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RFC 4006 - Diameter Credit-Control Application


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Network Working Group                                          H. Hakala
Request for Comments: 4006                                    L. Mattila
Category: Standards Track                                       Ericsson
                                                           J-P. Koskinen
                                                                M. Stura
                                                             J. Loughney
                                                                   Nokia
                                                             August 2005

                 Diameter Credit-Control Application

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 (2005).

Abstract

   This document specifies a Diameter application that can be used to
   implement real-time credit-control for a variety of end user services
   such as network access, Session Initiation Protocol (SIP) services,
   messaging services, and download services.

Table of Contents

   1.  Introduction.................................................   4
       1.1.   Requirements Language.................................   5
       1.2.   Terminology...........................................   5
       1.3.   Advertising Application Support.......................   7
   2.  Architecture Models..........................................   7
   3.  Credit-Control Messages......................................   9
       3.1.   Credit-Control-Request (CCR) Command..................   9
       3.2.   Credit-Control-Answer (CCA) Command...................  11
   4.  Credit-Control Application Overview..........................  11
       4.1.   Service-Specific Rating Input and Interoperability....  13
   5.  Session Based Credit-Control.................................  15
       5.1.   General Principles....................................  15
       5.2.   First Interrogation...................................  21
       5.3.   Intermediate Interrogation............................  27
       5.4.   Final Interrogation...................................  29

       5.5.   Server-Initiated Credit Re-Authorization..............  30
       5.6.   Graceful Service Termination..........................  32
       5.7.   Failure Procedures....................................  38
   6.  One Time Event...............................................  41
       6.1.   Service Price Enquiry.................................  42
       6.2.   Balance Check.........................................  42
       6.3.   Direct Debiting.......................................  43
       6.4.   Refund................................................  44
       6.5.   Failure Procedure.....................................  44
   7.  Credit-Control Application State Machine.....................  46
   8.  Credit-Control AVPs..........................................  55
       8.1.   CC-Correlation-Id AVP.................................  58
       8.2.   CC-Request-Number AVP.................................  58
       8.3.   CC-Request-Type AVP...................................  58
       8.4.   CC-Session-Failover AVP...............................  59
       8.5.   CC-Sub-Session-Id AVP.................................  59
       8.6.   Check-Balance-Result AVP..............................  60
       8.7.   Cost-Information AVP..................................  60
       8.8.   Unit-Value AVP........................................  61
       8.9.   Exponent AVP..........................................  61
       8.10.  Value-Digits AVP......................................  61
       8.11.  Currency-Code AVP.....................................  62
       8.12.  Cost-Unit AVP.........................................  62
       8.13.  Credit-Control AVP....................................  62
       8.14.  Credit-Control-Failure-Handling AVP...................  62
       8.15.  Direct-Debiting-Failure-Handling AVP..................  63
       8.16.  Multiple-Services-Credit-Control AVP..................  64
       8.17.  Granted-Service-Unit AVP..............................  65
       8.18.  Requested-Service-Unit AVP............................  66
       8.19.  Used-Service-Unit AVP.................................  66
       8.20.  Tariff-Time-Change AVP................................  67
       8.21.  CC-Time AVP...........................................  67
       8.22.  CC-Money AVP..........................................  67
       8.23.  CC-Total-Octets AVP...................................  68
       8.24.  CC-Input-Octets AVP...................................  68
       8.25.  CC-Output-Octets AVP..................................  68
       8.26.  CC-Service-Specific-Units AVP.........................  68
       8.27.  Tariff-Change-Usage AVP...............................  68
       8.28.  Service-Identifier AVP................................  69
       8.29.  Rating-Group AVP......................................  69
       8.30.  G-S-U-Pool-Reference AVP..............................  69
       8.31.  G-S-U-Pool-Identifier AVP.............................  70
       8.32.  CC-Unit-Type AVP......................................  70
       8.33.  Validity-Time AVP.....................................  70
       8.34.  Final-Unit-Indication AVP.............................  71
       8.35.  Final-Unit-Action AVP.................................  72
       8.36.  Restriction-Filter-Rule AVP...........................  72
       8.37.  Redirect-Server AVP...................................  73

       8.38.  Redirect-Address-Type AVP.............................  73
       8.39.  Redirect-Server-Address AVP...........................  74
       8.40.  Multiple-Services-Indicator AVP.......................  74
       8.41.  Requested-Action AVP..................................  74
       8.42.  Service-Context-Id AVP................................  75
       8.43.  Service-Parameter-Info AVP............................  76
       8.44.  Service-Parameter-Type AVP............................  76
       8.45.  Service-Parameter-Value AVP...........................  77
       8.46.  Subscription-Id AVP...................................  77
       8.47.  Subscription-Id-Type AVP..............................  77
       8.48.  Subscription-Id-Data AVP..............................  78
       8.49.  User-Equipment-Info AVP...............................  78
       8.50.  User-Equipment-Info-Type AVP..........................  78
       8.50.  User-Equipment-Info-Value AVP.........................  79
   9.  Result Code AVP Values.......................................  79
       9.1.   Transient Failures....................................  79
       9.2.   Permanent Failures....................................  80
   10. AVP Occurrence Table.........................................  80
       10.1.  Credit-Control AVP Table..............................  81
       10.2.  Re-Auth-Request/Answer AVP Table......................  82
   11. RADIUS/Diameter Credit-Control Interworking Model............  82
   12. IANA Considerations..........................................  85
       12.1.  Application Identifier................................  86
       12.2.  Command Codes.........................................  86
       12.3.  AVP Codes.............................................  86
       12.4.  Result-Code AVP Values................................  86
       12.5.  CC-Request-Type AVP...................................  86
       12.6.  CC-Session-Failover AVP...............................  86
       12.7.  CC-Unit-Type AVP......................................  87
       12.8.  Check-Balance-Result AVP..............................  87
       12.9.  Credit-Control AVP....................................  87
       12.10. Credit-Control-Failure-Handling AVP...................  87
       12.11. Direct-Debiting-Failure-Handling AVP..................  87
       12.12. Final-Unit-Action AVP.................................  87
       12.13. Multiple-Services-Indicator AVP.......................  87
       12.14. Redirect-Address-Type AVP.............................  88
       12.15. Requested-Action AVP..................................  88
       12.16. Subscription-Id-Type AVP..............................  88
       12.17. Tariff-Change-Usage AVP...............................  88
       12.18. User-Equipment-Info-Type AVP..........................  88
   13. Credit-Control Application Related Parameters................  88
   14. Security Considerations......................................  89
       14.1.  Direct Connection with Redirects......................  90
   15. References...................................................  91
       15.1.  Normative References..................................  91
       15.2.  Informative References................................  92
   16. Acknowledgements.............................................  93
   Appendix A Credit-Control Sequences..............................  94

       A.1.   Flow I................................................  94
       A.2.   Flow II...............................................  96
       A.3.   Flow III..............................................  98
       A.4.   Flow IV...............................................  99
       A.5.   Flow V................................................ 100
       A.6.   Flow VI............................................... 102
       A.7.   Flow VII.............................................. 103
       A.8.   Flow VIII............................................. 105
       A.9.   Flow IX............................................... 107
   Authors' Addresses............................................... 112
   Full Copyright Statement......................................... 114

1.  Introduction

   This document specifies a Diameter application that can be used to
   implement real-time credit-control for a variety of end user services
   such as network access, Session Initiation Protocol (SIP) services,
   messaging services, and download services.  It provides a general
   solution to real-time cost and credit-control.

   The prepaid model has been shown to be very successful, for instance,
   in GSM networks, where network operators offering prepaid services
   have experienced a substantial growth of their customer base and
   revenues.  Prepaid services are now cropping up in many other
   wireless and wire line based networks.

   In next generation wireless networks, additional functionality is
   required beyond that specified in the Diameter base protocol.  For
   example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
   that an application must be able to rate service information in
   real-time.  In addition, it is necessary to check that the end user's
   account provides coverage for the requested service prior to
   initiation of that service.  When an account is exhausted or expired,
   the user must be denied the ability to compile additional chargeable
   events.

   A mechanism has to be provided to allow the user to be informed of
   the charges to be levied for a requested service.  In addition, there
   are services such as gaming and advertising that may credit as well
   as debit a user account.

   The other Diameter applications provide service specific
   authorization, and they do not provide credit authorization for
   prepaid users.  The credit authorization shall be generic and
   applicable to all the service environments required to support
   prepaid services.

   To fulfill these requirements, it is necessary to facilitate credit-
   control communication between the network element providing the
   service (e.g., Network Access Server, SIP Proxy, and Application
   Server) and a credit-control server.

   The scope of this specification is the credit authorization.  Service
   specific authorization and authentication is out of the scope.

1.1.  Requirements Language

   In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
   "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
   described in [KEYWORDS].

1.2.  Terminology

   AAA

   Authentication, Authorization, and Accounting

   AA answer

   AA answer generically refers to a service specific authorization and
   authentication answer.  AA answer commands are defined in service
   specific authorization applications, e.g., [NASREQ] and [DIAMMIP].

   AA request

   AA request generically refers to a service specific authorization and
   authentication request.  AA request commands are defined in service
   specific authorization applications e.g., [NASREQ] and [DIAMMIP].

   Credit-control

   Credit-control is a mechanism that directly interacts in real-time
   with an account and controls or monitors the charges related to the
   service usage.  Credit-control is a process of checking whether
   credit is available, credit-reservation, deduction of credit from the
   end user account when service is completed and refunding of reserved
   credit that is not used.

   Diameter Credit-control Server

   A Diameter credit-control server acts as a prepaid server, performing
   real-time rating and credit-control.  It is located in the home
   domain and is accessed by service elements or Diameter AAA servers in

   real-time for purpose of price determination and credit-control
   before the service event is delivered to the end-user.  It may also
   interact with business support systems.

   Diameter Credit-control Client

   A Diameter credit-control client is an entity that interacts with a
   credit-control server.  It monitors the usage of the granted quota
   according to instructions returned by credit-control server.

   Interrogation

   The Diameter credit-control client uses interrogation to initiate a
   session based credit-control process.  During the credit-control
   process, it is used to report the used quota and request a new one.
   An interrogation maps to a request/answer transaction.

   One-time event

   Basically, a request/answer transaction of type event.

   Rating

   The act of determining the cost of the service event.

   Service

   A type of task performed by a service element for an end user.

   Service Element

   A network element that provides a service to the end users.  The
   Service Element may include the Diameter credit-control client, or
   another entity (e.g., RADIUS AAA server) that can act as a Credit-
   control client on behalf of the Service Element.  In the latter case,
   the interface between the Service Element and the Diameter credit-
   control client is outside the scope of this specification.  Examples
   of the Service Elements include Network Access Server (NAS), SIP
   Proxy, and Application Servers such as messaging server, content
   server, and gaming server.

   Service Event

   An event relating to a service provided to the end user.

   Session based credit-control

   A credit-control process that makes use of several interrogations:
   the first, a possible intermediate, and the final.  The first
   interrogation is used to reserve money from the user's account and to
   initiate the process.  The intermediate interrogations may be needed
   to request new quota while the service is being rendered.  The final
   interrogation is used to exit the process.  The credit-control server
   is required to maintain session state for session-based credit-
   control.

1.3.  Advertising Application Support

   Diameter nodes conforming to this specification MUST advertise
   support by including the value of 4 in the Auth-Application-Id of the
   Capabilities-Exchange-Request and Capabilities-Exchange-Answer
   command [DIAMBASE].

2.  Architecture Models

   The current accounting models specified in the Radius Accounting
   [RFC2866] and Diameter base [DIAMBASE] are not sufficient for real-
   time credit-control, where credit-worthiness is to be determined
   prior to service initiation.  Also, the existing Diameter
   authorization applications, [NASREQ] and [DIAMMIP], only provide
   service authorization, but do not provide credit authorization for
   prepaid users.  In order to support real-time credit-control, a new
   type of server is needed in the AAA infrastructure: Diameter credit-
   control server.  The Diameter credit-control server is the entity
   responsible for credit authorization for prepaid subscribers.

   A service element may authenticate and authorize the end user with
   the AAA server by using AAA protocols; e.g., RADIUS or a Diameter
   base protocol with a possible Diameter application.

   Accounting protocols such as RADIUS accounting and the Diameter base
   accounting protocol can be used to provide accounting data to the
   accounting server after service is initiated, and to provide possible
   interim reports until service completion.  However, for real-time
   credit-control, these authorization and accounting models are not
   sufficient.

   When real-time credit-control is required, the credit-control client
   contacts the credit-control server with information about a possible
   service event.  The credit-control process is performed to determine
   potential charges and to verify whether the end user's account
   balance is sufficient to cover the cost of the service being
   rendered.

   Figure 1 illustrates the typical credit-control architecture, which
   consists of a Service Element with an embedded Diameter credit-
   control client, a Diameter credit-control server, and an AAA server.
   A Business Support System is usually deployed; it includes at least
   the billing functionality.  The credit-control server and AAA server
   in this architecture model are logical entities.  The real
   configuration can combine them into a single host.  The credit-
   control protocol is the Diameter base protocol with the Diameter
   credit-control application.

   When an end user requests services such as SIP or messaging, the
   request is typically forwarded to a service element (e.g., SIP Proxy)
   in the user's home domain.  In some cases it might be possible that
   the service element in the visited domain can offer services to the
   end user; however, a commercial agreement must exist between the
   visited domain and the home domain.  Network access is an example of
   a service offered in the visited domain where the NAS, through an AAA
   infrastructure, authenticates and authorizes the user with the user's
   home network.

                   Service Element   AAA and CC
   +----------+      +---------+     Protocols+-----------+  +--------+
   |  End     |<---->|+-------+|<------------>|    AAA    |  |Business|
   |  User    |   +->|| CC    ||              |   Server  |->|Support |
   |          |   |  || Client||<-----+       |           |  |System  |
   +----------+   |  |+-------+|      |       +-----------+  |        |
                  |  +---------+      |             ^        +--------+
   +----------+   |                   | CC Protocol |             ^
   |  End     |<--+                   |       +-----v----+        |
   |  User    |                       +------>|Credit-   |        |
   +----------+                Credit-Control |Control   |--------+
                               Protocol       |Server    |
                                              +----------+

              Figure 1: Typical credit-control architecture

   There can be multiple credit-control servers in the system for
   redundancy and load balancing.  The system can also contain separate
   rating server(s), and accounts can be located in a centralized
   database.  To ensure that the end user's account is not debited or
   credited multiple times for the same service event, only one place in
   the credit-control system should perform duplicate detection.  System
   internal interfaces can exist to relay messages between servers and
   an account manager.  However, the detailed architecture of the
   credit-control system and its interfaces are implementation specific
   and are out of scope of this specification.

   Protocol transparent Diameter relays can exist between the credit-
   control client and credit-control server.  Also, Diameter Redirect
   agents that refer credit-control clients to credit-control servers
   and allow them to communicate directly can exist.  These agents
   transparently support the Diameter credit-control application.  The
   different roles of Diameter Agents are defined in Diameter base
   [DIAMBASE], section 2.8.

   If Diameter credit-control proxies exist between the credit-control
   client and the credit-control server, they MUST advertise the
   Diameter credit-control application support.

3.  Credit-Control Messages

   This section defines new Diameter message Command-Code values that
   MUST be supported by all Diameter implementations that conform to
   this specification.  The Command Codes are as follows:

   Command-Name                  Abbrev.    Code     Reference
   -----------------------------------------------------------
   Credit-Control-Request        CCR        272      3.1
   Credit-Control-Answer         CCA        272      3.2

   Diameter Base [DIAMBASE] defines in the section 3.2 the Command Code
   ABNF specification.  These formats are observed in Credit-Control
   messages.

3.1.  Credit-Control-Request (CCR) Command

   The Credit-Control-Request message (CCR) is indicated by the
   command-code field being set to 272 and the 'R' bit being set in the
   Command Flags field.  It is used between the Diameter credit-control
   client and the credit-control server to request credit authorization
   for a given service.

   The Auth-Application-Id MUST be set to the value 4, indicating the
   Diameter credit-control application.

   Message Format

      <Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
                                   < Session-Id >
                                   { Origin-Host }
                                   { Origin-Realm }
                                   { Destination-Realm }
                                   { Auth-Application-Id }
                                   { Service-Context-Id }
                                   { CC-Request-Type }
                                   { CC-Request-Number }
                                   [ Destination-Host ]
                                   [ User-Name ]
                                   [ CC-Sub-Session-Id ]
                                   [ Acct-Multi-Session-Id ]
                                   [ Origin-State-Id ]
                                   [ Event-Timestamp ]
                                  *[ Subscription-Id ]
                                   [ Service-Identifier ]
                                   [ Termination-Cause ]
                                   [ Requested-Service-Unit ]
                                   [ Requested-Action ]
                                  *[ Used-Service-Unit ]
                                   [ Multiple-Services-Indicator ]
                                  *[ Multiple-Services-Credit-Control ]
                                  *[ Service-Parameter-Info ]
                                   [ CC-Correlation-Id ]
                                   [ User-Equipment-Info ]
                                  *[ Proxy-Info ]
                                  *[ Route-Record ]
                                  *[ AVP ]

3.2.  Credit-Control-Answer (CCA) Command

   The Credit-Control-Answer message (CCA) is indicated by the command-
   code field being set to 272 and the 'R' bit being cleared in the
   Command Flags field.  It is used between the credit-control server
   and the Diameter credit-control client to acknowledge a Credit-
   Control-Request command.

   Message Format

      <Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
                                  < Session-Id >
                                  { Result-Code }
                                  { Origin-Host }
                                  { Origin-Realm }
                                  { Auth-Application-Id }
                                  { CC-Request-Type }
                                  { CC-Request-Number }
                                  [ User-Name ]
                                  [ CC-Session-Failover ]
                                  [ CC-Sub-Session-Id ]
                                  [ Acct-Multi-Session-Id ]
                                  [ Origin-State-Id ]
                                  [ Event-Timestamp ]
                                  [ Granted-Service-Unit ]
                                 *[ Multiple-Services-Credit-Control ]
                                  [ Cost-Information]
                                  [ Final-Unit-Indication ]
                                  [ Check-Balance-Result ]
                                  [ Credit-Control-Failure-Handling ]
                                  [ Direct-Debiting-Failure-Handling ]
                                  [ Validity-Time]
                                 *[ Redirect-Host]
                                  [ Redirect-Host-Usage ]
                                  [ Redirect-Max-Cache-Time ]
                                 *[ Proxy-Info ]
                                 *[ Route-Record ]
                                 *[ Failed-AVP ]
                                 *[ AVP ]

4.  Credit-Control Application Overview

   The credit authorization process takes place before and during
   service delivery to the end user and generally requires the user's
   authentication and authorization before any request is sent to the
   credit-control server.  The credit-control application defined in
   this specification supports two different credit authorization
   models: credit authorization with money reservation and credit

   authorization with direct debiting.  In both models, the credit-
   control client requests credit authorization from the credit-control
   server prior to allowing any service to be delivered to the end user.

   In the first model, the credit-control server rates the request,
   reserves a suitable amount of money from the user's account, and
   returns the corresponding amount of credit resources.  Note that
   credit resources may not imply actual monetary credit; credit
   resources may be granted to the credit control client in the form of
   units (e.g., data volume or time) to be metered.

   Upon receipt of a successful credit authorization answer with a
   certain amount of credit resources, the credit-control client allows
   service delivery to the end user and starts monitoring the usage of
   the granted resources.  When the credit resources granted to the user
   have been consumed or the service has been successfully delivered or
   terminated, the credit-control client reports back to the server the
   used amount.  The credit-control server deducts the used amount from
   the end user's account; it may perform rating and make a new credit
   reservation if the service delivery is continuing.  This process is
   accomplished with session based credit-control that includes the
   first interrogation, possible intermediate interrogations, and the
   final interrogation.  For session based credit-control, both the
   credit control client and the credit-control server are required to
   maintain credit-control session state.  Session based credit-control
   is described in more detail, with more variations, in section 5.

   In contrast, credit authorization with direct debiting is a single
   transaction process wherein the credit-control server directly
   deducts a suitable amount of money from the user's account as soon as
   the credit authorization request is received.  Upon receipt of a
   successful credit authorization answer, the credit-control client
   allows service delivery to the end user.  This process is
   accomplished with the one-time event.  Session state is not
   maintained.

   In a multi-service environment, an end user can issue an additional
   service request (e.g., data service) during an ongoing service (e.g.,
   voice call) toward the same account.  Alternatively, during an active
   multimedia session, an additional media type is added to the session,
   causing a new simultaneous request toward same account.
   Consequently, this needs to be considered when credit resources are
   granted to the services.

   The credit-control application also supports operations such as
   service price enquiry, user's balance check, and refund of credit on
   the user's account.  These operations are accomplished with the one-
   time event.  Session state is not maintained.

   A flexible credit-control application specific failure handling is
   defined in which the home service provider can model the credit-
   control client behavior according to its own credit risk management
   policy.

   The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
   Failure-Handling AVP are defined to determine what is done if the
   sending of credit-control messages to the credit-control server has
   been temporarily prevented.  The usage of the Credit-Control-
   Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP
   allows flexibility, as failure handling for the credit-control
   session and one time event direct debiting may be different.

4.1.  Service-Specific Rating Input and Interoperability

   The Diameter credit-control application defines the framework for
   credit-control; it provides generic credit-control mechanisms
   supporting multiple service applications.  The credit-control
   application, therefore, does not define AVPs that could be used as
   input in the rating process.  Listing the possible services that
   could use this Diameter application is out of scope for this generic
   mechanism.

   It is reasonable to expect that a service level agreement will exist
   between providers of the credit-control client and the credit-control
   server covering the charging, services offered, roaming agreements,
   agreed rating input (i.e., AVPs), and so on.

   Therefore, it is assumed that a Diameter credit-control server will
   provide service only for Diameter credit-control clients that have
   agreed beforehand as to the content of credit-control messages.
   Naturally, it is possible that any arbitrary Diameter credit-control
   client can interchange credit-control messages with any Diameter
   credit-control server, but with a higher likelihood that unsupported
   services/AVPs could be present in the credit-control message, causing
   the server to reject the request with an appropriate result-code.

4.1.1.  Specifying Rating Input AVPs

   There are two ways to provide rating input to the credit-control
   server: either by using AVPs or by including them in the Service-
   Parameter-Info AVP.  The general principles for sending rating
   parameters are as follows:

   1a. The service SHOULD re-use existing AVPs if it can use AVPs
   defined in existing Diameter applications (e.g., NASREQ for network
   access services).  Re-use of existing AVPs is strongly recommended in
   [DIAMBASE].

   For AVPs of type Enumerated, the service may require a new value to
   be defined.  Allocation of new AVP values is done as specified in
   [DIAMBASE], section 1.2.

   1b. New AVPs can be defined if the existing AVPs do not provide
   sufficient rating information.  In this case, the procedures defined
   in [DIAMBASE] for creating new AVPs MUST be followed.

   1c. For services specific only to one vendor's implementation, a
   Vendor-Specific AVP code for Private use can be used.  Where a
   Vendor-Specific AVP is implemented by more than one vendor,
   allocation of global AVPs is encouraged instead; refer to [DIAMBASE].

   2. The Service-Parameter-Info AVP MAY be used as a container to pass
   legacy rating information in its original encoded form (e.g., ASN.1
   BER).  This method can be used to avoid unnecessary conversions from
   an existing data format to an AVP format.  In this case, the rating
   input is embedded in the Service-Parameter-Info AVP as defined in
   section 8.43.

   New service applications SHOULD favor the use of explicitly defined
   AVPs as described in items 1a and 1b, to simplify interoperability.

4.1.2.  Service-Specific Documentation

   The service specific rating input AVPs, the contents of the Service-
   Parameter-Info AVP or Service-Context-Id AVP (defined in section
   8.42) are not within the scope of this document.  To facilitate
   interoperability, it is RECOMMENDED that the rating input and the
   values of the Service-Context-Id be coordinated via an informational
   RFC or other permanent and readily available reference.  The
   specification of another cooperative standardization body (e.g.,
   3GPP, OMA, and 3GPP2) SHOULD be used.  However, private services may
   be deployed that are subject to agreements between providers of the
   credit-control server and client.  In this case, vendor specific AVPs
   can be used.

   This specification, together with the above service specific
   documents, governs the credit-control message.  Service specific
   documents define which existing AVPs or new AVPs are used as input to
   the rating process (i.e., those that do not define new credit-control
   applications), and thus have to be included in the Credit-Control-
   Request command by a Diameter credit-control client supporting a
   given service as *[AVP].  Should Service-Parameter-Info be used, then
   the service specific document MUST specify the exact content of this
   grouped AVP.

   The Service-Context-Id AVP MUST be included at the command level of a
   Credit-Control Request to identify the service specific document that
   applies to the request.  The specific service or rating group the
   request relates to is uniquely identified by the combination of
   Service-Context-Id and Service-Identifier or Rating-Group.

4.1.3.  Handling of Unsupported/Incorrect Rating Input

   Diameter credit-control implementations are required to support the
   Mandatory rating AVPs defined in service specific documentation of
   the services they support, according to the 'M' bit rules in
   [DIAMBASE].

   If a rating input required for the rating process is incorrect in the
   Credit-control request, or if the credit-control server does not
   support the requested service context (identified by the Service-
   Context-Id AVP at command level), the Credit-control answer MUST
   contain the error code DIAMETER_RATING_FAILED.  A CCA message with
   this error MUST contain one or more Failed-AVP AVPs containing the
   missing and/or unsupported AVPs that caused the failure.  A Diameter
   credit-control client that receives the error code
   DIAMETER_RATING_FAILED in response to a request MUST NOT send similar
   requests in the future.

