of a signalling
   connection between two peer endpoints.  All associated resources
   should be released.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Importance                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     Importance                    Optional

   Implementation note: This message covers the following SCCP message:
   ReLease Complete (RLC).

3.3.8.  Reset Request (RESRE)

   This message is used to indicate that the sending SCCP/SUA wants to
   initiate a reset procedure (reinitialization of sequence numbers) to
   the peer endpoint.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source Reference Number                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0106          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           SCCP Cause                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory
     SCCP Cause                    Mandatory

   Implementation note: This message covers the following SCCP message:
   ReSet Request (RSR).

3.3.9.  Reset Confirm (RESCO)

   This message is used to confirm the Reset Request.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     Source Reference Number       Mandatory

   Implementation note: This message covers the following SCCP message:
   ReSet Confirmation (RSC).

3.3.10.  Connection Oriented Error (COERR)

   The COERR message is sent to indicate a protocol data unit error.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0106          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          SCCP Cause                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Destination Reference Number  Mandatory
     SCCP Cause                    Mandatory

   Implementation note: This message covers the following SCCP message:
   Protocol Data Unit ERRor (ERR).

3.3.11.  Connection Oriented Inactivity Test (COIT)

   This message is used for auditing the signalling connection state and
   the consistency of connection data at both ends of the signalling
   connection.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0115          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Protocol Class                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0104          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0105          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0107          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010A          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Credit                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Mandatory
     Protocol Class                Mandatory
     Source Reference Number       Mandatory
     Destination Reference number  Mandatory
     Sequence Number               Mandatory *1
     Credit                        Mandatory *1

   NOTE *1:    Information in these parameter fields reflects those
               values sent in the last data form 2 or data
               acknowledgement message.  They are ignored if the
               protocol class indicates class 2.

   Implementation note: This message covers the following SCCP message:
   Inactivity Test (IT).

3.4.  Signalling Network Management (SNM) Messages

3.4.1.  Destination Unavailable (DUNA)

   In the scope of SUA, this message is covered by the PC- or N-state
   indication passed between SCCP and local SCCP-user.  The DUNA message
   is sent from the SG or relay node to all concerned ASPs (servicing
   SCCP-users considered local to the SG or relay node, see chapter
   1.3.1.1), when a destination or SCCP-user has become unreachable. The
   SUA-User at the ASP is expected to stop traffic to the affected
   destination or SCCP-user through the SG or relay node initiating the
   DUNA.

   The format for DUNA Message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Affected Point Code                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8003          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SSN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0112          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SMI                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Affected Point Code           Mandatory *1
     SSN                           Optional *1
     SMI                           Optional
     Info String                   Optional

   Note 1:    When the SSN is included, the DUNA message
              corresponds to the SCCP N-STATE primitive.  When SSN
              is not, the DUNA message corresponds to the SCCP N-PCSTATE
              primitive.  The Affected Point Code parameter can only
              contain one point code when SSN is present.

3.4.2.  Destination Available (DAVA)

   In the scope of SUA, this message is covered by the PC- and N-state
   indication passed between SCCP and local SCCP-user.  The DAVA message
   is sent from the SG or relay node to all concerned ASPs (servicing
   SCCP-users considered local to the SG or relay node, see chapter
   1.3.1.1) to indicate that a destination (PC or SCCP-user) is now
   reachable.  The ASP SUA-User protocol is expected to resume traffic
   to the affected destination through the SG or relay node initiating
   the DAVA.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Affected Point Code                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8003          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SSN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0112          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SMI                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Affected Point Code           Mandatory *1
     SSN                           Optional *1
     SMI                           Optional
     Info String                   Optional

   Note 1:    When the SSN is included, the DAVA message corresponds to
              the SCCP N-STATE primitive.  When SSN is not included, the
              DAVA message corresponds to the SCCP N-PCSTATE primitive.
              The Affected Point Code can only contain one point code
              when SSN is present.

3.4.3.  Destination State Audit (DAUD)

   The DAUD message can be sent from the ASP to the SG (or relay node)
   to query the availability state of the routes to an affected
   destination.  A DAUD may be sent periodically after the ASP has
   received a DUNA, until a DAVA is received.  The DAUD can also be sent
   when an ASP recovers from isolation from the SG (or relay node).

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Affected Point Code                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8003          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SSN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010C          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           User/Cause                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Affected Point Code           Mandatory *1
     SSN                           Optional *1
     User / Cause                  Optional
     Info String                   Optional

   Note 1:    If the SSN is present, the DAUD is "soliciting" N-STATE
              primitives, otherwise it is "soliciting" N-PCSTATE
              primitives.

3.4.4.  Signalling Congestion (SCON)

   The SCON message can be sent from the SG or relay node to all
   concerned ASPs to indicate that the congestion level in the SS7
   network to a specified destination has changed.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Affected Point Code                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8003          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SSN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0118          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Congestion Level                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0112          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SMI                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Affected Point Code           Mandatory *1
     SSN                           Optional *1
     Congestion Level              Mandatory
     SMI                           Optional
     Info String                   Optional

   Note 1:    When the SSN is included, the SCON message corresponds to
              the SCCP N-STATE primitive.  When the SSN is not
              included, the SCON message corresponds to the SCCP

              N-PCSTATE primitive reporting signalling point or network
              congestion status.

3.4.5.  Destination User Part Unavailable (DUPU)

   The DUPU message is used by an SG to inform an ASP that a remote peer
   at an SS7 node is unavailable.

   The format for DUPU message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Affected Point Code                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010C          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           User/Cause                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                                                               \
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Affected Point Code           Mandatory *1
     User/Cause                    Mandatory
     Info String                   Optional

   Note 1:    The DUPU corresponds to the SCCP N-PCSTATE primitive.

3.4.6.  Destination Restricted (DRST)

   The DRST message is optionally sent from the SG to all concerned ASPs
   to indicate that the SG has determined that one or more destinations
   are now restricted from the point of view of the SG, or in response
   to a DAUD message if appropriate.  The SUA layer at the ASP is

   expected to send traffic to the affected destination via an alternate
   SG of equal priority, but only if such an alternate route exists and
   is available.  If the ASP currently considers the affected
   destination unavailable, the peer should be informed that traffic to
   the affected destination could be resumed.  In this case, the SUA
   layer should route the traffic through the SG initiating the DRST
   message.

   This message is optional for the SG to send and it is optional for
   the ASP to act on any information received in the message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Affected Point Code                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8003          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              SSN                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0112          |            Length = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Reserved                  |       SMI      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0004          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context               Optional
     Affected Point Code           Mandatory *1
     SSN                           Optional *1
     SMI                           Optional *1
     Info String                   Optional

   Note 1:    The Affected Point Code refers to the node to which
              become restricted or which has requested coordinated
              service outage.  When SSN is included in the message

              parameter, the DRST message corresponds to the SCCP
              N-COORD primitive.  If the SMI parameter is also included
              in the message, the DRST message corresponds to the
              N-COORD Request and N-COORD Indication primitives,
              otherwise, the DRST message correspondence to the N-COORD
              Response and N-COORD Confirm primitives.  The Affected
              Point Code can only contain one point code when SSN is
              present.  When SSN is not present, DRST corresponds to
              N-PCSTATE primitive.

3.5.  Application Server Process State Maintenance Messages

3.5.1.  ASP Up (UP)

   The ASP UP (UP) message is used to indicate to a remote SUA peer that
   the Adaptation layer is up and running.

    0                     1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0011       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0004       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     ASP Identifier                Optional *1
     Info String                   Optional

   Note 1:    ASP Identifier MUST be used where the IPSP/SGP cannot
              identify the ASP by provisioned address/port number
              information (e.g., where an ASP is resident on a Host
              using dynamic address/port number assignment).

3.5.2.  ASP Up Ack (UP ACK)

   The ASP UP Ack message is used to acknowledge an ASP-Up message
   received from a remote SUA peer.

    0                     1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0004       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /

   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Info String              Optional

3.5.3.  ASP Down (DOWN)

   The ASP Down (DOWN) message is used to indicate to a remote SUA peer
   that the adaptation layer is not running.

    0                     1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0004        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Info String         Optional

3.5.4.  ASP Down Ack (DOWN ACK)

   The ASP DOWN Ack message is used to acknowledge an ASP-Down message
   received from a remote SUA peer.

    0                     1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0004        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Info String         Optional

   Note:    ASP DOWN ACK will always be sent to acknowledge an ASP DOWN.

3.5.5.  Heartbeat (BEAT)

   The Heartbeat message is optionally used to ensure that the SUA peers
   are still available to each other.

   The format for the BEAT message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0009        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Heartbeat Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Heartbeat Data      Optional

3.5.6.  Heartbeat Ack (BEAT ACK)

   The Heartbeat ACK message is sent in response to a BEAT message.  A
   peer MUST send a BEAT ACK in response to a BEAT message.  It includes
   all the parameters of the received Heartbeat message, without any
   change.

   The format for the BEAT ACK message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0009        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Heartbeat Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Heartbeat Data      Optional

3.6.  ASP Traffic Maintenance Messages

3.6.1.  ASP Active (ACTIVE)

   The ASPAC message is sent by an ASP to indicate to a remote SUA peer
   that it is Active and ready to process signalling traffic for a
   particular Application Server.

   The format for the ACTIVE message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x000B        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Traffic Mode Type                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0006        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0110         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           TID Label                           |
   +-------------------------------+-------------------------------+
   |          Tag = 0x010F         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           DRN Label                           |
   +-------------------------------+-------------------------------+
   |           Tag = 0x0004        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Traffic Mode Type   Optional
     Routing Context     Optional
     TID Label           Optional
     DRN Label           Optional
     Info String         Optional

3.6.2.  ASP Active Ack (ACTIVE ACK)

   The ASPAC Ack message is used to acknowledge an ASP-Active message
   received from a remote SUA peer.

   The format for the ACTIVE Ack message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x000B        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Traffic Mode Type                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0006        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0004         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Traffic Mode Type   Optional
     Routing Context     Mandatory
     Info String         Optional

3.6.3.  ASP Inactive (INACTIVE)

   The INACTIVE message is sent by an ASP to indicate to a remote SUA
   peer that it is no longer processing signalling traffic within a
   particular Application Server.

   The format for the ASPIA message parameters is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0006        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0004        |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context     Optional
     INFO String         Optional

3.6.4.  ASP Inactive Ack (INACTIVE ACK)

   The INACTIVE Ack message is used to acknowledge an ASP-Inactive
   message received from a remote SUA peer.

   The format for the INACTIVE Ack message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0004         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          INFO String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Routing Context     Optional
     INFO String         Optional

3.7.  SUA Management Messages

   These messages are used for managing SUA and the representations of
   the SCCP subsystems in the SUA layer.

3.7.1.  Error (ERR)

   The ERR message is sent between two SUA peers to indicate an error
   situation.  The Diagnostic Information parameter is optional,
   possibly used for error logging and/or debugging.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x000C         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0012          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected PC 1                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Mask     |                 Affected PC n                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010D          |         Length = 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Network Appearance                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0007         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        Diagnostic Info                        /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameters
     Error Code                    Mandatory
     Routing Context               Mandatory *1
     Network Appearance            Mandatory *1
     Affected Point Code           Mandatory *1
     Diagnostic Information        Optional

   Note 1:    Only mandatory for specific error codes.

3.7.2.  Notify (NTFY)

   The Notify message used to provide an autonomous indication of SUA
   events to an SUA peer.

    0                     1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x000D         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Status                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0011       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0004         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The NTFY message contains the following parameters:

   Parameters
     Status                        Mandatory
     ASP Identifier                Optional *1
     Routing Context               Optional
     Info String                   Optional

   Note 1:    ASP Identifier MUST be used where the IPSP/SGP cannot
              identify the ASP by provisioned address/port number
              information (e.g., where an ASP is resident on a Host
              using dynamic address/port number assignment).

3.8.  Routing Key Management (RKM) Messages

3.8.1.  Registration Request (REG REQ)

   The REG REQ message is sent by an ASP to indicate to a remote SUA
   peer that it wishes to register one or more given Routing Keys with
   the remote peer.  Typically, an ASP would send this message to an
   SGP, and expects to receive a REG RSP message in return with an
   associated Routing Context value.

   The format for the REG REQ message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x010E         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                         Routing Key 1                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x010E         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                         Routing Key n                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Tag = 0x0109       |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Capabilities                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The REG REQ message contains the following parameters:

   Parameters
     Routing Key                   Mandatory *1
     ASP Capabilities              Optional

   Note 1:   One or more Routing Key parameters MAY be included in a
             single REG REQ message.

3.8.2.  Registration Response (REG RSP)

   The REG RSP message is sent by an SG to an ASP indicate the result of
   a previous REG REQ from an ASP.  It contains indications of
   success/failure for registration requests and returns a unique
   Routing Context value for successful registration requests, to be
   used in subsequent SUA Traffic Management protocol messages.

   The format for the REG RSP message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0014         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result 1                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0014         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Registration Result n                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The REG RSP message contains the following parameters:

   Parameters
     Registration Result           Mandatory *1

   Note 1:   One or more Registration Result parameters MAY be included
             in a single REG RSP message.  The number of results in a
             single REG RSP message can be anywhere from one to the
             total number of Routing Key parameters found in the
             corresponding REG REQ message.

3.8.3.  Deregistration Request (DEREG REQ)

   The DEREG REQ message is sent by an ASP to indicate to a remote SUA
   peer that it wishes to deregister a given Routing Key.  Typically, an
   ASP would send this message to an SGP, and expects to receive a DEREG
   RSP message in return with the associated Routing Context value.

   The format for the DEREG REQ message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0006            |           Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The DEREG REQ message contains the following parameters:

   Parameters
     Routing Context               Mandatory

3.8.4.  Deregistration Response (DEREG RSP)

   The DEREG RSP message is used as a response to the DEREG REQ message
   from a remote SUA peer.

   The format for the DEREG RSP message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0015         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Deregistration Result 1                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                              ...                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0015         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Deregistration Result n                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The DEREG RSP message contains the following parameters:

   Parameters
     Deregistration Result         Mandatory *1

   Note 1:    One or more Deregistration Result parameters MAY be
              included in one DEREG RSP message.  The number of results
              in a single DEREG RSP message can be anywhere from one to
              the total number of Routing Context parameters found in
              the corresponding DEREG REQ message.

3.9.  Common Parameters

   These TLV parameters are common across the different adaptation
   layers.

   Parameter Name                     Parameter ID
   ==============                     ============
   Reserved                             0x0000
   Not used in SUA                      0x0001
   Not used in SUA                      0x0002
   Not used in SUA                      0x0003
   Info String                          0x0004
   Not used in SUA                      0x0005
   Routing Context                      0x0006
   Diagnostic Info                      0x0007
   Not used in SUA                      0x0008
   Heartbeat Data                       0x0009
   Not Used in SUA                      0x000A
   Traffic Mode Type                    0x000B
   Error Code                           0x000C
   Status                               0x000D
   Not used in SUA                      0x000E
   Not used in SUA                      0x000F
   Not used in SUA                      0x0010
   ASP Identifier                       0x0011
   Affected Point Code                  0x0012
   Correlation ID                       0x0013
   Registration Result                  0x0014
   Deregistration Result                0x0015
   Registration Status                  0x0016
   Deregistration Status                0x0017
   Local Routing Key Identifier         0x0018

3.9.1.  Not Used

   Use of Parameter ID 0x0001 in SUA messages is not supported.

