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Versions: (draft-hakala-aaa-diameter-cc) 00 01 02 03 04 05 06 RFC 4006

   AAA Working Group
   Internet Draft                                         Harri Hakala
   Document: draft-ietf-aaa-diameter-cc-02.txt           Leena Mattila
   Expires: June 2004                                         Ericsson
                                                   Juha-Pekka Koskinen
                                                           Marco Stura
                                                         John Loughney
                                                                 Nokia
                                                     December 16, 2003


                  Diameter Credit-Control Application


Status of this memo

   This document is an Internet-Draft and is subject to all provisions of
   Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering Task
   Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference material
   or cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/lid-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This document is a product of the Authentication, Authorization and
   Accounting (AAA) Working Group of the Internet Engineering Task Force
   (IETF).  Comments are welcome should be submitted to the mailing list
   aaa-wg@merit.edu.

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, SIP services, messaging services, download
   services etc.







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   1. Introduction...................................................5
      1.1 Requirements language......................................5
      1.2 Terminology................................................6
      1.3 Advertising application support............................7
   2. Architecture Models............................................7
   3. Credit-Control Messages.......................................10
      3.1 Credit-Control-Request (CCR) Command......................10
      3.2 Credit-Control-Answer (CCA) Command.......................11
   4. Credit Control Application Overview...........................12
      4.1 Service-Specific Rating Input and Interoperability........13
   5. Session Based Credit-control..................................15
      5.1 First Interrogation.......................................16
      5.2 Intermediate Interrogation................................21
      5.3 Final Interrogation.......................................23
      5.4 Server-Initiated Credit Re-Authorization..................24
      5.5 Graceful Service Termination..............................25
      5.6 Failure Procedures........................................30
   6. One Time Event................................................33
      6.1 Service Price Enquiry.....................................34
      6.2 Balance Check.............................................34
      6.3 Direct Debiting...........................................35
      6.4 Refund....................................................36
      6.5 Failure Procedure.........................................36
   7. Credit Control Application State Machine......................38
   8. Credit Control AVPs...........................................48
      8.1 CC-Correlation-Id AVP.....................................50
      8.2 CC-Request-Number AVP.....................................50
      8.3 CC-Request-Type AVP.......................................50
      8.4 CC-Session-Failover AVP...................................51
      8.5 CC-Sub-Session-Id AVP.....................................52
      8.6 Check-Balance-Result AVP..................................52
      8.7 Cost-Information AVP......................................52
      8.8 Cost-Unit AVP.............................................53
      8.9 Credit-Control AVP........................................53
      8.10 Credit-Control-Failure-Handling AVP......................54
      8.11 Currency-Code AVP........................................55
      8.12 Direct-Debiting-Failure-Handling AVP.....................55
      8.13 Exponent AVP.............................................56
      8.14 Final-Unit-Action AVP....................................56
      8.15 Final-Unit-Indication AVP................................56
      8.16 Granted-Service-Unit AVP.................................57
      8.17 Redirect-Address-Type AVP................................58
      8.18 Redirect-Server AVP......................................59
      8.19 Redirect-Server-Address AVP..............................59
      8.20 Requested-Action AVP.....................................59
      8.21 Requested-Service-Unit AVP...............................60
      8.22 Restriction-Filter-Rule AVP..............................61
      8.23 Service-Parameter-Info AVP...............................61