4.1.4.  RADIUS Vendor-Specific Rating Attributes

   When service specific documents include RADIUS vendor specific
   attributes that could be used as input in the rating process, the
   rules described in [NASREQ] for formatting the Diameter AVP MUST be
   followed.

   For example, if the AVP code used is the vendor attribute type code,
   the Vendor-Specific flag MUST be set to 1 and the Vendor-ID MUST be
   set to the IANA Vendor identification value.  The Diameter AVP data
   field contains only the attribute value of the RADIUS attribute.

5.  Session Based Credit-Control

5.1.  General Principles

   For a session-based credit-control, several interrogations are
   needed: the first, intermediate (optional) and the final
   interrogations.  This is illustrated in Figures 2 and 3.

   If the credit-control client performs credit-reservation before
   granting service to the end user, it MUST use several interrogations
   toward the credit-control server (i.e., session based credit-

   control).  In this case, the credit-control server MUST maintain the
   credit-control session state.

   Each credit-control session MUST have a globally unique Session-Id as
   defined in [DIAMBASE], which MUST NOT be changed during the lifetime
   of a credit-control session.

   Certain applications require multiple credit-control sub-sessions.
   These applications would send messages with a constant Session-Id
   AVP, but with a different CC-Sub-Session-Id AVP.  If several credit
   sub-sessions will be used, all sub-sessions MUST be closed separately
   before the main session is closed so that units per sub-session may
   be reported.  The absence of this AVP implies that no sub-sessions
   are in use.

   Note that the service element might send a service specific re-
   authorization message to the AAA server due to expiration of the
   authorization-lifetime during an ongoing credit-control session.
   However, the service specific re-authorization does not influence the
   credit authorization that is ongoing between the credit-control
   client and credit-control server, as credit authorization is
   controlled by the burning rate of the granted quota.

   If service specific re-authorization fails, the user will be
   disconnected, and the credit-control client MUST send a final
   interrogation to the credit-control server.

   The Diameter credit-control server may seek to control the validity
   time of the granted quota and/or the production of intermediate
   interrogations.  Thus, it MAY include the Validity-Time AVP in the
   answer message to the credit-control client.  Upon expiration of the
   Validity-Time, the credit-control client MUST generate a credit-
   control update request and report the used quota to the credit-
   control server.  It is up to the credit-control server to determine
   the value of the Validity-Time to be used for consumption of the
   granted service units.  If the Validity-Time is used, its value
   SHOULD be given as input to set the session supervision timer Tcc
   (the session supervision timer MAY be set to two times the value of
   the Validity-Time, as defined in section 13).  Since credit-control
   update requests are also produced at the expiry of granted service
   units and/or for mid-session service events, the omission of
   Validity-Time does not mean that intermediate interrogation for the
   purpose of credit-control is not performed.

5.1.1.  Basic Tariff-Time Change Support

   The Diameter credit-control server and client MAY optionally support
   a tariff change mechanism.  The Diameter credit-control server may
   include a Tariff-Time-Change AVP in the answer message.  Note that
   the granted units should be allocated based on the worst-case
   scenario in case of forthcoming tariff change, so that the overall
   reported used units would never exceed the credit reservation.

   When the Diameter credit-control client reports the used units and a
   tariff change has occurred during the reporting period, the Diameter
   credit-control client MUST separately itemize the units used before
   and after the tariff change.  If the client is unable to distinguish
   whether units straddling the tariff change were used before or after
   the tariff change, the credit-control client MUST itemize those units
   in a third category.

   If a client does not support the tariff change mechanism and it
   receives a CCA message carrying the Tariff-Time-Change AVP, it MUST
   terminate the credit-control session, giving a reason of
   DIAMETER_BAD_ANSWER in the Termination-Cause AVP.

   For time based services, the quota is continuously consumed at the
   regular rate of 60 seconds per minute.  At the time when credit
   resources are allocated, the server already knows how many units will
   be consumed before the tariff time change and how many units will be
   consumed afterward.  Similarly, the server can determine the units
   consumed at the before rate and the units consumed at the rate
   afterward in the event that the end-user closes the session before
   the consumption of the allotted quota.  There is no need for
   additional traffic between client and server in the case of tariff
   time changes for continuous time based service.  Therefore, the
   tariff change mechanism is not used for such services.  For time-
   based services in which the quota is NOT continuously consumed at a
   regular rate, the tariff change mechanism described for volume and
   event units MAY be used.

5.1.2.  Credit-Control for Multiple Services within a (sub-)Session

   When multiple services are used within the same user session and each
   service or group of services is subject to different cost, it is
   necessary to perform credit-control for each service independently.
   Making use of credit-control sub-sessions to achieve independent
   credit-control will result in increased signaling load and usage of
   resources in both the credit-control client and the credit-control
   server.  For instance, during one network access session the end user
   may use several http-services subject to different access cost.  The
   network access specific attributes such as the quality of service

   (QoS) are common to all the services carried within the access
   bearer, but the cost of the bearer may vary depending on its content.

   To support these scenarios optimally, the credit-control application
   enables independent credit-control of multiple services in a single
   credit-control (sub-)session.  This is achieved by including the
   optional Multiple-Services-Credit-Control AVP in Credit-Control-
   Request/Answer messages.  It is possible to request and allocate
   resources as a credit pool shared between multiple services.  The
   services can be grouped into rating groups in order to achieve even
   further aggregation of credit allocation.  It is also possible to
   request and allocate quotas on a per service basis.  Where quotas are
   allocated to a pool by means of the Multiple-Services-Credit-Control
   AVP, the quotas remain independent objects that can be re-authorized
   independently at any time.  Quotas can also be given independent
   result codes, validity times, and Final-Unit-Indications.

   A Rating-Group gathers a set of services, identified by a Service-
   Identifier, and subject to the same cost and rating type (e.g.,
   $0.1/minute).  It is assumed that the service element is provided
   with Rating-Groups, Service-Identifiers, and their associated
   parameters that define what has to be metered by means outside the
   scope of this specification.  (Examples of parameters associated to
   Service-Identifiers are IP 5-tuple and HTTP URL.) Service-Identifiers
   enable authorization on a per-service based credit as well as
   itemized reporting of service usage.  It is up to the credit-control
   server whether to authorize credit for one or more services or for
   the whole rating-group.  However, the client SHOULD always report
   used units at the finest supported level of granularity.  Where quota
   is allocated to a rating-group, all the services belonging to that
   group draw from the allotted quota.  The following is a graphical
   representation of the relationship between service-identifiers,
   rating-groups, credit pools, and credit-control (sub-)session.

                          DCC (Sub-)Session
                                  |
         +------------+-----------+-------------+--------------- +
         |            |           |             |                |
   Service-Id a Service-Id b Service-Id c Service-Id d.....Service-Id z
        \        /                 \         /                /
         \      /                   \       /                /
          \    /                  Rating-Group 1.......Rating-Group n
           \  /                         |                    |
          Quota       ---------------Quota                 Quota
            |        /                                       |
            |       /                                        |
         Credit-Pool                                    Credit-Pool

   If independent credit-control of multiple services is used, the
   validity-time and final-unit-indication SHOULD be present either in
   the Multiple-Services-Credit-Control AVP(s) or at command level as
   single AVPs.  However, the Result-Code AVP MAY be present both on the
   command level and within the Multiple-Services-Credit-Control AVP.
   If the Result-Code on the command level indicates a value other than
   SUCCESS, then the Result-Code on command level takes precedence over
   any included in the Multiple-Services-Credit-Control AVP.

   The credit-control client MUST indicate support for independent
   credit-control of multiple services within a (sub-)session by
   including the Multiple-Services-Indicator AVP in the first
   interrogation.  A credit-control server not supporting this feature
   MUST treat the Multiple-Services-Indicator AVP and any received
   Multiple-Services-Credit-Control AVPs as invalid AVPs.

   If the client indicated support for independent credit-control of
   multiple services, a credit-control server that wishes to use the
   feature MUST return the granted units within the Multiple-Services-
   Credit-Control AVP associated to the corresponding service-identifier
   and/or rating-group.

   To avoid a situation where several parallel (and typically also
   small) credit reservations must be made on the same account (i.e.,
   credit fragmentation), and also to avoid unnecessary load on the
   credit-control server, it is possible to provide service units as a
   pool that applies to multiple services or rating groups.  This is
   achieved by providing the service units in the form of a quota for a
   particular service or rating group in the Multiple-Services-Credit-
   Control AVP, and also by including a reference to a credit pool for
   that unit type.

   The reference includes a multiplier derived from the rating
   parameter, which translates from service units of a specific type to
   the abstract service units in the pool.  For instance, if the rating
   parameter for service 1 is $1/MB and the rating parameter for service
   2 is $0.5/MB, the multipliers could be 10 and 5 for services 1 and 2,
   respectively.

   If S is the total service units within the pool, M1, M2, ..., Mn are
   the multipliers provided for services 1, 2, ..., n, and C1, C2, ...,
   Cn are the used resources within the session, then the pool credit is
   exhausted and re-authorization MUST be sought when:

         C1*M1 + C2*M2 + ... + Cn*Mn >= S

   The total credit in the pool, S, is calculated from the quotas, which
   are currently allocated to the pool as follows:

         S = Q1*M1 + Q2*M2 + ... + Qn*Mn

   If services or rating groups are added to or removed from the pool,
   then the total credit is adjusted appropriately.  Note that when the
   total credit is adjusted because services or rating groups are
   removed from the pool, the value that need to be removed is the
   consumed one (i.e., Cx*Mx).

   Re-authorizations for an individual service or rating group may be
   sought at any time; for example, if a 'non-pooled' quota is used up
   or the Validity-Time expires.

   Where multiple G-S-U-Pool-Reference AVPs (section 8.30) with the same
   G-S-U-Pool-Identifier are provided within a Multiple-Services-
   Credit-Control AVP (section 8.16) along with the Granted-Service-Unit
   AVP, then these MUST have different CC-Unit-Type values, and they all
   draw from the credit pool separately.  For instance, if one
   multiplier for time (M1t) and one multiplier for volume (M1v) are
   given, then the used resources from the pool is the sum C1t*M1t +
   C1v*M1v, where C1t is the time unit and C1v is the volume unit.

   Where service units are provided within a Multiple-Services-Credit-
   Control AVP without a corresponding G-S-U-Pool-Reference AVP, then
   these are handled independently from any credit pool and from any
   other services or rating groups within the session.

   The credit pool concept is an optimal tool to avoid the over-
   reservation effect of the basic single quota tariff time change
   mechanism (the mechanism described in section 5.1.1).  Therefore,
   Diameter credit-control clients and servers implementing the
   independent credit-control of multiple services SHOULD leverage the
   credit pool concept when supporting the tariff time change.  The
   Diameter credit-control server SHOULD include both the Tariff-Time-
   Change and Tariff-Change-Usage AVPs in two quota allocations in the
   answer message (i.e., two instances of the Multiple-Services-Credit-
   Control AVP).  One of the granted units is allocated to be used
   before the potential tariff change, while the second granted units
   are for use after a tariff change.  Both granted unit quotas MUST
   contain the same Service-Identifier and/or Rating-Group.  This dual
   quota mechanism ensures that the overall reported used units would
   never exceed the credit reservation.  The Diameter credit-control
   client reports both the used units before and after the tariff change
   in a single instance of the Multiple-Services-Credit-Control AVP.

   The failure handling for credit-control sessions is defined in
   section 5.7 and reflected in the basic credit-control state machine
   in section 7.  Credit-control clients and servers implementing the
   independent credit-control of multiple services in a (sub-)session
   functionality MUST ensure failure handling and general behavior fully
   consistent with the above mentioned sections, while maintaining the
   ability to handle parallel ongoing credit re-authorization within a
   (sub-)session.  Therefore, it is RECOMMENDED that Diameter credit-
   control clients maintain a PendingU message queue and restart the Tx
   timer (section 13) every time a CCR message with the value
   UPDATE_REQUEST is sent while they are in PendingU state.  When
   answers to all pending messages are received, the state machine moves
   to OPEN state, and Tx is stopped.  Naturally, the action performed
   when a problem for the session is detected according to section 5.7
   affects all the ongoing services (e.g., failover to a backup server
   if possible affect all the CCR messages with the value UPDATE_REQUEST
   in the PendingU queue).

   Since the client may send CCR messages with the value UPDATE_REQUEST
   while in PendingU (i.e., without waiting for an answer to ongoing
   credit re-authorization), the time space between these requests may
   be very short, and the server may not have received the previous
   request(s) yet.  Therefore, in this situation the server may receive
   out of sequence requests and SHOULD NOT consider this an error
   condition.  A proper answer is to be returned to each of those
   requests.

5.2.  First Interrogation

   When session based credit-control is required (e.g., the
   authentication server indicated a prepaid user), the first
   interrogation MUST be sent before the Diameter credit-control client
   allows any service event to the end user.  The CC-Request-Type is set
   to the value INITIAL_REQUEST in the request message.

   If the Diameter credit-control client knows the cost of the service
   event (e.g., a content server delivering ringing tones may know their
   cost) the monetary amount to be charged is included in the
   Requested-Service-Unit AVP.  If the Diameter credit-control client
   does not know the cost of the service event, the Requested-Service-
   Unit AVP MAY contain the number of requested service events.  Where
   the Multiple-Services-Credit-Control AVP is used, it MUST contain the
   Requested-Service-Unit AVP to indicate that the quota for the
   associated service/rating-group is requested.  In the case of
   multiple services, the Service-Identifier AVP or the Rating-Group AVP
   within the Multiple-Services-Credit-Control AVP always indicates the
   service concerned.  Additional service event information to be rated

   MAY be sent as service specific AVPs or MAY be sent within the
   Service-Parameter-Info AVP at command level.  The Service-Context-Id
   AVP indicates the service specific document applicable to the
   request.

   The Event-Timestamp AVP SHOULD be included in the request and
   contains the time when the service event is requested in the service
   element.  The Subscription-Id AVP SHOULD be included to identify the
   end user in the credit-control server.  The credit-control client MAY
   include the User-Equipment-Info AVP so that the credit-control server
   has some indication of the type and capabilities of the end user
   access device.  How the credit-control server uses this information
   is outside the scope of this document.

   The credit-control server SHOULD rate the service event and make a
   credit-reservation from the end user's account that covers the cost
   of the service event.  If the type of the Requested-Service-Unit AVP
   is money, no rating is needed, but the corresponding monetary amount
   is reserved from the end user's account.

   The credit-control server returns the Granted-Service-Unit AVP in the
   Answer message to the Diameter credit-control client.  The Granted-
   Service-Unit AVP contains the amount of service units that the
   Diameter credit-control client can provide to the end user until a
   new Credit-Control-Request MUST be sent to the credit-control server.
   If several unit types are sent in the Answer message, the credit-
   control client MUST handle each unit type separately.  The type of
   the Granted-Service-Unit AVP can be time, volume, service specific,
   or money, depending on the type of service event.  The unit type(s)
   SHOULD NOT be changed within an ongoing credit-control session.

   There MUST be a maximum of one instance of the same unit type in one
   Answer message.  However, if multiple quotas are conveyed to the
   credit-control client in the Multiple-Services-Credit-Control AVPs,
   it is possible to carry two instances of the same unit type
   associated to a service-identifier/rating-group.  This is typically
   the case when a tariff time change is expected and the credit-control
   server wants to make a distinction between the granted quota before
   and after tariff change.

   If the credit-control server determines that no further control is
   needed for the service, it MAY include the result code indicating
   that the credit-control is not applicable (e.g., if the service is
   free of charge).  This result code at command level implies that the
   credit-control session is to be terminated.

   The Credit-Control-Answer message MAY also include the Final-Unit-
   Indication AVP to indicate that the answer message contains the final

   units for the service.  After the end user has consumed these units,
   the Diameter credit-control-client MUST behave as described in
   section 5.6.

   This document defines two different approaches to perform the first
   interrogation to be used in different network architectures.  The
   first approach uses credit-control messages after the user's
   authorization and authentication takes place.  The second approach
   uses service specific authorization messages to perform the first
   interrogation during the user's authorization/authentication phase,
   and credit-control messages for the intermediate and final
   interrogations.  If an implementation of the credit-control client
   supports both the methods, determining which method to use SHOULD be
   configurable.

   In service environments such as the Network Access Server (NAS), it
   is desired to perform the first interrogation as part of the
   authorization/authentication process for the sake of protocol
   efficiency.  Further credit authorizations after the first
   interrogation are performed with credit-control commands defined in
   this specification.  Implementations of credit-control clients
   operating in the mentioned environments SHOULD support this method.
   If the credit-control server and AAA server are separate physical
   entities, the service element sends the request messages to the AAA
   server, which then issues an appropriate request or proxies the
   received request forward to the credit-control server.

   In other service environments, such as the 3GPP network and some SIP
   scenarios, there is a substantial decoupling between
   registration/access to the network and the actual service request
   (i.e., the authentication/authorization is executed once at
   registration/access to the network and is not executed for every
   service event requested by the subscriber).  In these environments,
   it is more appropriate to perform the first interrogation after the
   user has been authenticated and authorized.  The first, the
   intermediate, and the final interrogations are executed with credit-
   control commands defined in this specification.

   Other IETF standards or standards developed by other standardization
   bodies may define the most suitable method in their architectures.

5.2.1.  First Interrogation after Authorization and Authentication

   The Diameter credit-control client in the service element may get
   information from the authorization server as to whether credit-
   control is required, based on its knowledge of the end user.  If
   credit-control is required the credit-control server needs to be
   contacted prior to initiating service delivery to the end user.  The

   accounting protocol and the credit-control protocol can be used in
   parallel.  The authorization server may also determine whether the
   parallel accounting stream is required.

   The following diagram illustrates the case where both protocols are
   used in parallel and the service element sends credit-control
   messages directly to the credit-control server.  More credit-control
   sequence examples are given in Annex A.

                                           Diameter
   End User        Service Element        AAA Server         CC Server
                     (CC Client)
      | Registration      | AA request/answer(accounting,cc or both)|
      |<----------------->|<------------------>|                    |
      |        :          |                    |                    |
      |        :          |                    |                    |
      | Service Request   |                    |                    |
      |------------------>|                    |                    |
      |                   | CCR(Initial,Credit-Control AVPs)        |
      |                  +|---------------------------------------->|
      |         CC stream||                    |  CCA(Granted-Units)|
      |                  +|<----------------------------------------|
      | Service Delivery  |                    |                    |
      |<----------------->| ACR(start,Accounting AVPs)              |
      |         :         |------------------->|+                   |
      |         :         |                ACA || Accounting stream |
      |                   |<-------------------|+                   |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |                   | CCR(Update,Used-Units)                  |
      |                   |---------------------------------------->|
      |                   |                    |  CCA(Granted-Units)|
      |                   |<----------------------------------------|
      |         :         |                    |                    |
      |         :         |                    |                    |
      | End of Service    |                    |                    |
      |------------------>| CCR(Termination, Used-Units)            |
      |                   |---------------------------------------->|
      |                   |                    |               CCA  |
      |                   |<----------------------------------------|
      |                   | ACR(stop)          |                    |
      |                   |------------------->|                    |
      |                   |                ACA |                    |
      |                   |<-------------------|                    |

    Figure 2: Protocol example with first interrogation after user's
                      authorization/authentication

5.2.2.  Authorization Messages for First Interrogation

   The Diameter credit-control client in the service element MUST
   actively co-operate with the authorization/authentication client in
   the construction of the AA request by adding appropriate credit-
   control AVPs.  The credit-control client MUST add the Credit-Control
   AVP to indicate credit-control capabilities and MAY add other
   relevant credit-control specific AVPs to the proper
   authorization/authentication command to perform the first
   interrogation toward the home Diameter AAA server.  The Auth-
   Application-Id is set to the appropriate value, as defined in the
   relevant service specific authorization/authentication application
   document (e.g., [NASREQ], [DIAMMIP]).  The home Diameter AAA server
   authenticates/authorizes the subscriber and determines whether
   credit-control is required.

   If credit-control is not required for the subscriber, the home
   Diameter AAA server will respond as usual, with an appropriate AA
   answer message.  If credit-control is required for the subscriber and
   the Credit-Control AVP with the value set to CREDIT_AUTHORIZATION was
   present in the authorization request, the home AAA server MUST
   contact the credit-control server to perform the first interrogation.
   If credit-control is required for the subscriber and the Credit-
   Control AVP was not present in the authorization request, the home
   AAA server MUST send an authorization reject answer message.

   The Diameter AAA server supporting credit-control is required to send
   the Credit-Control-Request command (CCR) defined in this document to
   the credit-control server.  The Diameter AAA server populates the CCR
   based on service specific AVPs used for input to the rating process,
   and possibly on credit-control AVPs received in the AA request.  The
   credit-control server will reserve money from the user's account,
   will rate the request and will send a Credit-Control-Answer message
   to the home Diameter AAA server.  The answer message includes the
   Granted-Service-Unit AVP(s) and MAY include other credit-control
   specific AVPs, as appropriate.  Additionally, the credit-control
   server MAY set the Validity-Time and MAY include the Credit-Control-
   Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP to
   determine what to do if the sending of credit-control messages to the
   credit-control server has been temporarily prevented.

   Upon receiving the Credit-Control-Answer message from the credit-
   control server, the home Diameter AAA server will populate the AA
   answer with the received credit-control AVPs and with the appropriate
   service attributes according to the authorization/authentication
   specific application (e.g., [NASREQ], [DIAMMIP]).  It will then
   forward the packet to the credit-control client.  If the home
   Diameter AAA server receives a credit-control reject message, it will

   simply generate an appropriate authorization reject message to the
   credit-control client, including the credit-control specific error
   code.

   In this model, the credit-control client sends further credit-control
   messages to the credit-control server via the home Diameter AAA
   server.  Upon receiving a successful authorization answer message
   with the Granted-Service-Unit AVP(s), the credit-control client will
   grant the service to the end user and will generate an intermediate
   credit-control request, as required by using credit-control commands.
   The CC-Request-Number of the first UPDATE_REQUEST MUST be set to 1
   (for how to produce unique value for the CC-Request-Number AVP, see
   section 8.2).

   If service specific re-authorization is performed (i.e.,
   authorization-lifetime expires), the credit-control client MUST add
   to the service specific re-authorization request the Credit-Control
   AVP with a value set to RE_AUTHORIZATION to indicate that the
   credit-control server MUST NOT be contacted.  When session based
   credit-control is used for the subscriber, a constant credit-control
   message stream flows through the home Diameter AAA server.  The home
   Diameter AAA server can make use of this credit-control message flow
   to deduce that the user's activity is ongoing; therefore, it is
   recommended to set the authorization-lifetime to a reasonably high
   value when credit-control is used for the subscriber.

   In this scenario, the home Diameter AAA server MUST advertise support
   for the credit-control application to its peers during the capability
   exchange process.

   The following diagram illustrates the use of
   authorization/authentication messages to perform the first
   interrogation.  The parallel accounting stream is not shown in the
   figure.

                    Service Element         Diameter
   End User          (CC Client)           AAA Server          CC Server
      | Service Request   | AA Request (CC AVPs)                    |
      |------------------>|------------------->|                    |
      |                   |                    | CCR(Initial, CC AVPs)
      |                   |                    |------------------->|
      |                   |                    |    CCA(Granted-Units)
      |                   |                    |<-------------------|
      |                   | AA Answer(Granted-Units)                |
      | Service Delivery  |<-------------------|                    |
      |<----------------->|                    |                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |                   |                    |                    |
      |                   | CCR(Update,Used-Units)                  |
      |                   |------------------->| CCR(Update,Used-Units)
      |                   |                    |------------------->|
      |                   |                    |  CCA(Granted-Units)|
      |                   |  CCA(Granted-Units)|<-------------------|
      |                   |<-------------------|                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      | End of Service    |                    |                    |
      |------------------>| CCR(Termination,Used-Units)             |
      |                   |------------------->| CCR(Term.,Used-Units)
      |                   |                    |------------------->|
      |                   |                    |                CCA |
      |                   |                CCA |<-------------------|
      |                   |<-------------------|                    |

                Figure 3: Protocol example with use of the
           authorization messages for the first interrogation

5.3.  Intermediate Interrogation

   When all the granted service units for one unit type are spent by the
   end user or the Validity-Time is expired, the Diameter credit-control
   client MUST send a new Credit-Control-Request to the credit-control
   server.  In the event that credit-control for multiple services is
   applied in one credit-control session (i.e., units associated to
   Service-Identifier(s) or Rating-Group are granted), a new Credit-
   Control-Request MUST be sent to the credit-control server when the

   credit reservation has been wholly consumed, or upon expiration of
   the Validity-Time.  It is always up to the Diameter credit-control
   client to send a new request well in advance of the expiration of the
   previous request in order to avoid interruption in the service
   element.  Even if the granted service units reserved by the credit-
   control server have not been spent upon expiration of the Validity-
   Time, the Diameter credit-control client MUST send a new Credit-
   Control-Request to the credit-control server.

   There can also be mid-session service events, which might affect the
   rating of the current service events.  In this case, a spontaneous
   updating (a new Credit-Control-Request) SHOULD be sent including
   information related to the service event even if all the granted
   service units have not been spent or the Validity-Time has not
   expired.

   When the used units are reported to the credit-control server, the
   credit-control client will not have any units in its possession
   before new granted units are received from the credit-control server.
   When the new granted units are received, these units apply from the
   point where the measurement of the reported used units stopped.
   Where independent credit-control of multiple services is supported,
   this process may be executed for one or more services, a single
   rating-group, or a pool within the (sub)session.