3.9.2.  Not Used

   Use of Parameter ID 0x0002 in SUA messages is not supported.

3.9.3.  Not Used

   Use of Parameter ID 0x0003 in SUA messages is not supported.

3.9.4.  Info String

   The optional INFO String parameter can carry any meaningful UTF-8
   [3629] character string along with the message.  Length of the INFO
   String parameter is from 0 to 255 octets.  No procedures are
   presently identified for its use but service providers may use the
   INFO String for debugging purposes.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0004         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                          Info String                          /

   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.9.5.  Not Used in SUA

   Use of Parameter ID 0x0005 in SUA messages is not supported.

3.9.6.  Routing Context

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Routing Context                         /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Routing Context parameter contains (a list of) 4-byte unsigned
   integers indexing the Application Server traffic that the sending ASP
   is configured/registered to receive.  There is a one-to-one
   relationship between an index entry and a Routing Key or AS Name.

   An Application Server Process may be configured to process traffic
   for more than one logical Application Server.  From the perspective
   of an ASP, a Routing Context defines a range of signalling traffic
   that the ASP is currently configured to receive from the SG.

   Additionally, the Routing Context parameter identifies the SS7
   network context for the message, for the purposes of logically
   separating the signalling traffic between the SGP and the Application
   Server Process over a common SCTP Association, when needed.  An
   example is where an SGP is logically partitioned to appear as an

   element in several different national SS7 networks.  It implicitly
   defines the SS7 Point Code format used, the SS7 Network Indicator
   value and SCCP protocol type/variant/version used within a separate
   SS7 network.  It also defines the network context for the PC and SSN
   values.  Where an SGP operates in the context of a single SS7
   network, or individual SCTP associations are dedicated to each SS7
   network context, this functionality is not needed.

   If the Routing Context parameter is present, it SHOULD be the first
   parameter in the message as it defines the format and/or
   interpretation of the parameters containing a PC or SSN value.

3.9.7.  Diagnostic Information

   The Diagnostic Information can be used to convey any information
   relevant to an error condition, to assist in the identification of
   the error condition.  In the case of an Adaptation Layer Identifier
   or Traffic Handling Mode, the Diagnostic Information includes the
   received parameter.  In the other cases, the Diagnostic information
   may be the first 40 bytes of the offending message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0007          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                     Diagnostic Information                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.9.8.  Not Used

   Parameter ID 0x0008 is not used in SUA.

3.9.9.  Heartbeat Data

   The sending node defines the Heartbeat Data field contents.  It may
   include a Heartbeat Sequence Number and/or Timestamp, or other
   implementation specific details.

   The receiver of a Heartbeat message does not process this field as it
   is only of significance to the sender.  The receiver echoes the
   content of the Heartbeat Data in a BEAT-Ack message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0009          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Heartbeat Data                          /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The data field can be used to store information in the heartbeat
   message useful to the sending node (e.g., the data field can contain
   a time stamp, a sequence number, etc.).

3.9.10.  Not Used

   Parameter ID 0x000A is not used in SUA.

3.9.11.  Traffic Mode Type

   The Traffic Mode Type parameter identifies the traffic mode of
   operation of the ASP within an AS.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x000B         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Traffic Mode Type                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Type are shown in the following table.

      1         Override
      2         Loadshare
      3         Broadcast

   Within a Routing Context, Override, Loadshare Types and Broadcast
   cannot be mixed.  The Override value indicates that the ASP is
   operating in Override mode, and the ASP wishes to take over all
   traffic for an Application Server (i.e., primary/backup operation),
   overriding any currently active ASP in the AS.  In Loadshare mode,
   the ASP wishes to share in the traffic distribution with any other
   currently active ASPs.  In Broadcast mode, the ASP wishes to receive
   the same traffic as any other currently active ASPs.  When there are
   insufficient ASPs, the sender may immediately move the ASP to Active.

3.9.12.  Error Code

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Tag =0x000C            |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Error Code                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Error Code parameter indicates the reason for the Error Message.
   The Error parameter value can be one of the following values:

      0x01      Invalid Version
      0x02      Not Used in SUA
      0x03      Unsupported Message Class
      0x04      Unsupported Message Type
      0x05      Unsupported Traffic Handling Mode
      0x06      Unexpected Message
      0x07      Protocol Error
      0x08      Not used in SUA
      0x09      Invalid Stream Identifier
      0x0a      Not used in SUA
      0x0b      Not used in SUA
      0x0c      Not used in SUA
      0x0d      Refused - Management Blocking
      0x0e      ASP Identifier Required
      0x0f      Invalid ASP Identifier
      0x10      Not Used in SUA
      0x11      Invalid Parameter Value
      0x12      Parameter Field Error
      0x13      Unexpected Parameter
      0x14      Destination Status Unknown
      0x15      Invalid Network Appearance
      0x16      Missing Parameter
      0x17      Not Used in SUA
      0x18      Not Used in SUA
      0x19      Invalid Routing Context
      0x1a      No Configured AS for ASP
      0x1b      Subsystem Status Unknown
      0x1c      Invalid loadsharing label

   The "Invalid Version" error is sent if a message was received with an
   invalid or unsupported version.  The Error message contains the
   supported version in the Common header.  The Error message could
   optionally provide the unsupported version in the Diagnostic
   information area.

   The "Unsupported Message Class" error is sent if a message with an
   unexpected or unsupported Message Class is received.

   The "Unsupported Message Type" error is sent if a message with an
   unexpected or unsupported Message Type is received.

   The "Unsupported Traffic Handling Mode" error is sent by a SGP if an
   ASP sends an ASP Active message with an unsupported Traffic Mode Type
   or a Traffic Mode Type that is inconsistent with the presently
   configured mode for the Application Server.  An example would be a
   case in which the SGP did not support loadsharing.

   The "Unexpected Message" error MAY be sent if a defined and
   recognized message is received that is not expected in the current
   state (in some cases the ASP may optionally silently discard the
   message and not send an Error message).  For example, silent discard
   is used by an ASP if it received a DATA message from an SGP while it
   was in the ASP-INACTIVE state.  If the Unexpected message contained
   Routing Context(s), the Routing Context(s) SHOULD be included in the
   Error message.

   The "Protocol Error" error is sent for any protocol anomaly (i.e.,
   reception of a parameter that is syntactically correct but unexpected
   in the current situation.

   The "Invalid Stream Identifier" error is sent if a message is
   received on an unexpected SCTP stream.

   The "Refused - Management Blocking" error is sent when an ASP Up or
   ASP Active message is received and the request is refused for
   management reasons (e.g., management lockout").  If this error is in
   response to an ASP Active message, the Routing Context(s) in the ASP
   Active message SHOULD be included in the Error message.

   The "ASP Identifier Required" is sent by a SGP in response to an ASP
   Up message that does not contain an ASP Identifier parameter when the
   SGP requires one.  The ASP SHOULD resend the ASP Up message with an
   ASP Identifier.

   The "Invalid ASP Identifier" is send by a SGP in response to an ASP
   Up message with an invalid ASP Identifier.

   The "Invalid Parameter Value" error is sent if a message is received
   with an invalid parameter value (e.g., a DUPU message was received
   with a Mask value other than "0".

   The "Parameter Field Error" would be sent if a message is received
   with a parameter having a wrong length field.

   The "Unexpected Parameter" error would be sent if a message contains
   an invalid parameter.

   The "Invalid Network Appearance" error is sent by a SGP if an ASP
   sends a message with an invalid (not configured) Network Appearance
   value.  For this error, the invalid (not configured) Network
   Appearance MUST be included in the Network Appearance parameter.

   The "Missing Parameter" error would be sent if a mandatory parameter
   were not included in a message.

   The "Invalid Routing Context" error would be sent by a SG if an ASP
   sends a message with an invalid (not configured) Routing Context
   value.  For this error, the invalid (not configured) Routing
   Context(s) MUST be included in the Routing Context parameter.

   The "No Configured AS for ASP" error is sent if a message is received
   from a peer without a Routing Context parameter and it is not known
   by configuration data, which Application Servers are referenced.

   The "Destination Status Unknown" Error MAY be sent if a DAUD is
   received at an SG inquiring of the availability or congestion status
   of a destination, and the SG does not wish to provide the status
   (e.g., the sender is not authorized to know the status).  For this
   error, the invalid or unauthorized Point Code(s) MUST be included
   along with the Network Appearance and Routing Context associated with
   the Point Code(s).

   The "Subsystem Status Unknown" Error MAY be sent if a DAUD is
   received at an SG inquiring of the availability or congestion status
   of a subsystem, and the SG does not wish to provide the status (e.g.,
   the sender is not authorized to know the status).  For this error,
   the invalid or unauthorized Point Code and Subsystem Number MUST be
   included along with the Network Appearance and Routing Context
   associated with the Point Code and Subsystem Number.

3.9.13.  Status

   The Status parameter identifies the type of the status that is being
   notified and the Status ID.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x000D         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Status Type           |            Status ID          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The valid values for Status Type (16 bit unsigned integer) are:

      1     Application Server state change (AS_State_Change)
      2     Other

   The Status ID parameter contains more detailed information for the
   notification, based on the value of the Status Type.

   If the Status Type is AS_STATE_CHANGE, then the Status ID (16 bit
   unsigned integer) values are:

      1    reserved
      2    Application Server Inactive (AS-Inactive)
      3    Application Server Active (AS-Active)
      4    Application Server Pending (AS-Pending)

   These notifications are sent from an SGP to an ASP upon a change in
   status of a particular Application Server.  The value reflects the
   new state of the Application Server.

   If the Status Type is "Other", then the following Status Information
   values are defined:

      1    Insufficient ASP resources active in AS
      2    Alternate ASP Active
      3    ASP failure

   These notifications are not based on the SGP reporting the state
   change of an ASP or AS.  In the Insufficient ASP Resources case, the
   SGP is indicating to an "Inactive" ASP(s) in the AS that another ASP
   is required to handle the load of the AS (Loadsharing mode or
   Broadcast mode).  For the Alternate ASP Active case, an ASP is
   informed when an alternate ASP transitions to the ASP-Active state in
   Override mode.

3.9.14.  Not Used in SUA

   Parameter ID 0x000E is not used in SUA.

3.9.15.  Not Used in SUA

   Parameter ID 0x000F is not used in SUA.

3.9.16.  Not Used in SUA

   Parameter ID 0x0010 is not used in SUA.

3.9.17.  ASP Identifier

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0011          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        ASP Identifier                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ASP Identifier field: 32-bits (unsigned integer)

   The ASP Identifier field contains a unique value that is locally
   significant among the ASPs that support an AS.  The SGP should save
   the ASP Identifier to be used, if necessary, with the Notify message
   (see Section 3.7.2).

3.9.18.  Affected Point Code

   The Affected Point Code Destinations parameter contains a list of
   Affected Point Code fields, each a three-octet parameter to allow for
   14-, 16- and 24-bit binary formatted SS7 Point Codes.  Affected Point
   Codes that are less than 24-bits are padded on the left to the 24-bit
   boundary.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0012         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Mask       |                 Affected PC 1                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             . . .                             /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The encoding is shown below for ANSI and ITU Point Code examples.

   ANSI 24-bit Point Code:

    0                   1                   2                   3-->
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |    Network    |    Cluster    |     Member    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |MSB-----------------------------------------LSB|

   ITU 14-bit Point Code:

    0                   1                   2                   3-->
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |0 0 0 0 0 0 0 0 0 0|Zone |     Region    | SP  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                        |MSB--------------------LSB|

   It is OPTIONAL for an implementation to generate an Affected Point
   Code parameter with more than on Affected PC but the implementation
   MUST accept and process an Affected Point Code parameter with more
   than one Affected PC.

   Mask: 8-bits

   The Mask parameter can be used to identify a contiguous range of
   Affected Destination Point Codes, independent of the point code
   format.  Identifying a contiguous range of Affected PCs may be useful
   when reception of an MTP3 management message or a linkset event
   simultaneously affects the availability status of a series of
   destinations at an SG.

   The Mask parameter is an integer representing a bit mask that can be
   applied to the related Affected PC field.  The bit mask identifies
   how many bits of the Affected PC field are significant and which are
   effectively "wild-carded".  For example, a mask of "8" indicates that
   the last eight bits of the PC is "wild-carded".  For an ANSI 24-bit
   Affected PC, this is equivalent to signalling that all PCs in an ANSI
   Cluster are unavailable.  A mask of "3" indicates that the last three
   bits of the PC is "wild-carded".  For a 14-bit ITU Affected PC, this
   is equivalent to signalling that an ITU Region is unavailable.

3.9.19.  Correlation ID

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0013         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Correlation ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Correlation ID is a 32-bit identifier that is attached to CLDT
   messages to indicate to a newly entering ASP in a Broadcast AS where
   in the traffic flow of CLDT messages the ASP is joining.  It is
   attached to the first CLDT message sent to an ASP by an SG after
   sending an ASP Active Ack or otherwise starting traffic to an ASP.
   The Correlation ID is only significant within a Routing Context.

   Implementation note: Correlation ID parameter can be used for
   features like Synchronisation of ASPs/SGPs in a Broadcast Mode AS/SG;
   avoid message duplication and mis-sequencing in case of failover of
   association from one ASP/SGP to other ASP/SGP etc.

3.9.20.  Registration Result

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0018         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Routing Key Identifier                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0016         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Registration Status                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Routing Context                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Routing Key Identifier contains the same TLV formatted parameter
   value as found in the matching Routing Key parameter in the REG REQ
   message.

   Routing Context contains the same TLV formatted Routing Context
   parameter for the associated Routing Key if the registration was
   successful.  It is set to "0" if the registration was not successful.

3.9.21.  Deregistration Result

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0006         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Routing Context                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0017         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Deregistration Status                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Routing Context: 32-bit integer

      Routing Context contains the Routing Context value of the matching
      Routing key to deregister, as found in the DEREG REQ message.

   Deregistration Status: 32-bit integer

      Deregistration Status parameter indicates the success or the
      reason for failure of the deregistration.

3.9.22.  Registration Status

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0016      |          Length = 8             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Registration Status                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Registration Status: 32-bits (unsigned integer)

      The Registration Status field indicates the success or the reason
      for failure of a registration request.

   Its values may be:
             0           Successfully Registered
             1           Error - Unknown
             2           Error - Invalid Destination Address
             3           Error - Invalid Network Appearance
             4           Error - Invalid Routing Key
             5           Error - Permission Denied
             6           Error - Cannot Support Unique Routing
             7           Error - Routing Key not Currently Provisioned

             8           Error - Insufficient Resources
             9           Error - Unsupported RK parameter Field
            10           Error - Unsupported/Invalid Traffic Mode Type
            11           Error - Routing Key Change Refused

3.9.23.  Deregistration Status

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0017      |          Length = 8             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Deregistration Status                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Deregistration Status: 32-bit integer

   The Deregistration Result Status field indicates the success or the
   reason for failure of the deregistration.

   Its values may be:

   0           Successfully Deregistered
   1           Error - Unknown
   2           Error - Invalid Routing Context
   3           Error - Permission Denied
   4           Error - Not Registered
   5           Error - ASP Currently Active for Routing Context

3.9.24.  Local Routing Key Identifier

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Tag = 0x0018        |        Length = 8             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Local Routing Key Identifier                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Local Routing Key Identifier field is a 32-bits unsigned integer.
   The Identifier value is assigned by the ASP and is used to correlate
   the response in a REG RSP message with the original registration
   request.  The Identifier value must remain unique until the REG RSP
   message is received.