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      8.24 Service-Parameter-Type AVP...............................61
      8.25 Service-Parameter-Value AVP..............................62
      8.26 Subscription-Id AVP......................................62
      8.27 Subscription-Id-Data AVP.................................62
      8.28 Subscription-Id-Type AVP.................................62
      8.29 Unit-Value AVP...........................................63
      8.30 Used-Service-Unit AVP....................................63
      8.31 Value-Digits AVP.........................................64
      8.32 Validity-Time AVP........................................64
      8.33 CC-Input-Octets AVP......................................64
      8.34 CC-Money AVP.............................................64
      8.35 CC-Output-Octets AVP.....................................65
      8.36 CC-Service-Specific-Units AVP............................65
      8.37 CC-Time AVP..............................................65
      8.38 CC-Total-Octets AVP......................................65
      8.39 Rating-Group AVP.........................................65
      8.40 Service-Identifier AVP...................................65
      8.41 Tariff-Time-Change AVP...................................66
      8.42 Tariff-Change-Usage AVP..................................66
   9. Result Code AVP values........................................67
      9.1 Transient Failure.........................................67
      9.2 Permanent Failures........................................67
   10. AVP Occurrence Table.........................................68
      10.1 Credit Control AVP Table.................................68
   11. RADIUS/Diameter Credit-control Interworking..................69
      11.1 Initial RADIUS Access-Request............................70
      11.2 Subsequent RADIUS Access-Request message.................71
      11.3 RADIUS Vendor Specific Attributes for Credit Control.....72
   12. IANA Considerations..........................................72
      12.1 Application Identifier...................................73
      12.2 Command Codes............................................73
      12.3 AVP Codes................................................73
      12.4 Result-Code AVP Values...................................73
      12.5 CC-Request-Type AVP......................................73
      12.6 CC-Session-Failover AVP..................................73
      12.7 Check-Balance-Result AVP.................................73
      12.8 Credit-Control AVP.......................................73
      12.9 Credit-Control-Failure-Handling AVP......................73
      12.10 Direct-Debiting-Failure-Handling AVP....................74
      12.11 Final-Unit-Action AVP...................................74
      12.12 Redirect-Address-Type AVP...............................74
      12.13 Requested-Action AVP....................................74
      12.14 Subscription-Id-Type AVP................................74
      12.15 Tariff-Change-Usage AVP.................................74
   13. Credit-control Application Related Parameters................74
   14. Security Consideration.......................................75
      14.1 Direct Connection with Redirects.........................76
   15. References...................................................77
      15.1 Normative................................................77


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      15.2 Non-Normative............................................77
   16. Acknowledgement..............................................78
   17. Author's Address.............................................78
   18. Full Copyright Statement.....................................79
   19. Notices......................................................79
   20. Expiration Date..............................................80
   Appendix A Credit Control sequences..............................80
      A.1  Flow I...................................................80
      A.2  Flow II..................................................82
      A.3  Flow III.................................................83
      A.4  Flow IV..................................................85
      A.5  Flow V...................................................86
      A.6  Flow VI..................................................87
      A.7  Flow VII.................................................88
      A.8  Flow VIII................................................89
      A.9  Flow IX..................................................90
      A.10 Flow X...................................................92


































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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, SIP services, messaging services, download
   services etc. It provides a general solution to the real-time cost and
   credit control.

   The prepaid model 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 as well.

   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 needs 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
   deduct from a user account.

   The currently existing 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
   communication between the network element providing the service (e.g.
   NAS, SIP Proxy, Application Server etc.) and a credit-control server,
   in order to minimize financial risk.

   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].



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1.2 Terminology

   AAA

   Authentication, Authorization and Accounting

   AA answer

   AA answer does generically refer 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 does generically refer 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, which 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 if credit is
   available, credit-reservation, deduction of credit from the end user
   account when service is completed and refunding of reserved credit not
   used.

   Diameter Credit-control Server

   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 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 and during the credit-control
   process to report the used quota and request a new one. An
   interrogation maps to a request/answer transaction.



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   One-time event

   Basically a request/answer transaction of type event. The credit-
   control server is not required to maintain session state for one-time
   event.

   Rating

   The act of determining the cost of the service event.

   Service

   A type of task that is 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 Credit-control Client, or another
   entity (e.g. RADIUS AAA server) 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 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

   Credit-control process that makes use of several interrogations: the
   first, possible intermediates and the final interrogation. The first
   interrogation is used to reserve money from the user's account and
   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



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   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 provides 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
   of credit authorization for prepaid subscribers.

   A service element may authenticate and authorize the end user with the
   AAA server 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 possible service event
   information included before the service is provided to the end user.
   This process is performed in order 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
   consist of a Service Element with 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 for instance SIP services
   or messaging services, 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 credit-control


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   +----------+      +---------+    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

  Other entities, such as RADIUS AAA server, may act as a Diameter
  credit-control client towards the Diameter credit-control server for
  service elements that use credit control mechanisms other than
  Diameter credit-control. In this case the AAA server contact the
  Diameter credit-control server as part of the authorization process.
  The interworking architecture is illustrated in Figure 2, the
  interaction between the Diameter credit-control client and the service
  element is outside the scope of this specification. Interworking with
  RADIUS is addressed in section 11 and Annex A.