   The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
   intermediate request message.  The Subscription-Id AVP SHOULD be
   included in the intermediate message to identify the end user in the
   credit-control server.  The Service-Context-Id AVP indicates the
   service specific document applicable to the request.

   The Requested-Service-Unit AVP MAY contain the new amount of
   requested service units.  Where the Multiple-Services-Credit-Control
   AVP is used, it MUST contain the Requested-Service-Unit AVP if a new
   quota is requested for the associated service/rating-group.  The
   Used-Service-Unit AVP contains the amount of used service units
   measured from the point when the service became active or, if interim
   interrogations are used during the session, from the point when the
   previous measurement ended.  The same unit types used in the previous
   message SHOULD be used.  If several unit types were included in the
   previous answer message, the used service units for each unit type
   MUST be reported.

   The Event-Timestamp AVP SHOULD be included in the request and
   contains the time of the event that triggered the sending of the new
   Credit-Control-Request.

   The credit-control server MUST deduct the used amount from the end
   user's account.  It MAY rate the new request and make a new credit-
   reservation from the end user's account that covers the cost of the
   requested service event.

   A Credit-Control-Answer message with the CC-Request-Type AVP set to
   the value UPDATE_REQUEST MAY include the Cost-Information AVP
   containing the accumulated cost estimation for the session, without
   taking any credit-reservation into account.

   The Credit-Control-Answer message MAY also include the Final-Unit-
   Indication AVP to indicate that the answer message contains the final
   units for the service.  After the end user has consumed these units,
   the Diameter credit-control-client MUST behave as described in
   section 5.6.

   There can be several intermediate interrogations within a session.

5.4.  Final Interrogation

   When the end user terminates the service session, or when the
   graceful service termination described in section 5.6 takes place,
   the Diameter credit-control client MUST send a final Credit-Control-
   Request message to the credit-control server.  The CC-Request-Type
   AVP is set to the value TERMINATION_REQUEST.  The Service-Context-Id
   AVP indicates the service specific document applicable to the
   request.

   The Event-Timestamp AVP SHOULD be included in the request and
   contains the time when the session was terminated.

   The Used-Service-Unit AVP contains the amount of used service units
   measured from the point when the service became active or, if interim
   interrogations are used during the session, from the point when the
   previous measurement ended.  If several unit types were included in
   the previous answer message, the used service units for each unit
   type MUST be reported.

   After final interrogation, the credit-control server MUST refund the
   reserved credit amount not used to the end user's account and deduct
   the used monetary amount from the end user's account.

   A Credit-Control-Answer message with the CC-Request-Type set to the
   value TERMINATION_REQUEST MAY include the Cost-Information AVP
   containing the estimated total cost for the session in question.

   If the user logs off during an ongoing credit-control session, or if
   some other reason causes the user to become logged off (e.g., final-

   unit indication causes user logoff according to local policy), the
   service element, according to application specific policy, may send a
   Session-Termination-Request (STR) to the home Diameter AAA server as
   usual [DIAMBASE].  Figure 4 illustrates the case when the final-unit
   indication causes user logoff upon consumption of the final granted
   units and the generation of STR.

                   Service Element        AAA Server        CC Server
   End User         (CC Client)
      | Service Delivery  |                    |                    |
      |<----------------->|                    |                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |                   |                    |                    |
      |                   | CCR(Update,Used-Units)                  |
      |                   |------------------->| CCR(Update,Used-Units)
      |                   |                    |------------------->|
      |                   |                  CCA(Final-Unit, Terminate)
      |              CCA(Final-Unit, Terminate)|<-------------------|
      |                   |<-------------------|                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |  Disconnect user  |                    |                    |
      |<------------------| CCR(Termination,Used-Units)             |
      |                   |------------------->| CCR(Term.,Used-Units)
      |                   |                    |------------------->|
      |                   |                    |                CCA |
      |                   |                CCA |<-------------------|
      |                   |<-------------------|                    |
      |                   | STR                |                    |
      |                   |------------------->|                    |
      |                   |               STA  |                    |
      |                   |<-------------------|                    |

           Figure 4: User disconnected due to exhausted account

5.5.  Server-Initiated Credit Re-Authorization

   The Diameter credit-control application supports server-initiated
   re-authorization.  The credit-control server MAY optionally initiate
   the credit re-authorization by issuing a Re-Auth-Request (RAR) as
   defined in the Diameter base protocol [DIAMBASE].  The Auth-
   Application-Id in the RAR message is set to 4 to indicate Diameter
   Credit Control, and the Re-Auth-Request-Type is set to
   AUTHORIZE_ONLY.

   Section 5.1.2 defines the feature to enable credit-control for
   multiple services within a single (sub-)session where the server can
   authorize credit usage at a different level of granularity.  Further,
   the server may provide credit resources to multiple services or
   rating groups as a pool (see section 5.1.2 for details and
   definitions).  Therefore, the server, based on its service logic and
   its knowledge of the ongoing session, can decide to request credit
   re-authorization for a whole (sub-)session, a single credit pool, a
   single service, or a single rating-group.  To request credit re-
   authorization for a credit pool, the server includes in the RAR
   message the G-S-U-Pool-Identifier AVP indicating the affected pool.
   To request credit re-authorization for a service or a rating-group,
   the server includes in the RAR message the Service-Identifier AVP or
   the Rating-Group AVP, respectively.  To request credit re-
   authorization for all the ongoing services within the (sub-)session,
   the server includes none of the above mentioned AVPs in the RAR
   message.

   If a credit re-authorization is not already ongoing (i.e., the
   credit-control session is in Open state), a credit control client
   that receives an RAR message with Session-Id equal to a currently
   active credit-control session MUST acknowledge the request by sending
   the Re-Auth-Answer (RAA) message and MUST initiate the credit re-
   authorization toward the server by sending a Credit-Control-Request
   message with the CC-Request-Type AVP set to the value UPDATE_REQUEST.
   The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the
   RAA message to indicate that an additional message (i.e., CCR message
   with the value UPDATE_REQUEST) is required to complete the procedure.
   If a quota was allocated to the service, the credit-control client
   MUST report the used quota in the Credit-Control-Request.  Note that
   the end user does not need to be prompted for the credit re-
   authorization, since the credit re-authorization is transparent to
   the user (i.e., it takes place exclusively between the credit-control
   client and the credit-control server).

   Where multiple services in a user's session are supported, the
   procedure in the above paragraph will be executed at the granularity
   requested by the server in the RAR message.

   If credit re-authorization is ongoing at the time when the RAR
   message is received (i.e., RAR-CCR collision), the credit-control
   client successfully acknowledges the request but does not initiate a
   new credit re-authorization.  The Result-Code 2001 (DIAMETER_SUCCESS)
   SHOULD be used in the RAA message to indicate that a credit re-
   authorization procedure is already ongoing (i.e., the client was in
   PendingU state when the RAR was received).  The credit-control server
   SHOULD process the Credit-Control-Request as if it was received in
   answer to the server initiated credit re-authorization, and should

   consider the server initiated credit re-authorization process
   successful upon reception of the Re-Auth-Answer message.

   When multiple services are supported in a user's session, the server
   may request credit re-authorization for a credit pool (or for the
   (sub-)session) while a credit re-authorization is already ongoing for
   some of the services or rating-groups.  In this case, the client
   acknowledges the server request with an RAA message and MUST send a
   new Credit-Control-Request message to perform re-authorization for
   the remaining services/rating-groups.  The Result-Code 2002
   (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the RAA message to
   indicate that an additional message (i.e., CCR message with value
   UPDATE_REQUEST) is required to complete the procedure.  The server
   processes the received requests and returns an appropriate answer to
   both requests.

   The above-defined procedures are enabled for each of the possibly
   active Diameter credit-control sub-sessions.  The server MAY request
   re-authorization for an active sub-session by including the CC-Sub-
   Session-Id AVP in the RAR message in addition to the Session-Id AVP.

5.6.  Graceful Service Termination

   When the user's account runs out of money, the user may not be
   allowed to compile additional chargeable events.  However, the home
   service provider may offer some services; for instance, access to a
   service portal where it is possible to refill the account, for which
   the user is allowed to benefit for a limited time.  The length of
   this time is usually dependent on the home service provider policy.

   This section defines the optional graceful service termination
   feature that MAY be supported by the credit-control server.  Credit-
   control client implementations MUST support the Final-Unit-Indication
   with at least the teardown of the ongoing service session once the
   subscriber has consumed all the final granted units.

   Where independent credit-control of multiple services in a single
   credit-control (sub-)session is supported, it is possible to use the
   graceful service termination for each of the services/rating-groups
   independently.  Naturally, the graceful service termination process
   defined in the following sub-sections will apply to the specific
   service/rating-group as requested by the server.

   In some service environments (e.g., NAS), the graceful service
   termination may be used to redirect the subscriber to a service
   portal for online balance refill or other services offered by the
   home service provider.  In this case, the graceful termination
   process installs a set of packet filters to restrict the user's

   access capability only to/from the specified destinations.  All the
   IP packets not matching the filters will be dropped or, possibly,
   re-directed to the service portal.  The user may also be sent an
   appropriate notification as to why the access has been limited.
   These actions may be communicated explicitly from the server to the
   client or may be configured per-service at the client.  Explicitly
   signaled redirect or restrict instructions always take precedence
   over configured ones.

   It is also possible use the graceful service termination to connect
   the prepaid user to a top-up server that plays an announcement and
   prompts the user to replenish the account.  In this case, the
   credit-control server sends only the address of the top-up server
   where the prepaid user shall be connected after the final granted
   units have been consumed.  An example of this is given in Appendix A
   (Flow VII).

   The credit-control server MAY initiate the graceful service
   termination by including the Final-Unit-Indication AVP in the
   Credit-Control-Answer to indicate that the message contains the final
   units for the service.

   When the credit-control client receives the Final-Unit-Indication AVP
   in the answer from the server, its behavior depends on the value
   indicated in the Final-Unit-Action AVP.  The server may request the
   following actions: TERMINATE, REDIRECT, or RESTRICT_ACCESS.

   A following figure illustrates the graceful service termination
   procedure described in the following sub-sections.

                                            Diameter
   End User        Service Element         AAA Server          CC Server
                    (CC Client)
      |  Service Delivery |                    |                    |
      |<----------------->|                    |                    |
      |                   |CCR(Update,Used-Units)                   |
      |                   |------------------->|CCR(Update,Used-Units)
      |         :         |                    |------------------->|
      |         :         |                    |CCA(Final-Unit,Action)
      |         :         |                    |<-------------------|
      |                   |CCA(Final-Unit,Action)                   |
      |                   |<-------------------|                    |
      |                   |                    |                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      | ///////////////   |CCR(Update,Used-Units)                   |
      |/Final Units End/->|------------------->|CCR(Update,Used-Units)
      |/Action and    //  |                    |------------------->|
      |/Restrictions //   |                    |  CCA(Validity-Time)|
      |/Start       //    |  CCA(Validity-Time)|<-------------------|
      | /////////////     |<-------------------|                    |
      |         :         |                    |                    |
      |         :         |                    |                    |
      |                 Replenish Account            +-------+      |
      |<-------------------------------------------->|Account|      |
      |                   |                    |     +-------+      |
      |                   |                    |                RAR |
      |                 + |                RAR |<===================|
      |                 | |<===================|                    |
      |                 | | RAA                |                    |
      |  /////////////  | |===================>| RAA                |
      | /If supported / | | CCR(Update)        |===================>|
      | /by CC Server/  | |===================>| CCR(Update)        |
      | /////////////   | |                    |===================>|
      |                 | |                    |   CCA(Granted-Unit)|
      |                 | |   CCA(Granted-Unit)|<===================|
      |  Restrictions ->+ |<===================|                    |
      |  removed          |                    |                    |
      |         :         |                    |                    |
      |        OR         | CCR(Update)        |                    |
      |   Validity-Time ->|------------------->| CCR(Update)        |
      |   expires         |                    |------------------->|
      |                   |                    |   CCA(Granted-Unit)|
      |                   |   CCA(Granted-Unit)|<-------------------|
      |    Restrictions ->|<-------------------|                    |
      |    removed        |                    |                    |

         Figure 5: Optional graceful service termination procedure

5.6.1.  Terminate Action

   The Final-Unit-Indication AVP with Final-Unit-Action TERMINATE does
   not include any other information.  When the subscriber has consumed
   the final granted units, the service element MUST terminate the
   service.  This is the default handling applicable whenever the
   credit-control client receives an unsupported Final-Unit-Action value
   and MUST be supported by all the Diameter credit-control client
   implementations conforming to this specification.  A final Credit-
   Control-Request message to the credit-control server MUST be sent if
   the Final-Unit-Indication AVP indicating action TERMINATE was present
   at command level.  The CC-Request-Type AVP in the request is set to
   the value TERMINATION_REQUEST.

5.6.2.  Redirect Action

   The Final-Unit-Indication AVP with Final-Unit-Action REDIRECT
   indicates to the service element supporting this action that, upon
   consumption of the final granted units, the user MUST be re-directed
   to the address specified in the Redirect-Server AVP as follows.

   The credit-control server sends the Redirect-Server AVP in the
   Credit-Control-Answer message.  In such a case, the service element
   MUST redirect or connect the user to the destination specified in the
   Redirect-Server AVP, if possible.  When the end user is redirected
   (by using protocols others than Diameter) to the specified server or
   connected to the top-up server, an additional authorization (and
   possibly authentication) may be needed before the subscriber can
   replenish the account; however, this is out of the scope of this
   specification.

   In addition to the Redirect-Server AVP, the credit-control server MAY
   include one or more Restriction-Filter-Rule AVPs or one or more
   Filter-Id AVPs in the Credit-Control-Answer message to enable the
   user to access other services (for example, zero-rated services).  In
   such a case, the access device MUST drop all the packets not matching
   the IP filters specified in the Credit-Control-Answer message and, if
   possible, redirect the user to the destination specified in the
   Redirect-Server AVP.

   An entity other than the credit-control server may provision the
   access device with appropriate IP packet filters to be used in
   conjunction with the Diameter credit-control application.  This case
   is considered in section 5.6.3.

   When the final granted units have been consumed, the credit-control
   client MUST perform an intermediate interrogation.  The purpose of
   this interrogation is to indicate to the credit-control server that
   the specified action started and to report the used units.  The
   credit-control server MUST deduct the used amount from the end user's
   account but MUST NOT make a new credit reservation.  The credit-
   control client, however, may send intermediate interrogations before
   all the final granted units have been consumed for which rating and
   money reservation may be needed; for instance, upon Validity-Time
   expires or upon mid-session service events that affect the rating of
   the current service.  Therefore, the credit-control client MUST NOT
   include any rating related AVP in the request sent once all the final
   granted units have been consumed as an indication to the server that
   the requested final unit action started, rating and money reservation
   are not required (when the Multiple-Services-Credit-Control AVP is
   used, the Service-Identifier or Rating-Group AVPs is included to
   indicate the concerned services).  Naturally, the Credit-Control-
   Answer message does not contain any granted service unit and MUST
   include the Validity-Time AVP to indicate to the credit-control
   client how long the subscriber is allowed to use network resources
   before a new intermediate interrogation is sent to the server.

   At the expiry of Validity-Time, the credit-control client sends a
   Credit-Control-Request (UPDATE_REQUEST) as usual.  This message does
   not include the Used-Service-Unit AVP, as there is no allotted quota
   to report.  The credit-control server processes the request and MUST
   perform the credit reservation.  If during this time the subscriber
   did not replenish his/her account, whether he/she will be
   disconnected or will be granted access to services not controlled by
   a credit-control server for an unlimited time is dependent on the
   home service provider policy (note: the latter option implies that
   the service element should not remove the restriction filters upon
   termination of the credit-control).  The server will return the
   appropriate Result-Code (see section 9.1) in the Credit-Control-
   Answer message in order to implement the policy-defined action.
   Otherwise, new quota will be returned, the service element MUST
   remove all the possible restrictions activated by the graceful
   service termination process and continue the credit-control session
   and service session as usual.

   The credit-control client may not wait until the expiration of the
   Validity-Time and may send a spontaneous update (a new Credit-
   Control-Request) if the service element can determine, for instance,
   that communication between the end user and the top-up server took
   place.  An example of this is given in Appendix A (Figure A.8).

   Note that the credit-control server may already have initiated the
   above-described process for the first interrogation.  However, the
   user's account might be empty when this first interrogation is
   performed.  In this case, the subscriber can be offered a chance to
   replenish the account and continue the service.  The credit-control
   client receives a Credit-Control-Answer or service specific
   authorization answer with the Final-Unit-Indication and Validity-Time
   AVPs but no Granted-Service-Unit.  It immediately starts the graceful
   service termination without sending any message to the server.  An
   example of this case is illustrated in Appendix A.

5.6.3.  Restrict Access Action

   A Final-Unit-Indication AVP with the Final-Unit-Action
   RESTRICT_ACCESS indicates to the device supporting this action that
   the user's access MUST be restricted according to the IP packet
   filters given in the Restriction-Filter-Rule AVP(s) or according to
   the IP packet filters identified by the Filter-Id AVP(s).  The
   credit-control server SHOULD include either the Restriction-Filter-
   Rule AVP or the Filter-Id AVP in the Credit-Control-Answer message.

   An entity other than the credit-control server may provision the
   access device with appropriate IP packet filters to be used in
   conjunction with the Diameter credit-control application.  Such an
   entity may, for instance, configure the access device with IP flows
   to be passed when the Diameter credit-control application indicates
   RESTRICT_ACCESS or REDIRECT.  The access device passes IP packets
   according to the filter rules that may have been received in the
   Credit-Control-Answer message in addition to those that may have been
   configured by the other entity.  However, when the user's account
   cannot cover the cost of the requested service, the action taken is
   the responsibility of the credit-control server that controls the
   prepaid subscriber.

   If another entity working in conjunction with the Diameter credit-
   control application already provisions the access device with all the
   required filter rules for the end user, the credit-control server
   presumably need not send any additional filter.  Therefore, it is
   RECOMMENDED that credit-control server implementations supporting the
   graceful service termination be configurable for sending the
   Restriction-Filter-Rule AVP, the Filter-Id AVP, or none of the above.

   When the final granted units have been consumed, the credit-control
   client MUST perform an intermediate interrogation.  The credit-
   control client and the credit-control server process this
   intermediate interrogation and execute subsequent procedures, as
   specified in the previous section for the REDIRECT action.

   The credit-control server may initiate the graceful service
   termination with action RESTRICT_ACCESS already for the first
   interrogation, as specified in the previous section for the REDIRECT
   action.

5.6.4.  Usage of the Server-Initiated Credit Re-Authorization

   Once the subscriber replenishes the account, she presumably expects
   all the restrictions placed by the graceful termination procedure to
   be removed immediately and unlimited service' access to be resumed.
   For the best user experience, the credit-control server
   implementation MAY support the server-initiated credit re-
   authorization (see section 5.5).  In such a case, upon the successful
   account top-up, the credit-control server sends the Re-Auth-Request
   (RAR) message to solicit the credit re-authorization.  The credit-
   control client initiates the credit re-authorization by sending the
   Credit-Control-Request message with the CC-Request-Type AVP set to
   the value UPDATE_REQUEST.  The Used-Service-Unit AVP is not included
   in the request, as there is no allotted quota to report.  The
   Requested-Service-Unit AVP MAY be included in the request.  After the
   credit-control client successfully receives the Credit-Control-Answer
   with new Granted-Service-Unit, all the possible restrictions
   activated for the purpose of the graceful service termination MUST be
   removed in the service element.  The credit-control session and the
   service session continue as usual.

5.7.  Failure Procedures

   The Credit-Control-Failure-Handling AVP (CCFH), as described in this
   section, determines the behavior of the credit-control client in
   fault situations.  The CCFH may be received from the Diameter home
   AAA server, from the credit-control server, or may be configured
   locally.  The CCFH value received from the home AAA server overrides
   the locally configured value.  The CCFH value received from the
   credit-control server in the Credit-Control-Answer message always
   overrides any existing value.

   The authorization server MAY include the Accounting-Realtime-Required
   AVP to determine what to do if the sending of accounting records to
   the accounting server has been temporarily prevented, as defined in
   [DIAMBASE].  It is RECOMMENDED that the client complement the
   credit-control failure procedures with backup accounting flow toward
   an accounting server.  By using different combinations of
   Accounting-Realtime-Required and Credit-Control-Failure-Handling
   AVPs, different safety levels can be built.  For example, by choosing
   a Credit-Control-Failure-Handling AVP equal to CONTINUE for the
   credit-control flow and a Accounting-Realtime-Required AVP equal to
   DELIVER_AND_GRANT for the accounting flow, the service can be granted

   to the end user even if the connection to the credit-control server
   is down, as long as the accounting server is able to collect the
   accounting information and information exchange is taking place
   between the accounting server and credit-control server.

   As the credit-control application is based on real-time bi-
   directional communication between the credit-control client and the
   credit-control server, the usage of alternative destinations and the
   buffering of messages may not be sufficient in the event of
   communication failures.  Because the credit-control server has to
   maintain session states, moving the credit-control message stream to
   a backup server requires a complex context transfer solution.
   Whether the credit-control message stream is moved to a backup
   credit-control server during an ongoing credit-control session
   depends on the value of the CC-Session-Failover AVP.  However,
   failover may occur at any point in the path between the credit-
   control client and the credit-control server if a transport failure
   is detected with a peer, as described in [DIAMBASE].  As a
   consequence, the credit-control server might receive duplicate
   messages.  These duplicates or out of sequence messages can be
   detected in the credit-control server based on the credit-control
   server session state machine (section 7), Session-Id AVP, and CC-
   Request-Number AVP.

   If a failure occurs during an ongoing credit-control session, the
   credit-control client may move the credit-control message stream to
   an alternative server if the CC-server indicated FAILOVER_SUPPORTED
   in the CC-Session-Failover AVP.  A secondary credit-control server
   name, either received from the home Diameter AAA server or configured
   locally, can be used as an address of the backup server.  If the CC-
   Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED, the credit-
   control message stream MUST NOT be moved to a backup server.

   For new credit-control sessions, failover to an alternative credit-
   control server SHOULD be performed if possible.  For instance, if an
   implementation of the credit-control client can determine primary
   credit-control server unavailability, it can establish the new
   credit-control sessions with a possibly available secondary credit-
   control server.

   The AAA transport profile [AAATRANS] defines the application layer
   watchdog algorithm that enables failover from a peer that has failed
   and is controlled by a watchdog timer (Tw) defined in [AAATRANS].
   The recommended default initial value for Tw (Twinit) is 30 seconds.
   Twinit may be set as low as 6 seconds; however, according to
   [AAATRANS], setting too low a value for Twinit is likely to result in
   an increased probability of duplicates, as well as an increase in
   spurious failover and failback attempts.  The Diameter base protocol

   is common to several different types of Diameter AAA applications
   that may be run in the same service element.  Therefore, tuning the
   timer Twinit to a lower value in order to satisfy the requirements of
   real-time applications, such as the Diameter credit-control
   application, will certainly cause the above mentioned problems.  For
   prepaid services, however, the end user expects an answer from the
   network in a reasonable time.  Thus, the Diameter credit-control
   client will react faster than would the underlying base protocol.
   Therefore this specification defines the timer Tx that is used by the
   credit-control client (as defined in section 13) to supervise the
   communication with the credit-control server.  When the timer Tx
   elapses, the credit-control client takes an action to the end user
   according to the Credit-Control-Failure-Handling AVP.

   When Tx expires, the Diameter credit-control client always terminates
   the service if the Credit-Control-Failure-Handling (CCFH) AVP is set
   to the value TERMINATE.  The credit-control session may be moved to
   an alternative server only if a protocol error DIAMETER_TOO_BUSY or
   DIAMETER_UNABLE_TO_DELIVER is received before Tx expires.  Therefore,
   the value TERMINATE is not appropriate if proper failover behavior is
   desired.

   If the Credit-Control-Failure-Handling AVP is set to the value
   CONTINUE or RETRY_AND_TERMINATE, the service will be granted to the
   end user when the timer Tx expires.  An answer message with granted-
   units may arrive later if the base protocol transport failover
   occurred in the path to the credit-control server.  (The Twinit
   default value is 3 times more than the Tx recommended value.) The
   credit-control client SHOULD grant the service to the end user, start
   monitoring the resource usage, and wait for the possible late answer
   until the timeout of the request (e.g., 120 seconds).  If the request
   fails and the CC-Session-Failover AVP is set to
   FAILOVER_NOT_SUPPORTED, the credit-control client terminates or
   continues the service depending on the value set in the CCFH and MUST
   free all the reserved resources for the credit-control session.  If
   the protocol error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is
   received or the request times out and the CC-Session-Failover AVP is
   set to FAILOVER_SUPPORTED, the credit-control client MAY send the
   request to a backup server, if possible.  If the credit-control
   client receives a successful answer from the backup server, it
   continues the credit-control session with such a server.  If the re-
   transmitted request also fails, the credit-control client terminates
   or continues the service depending on the value set in the CCFH and
   MUST free all the reserved resources for the credit-control session.

   If a communication failure occurs during the graceful service
   termination procedure, the service element SHOULD always terminate
   the ongoing service session.

   If the credit-control server detects a failure during an ongoing
   credit-control session, it will terminate the credit-control session
   and return the reserved units back to the end user's account.

   The supervision session timer Tcc (as defined in section 13) is used
   in the credit-control server to supervise the credit-control session.