3.10.  SUA-Specific parameters

   These TLV parameters are specific to the SUA protocol.

   Parameter Name                     Parameter ID
   ==============                     ============
   SS7 Hop Counter                      0x0101
   Source Address                       0x0102
   Destination Address                  0x0103
   Source Reference Number              0x0104
   Destination Reference Number         0x0105
   SCCP Cause                           0x0106
   Sequence Number                      0x0107
   Receive Sequence Number              0x0108
   ASP Capabilities                     0x0109
   Credit                               0x010A
   Data                                 0x010B
   User/Cause                           0x010C
   Network Appearance                   0x010D
   Routing Key                          0x010E
   DRN Label                            0x010F
   TID Label                            0x0110
   Address Range                        0x0111
   SMI                                  0x0112
   Importance                           0x0113
   Message Priority                     0x0114
   Protocol Class                       0x0115
   Sequence Control                     0x0116
   Segmentation                         0x0117
   Congestion Level                     0x0118

   Destination/Source Address Sub-Parameters
   ===========================================
   Global Title                         0x8001
   Point Code                           0x8002
   Subsystem Number                     0x8003
   IPv4 Address                         0x8004
   Hostname                             0x8005
   IPv6 Addresses                       0x8006

3.10.1.  SS7 Hop counter

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0101          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Reserved                         | SS7 Hop Count |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   SS7 Hop Counter (3.18/Q.713)

   The value of the SS7 Hop Counter is decremented with each global
   title translation and is in the range 15 to 1.

3.10.2.  Source Address

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0102         |      Parameter Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Routing Indicator        |       Address Indicator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Address parameter(s)                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The following combinations of address parameters are valid:

   -  Global Title (e.g., E.164 number) + optional PC and/or SSN, SSN
      may be zero, when routing is done on Global Title

   -  SSN (non-zero) + optional PC and/or Global Title, when routing is
      done on PC + SSN.  The PC is mandatory in the source address when
      sending from SGP to ASP, and in the destination address when
      sending from ASP to SGP to reach the SS7 SEP.

   -  Hostname + optional SSN, when routing is done by Hostname

   -  SSN (non-zero) and optional IP address (IPv4 or IPv6) when routing
      is done on IP address + SSN

3.10.2.1.  Routing Indicator

   The following values are valid for the routing indicator:

      Reserved                      0
      Route on Global Title         1
      Route on SSN + PC             2
      Route on Hostname             3
      Route on SSN + IP Address     4

   The routing indicator determines which address parameters need to be
   present in the address parameters field.

3.10.2.2.  Address Indicator

   This parameter is needed for interworking with SS7 networks.  The
   address indicator specifies what address parameters are actually
   received in the SCCP address from the SS7 network, or are to be
   populated in the SCCP address when the message is sent into the SS7
   network.  The value of the routing indicator needs to be taken into
   account.  It is used in the ASP to SG direction.  For example, the PC
   parameter is present in the destination address of the CLDT sent from
   ASP->SG, but bit 2 is set to "0" meaning "do not populate this in the
   SCCP called party address".  The effect is that the SG only uses the
   PC to populate the MTP routing label DPC field, but does not include
   it in the SCCP called party address.

   In the SG->ASP direction, the source address PC parameter is present
   (PC of SS7 SEP).  However, this may have been populated from the OPC
   in the received MTP routing label, not from the PC field in the SCCP
   calling party address.  In this case, bit 2 = "0" denotes that.  The
   AI gives further instructions to the SG how and when to populate the
   SCCP addresses; in the SG->ASP direction, the AI gives information to
   the ASP as to what was actually present in the received SCCP
   addresses.

   The address indicator is coded as follows:

   Bit 1 is used to indicate inclusion of the SSN

   0         Do not include SSN when optional
    1         Include SSN

   Bit 2 is used to indicate inclusion of the PC

   0         Do not include PC, regardless of the routing indicator
             value
    1        Include PC

   Bit 3 is used to indicate inclusion of the Global Title

   0         Do not include GT when optional (routing indicator /= 1)
    1        Include GT

   The remaining bits are spare and SHOULD be coded zero, and MUST be
   ignored by the receiver.

3.10.2.3.  Global Title

   0                 1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8001          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Reserved                       |      GTI      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   No. Digits  | Trans. type   |    Num. Plan  | Nature of Add |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                         Global Title Digits                   /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Number of Digits:

   This is the number of digits contained in the Global Title.

   GTI (Global Title Indicator, defined in chapter 3.4.2.3 of Q.713).

   0000     Invalid
   0001     Nature of Address is taken over. It is implicitly assumed
             that the Translation Type = Unknown and Numbering Plan =
             E.164 (value 1).
   0010     This is most commonly used in North American networks.
             The Translation Type implicitly determines Nature of
             Address and Numbering Plan.  This data can be configured
             in the SG.  The number of digits is always even and
             determined by the SCCP address length.
   0011     Numbering Plan and Translation Type are taken over.  It is
             implicitly assumed that the Nature of Address = Unknown.
   0100     This format is used in international networks and most
             commonly in networks outside North America.  All
             information to populate the source address is present in
             the SCCP Address.

   Translation type:

   0              Unknown
   1 - 63         International services
   64 - 127       Spare
   128 - 254      National network specific
   255            Reserved

   Numbering Plan:

   0         unknown
   1         ISDN/telephony numbering plan (Recommendations E.163 and
             E.164)
   2         generic numbering plan
   3         data numbering plan (Recommendation X.121)
   4         telex numbering plan (Recommendation F.69)
   5         maritime mobile numbering plan (Recommendations E.210,
             E.211)
   6         land mobile numbering plan (Recommendation E.212)
   7         ISDN/mobile numbering plan (Recommendation E.214)
   8 - 13    spare
   14        private network or network-specific numbering plan
   15 - 126  spare
   127       reserved.

   Nature of Address:

   0         unknown
   1         subscriber number
   2         reserved for national use
   3         national significant number
   4         international number
   5 - 255   Spare

   Global Title:

   Octets contain a number of address signals and possibly filler as
   shown:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |2 addr.|1 addr.|4 addr.|3 addr.|6 addr.|5 addr.|8 addr.|7 addr.|
   |  sig. | sig.  |  sig. | sig.  |  sig. | sig.  |  sig. | sig.  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        .............          |filler |N addr.|   filler      |
   |                               |if req | sig.  |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All filler bits SHOULD be set to 0.

   Address signals to be coded as defined in ITU-T Q.713 Section
   3.4.2.3.1.

3.10.2.4.  Point Code

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8002          |            Length = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Point Code                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   See chapter 3.9.18 Affected Point Code for the layout of the Point
   Code field.

3.10.2.5.  Subsystem Number

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8003          |            Length = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Reserved                      |   SSN value   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The internationally standardized SSN values are described in chapter
   3.4.2.2 of Q.713.

3.10.2.6.  IP Addresses

   The IP address formats can use different tags.  It should be noted
   that if the source address is in a certain IP version, the
   destination address should also be in the same IP version.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Tag = 0x8004/0x8006      |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                        IPv4 or IPv6 Address                   /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Note:    The tag value 0x8004 is for an IPv4 address and 0x8006 is
            for IPv6.

3.10.2.7.  Hostname

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x8005          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                           Host Name                           /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Host Name: variable length

   This field contains a host name in "host name syntax" per RFC 1123
   Section 2.1 [1123].  The method for resolving the host name is out of
   scope for this document.

   Note:    At least one null terminator is included in the Host Name
            string and must be included in the length.

3.10.3.  Destination Address

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0103         |      Parameter Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Routing Indicator        |       Address Indicator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                       Address Parameter(s)                    /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of this parameter is identical to the Source Address
   parameter.

3.10.4.  Source Reference Number

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0104         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source Reference Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The source reference number is a 4 octet long integer.  This is
   allocated by the source SUA instance.

3.10.5.  Destination Reference Number

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0105         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Destination Reference Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The destination reference number is a 4 octet long integer.  This is
   allocated by the destination SUA instance.

3.10.6.  SCCP Cause

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0106          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reserved              |   Cause Type  |  Cause Value  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter bundles the SCCP parameters Release cause, Return
   cause, Reset cause, Error cause and Refusal cause.

   Cause Type can have the following values:

      Return Cause          0x1
      Refusal Cause         0x2
      Release Cause         0x3
      Reset Cause           0x4
      Error Cause           0x5

   Cause Value contains the specific cause value.  Below gives examples
   for ITU SCCP values.  ANSI references can be found in ANSI T1.112.3

   Cause value in        Correspondence with Reference
   SUA message           SCCP parameter
   ------------------    -----------------   ---------
   CLDR                  Return Cause        ITU-T Q.713 Chap 3.12
   COREF                 Refusal Cause       ITU-T Q.713 Chap 3.15
   RELRE                 Release Cause       ITU-T Q.713 Chap 3.11
   RESRE                 Reset Cause         ITU-T Q.713 Chap 3.13
   ERR                   Error Cause         ITU-T Q.713 Chap 3.14

3.10.7.  Sequence Number

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0107         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reserved              |  Rec Seq Num|M| Sent Seq Num  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter is used to indicate whether "more" data will follow in
   subsequent CODT messages, and/or to number each CODT message
   sequentially for the purpose of flow control.  It contains the
   received as well as the sent sequence number, P(R) and P(S) in Q.713,
   chapters 3.7 and 3.9.

   As such it can also be used to acknowledge the receipt of data
   transfers from the peer in case of protocol class 3.

   Sent Sequence Number is one octet and is coded as follows:

      Bits 2-8 are used to indicate the Send Sequence Number P(S).
      Bit 1 (LSB) of octet 1 is spare.

   Received Sequence Number is one octet, and is coded as follows:

      Bits 2-8 are used to indicate the Received Sequence Number
      P(R).
      Bit 1 (LSB) is used for the more data indication, as follows:

      0         no more data
      1         more data

3.10.8.  Receive Sequence Number

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0108         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Reserved                   |  Rec Seq Num  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter is used exclusively for protocol class 3 in the data
   acknowledgement message to indicate the lower edge of the receiving
   window.  See Q.713, chapter 3.9.

   It is a 1 octet long integer coded as follows:

      Bits 8-2 are used to indicate the Received Sequence Number P(R).

      Bit 1 is spare.

3.10.9.  ASP Capabilities

   This parameter is used so that the ASP can report its capabilities
   regarding SUA for supporting different protocol classes and
   interworking scenarios.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0109         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reserved              |0 0 0 0|a|b|c|d| Interworking  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flags

     a - Protocol Class 3
     b - Protocol Class 2
     c - Protocol Class 1
     d - Protocol Class 0

   It is mandatory to support at least Protocol Class 0.

   Interworking

   Values

     0x0 indicates no interworking with SS7 Networks.
     0x1 indicates IP Signalling Endpoint (ASP), interworking with SS7
        networks.
     0x2 indicates Signalling Gateway.
     0x3 indicates relay node support.

3.10.10.  Credit

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x010A         |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Reserved                     |     Credit     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The length of the credit field is one octet.  See ITU-T Q.713 Chapter
   3.10.  The parameter is used for protocol class 3 exclusively.

3.10.11.  Data

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x010b         |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                             Data                              /
   \                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Data parameter field contains the SS7 SCCP-User application
   message, for example an INAP/TCAP message.

3.10.12.  User/Cause

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010c          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Cause             |            User               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   "User" is coded to that SCCP's SI value.  There may be several SCCP's
   at a given point code, each with different SI values, although
   normally there is only one with SI = 3.

   Cause may take the following values

   0    remote SCCP unavailable, reason unknown;
   1    remote SCCP unequipped;
   2    remote SCCP inaccessible;

3.10.13.  Network Appearance

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x010D          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Network Appearance                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Network Appearance field: 32-bits (unsigned integer)

      The Network Appearance field identifies the SS7 network context
      for the Routing Key.  The Network Appearance value is of local
      significance only, coordinated between the SG and ASP.  Therefore,
      in the case where the ASP is connected to more than one SG, the
      same SS7 Network context may be identified by different Network
      Appearance values depending upon to which SG the ASP is
      registering.

      In the Routing Key, the Network Appearance identifies the SS7
      Point Code and Global Title Translation Type format used, and the
      SCCP and possibly the SCCP-User protocol (type, variant and
      version) used within the specific SS7 network.

3.10.14.  Routing Key

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x010E          |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Tag = 0x0018          |        Length = 8             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Local Routing Key Identifier                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      \                         Key parameter(s)                      \
      /                                                               /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Local Routing Key Identifier field: 32-bits (unsigned integer)

      Key field: variable

   The Key field contains the following parameters:

      Parameter
         Traffic Mode Type          Optional
         Network Appearance         Optional *1
         Source Address             Optional
         Destination Address        Optional
         Address Range              Optional

   Note 1:    The Network Appearance parameter must be included in the
              Routing Key when the ASP is able to register in multiple
              SS7 Network contexts.

3.10.15.  DRN Label

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x010F         |            Length = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     start     |      end      |         label value           |
   +---------------+---------------+-------------------------------+

   The Start parameter is the start position of label, between 0 (LSB)
   and 23 (MSB).

   The End parameter is the end position of label, between 0 (LSB) and
   23 (MSB).

   Label value is a 16-bit integer, which is unique across an AS.

3.10.16.  TID Label

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Tag = 0x0110         |            Length = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     start     |      end      |         label value           |
   +---------------+---------------+-------------------------------+

   The Start parameter is the start position of label, between 0 (LSB)
   and 31 (MSB).

   The End parameter is the end position of label, between 0 (LSB) and
   31 (MSB).

   Label value is a 16-bit integer, which is unique across an AS.

3.10.17.  Address Range

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0111          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \                       Address parameter(s)                    \
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Address field:

   The Address field the following parameters:

   Parameter
     Source Address              Optional *1
     Destination Address         Optional *1

   Note 1:    The Address field must contain pairs of Source Addresses
              or pairs of Destination Addresses but MUST NOT mix Source
              Addresses with Destination Addresses in the same Address
              field.

3.10.18.  SMI

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0112          |            Length = 8         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Reserved                   |      SMI      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Subsystem Multiplicity Indicator (SMI) can have the following
   values:

   0x00       Reserved/Unknown
   0x01       Solitary
   0x02       Duplicated
   0x03       Triplicated
   0x04       Quadruplicated
   0xff       Unspecified

3.10.19.  Importance

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0113          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Reserved                       |   Importance  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Importance (3.19/Q.713)

   Possible values of the Importance Parameter are between 0 and 7,
   where the value of 0 indicates the least important and 7 indicates
   the most important.

3.10.20.  Message Priority (or Priority)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0114          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Reserved                         |  Msg Priority |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Priority

   Priority value ranges from 0 to 3.  If the Priority value has not
   been specified by the SCCP user, it should be set to 0xFF.  The SG
   MAY take the priority into account for determining the MTP message
   priority.  In the all-IP case, this parameter MAY be used.

   The Message Priority parameter is optional in the CLDT, CLDR, CORE,
   COAK and CODT messages.  However, for networks, which support Message
   Priority (e.g., ANSI), this parameter MUST be included but it is not
   required for those which don't (e.g., International).

3.10.21.  Protocol Class

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0115          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Reserved                         |  Protocol Cl. |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Protocol class (3.6/Q.713)

   Bits 1-2 indicate the protocol class.