                                     AAA
   +--------+       +---------+    protocol  +------------+   +--------+
   |  End   |<----->| Service |<------------>|    AAA     |   |Business|
   |  User  |       | Element |              |  Server    |   |Support |
   +--------+   +-->|         |              |+----------+|-->|System  |
                |   +---------+              ||CC client ||   |        |
                |                            |+----------+|   |        |
   +--------+   |                            +------^-----+   +--------+
   |  End   |<--+                  credit-control   |               ^
   |  User  |                            protocol   |               |
   +--------+                               +-------V------+        |
                                            |Credit-control|--------+
                                            |   Server     |
                                            +--------------+

     Figure 2: Credit-control architecture with Service Element not
                supporting the credit-control protocol

   There can be multiple credit-control servers in the system for reasons
   of redundancy and load balancing. The system can also contain separate
   rating server(s) and accounts can locate in a centralized database.
   For duplicate detection only one place in the credit-control system
   should perform duplicate detection to ensure that the end user's
   account is not debited or credited multiple times for the same service


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   event. System internal interfaces can exist to relay messages between
   servers and an account manager. However the detailed architecture of
   credit-control system and its interfaces are implementation specific
   and are out of scope of this specification.

   There can exist protocol transparent Diameter relays and redirect
   agents between credit-control client and credit-control server. Also
   Diameter Redirect agents, which 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.

   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:

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

3.1 Credit-Control-Request (CCR) Command

   The Credit-Control-Request message (CCR), indicated by the command-
   code field set to 272 and the 'R' bit set in the Command Flags field,
   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 }
                                     { CC-Request-Type }
                                     { CC-Request-Number }
                                     [ Destination-Host ]
                                     [ User-Name ]


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                                     [ 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 ]
                                    *[ Service-Parameter-Info ]
                                    *[ CC-Correlation-Id ]
                                    *[ Proxy-Info ]
                                     [ Redirect-Host AVP ]
                                     [ Redirect-Host-Usage AVP ]
                                     [ Redirect-Max-Cache-Time AVP ]
                                    *[ Route-Record ]
                                    *[ AVP ]

3.2 Credit-Control-Answer (CCA) Command

   The Credit-Control-Answer message (CCA), indicated by the command-code
   field set to 272 and the 'R' bit cleared in the Command Flags field,
   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 ]
                                    [ Subscription-Id ]
                                   *[ Granted-Service-Unit ]
                                    [ Cost-Information]
                                    [ Final-Unit-Indication ]
                                    [ Check-Balance-Result ]
                                    [ Credit-Control-Failure-Handling ]
                                    [ Direct-Debiting-Failure-Handling ]


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                                    [ Validity-Time]
                                   *[ Proxy-Info ]
                                   *[ Route-Record ]
                                   *[ AVP ]

4. Credit Control Application Overview

   The credit authorization process takes place before and during service
   delivery to the end user, it generally requires user's authentication
   and authorization before any request is sent to the credit-control
   server.

   The credit control application defined in this specification supports
   for two different credit authorization models: credit authorization
   with money reservation and credit authorization with direct debiting.
   In both the models, the credit control client requests credit
   authorization to the credit control server prior to allow any service
   to be delivered to the end user.

   In the first model, the credit control server rates the request,
   reserve a suitable amount of money from the user's account and return
   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 form of units (e.g. data
   volume or time) to be metered.

   Upon reception 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 start 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.

   In contrast, credit authorization with direct debiting is a single
   transaction process where the credit control server directly deducts
   the suitable amount of money from the user's account as soon as the
   credit authorization request is received. Upon reception 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.



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

   The credit control application also support for 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 where the home service provider can model the credit control
   client behavior according to own credit risk management policy.
   The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
   Failure-Handling AVP are defined to determine what to do if the
   sending of credit-control messages to the credit-control server has
   been temporarily prevented. The usage of Credit-Control-Failure-
   Handling AVP and the Direct-Debiting-Failure- Handling AVP gives
   flexibility to have different failure handling for credit-control
   session and one time event direct debiting.