   In order to support failover between credit-control servers,
   information transfer about the credit-control session and account
   state SHOULD take place between the primary and the secondary
   credit-control server.  Implementations supporting the credit-control
   session failover MUST also ensure proper detection of duplicate or
   out of sequence messages.  The communication between the servers is
   regarded as an implementation issue and is outside of the scope of
   this specification.

6.  One Time Event

   The one-time event is used when there is no need to maintain any
   state in the Diameter credit-control server; for example, enquiring
   about the price of the service.  The use of a one-time event implies
   that the user has been authenticated and authorized beforehand.

   The one time event can be used when the credit-control client wants
   to know the cost of the service event or to check the account balance
   without any credit-reservation.  It can also be used for refunding
   service units on the user's account or for direct debiting without
   any credit-reservation.  The one time event is shown in Figure 6.

                                           Diameter
   End User        Service Element        AAA Server        CC Server
                     (CC Client)
      | Service Request   |                    |                    |
      |------------------>|                    |                    |
      |                   | CCR(Event)         |                    |
      |                   |------------------->| CCR(Event)         |
      |                   |                    |------------------->|
      |                   |                    |  CCA(Granted-Units)|
      |                   |  CCA(Granted-Units)|<-------------------|
      |  Service Delivery |<-------------------|                    |
      |<----------------->|                    |                    |

                         Figure 6: One time event

   In environments such as the 3GPP architecture, the one time event can
   be sent from the service element directly to the credit-control
   server.

6.1.  Service Price Enquiry

   The credit-control client may need to know the price of the service
   event.  Services offered by application service providers whose
   prices are not known in the credit-control client might exist.  The
   end user might also want to get an estimation of the price of a
   service event before requesting it.

   A Diameter credit-control client requesting the cost information MUST
   set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
   Requested-Action AVP set to PRICE_ENQUIRY, and set the requested
   service event information into the Service-Identifier AVP in the
   Credit-Control-Request message.  Additional service event information
   may be sent as service specific AVPs or within the Service-
   Parameter-Info AVP.  The Service-Context-Id AVP indicates the service
   specific document applicable to the request.

   The credit-control server calculates the cost of the requested
   service event, but it does not perform any account balance check or
   credit-reservation from the account.

   The estimated cost of the requested service event is returned to the
   credit-control client in the Cost-Information AVP in the Credit-
   Control-Answer message.

6.2.  Balance Check

   The Diameter credit-control client may only have to verify that the
   end user's account balance covers the cost of a certain service
   without reserving any units from the account at the time of the
   inquiry.  This method does not guarantee that credit would be left
   when the Diameter credit-control client requests the debiting of the
   account with a separate request.

   A Diameter credit-control client requesting the balance check MUST
   set the CC-Request-Type AVP equal to EVENT_REQUEST, include a
   Requested-Action AVP set to CHECK_BALANCE, and include the
   Subscription-Id AVP in order to identify the end user in the credit-
   control server.  The Service-Context-Id AVP indicates the service
   specific document applicable to the request.

   The credit-control server makes the balance check, but it does not
   make any credit-reservation from the account.

   The result of balance check (ENOUGH_CREDIT/NO_CREDIT) is returned to
   the credit-control client in the Check-Balance-Result AVP in the
   Credit-Control-Answer message.

6.3.  Direct Debiting

   There are certain service events for which service execution is
   always successful in the service environment.  The delay between the
   service invocation and the actual service delivery to the end user
   can be sufficiently long that the use of the session-based credit-
   control would lead to unreasonably long credit-control sessions.  In
   these cases, the Diameter credit-control client can use the one-time
   event scenario for direct debiting.  The Diameter credit-control
   client SHOULD be sure that the requested service event execution
   would be successful when this scenario is used.

   In the Credit-Control-Request message, the CC-Request-Type is set to
   the value EVENT_REQUEST and the Requested-Action AVP is set to
   DIRECT_DEBITING.  The Subscription-Id AVP SHOULD be included to
   identify the end user in the credit-control server.  The Event-
   Timestamp AVP SHOULD be included in the request and contain the time
   when the service event is requested in the service element.  The
   Service-Context-Id AVP indicates the service specific document
   applicable to the request.

   The Diameter credit-control client MAY include the monetary amount to
   be charged in the Requested-Service-Unit AVP, if it knows the cost of
   the service event.  If the Diameter credit-control client does not
   know the cost of the service event, the Requested-Service-Unit AVP
   MAY contain the number of requested service events.  The Service-
   Identifier AVP always indicates the service concerned.  Additional
   service event information to be rated MAY be sent as service specific
   AVPs or within the Service-Parameter-Info AVP.

   The credit-control server SHOULD rate the service event and deduct
   the corresponding monetary amount from the end user's account.  If
   the type of the Requested-Service-Unit AVP is money, no rating is
   needed, but the corresponding monetary amount is deducted from the
   end user's account.

   The credit-control server returns the Granted-Service-Unit AVP in the
   Credit-Control-Answer message to the Diameter credit-control client.
   The Granted-Service-Unit AVP contains the amount of service units
   that the Diameter credit-control client can provide to the end user.
   The type of the Granted-Service-Unit can be time, volume, service
   specific, or money, depending on the type of service event.

   If the credit-control server determines that no credit-control is
   needed for the service, it can include the result code indicating
   that the credit-control is not applicable (e.g., service is free of
   charge).

   For informative purposes, the Credit-Control-Answer message MAY also
   include the Cost-Information AVP containing the estimated total cost
   of the requested service.

6.4.  Refund

   Some services may refund service units to the end user's account; for
   example, gaming services.

   The credit-control client MUST set CC-Request-Type to the value
   EVENT_REQUEST and the Requested-Action AVP to REFUND_ACCOUNT in the
   Credit-Control-Request message.  The Subscription-Id AVP SHOULD be
   included to identify the end user in the credit-control server.  The
   Service-Context-Id AVP indicates the service specific document
   applicable to the request.

   The Diameter credit-control client MAY include the monetary amount to
   be refunded in the Requested-Service-Unit AVP.  The Service-
   Identifier AVP always indicates the concerned service.  If the
   Diameter credit-control client does not know the monetary amount to
   be refunded, in addition to the Service-Identifier AVP it MAY send
   service specific AVPs or the Service-Parameter-Info AVP containing
   additional service event information to be rated.

   For informative purposes, the Credit-Control-Answer message MAY also
   include the Cost-Information AVP containing the estimated monetary
   amount of refunded unit.

6.5.  Failure Procedure

   Failover to an alternative credit-control server is allowed for a one
   time event, as the server is not maintaining session states.  For
   instance, if the credit-control client receives a protocol error
   DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY, it can re-send the
   request to an alternative server, if possible.  There MAY be protocol
   transparent Diameter relays and redirect agents or Diameter credit-
   control proxies between the credit-control client and credit-control
   server.  Failover may occur at any point in the path between the
   credit-control client and the credit-control server if a transport
   failure is detected with a peer, as described in [DIAMBASE].  Because
   there can be duplicate requests for various reasons, the credit-
   control server is responsible for real time duplicate detection.
   Implementation issues for duplicate detection are discussed in
   [DIAMBASE], Appendix C.

   When the credit-control client detects a communication failure with
   the credit-control server, its behavior depends on the requested
   action.  The timer Tx (as defined in section 13) is used in the

   credit-control client to supervise the communication with the
   credit-control server.

   If the requested action is PRICE_ENQUIRY or CHECK_BALANCE and
   communication failure is detected, the credit-control client SHOULD
   forward the request messages to an alternative credit-control server,
   if possible.  The secondary credit-control server name, if received
   from the home Diameter AAA server, can be used as an address of
   backup server.

   If the requested action is DIRECT_DEBITING, the Direct-Debiting-
   Failure-Handling AVP (DDFH) controls the credit-control client's
   behavior.  The DDFH may be received from the home Diameter AAA server
   or may be locally configured.  The credit-control server may also
   send the DDFH in any CCA message to be used for direct debiting
   events compiled thereafter.  The DDFH value received from the home
   Diameter AAA server overrides the locally configured value, and the
   DDFH value received from the credit-control server in a Credit-
   Control-Answer message always overrides any existing value.

   If the DDFH is set to TERMINATE_OR_BUFFER, the credit-control client
   SHOULD NOT grant the service if it can determine, eventually after a
   possible re-transmission attempt to an alternative credit-control
   server, from the result code or error code in the answer message that
   units have not been debited.  Otherwise, the credit-control client
   SHOULD grant the service to the end user and store the request in the
   credit-control application level non-volatile storage.  (Note that
   re-sending the request at a later time is not a guarantee that the
   service will be debited, as the user's account may be empty when the
   server successfully processes the request.)  The credit-control
   client MUST mark these request messages as possible duplicates by
   setting the T-flag in the command header as described in [DIAMBASE],
   section 3.

   If the Direct-Debiting-Failure-Handling AVP is set to CONTINUE, the
   service SHOULD be granted, even if credit-control messages cannot be
   delivered and messages are not buffered.

   If the timer Tx expires, the credit-control client MUST continue the
   service and wait for a possible late answer.  If the request times
   out, the credit-control client re-transmits the request (marked with
   T-flag) to a backup credit-control server, if possible.  If the re-
   transmitted request also times out, or if a temporary error is
   received in answer, the credit-control client buffers the request if
   the value of the Direct-Debiting-Failure-Handling AVP is set to
   TERMINATE_OR_BUFFER.  If a failed answer is received for the

   re-transmitted request, the credit-control client frees all the
   resources reserved for the event message and deletes the request
   regardless of the value of the DDFH.

   The Credit-Control-Request with the requested action REFUND_ACCOUNT
   should always be stored in the credit-control application level non-
   volatile storage in case of temporary failure.  The credit-control
   client MUST mark the re-transmitted request message as a possible
   duplicate by setting the T-flag in the command header as described in
   [DIAMBASE], section 3.

   For stored requests, the implementation may choose to limit the
   number of re-transmission attempts and to define a re-transmission
   interval.

   Note that only one place in the credit-control system SHOULD be
   responsible for duplicate detection.  If there is only one credit-
   control server within the given realm, the credit-control server may
   perform duplicate detection.  If there is more than one credit-
   control server in a given realm, only one entity in the credit-
   control system should be responsible, to ensure that the end user's
   account is not debited or credited multiple times for the same
   service event.

7.  Credit-Control Application State Machine

   This section defines the credit-control application state machine.

   The first four state machines are to be observed by credit-control
   clients.  The first one describes the session-based credit-control
   when the first interrogation is executed as part of the
   authorization/authentication process.  The second describes the
   session-based credit-control when the first interrogation is executed
   after the authorization/authentication process.  The requirements as
   to what state machines have to be supported are discussed in section
   5.2.

   The third state machine describes the session-based credit-control
   for the intermediate and final interrogations.  The fourth one
   describes the event-based credit-control.  These latter state
   machines are to be observed by all implementations that conform to
   this specification.

   The fifth state machine describes the credit-control session from a
   credit-control server perspective.

   Any event not listed in the state machines MUST be considered an
   error condition, and a corresponding answer, if applicable, MUST be
   returned to the originator of the message.

   In the state table, the event 'Failure to send' means that the
   Diameter credit-control client is unable to communicate with the
   desired destination or, if failover procedure is supported, with a
   possibly defined alternative destination (e.g., the request times out
   and the answer message is not received).  This could be due to the
   peer being down, or due to a physical link failure in the path to or
   from the credit-control server.

   The event 'Temporary error' means that the Diameter credit-control
   client received a protocol error notification (DIAMETER_TOO_BUSY,
   DIAMETER_UNABLE_TO_DELIVER, or DIAMETER_LOOP_DETECTED) in the
   Result-Code AVP of the Credit-Control-Answer command.  The above
   protocol error notification may ultimately be received in answer to
   the re-transmitted request to a defined alternative destination, if
   failover is supported.

   The event 'Failed answer' means that the Diameter credit-control
   client received non-transient failure (permanent failure)
   notification in the Credit-Control-Answer command.  The above
   permanent failure notification may ultimately be received in answer
   to the re-transmitted request to a defined alternative destination,
   if failover is supported.

   The action 'store request' means that a request is stored in the
   credit-control application level non-volatile storage.

   The event 'Not successfully processed' means that the credit-control
   server could not process the message; e.g., due to an unknown end
   user, account being empty, or errors defined in [DIAMBASE].

   The event 'User service terminated' can be triggered by various
   reasons, e.g., normal user termination, network failure, and ASR
   (Abort-Session-Request).  The Termination-Cause AVP contains
   information about the termination reason, as specified in [DIAMBASE].

   The Tx timer, which is used to control the waiting time in the
   credit-control client in the Pending state, is stopped upon exit of
   the Pending state.  The stopping of the Tx timer is omitted in the
   state machine when the new state is Idle, as moving to Idle state
   implies the clearing of the session and all the variables associated
   to it.

   The states PendingI, PendingU, PendingT, PendingE, and PendingB stand
   for pending states to wait for an answer to a credit-control request
   related to Initial, Update, Termination, Event, or Buffered request,
   respectively.

   The acronyms CCFH and DDFH stand for Credit-Control-Failure-Handling
   and Direct-Debiting-Failure-Handling, respectively.

   In the following state machine table, the failover to a secondary
   server upon 'Temporary error' or 'Failure to send' is not explicitly
   described.  Moving an ongoing credit-control message stream to an
   alternative server is, however, possible if the CC-Session-Failover
   AVP is set to FAILOVER_SUPPORTED, as described in section 5.7.

   Re-sending a credit-control event to an alternative server is
   supported as described in section 6.5.

   CLIENT, SESSION BASED for the first interrogation with AA request

    State      Event                         Action       New State
    ---------------------------------------------------------------
    Idle       Client or device requests     Send          PendingI
               access/service                AA request
                                             with added
                                             CC AVPs,
                                             start Tx

    PendingI  Successful AA req.             Grant         Open
              answer received                service to
                                             end user,
                                             stop Tx

    PendingI  Tx expired                     Disconnect    Idle
                                             user/dev

    PendingI  Failed AA answer received      Disconnect    Idle
                                             user/dev

    PendingI  AA answer                      Grant         Idle
              received with result code      service
              equal to CREDIT_CONTROL_       to end user
              NOT_APPLICABLE

    PendingI  User service terminated        Queue         PendingI
                                             termination
                                             event

    PendingI  Change in rating condition     Queue         PendingI
                                             changed
                                             rating
                                             condition
                                             event

      CLIENT, SESSION BASED for the first interrogation with CCR

    State      Event                          Action       New State
    ----------------------------------------------------------------

    Idle      Client or device requests      Send         PendingI
              access/service                 CC initial
                                             req.,
                                             start Tx

    PendingI  Successful CC initial          Stop Tx      Open
              answer received

    PendingI  Failure to send, or            Grant        Idle
              temporary error and            service to
              CCFH equal to CONTINUE         end user

    PendingI  Failure to send, or            Terminate    Idle
              temporary error and            end user's
              CCFH equal to TERMINATE        service
              or to RETRY_AND_TERMINATE

    PendingI  Tx expired and CCFH            Terminate    Idle
              equal to TERMINATE             end user's
                                             service

    PendingI  Tx expired and CCFH equal      Grant        PendingI
              to CONTINUE or to              service to
              RETRY_AND_TERMINATE            end user

    PendingI  CC initial answer              Terminate    Idle
              received with result code      end user's
              END_USER_SERVICE_DENIED or     service
              USER_UNKNOWN

    PendingI  CC initial answer              Grant        Idle
              received with result code      service
              equal to CREDIT_CONTROL_       to end user
              NOT_APPLICABLE

    PendingI  Failed CC initial answer       Grant        Idle
              received and CCFH equal to     service to
              CONTINUE                       end user

    PendingI  Failed CC initial answer       Terminate    Idle
              received and CCFH equal        end user's
              to TERMINATE or to             service
              RETRY_AND_TERMINATE

    PendingI  User service terminated        Queue        PendingI
                                             termination
                                             event

    PendingI  Change in rating condition     Queue        PendingI
                                             changed
                                             rating
                                             condition
                                             event

     CLIENT, SESSION BASED for intermediate and final interrogations

    State     Event                          Action       New State
    ----------------------------------------------------------------

    Open      Granted unit elapses           Send         PendingU
              and no final unit              CC update
              indication received            req.,
                                             start Tx

    Open      Granted unit elapses           Terminate    PendingT
              and final unit action          end user's
              equal to TERMINATE             service, send
              received                       CC termination
                                             req.

    Open      Change in rating condition     Send         PendingU
              in queue                       CC update
                                             req.,
                                             Start Tx

    Open      Service terminated in queue    Send         PendingT
                                             CC termination
                                             req.

    Open      Change in rating condition     Send         PendingU
              or Validity-Time elapses       CC update
                                             req.,
                                             Start Tx

    Open      User service terminated        Send         PendingT
                                             CC termination
                                             req.

    Open      RAR received                   Send RAA     PendingU
                                             followed by
                                             CC update req.,
                                             start Tx

    PendingU  Successful CC update           Stop Tx      Open
              answer received

    PendingU  Failure to send, or            Grant        Idle
              temporary error and            service to
              CCFH equal to CONTINUE         end user

    PendingU  Failure to send, or            Terminate    Idle
              temporary error and            end user's
              CCFH equal to TERMINATE        service
              or to RETRY_AND_TERMINATE

    PendingU  Tx expired and CCFH            Terminate    Idle
              equal to TERMINATE             end user's
                                             service

    PendingU  Tx expired and CCFH equal      Grant        PendingU
              to CONTINUE or to              service to
              RETRY_AND_TERMINATE            end user

    PendingU  CC update answer               Terminate    Idle
              received with result code      end user's
              END_USER_SERVICE_DENIED        service

    PendingU  CC update answer               Grant        Idle
              received with result code      service
              equal to CREDIT_CONTROL_       to end user
              NOT_APPLICABLE

    PendingU  Failed CC update               Grant        Idle
              answer received and            service to
              CCFH equal to CONTINUE         end user

    PendingU  Failed CC update               Terminate    Idle
              answer received and CCFH       end user's
              equal to TERMINATE or          service
              to RETRY_AND_TERMINATE

    PendingU  User service terminated        Queue        PendingU
                                             termination
                                             event

    PendingU  Change in rating               Queue        PendingU
              condition                      changed
                                             rating
                                             condition
                                             event

    PendingU  RAR received                   Send RAA     PendingU

    PendingT  Successful CC                               Idle
              termination answer received

    PendingT  Failure to send, temporary                  Idle
              error, or failed answer

    PendingT  Change in rating condition                  PendingT

                       CLIENT, EVENT BASED

    State     Event                          Action        New State
    ----------------------------------------------------------------
    Idle      Client or device requests      Send          PendingE
              a one-time service             CC event
                                             req.,
                                             Start Tx

    Idle      Request in storage             Send          PendingB
                                             stored
                                             request

    PendingE  Successful CC event            Grant         Idle
              answer received                service to
                                             end user

    PendingE  Failure to send, temporary     Indicate      Idle
              error, failed CC event         service
              answer received, or            error
              Tx expired; requested
              action CHECK_BALANCE or
              PRICE_ENQUIRY

    PendingE  CC event answer                Terminate     Idle
              received with result code      end user's
              END_USER_SERVICE_DENIED or     service
              USER_UNKNOWN and Tx running

    PendingE  CC event answer                Grant         Idle
              received with result code      service
              CREDIT_CONTROL_NOT_APPLICABLE; to end
              requested action               user
              DIRECT_DEBITING

    PendingE  Failure to send, temporary     Grant         Idle
              error, or failed CC event      service
              answer received; requested     to end
              action DIRECT_DEBITING;        user
              DDFH equal to CONTINUE

    PendingE  Failed CC event                Terminate     Idle
              answer received or temporary   end user's
              error; requested action        service
              DIRECT_DEBITING;
              DDFH equal to
              TERMINATE_OR_BUFFER and
              Tx running

    PendingE  Tx expired; requested          Grant         PendingE
              action DIRECT_DEBITING         service
                                             to end
                                             user

    PendingE  Failure to send; requested     Store         Idle
              action DIRECT_DEBITING;        request with
              DDFH equal to                  T-flag
              TERMINATE_OR_BUFFER

    PendingE  Temporary error; requested     Store         Idle
              action DIRECT_DEBITING;        request
              DDFH equal to
              TERMINATE_OR_BUFFER;
              Tx expired

    PendingE  Failed answer or answer                      Idle
              received with result code
              END_USER_SERVICE DENIED or
              USER_UNKNOWN; requested action
              DIRECT_DEBITING; Tx expired

    PendingE  Failed CC event answer         Indicate      Idle
              received; requested            service
              action REFUND_ACCOUNT          error and
                                             delete request

    PendingE  Failure to send or             Store         Idle
              Tx expired; requested          request
              action REFUND_ACCOUNT          with T-flag

    PendingE  Temporary error,               Store         Idle
              and requested action           request
              REFUND_ACCOUNT

    PendingB  Successful CC answer           Delete        Idle
              received                       request

    PendingB  Failed CC answer               Delete        Idle
              received                       request

    PendingB  Failure to send or                           Idle
              temporary error

                   SERVER, SESSION AND EVENT BASED

    State     Event                          Action        New State
    ----------------------------------------------------------------

    Idle      CC initial request             Send          Open
              received and successfully      CC initial
              processed                      answer,
                                             reserve units,
                                             start Tcc

    Idle      CC initial request             Send          Idle
              received but not               CC initial
              successfully processed         answer with
                                             Result-Code
                                             != SUCCESS

    Idle      CC event request               Send          Idle
              received and successfully      CC event
              processed                      answer

    Idle      CC event request               Send          Idle
              received but not               CC event
              successfully processed         answer with
                                             Result-Code
                                             != SUCCESS

    Open      CC update request              Send CC       Open
              received and successfully      update answer,
              processed                      debit used
                                             units,
                                             reserve
                                             new units,
                                             restart Tcc

    Open      CC update request              Send          Idle
              received but not               CC update
              successfully processed         answer with
                                             Result-Code
                                             != SUCCESS,
                                             debit used
                                             units

    Open      CC termination request         Send          Idle
              received and successfully      CC termin.
              processed                      answer,
                                             Stop Tcc,
                                             debit used
                                             units

    Open      CC termination request         Send          Idle
              received but not               CC termin.
              successfully processed         answer with
                                             Result-Code
                                             != SUCCESS,
                                             debit used
                                             units

    Open      Session supervision timer Tcc  Release       Idle
              expired                        reserved
                                             units

8.  Credit-Control AVPs

   This section defines the credit-control AVPs that are specific to
   Diameter credit-control application and that MAY be included in the
   Diameter credit-control messages.

   The AVPs defined in this section MAY also be included in
   authorization commands defined in authorization-specific
   applications, such as [NASREQ] and [DIAMMIP], if the first
   interrogation is performed as part of the
   authorization/authentication process, as described in section 5.2.

   The Diameter AVP rules are defined in the Diameter Base [DIAMBASE],
   section 4.  These AVP rules are observed in AVPs defined in this
   section.

   The following table describes the Diameter AVPs defined in the
   credit-control application, their AVP Code values, types, possible
   flag values, and whether the AVP MAY be encrypted.  The Diameter base
   [DIAMBASE] specifies the AVP Flag rules for AVPs in section 4.5.