      Value     Description
        0       Class 0 (connectionless service)
        1       Class 1 (connectionless service)
        2       Class 2 (connection-oriented service)
        3       Class 3 (connection-oriented service)

   Bit 8 indicates the use of the return on error procedure.

       Value     Description
        0x0      No special options
        0x1      Return message on error

   Bits 3-7 are spare and SHOULD be coded zero, and MUST be
   ignored by the receiver.

3.10.22.  Sequence Control

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0116          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence  Control         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Control (6.2.2.2.2/Q.711)

   The field is coded with the value of the sequence control parameter
   associated with a group of messages and are chosen so as to ensure
   proper loadsharing of message groups over SLS values while ensuring
   that sequence control values within message groups have the sequence
   control value coded with the same value as the initial message of the
   message group.

3.10.23.  Segmentation

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0117          |            Length = 32        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | first/remain  |             Segmentation Reference            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The first/remaining segments field is formatted as follows: bit 8
   (MSB): indicates whether this is the first segment (1) or not (0)

   bits 1-7: indicate the number of remaining segments, value between 0
   and 15

   The field would thus be coded 1000 0000 (first, no remaining
   segments) for a unsegmented CLDT.

   The segmentation reference field is a 3 byte integer, assigned by the
   ASP.

3.10.24.  Congestion Level

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Tag = 0x0118          |             Length = 8        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Congestion Level                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Congestion Level field: 8-bits (unsigned integer)

   The Congestion Level field contains the level at which congestion has
   occurred.

   When the Congestion Level parameter is included in a SCON message
   that corresponds to an N-PCSTATE primitive, the Congestion Level
   field indicates the MTP congestion level experienced by the local or
   affected signalling point as indicated by the Affected Point Code(s)
   also in the SCON message.  In this case, valid values for the
   Congestion Level field are as follows:

      0  No Congestion or Undefined
      1  Congestion Level 1
      2  Congestion Level 2
      3  Congestion Level 3

   When the Congestion Level parameter is included in a SCON message
   that corresponds to an N-STATE primitive, the Congestion Level field
   indicates the SCCP restricted importance level experienced by the
   local or affected subsystem as indicated by the Affected Point Code
   and Subsystem Number also in the SCON message. In this case, valid
   values for the Congestion Level field range from 0 to 7, where 0
   indicates the least congested and 7 indicates the most congested
   subsystem.

4.  Procedures

   The SUA layer needs to respond to various local primitives it
   receives from other layers as well as the messages that it receives
   from the peer SUA layer.  This section describes the SUA procedures
   in response to these events.

4.1.  Procedures to Support the SUA-User Layer

4.1.1.  Receipt of Primitives from SCCP

   When an SCCP Subsystem Management (SCMG) message is received from the
   SS7 network, the SGP needs to determine whether there are concerned
   Application Servers interested in subsystem status changes.  The SUA
   management function is informed with the N-State or N-Coord primitive
   upon which it formats and transfers the applicable SNMM message to
   the list of concerned ASPs using stream ID "0".

   When MTP-3 Management indications are received (MTP-PAUSE, MTP-
   RESUME, MTP-STATUS), SCCP Subsystem Management determines whether
   there are concerned local SCCP-users.  When these local SCCP-users
   are in fact Application Servers, serviced by ASPs, SUA management is
   informed with the N-PCSTATE indication primitive upon which it
   formats and transfers the applicable SNM message (DUNA, DAVA, DRST or
   SCON) to the list of concerned ASPs using stream ID "0".

   The SUA message distribution function determines the Application
   Server (AS) based on comparing the information in the N-UNITDATA
   request primitive with a provisioned Routing Key.

   From the list of ASPs within the AS table, an ASP in the ASP-ACTIVE
   state is selected and a DATA message is constructed and issued on the
   corresponding SCTP association.  If more than one ASP is in the ASP-
   ACTIVE state (i.e., traffic is to be load-shared across more than one
   ASP), one of the ASPs in the ASP_ACTIVE state is selected from the
   list.  If the ASPs are in Broadcast Mode, all active ASPs will be
   selected and the message sent to each of the active ASPs.  The
   selection algorithm is implementation dependent but could, for
   example, be round robin or based on the SLS.  The appropriate

   selection algorithm must be chosen carefully as it is dependent on
   application assumptions and understanding of the degree of state
   coordination between the ASP_ACTIVE ASPs in the AS.

   In addition, the message needs to be sent on the appropriate SCTP
   stream, again taking care to meet the message sequencing needs of the
   signalling application.  DATA messages MUST be sent on an SCTP stream
   other than stream '0' when there is more than one stream.

   When there is no Routing Key match, or only a partial match, for an
   incoming SS7 message, a default treatment MAY be specified.  Possible
   solutions are to provide a default Application Server at the SGP that
   directs all unallocated traffic to a (set of) default ASP(s), or to
   drop the message and provide a notification to Layer Management in an
   M-ERROR indication primitive.  The treatment of unallocated traffic
   is implementation dependent.

4.2.  Receipt of Primitives from the Layer Management

   On receiving primitives from the local Layer Management, the SUA
   layer will take the requested action and provide an appropriate
   response primitive to Layer Management.

   An M-SCTP_ESTABLISH request primitive from Layer Management at an ASP
   or IPSP will initiate the establishment of an SCTP association.  The
   SUA layer will attempt to establish an SCTP association with the
   remote SUA peer by sending an SCTP-ASSOCIATE primitive to the local
   SCTP layer.

   When an SCTP association has been successfully established, the SCTP
   will send an SCTP-COMMUNICATION_UP notification primitive to the
   local SUA layer.  At the ASP or IPSP that initiated the request, the
   SUA layer will send an M-SCTP_ESTABLISH confirm primitive to Layer
   Management when the association setup is complete.  At the peer SUA
   layer, an M-SCTP_ESTABLISH indication primitive is sent to Layer
   Management upon successful completion of an incoming SCTP association
   setup.

   An M-SCTP_RELEASE request primitive from Layer Management initiates
   the shutdown of an SCTP association.  The SUA layer accomplishes a
   graceful shutdown of the SCTP association by sending an SCTP-SHUTDOWN
   primitive to the SCTP layer.

   When the graceful shutdown of the SCTP association has been
   accomplished, the SCTP layer returns an SCTP-SHUTDOWN_COMPLETE
   notification primitive to the local SUA layer.  At the SUA Layer that
   initiated the request, the SUA layer will send an M-SCTP_RELEASE
   confirm primitive to Layer Management when the association shutdown

   is complete.   At the peer SUA Layer, an M-SCTP_RELEASE indication
   primitive is sent to Layer Management upon abort or successful
   shutdown of an SCTP association.

   An M-SCTP_STATUS request primitive supports a Layer Management query
   of the local status of a particular SCTP association.  The SUA layer
   simply maps the M-SCTP_STATUS request primitive to an SCTP-STATUS
   primitive to the SCTP layer.  When the SCTP responds, the SUA layer
   maps the association status information to an M-SCTP_STATUS confirm
   primitive.  No peer protocol is invoked.

   Similar LM-to-SUA-to-SCTP and/or SCTP-to-SUA-to-LM primitive mappings
   can be described for the various other SCTP Upper Layer primitives in
   RFC 2960 [2960] such as INITIALIZE, SET PRIMARY, CHANGE HEARTBEAT,
   REQUEST HEARTBEAT, GET SRTT REPORT, SET FAILURE THRESHOLD, SET
   PROTOCOL PARAMETERS, DESTROY SCTP INSTANCE, SEND FAILURE, AND NETWORK
   STATUS CHANGE.  Alternatively, these SCTP Upper Layer primitives (and
   Status as well) can be considered for modeling purposes as a Layer
   Management interaction directly with the SCTP Layer.

   M-NOTIFY indication and M-ERROR indication primitives indicate to
   Layer Management the notification or error information contained in a
   received SUA Notify or Error message respectively.  These indications
   can also be generated based on local SUA events.

   An M-ASP_STATUS request primitive supports a Layer Management query
   of the status of a particular local or remote ASP.  The SUA layer
   responds with the status in an M-ASP_STATUS confirm primitive.  No
   SUA peer protocol is invoked.  An M-AS_STATUS request supports a
   Layer Management query of the status of a particular AS.  The SUA
   responds with an M-AS_STATUS confirm primitive.  No SUA peer protocol
   is invoked.

   M-ASP_UP request, M-ASP_DOWN request, M-ASP_ACTIVE request and M-
   ASP_INACTIVE request primitives allow Layer Management at an ASP to
   initiate state changes.  Upon successful completion, a corresponding
   confirm primitive is provided by the SUA layer to Layer Management.
   If an invocation is unsuccessful, an Error indication primitive is
   provided in the primitive.  These requests result in outgoing ASP Up,
   ASP Down, ASP Active and ASP Inactive messages to the remote SUA peer
   at an SGP or IPSP.

4.2.1.  Receipt of SUA Peer Management Messages

   Upon successful state changes resulting from reception of ASP Up, ASP
   Down, ASP Active and ASP Inactive messages from a peer SUA, the SUA
   layer MAY invoke corresponding M-ASP_UP, M-ASP_DOWN, M-ASP_ACTIVE and
   M-ASP_INACTIVE, M-AS_ACTIVE, M-AS_INACTIVE, and M-AS_DOWN indication
   primitives to the local Layer Management.

   M-NOTIFY indication and M-ERROR indication primitives indicate to
   Layer Management the notification or error information contained in a
   received SUA Notify or Error message.  These indications can also be
   generated based on local SUA events.

   All non-Transfer and non-SSNM messages, except BEAT and BEAT Ack,
   SHOULD be sent with sequenced delivery to ensure ordering.  All non-
   Transfer messages, with the exception of ASPTM, BEAT and BEAT Ack
   messages SHOULD be sent on SCTP stream '0'.  ASPTM messages MAY be
   sent on one of the streams used to carry data traffic related to the
   Routing Context(s), to minimize possible message loss.  BEAT and BEAT
   Ack messages MAY be sent using out-of-order delivery, and MAY be sent
   on any stream.

4.3.  AS and ASP State Maintenance

   The SUA layer on the SGP maintains the state of each remote ASP, in
   each Application Server that the ASP is configured to receive
   traffic, as input to the SUA message distribution function.
   Similarly, where IPSPs use SUA in a point-to-point fashion, the SUA
   layer in an IPSP maintains the state of remote IPSPs.

   Two IPSP models are defined with regards to the number of messages
   that are needed to a IPSP state change.  They are defined as follows:

   1. IPSP Single Exchange (SE) model.  Only a single exchange of ASPTM
      or ASPSM messages is needed to change the IPSP state. This means
      that a set of request from one end and acknowledge from the other
      will be enough.

   2. IPSP Double Exchange (DE) model.  Both IPSPs have to send request
      messages and both IPSPs have to acknowledge the request messages
      from the other end.  This results in a double exchange of ASPTM
      and ASPSM message, one from each end.  This configuration supports
      dynamic routing key configuration by using RKM messages in the
      same way as ASP-SGP scenario.

   To ensure interoperability, an SUA implementation supporting IPSP
   communication MUST support IPSP SE model and MAY implement IPSP DE
   model.

   In section 4.3.1: ASP/IPSP States, only the SGP-ASP and the IPSP SE
   scenarios are described.  For the IPSP DE model, both IPSPs MUST
   follow the SGP side of the SGP-ASP procedures.

   In section 4.3.2, only the SGP-ASP scenario is described.  All of the
   procedures referring to an AS served by ASPs are also applicable to
   ASs served by IPSPs.

   In section 4.3.3, only the Management procedures for the SGP-ASP
   scenario are described.  The corresponding Management procedures for
   IPSPs are directly inferred.

   The remaining sections contain specific IPSP Considerations
   subsections.

4.3.1.  ASP States

   The state of each remote ASP/IPSP, in each AS that it is configured
   to operate, is maintained in the peer SUA layer (i.e., in the SGP or
   peer IPSP, respectively).  The state of a particular ASP/IPSP in a
   particular AS changes due to events.  The events include:

   * Reception of messages from the peer SUA layer at the ASP/IPSP;
   * Reception of some messages from the peer SUA layer at other
     ASPs/IPSPs in the AS (e.g., ASP Active message indicating
     "Override");
   * Reception of indications from the SCTP layer; or
   * Local Management intervention.

   The ASP/IPSP state transition diagram is shown in Figure 1.  The
   possible states of an ASP/IPSP are:

   ASP-DOWN: The remote SUA peer at the ASP/IPSP is unavailable and/or
   the related SCTP association is down.  Initially all ASPs/IPSPs will
   be in this state.  An ASP/IPSP in this state SHOULD NOT be sent any
   SUA messages, with the exception of Heartbeat, ASP Down Ack and Error
   messages.

   ASP-INACTIVE: The remote SUA peer at the ASP/IPSP is available (and
   the related SCTP association is up) but application traffic is
   stopped.  In this state the ASP/IPSP SHOULD NOT be sent any DATA or
   SSNM messages for the AS for which the ASP/IPSP is inactive.

   ASP-ACTIVE: The remote SUA peer at the ASP/IPSP is available and
   application traffic is active (for a particular Routing Context or
   set of Routing Contexts).

   Figure 1: ASP/IPSP State Transition Diagram, per AS

                                      +--------------+
                                      |              |
               +----------------------|  ASP-ACTIVE  |
               |   Other ASP/ +-------|              |
               |   IPSP in AS |       +--------------+
               |   Overrides  |           ^     |
               |              |    ASPAC/ |     | ASPIA/
               |              |[ASPAC-Ack]|     | [ASPIA-Ack]
               |              |           |     v
               |              |       +--------------+
               |              |       |              |
               |              +------>| ASP-INACTIVE |
               |                      |              |
               |                      +--------------+
               |                          ^       |
        ASPDN/ |                          |     | ASPDN /
   [ASPDN-Ack/]|                   ASPUP/ |     | [ASPDN-Ack /]
     SCTP CDI/ |              [ASPUP-Ack] |     | SCTP CDI/
     SCTP RI   |                          |     | SCTP RI
               |                          |     v
               |                      +--------------+
               |                      |              |
               +--------------------->|   ASP-DOWN   |
                                      |              |
                                      +--------------+

   The transitions in brackets are just valid for the IPSP SE model
   communication while the rest are valid for both ASPs and IPSPs.

   SCTP CDI: The SCTP CDI denotes the local SCTP layer's Communication
   Down Indication to the Upper Layer Protocol (SUA) on an SGP.  The
   local SCTP layer will send this indication when it detects the loss
   of connectivity to the ASP's peer SCTP layer.  SCTP CDI is understood
   as either a SHUTDOWN_COMPLETE notification or COMMUNICATION_LOST
   notification from the SCTP layer.

   SCTP RI: The local SCTP layer's Restart indication to the upper layer
   protocol (SUA) on an SG.  The local SCTP will send this indication
   when it detects a restart from the ASP's peer SCTP layer.

4.3.2.  AS States

   The state of the AS is maintained in the SUA layer on the SGP.  The
   state of an AS changes due to events.  These events include:

      * ASP state transitions
      * Recovery timer triggers

   The possible states of an AS are:

   AS-DOWN:     The Application Server is unavailable.  This state
                implies that all related ASPs are in the ASP-DOWN state
                for this AS.  Initially the AS will be in this state.
                An Application Server is in the AS-DOWN state before it
                can be removed from a configuration.