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 seen as out of scope for this generic
   mechanisms as well.

   It is reasonable to expect that there will exist a service level
   agreement between providers of the credit control client and the
   credit control server covering the charging, services offered, roaming
   agreements, agreed rating input, etc.

   There are two ways for providing rating input to the credit control
   server, either by using AVPs or by including them in the Service-
   Parameter-Info AVP. The general principle for sending rating
   parameters is that the service SHOULD re-use existing AVPs, if the
   service can use AVPs defined in existing service specific Diameter
   applications (e.g. NASREQ for network access services).
   Alternatively, new AVPs can be defined if the existing AVPs do not
   provide sufficient rating information. 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). In that case the rating input
   is embedded in the Service-Parameter-Info AVP as defined in section


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   8.23. New service applications SHOULD favor the use of explicitly
   defined AVPs, to simplify interoperability.

   The service specific rating input AVPs, the contents of the Service-
   Parameter-Info AVP or Service-Identifier AVP are not within the scope
   of this document. To facilitate interoperability, it is RECOMMENDED
   that the rating input and values of service identifiers are
   coordinated via an informational RFC or other permanent and readily
   available reference such as 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 service specific documents, is
   governing the credit control message. The rule is that service
   specific documents only define what existing AVPs or new AVPs are used
   as input to the rating process (i.e. they do not define new credit
   control applications), and thus need to be included in the Credit-
   Control-Request command by a Diameter Credit Control Client supporting
   a given service as *[AVP]. In order to define new AVPs, service
   specific documents MUST follow the practices defined in
   [DIAMBASE]. The service SHOULD be identified using the Service-
   Identifier AVP at command level. The Service-Identifier AVP SHOULD be
   a unique identifier for a given service as defined in section 8.40.
   As a result it is the combination of support of the Diameter Credit
   Control Application (DCC) and the service defined in the Service-
   Identifier AVP, which defines interoperability between any given DCC
   client and server.

   Diameter credit control implementations are required to support the
   Mandatory rating AVPs defined in service specific documentation of the
   services they support. Introducing new credit control mechanisms not
   defined in this specification implies the definition of a new version
   of the Diameter Credit Control Application and corresponding
   Application Identifier.

   In case a rating input required for the rating process is missing from
   the Credit control request, or the credit control server does not
   support the requested service (i.e. does not support one or more
   Mandatory rating AVPs included in the request command), the Credit
   control answer MUST contain error code DIAMETER_RATING_FAILED. A CCR
   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 receiving error code
   DIAMETER_RATING_FAILED in answer to a request MUST NOT send such
   similar requests in the future.




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5. Session Based Credit-control

   For a session-based credit-control, several interrogations are needed:
   the first, intermediate (optional) and the final interrogation. This
   is illustrated in Figure 3 and Figure 4.

   If the credit-control client performs credit-reservation before
   granting service to the end user it MUST use several interrogations
   towards 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 globally unique Session-Id as
   defined in [DIAMBASE] and it MUST NOT be changed during the lifetime
   of a credit-control session.

   There are certain applications that require multiple credit control
   sub-sessions. Such applications would send messages with a constant
   Session-Id AVP, but a different CC-Sub-Session-Id AVP. If several
   credit sub-sessions will be used, all sub-sessions MUST be closed
   separately before the closing the main session to be able to report
   used units per sub-session. The absence of this AVP implies no sub-
   sessions are in use.

   When multiple services are used within one user session and each
   service or group of services are subject to different cost, making use
   of credit control sub-sessions will result in increased signaling load
   and resources usage 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. To optimally support these scenarios, the credit control
   application enables for multiple services credit control in a single
   credit control session. It is possible to request and allocate
   multiple quotas as a credit pool that is shared between multiple
   services. The services can be further grouped into rating groups in
   order to achieve even further aggregation of credit allocation. It is
   also possible to request and allocate multiple quotas on a per service
   basis. The mechanism is illustrated in Appendix A (Flow X).

   It should be noted that the service element might send a service
   specific re-authorization message to the Diameter 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 credit-
   control client and credit-control server since credit authorization is
   controlled by the burning rate of the granted quota.
   In the event that 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.


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   The Diameter credit-control server may want 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 are
   not performed.