                                            +--------------------+
                                            |    AVP Flag rules  |
                                            |----+-----+----+----|----+
                     AVP  Section           |    |     |SHLD|MUST|    |
   Attribute Name    Code Defined Data Type |MUST| MAY | NOT|NOT |Encr|
   -----------------------------------------|----+-----+----+----|----|
   CC-Correlation-Id 411  8.1    OctetString|    | P,M |    |  V | Y  |
   CC-Input-Octets   412  8.24   Unsigned64 | M  |  P  |    |  V | Y  |
   CC-Money          413  8.22   Grouped    | M  |  P  |    |  V | Y  |
   CC-Output-Octets  414  8.25   Unsigned64 | M  |  P  |    |  V | Y  |
   CC-Request-Number 415  8.2    Unsigned32 | M  |  P  |    |  V | Y  |
   CC-Request-Type   416  8.3    Enumerated | M  |  P  |    |  V | Y  |
   CC-Service-       417  8.26   Unsigned64 | M  |  P  |    |  V | Y  |
     Specific-Units                         |    |     |    |    |    |
   CC-Session-       418  8.4    Enumerated | M  |  P  |    |  V | Y  |
     Failover                               |    |     |    |    |    |
   CC-Sub-Session-Id 419  8.5    Unsigned64 | M  |  P  |    |  V | Y  |
   CC-Time           420  8.21   Unsigned32 | M  |  P  |    |  V | Y  |
   CC-Total-Octets   421  8.23   Unsigned64 | M  |  P  |    |  V | Y  |
   CC-Unit-Type      454  8.32   Enumerated | M  |  P  |    |  V | Y  |
   Check-Balance-    422  8.6    Enumerated | M  |  P  |    |  V | Y  |
     Result                                 |    |     |    |    |    |
   Cost-Information  423  8.7    Grouped    | M  |  P  |    |  V | Y  |
   Cost-Unit         424  8.12   UTF8String | M  |  P  |    |  V | Y  |
   Credit-Control    426  8.13   Enumerated | M  |  P  |    |  V | Y  |
   Credit-Control-   427  8.14   Enumerated | M  |  P  |    |  V | Y  |
     Failure-Handling                       |    |     |    |    |    |
   Currency-Code     425  8.11   Unsigned32 | M  |  P  |    |  V | Y  |
   Direct-Debiting-  428  8.15   Enumerated | M  |  P  |    |  V | Y  |
     Failure-Handling                       |    |     |    |    |    |
   Exponent          429  8.9    Integer32  | M  |  P  |    |  V | Y  |
   Final-Unit-Action 449  8.35   Enumerated | M  |  P  |    |  V | Y  |
   Final-Unit-       430  8.34   Grouped    | M  |  P  |    |  V | Y  |
     Indication                             |    |     |    |    |    |
   Granted-Service-  431  8.17   Grouped    | M  |  P  |    |  V | Y  |
     Unit                                   |    |     |    |    |    |
   G-S-U-Pool-       453  8.31   Unsigned32 | M  |  P  |    |  V | Y  |
     Identifier                             |    |     |    |    |    |

   G-S-U-Pool-       457  8.30   Grouped    | M  |  P  |    |  V | Y  |
     Reference                              |    |     |    |    |    |
   Multiple-Services 456  8.16   Grouped    | M  |  P  |    |  V | Y  |
    -Credit-Control                         |    |     |    |    |    |
   Multiple-Services 455  8.40   Enumerated | M  |  P  |    |  V | Y  |
    -Indicator                              |    |     |    |    |    |
   Rating-Group      432  8.29   Unsigned32 | M  |  P  |    |  V | Y  |
   Redirect-Address  433  8.38   Enumerated | M  |  P  |    |  V | Y  |
     -Type                                  |    |     |    |    |    |
   Redirect-Server   434  8.37   Grouped    | M  |  P  |    |  V | Y  |
   Redirect-Server   435  8.39   UTF8String | M  |  P  |    |  V | Y  |
     -Address                               |    |     |    |    |    |
   Requested-Action  436  8.41   Enumerated | M  |  P  |    |  V | Y  |
   Requested-Service 437  8.18   Grouped    | M  |  P  |    |  V | Y  |
     -Unit                                  |    |     |    |    |    |
   Restriction       438  8.36   IPFiltrRule| M  |  P  |    |  V | Y  |
     -Filter-Rule                           |    |     |    |    |    |
   Service-Context   461  8.42   UTF8String | M  |  P  |    |  V | Y  |
     -Id                                    |    |     |    |    |    |
   Service-          439  8.28   Unsigned32 | M  |  P  |    |  V | Y  |
     Identifier                             |    |     |    |    |    |
   Service-Parameter 440  8.43   Grouped    |    | P,M |    |  V | Y  |
     -Info                                  |    |     |    |    |    |
   Service-          441  8.44   Unsigned32 |    | P,M |    |  V | Y  |
     Parameter-Type                         |    |     |    |    |    |
   Service-          442  8.45   OctetString|    | P,M |    |  V | Y  |
     Parameter-Value                        |    |     |    |    |    |
   Subscription-Id   443  8.46   Grouped    | M  |  P  |    |  V | Y  |
   Subscription-Id   444  8.48   UTF8String | M  |  P  |    |  V | Y  |
     -Data                                  |    |     |    |    |    |
   Subscription-Id   450  8.47   Enumerated | M  |  P  |    |  V | Y  |
     -Type                                  |    |     |    |    |    |
   Tariff-Change     452  8.27   Enumerated | M  |  P  |    |  V | Y  |
     -Usage                                 |    |     |    |    |    |
   Tariff-Time       451  8.20   Time       | M  |  P  |    |  V | Y  |
     -Change                                |    |     |    |    |    |
   Unit-Value        445  8.8    Grouped    | M  |  P  |    |  V | Y  |
   Used-Service-Unit 446  8.19   Grouped    | M  |  P  |    |  V | Y  |
   User-Equipment    458  8.49   Grouped    |    | P,M |    |  V | Y  |
     -Info                                  |    |     |    |    |    |
   User-Equipment    459  8.50   Enumerated |    | P,M |    |  V | Y  |
     -Info-Type                             |    |     |    |    |    |
   User-Equipment    460  8.51   OctetString|    | P,M |    |  V | Y  |
     -Info-Value                            |    |     |    |    |    |
   Value-Digits      447  8.10   Integer64  | M  |  P  |    |  V | Y  |
   Validity-Time     448  8.33   Unsigned32 | M  |  P  |    |  V | Y  |

8.1.  CC-Correlation-Id AVP

   The CC-Correlation-Id AVP (AVP Code 411) is of type OctetString and
   contains information to correlate credit-control requests generated
   for different components of the service; e.g., transport and service
   level.  The one who allocates the Service-Context-Id (i.e., unique
   identifier of a service specific document) is also responsible for
   defining the content and encoding of the CC-Correlation-Id AVP.

8.2.  CC-Request-Number AVP

   The CC-Request-Number AVP (AVP Code 415) is of type Unsigned32 and
   identifies this request within one session.  As Session-Id AVPs are
   globally unique, the combination of Session-Id and CC-Request-Number
   AVPs is also globally unique and can be used in matching credit-
   control messages with confirmations.  An easy way to produce unique
   numbers is to set the value to 0 for a credit-control request of type
   INITIAL_REQUEST and EVENT_REQUEST and to set the value to 1 for the
   first UPDATE_REQUEST, to 2 for the second, and so on until the value
   for TERMINATION_REQUEST is one more than for the last UPDATE_REQUEST.

8.3.  CC-Request-Type AVP

   The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
   contains the reason for sending the credit-control request message.
   It MUST be present in all Credit-Control-Request messages.  The
   following values are defined for the CC-Request-Type AVP:

   INITIAL_REQUEST                 1
      An Initial request is used to initiate a credit-control session,
      and contains credit control information that is relevant to the
      initiation.

   UPDATE_REQUEST                  2
      An Update request contains credit-control information for an
      existing credit-control session.  Update credit-control requests
      SHOULD be sent every time a credit-control re-authorization is
      needed at the expiry of the allocated quota or validity time.
      Further, additional service-specific events MAY trigger a
      spontaneous Update request.

   TERMINATION_REQUEST             3
      A Termination request is sent to terminate a credit-control
      session and contains credit-control information relevant to the
      existing session.

   EVENT_REQUEST                   4
      An Event request is used when there is no need to maintain any
      credit-control session state in the credit-control server.  This
      request contains all information relevant to the service, and is
      the only request of the service.  The reason for the Event request
      is further detailed in the Requested-Action AVP.  The Requested-
      Action AVP MUST be included in the Credit-Control-Request message
      when CC-Request-Type is set to EVENT_REQUEST.

8.4.  CC-Session-Failover AVP

   The CC-Session-Failover AVP (AVP Code 418) is type of Enumerated and
   contains information as to whether moving the credit-control message
   stream to a backup server during an ongoing credit-control session is
   supported.  In communication failures, the credit-control message
   streams can be moved to an alternative destination if the credit-
   control server supports failover to an alternative server.  The
   secondary credit-control server name, if received from the home
   Diameter AAA server, can be used as an address of the backup server.
   An implementation is not required to support moving a credit-control
   message stream to an alternative server, as this also requires moving
   information related to the credit-control session to backup server.

   The following values are defined for the CC-Session-Failover AVP:

   FAILOVER_NOT_SUPPORTED          0
      When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED,
      the credit-control message stream MUST NOT to be moved to an
      alternative destination in the case of communication failure.

      This is the default behavior if the AVP isn't included in the
      reply from the authorization or credit-control server.

   FAILOVER_SUPPORTED              1
      When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
      credit-control message stream SHOULD be moved to an alternative
      destination in the case of communication failure.  Moving the
      credit-control message stream to a backup server MAY require that
      information related to the credit-control session should also be
      forwarded to alternative server.

8.5.  CC-Sub-Session-Id AVP

   The CC-Sub-Session-Id AVP (AVP Code 419) is of type Unsigned64 and
   contains the credit-control sub-session identifier.  The combination
   of the Session-Id and this AVP MUST be unique per sub-session, and

   the value of this AVP MUST be monotonically increased by one for all
   new sub-sessions.  The absence of this AVP implies that no sub-
   sessions are in use.

8.6.  Check-Balance-Result AVP

   The Check Balance Result AVP (AVP Code 422) is of type Enumerated and
   contains the result of the balance check.  This AVP is applicable
   only when the Requested-Action AVP indicates CHECK_BALANCE in the
   Credit-Control-Request command.

   The following values are defined for the Check-Balance-Result AVP.

   ENOUGH_CREDIT                   0
      There is enough credit in the account to cover the requested
      service.

   NO_CREDIT                       1
      There isn't enough credit in the account to cover the requested
      service.

8.7.  Cost-Information AVP

   The Cost-Information AVP (AVP Code 423) is of type Grouped, and it is
   used to return the cost information of a service, which the credit-
   control client can transfer transparently to the end user.  The
   included Unit-Value AVP contains the cost estimate (always type of
   money) of the service, in the case of price enquiry, or the
   accumulated cost estimation, in the case of credit-control session.

   The Currency-Code specifies in which currency the cost was given.
   The Cost-Unit specifies the unit when the service cost is a cost per
   unit (e.g., cost for the service is $1 per minute).

   When the Requested-Action AVP with value PRICE_ENQUIRY is included in
   the Credit-Control-Request command, the Cost-Information AVP sent in
   the succeeding Credit-Control-Answer command contains the cost
   estimation of the requested service, without any reservation being
   made.

   The Cost-Information AVP included in the Credit-Control-Answer
   command with the CC-Request-Type set to UPDATE_REQUEST contains the
   accumulated cost estimation for the session, without taking any
   credit reservation into account.

   The Cost-Information AVP included in the Credit-Control-Answer
   command with the CC-Request-Type set to EVENT_REQUEST or
   TERMINATION_REQUEST contains the estimated total cost for the
   requested service.

   It is defined as follows (per the grouped-avp-def of
   RFC 3588 [DIAMBASE]):

                Cost-Information ::= < AVP Header: 423 >
                                     { Unit-Value }
                                     { Currency-Code }
                                     [ Cost-Unit ]

8.8.  Unit-Value AVP

   Unit-Value AVP is of type Grouped (AVP Code 445) and specifies the
   units as decimal value.  The Unit-Value is a value with an exponent;
   i.e., Unit-Value = Value-Digits AVP * 10^Exponent.  This
   representation avoids unwanted rounding off.  For example, the value
   of 2,3 is represented as Value-Digits = 23 and Exponent = -1.  The
   absence of the exponent part MUST be interpreted as an exponent equal
   to zero.

   It is defined as follows (per the grouped-avp-def of
   RFC 3588 [DIAMBASE]):

                    Unit-Value ::= < AVP Header: 445 >
                                   { Value-Digits }
                                   [ Exponent ]

8.9.  Exponent AVP

   Exponent AVP is of type Integer32 (AVP Code 429) and contains the
   exponent value to be applied for the Value-Digit AVP within the
   Unit-Value AVP.

8.10.  Value-Digits AVP

   The Value-Digits AVP is of type Integer64 (AVP Code 447) and contains
   the significant digits of the number.  If decimal values are needed
   to present the units, the scaling MUST be indicated with the related
   Exponent AVP.  For example, for the monetary amount $ 0.05 the value
   of Value-Digits AVP MUST be set to 5, and the scaling MUST be
   indicated with the Exponent AVP set to -2.

8.11.  Currency-Code AVP

   The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and
   contains a currency code that specifies in which currency the values
   of AVPs containing monetary units were given.  It is specified by
   using the numeric values defined in the ISO 4217 standard [ISO4217].

8.12.  Cost-Unit AVP

   The Cost-Unit AVP (AVP Code 424) is of type UTF8String, and it is
   used to display a human readable string to the end user.  It
   specifies the applicable unit to the Cost-Information when the
   service cost is a cost per unit (e.g., cost of the service is $1 per
   minute).  The Cost-Unit can be minutes, hours, days, kilobytes,
   megabytes, etc.

8.13.  Credit-Control AVP

   The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
   be included in AA requests when the service element has credit-
   control capabilities.

   CREDIT_AUTHORIZATION            0
      If the home Diameter AAA server determines that the user has
      prepaid subscription, this value indicates that the credit-control
      server MUST be contacted to perform the first interrogation.  The
      value of the Credit-Control AVP MUST always be set to 0 in an AA
      request sent to perform the first interrogation and to initiate a
      new credit-control session.

   RE_AUTHORIZATION                1
      This value indicates to the Diameter AAA server that a credit-
      control session is ongoing for the subscriber and that the
      credit-control server MUST not be contacted.  The Credit-Control
      AVP set to the value of 1 is to be used only when the first
      interrogation has been successfully performed and the credit-
      control session is ongoing (i.e., re-authorization triggered by
      Authorization-Lifetime).  This value MUST NOT be used in an AA
      request sent to perform the first interrogation.

8.14.  Credit-Control-Failure-Handling AVP

   The Credit-Control-Failure-Handling AVP (AVP Code 427) is of type
   Enumerated.  The credit-control client uses information in this AVP
   to decide what to do if sending credit-control messages to the
   credit-control server has been, for instance, temporarily prevented
   due to a network problem.  Depending on the service logic, the
   credit-control server can order the client to terminate the service

   immediately when there is a reason to believe that the service cannot
   be charged, or to try failover to an alternative server, if possible.
   Then the server could either terminate or grant the service, should
   the alternative connection also fail.

   TERMINATE                       0
      When the Credit-Control-Failure-Handling AVP is set to TERMINATE,
      the service MUST only be granted for as long as there is a
      connection to the credit-control server.  If the credit-control
      client does not receive any Credit-Control-Answer message within
      the Tx timer (as defined in section 13), the credit-control
      request is regarded as failed, and the end user's service session
      is terminated.

      This is the default behavior if the AVP isn't included in the
      reply from the authorization or credit-control server.

   CONTINUE                       1
      When the Credit-Control-Failure-Handling AVP is set to CONTINUE,
      the credit-control client SHOULD re-send the request to an
      alternative server in the case of transport or temporary failures,
      provided that a failover procedure is supported in the credit-
      control server and the credit-control client, and that an
      alternative server is available.  Otherwise, the service SHOULD be
      granted, even if credit-control messages can't be delivered.

   RETRY_AND_TERMINATE            2
      When the Credit-Control-Failure-Handling AVP is set to
      RETRY_AND_TERMINATE, the credit-control client SHOULD re-send the
      request to an alternative server in the case of transport or
      temporary failures, provided that a failover procedure is
      supported in the credit-control server and the credit-control
      client, and that an alternative server is available.  Otherwise,
      the service SHOULD not be granted when the credit-control messages
      can't be delivered.

8.15.  Direct-Debiting-Failure-Handling AVP

   The Direct-Debiting-Failure-Handling AVP (AVP Code 428) is of type
   Enumerated.  The credit-control client uses information in this AVP
   to decide what to do if sending credit-control messages (Requested-
   Action AVP set to DIRECT_DEBITING) to the credit-control server has
   been, for instance, temporarily prevented due to a network problem.

   TERMINATE_OR_BUFFER             0
      When the Direct-Debiting-Failure-Handling AVP is set to
      TERMINATE_OR_BUFFER, the service MUST be granted for as long as
      there is a connection to the credit-control server.  If the

      credit-control client does not receive any Credit-Control-Answer
      message within the Tx timer (as defined in section 13) the
      credit-control request is regarded as failed.  The client SHOULD
      terminate the service if it can determine from the failed answer
      that units have not been debited.  Otherwise the credit-control
      client SHOULD grant the service, store the request in application
      level non-volatile storage, and try to re-send the request.  These
      requests MUST be marked as possible duplicates by setting the T-
      flag in the command header as described in [DIAMBASE] section 3.

      This is the default behavior if the AVP isn't included in the
      reply from the authorization server.

   CONTINUE                                              1
      When the Direct-Debiting-Failure-Handling AVP is set to CONTINUE,
      the service SHOULD be granted, even if credit-control messages
      can't be delivered, and the request should be deleted.

8.16.  Multiple-Services-Credit-Control AVP

   Multiple-Services-Credit-Control AVP (AVP Code 456) is of type
   Grouped and contains the AVPs related to the independent credit-
   control of multiple services feature.  Note that each instance of
   this AVP carries units related to one or more services or related to
   a single rating group.

   The Service-Identifier and the Rating-Group AVPs are used to
   associate the granted units to a given service or rating group.  If
   both the Service-Identifier and the Rating-Group AVPs are included,
   the target of the service units is always the service(s) indicated by
   the value of the Service-Identifier AVP(s).  If only the Rating-
   Group-Id AVP is present, the Multiple-Services-Credit-Control AVP
   relates to all the services that belong to the specified rating
   group.

   The G-S-U-Pool-Reference AVP allows the server to specify a G-S-U-
   Pool-Identifier identifying a credit pool within which the units of
   the specified type are considered pooled.  If a G-S-U-Pool-Reference
   AVP is present, then actual service units of the specified type MUST
   also be present.  For example, if the G-S-U-Pool-Reference AVP
   specifies Unit-Type TIME, then the CC-Time AVP MUST be present.

   The Requested-Service-Unit AVP MAY contain the amount of requested
   service units or the requested monetary value.  It MUST be present in
   the initial interrogation and within the intermediate interrogations
   in which new quota is requested.  If the credit-control client does
   not include the Requested-Service-Unit AVP in a request command,
   because for instance, it has determined that the end-user terminated

   the service, the server MUST debit the used amount from the user's
   account but MUST NOT return a new quota in the corresponding answer.
   The Validity-Time, Result-Code, and Final-Unit-Indication AVPs MAY be
   present in an answer command as defined in sections 5.1.2 and 5.6 for
   the graceful service termination.

   When both the Tariff-Time-Change and Tariff-Change-Usage AVPs are
   present, the server MUST include two separate instances of the
   Multiple-Services-Credit-Control AVP with the Granted-Service-Unit
   AVP associated to the same service-identifier and/or rating-group.
   Where the two quotas are associated to the same pool or to different
   pools, the credit pooling mechanism defined in section 5.1.2 applies.
   The Tariff-Change-Usage AVP MUST NOT be included in request commands
   to report used units before, and after tariff time change the Used-
   Service-Unit AVP MUST be used.

   A server not implementing the independent credit-control of multiple
   services functionality MUST treat the Multiple-Services-Credit-
   Control AVP as an invalid AVP.

   The Multiple-Services-Control AVP is defined as follows (per the
   grouped-avp-def of RFC 3588 [DIAMBASE]):

      Multiple-Services-Credit-Control ::= < AVP Header: 456 >
                                           [ Granted-Service-Unit ]
                                           [ Requested-Service-Unit ]
                                          *[ Used-Service-Unit ]
                                           [ Tariff-Change-Usage ]
                                          *[ Service-Identifier ]
                                           [ Rating-Group ]
                                          *[ G-S-U-Pool-Reference ]
                                           [ Validity-Time ]
                                           [ Result-Code ]
                                           [ Final-Unit-Indication ]
                                          *[ AVP ]

8.17.  Granted-Service-Unit AVP

   Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
   contains the amount of units that the Diameter credit-control client
   can provide to the end user until the service must be released or the
   new Credit-Control-Request must be sent.  A client is not required to
   implement all the unit types, and it must treat unknown or
   unsupported unit types in the answer message as an incorrect CCA
   answer.  In this case, the client MUST terminate the credit-control
   session and indicate in the Termination-Cause AVP reason
   DIAMETER_BAD_ANSWER.

   The Granted-Service-Unit AVP is defined as follows (per the grouped-
   avp-def of RFC 3588 [DIAMBASE]):

      Granted-Service-Unit ::= < AVP Header: 431 >
                                 [ Tariff-Time-Change ]
                                 [ CC-Time ]
                                 [ CC-Money ]
                                 [ CC-Total-Octets ]
                                 [ CC-Input-Octets ]
                                 [ CC-Output-Octets ]
                                 [ CC-Service-Specific-Units ]
                                *[ AVP ]

8.18.  Requested-Service-Unit AVP

   The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
   contains the amount of requested units specified by the Diameter
   credit-control client.  A server is not required to implement all the
   unit types, and it must treat unknown or unsupported unit types as
   invalid AVPs.

   The Requested-Service-Unit AVP is defined as follows (per the
   grouped-avp-def of RFC 3588 [DIAMBASE]):

      Requested-Service-Unit ::= < AVP Header: 437 >
                                 [ CC-Time ]
                                 [ CC-Money ]
                                 [ CC-Total-Octets ]
                                 [ CC-Input-Octets ]
                                 [ CC-Output-Octets ]
                                 [ CC-Service-Specific-Units ]
                                *[ AVP ]

8.19.  Used-Service-Unit AVP

   The Used-Service-Unit AVP is of type Grouped (AVP Code 446) and
   contains the amount of used units measured from the point when the
   service became active or, if interim interrogations are used during
   the session, from the point when the previous measurement ended.

   The Used-Service-Unit AVP is defined as follows (per the grouped-
   avp-def of RFC 3588 [DIAMBASE]):

      Used-Service-Unit ::= < AVP Header: 446 >
                            [ Tariff-Change-Usage ]
                            [ CC-Time ]
                            [ CC-Money ]
                            [ CC-Total-Octets ]
                            [ CC-Input-Octets ]
                            [ CC-Output-Octets ]
                            [ CC-Service-Specific-Units ]
                           *[ AVP ]

8.20.  Tariff-Time-Change AVP

   The Tariff-Time-Change AVP (AVP Code 451) is of type Time.  It is
   sent from the server to the client and includes the time in seconds
   since January 1, 1900, 00:00 UTC, when the tariff of the service will
   be changed.

   The tariff change mechanism is optional for the client and server,
   and it is not used for time-based services defined in section 5.  If
   a client does not support the tariff time change mechanism, it MUST
   treat Tariff-Time-Change AVP in the answer message as an incorrect
   CCA answer.  In this case, the client terminates the credit-control
   session and indicates in the Termination-Cause AVP reason
   DIAMETER_BAD_ANSWER.

   Omission of this AVP means that no tariff change is to be reported.

8.21.  CC-Time AVP

   The CC-Time AVP (AVP Code 420) is of type Unsigned32 and indicates
   the length of the requested, granted, or used time in seconds.

8.22.  CC-Money AVP

   The CC-Money AVP (AVP Code 413) is of type Grouped and specifies the
   monetary amount in the given currency.  The Currency-Code AVP SHOULD
   be included.  It is defined as follows (per the grouped-avp-def of
   RFC 3588 [DIAMBASE]):

      CC-Money ::= < AVP Header: 413 >
                   { Unit-Value }
                   [ Currency-Code ]

8.23.  CC-Total-Octets AVP

   The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64 and
   contains the total number of requested, granted, or used octets
   regardless of the direction (sent or received).

8.24.  CC-Input-Octets AVP

   The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64 and
   contains the number of requested, granted, or used octets that can
   be/have been received from the end user.

8.25.  CC-Output-Octets AVP

   The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64 and
   contains the number of requested, granted, or used octets that can
   be/have been sent to the end user.

8.26.  CC-Service-Specific-Units AVP

   The CC-Service-Specific-Units AVP (AVP Code 417) is of type
   Unsigned64 and specifies the number of service-specific units (e.g.,
   number of events, points) given in a selected service.  The service-
   specific units always refer to the service identified in the
   Service-Identifier AVP (or Rating-Group AVP when the Multiple-
   Services-Credit-Control AVP is used).

8.27.  Tariff-Change-Usage AVP

   The Tariff-Change-Usage AVP (AVP Code 452) is of type Enumerated and
   defines whether units are used before or after a tariff change, or
   whether the units straddled a tariff change during the reporting
   period.  Omission of this AVP means that no tariff change has
   occurred.

   In addition, when present in answer messages as part of the
   Multiple-Services-Credit-Control AVP, this AVP defines whether units
   are allocated to be used before or after a tariff change event.

   When the Tariff-Time-Change AVP is present, omission of this AVP in
   answer messages means that the single quota mechanism applies.

   Tariff-Change-Usage can be one of the following:

   UNIT_BEFORE_TARIFF_CHANGE       0
      When present in the Multiple-Services-Credit-Control AVP, this
      value indicates the amount of the units allocated for use before a
      tariff change occurs.

      When present in the Used-Service-Unit AVP, this value indicates
      the amount of resource units used before a tariff change had
      occurred.

   UNIT_AFTER_TARIFF_CHANGE        1
      When present in the Multiple-Services-Credit-Control AVP, this
      value indicates the amount of the units allocated for use after a
      tariff change occurs.

      When present in the Used-Service-Unit AVP, this value indicates
      the amount of resource units used after tariff change had
      occurred.

   UNIT_INDETERMINATE              2
      The used unit contains the amount of units that straddle the
      tariff change (e.g., the metering process reports to the credit-
      control client in blocks of n octets, and one block straddled the
      tariff change).  This value is to be used only in the Used-
      Service-Unit AVP.

8.28.  Service-Identifier AVP

   The Service-Identifier AVP is of type Unsigned32 (AVP Code 439) and
   contains the identifier of a service.  The specific service the
   request relates to is uniquely identified by the combination of
   Service-Context-Id and Service-Identifier AVPs.

   A usage example of this AVP is illustrated in Appendix A (Flow IX).

8.29.  Rating-Group AVP

   The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and
   contains the identifier of a rating group.  All the services subject
   to the same rating type are part of the same rating group.  The
   specific rating group the request relates to is uniquely identified
   by the combination of Service-Context-Id and Rating-Group AVPs.

   A usage example of this AVP is illustrated in Appendix A (Flow IX).

8.30.  G-S-U-Pool-Reference AVP

   The G-S-U-Pool-Reference AVP (AVP Code 457) is of type Grouped.  It
   is used in the Credit-Control-Answer message, and associates the
   Granted-Service-Unit AVP within which it appears with a credit pool
   within the session.