   AS-INACTIVE: The Application Server is available but no application
                traffic is active (i.e., one or more related ASPs are in
                the ASP-INACTIVE state, but none in the ASP-ACTIVE
                state).  The recovery timer T(r) is not running or has
                expired.

   AS-ACTIVE :  The Application Server is available and application
                traffic is active.  This state implies that at least one
                ASP is in the ASP-ACTIVE state.

   AS-PENDING:  An active ASP has transitioned to ASP-INACTIVE or ASP-
                DOWN and it was the last remaining active ASP in the AS.
                A recovery timer T(r) SHOULD be started and all incoming
                signalling messages SHOULD be queued by the SGP.  If an
                ASP becomes ASP-ACTIVE before T(r) expires, the AS is
                moved to the AS-ACTIVE state and all the queued messages
                will be sent to the ASP.

   If T(r) expires before an ASP becomes ASP-ACTIVE, and the SGP has no
   alternative, the SGP may stop queueing messages and discard all
   previously queued messages.  The AS will move to the AS-INACTIVE
   state if at least one ASP is in ASP-INACTIVE state, otherwise it will
   move to AS-DOWN state.

   Figure 2 shows an example AS state machine for the case where the
   AS/ASP data is provisioned.  For other cases where the AS/ASP
   configuration data is created dynamically, there would be differences
   in the state machine, especially at creation of the AS.

   For example, where the AS/ASP configuration data is not created until
   Registration of the first ASP, the AS-INACTIVE state is entered
   directly upon the first successful REG REQ from an ASP.  Another
   example is where the AS/ASP configuration data is not created until
   the first ASP successfully enters the ASP-ACTIVE state.  In this case
   the AS-ACTIVE state is entered directly.

                    Figure 2: AS State Transition Diagram

        +----------+   one ASP trans to ACTIVE   +-------------+
        |    AS-   |---------------------------->|     AS-     |
        | INACTIVE |                             |   ACTIVE    |
        |          |<---                         |             |
        +----------+    \                        +-------------+
           ^   |         \ Tr Expiry,                ^    |
           |   |          \ at least one             |    |
           |   |           \ ASP in ASP-INACTIVE     |    |
           |   |            \                        |    |
           |   |             \                       |    |
           |   |              \                      |    |
   one ASP |   | all ASP       \            one ASP  |    | Last ACTIVE
   trans   |   | trans to       \           trans to |    | ASP trans to
   to      |   | ASP-DOWN        -------\   ASP-     |    | ASP-INACTIVE
   ASP-    |   |                         \  ACTIVE   |    | or ASP-DOWN
   INACTIVE|   |                          \          |    | (start Tr)
           |   |                           \         |    |
           |   |                            \        |    |
           |   v                             \       |    v
        +----------+                          \  +-------------+
        |          |                           --|             |
        | AS-DOWN  |                             | AS-PENDING  |
        |          |                             |  (queueing) |
        |          |<----------------------------|             |
        +----------+    Tr Expiry and no ASP     +-------------+
                        in ASP-INACTIVE state

       Tr = Recovery Timer

4.3.2.1.  IPSP Considerations

   The AS state diagram for the AS-SG case is applicable for IPSP
   communication.

4.3.3.  SUA Management Procedures for Primitives

   Before the establishment of an SCTP association the ASP state at both
   the SGP and ASP is assumed to be in the state ASP-DOWN.

   Once the SCTP association is established (see Section 4.2.1) and
   assuming that the local SUA-User is ready, the local SUA ASP
   Maintenance (ASPM) function will initiate the relevant procedures,
   using the ASP Up/ASP Down/ASP Active/ASP Inactive messages to convey
   the ASP state to the SGP (see Section 4.3.4).

   If the SUA layer subsequently receives an SCTP-COMMUNICATION_DOWN or
   SCTP-RESTART indication primitive from the underlying SCTP layer, it
   will inform the Layer Management by invoking the M-SCTP_STATUS
   indication primitive.  The state of the ASP will be moved to ASP-
   DOWN.

   In the case of SCTP-COMMUNICATION_DOWN, the SCTP client MAY try to
   reestablish the SCTP association.  This MAY be done by the SUA layer
   automatically, or Layer Management MAY reestablish using the M-
   SCTP_ESTABLISH request primitive.

   In the case of an SCTP-RESTART indication at an ASP, the ASP is now
   considered by its SUA peer to be in the ASP-DOWN state.  The ASP, if
   it is to recover, must begin any recovery with the ASP-Up procedure.

4.3.4.  ASPM Procedures for Peer-to-Peer Messages

4.3.4.1.  ASP Up Procedures

   After an ASP has successfully established an SCTP association to an
   SGP, the SGP waits for the ASP to send an ASP Up message, indicating
   that the ASP SUA peer is available.  The ASP is always the initiator
   of the ASP Up message.  This action MAY be initiated at the ASP by an
   M-ASP_UP request primitive from Layer Management or MAY be initiated
   automatically by an SUA management function.

   When an ASP Up message is received at an SGP and internally the
   remote ASP is in the ASP-DOWN state and not considered locked-out for
   local management reasons, the SGP marks the remote ASP in the state
   ASP-INACTIVE and informs Layer Management with an M-ASP_Up indication
   primitive.  If the SGP is aware, via current configuration data,
   which Application Servers the ASP is configured to operate in, the
   SGP updates the ASP state to ASP-INACTIVE in each AS that it is a
   member.

   Alternatively, the SGP may move the ASP into a pool of Inactive ASPs
   available for future configuration within Application Server(s),
   determined in a subsequent Registration Request or ASP Active
   procedure.  If the ASP Up message contains an ASP Identifier, the SGP
   should save the ASP Identifier for that ASP.  The SGP MUST send an
   ASP Up Ack message in response to a received ASP Up message even if
   the ASP is already marked as ASP-INACTIVE at the SGP.

   If for any local reason (e.g., management lock-out) the SGP cannot
   respond with an ASP Up Ack message, the SGP responds to an ASP Up
   message with an Error message with Reason "Refused - Management
   Blocking".

   At the ASP, the ASP Up Ack message received is not acknowledged.
   Layer Management is informed with an M-ASP_UP confirm primitive.

   When the ASP sends an ASP Up message it starts timer T(ack).  If the
   ASP does not receive a response to an ASP Up message within T(ack),
   the ASP MAY restart T(ack) and resend ASP Up messages until it
   receives an ASP Up Ack message.  T(ack) is provisioned, with a
   default of 2 seconds.  Alternatively, retransmission of ASP Up
   messages MAY be put under control of Layer Management.  In this
   method, expiry of T(ack) results in an M-ASP_UP confirm primitive
   carrying a negative indication.

   The ASP must wait for the ASP Up Ack message before sending any other
   SUA messages (e.g., ASP Active or REG REQ).  If the SGP receives any
   other SUA messages before ASPUP message is received (other than ASPDN
   - see section 4.3.4.2), the SGP SHOULD discard them.

   If an ASP Up message is received and internally the remote ASP is in
   the ASP-ACTIVE state, an ASP Up Ack message is returned, as well as
   an Error message ("Unexpected Message), and the remote ASP state is
   changed to ASP-INACTIVE in all relevant Application Servers.

   If an ASP Up message is received and internally the remote ASP is
   already in the ASP-INACTIVE state, an ASP Up Ack message is returned
   and no further action is taken.

4.3.4.1.1.  SUA Version Control

   If an ASP Up message with an unsupported version is received, the
   receiving end responds with an Error message, indicating the version
   the receiving node supports and notifies Layer Management.

   This is useful when protocol version upgrades are being performed in
   a network.  A node upgraded to a newer version should support the
   older versions used on other nodes it is communicating with.  Because
   ASPs initiate the ASP Up procedure it is assumed that the Error
   message would normally come from the SGP.

4.3.4.1.2.  IPSP Considerations

   An IPSP may be considered in the ASP-INACTIVE state after and ASPUP
   or ASPUP Ack has been received from it.  An IPSP can be considered in
   the ASP-DOWN state after an ASPDN or ASPDN Ack has been received from
   it.  The IPSP may inform Layer Management of the change in state of
   the remote IPSP using M-ASP_UP or M-ASP_DN indication or confirmation
   primitives.

   Alternatively, when using IPSP DE model, an interchange of ASP Up
   messages from each end MUST be performed.  Four messages are needed
   for completion.

   If for any local reason (e.g., management lock-out) and IPSP cannot
   respond to an ASP Up message with an ASP Up Ack message, it responds
   to an ASP Up message with an Error message with Reason "Refused -
   Management Blocking" and leaves the remote IPSP in the ASP-DOWN
   state.

4.3.4.2.  ASP Down Procedures

   The ASP will send an ASP Down message to an SGP when the ASP wishes
   to be removed from service in all Application Servers that it is a
   member and no longer receive any Connectionless or Connection -
   Oriented, SSNM or ASPTM messages.  This action MAY be initiated at
   the ASP by an M-ASP_DOWN request primitive from Layer Management or
   MAY be initiated automatically by an SUA management function.

   Whether the ASP is permanently removed from any AS is a function of
   configuration management.  In the case where the ASP previously used
   the Registration procedures (see Section 4.4.1) to register within
   Application Servers but has not deregistered from all of them prior
   to sending the ASP Down message, the SGP MUST consider the ASP as
   deregistered in all Application Servers that it is still a member.

   The SGP marks the ASP as ASP-DOWN, informs Layer Management with an
   M-ASP_Down indication primitive, and returns an ASP Down Ack message
   to the ASP.

   The SGP MUST send an ASP Down Ack message in response to a received
   ASP Down message from the ASP even if the ASP is already marked as
   ASP-DOWN at the SGP.

   At the ASP, the ASP Down Ack message received is not acknowledged.
   Layer Management is informed with an M-ASP_DOWN confirm primitive. If
   the ASP receives an ASP Down Ack without having sent an ASP Down
   message, the ASP should now consider itself as in the ASP-DOWN state.
   If the ASP was previously in the ASP-ACTIVE or ASP_INACTIVE state,
   the ASP should then initiate procedures to return itself to its
   previous state.

   When the ASP sends an ASP Down message it starts timer T(ack).  If
   the ASP does not receive a response to an ASP Down message within
   T(ack), the ASP MAY restart T(ack) and resend ASP Down messages until
   it receives an ASP Down Ack message.  T(ack) is provisioned, with a
   default of 2 seconds.  Alternatively, retransmission of ASP Down

   messages MAY be put under control of Layer Management.  In this
   method, expiry of T(ack) results in an M-ASP_DOWN confirm primitive
   carrying a negative indication.

4.3.4.3.  ASP Active Procedures

   Anytime after the ASP has received an ASP Up Ack message from the SGP
   or IPSP, the ASP MAY send an ASP Active message to the SGP indicating
   that the ASP is ready to start processing traffic.  This action MAY
   be initiated at the ASP by an M-ASP_ACTIVE request primitive from
   Layer Management or MAY be initiated automatically by an SUA
   management function.  In the case where an ASP wishes to process the
   traffic for more than one Application Server across a common SCTP
   association, the ASP Active message(s) SHOULD contain a list of one
   or more Routing Contexts to indicate for which Application Servers
   the ASP Active message applies.  It is not necessary for the ASP to
   include all Routing Contexts of interest in a single ASP Active
   message, thus requesting to become active in all Routing Contexts at
   the same time.  Multiple ASP Active messages MAY be used to activate
   within the Application Servers independently, or in sets.  In the
   case where an ASP Active message does not contain a Routing Context
   parameter, the receiver must know, via configuration data, which
   Application Server(s) the ASP is a member.

   For the Application Servers that the ASP can be successfully
   activated, the SGP or IPSP responds with one or more ASP Active Ack
   messages, including the associated Routing Context(s) and reflecting
   any Traffic Mode Type value present in the related ASP Active
   message.  The Routing Context parameter MUST be included in the ASP
   Active Ack message(s) if the received ASP Active message contained
   any Routing Contexts.  Depending on any Traffic Mode Type request in
   the ASP Active message, or local configuration data if there is no
   request, the SGP moves the ASP to the correct ASP traffic state
   within the associated Application Server(s).  Layer Management is
   informed with an M-ASP_Active indication.  If the SGP or IPSP
   receives any Data messages before an ASP Active message is received,
   the SGP or IPSP MAY discard them.  By sending an ASP Active Ack
   message, the SGP or IPSP is now ready to receive and send traffic for
   the related Routing Context(s).  The ASP SHOULD NOT send Data or SSNM
   messages for the related Routing Context(s) before receiving an ASP
   Active Ack message, or it will risk message loss.

   Multiple ASP Active Ack messages MAY be used in response to an ASP
   Active message containing multiple Routing Contexts, allowing the SGP
   or IPSP to independently acknowledge the ASP Active message for
   different (sets of) Routing Contexts.  The SGP or IPSP MUST send an
   Error message ("Invalid Routing Context") for each Routing Context
   value that cannot be successfully activated.

   In the case where an "out-of-the-blue" ASP Active message is received
   (i.e., the ASP has not registered with the SG or the SG has no static
   configuration data for the ASP), the message MAY be silently
   discarded.

   The SGP MUST send an ASP Active Ack message in response to a received
   ASP Active message from the ASP, if the ASP is already marked in the
   ASP-ACTIVE state at the SGP.

   At the ASP, the ASP Active Ack message received is not acknowledged.
   Layer Management is informed with an M-ASP_ACTIVE confirm primitive.
   It is possible for the ASP to receive Data message(s) before the ASP
   Active Ack message as the ASP Active Ack and Data messages from an SG
   or IPSP may be sent on different SCTP streams.  Message loss is
   possible, as the ASP does not consider itself in the ASP-ACTIVE state
   until reception of the ASP Active Ack message.

   When the ASP sends an ASP Active message it starts timer T(ack).  If
   the ASP does not receive a response to an ASP Active message within
   T(ack), the ASP MAY restart T(ack) and resend ASP Active messages
   until it receives an ASP Active Ack message.  T(ack) is provisioned,
   with a default of 2 seconds.  Alternatively, retransmission of ASP
   Active messages MAY be put under control of Layer Management.  In
   this method, expiry of T(ack) results in an M-ASP_ACTIVE confirm
   primitive carrying a negative indication.

   There are three modes of Application Server traffic handling in the
   SGP SUA layer: Override, Loadshare and Broadcast.  When included, the
   Traffic Mode Type parameter in the ASP Active message indicates the
   traffic-handling mode to be used in a particular Application Server.
   If the SGP determines that the mode indicated in an ASP Active
   message is unsupported or incompatible with the mode currently
   configured for the AS, the SGP responds with an Error message
   ("Unsupported / Invalid Traffic Handling Mode").  If the traffic-
   handling mode of the Application Server is not already known via
   configuration data, then the traffic-handling mode indicated in the
   first ASP Active message causing the transition of the Application
   Server state to AS-ACTIVE MAY be used to set the mode.

   In the case of an Override mode AS, reception of an ASP Active
   message at an SGP causes the (re)direction of all traffic for the AS
   to the ASP that sent the ASP Active message.  Any previously active
   ASP in the AS is now considered to be in state ASP-INACTIVE and
   SHOULD no longer receive traffic from the SGP within the AS.  The SGP
   or IPSP then MUST send a Notify message ("Alternate ASP Active") to
   the previously active ASP in the AS, and SHOULD stop traffic to/from

   that ASP.  The ASP receiving this Notify MUST consider itself now in
   the ASP-INACTIVE state, if it is not already aware of this via
   inter-ASP communication with the Overriding ASP.