   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 then the
   Diameter credit-control client SHOULD itemize the units used before
   and after the tariff change. In case some units straddled the tariff
   change, the credit-control client SHOULD itemize those units as well.

5.1 First Interrogation

   When session based credit-control is required (e.g. the authentication
   server indicated 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 and the Service-
   Parameter-Info AVP MAY contain the service event information to be
   rated by the credit-control server. The Service-Parameter-Info AVP
   always refers to the requested service units. Alternatively, service
   event information to be rated can be sent as service specific AVPs.



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   The Event-Timestamp AVP contains the time when the service event is
   requested in the service element.

   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 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.  There MUST be maximum
   one instance of the same unit type in one Answer message. In case
   multiple quotas are conveyed to the credit control client, there MUST
   be maximum one instance of the same unit type associated to a Service-
   Identifier, or set of Service-Identifiers, or associated to a Rating-
   Group. The type of the Granted-Service-Unit AVP can be time, volume,
   service specific or money depending on the type of service event. It
   is not allowed to change the unit type(s) within the session.

   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. service is free of charge)
   and terminate the credit-control session.

   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 session. After the end user has consumed these
   units, the Diameter credit-control-client MUST behave as described in
   section 5.5.

   Two different approaches are defined for the first interrogation to
   suit properly in all the possible architectures. The first approach
   uses credit-control messages after user's authorization and
   authentication took 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 the final interrogations.
   In case an implementation of the credit-control client supports both
   the methods, it SHOULD be configurable what method to use.

   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


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   interrogation took place are performed with credit control commands
   defined in this specification. Implementations of credit-control
   client operating in the mentioned environments SHOULD support this
   method. In case the credit-control server and AAA server are separate
   physical entities the service element send the request messages to the
   AAA server, which then issue an appropriate request or proxy the
   received request forward to the credit-control server.

   In other service environments, such as the 3GPP network and some SIP
   scenario, 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 such environments it is
   more appropriate to perform the first interrogation after the user has
   been authenticated and authorized. The first interrogation, the
   intermediate and final interrogations are executed with credit control
   commands defined in this specification.

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

5.1.1 First Interrogation after Authorization and Authentication

   The Diameter credit-control client in the service element may get
   information from the authorization server 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
   initiate the service delivery to the end user. The accounting protocol
   and the credit-control protocol can be used in parallel, the
   authorization server may also drive 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.

    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)        |
       |                  +|---------------------------------------->|


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       |         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 3: Protocol example with first interrogation after user's
                        authorization/authentication

5.1.2 Authorization Messages for First Interrogation

   The Diameter credit-control client in the service element MUST
   actively contribute 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 towards 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
   authenticate/authorize the subscriber and determine whether or not
   credit-control is required.

   If credit-control is not required for the subscriber the home AAA
   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-


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   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 credit-control AVPs received in the AA request. The
  credit-control server will make money reservation 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 usual service
   attributes according to the authorization/authentication specific
   application (e.g. [NASREQ], [DiamMIP]) and forward the packet to the
   credit-control client. If the home 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.

   The credit-control client in this model sends further credit-control
   messages to the credit-control server via the home AAA server.
   Upon receiving 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 intermediate credit-control
   request as required by using Credit-Control commands. The CC-Request-
   Number of the first intermediate 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 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 messages stream is flowing
   through the Diameter AAA server. The Diameter AAA server can make use
   of this credit-control messages flow to deduce that user's activity is
   ongoing; hence it is recommended to set the authorization-lifetime to



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   a reasonably high value when credit-control is used for the
   subscriber.

   In this scenario the home 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.

   End-User        Service Element        AAA Server           CC Server
                    (CC Client)
      | 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 4: Protocol example with use of the
            authorization messages for the first interrogation.


5.2 Intermediate Interrogation




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   When all of 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
   in one credit control session is applied (i.e. units are granted
   associated to Service-Identifier(s) or Rating-Group), a new Credit-
   Control-Request MUST be sent to the credit-control server when the
   whole credit reservation has been consumed, or upon expiration of the
   Validity-Time. In the case when the Validity-Time is used, it is
   always up to the Diameter credit-control client to send a new request
   well in advance before the expiration of the previous request in order
   to avoiding 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 be also 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 from the credit-control server
   these units apply from the point where the measurement of the reported
   used units stopped.