   The G-S-U-Pool-Identifier AVP specifies the credit pool from which
   credit is drawn for this unit type.

   The CC-Unit-Type AVP specifies the type of units for which credit is
   pooled.

   The Unit-Value AVP specifies the multiplier, which converts between
   service units of type CC-Unit-Type and abstract service units within
   the credit pool (and thus to service units of any other service or
   rating group associated with the same pool).

   The G-S-U-Pool-Reference AVP is defined as follows (per the grouped-
   avp-def of RFC 3588 [DIAMBASE]):

      G-S-U-Pool-Reference    ::= < AVP Header: 457 >
                                  { G-S-U-Pool-Identifier }
                                  { CC-Unit-Type }
                                  { Unit-Value }

8.31.  G-S-U-Pool-Identifier AVP

   The G-S-U-Pool-Identifier AVP (AVP Code 453) is of type Unsigned32
   and identifies a credit pool within the session.

8.32.  CC-Unit-Type AVP

   The CC-Unit-Type AVP (AVP Code 454) is of type Enumerated and
   specifies the type of units considered to be pooled into a credit
   pool.

   The following values are defined for the CC-Unit-Type AVP:

      TIME                         0
      MONEY                        1
      TOTAL-OCTETS                 2
      INPUT-OCTETS                 3
      OUTPUT-OCTETS                4
      SERVICE-SPECIFIC-UNITS       5

8.33.  Validity-Time AVP

   The Validity-Time AVP is of type Unsigned32 (AVP Code 448).  It is
   sent from the credit-control server to the credit-control client.
   The AVP contains the validity time of the granted service units.  The
   measurement of the Validity-Time is started upon receipt of the
   Credit-Control-Answer Message containing this AVP.  If the granted
   service units have not been consumed within the validity time
   specified in this AVP, the credit-control client MUST send a Credit-
   Control-Request message to the server, with CC-Request-Type set to
   UPDATE_REQUEST.  The value field of the Validity-Time AVP is given in
   seconds.

   The Validity-Time AVP is also used for the graceful service
   termination (see section 5.6) to indicate to the credit-control
   client how long the subscriber is allowed to use network resources
   after the specified action (i.e., REDIRECT or RESTRICT_ACCESS)
   started.  When the Validity-Time elapses, a new intermediate
   interrogation is sent to the server.

8.34.  Final-Unit-Indication AVP

   The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
   indicates that the Granted-Service-Unit AVP in the Credit-Control-
   Answer, or in the AA answer, contains the final units for the
   service.  After these units have expired, the Diameter credit-control
   client is responsible for executing the action indicated in the
   Final-Unit-Action AVP (see section 5.6).

   If more than one unit type is received in the Credit-Control-Answer,
   the unit type that first expired SHOULD cause the credit-control
   client to execute the specified action.

   In the first interrogation, the Final-Unit-Indication AVP with
   Final-Unit-Action REDIRECT or RESTRICT_ACCESS can also be present
   with no Granted-Service-Unit AVP in the Credit-Control-Answer or in
   the AA answer.  This indicates to the Diameter credit-control client
   to execute the specified action immediately.  If the home service
   provider policy is to terminate the service, naturally, the server
   SHOULD return the appropriate transient failure (see section 9.1) in
   order to implement the policy-defined action.

   The Final-Unit-Action AVP defines the behavior of the service element
   when the user's account cannot cover the cost of the service and MUST
   always be present if the Final-Unit-Indication AVP is included in a
   command.

   If the Final-Unit-Action AVP is set to TERMINATE, no other AVPs MUST
   be present.

   If the Final-Unit-Action AVP is set to REDIRECT at least the
   Redirect-Server AVP MUST be present.  The Restriction-Filter-Rule AVP
   or the Filter-Id AVP MAY be present in the Credit-Control-Answer
   message if the user is also allowed to access other services that are
   not accessible through the address given in the Redirect-Server AVP.

   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
   Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.

   The Filter-Id AVP is defined in [NASREQ].  The Filter-Id AVP can be
   used to reference an IP filter list installed in the access device by
   means other than the Diameter credit-control application, e.g.,
   locally configured or configured by another entity.

   The Final-Unit-Indication AVP is defined as follows (per the
   grouped-avp-def of RFC 3588 [DIAMBASE]):

      Final-Unit-Indication ::= < AVP Header: 430 >
                                { Final-Unit-Action }
                               *[ Restriction-Filter-Rule ]
                               *[ Filter-Id ]
                                [ Redirect-Server ]

8.35.  Final-Unit-Action AVP

   The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
   indicates to the credit-control client the action to be taken when
   the user's account cannot cover the service cost.

   The Final-Unit-Action can be one of the following:

   TERMINATE                       0
      The credit-control client MUST terminate the service session.
      This is the default handling, applicable whenever the credit-
      control client receives an unsupported Final-Unit-Action value,
      and it MUST be supported by all the Diameter credit-control client
      implementations conforming to this specification.

   REDIRECT                        1
      The service element MUST redirect the user to the address
      specified in the Redirect-Server-Address AVP.  The redirect action
      is defined in section 5.6.2.

   RESTRICT_ACCESS                 2
      The access device MUST restrict the user access according to the
      IP packet filters defined in the Restriction-Filter-Rule AVP or
      according to the IP packet filters identified by the Filter-Id
      AVP.  All the packets not matching the filters MUST be dropped
      (see section 5.6.3).

8.36.  Restriction-Filter-Rule AVP

   The Restriction-Filter-Rule AVP (AVP Code 438) is of type
   IPFilterRule and provides filter rules corresponding to services that
   are to remain accessible even if there are no more service units
   granted.  The access device has to configure the specified filter

   rules for the subscriber and MUST drop all the packets not matching
   these filters.  Zero, one, or more such AVPs MAY be present in a
   Credit-Control-Answer message or in an AA answer message.

8.37.  Redirect-Server AVP

   The Redirect-Server AVP (AVP Code 434) is of type Grouped and
   contains the address information of the redirect server (e.g., HTTP
   redirect server, SIP Server) with which the end user is to be
   connected when the account cannot cover the service cost.  It MUST be
   present when the Final-Unit-Action AVP is set to REDIRECT.

   It is defined as follows (per the grouped-avp-def of RFC 3588
   [DIAMBASE]):

      Redirect-Server ::= < AVP Header: 434 >
                          { Redirect-Address-Type }
                          { Redirect-Server-Address }

8.38.  Redirect-Address-Type AVP

   The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated
   and defines the address type of the address given in the Redirect-
   Server-Address AVP.

   The address type can be one of the following:

   IPv4 Address                    0
      The address type is in the form of "dotted-decimal" IPv4 address,
      as defined in [IPv4].

   IPv6 Address                    1
      The address type is in the form of IPv6 address, as defined in
      [IPv6Addr].  The address is a text representation of the address
      in either the preferred or alternate text form [IPv6Addr].
      Conformant implementations MUST support the preferred form and
      SHOULD support the alternate text form for IPv6 addresses.

   URL                             2
      The address type is in the form of Uniform Resource Locator, as
      defined in [URL].

   SIP URI                         3
      The address type is in the form of SIP Uniform Resource
      Identifier, as defined in [SIP].

8.39.  Redirect-Server-Address AVP

   The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String
   and defines the address of the redirect server (e.g., HTTP redirect
   server, SIP Server) with which the end user is to be connected when
   the account cannot cover the service cost.

8.40.  Multiple-Services-Indicator AVP

   The Multiple-Services-Indicator AVP (AVP Code 455) is of type
   Enumerated and indicates whether the Diameter credit-control client
   is capable of handling multiple services independently within a
   (sub-) session.  The absence of this AVP means that independent
   credit-control of multiple services is not supported.

   A server not implementing the independent credit-control of multiple
   services MUST treat the Multiple-Services-Indicator AVP as an invalid
   AVP.

   The following values are defined for the Multiple-Services-Indicator
   AVP:

   MULTIPLE_SERVICES_NOT_SUPPORTED 0
      Client does not support independent credit-control of multiple
      services within a (sub-)session.

   MULTIPLE_SERVICES_SUPPORTED     1
      Client supports independent credit-control of multiple services
      within a (sub-)session.

8.41.  Requested-Action AVP

   The Requested-Action AVP (AVP Code 436) is of type Enumerated and
   contains the requested action being sent by Credit-Control-Request
   command where the CC-Request-Type is set to EVENT_REQUEST.  The
   following values are defined for the Requested-Action AVP:

   DIRECT_DEBITING                 0
      This indicates a request to decrease the end user's account
      according to information specified in the Requested-Service-Unit
      AVP and/or Service-Identifier AVP (additional rating information
      may be included in service-specific AVPs or in the Service-
      Parameter-Info AVP).  The Granted-Service-Unit AVP in the Credit-
      Control-Answer command contains the debited units.

   REFUND_ACCOUNT                  1
      This indicates a request to increase the end user's account
      according to information specified in the Requested-Service-Unit
      AVP and/or Service-Identifier AVP (additional rating information
      may be included in service-specific AVPs or in the Service-
      Parameter-Info AVP).  The Granted-Service-Unit AVP in the Credit-
      Control-Answer command contains the refunded units.

   CHECK_BALANCE                   2
      This indicates a balance check request.  In this case, the
      checking of the account balance is done without any credit
      reservation from the account.  The Check-Balance-Result AVP in the
      Credit-Control-Answer command contains the result of the balance
      check.

   PRICE_ENQUIRY                   3
      This indicates a price enquiry request.  In this case, neither
      checking of the account balance nor reservation from the account
      will be done; only the price of the service will be returned in
      the Cost-Information AVP in the Credit-Control-Answer Command.

8.42.  Service-Context-Id AVP

   The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and
   contains a unique identifier of the Diameter credit-control service
   specific document that applies to the request (as defined in section
   4.1.2).  This is an identifier allocated by the service provider, by
   the service element manufacturer, or by a standardization body, and
   MUST uniquely identify a given Diameter credit-control service
   specific document.  The format of the Service-Context-Id is:

   "service-context" "@" "domain"

   service-context = Token

   The Token is an arbitrary string of characters and digits.

   'domain' represents the entity that allocated the Service-Context-Id.
   It can be ietf.org, 3gpp.org, etc., if the identifier is allocated by
   a standardization body, or it can be the FQDN of the service provider
   (e.g., provider.example.com) or of the vendor (e.g.,
   vendor.example.com) if the identifier is allocated by a private
   entity.

   This AVP SHOULD be placed as close to the Diameter header as
   possible.

   Service-specific documents that are for private use only (i.e., to
   one provider's own use, where no interoperability is deemed useful)
   may define private identifiers without need of coordination.
   However, when interoperability is wanted, coordination of the
   identifiers via, for example, publication of an informational RFC is
   RECOMMENDED in order to make Service-Context-Id globally available.

8.43.  Service-Parameter-Info AVP

   The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
   contains service-specific information used for price calculation or
   rating.  The Service-Parameter-Type AVP defines the service parameter
   type, and the Service-Parameter-Value AVP contains the parameter
   value.  The actual contents of these AVPs are not within the scope of
   this document and SHOULD be defined in another Diameter application,
   in standards written by other standardization bodies, or in service-
   specific documentation.

   In the case of an unknown service request (e.g., unknown Service-
   Parameter-Type), the corresponding answer message MUST contain the
   error code DIAMETER_RATING_FAILED.  A Credit-Control-Answer message
   with this error MUST contain one or more Failed-AVP AVPs containing
   the Service-Parameter-Info AVPs that caused the failure.

   It is defined as follows (per the grouped-avp-def of RFC 3588
   [DIAMBASE]):

      Service-Parameter-Info ::= < AVP Header: 440 >
                                 { Service-Parameter-Type }
                                 { Service-Parameter-Value }

8.44.  Service-Parameter-Type AVP

   The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)
   and defines the type of the service event specific parameter (e.g.,
   it can be the end-user location or service name).  The different
   parameters and their types are service specific, and the meanings of
   these parameters are not defined in this document.  Whoever allocates
   the Service-Context-Id (i.e., unique identifier of a service-specific
   document) is also responsible for assigning Service-Parameter-Type
   values for the service and ensuring their uniqueness within the given
   service.  The Service-Parameter-Value AVP contains the value
   associated with the service parameter type.

8.45.  Service-Parameter-Value AVP

   The Service-Parameter-Value AVP is of type OctetString (AVP Code 442)
   and contains the value of the service parameter type.

8.46.  Subscription-Id AVP

   The Subscription-Id AVP (AVP Code 443) is used to identify the end
   user's subscription and is of type Grouped.  The Subscription-Id AVP
   includes a Subscription-Id-Data AVP that holds the identifier and a
   Subscription-Id-Type AVP that defines the identifier type.

   It is defined as follows (per the grouped-avp-def of RFC 3588
   [DIAMBASE]):

      Subscription-Id ::= < AVP Header: 443 >
                          { Subscription-Id-Type }
                          { Subscription-Id-Data }

8.47.  Subscription-Id-Type AVP

   The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated,
   and it is used to determine which type of identifier is carried by
   the Subscription-Id AVP.

   This specification defines the following subscription identifiers.
   However, new Subscription-Id-Type values can be assigned by an IANA
   designated expert, as defined in section 12.  A server MUST implement
   all the Subscription-Id-Types required to perform credit
   authorization for the services it supports, including possible future
   values.  Unknown or unsupported Subscription-Id-Types MUST be treated
   according to the 'M' flag rule, as defined in [DIAMBASE].

   END_USER_E164                   0
      The identifier is in international E.164 format (e.g., MSISDN),
      according to the ITU-T E.164 numbering plan defined in [E164] and
      [CE164].

   END_USER_IMSI                   1
      The identifier is in international IMSI format, according to the
      ITU-T E.212 numbering plan as defined in [E212] and [CE212].

   END_USER_SIP_URI                2
      The identifier is in the form of a SIP URI, as defined in [SIP].

   END_USER_NAI                    3
      The identifier is in the form of a Network Access Identifier, as
      defined in [NAI].

   END_USER_PRIVATE                4
      The Identifier is a credit-control server private identifier.

8.48.  Subscription-Id-Data AVP

   The Subscription-Id-Data AVP (AVP Code 444) is used to identify the
   end user and is of type UTF8String.  The Subscription-Id-Type AVP
   defines which type of identifier is used.

8.49.  User-Equipment-Info AVP

   The User-Equipment-Info AVP (AVP Code 458) is of type Grouped and
   allows the credit-control client to indicate the identity and
   capability of the terminal the subscriber is using for the connection
   to network.

   It is defined as follows (per the grouped-avp-def of RFC 3588
   [DIAMBASE]):

      User-Equipment-Info ::= < AVP Header: 458 >
                              { User-Equipment-Info-Type }
                              { User-Equipment-Info-Value }

8.50.  User-Equipment-Info-Type AVP

   The User-Equipment-Info-Type AVP is of type Enumerated  (AVP Code
   459) and defines the type of user equipment information contained in
   the User-Equipment-Info-Value AVP.

   This specification defines the following user equipment types.
   However, new User-Equipment-Info-Type values can be assigned by an
   IANA designated expert, as defined in section 12.

   IMEISV                          0
      The identifier contains the International Mobile Equipment
      Identifier and Software Version in the international IMEISV format
      according to 3GPP TS 23.003 [3GPPIMEI].

   MAC                             1
      The 48-bit MAC address is formatted as described in [RAD802.1X].

   EUI64                           2
      The 64-bit identifier used to identify hardware instance of the
      product, as defined in [EUI64].

   MODIFIED_EUI64                  3
      There are a number of types of terminals that have identifiers
      other than IMEI, IEEE 802 MACs, or EUI-64.  These identifiers can
      be converted to modified EUI-64 format as described in [IPv6Addr]
      or by using some other methods referred to in the service-specific
      documentation.

8.51.  User-Equipment-Info-Value AVP

   The User-Equipment-Info-Value AVP (AVP Code 460) is of type
   OctetString.  The User-Equipment-Info-Type AVP defines which type of
   identifier is used.

9.  Result Code AVP Values

   This section defines new Result-Code AVP [DIAMBASE] values that must
   be supported by all Diameter implementations that conform to this
   specification.

   The Credit-Control-Answer message includes the Result-Code AVP, which
   may indicate that an error was present in the Credit-Control-Request
   message.  A rejected Credit-Control-Request message SHOULD cause the
   user's session to be terminated.

9.1.  Transient Failures

   Errors that fall within the transient failures category are used to
   inform a peer that the request could not be satisfied at the time it
   was received, but that the request MAY be able to be satisfied in the
   future.

   DIAMETER_END_USER_SERVICE_DENIED           4010
      The credit-control server denies the service request due to
      service restrictions.  If the CCR contained used-service-units,
      they are deducted, if possible.

   DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE     4011
      The credit-control server determines that the service can be
      granted to the end user but that no further credit-control is
      needed for the service (e.g., service is free of charge).

   DIAMETER_CREDIT_LIMIT_REACHED              4012
      The credit-control server denies the service request because the
      end user's account could not cover the requested service.  If the
      CCR contained used-service-units they are deducted, if possible.

9.2.  Permanent Failures

   Errors that fall within the permanent failure category are used to
   inform the peer that the request failed and should not be attempted
   again.

   DIAMETER_USER_UNKNOWN                      5030
      The specified end user is unknown in the credit-control server.

   DIAMETER_RATING_FAILED                     5031
      This error code is used to inform the credit-control client that
      the credit-control server cannot rate the service request due to
      insufficient rating input, an incorrect AVP combination, or an AVP
      or an AVP value that is not recognized or supported in the rating.
      The Failed-AVP AVP MUST be included and contain a copy of the
      entire AVP(s) that could not be processed successfully or an
      example of the missing AVP complete with the Vendor-Id if
      applicable.  The value field of the missing AVP should be of
      correct minimum length and contain zeros.

10.  AVP Occurrence Table

   The following table presents the AVPs defined in this document and
   specifies in which Diameter messages they MAY or MAY NOT be present.
   Note that AVPs that can only be present within a Grouped AVP are not
   represented in this table.

   The table uses the following symbols:

      0     The AVP MUST NOT be present in the message.
      0+    Zero or more instances of the AVP MAY be present in the
            message.
      0-1   Zero or one instance of the AVP MAY be present in the
            message.  It is considered an error if there is more
            than one instance of the AVP.
      1     One instance of the AVP MUST be present in the message.
      1+    At least one instance of the AVP MUST be present in the
            message.

10.1.  Credit-Control AVP Table

   The table in this section is used to represent which credit-control
   applications specific AVPs defined in this document are to be present
   in the credit-control messages.

                                       +-----------+
                                       |  Command  |
                                       |   Code    |
                                       |-----+-----+
         Attribute Name                | CCR | CCA |
         ------------------------------|-----+-----+
         Acct-Multi-Session-Id         | 0-1 | 0-1 |
         Auth-Application-Id           | 1   | 1   |
         CC-Correlation-Id             | 0-1 | 0   |
         CC-Session-Failover           | 0   | 0-1 |
         CC-Request-Number             | 1   | 1   |
         CC-Request-Type               | 1   | 1   |
         CC-Sub-Session-Id             | 0-1 | 0-1 |
         Check-Balance-Result          | 0   | 0-1 |
         Cost-Information              | 0   | 0-1 |
         Credit-Control-Failure-       | 0   | 0-1 |
            Handling                   |     |     |
         Destination-Host              | 0-1 | 0   |
         Destination-Realm             | 1   | 0   |
         Direct-Debiting-Failure-      | 0   | 0-1 |
            Handling                   |     |     |
         Event-Timestamp               | 0-1 | 0-1 |
         Failed-AVP                    | 0   | 0+  |
         Final-Unit-Indication         | 0   | 0-1 |
         Granted-Service-Unit          | 0   | 0-1 |
         Multiple-Services-Credit-     | 0+  | 0+  |
            Control                    |     |     |
         Multiple-Services-Indicator   | 0-1 | 0   |
         Origin-Host                   | 1   | 1   |
         Origin-Realm                  | 1   | 1   |
         Origin-State-Id               | 0-1 | 0-1 |
         Proxy-Info                    | 0+  | 0+  |
         Redirect-Host                 | 0   | 0+  |
         Redirect-Host-Usage           | 0   | 0-1 |
         Redirect-Max-Cache-Time       | 0   | 0-1 |
         Requested-Action              | 0-1 | 0   |
         Requested-Service-Unit        | 0-1 | 0   |
         Route-Record                  | 0+  | 0+  |
         Result-Code                   | 0   | 1   |
         Service-Context-Id            | 1   | 0   |
         Service-Identifier            | 0-1 | 0   |
         Service-Parameter-Info        | 0+  | 0   |

         Session-Id                    | 1   | 1   |
         Subscription-Id               | 0+  | 0   |
         Termination-Cause             | 0-1 | 0   |
         User-Equipment-Info           | 0-1 | 0   |
         Used-Service-Unit             | 0+  | 0   |
         User-Name                     | 0-1 | 0-1 |
         Validity-Time                 | 0   | 0-1 |
         ------------------------------|-----+-----+

10.2.  Re-Auth-Request/Answer AVP Table

   This section defines AVPs that are specific to the Diameter credit-
   control application and that MAY be included in the Diameter Re-
   Auth-Request/Answer (RAR/RAA) message [DIAMBASE].

   Re-Auth-Request/Answer command MAY include the following additional
   AVPs:

                                       +---------------+
                                       | Command Code  |
                                       |-------+-------+
         Attribute Name                |  RAR  |  RAA  |
         ------------------------------+-------+-------+
         CC-Sub-Session-Id             |  0-1  |  0-1  |
         G-S-U-Pool-Identifier         |  0-1  |  0-1  |
         Service-Identifier            |  0-1  |  0-1  |
         Rating-Group                  |  0-1  |  0-1  |
         ------------------------------+-------+-------+

11.  RADIUS/Diameter Credit-Control Interworking Model

   This section defines the basic principles for the Diameter credit-
   control/RADIUS prepaid inter-working model; that is, a message
   translation between a RADIUS based prepaid solution and a Diameter
   credit-control application.  A complete description of the protocol
   translations between RADIUS and the Diameter credit-control
   application is beyond the scope of this specification and SHOULD be
   addressed in another appropriate document, such as the RADIUS prepaid
   specification.

   The Diameter credit-control architecture may have a Translation Agent
   capable of translation between RADIUS prepaid and Diameter credit-
   control protocols.  An AAA server (usually the home AAA server) may
   act as a Translation Agent and as a Diameter credit-control client
   for service elements that use credit-control mechanisms other than
   Diameter credit control for instance, RADIUS prepaid.  In this case,
   the home AAA server contacts the Diameter credit-control server as
   part of the authorization process.  The interworking architecture is

   illustrated in Figure 7, and interworking flow in Figure 8.  In a
   roaming situation the service element (e.g., the NAS) may be located
   in the visited network, and a visited AAA server is usually
   contacted.  The visited AAA server connects then to the home AAA
   server.

                                  RADIUS Prepaid
   +--------+       +---------+   protocol +------------+  +--------+
   |  End   |<----->| Service |<---------->| Home AAA   |  |Business|
   |  User  |       | Element |            |  Server    |  |Support |
   +--------+   +-->|         |            |+----------+|->|System  |
                |   +---------+            ||CC Client ||  |        |
                |                          |+----------+|  |        |
   +--------+   |                          +------^-----+  +----^---+
   |  End   |<--+                Credit-Control   |             |
   |  User  |                          Protocol   |             |
   +--------+                             +-------V--------+    |
                                          |Credit-Control  |----+
                                          |   Server       |
                                          +----------------+

        Figure 7: Credit-control architecture with service element
                  containing translation agent, translating RADIUS
                  prepaid to Diameter credit-control protocol

   When the AAA server acting as a Translation Agent receives an initial
   RADIUS Access-Request message from service element (e.g., NAS
   access), it performs regular authentication and authorization.  If
   the RADIUS Access-Request message indicates that the service element
   is capable of credit-control, and if the home AAA server finds that
   the subscriber is a prepaid subscriber, then a Diameter credit-
   control request SHOULD be sent toward the credit-control server to
   perform credit authorization and to establish a credit-control
   session.  After the Diameter credit-control server checks the end
   user's account balance, rates the service, and reserves credit from
   the end user's account, the reserved quota is returned to the home
   AAA server in the Diameter Credit-Control-Answer.  Then the home AAA
   server sends the reserved quota to the service element in the RADIUS
   Access-Accept.

   At the expiry of the allocated quota, the service element sends a new
   RADIUS Access-Request containing the units used this far to the home
   AAA server.  The home AAA server shall map a RADIUS Access-Request
   containing the reported units to the Diameter credit-control server
   in a Diameter Credit-Control-Request (UPDATE_REQUEST).  The Diameter
   credit-control server debits the used units from the end user's
   account and allocates a new quota that is returned to the home AAA
   server in the Diameter Credit-Control-Answer.  The quota is

   transferred to the service element in the RADIUS Access-Accept.  When
   the end user terminates the service, or when the entire quota has
   been used, the service element sends a RADIUS Access-Request.  To
   debit the used units from the end user's account and to stop the
   credit-control session, the home AAA server sends a Diameter Credit-
   Control-Request (TERMINATION_REQUEST) to the credit-control server.
   The Diameter credit-control server acknowledges the session
   termination by sending a Diameter Credit-Control-Answer to the home
   AAA server.  The RADIUS Access-Accept is sent to the NAS.

   A following diagram illustrates a RADIUS prepaid - Diameter credit-
   control interworking sequence.