   In the case of a Loadshare mode AS, reception of an ASP Active
   message at an SGP or IPSP causes the direction of traffic to the ASP
   sending the ASP Active message, in addition to all the other ASPs
   that are currently active in the AS.  The algorithm at the SGP for
   loadsharing traffic within an AS to all the active ASPs is
   implementation dependent.  The algorithm could, for example, be round
   robin or based on information in the Data message (e.g., the SLS or
   SSN).

   An SGP or IPSP, upon reception of an ASP Active message for the first
   ASP in a Loadshare AS, MAY choose not to direct traffic to a newly
   active ASP until it determines that there are sufficient resources to
   handle the expected load (e.g., until there are "n" ASPs in state
   ASP-ACTIVE in the AS).

   All ASPs within a load-sharing mode AS must be able to process any
   Data message received for the AS, to accommodate any potential fail-
   over or rebalancing of the offered load.

   In the case of a Broadcast mode AS, reception of an ASP Active
   message at an SGP or IPSP causes the direction of traffic to the ASP
   sending the ASP Active message, in addition to all the other ASPs
   that are currently active in the AS.  The algorithm at the SGP for
   broadcasting traffic within an AS to all the active ASPs is a simple
   broadcast algorithm, where every message is sent to each of the
   active ASPs.  An SGP or IPSP, upon reception of an ASP Active message
   for the first ASP in a Broadcast AS, MAY choose not to direct traffic
   to a newly active ASP until it determines that there are sufficient
   resources to handle the expected load (e.g., until there are "n" ASPs
   in state ASP-ACTIVE in the AS).

   Whenever an ASP in a Broadcast mode AS becomes ASP-ACTIVE, the SGP
   MUST tag the first DATA message broadcast in each traffic flow with a
   unique Correlation Id parameter.  The purpose of this Correlation Id
   is to permit the newly active ASP to synchronize its processing of
   traffic in each traffic flow with the other ASPs in the broadcast
   group.

4.3.4.3.1.  IPSP Considerations

   Either of the IPSPs can initiate communication.  When an IPSP
   receives an ASP Active, it should mark the peer as ASP-ACTIVE and
   return an ASP Active Ack message.  An ASP receiving an ASP Active Ack
   message may mark the peer as ASP-Active, if it is not already in the
   ASP-ACTIVE state.

   Alternatively, when using IPSP DE model, an interchange of ASP Active
   messages from each end MUST be performed.  Four messages are needed
   for completion.

4.3.4.4.  ASP Inactive Procedures

   When an ASP wishes to withdraw from receiving traffic within an AS,
   or the ASP wants to initiate the process of deactivation, the ASP
   sends an ASP Inactive message to the SGP or IPSP.

   An ASP Inactive message MUST be always responded by the peer
   (although other messages may be sent in the middle):

   -  If the corresponding RK is registered (statically or dynamically),
      the peer should respond with an ASP Inactive Ack message.

   -  If the RK is not registered, or the RC information is not valid,
      the peer must respond with an ERROR message with Error Code =
      "Invalid Routing Context".

   -  If the RC is missing and its specification is needed according to
      the used configuration, the peer must respond with an ERROR
      message with Error Code = "No Configured AS for ASP".

   The action of sending the ASP Inactive message MAY be initiated at
   the ASP by an M-ASP_INACTIVE request primitive from Layer Management
   or MAY be initiated automatically by an SUA management function.  In
   the case where an ASP is processing the traffic for more than one
   Application Server across a common SCTP association, the ASP Inactive
   message contains one or more Routing Contexts to indicate for which
   Application Servers the ASP Inactive message applies.

   In the case where an ASP Inactive message does not contain a Routing
   Context parameter, the receiver must know, via configuration data,
   which Application Servers the ASP is a member and move the ASP to the
   ASP-INACTIVE state in each all Application Servers.

   In the case of an Override mode AS, where another ASP has already
   taken over the traffic within the AS with an ASP Active ("Override")
   message, the ASP that sends the ASP Inactive message is already

   considered by the SGP to be in state ASP-INACTIVE.  An ASP Inactive
   Ack message is sent to the ASP, after ensuring that all traffic is
   stopped to the ASP.

   In the case of a Loadshare mode AS, the SGP moves the ASP to the
   ASP-INACTIVE state and the AS traffic is reallocated across the
   remaining ASPs in the state ASP-ACTIVE, as per the loadsharing
   algorithm currently used within the AS.  A Notify message
   ("Insufficient ASP resources active in AS") MAY be sent to all
   inactive ASPs, if required.  An ASP Inactive Ack message is sent to
   the ASP after all traffic is halted and Layer Management is informed
   with an M-ASP_INACTIVE indication primitive.

   In the case of a Broadcast mode AS, the SGP moves the ASP to the
   ASP-INACTIVE state and the AS traffic is broadcast only to the
   remaining ASPs in the state ASP-ACTIVE.  A Notify message
   ("Insufficient ASP resources active in AS") MAY be sent to all
   inactive ASPs, if required.  An ASP Inactive Ack message is sent to
   the ASP after all traffic is halted and Layer Management is informed
   with an M-ASP_INACTIVE indication primitive.

   Multiple ASP Inactive Ack messages MAY be used in response to an ASP
   Inactive message containing multiple Routing Contexts, allowing the
   SGP or IPSP to independently acknowledge for different (sets of)
   Routing Contexts.  The SGP or IPSP sends an Error message ("Invalid
   Routing Context") message for each invalid or not configured Routing
   Context value in a received ASP Inactive message.

   The SGP MUST send an ASP Inactive Ack message in response to a
   received ASP Inactive message from the ASP and the ASP is already
   marked as ASP-INACTIVE at the SGP.

   At the ASP, the ASP Inactive Ack message received is not
   acknowledged.  Layer Management is informed with an M-ASP_INACTIVE
   confirm primitive.  If the ASP receives an ASP Inactive Ack without
   having sent an ASP Inactive message, the ASP should now consider
   itself as in the ASP-INACTIVE state.  If the ASP was previously in
   the ASP-ACTIVE state, the ASP should then initiate procedures to
   return itself to its previous state.  When the ASP sends an ASP
   Inactive message it starts timer T(ack).  If the ASP does not receive
   a response to an ASP Inactive message within T(ack), the ASP MAY
   restart T(ack) and resend ASP Inactive messages  until it receives an
   ASP Inactive Ack message.  T(ack) is provisioned, with a default of 2
   seconds.  Alternatively, retransmission of ASP Inactive messages MAY
   be put under control of Layer Management.  In this method, expiry of
   T(ack) results in a M-ASP_Inactive confirm primitive carrying a
   negative indication.

   If no other ASPs in the Application Server are in the state ASP-
   ACTIVE, the SGP MUST send a Notify message ("AS-Pending") to all of
   the ASPs in the AS which are in the state ASP-INACTIVE.  The SGP
   SHOULD start buffering the incoming messages for T(r) seconds, after
   which messages MAY be discarded.  T(r) is configurable by the network
   operator.  If the SGP receives an ASP Active message from an ASP in
   the AS before expiry of T(r), the buffered traffic is directed to
   that ASP and the timer is cancelled.  If T(r) expires, the AS is
   moved to the AS-INACTIVE state.

4.3.4.4.1.  IPSP Considerations

   An IPSP may be considered in the ASP-INACTIVE state by a remote IPSP
   after an ASP Inactive or ASP Inactive Ack message has been received
   from it.

   Alternatively, when using IPSP DE model, an interchange of ASP
   Inactive messages from each end MUST be performed.  Four messages are
   needed for completion.

4.3.4.5.  Notify Procedures

   A Notify message reflecting a change in the AS state MUST be sent to
   all ASPs in the AS, except those in the ASP-DOWN state, with
   appropriate Status Information and any ASP Identifier of the failed
   ASP.  At the ASP, Layer Management is informed with an M-NOTIFY
   indication primitive.  The Notify message must be sent whether the AS
   state change was a result of an ASP failure or reception of an ASP
   State management (ASPSM) / ASP Traffic Management (ASPTM) message.
   In the second case, the Notify message MUST be sent after any ASP
   State or Traffic Management related acknowledgement messages  (e.g.,
   ASP Up Ack, ASP Down Ack, ASP Active Ack, or ASP Inactive Ack).

   In the case where a Notify ("AS-PENDING") message is sent by an SGP
   that now has no ASPs active to service the traffic, or where a Notify
   ("Insufficient ASP resources active in AS") message MUST be sent in
   the Loadshare or Broadcast mode, the Notify message does not
   explicitly compel the ASP(s) receiving the message to become active.
   The ASPs remain in control of what (and when) traffic action is
   taken.

   In the case where a Notify message does not contain a Routing Context
   parameter, the receiver must know, via configuration data, of which
   Application Servers the ASP is a member and take the appropriate
   action in each AS.

4.3.4.5.1.  IPSP Considerations (NTFY)

   Notify works in the same manner as in the SG-AS case.  One of the
   IPSPs can send this message to any remote IPSP that is not in the
   ASP-DOWN state.

4.3.4.6.  Heartbeat Procedures

   The optional Heartbeat procedures MAY be used when operating over
   transport layers that do not have their own heartbeat mechanism for
   detecting loss of the transport association (i.e., other than SCTP).

   Either SUA peer may optionally send Heartbeat messages periodically,
   subject to a provisioned timer T(beat).  Upon receiving a Heartbeat
   message, the SUA peer MUST respond with a Heartbeat Ack message.

   If no Heartbeat Ack message (or any other SUA message) is received
   from the SUA peer within 2*T(beat), the remote SUA peer is considered
   unavailable.  Transmission of Heartbeat messages is stopped and the
   signalling process SHOULD attempt to reestablish communication if it
   is configured as the client for the disconnected SUA peer.

   The Heartbeat message may optionally contain an opaque Heartbeat Data
   parameter that MUST be echoed back unchanged in the related Heartbeat
   Ack message.  The sender, upon examining the contents of the returned
   Heartbeat Ack message, MAY choose to consider the remote SUA peer as
   unavailable.  The contents/format of the Heartbeat Data parameter is
   implementation-dependent and only of local interest to the original
   sender.  The contents may be used, for example, to support a
   Heartbeat sequence algorithm (to detect missing Heartbeats), and/or a
   timestamp mechanism (to evaluate delays).

   Note: Heartbeat related events are not shown in Figure 2 "ASP state
   transition diagram".

4.4.  Routing Key Management Procedures

4.4.1.  Registration

   An ASP MAY dynamically register with an SGP as an ASP within an
   Application Server using the REG REQ message.  A Routing Key
   parameter in the REG REQ message specifies the parameters associated
   with the Routing Key.

   The SGP examines the contents of the received Routing Key parameter
   and compares it with the currently provisioned Routing Keys.  If the
   received Routing Key matches an existing SGP Routing Key entry, and
   the ASP is not currently included in the list of ASPs for the related

   Application Server, the SGP MAY authorize the ASP to be added to the
   AS.  Or, if the Routing Key does not currently exist and the received
   Routing Key data is valid and unique, an SGP supporting dynamic
   configuration MAY authorize the creation of a new Routing Key and
   related Application Server and add the ASP to the new AS.  In either
   case, the SGP returns a Registration Response message to the ASP,
   containing the same Local-RK-Identifier as provided in the initial
   request, and a Registration Result "Successfully Registered".  A
   unique Routing Context value assigned to the SGP Routing Key is
   included.  The method of Routing Context value assignment at the SGP
   is implementation dependent but must be guaranteed to be unique for
   each Application Server or Routing Key supported by the SGP.  If the
   SGP determines that the received Routing Key data is invalid, or
   contains invalid parameter values, the SGP returns a Registration
   Response message to the ASP, containing a Registration Result "Error
   - Invalid Routing Key", "Error - Invalid DPC", "Error - Invalid
   Network Appearance" as appropriate.

   If the SGP does not support the registration procedure, the SGP
   returns an Error message to the ASP, with an error code of
   "Unsupported Message Type".

   If the SGP determines that a unique Routing Key cannot be created,
   the SGP returns a Registration Response message to the ASP, with a
   Registration Status of "Error - Cannot Support Unique Routing".  An
   incoming signalling message received at an SGP should not match
   against more than one Routing Key.

   If the SGP does not authorize the registration request, the SGP
   returns a REG RSP message to the ASP containing the Registration
   Result "Error - Permission Denied".

   If an SGP determines that a received Routing Key does not currently
   exist and the SGP does not support dynamic configuration, the SGP
   returns a Registration Response message to the ASP, containing a
   Registration Result "Error - Routing Key not Currently Provisioned".

   If an SGP determines that a received Routing Key does not currently
   exist and the SGP supports dynamic configuration but does not have
   the capacity to add new Routing Key and Application Server entries,
   the SGP returns a Registration Response message to the ASP,
   containing a Registration Result "Error - Insufficient Resources".

   If an SGP determines that one or more of the Routing Key parameters
   are not supported for the purpose of creating new Routing Key
   entries, the SGP returns a Registration Response message to the ASP,

   containing a Registration Result "Error - Unsupported RK parameter
   field".  This result MAY be used if, for example, the SGP does not
   support RK Address parameter.

   A Registration Response "Error - Unsupported Traffic Handling Mode"
   is returned if the Routing Key in the REG REQ contains a Traffic
   Handling Mode that is inconsistent with the presently configured mode
   for the matching Application Server.

   An ASP MAY register multiple Routing Keys at once by including a
   number of Routing Key parameters in a single REG REQ message.  The
   SGP MAY respond to each registration request in a single REG RSP
   message, indicating the success or failure result for each Routing
   Key in a separate Registration Result parameter.  Alternatively the
   SGP MAY respond with multiple REG RSP messages, each with one or more
   Registration Result parameters.  The ASP uses the Local-RK-Identifier
   parameter to correlate the requests with the responses.

   An ASP MAY modify an existing Routing Key by including a Routing
   Context parameter in the REG REQ.  If the SGP determines that the
   Routing Context applies to an existing Routing Key, the SG MAY adjust
   the existing Routing Key to match the new information provided in the
   Routing Key parameter.  A Registration Response "Routing Key Change
   Refused" is returned if the SGP does not accept the modification of
   the Routing Key.

   Upon successful registration of an ASP in an AS, the SGP can now send
   related SS7 Signalling Network Management messaging, if this did not
   previously start upon the ASP transitioning to state ASP-INACTIVE.

4.4.2.  Deregistration

   An ASP MAY dynamically deregister with an SGP as an ASP within an
   Application Server using the DEREG REQ message.  A Routing Context
   parameter in the DEREG REQ message specifies which Routing Keys to
   deregister.  An ASP SHOULD move to the ASP-INACTIVE state for an
   Application Server before attempting to deregister the Routing Key
   (i.e., deregister after receiving an ASP Inactive Ack).  Also, an ASP
   SHOULD deregister from all Application Servers that it is a member
   before attempting to move to the ASP-Down state.

   The SGP examines the contents of the received Routing Context
   parameter and validates that the ASP is currently registered in the
   Application Server(s) related to the included Routing Context(s).  If
   validated, the ASP is deregistered as an ASP in the related
   Application Server.

   The deregistration procedure does not necessarily imply the deletion
   of Routing Key and Application Server configuration data at the SGP.
   Other ASPs may continue to be associated with the Application Server,
   in which case the Routing Key data SHOULD NOT be deleted.  If a
   Deregistration results in no more ASPs in an Application Server, an
   SGP MAY delete the Routing Key data.