   The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
   intermediate request message. The Subscription-Id-Data AVP SHOULD be
   included in the intermediate message to identify the end user in the
   credit-control server.

   The Requested-Service-Unit AVP contains the new amount of requested
   service units. The Used-Service-Unit AVP contains the amount of used
   service units measured from the point when the service became active
   or, in case of interim interrogations are used during the session,
   from the point when the previous measurement ended. The same unit
   types that are used in the previous message MUST 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 contains the time of the event that triggered
   the sending of the new Credit-Control-Request.




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   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.

   The 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 session. After the end user has consumed these
   units, the Diameter credit-control-client MUST behave as described in
   section 5.5.

   There can be several intermediate interrogations within a session.

5.3 Final Interrogation

   When the end user terminates the service session or according to the
   graceful service termination as described in section 5.5, 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 Event-Timestamp AVP MAY contain the time of 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, in case of
   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.

   The 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 logoff during an ongoing credit-control session or some
   other reason causes the user to be 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


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   [DIAMBASE]. Figure 5 illustrates the case when the final-unit
   indication causes the user logoff upon consumption of the final
   granted units and STR is generated.

   End-User        Service Element        AAA Server           CC Server
                    (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 5: User disconnected due to account exhausted

5.4 Server-Initiated Credit Re-Authorization

   The Diameter Credit Control Application supports the 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 the Diameter
   Credit Control Application and the Re-Auth-Request-Type is set to
   AUTHORIZE_ONLY.

   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 such a RAR message with Session-Id equal to a currently
   active credit control session acknowledges the request by sending the
   Re-Auth-Answer (RAA) message and MUST initiate the credit re-
   authorization towards the server by sending a Credit-Control-Request


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   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 an additional message (i.e. CCR[Update]) is
   required to complete the procedure. If a quota was allocated to the
   session, 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).

   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 it does not initiate a new
   credit re-authorization. The Result-Code 2001 (DIAMETER_SUCCESS)
   SHOULD be used in the RAA message to indicate 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.

   If several credit control sub-sessions are in use, a credit control
   client receiving the RAR command for a given session will trigger
   credit re-authorization for all the sub-session separately.

5.5 Graceful Service Termination

   When the user's account runs out of money the user must be denied to
   compile additional chargeable events. However, the home service
   provider may offer free access services, for instance access to a
   service portal where it is possible to top-up the account, for which
   the user is allowed to benefit for a limited amount of time. This time
   is usually dependant on the home service provider policy.

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

   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 top-up or other zero-rated 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


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   the service portal. The user may also be displayed an appropriate
   notification why the access has been limited.

   It is also possible use the graceful service termination to connect
   the prepaid user to a top-up server that play an announcement and
   prompt the user to replenish the account. In such a 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 VIII).

   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 session.
   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 and RESTRICT_ACCESS.

   The following Figure illustrates the graceful service termination
   procedure described in the following sub-sections.

   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|      |
      |                   |                    |     +-------+      |



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      |                   |                    |                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 6: Optional graceful service termination procedure

5.5.1 Terminate Action

   The Final-Unit-Indication AVP with Final-Unit-Action TERMINATE does
   not include any other information. Upon the subscriber has consumed
   the final granted units the service element MUST terminate the service
   session and MUST send a final Credit-Control-Request message to the
   credit control server. The CC-Request-Type AVP in the request is set
   to the value TERMINATION_REQUEST. 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.

5.5.2 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 follow.

   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 other protocols 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


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   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 AVP or one or more Filter-
   Id AVP in the Credit-Control-Answer message in order to enable the
   user to access other 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 redirect the user to the
   destination specified in the Redirect-Server AVP, if possible.

   Another entity 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 5.5.3.

   When the final granted units have been consumed the credit control
   client MUST perform an intermediate interrogation. The purpose of this
   intermediate 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 event that affect the rating of the current
   service. Therefore, the credit control client MUST NOT include any
   rating related AVP in the request sent upon all the final granted
   units have been consumed as a hint to the server that the requested
   final unit action started, rating and money reservation are not
   required. 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 since 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 zero-rated services for 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 session). The server
   will return the appropriate Result-Code (see section 9.1) in the
   Credit-Control-Answer message in order to close the credit control
   session and implement the policy-defined action. Otherwise new quota


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   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 the service session as usual.