      Service Element         Translation Agent
        (e.g., NAS)               (CC Client)             CC Server
            |     Access-Request     |                        |
            |----------------------->|                        |
            |                        |    CCR (initial)       |
            |                        |----------------------->|
            |                        |    CCA (Granted-Units) |
            |                        |<-----------------------|
            |     Access-Accept      |                        |
            |     (Granted-Units)    |                        |
            |<-----------------------|                        |
            :                        :                        :
            |     Access-Request     |                        |
            |     (Used-Units)       |                        |
            |----------------------->|                        |
            |                        |    CCR (update,        |
            |                        |         Used-Units)    |
            |                        |----------------------->|
            |                        |    CCA (Granted-Units) |
            |                        |<-----------------------|
            |     Access-Accept      |                        |
            |     (Granted-Units)    |                        |
            |<-----------------------|                        |
            :                        :                        :
            |     Access-Request     |                        |
            |----------------------->|                        |
            |                        |     CCR (terminate,    |
            |                        |          Used-Units)   |
            |                        |----------------------->|
            |                        |     CCA                |
            |                        |<-----------------------|
            |     Access-Accept      |                        |
            |<-----------------------|                        |
            |                        |                        |

           Figure 8: Message flow example with RADIUS prepaid -
                  Diameter credit-control interworking

12.  IANA Considerations

   This section contains the namespaces that have either been created in
   this specification, or the values assigned to existing namespaces
   managed by IANA.

   In the subsections below, when we speak about review by a Designated
   Expert, please note that the designated expert will be assigned by
   the IESG.  Initially, such Expert discussions take place on the AAA
   WG mailing list.

12.1.  Application Identifier

   This specification assigns the value 4, 'Diameter Credit Control', to
   the Application Identifier namespace defined in [DIAMBASE].  See
   section 1.3 for more information.

12.2.  Command Codes

   This specification uses the value 272 from the Command code namespace
   defined in [DIAMBASE] for the Credit-Control-Request (CCR) and
   Credit-Control-Answer (CCA) commands.

12.3.  AVP Codes

   This specification assigns the values 411 - 461 from the AVP code
   namespace defined in [DIAMBASE].  See section 8 for the assignment of
   the namespace in this specification.

12.4.  Result-Code AVP Values

   This specification assigns the values 4010, 4011, 4012, 5030, 5031
   from the Result-Code AVP value namespace defined in [DIAMBASE].  See
   section 9 for the assignment of the namespace in this specification.

12.5.  CC-Request-Type AVP

   As defined in section 8.3, the CC-Request-Type AVP includes
   Enumerated type values 1 - 4.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.6.  CC-Session-Failover AVP

   As defined in section 8.4, the CC-Failover-Supported AVP includes
   Enumerated type values 0 - 1.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.7.  CC-Unit-Type AVP

   As defined in section 8.32, the CC-Unit-Type AVP includes Enumerated
   type values 0 - 5.  IANA has created and is maintaining a namespace
   for this AVP.  All remaining values are available for assignment by a
   Designated Expert [IANA].

12.8.  Check-Balance-Result AVP

   As defined in section 8.6, the Check-Balance-Result AVP includes
   Enumerated type values 0 - 1.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.9.  Credit-Control AVP

   As defined in section 8.13, the Credit-Control AVP includes
   Enumerated type values 0 - 1.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.10.  Credit-Control-Failure-Handling AVP

   As defined in section 8.14, the Credit-Control-Failure-Handling AVP
   includes Enumerated type values 0 - 2.  IANA has created and is
   maintaining a namespace for this AVP.  All remaining values are
   available for assignment by a Designated Expert [IANA].

12.11.  Direct-Debiting-Failure-Handling AVP

   As defined in section 8.15, the Direct-Debiting-Failure-Handling AVP
   includes Enumerated type values 0 - 1.  IANA has created and is
   maintaining a namespace for this AVP.  All remaining values are
   available for assignment by a Designated Expert [IANA].

12.12.  Final-Unit-Action AVP

   As defined in section 8.35, the Final-Unit-Action AVP includes
   Enumerated type values 0 - 2.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.13.  Multiple-Services-Indicator AVP

   As defined in section 8.40, the Multiple-Services-Indicator AVP
   includes Enumerated type values 0 - 1.  IANA has created and is
   maintaining a namespace for this AVP.  All remaining values are
   available for assignment by a Designated Expert [IANA].

12.14.  Redirect-Address-Type AVP

   As defined in section 8.38, the Redirect-Address-Type AVP includes
   Enumerated type values 0 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.15.  Requested-Action AVP

   As defined in section 8.41, the Requested-Action AVP includes
   Enumerated type values 0 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.16.  Subscription-Id-Type AVP

   As defined in section 8.47, the Subscription-Id-Type AVP  includes
   Enumerated type values 0 - 4.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.17.   Tariff-Change-Usage AVP

   As defined in section 8.27, the Tariff-Change-Usage AVP includes
   Enumerated type values 0 - 2.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

12.18.   User-Equipment-Info-Type AVP

   As defined in section 8.50, the User-Equipment-Info-Type AVP includes
   Enumerated type values 0 - 3.  IANA has created and is maintaining a
   namespace for this AVP.  All remaining values are available for
   assignment by a Designated Expert [IANA].

13.  Credit-Control Application Related Parameters

   Tx timer

      When real-time credit-control is required, the credit-control
      client contacts the credit-control server before and while the
      service is provided to an end user.  Due to the real-time nature
      of the application, the communication delays SHOULD be minimized;
      e.g., to avoid an overly long service setup time experienced by
      the end user.  The Tx timer is introduced to control the waiting
      time in the client in the Pending state.  When the Tx timer
      elapses, the credit-control client takes an action to the end user
      according to the value of the Credit-Control-Failure-Handling AVP

      or Direct-Debiting-Failure-Handling AVP.  The recommended value is
      10 seconds.

   Tcc timer

      The Tcc timer supervises an ongoing credit-control session in the
      credit-control server.  It is RECOMMENDED to use the Validity-Time
      as input to set the Tcc timer value.  In case of transient
      failures in the network, the Diameter credit-control server might
      change to Idle state.  To avoid this, the Tcc timer MAY be set so
      that Tcc equals to 2 x Validity-Time.

   Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling

      Client implementations may offer the possibility of locally
      configuring these AVPs.  In such a case their value and behavior
      is defined in section 5.7 for the Credit-Control-Failure-Handling
      and in section 6.5 for the Direct-Debiting-Failure-Handling.

14.  Security Considerations

   The Diameter base protocol [DIAMBASE] requires that each Diameter
   implementation use underlying security; i.e., IPsec or TLS.  These
   mechanisms are believed to provide sufficient protection under the
   normal Internet threat model; that is, assuming that the authorized
   nodes engaging in the protocol have not been compromised, but that
   the attacker has complete control over the communication channels
   between them.  This includes eavesdropping, message modification,
   insertion, and man-in-the-middle and replay attacks.  Note also that
   this application includes a mechanism for application layer replay
   protection by means of the Session-Id from [DIAMBASE] and CC-
   Request-Number, which is specified in this document.  The Diameter
   credit-control application is often used within one domain, and there
   may be a single hop between the peers.  In these environments, the
   use of TLS or IPsec is sufficient.  The details of TLS and IPsec
   related security considerations are discussed in the [DIAMBASE].

   Because this application handles monetary transactions (directly or
   indirectly), it increases the interest for various security attacks.
   Therefore, all parties communicating with each other MUST be
   authenticated, including, for instance, TLS client-side
   authentication.  In addition, authorization of the client SHOULD be
   emphasized; i.e., that the client is allowed to perform credit-
   control for a certain user.  The specific means of authorization are
   outside of the scope of this specification but can be, for instance,
   manual configuration.

   Another kind of threat is malicious modification, injection, or
   deletion of AVPs or complete credit-control messages.  The credit-
   control messages contain sensitive billing related information (such
   as subscription Id, granted units, used units, cost information)
   whose malicious modification can have financial consequences.
   Sometimes simply delaying the credit-control messages can cause
   disturbances in the credit-control client or server.

   Even without any modification to the messages, an adversary can
   invite a security threat by eavesdropping, as the transactions
   contain private information about the user.  Also, by monitoring the
   credit-control messages one can collect information about the
   credit-control server's billing models and business relationships.

   When third-party relays or proxy are involved, the hop-by-hop
   security does not necessarily provide sufficient protection for
   Diameter user session.  In some cases, it may be inappropriate to
   send Diameter messages, such as CCR and CCA, containing sensitive
   AVPs via untrusted Diameter proxy agents, as there are no assurances
   that third-party proxies will not modify the credit-control commands
   or AVP values.

14.1.  Direct Connection with Redirects

   A Diameter credit-control agent cannot always know whether agents
   between it and the end user's Diameter credit-control server are
   reliable.  In this case, the Diameter credit-control agent doesn't
   have a routing entry in its Diameter Routing Table (defined in
   [DIAMBASE], section 2.7) for the realm of the credit-control server
   in the end user's home domain.  The Diameter credit-control agent can
   have a default route configured to a local Redirect agent, and it
   redirects the CCR message to the redirect agent.  The local Redirect
   agent then returns a redirect notification (Result-code 3006,
   DIAMETER_REDIRECT_INDICATION) to the credit-control agent, as well as
   Diameter credit-control server(s) information (Redirect-Host AVP) and
   information (Redirect-Host-Usage AVP) about how the routing entry
   resulting from the Redirect-Host is to be used.  The Diameter
   credit-control agent then forwards the CCR message directly to one of
   the hosts identified by the CCA message from the redirect agent.  If
   the value of the Redirect-Host-Usage AVP is unequal to zero, all
   following messages are sent to the host specified in the Redirect-
   Host AVP until the time specified by the Redirect-Max-Cache-Time AVP
   is expired.

   There are some authorization issues even with redirects.  There may
   be attacks toward nodes that have been properly authorized, but that
   abuse their authorization or have been compromised.  These issues are
   discussed more widely in [DIAMEAP], section 8.

15.  References

15.1.  Normative References

   [DIAMBASE]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
               Arkko, "Diameter Base Protocol", RFC 3588, September
               2003.

   [3GPPCHARG] 3rd Generation Partnership Project; Technical
               Specification Group Services and System Aspects, Service
               aspects; Charging and Billing, (release 5), 3GPP TS
               22.115 v. 5.2.1, 2002-03.

   [SIP]       Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
               A., Peterson, J., Sparks, R., Handley, M., and E.
               Schooler, "SIP:  Session Initiation Protocol", RFC 3261,
               June 2002.

   [NAI]       Aboba, B. and M. Beadles, "The Network Access
               Identifier", RFC 2486, January 1999.

   [E164]      Recommendation E.164/I.331 (05/97): The International
               Public Telecommunication Numbering Plan. 1997.

   [CE164]     Complement to ITU-T Recommendation E.164 (05/1997):"List
               of ITU-T Recommendation E.164 assigned country codes",
               June 2000.

   [E212]      Recommendation E.212 (11/98): The international
               identification plan for mobile terminals and mobile
               users. 1998.

   [CE212]     Complement to ITU-T Recommendation E.212 (11/1997):" List
               of mobile country or geographical area codes", February
               1999.

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

   [IPv4]      Postel, J., "Internet Protocol", STD 5, RFC 791,
               September 1981.

   [IPv6Addr]  Hinden, R. and S. Deering, "Internet Protocol Version 6
               (IPv6) Addressing Architecture", RFC 3513, April 2003.

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

   [ISO4217]   Codes for the representation of currencies and funds,
               International Standard ISO 4217,2001

   [NASREQ]    Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
               "Diameter Network Access Server Application", RFC 4005,
               August 2005.

   [AAATRANS]  Aboba, B. and J. Wood, "Authentication, Authorization and
               Accounting (AAA) Transport Profile", RFC 3539, June 2003.

   [URL]       Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
               Resource Locators (URL)", RFC 1738, December 1994.

   [RAD802.1X] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J.
               Roese, "IEEE 802.1X Remote Authentication Dial In User
               Service (RADIUS) Usage Guidelines", RFC 3580, September
               2003.

   [EUI64]     IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
               Registration Authority",
               http://standards.ieee.org/regauth/oui/tutorials/
               EUI64.html March 1997.

   [3GPPIMEI]  3rd Generation Partnership Project; Technical
               Specification Group Core Network, Numbering, addressing
               and identification, (release 5), 3GPP TS 23.003 v. 5.8.0,
               2003-12

15.2.  Informative References

   [RFC2866]   Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.

   [DIAMMIP]   Calhoun, P., Johansson, T., Perkins, C., Hiller, T., and
               P. McCann, "Diameter Mobile IPv4 Application", RFC 4004,
               August 2005.

   [DIAMEAP]   Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
               Authentication Protocol (EAP) Application", Work in
               Progress.

   [RFC3725]   Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
               Camarillo, "Best Current Practices for Third Party Call
               Control (3pcc) in the Session Initiation Protocol (SIP)",
               BCP 85, RFC 3725, April 2004.

16.  Acknowledgements

   The authors would like to thank Bernard Aboba, Jari Arkko, Robert
   Ekblad, Pasi Eronen, Benny Gustafsson, Robert Karlsson, Avi Lior,
   Paco Marin, Jussi Maki, Jeff Meyer, Anne Narhi, John Prudhoe,
   Christopher Richards, Juha Vallinen, and Mark Watson for their
   comments and suggestions.

Appendix A.  Credit-Control Sequences

A.1.  Flow I

                         NAS
   End User          (CC Client)         AAA Server           CC Server
      |(1)User Logon      |(2)AA Request (CC AVPs)                  |
      |------------------>|------------------->|                    |
      |                   |                    |(3)CCR(initial, CC AVPs)
      |                   |                    |------------------->|
      |                   |                    | (4)CCA(Granted-Units)
      |                   |                    |<-------------------|
      |                   |(5)AA Answer(Granted-Units)              |
      |(6)Access granted  |<-------------------|                    |
      |<----------------->|                    |                    |
      |                   |                    |                    |
      :                   :                    :                    :
      |                   |(7)CCR(update,Used-Units)                |
      |                   |------------------->|(8)CCR              |
      |                   |                    |   (update,Used-Units)
      |                   |                    |------------------->|
      |                   |                    |(9)CCA(Granted-Units)
      |                   |(10)CCA(Granted-Units)<------------------|
      |                   |<-------------------|                    |
      :                   :                    :                    :
      |         (Auth. lifetime expires)       |                    |
      |                   |(11) AAR (CC AVP)   |                    |
      |                   |------------------->|                    |
      |                   |          (12) AAA  |                    |
      |                   |<-------------------|                    |
      :                   :                    :                    :
      :                   :                    :                    :
      |(13) User logoff   |                    |                    |
      |------------------>|(14)CCR(term.,Used-Units)                |
      |                   |------------------->|(15)CCR             |
      |                   |                    |   (term.,Used-Units)
      |                   |                    |------------------->|
      |                   |                    |            (16)CCA |
      |                   |            (17)CCA |<-------------------|
      |                   |<-------------------|                    |
      |                   |(18)STR             |                    |
      |                   |------------------->|                    |
      |                   |            (19)STA |                    |
      |                   |<-------------------|                    |

                            Figure A.1: Flow I

   A credit-control flow for Network Access Services prepaid is shown in
   Figure A.1.  The Diameter [NASREQ] is implemented in the Network
   Access Server (NAS).  The focus of this flow is in the credit
   authorization.

   The user logs on to the network (1).  The Diameter NAS sends a
   Diameter AA-Request (AAR) to the home Diameter AAA server.  The
   credit-control client populates the AAR with the Credit-Control AVP
   set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,
   as usual [NASREQ].  The home Diameter AAA server performs service-
   specific Authentication and Authorization, as usual.  The home
   Diameter AAA server determines that the user is a prepaid user and
   notices from the Credit-Control AVP that the NAS has credit-control
   capabilities.  It sends a Diameter Credit-Control-Request with CC-
   Request-Type set to INITIAL_REQUEST to the Diameter credit-control
   server to perform credit authorization (3) and to establish a
   credit-control session.  (The home Diameter AAA server may forward
   service-specific AVPs received from the NAS as input for the rating
   process.)  The Diameter credit-control server checks the end user's
   account balance, rates the service, and reserves credit from the end
   user's account.  The reserved quota is returned to the home Diameter
   AAA server in the Diameter Credit-Control-Answer (4).  The home
   Diameter AAA server sends the reserved quota to the NAS in the
   Diameter AA-Answer (AAA).  Upon successful AAA, the NAS starts the
   credit-control session and starts monitoring the granted units (5).
   The NAS grants access to the end user (6).  At the expiry of the
   allocated quota, the NAS sends a Diameter Credit-Control-Request with
   CC-Request-Type set to UPDATE_REQUEST to the Home Diameter AAA server
   (7).  This message contains the units used thus far.  The home
   Diameter AAA server forwards the CCR to the Diameter credit-control
   server (8).  The Diameter credit-control server debits the used units
   from the end user's account and allocates a new quota that is
   returned to the home Diameter AAA server in the Diameter Credit-
   Control-Answer (9).  The message is forwarded to the NAS (10).
   During the ongoing credit-control session, the authorization lifetime
   expires, and the authorization/authentication client in the NAS
   performs service specific re-authorization to the home Diameter AAA
   server, as usual.  The credit-control client populates the AAR with
   the Credit-Control AVP set to RE_AUTHORIZATION, indicating that the
   credit-control server shall not be contacted, as the credit
   authorization is controlled by the burning rate of the granted units
   (11).  The home Diameter AAA server performs service-specific re-
   authorization as usual and returns the AA-Answer to the NAS (12).
   The end user logs off from the network (13).  To debit the used units
   from the end user's account and to stop the credit-control session,
   the NAS sends a Diameter Credit-Control-Request with CC-Request-Type
   set to TERMINATION_REQUEST to the home Diameter AAA server (14).  The
   home Diameter AAA server forwards the CCR to the credit-control

   server (15).  The Diameter credit-control server acknowledges the
   session termination by sending a Diameter Credit-Control-Answer to
   the home Diameter AAA server (16).  The home Diameter AAA server
   forwards the answer to the NAS (17).  STR/STA takes place between the
   NAS and home Diameter AAA server, as usual (18-19).

A.2.  Flow II

              SIP Proxy/Registrar   AAA
        A           (CC Client)     Server           B        CC Server
        |(i)  REGISTER |              |              |              |
        |------------->|(ii)          |              |              |
        |              |------------->|              |              |
        |              |authentication &             |              |
        |              |authorization |              |              |
        |              |<-------------|              |              |
        |(iii)200 OK   |                             |              |
        |<-------------|                             |              |
        :              :                             :              :
        |(1)  INVITE   |                                            :
        |------------->|
        |              |(2)  CCR (Initial, SIP specific AVP)        |
        |              |------------------------------------------->|
        |              |(3)  CCA (Granted-Units)                    |
        |              |<-------------------------------------------|
        |              |(4)  INVITE                  |              |
        |              |---------------------------->|              |
        :              :                             :              :
        |              |(5)  CCR (update, Used-Units)               |
        |              |------------------------------------------->|
        |              |(6)  CCA (Granted-Units)                    |
        |              |<-------------------------------------------|
        :              :                             :              :
        |(7)  BYE      |                             |              |
        |------------->|                             |              |
        |              |(8)  BYE                     |              |
        |              |---------------------------->|              |
        |              |(9)  CCR (termination, Used-Units)          |
        |              |------------------------------------------->|
        |              |(10) CCA ()                                 |
        |              |<-------------------------------------------|
        |              |                             |              |

                           Figure A.2: Flow II

   This is an example of Diameter credit-control for SIP sessions.
   Although the flow focuses on illustrating the usage of credit-control
   messages, the SIP signaling is inaccurate, and the diagram is not by
   any means an attempt to define a service provider's SIP network.
   However, for the sake of this example, some assumptions are made
   below.

   Typically, prepaid services based, for example, on time usage for SIP
   session require an entity in the service provider network to
   intercept all the requests within the SIP dialog in order to detect
   events, such as session establishment and session release, that are
   essential to perform credit-control operations with the credit-
   control server.  Therefore, in this example, it is assumed that the
   SIP Proxy adds a Record-Route header in the initial SIP INVITE to
   make sure that all the future requests in the created dialog traverse
   through it (for the definitions of 'Record-Route' and 'dialog' please
   refer to [SIP]).  Finally, the degree of credit-control measuring of
   the media by the proxy depends on the business model design used in
   setting up the end system and proxies in the SIP network.

   The end user (SIP User Agent A) sends REGISTER with credentials (i).
   The SIP Proxy sends a request to the home AAA server to perform
   Multimedia authentication and authorization by using, for instance,
   Diameter Multimedia application (ii).  The home AAA server checks
   that the credentials are correct and checks the user profile.
   Eventually, 200 OK response (iii) is sent to the UA.  Note that the
   Authentication and Authorization is valid for the registration
   validity period duration (i.e., until re-registration is performed).
   Several SIP sessions may be established without re-authorization.

   UA A sends an INVITE (1).  The SIP Proxy sends a Diameter Credit-
   Control-Request (INITIAL_REQUEST) to the Diameter credit-control
   server (2).  The Credit-Control-Request contains information obtained
   from the SIP signaling describing the requested service (e.g.,
   calling party, called party, Session Description Protocol
   attributes).  The Diameter credit-control server checks the end
   user's account balance, rates the service, and reserves credit from
   the end user's account.  The reserved quota is returned to the SIP
   Proxy in the Diameter Credit-Control-Answer (3).  The SIP Proxy
   forwards the SIP INVITE to UA B (4).  B's phone rings, and B answers.
   The media flows between them, and the SIP Proxy starts measuring the
   quota.  At the expiry of the allocated quota, the SIP Proxy sends a
   Diameter Credit-Control-Request (UPDATE_REQUEST) to the Diameter
   credit-control server (5).  This message contains the units used thus
   far.  The Diameter credit-control server debits the used units from
   the end user's account and allocates new credit that is returned to
   the SIP Proxy in the Diameter Credit-Control-Answer (6).  The end
   user terminates the service by sending a BYE (7).  The SIP Proxy

   forwards the BYE message to UA B (8) and sends a Diameter Credit-
   Control-Request (TERMINATION_REQUEST) to the credit-control server
   (9).  The Diameter credit-control server acknowledges the session
   termination by sending a Diameter Credit-Control-Answer to the SIP
   Proxy (10).

A.3.  Flow III

                          MMS Server
             A           (CC Client)           B           CC Server
             |(1) Send MMS    |                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, DIRECT_DEBITING,|
             |                |          MMS specific AVP)      |
             |                |-------------------------------->|
             |                |(3)  CCA (Granted-Units)         |
             |                |<--------------------------------|
             |(4) Send MMS Ack|                |                |
             |<---------------|                |                |
             |                |(5) Notify MMS  |                |
             |                |--------------->|                |
             :                :                :                :
             |                |(6) Retrieve MMS|                |
             |                |<---------------|                |
             |                |(7) Retrieve MMS|                |
             |                |    Ack         |                |
             |                |--------------->|                |
             |                |                |                |

                             Figure A.3: Flow III

   A credit-control flow for Multimedia Messaging Services is shown in
   Figure A.3.  The sender is charged as soon as the messaging server
   successfully stores the message.

   The end user A sends a Multimedia Message (MMS) to the MMS server
   (1).  The MMS server stores the message and sends a Diameter Credit-
   Control-Request (EVENT_REQUEST with Requested-Action DIRECT_DEBITING)
   to the Diameter credit-control server (2).  The Credit-Control-
   Request contains information about the MMS message (e.g., size,
   recipient address, image coding type).  The Diameter credit-control
   server checks the end user's account balance, rates the service, and
   debits the service from the end user's account.  The granted quota is
   returned to the MMS server in the Diameter Credit-Control-Answer (3).
   The MMS server acknowledges the successful reception of the MMS
   message (4).  The MMS Server notifies the recipient about the new MMS
   (5), and end user B retrieves the message from the MMS message store
   (6),(7).

A.4.  Flow IV

                          MMS Server
      Content Server     (CC Client)           B           CC Server
             |(1) Send MMS    |                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, CHECK_BALANCE,  |
             |                |          MMS specific AVP)      |
             |                |-------------------------------->|
             |                |(3)  CCA (ENOUGH_CREDIT)         |
             |                |<--------------------------------|
             |(4) Send MMS Ack|                |                |
             |<---------------|                |                |
             |                |(5) Notify MMS  |                |
             |                |--------------->|                |
             :                :                :                :
             |                |(6) Retrieve MMS|                |
             |                |<---------------|                |
             |                |(7)  CCR (event, DIRECT_DEBITING,|
             |                |          MMS specific AVP)      |
             |                |-------------------------------->|
             |                |(8)  CCA (Granted-Units)         |
             |                |<--------------------------------|
             |                |(9) Retrieve MMS|                |
             |                |    Ack         |                |
             |                |--------------->|                |
             |                |                |                |

                              Figure A.4: Flow IV

   This is an example of Diameter credit-control for direct debiting
   using the Multimedia Messaging Service environment.  Although the
   flow focuses on illustrating the usage of credit-control messages,
   the MMS signaling is inaccurate, and the diagram is not by any means
   an attempt to define any service provider's MMS configuration or
   billing model.

   A credit-control flow for Multimedia Messaging Service is shown in
   Figure A.4.  The recipient is charged at the message delivery.