   The SGP acknowledges the deregistration request by returning a DEREG
   RSP message to the requesting ASP.  The result of the deregistration
   is found in the Deregistration Result parameter, indicating success
   or failure with cause.

   An ASP MAY deregister multiple Routing Contexts at once by including
   a number of Routing Contexts in a single DEREG REQ message.  The SGP
   MAY respond to each deregistration request in a single DEREG RSP
   message, indicating the success or failure result for each Routing
   Context in a separate Deregistration Result parameter.

4.4.3.  IPSP Considerations (REG/DEREG)

   The Registration/Deregistration procedures work in the IPSP cases in
   the same way as in AS-SG cases.  An IPSP may register an RK in the
   remote IPSP.  An IPSP is responsible for deregistering the RKs that
   it has registered.

4.5.  Availability and/or Congestion Status of SS7 Destination Support

4.5.1.  At an SGP

   On receiving a N-STATE, N-PCSTATE and N-INFORM indication primitive
   from the nodal interworking function at an SGP, the SGP SUA layer
   will send a corresponding SS7 Signalling Network Management (SNM)
   DUNA, DAVA, SCON, or DUPU message (see Section 3.4) to the SUA peers
   at concerned ASPs.  The SUA layer must fill in various fields of the
   SNM messages consistently with the information received in the
   primitives.

   The SGP SUA layer determines the set of concerned ASPs to be informed
   based on the specific SS7 network for which the primitive indication
   is relevant.  In this way, all ASPs configured to send/receive
   traffic within a particular network appearance are informed.  If the
   SGP operates within a single SS7 network appearance, then all ASPs
   are informed.

   DUNA, DAVA, SCON, and DRST messages are sent sequentially and
   processed at the receiver in the order sent.  SCTP stream 0 SHOULD
   NOT be used.  The Unordered bit in the SCTP DATA chunk MAY be used
   for the SCON message.

   Sequencing is not required for the DUPU or DAUD messages, which MAY
   be sent unordered.  SCTP stream 0 is used, with optional use of the
   Unordered bit in the SCTP DATA chunk.

4.5.2.  At an ASP

4.5.2.1.  Single SG Configurations

   At an ASP, upon receiving an SS7 Signalling Network Management (SSNM)
   message from the remote SUA Peer, the SUA layer invokes the
   appropriate primitive indications to the resident SUA-Users.  Local
   management is informed.

   In the case where a local event has caused the unavailability or
   congestion status of SS7 destinations, the SUA layer at the ASP
   SHOULD pass up appropriate indications in the primitives to the SUA
   User, as though equivalent SSNM messages were received.  For example,
   the loss of an SCTP association to an SGP may cause the
   unavailability of a set of SS7 destinations.  N-PCSTATE indication
   primitives to the SUA User are appropriate.

   Implementation Note: To accomplish this, the SUA layer at an ASP
   maintains the status of routes via the SG.

4.5.2.2.  Multiple SG Configurations

   At an ASP, upon receiving a Signalling Network Management message
   from the remote SUA Peer, the SUA layer updates the status of the
   affected route(s) via the originating SG and determines, whether or
   not the overall availability or congestion status of the effected
   destination(s) has changed.  If so, the SUA layer invokes the
   appropriate primitive indications to the resident SUA-Users.  Local
   management is informed.

4.5.3.  ASP Auditing

   An ASP may optionally initiate an audit procedure to inquire of an
   SGP the availability and, if the national congestion method with
   multiple congestion levels and message priorities is used, congestion
   status of an SS7 destination or set of destinations.  A Destination
   Audit (DAUD) message is sent from the ASP to the SGP requesting the
   current availability and congestion status of one or more SS7
   destinations or subsystems.

   The DAUD message MAY be sent unordered.  The ASP MAY send the DAUD in
   the following cases:

   - Periodic.  A Timer originally set upon reception of a DUNA, SCON or
                DRST message has expired without a subsequent DAVA,
                DUNA, SCON or DRST message updating the
                availability/congestion status of the affected
                Destination Point Code.  The Timer is reset upon issuing
                a DAUD.  In this case the DAUD is sent to the SGP that
                originally sent the SSNM message.

   - Isolation. The ASP is newly ASP-ACTIVE or has been isolated from an
                SGP for an extended period.  The ASP MAY request the
                availability/congestion status of one or more SS7
                destinations to which it expects to communicate.

   Implementation Note:

      In the first of the cases above, the auditing procedure must not
      be invoked for the case of a received SCON message containing a
      congestion level value of "no congestion" or undefined" (i.e.,
      congestion Level = "0").  This is because the value indicates
      either congestion abatement or that the ITU MTP3 international
      congestion method is being used.  In the international congestion
      method, the MTP3 layer at the SGP does not maintain the congestion
      status of any destinations and therefore the SGP cannot provide
      any congestion information in response to the DAUD.  For the same
      reason, in the second of the cases above a DAUD message cannot
      reveal any congested destination(s).

   The SGP SHOULD respond to a DAUD message with the availability and
   congestion status of the subsystem.  The status of each SS7
   destination or subsystem requested is indicated in a DUNA message (if
   unavailable), a DAVA message (if available), or a DRST (if restricted
   and the SGP supports this feature).  If the SS7 destination or
   subsystem is available and congested, the SGP responds with an SCON
   message in addition to the DAVA message.  If the SS7 destination or
   subsystem is restricted and congested, the SGP responds with an SCON
   message in addition to the DRST.  If the SGP has no information on
   the availability / congestion status of the SS7 destination or
   subsystem, the SGP responds with a DUNA message, as it has no routing
   information to allow it to route traffic to this destination or
   subsystem.

   An SG MAY refuse to provide the availability or congestion status of
   a destination or subsystem if, for example, the ASP is not authorized
   to know the status of the destination or subsystem.  The SG MAY
   respond with an Error Message (Error Code = "Destination Status
   Unknown") or Error Message (Error Code = "Subsystem Status Unknown").

4.6.  MTP3 Restart

   In the case where the MTP3 in the SG undergoes an MTP restart, event
   communication SHOULD be handled as follows:

   When the SG discovers SS7 network isolation, the SGPs send an
   indication to all concerned available ASPs (i.e., ASPs in the ASP-
   ACTIVE state) using DUNA messages for the concerned destinations.
   When the SG has completed the MTP Restart procedure, the SUA layer at
   the SGPs inform all concerned ASPs in the ASP-ACTIVE state of any
   available/restricted SS7 destinations using the DAVA/DRST message.
   No message is necessary for those destinations still unavailable
   after the restart procedure.

   When the SUA layer at an ASP receives a DUNA message indicating SS7
   destination unavailability at an SG, SCCP Users will receive an N-
   PCSTATE indication and will stop any affected traffic to this
   destination.  When the SUA receives a DAVA/DRST message, SCCP Users
   will receive an N-PCSTATE indication and can resume traffic to the
   newly available SS7 destination via this SGP, provided the ASP is in
   the ASP-ACTIVE state toward this SGP.

   The ASP MAY choose to audit the availability of unavailable
   destinations by sending DAUD messages.  This would be for example the
   case when an AS becomes active at an ASP and does not have current
   destination statuses.  If MTP restart is in progress at the SG, the
   SGP returns a DUNA message for that destination, even if it received
   an indication that the destination became available or restricted.

4.7.  SCCP - SUA Interworking at the SG

4.7.1.  Segmenting / Reassembly

   When it is expected that signalling messages will not fit into a PDU
   of the most restrictive transport technology used (e.g., 272-SIF of
   MTP3), then segmenting/reassembly could be performed at the SG, ASP
   or IPSP.  If the SG, ASP or IPSP is incapable of performing a
   necessary segmentation/reassembly, it can inform the peer of the
   failure using the appropriate error in a CLDR or RESRE/COERR message.

4.7.2.  Support for Loadsharing

   Within an AS (identified by RK/RC parameters) several loadsharing
   ASPs may be active.

   However, to assure the correct processing of TCAP transactions or
   SCCP connections, the loadsharing scheme used at the SG must make
   sure that messages continuing or ending the transactions/connections
   arrive at the same ASP where the initial message (TC_Query, TC_Begin,
   CR) was sent to/received from.

   When the ASP can be identified uniquely based on RK parameters (e.g.,
   unique DPC or GT), loadsharing is not required.  When the ASPs in the
   AS share state or use an internal distribution mechanism, the SG must
   only take into account the in-sequence-delivery requirement.  In case
   of SCCP CO traffic, when the coupled approach is used, loadsharing of
   messages other than CR is not required.

   If these assumptions cannot be made, both SG and ASP should support
   the following general procedure in a loadsharing environment.

4.7.2.1.  Association Setup, ASP going active

   After association setup and registration, an ASP normally goes active
   for each AS it registered for.  In the ASPAC message, the ASP
   includes a TID and/or DRN Label Parameter, if applicable for the AS
   in question.  All the ASPs within the AS must specify a unique label
   at a fixed position in the TID or DRN parameter.  The same ASPAC
   message is sent to each SG used for interworking with the SS7
   network.

   The SG builds, per RK, a list of ASPs that have registered for it.
   The SG can now build up and update a distribution table for a certain
   Routing Context, any time the association is (re-)established and the
   ASP goes active.  The SG has to perform some trivial plausibility
   checks on the parameters:

   - Start and End parameters values are between 0 and 31 for TID.
   - Start and End parameters values are between 0 and 23 for DRN
   - 0 < (Start - End + 1) <= 16 (label length maximum 16-bit)
   - Start values are the same for each ASP within a RC
   - End values are the same for each ASP within a RC
   - TID and DRN Label values must be unique across the RC

   If any of these checks fail, the SG refuses the ASPAC request, with
   an error, "Invalid loadsharing label."

4.7.3.  Routing and message distribution at the SG

4.7.3.1.  TCAP traffic

   Messages not containing a destination (or "responding") TID, i.e.,
   Query, Begin, Unidirectional, are loadshared among the available
   ASPs.  Any scheme permitting a fair load distribution among the ASPs
   is allowed (e.g., round robin).

   When a destination TID is present, the SG extracts the label and
   selects the ASP that corresponds with it.

   If an ASP is not available, the SG may generate (X)UDTS "routing
   failure", if the return option is used.

4.7.3.2.  SCCP Connection Oriented traffic

   Messages not containing a destination reference number (DRN), i.e., a
   Connection Request, MAY be loadshared among the available ASPs.  The
   load distribution mechanism is an implementation issue.  When a DRN
   is present, the SG extracts the label and selects the ASP that
   corresponds with it.  If an ASP is not available, the SG discards the
   message.

4.7.4.  Multiple SGs, SUA Relay Function

   It is important that each ASP send its unique label (within the AS)
   to each SGP.  For a better robustness against association failures,
   the SGs MAY cooperate to provide alternative routes toward an ASP.
   Mechanisms for SG cooperation/coordination are outside of the scope
   of this document.

5.  Examples of SUA Procedures

   The following sequence charts overview the procedures of SUA.  These
   are meant as examples, they do not, in and of themselves, impose
   additional requirements upon an instance of SUA.

5.1.  SG Architecture

   The sequences below outline logical steps for a variety of scenarios
   within a SG architecture.  Please note that these scenarios cover a
   Primary/Backup configuration.  Where there is a load-sharing
   configuration then the SGP can declare availability when 1 ASP issues
   ASPAC but can only declare unavailability when all ASPs have issued
   ASPIA.

5.1.1.  Establishment of SUA connectivity

   The following is established before traffic can flow.

   Each node is configured (via MIB, for example) with the connections
   that need to be setup.

    ASP-a1            ASP-a2                SG                  SEP
   (Primary)           (Backup)
      |------Establish SCTP Association------|
                         |--Estab. SCTP Ass--|
                                             |--Align SS7 link---|
      +----------------ASP Up---------------->
      <--------------ASP Up Ack--------------+
                         +------ASP Up------->
                         <---ASP Up Ack------+
      +-------------ASP Active--------------->
      <----------ASP Active Ack--------------+
      <----------NTFY (ASP Active)-----------+
                         <-NTFY (ASP Active)-+
                                             +--------SSA-------->
                                             <--------SSA--------+
      <-----------------DAVA-----------------+
      +-----------------CLDT----------------->
                                             +--------UDT-------->

5.1.2.  Fail-over scenarios

   The following sequences address fail-over of SEP and ASP.

5.1.2.1.  SEP Fail-over

   The SEP knows that the SGP is 'concerned' about its availability.
   Similarly, the SGP knows that ASP-a1 is concerned about the SEPs
   availability.

     ASP-a1            ASP-a2                SG                  SEP
   (Primary)           (Backup)
                                              <--------SSP--------+
       <-----------------DUNA-----------------+
       +-----------------DAUD----------------->
                                              +--------SST-------->

5.1.2.2.  Successful ASP Fail-over scenario

   The following is an example of a successful fail-over scenario, where
   there is a fail-over from ASP-a1 to ASP-a2, i.e., Primary to Backup.
   During the fail-over, the SGP buffers any incoming data messages from
   the SEP, forwarding them when the Backup becomes available.

     ASP-a1            ASP-a2                SG                  SEP
   (Primary)           (Backup)
       +-------------ASP Inactive------------->
       <-----------ASP Inactive ACK-----------+
       <--------------------NTFY (AS Pending)-+
                          <-NTFY (AS Pending)-+
                          +----ASP Active----->
                          <--ASP Active Ack---+
                          <-NTFY (AS Active)--+
       <----------NTFY (AS Active)------------+

5.1.2.3.  Unsuccessful ASP Fail-over scenario

     ASP-a1            ASP-a2                SG                  SEP
   (Primary)           (Backup)
       +-------------ASP Inactive------------->
       <-----------ASP Inactive ACK-----------+
       <--------------------NTFY (AS Pending)-+
                         <--NTFY (AS Pending)-+
             After some time elapses (i.e., timeout).
                                              +--------SSP-------->
                                              <--------SST--------+
       <-------------------NTFY (AS Inactive)-+
                         <-NTFY (AS Inactive)-+

5.2.  IPSP Examples

   The sequences below outline logical steps for a variety of scenarios
   within an IP-IP architecture.  Please note that these scenarios cover
   a Primary/Backup configuration.  Where there is a load-sharing
   configuration then the AS can declare availability when 1 ASP issues
   ASPAC but can only declare unavailability when all ASPs have issued
   ASPIA.

5.2.1.  Establishment of SUA connectivity

   The following shows an example establishment of SUA connectivity. In
   this example, each IPSP consists of an Application Server and two
   ASPs.  The following is established before SUA traffic can flow.  A
   connectionless flow is shown for simplicity.

   Establish SCTP Connectivity - as per RFC 2960.  Note that SCTP
   connections are bidirectional.  The endpoint that establishes SCTP
   connectivity MUST also establish UA connectivity (see RFC 2960,
   section 5.2.1 for handling collisions) [2960].

   IP SEP A                                                  IP SEP B
   AS A                                                          AS B
   ASP-a1     ASP-a2                                 ASP-b2    ASP-b1

   [All ASPs are in the ASP-DOWN state]

   +-------------------------------ASP Up-------------------------->
   <-----------------------------ASP Up Ack------------------------+

                 +--------------ASP Up--------------->
                 <------------ASP Up Ack-------------+

   +---------------------------ACTIVE------------------------------->
   <-------------------------ACTIVE Ack-----------------------------+

   [Traffic can now flow directly between ASPs]

   +-----------------------------CLDT------------------------------->

5.2.2.  Fail-over scenarios

   The following sequences address fail-over of ASP.