   The credit control client may not wait until the expiration of the
   Validity-Time and may send a spontaneous updating (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).

   It is worth noting that the credit control server may initiate the
   above-described process already for the first interrogation. However,
   the user's account might be empty at the time when the 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 AVP, Validity-Time
   AVP but no Granted-Unit. In such a case it starts immediately the
   graceful service termination without sending any message to the
   server. An example of this case is illustrated in Appendix A.

5.5.3 Restrict Access Action

   The Final-Unit-Indication AVP with Final-Unit-Action RESTRICT_ACCESS
   indicates to the access device supporting this action that the user
   MUST be restricted access 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.

   Another entity 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, for
   instance, may configure the access device with "zero-rated" IP flows
   that are 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 possibly received in the Credit-
   Control-Answer message in addition to the filter rules possibly
   configured by the other entity. However, the action to be taken when
   the user's account cannot cover the cost of the requested service 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, it is presumably not needed
   for the credit control server to send any additional filter. Therefore
   it is RECOMMENDED that credit control server implementations


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   supporting the graceful service termination can be configurable
   whether to send 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.

5.5.4 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 be
   immediately removed and unlimited services' access be resumed. For the
   best user experience the credit control server implementation MAY
   support the server-initiated credit re-authorization (see section
   5.4). In such a case, upon the successful account top-up took place,
   the credit control server sends the Re-Auth-Request (RAR) message to
   solicit the credit re-authorization. The credit control client
   initiates then 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 since 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.

5.6 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 locally configured.
   The CCFH value received from the home AAA server overrides the locally
   configured value and the CCFH value received from the credit control
   server in the Credit-Control-Answer message always override any
   already existing value.

   The authorization server MAY include the Accounting-Realtime-Required
   AVP to determine what to do if the sending of accounting records to


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   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 towards an
   accounting server. Using different combinations of Accounting-
   Realtime-Required and Credit-Control-Failure-Handling AVPs different
   safety levels can be built. For example by choosing the Credit-
   Control-Failure-Handling AVP equal to CONTINUE for the credit control
   flow and 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 but the
   accounting server is able to collect the accounting information,
   provided that there is information exchange taking place between the
   accounting server and credit-control server.

   Since 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. Since 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 credit-control client and credit-control
   server in the event that 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,
   received from the AAA server or locally configured, 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 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.




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   The AAA client/agent is typically using only a single persistent
   transport connection to the AAA agent or server, but it may have
   connections to multiple AAA agents or servers and treat them as
   primary/secondary or balance load between them. The AAA transport
   profile [AAATRANS] defines the application layer watchdog algorithm
   that enables failover from a peer that has failed and is controlled by
   the timer Twinit. The recommended default value for Twinit is 30
   seconds. Since the AAA infrastructure is common to several different
   types of AAA applications, 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 increase the
   probability of premature failover significantly and potentially cause
   congestive collapse in heavy loaded networks. For prepaid services,
   however, the end user expects an answer from the network in a
   reasonable time, thus the Diameter credit control client shall react
   faster than 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 in case 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 upon the timer Tx expires. An answer message with granted-
   units may arrive later on due to the base protocol transport failover
   occurred in the path to the Credit Control Server (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 a protocol error
   DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is received or the
   request timeout 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 also the re-transmitted request fails, the


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   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 the 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 the price
   of the service. The use of 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 without any credit-reservation or
   to check the account balance without any credit-reservation. It can be
   used also for refunding service units on the user's account or direct
   debiting without any credit-reservation. The one time event is shown
   in Figure 7.

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


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                          Figure 7: 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. There might exist services offered by application service
   providers, whose prices are not known in the credit-control client.
   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-Parameter-Info AVP in the
   Credit-Control-Request message.

   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 need only to verify that the
   end user's account balance covers the cost for a certain service
   without reserving any units from the account at the time of the
   inquiry. This method does not guarantee that there would be credit
   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 Requested-
   Action AVP set to CHECK_BALANCE and include the Subscription-Id-Data
   to identify the End-User in the credit-control server.

   The credit-control server makes the balance check, but it does not do
   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.