   A content server sends a Multimedia Message (MMS) to the MMS server
   (1) that stores the message.  The message recipient will be charged
   for the MMS message in this case.  As there can be a substantially
   long time between the receipt of the message at the MMS server and
   the actual retrieval of the message, the MMS server does not
   establish any credit-control session to the Diameter credit-control
   server but performs first only a balance check (without any credit
   reservation) by sending a Diameter Credit-Control-Request

   (EVENT_REQUEST with Requested-Action CHECK_BALANCE) to verify that
   end user B can cover the cost for the MMS (2).  The Diameter credit-
   control server checks the end user's account balance and returns the
   answer to the MMS server in the Diameter Credit-Control-Answer (3).
   The MMS server acknowledges the successful reception of the MMS
   message (4).  The MMS server notifies the recipient of the new MMS
   (5), and after some time end user B retrieves the message from the
   MMS message store (6).  The MMS server sends a Diameter Credit-
   Control-Request (EVENT_REQUEST with Requested-Action:
   DIRECT_DEBITING) to the Diameter credit-control server (7).  The
   Credit-Control-Request contains information about the MMS message
   (e.g., size, recipient address, coding type).  The Diameter credit-
   control server checks the end user's account balance, rates the
   service, and debits the service from the end user's account.  The
   granted quota is returned to the MMS server in the Diameter Credit-
   Control-Request (8).  The MMS is transferred to end user B (9).

   Note that the transfer of the MMS message can take an extended time
   and can fail, in which case a recovery action is needed.  The MMS
   server should return the already debited units to the user's account
   by using the REFUND action described in section 6.4.

A.5.  Flow V

                        SIP Controller
             A           (CC Client)           B           CC Server
             |(1)INVITE B(SDP)|                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, PRICE_ENQUIRY,  |
             |                |          SIP specific AVPs)     |
             |                |-------------------------------->|
             |                |(3)  CCA (Cost-Information)      |
             |                |<--------------------------------|
             | (4)MESSAGE(URL)|                |                |
             |<---------------|                |                |
             |(5)HTTP GET     |                |                |
             |--------------->|                |                |
             |(6)HTTP POST    |                |                |
             |--------------->|(7)INVITE(SDP)  |                |
             |                |--------------->|                |
             |                |      (8)200 OK |                |
             |      (9)200 OK |<---------------|                |
             |<---------------|                |                |

                            Figure A.5: Flow V

   This is an example of Diameter credit-control for SIP sessions.
   Although the flow focuses on illustrating the usage of credit-control
   messages, the SIP signaling is inaccurate, and the diagram is not by
   any means an attempt to define a service provider's SIP network.

   Figure A.5 is an example of Advice of Charge (AoC) service for SIP
   call.  User A can be either a postpaid or prepaid subscriber using
   the AoC service.  It is assumed that the SIP controller also has HTTP
   capabilities and delivers an interactive AoC web page with, for
   instance, the cost information, the details of the call derived from
   the SDP, and a button to accept/not accept the charges.  (There may
   be many other ways to deliver AoC information; however, this flow
   focuses on the use of the credit-control messages.)  The user has
   been authenticated and authorized prior to initiating the call and
   subscribed to AoC service.

   UA A sends an INVITE with SDP to B (1).  The SIP controller
   determines that the user is subscribed to AoC service and sends a
   Diameter Credit-Control-Request (EVENT_REQUEST with Requested-Action:
   PRICE_ENQUIRY) to the Diameter credit-control server (2).  The
   Credit-Control-Request contains SIP specific AVPs derived from the
   SIP signaling, describing the requested service (e.g., calling party,
   called party, Session Description Protocol attributes).  The Diameter
   credit-control server determines the cost of the service and returns
   the Credit-Control-Answer including the Cost-Information AVP (3).
   The SIP controller manufactures the AoC web page with information
   received in SIP signaling and with the cost information received from
   the credit-control server.  Then it sends a SIP MESSAGE that contains
   a URL pointing to the AoC information web page (4).  At the receipt
   of the SIP MESSAGE, A's UA automatically invokes the web browser that
   retrieves the AoC information (5).  The user clicks on a proper
   button and accepts the charges (6).  The SIP controller continues the
   session and sends the INVITE to the B party, which accepts the call
   (7,8,9).

A.6.  Flow VI

                             Gaming Server
      End User                (CC Client)              CC Server
         |  (1)Service Delivery   |                        |
         |<---------------------->|                        |
         :                        :                        :
         :                        :                        :
         |                        |(2)CCR(event,REFUND,Requested-
         |                        |Service-Unit,Service-Parameter-Info)
         |                        |----------------------->|
         |                        |  (3)CCA(Cost-Information)
         |                        |<-----------------------|
         |        (4)Notification |                        |
         |<-----------------------|                        |

                          Figure A.6: Flow VI

   Figure A.6 illustrates a credit-control flow for the REFUND case.  It
   is assumed that there is a trusted relationship and secure connection
   between the Gaming server and the Diameter credit-control server.
   The end user may be a prepaid subscriber or a postpaid subscriber.

   While the end user is playing the game (1), she enters a new level
   that entitles her to a bonus.  The Gaming server sends a Diameter
   Credit-Control-Request (EVENT_REQUEST with Requested-Action:
   REFUND_ACCOUNT) to the Diameter credit-control server (2).  The
   Credit-Control-Request Request contains the Requested-Service-Unit
   AVP with the CC-Service-Specific-Units containing the number of
   points the user just won.  The Service-Parameter-Info AVP is also
   included in the request and specifies the service event to be rated
   (e.g., Tetris Bonus).  From information received, the Diameter
   credit-control server determines the amount to be credited, refunds
   the user's account, and returns the Credit-Control-Answer, including
   the Cost-Information AVP (3).  The Cost-Information indicates the
   credited amount.  At the first opportunity, the Gaming server
   notifies the end user of the credited amount (4).

A.7.  Flow VII

                  SIP Controller    Top-Up
        A          (CC Client)      Server           B      CC Server
        |               |              |             |              |
        |               | (1) CCR(Update,Used-Unit)  |              |
        |               |------------------------------------------>|
        |               |              (2) CCA(Final-Unit, Redirect)|
        |               |<------------------------------------------|
        :               :              :             :              :
        :               :              :             :              :
        |               | (3) CCR(Update, Used-Units)|              |
        |               |------------------------------------------>|
        |               | (3a)INVITE("hold")         |              |
        |               |--------------------------->|              |
        |               |              |      (4) CCA(Validity-Time)|
        |               |<------------------------------------------|
        |     (5)INVITE | (6)INVITE    |             |              |
        |<--------------|------------->|             |              |
        |            (7)RTP            |             |              |
        |..............................|             |              |
        |               |       (8)BYE |             |              |
        |               |<-------------|             |              |
        |               | (9)CCR(Update)             |              |
        |               |------------------------------------------>|
        |               |                     (10)CCA(Granted-Unit) |
        |               |<------------------------------------------|
        |    (12)INVITE | (11)INVITE                 |              |
        |<--------------|--------------------------->|              |

                           Figure A.7: Flow VII

   Figure A.7 is an example of the graceful service termination for a
   SIP call.  It is assumed that the call is set up so that the
   controller is in the call as a B2BUA (Back to Back User Agent)
   performing third-party call control (3PCC).  Note that the SIP
   signaling is inaccurate, as the focus of this flow is in the graceful
   service termination and credit-control authorization.  The best
   practice for 3PCC is defined in [RFC3725].

   The call is ongoing between users A and B; user A has a prepaid
   subscription.  At the expiry of the allocated quota, the SIP
   controller sends a Diameter Credit-Control-Request (UPDATE_REQUEST)
   to the Diameter credit-control server (1).  This message contains the
   units used thus far.  The Diameter credit-control server debits the
   used units from the end user's account and allocates the final quota
   returned to the SIP controller in the Diameter Credit-Control-Answer
   (2).  This message contains the Final-Unit-Indication AVP with the

   Final-Unit-Action set to REDIRECT, the Redirect-Address-Type set to
   SIP URI, and the Redirect-Server-Address set to the Top-up server
   name (e.g., sip:sip-topup-server@domain.com).  At the expiry of the
   final allocated quota, the SIP controller sends a Diameter Credit-
   Control-Request (UPDATE_REQUEST) to the Diameter credit-control
   server (3) and places the called party on "hold" by sending an INVITE
   with the appropriate connection address in the SDP (3a).  The
   Credit-Control-Request message contains the units used thus far.  The
   Diameter credit-control server debits the used units from the end
   user's account but does not make any credit reservation.  The
   Credit-Control-Answer message, which contains the Validity-Time to
   supervise the graceful service termination, is returned to the SIP
   controller (4).  The SIP controller establishes a SIP session between
   the prepaid user and the Top-up server (5, 6).  The Top-up server
   plays an announcement and prompts the user to enter a credit card
   number and the amount of money to be used to replenish the account
   (7).  The Top-up server validates the credit card number and
   replenishes the user's account (using some means outside the scope of
   this specification) and releases the SIP session (8).  The SIP
   controller can now assume that communication between the prepaid user
   and the Top-up server took place.  It sends a spontaneous Credit-
   Control-Request (UPDATE_REQUEST) to the Diameter credit-control
   server to check whether the account has been replenished (9).  The
   Diameter credit-control server reserves credit from the end user's
   account and returns the reserved quota to the SIP controller in the
   Credit-Control-Answer (10).  At this point, the SIP controller re-
   connects the caller and the called party (11,12).

A.8.  Flow VIII

                         NAS                           Top-up      CC
   End-User         (CC Client)          AAA Server    Server    Server
     |(1)User Logon      |(2)AA Request (CC AVPs)        |         |
     |------------------>|------------------->|          |         |
     |                   |                    |(3)CCR(initial, CC AVPs)
     |                   |                    |------------------->|
     |                   |                    |(4)CCA(Final-Unit,  |
     |                   |                    |      Validity-Time)|
     |                   |                    |<-------------------|
     |                   |(5)AA Answer(Final-Unit,Validity-Time)   |
     |(6)Limited Access  |<-------------------|          |         |
     |      granted      |                    |          |         |
     |<----------------->|                    |          |         |
     |                   |                    |          |         |
     |   (7)TCP/HTTP     |        (8)TCP/HTTP            |         |
     |<----------------->|<----------------------------->|         |
     |                 (9) Replenish account             |         |
     |<------------------------------------------------->|         |
     |                   |                    |            (10)RAR |
     |                   |<-------------------|<-------------------|
     |                   | (11) RAA           |                    |
     |                   |------------------->|------------------->|
     |                   |(12)CCR(update)     |                    |
     |                   |------------------->|(13)CCR(Update)     |
     |                   |                    |------------------->|
     |                   |                    |(14)CCA(Granted-Units)
     |                   |(15)CCA(Granted-Units)<------------------|
     |                   |<-------------------|                    |

                         Figure A.8: Flow VIII

   Figure A.8 is an example of the graceful service termination
   initiated when the first interrogation takes place because the user's
   account is empty.  In this example, the credit-control server
   supports the server-initiated credit re-authorization.  The Diameter
   [NASREQ] is implemented in the Network Access Server (NAS).

   The user logs on to the network (1).  The Diameter NAS sends a
   Diameter AA-Request to the home Diameter AAA server.  The credit-
   control client populates the AAR with the Credit-Control AVP set to
   CREDIT_AUTHORIZATION, and service specific AVPs are included, as
   usual [NASREQ].  The home Diameter AAA server performs service
   specific Authentication and Authorization, as usual.  The home
   Diameter AAA server determines that the user has a prepaid
   subscription and notices from the Credit-Control AVP that the NAS has
   credit-control capabilities.  It sends a Diameter Credit-Control-

   Request with CC-Request-Type set to INITIAL_REQUEST to the Diameter
   credit-control server to perform credit authorization (3) and to
   establish a credit-control session.  (The home Diameter AAA server
   may forward service specific AVPs received from the NAS as input for
   the rating process.)  The Diameter credit-control server checks the
   end user's account balance, determines that the account cannot cover
   the cost of the service, and initiates the graceful service
   termination.  The Credit-Control-Answer is returned to the home
   Diameter AAA server (4).  This message contains the Final-Unit-
   Indication AVP and the Validity-Time AVP set to a reasonable amount
   of time to give the user a chance to replenish his/her account (e.g.,
   10 minutes).  The Final-Unit-Indication AVP includes the Final-Unit-
   Action set to REDIRECT, the Redirect-Address-Type set to URL, and the
   Redirect-Server-Address set to the HTTP Top-up server name.  The home
   Diameter AAA server sends the received credit-control AVPs to the NAS
   in the Diameter AA-Answer (5).  Upon successful AAA, the NAS starts
   the credit-control session and immediately starts the graceful
   service termination, as instructed by the server.  The NAS grants
   limited access to the user (6).  The HTTP client software running in
   the user's device opens the transport connection redirected by the
   NAS to the Top-up server (7,8).  The user is displayed an appropriate
   web page on which to enter the credit card number, and the amount of
   money to be used to replenish the account, and with a notification
   message that she is granted unlimited access if the replenishment
   operation will be successfully executed within the next, for example,
   10 minutes.  The Top-up server validates the credit card number and
   replenishes the user's account (using some means outside the scope of
   this specification)(9).  After successful account top-up, the
   credit-control server sends a Re-Auth-Request message to the NAS
   (10).  The NAS acknowledges the request by returning the Re-Auth-
   Answer message (11) and initiates the credit re-authorization by
   sending a Credit-Control-request (UPDATE_REQUEST) to the Diameter
   credit-control server (12,13).

   The Diameter credit-control server reserves credit from the end
   user's account and returns the reserved quota to the NAS via the home
   Diameter AAA server in the Credit-Control-Answer (14,15).  The NAS
   removes the restriction placed by the graceful service termination
   and starts monitoring the granted units.

A.9.  Flow IX

   The Diameter credit-control application defines the Multiple-
   Services-Credit-Control AVP that can be used to support independent
   credit-control of multiple services in a single credit-control (sub-)
   session for service elements that have such capabilities.  It is
   possible to request and allocate resources as a credit pool that is
   shared between services or rating groups.

   The flow example hereafter illustrates a usage scenario where the
   credit-control client and server support independent credit-control
   of multiple services, as defined in section 5.1.2.  It is assumed
   that Service-Identifiers, Rating-Groups, and their associated
   parameters (e.g., IP 5-tuple) are locally configured in the service
   element or provisioned by an entity other than the credit-control
   server.

   End User         Service Element                           CC Server
                       (CC client)
      |(1)User logon      |                                         |
      |------------------>|(2)CCR(initial, Service-Id access,       |
      |                   |        Access specific AVPs,            |
      |                   |        Multiple-Service-Indicator)      |
      |                   |---------------------------------------->|
      |                   |(3)CCA(Multiple-Services-CC (            |
      |                   |        Granted-Units(Total-Octets),     |
      |                   |        Service-Id access,               |
      |                   |        Validity-time,                   |
      |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
      |                   |          Multiplier 10)))               |
      |                   |<----------------------------------------|
      :                   :                                         :
      |(4)Service-Request (Service 1)                               |
      |------------------>|(5)CCR(update, Multiple-Services-CC(     |
      |                   |        Requested-Units(), Service-Id 1, |
      |                   |        Rating-Group 1))                 |
      |                   |---------------------------------------->|
      |                   |(6)CCA(Multiple-Services-CC (            |
      |                   |        Granted-Units(Time),             |
      |                   |        Rating-Group 1,                  |
      |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
      |                   |          Multiplier 1)))                |
      |                   |<----------------------------------------|
      :                   :                                         :
      |(7)Service-Request (Service 2)                               |
      |------------------>|                                         |

      :                   :                                         :
      :                   :                                         :
      |(8)Service-Request (Service 3&4)                             |
      |------------------>|(9)CCR(update, Multiple-Services-CC (    |
      |                   |        Requested-Units(), Service-Id 3, |
      |                   |        Rating-Group 2),                 |
      |                   |        Multiple-Services-CC (           |
      |                   |        Requested-Units(), Service-Id 4, |
      |                   |        Rating-Group 3))                 |
      |                   |---------------------------------------->|
      |                   |(10)CCA(Multiple-Services-CC (           |
      |                   |        Granted-Units(Total-Octets),     |
      |                   |        Service-Id 3, Rating-Group 2,    |
      |                   |        Validity-time,                   |
      |                   |        G-S-U-Pool-Reference(Pool-Id 2,  |
      |                   |          Multiplier 2)),                |
      |                   |        Multiple-Services-CC (           |
      |                   |        Granted-Units(Total-Octets),     |
      |                   |        Service-Id 4, Rating-Group 3     |
      |                   |        Validity-Time,                   |
      |                   |        Final-Unit-Ind.(Terminate),      |
      |                   |        G-S-U-Pool-Reference(Pool-Id 2,  |
      |                   |          Multiplier 5)))                |
      |                   |<----------------------------------------|
      :                   :                                         :
      :                   :                                         :
      | +--------------+  |                                         |
      | |Validity time |  |(11)CCR(update,                          |
      | |expires for   |  |        Multiple-Services-CC (           |
      | |Service-Id    |  |        Requested-Unit(),                |
      | | access       |  |        Used-Units(In-Octets,Out-Octets),|
      | +--------------+  |        Service-Id access))              |
      |                   |---------------------------------------->|
      |                   |(12)CCA(Multiple-Services-CC (           |
      |                   |        Granted-Units(Total-Octets),     |
      |                   |        Service-Id access,               |
      |                   |        Validity-Time,                   |
      |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
      |                   |          Multiplier 10)))               |
      |                   |<----------------------------------------|
      :                   :                                         :
      :                   :                                         :

      | +--------------+  |                                         |
      | |Total Quota   |  |(13)CCR(update,                          |
      | |elapses for   |  |       Multiple-Services-CC (            |
      | |pool 2:       |  |        Requested-Unit(),                |
      | |service 4 not |  |        Used-Units(In-Octets,Out-Octets),|
      | |allowed,      |  |        Service-Id 3, Rating-group 2),   |
      | |service 3 cont|  |       Multiple-Services-CC (            |
      | +--------------+  |        Used-Units(In-Octets,Out-Octets),|
      |                   |        Service-Id 4, Rating-Group 3))   |
      |                   |---------------------------------------->|
      |                   |(14)CCA(Multiple-Services-CC (           |
      |                   |        Result-Code 4011,                |
      |                   |        Service-Id 3))                   |
      |                   |<----------------------------------------|
      :                   :                                         :
      :                   :                                         :
      |(15) User logoff   |                                         |
      |------------------>|(16)CCR(term,                            |
      |                   |       Multiple-Services-CC (            |
      |                   |        Used-Units(In-Octets,Out-Octets),|
      |                   |        Service-Id access),              |
      |                   |       Multiple-Services-CC (            |
      |                   |        Used-Units(Time),                |
      |                   |        Service-Id 1, Rating-Group 1),   |
      |                   |       Multiple-Services-CC (            |
      |                   |        Used-Units(Time),                |
      |                   |        Service-Id 2, Rating-Group 1))   |
      |                   |---------------------------------------->|
      |                   |(17)CCA(term)                            |
      |                   |<----------------------------------------|

      Figure A.9: Flow example independent credit-control of multiple
                  services in a  credit-control (sub-)Session

   The user logs on to the network (1).  The service element sends a
   Diameter Credit-Control-Request with CC-Request-Type set to
   INITIAL_REQUEST to the Diameter credit-control server to perform
   credit authorization for the bearer service (e.g., Internet access
   service) and to establish a credit-control session (2).  In this
   message, the credit-control client indicates support for independent
   credit-control of multiple services within the session by including
   the Multiple-Service-Indicator AVP.  The Diameter credit-control
   server checks the end user's account balance, with rating information
   received from the client (i.e., Service-Id and access specific AVPs),
   rates the request, and reserves credit from the end user's account.
   Suppose that the server reserves $5 and determines that the cost is
   $1/MB.  It then returns to the service element a Credit-Control-
   Answer message that includes the Multiple-Services-Credit-Control AVP

   with a quota of 5MB associated to the Service-Id (access), to a
   multiplier value of 10, and to the Pool-Id 1 (3).

   The user uses Service 1 (4).  The service element sends a Diameter
   Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to
   the credit-control server to perform credit authorization for service
   1 (5).  This message includes the Multiple-Services-Credit-Control
   AVP to request service units for Service 1 that belong to Rating-
   Group 1.  The Diameter credit-control server determines that Service
   1 draws credit resources from the same account as the access service
   (i.e., pool 1).  It rates the request according to Service-
   Id/Rating-Group and updates the existing reservation by requesting
   more credit.  Suppose that the server reserves $5 more (now the
   reservation is $10) and determines that the cost is $0.1/minute.  The
   server authorizes the whole Rating-Group.  It then returns to the
   service element a Credit-Control-Answer message that includes the
   Multiple-Services-Credit-Control AVP with a quota of 50min.
   associated to the Rating-Group 1, to a multiplier value of 1, and to
   the Pool-Id 1 (6).  The client adjusts the total amount of resources
   for pool 1 according the received quota, which gives S for Pool 1 =
   100.

   The user uses Service 2, which belongs to the authorized Rating-
   Group, 1 (7).  Resources are then consumed from the pool 1.

   The user now requests Services 3 and 4 as well, which are not
   authorized (8).  The service element sends a Diameter Credit-
   Control-Request with CC-Request-Type set to UPDATE_REQUEST to the
   credit-control server in order to perform credit authorization for
   Services 3 and 4 (9).  This message includes two instances of the
   Multiple-Services-Credit-Control AVP to request service units for
   Service 3 that belong to Rating-Group 2 and for Service 4 that belong
   to Rating-Group 3.  The Diameter credit-control server determines
   that Services 3 and 4 draw credit resources from another account
   (i.e., pool 2).  It checks the end user's account balance and,
   according to Service-Ids/Rating-Groups information, rates the
   request.  Then it reserves credit from pool 2.

   For example, the server reserves $5 and determines that Service 3
   costs $0.2/MB and Service 4 costs $0.5/MB.  The server authorizes
   only Services 3 and 4.  It returns to the service element a Credit-
   Control-Answer message that includes two instances of the Multiple-
   Services-Credit-Control AVP (10).  One instance grants a quota of
   12.5MB associated to the Service-Id 3 to a multiplier value of 2 and
   to the Pool-Id 2.  The other instance grants a quota of 5 MB
   associated to the Service-Id 4 to a multiplier value of 5 and to the
   Pool-Id 2.

   The server also determines that pool 2 is exhausted and Service 4 is
   not allowed to continue after these units will be consumed.
   Therefore the Final-Unit-Indication AVP with action TERMINATE is
   associated to the Service-Id 4.  The client calculates the total
   amount of resources that can be used for pool 2 according the
   received quotas and multipliers, which gives S for Pool 2 = 50.

   The Validity-Time for the access service expires.  The service
   element sends a Credit-Control-Request message to the server in order
   to perform credit re-authorization for Service-Id (access) (11).
   This message carries one instance of the Multiple-Services-Credit-
   Control AVP that includes the units used by this service.  Suppose
   that the total amount of used units is 4MB.  The client adjusts the
   total amount of resources for pool 1 accordingly, which gives S for
   Pool 1 = 60.

   The server deducts $4 from the user's account and updates the
   reservation by requesting more credit.  Suppose that the server
   reserves $5 more (now the reservation is $11) and already knows the
   cost of the Service-Id (access), which is $1/MB.  It then returns to
   the service element a Credit-Control-Answer message that includes the
   Multiple-Services-Credit-Control AVP with a quota of 5 MB associated
   to the Service-Id (access), to a multiplier value of 10, and to the
   Pool-Id 1 (12).  The client adjusts the total amount of resources for
   pool 1 according the received quota, which gives S for Pool 1 = 110.

   Services 3 and 4 consume the total amount of pool 2 credit resources
   (i.e., C1*2 + C2*5 >= S).  The service element immediately starts the
   TERMINATE action concerning Service 4 and sends a Credit-Control-
   Request message with CC-Request-Type set to UPDATE_REQUEST to the
   credit-control server in order to perform credit re-authorization for
   Service 3 (13).  This message contains two instances of the
   Multiple-Services-Credit-Control AVP to report the units used by
   Services 3 and 4.  The server deducts the last $5 from the user's
   account (pool 2) and returns the answer with Result-Code 4011 in the
   Multiple-Services-Credit-Control AVP to indicate that Service 3 can
   continue without credit-control (14).

   The end user logs off from the network (15).  To debit the used units
   from the end user's account and to stop the credit-control session,
   the service element sends a Diameter Credit-Control-Request with CC-
   Request-Type set to TERMINATION_REQUEST to the credit-control server
   (16).  This message contains the units consumed by each of the used
   services in multiple instances of the Multiple-Services-Credit-
   Control AVP.  The used units are associated with the relevant
   Service-Identifier and Rating-Group.  The Diameter credit-control

   server debits the used units to the user's account (Pool 1) and
   acknowledges the session termination by sending a Diameter Credit-
   Control-Answer to the service element (17).

Authors' Addresses

   Harri Hakala
   Oy L M Ericsson Ab
   Joukahaisenkatu 1
   20520 Turku
   Finland

   Phone: +358 2 265 3722
   EMail: Harri.Hakala@ericsson.com

   Leena Mattila
   Oy L M Ericsson Ab
   Joukahaisenkatu 1
   20520 Turku
   Finland

   Phone: +358 2 265 3731
   EMail: Leena.Mattila@ericsson.com

   Juha-Pekka Koskinen
   Nokia Networks
   Hatanpaanvaltatie 30
   33100 Tampere
   Finland

   Phone: +358 7180 74027
   EMail: juha-pekka.koskinen@nokia.com

   Marco Stura
   Nokia Networks
   Hiomotie 32
   00380 Helsinki
   Finland

   Phone: +358 7180 64308
   EMail: marco.stura@nokia.com

   John Loughney
   Nokia Research Center
   Itamerenkatu 11-13
   00180 Helsinki
   Finland

   Phone: +358 50 483 642
   EMail: John.Loughney@nokia.com

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