5.2.2.1.  Successful ASP Fail-over scenario

   The following is an example of a successful fail-over scenario, where
   there is a fail-over from ASP-a1 to ASP-a2, i.e., Primary to Backup.
   Since data transfer passes directly between peer ASPs, ASP-b1 is
   notified of the fail-over of ASP-a1 and buffers outgoing data
   messages until ASP-a2 becomes available.

   IP SEP A                                                  IP SEP B
   ASP-a1     ASP-a2                                 ASP-b2    ASP-b1

   +-----------------------------ASP Inact------------------------>
   <---------------------------ASP Inact Ack----------------------+
              <---------------NTFY (ASP-a1 Inactive)--------------+
              +---------------------ASP Act----------------------->
              <-------------------ASP Act Ack---------------------+

5.2.2.2.  Unsuccessful ASP Fail-over scenario

   The sequence is the same as 5.2.2.1 except that, since the backup
   fails to come in then, the Notify messages declaring the availability
   of the backup are not sent.

6.  Security Considerations

   The security considerations discussed for the 'Security
   Considerations for SIGTRAN Protocols' [3788] document apply to this
   document.

7.  IANA Considerations

7.1.  SCTP Payload Protocol ID

   IANA has assigned a SUA value for the Payload Protocol Identifier in
   the SCTP DATA chunk.  The following SCTP Payload Protocol Identifier
   is registered:

      SUA    "4"

   The SCTP Payload Protocol Identifier value "4" SHOULD be included in
   each SCTP DATA chunk, to indicate that the SCTP is carrying the SUA
   protocol.  The value "0" (unspecified) is also allowed but any other
   values MUST not be used.  This Payload Protocol Identifier is not
   directly used by SCTP but MAY be used by certain network entities to
   identify the type of information being carried in a DATA chunk.

   The User Adaptation peer MAY use the Payload Protocol Identifier, as
   a way of determining additional information about the data being
   presented to it by SCTP.

7.2.  Port Number

   IANA has registered SCTP Port Number 14001 for SUA.  It is
   recommended that SGPs use this SCTP port number for listening for new
   connections.  SGPs MAY also use statically configured SCTP port
   numbers instead.

7.3.  Protocol Extensions

   This protocol may also be extended through IANA in three ways:

   -  Through definition of additional message classes.
   -  Through definition of additional message types.
   -  Through definition of additional message parameters.

   The definition and use of new message classes, types and parameters
   is an integral part of SIGTRAN adaptation layers.  Thus, these
   extensions are assigned by IANA through an IETF Consensus action as
   defined in [2434].

   The proposed extension MUST in no way adversely affect the general
   working of the protocol.

   A new registry has been created by IANA to allow the protocol to be
   extended.

7.3.1.  IETF Defined Message Classes

   The documentation for a new message class MUST include the following
   information:

   (a) A long and short name for the message class;
   (b) A detailed description of the purpose of the message class.

7.3.2.  IETF Defined Message Types

   Documentation of the message type MUST contain the following
   information:

   (a) A long and short name for the new message type;
   (b) A detailed description of the structure of the message.
   (c) A detailed definition and description of intended use of each
       field within the message.
   (d) A detailed procedural description of the use of the new message
       type within the operation of the protocol.
   (e) A detailed description of error conditions when receiving this
       message type.

   When an implementation receives a message type which it does not
   support, it MUST respond with an Error (ERR) message, with an Error
   Code = Unsupported Message Type.

7.3.4.  IETF-defined TLV Parameter Extension

   Documentation of the message parameter MUST contain the following
   information:

   (a) Name of the parameter type.
   (b) Detailed description of the structure of the parameter field.
       This structure MUST conform to the general type-length-value
       format described earlier in the document.
   (c) Detailed definition of each component of the parameter value.

   (d) Detailed description of the intended use of this parameter type,
       and an indication of whether and under what circumstances
       multiple instances of this parameter type may be found within the
       same message type.

8.  Timer Values

   Ta                                      2 seconds
   Tr                                      2 seconds
   T(ack)                                  2 seconds
   T(ias)    Inactivity Send timer         7 minutes
   T(iar)    Inactivity Receive timer      15 minutes
   T(beat)   Heartbeat Timer               30 seconds

9.  Acknowledgements

   The authors would like to thank (in alphabetical order) Richard
   Adams, Javier Pastor-Balbas, Andrew Booth, Martin Booyens, F.
   Escobar, S. Furniss Klaus Gradischnig, Miguel A. Garcia, Marja-Liisa
   Hamalainen, Sherry Karl, S. Lorusso, Markus Maanoja, Sandeep Mahajan,
   Ken Morneault, Guy Mousseau, Chirayu Patel, Michael Purcell, W.
   Sully, Michael Tuexen, Al Varney, Tim Vetter, Antonio Villena, Ben
   Wilson, Michael Wright and James Yu for their insightful comments and
   suggestions.

10.  References

10.1.  Normative References

   [1123]         Braden, R., Ed., "Requirements for Internet Hosts -
                  Application and Support", STD 3, RFC 1123, October
                  1989.

   [2119]         Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

   [2960]         Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
                  Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
                  Zhang, L., and V. Paxson, "Stream Control Transmission
                  Protocol", RFC 2960, October 2000.

   [3629]         Yergeau, F., "UTF-8, a transformation format of ISO
                  10646", STD 63, RFC 3629, November 2003.

   [3788]         Loughney, J., Tuexen, M., Ed., and J. Pastor-Balbas,
                  "Security Considerations for Signaling Transport
                  (SIGTRAN) Protocols", RFC 3788, June 2004.

   [ANSI SCCP]    ANSI T1.112 "Signalling System Number 7 - Signalling
                  Connection Control Part".

   [ITU SCCP]     ITU-T Recommendations Q.711-714, "Signalling System
                  No. 7 (SS7) - Signalling Connection Control Part
                  (SCCP)."  ITU-T Telecommunication Standardization
                  Sector of ITU, formerly CCITT, Geneva (July 1996).

10.2.  Informative References

   [2434]         Narten, T. and H. Alvestrand, "Guidelines for Writing
                  an IANA Considerations Section in RFCs", BCP 26, RFC
                  2434, October 1998.

   [2719]         Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H.,
                  Coene, L., Lin, H., Juhasz, I., Holdrege, M., and C.
                  Sharp, "Framework Architecture for Signalling
                  Transport", RFC 2719, October 1999.

   [3761]         Falstrom, P. and M. Mealling, "The E.164 to Uniform
                  Resource Identifiers (URI) Dynamic Delegation
                  Discovery System (DDDS) Application (ENUM)", RFC 3761,
                  April 2004.

   [ANSI TCAP]    ANSI T1.114 'Signalling System Number 7 - Transaction
                  Capabilities Application Part'

   [ITU TCAP]     ITU-T Recommendation Q.771-775 'Signalling System No.
                  7 SS7) - Transaction Capabilities (TCAP).'

   [RANAP]        3G TS 25.413 V3.5.0 (2001-03) 'Technical Specification
                  3rd Generation Partnership Project; Technical
                  Specification Group Radio Access Network; UTRAN Iu
                  Interface RANAP Signalling'

Appendix A.  Signalling Network Architecture

A.1.  Generalized Peer-to-Peer Network Architecture

   Figure 3 shows an example network architecture that can support
   robust operation and fail-over.  There needs to be some management
   resources at the AS to manage traffic.

   ***********
   *   AS1   *
   * +-----+ * SCTP Associations
   * |ASP1 +-------------------+
   * +-----+ *                 |                   ***********
   *         *                 |                   *   AS3   *
   * +-----+ *                 |                   * +-----+ *
   * |ASP2 +-----------------------------------------+ASP1 | *
   * +-----+ *                 |                   * +-----+ *
   *         *                 |                   *         *
   * +-----+ *                 |                   * +-----+ *
   * |ASP3 | *            +--------------------------+ASP2 | *
   * +-----+ *            |    |                   * +-----+ *
   ***********            |    |                   ***********
                          |    |
   ***********            |    |                   ***********
   *   AS2   *            |    |                   *   AS4   *
   * +-----+ *            |    |                   * +-----+ *
   * |ASP1 +--------------+    +---------------------+ASP1 | *
   * +-----+ *                                     * +-----+ *
   *         *                                     *         *
   * +-----+ *                                     * +-----+ *
   * |ASP2 +-----------------------------------------+ASP1 | *
   * +-----+ *                                     * +-----+ *
   *         *                                     ***********
   * +-----+ *
   * |ASP3 | *
   * +-----+ *
   *         *
   ***********

              Figure 3: Generalized Architecture

   In this example, the Application Servers are shown residing within
   one logical box, with ASPs located inside.  In fact, an AS could be
   distributed among several hosts.  In such a scenario, the host should
   share state as protection in the case of a failure.  This is out of
   scope of this protocol.  Additionally, in a distributed system, one
   ASP could be registered to more than one AS.  This document should
   not restrict such systems - though such a case in not specified.

A.2.  Signalling Gateway Network Architecture

   When interworking between SS7 and IP domains is needed, the SGP acts
   as the gateway node between the SS7 network and the IP network.  The
   SGP will transport SCCP-user signalling traffic from the SS7 network
   to the IP-based signalling nodes (for example IP-resident Databases).
   The Signalling Gateway can be considered as a group of Application
   Servers with additional functionality to interface toward an SS7
   network.

   The SUA protocol should be flexible enough to allow different
   configurations and transport technology to allow the network
   operators to meet their operation, management and performance
   requirements.

   An ASP may be connected to multiple SGPs (see figure 4).  In such a
   case, a particular SS7 destination may be reachable via more than SG,
   therefore, more than one route.  Given that proper SLS selection,
   loadsharing, and SG selection based on point code availability is
   performed at the ASP, it will be necessary for the ASP to maintain
   the status of each distant SGPs to which it communicates on the basis
   of the SG through which it may route.

   Signalling Gateway
                            SCTP Associations
      +----------+                                       **************
      | SG1      |                                       *  AS3       *
      | ******** |                                       *  ********  *
      | * SGP11+--------------------------------------------+ ASP1 *  *
      | ******** |                                 /     *  ********  *
      | ******** |                                 |     *  ********  *
      | * SGP12+--------------------------------------------+ ASP2 *  *
      | ******** |                   \           / |     *  ********  *
      +----------+                    \          | |     *      .     *
                                       \         | |     *      .     *
      +----------                       \        | |     *      .     *
      | SG2      |                       \       | |     *      .     *
      | ******** |                        \      | |     *  ********  *
      | * SGP21+---------------------------------+-+     *  * ASPN *  *
      | ******** |                          \            *  ********  *
      | ******** |                           \           **************
      | * SGP22+---+--+                       \
      | ******** | |  |                        \         **************
      +----------+ |  |                         \        *  AS4       *
                   |  |                          \       *  ********  *
                   |  +-------------------------------------+ ASP1 *  *
                   |                                     *  ********  *
                   |                                     *      .     *
                   |                                     *      .     *
                   |                                     *            *
                   |                                     *  ********  *
                   +----------------------------------------+ ASPn *  *
                                                         *  ********  *
                                                         **************

                Figure 4: Signalling Gateway Architecture

   The pair of SGs can either operate as replicated endpoints or as
   replicated relay points from the SS7 network point of view.

   Replicated endpoints: the coupling between the SGs and the ASPs when
   the SGs act as replicated endpoints is an implementation issue.

   Replicated relay points: in normal circumstances, the path from SEP
   to ASP will always go via the same SGP when in-sequence-delivery is
   requested.  However, linkset failures may cause MTP to reroute to the
   other SG.

A.3.  Signalling Gateway Message Distribution Recommendations

A.3.1.  Connectionless Transport

   By means of configuration, the SG knows the local SCCP-user is
   actually represented by an AS, and serviced by a set of ASPs working
   in n+k redundancy mode.  An ASP is selected and a CLDT message is
   sent on the appropriate SCTP association/stream.

   The selection criterion can be based on a round robin mechanism, or
   any other method that guarantees a balanced loadsharing over the
   active ASPs.  However, when TCAP messages are transported, load
   sharing is only possible for the first message in a TCAP dialogue
   (TC_Begin, TC_Query, TC_Unidirectional).  All other TCAP messages in
   the same dialogue are sent to the same ASP that was selected for the
   first message, unless the ASPs are able to share state and maintain
   sequenced delivery.  To this end, the SGP needs to know the TID
   allocation policy of the ASPs in a single AS:

   -  State sharing
   -  Fixed range of TIDs per ASP in the AS

   This information may be provisioned in the SG, or may be dynamically
   exchanged via the ASP_Active message.

   An example for an INAP/TCAP message exchange between SEP and ASP is
   given below.

   Address information in CLDT message (e.g., TC_Query) from SGP to ASP,
   with association ID = SG-ASP, Stream ID based on sequence control and
   possibly other parameters, e.g., OPC:

   -  Routing Context: based on SS7 Network ID and AS membership, so
      that the message can be transported to the correct ASP.
   -  Source address: valid combination of SSN, PC and GT, as needed for
      back routing to the SEP.
   -  Destination address: at least SSN, to select the SCCP/SUA-user at
      the ASP.

   Address information in CLDT message (e.g., TC_Response) from ASP to
   SG, with association ID = ASP-SG, stream ID selected by
   implementation dependent means with regards to in-sequence-delivery:

   -  Routing Context: as received in previous message.
   -  Source address: unique address provided so that when used as the
      SCCP called party address in the SEP, it must yield the same AS,
      the SSN might be sufficient.

   -  Destination address: copied from source address in received CLDT
      message.

   Further messages from the SEP belonging to the same TCAP transaction
   will now reach the same ASP.

A.3.2.  Connection-Oriented Transport

   Further messages for this connection are routed on DPC in the SS7
   connection section (MTP routing label), and on IP address in the IP
   connection section (SCTP header).  No other routing information is
   present in the SCCP or SUA messages themselves.  Resources are kept
   within the SG to forward messages from one section to another and to
   populate the MTP routing label or SCTP header, based on the
   destination local reference of these messages (Connect Confirm, Data
   Transfer, etc.)

   This means that in the SG, two local references are allocated, one
   3-byte value used for the SS7 section and one 4-byte value for the IP
   section.  Also a resource containing the connection data for both
   sections is allocated, and either of the two local references can be
   used to retrieve this data e.g., for an incoming DT1 or CODT, for
   example.

Authors' Addresses

   John Loughney
   Nokia Research Center
   PO Box 407
   FIN-00045 Nokia Group
   Finland

   EMail: john.Loughney@nokia.com

   Greg Sidebottom
   Signatus Technologies
   Kanata, Ontario
   Canada

   EMail: greg@signatustechnologies.com

   Lode Coene
   Siemens n.v.
   Atealaan 34
   B-2200 Herentals
   Belgium

   Phone: +32-14-252081
   EMail: lode.coene@siemens.com

   Gery Verwimp
   Siemens n.v.
   34 Atealaan
   PO 2200
   Herentals
   Belgium

   Phone: +32 14 25 3424
   EMail: gery.verwimp@siemens.com

   Joe Keller
   Tekelec
   5200 Paramount Parkway
   Morrisville, NC 27560
   USA

   EMail: joe.keller@tekelec.com

   Brian Bidulock
   OpenSS7 Corporation
   1469 Jeffreys Crescent
   Edmonton, AB  T6L 6T1
   Canada

   Phone: +1 780 490 1141
   EMail: bidulock@openss7.org

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