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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 unreasonable 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.

   The CC-Request-Type is set to the value EVENT_REQUEST and the
   Requested-Action AVP set to DIRECT_DEBITING in the Credit-Control-
   Request message. The Subscription-Id-Data AVP SHOULD be included to
   identify the End-User in the credit-control server. The Event-
   Timestamp AVP contains the time when the service event is requested in
   the service element.

   The Diameter credit-control client can include the monetary amount to
   be charged in the Request-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, then the Service-Parameter-Info AVP
   SHOULD contain the service event information to be rated by the
   credit-control server. The Service-Parameter-Info AVP always refers to
   the requested service unit.

   The credit-control server SHOULD rate the service event and deduct the
   corresponding monetary amount from 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
   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.




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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 in the Credit-
   Control-Request message. The Subscription-Id-Data AVP SHOULD be
   included to identify the End-User in the credit-control server.

   The Diameter credit-control client MAY include the monetary amount to
   be refunded in the Requested-Service-Unit AVP. If the Diameter credit-
   control client does not know the monetary amount to be refunded, then
   the Service-Parameter-Info AVP, or other rating AVPs, SHOULD contain
   the service event information to be rated by the credit-control
   server.

   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 one
   time event since 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 exist protocol
   transparent Diameter relays and redirect agents or Diameter credit-
   control proxies between credit-control client and credit-control
   server. Failover may occur at any point in the path between credit-
   control client and credit-control server in the event that 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 therefore responsible for the real time duplicate detection.
   Implementation issues for duplicate detection are discussed in
   [DIAMBASE] Appendix C.

   When the credit-control client detects a communication failure to 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.

   In case the requested action is PRICE_ENQUIRY or BALANCE_CHECK 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 AAA server, can be used as an address of backup server.



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  If the requested action is DIRECT_DEBITING the Direct-Debiting-
  Failure-Handling AVP (DDFH) controls the credit control client
  behavior. The DDFH may be received from the Diameter home 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 AAA server
  overrides the locally configured value and the DDFH value received
  from the credit control server in a Credit-Control-Answer message
  always override any already 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, since the user's account may be empty at the time when the
  server successfully processes the request). The credit-control client
  MUST mark these request messages as possible duplicate 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 timeout
   the credit control client re-transmit the request (marked with T-flag)
   to a backup credit control server if possible. In the event that also
   the re-transmitted request timeout or a temporary error is received in
   answer to such a request, 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 the
   value of the DDFH.

   The Credit-Control-Request with requested action REFUND 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 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 define a re-transmission interval.

   It should be noted 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. In case when more than one


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   credit-control servers are serving 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 one describes the
   session-based credit-control when the first interrogation is executed
   after the authorization/authentication process. The requirements what
   state machine need to be supported are discussed in section 5.1.

   The third state machine describes the session-based credit-control for
   intermediate and final interrogations. The fourth one describes the
   event-based credit-control. These latter state machines are to be
   observed by all the 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 as 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 with a possibly defined alternative destination
   in case failover procedure is supported (e.g. the request timeout 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/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 be ultimately received in answer to the re-
   transmitted request to a possibly 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


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   notification may be ultimately received in answer to the re-
   transmitted request to a possibly 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 unknown end user,
   account being empty or due to errors defined in [DIAMBASE].

   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 abbreviations 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 possibly
   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 5.6.

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

























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   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 N/A    to end user

     PendingI  User service terminated        Queue         PendingI
                                              termination
                                              event

     PendingI  Change in rating condition     Queue         PendingI
                                              changed
                                              rating
                                              condition
                                              event

















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       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 equal 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 equal to        service to
               RETRY_AND_TERMINATE            end user

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

     PendingI  CC initial answer              Grant        Idle
               received with result code      service
               equal to credit-control N/A    to end user

     PendingI  Failed CC initial answer       Grant        Idle
               received 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 equal to       service
               RETRY_AND_TERMINATE


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     PendingI  User service terminated        Queue        PendingI
                                              termination
                                              event

     PendingI  Change in rating condition     Queue        PendingI
                                              changed
                                              rating
                                              condition
                                              event









































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      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


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               CCFH equal to TERMINATE        service
               or equal 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 equal to        service to
               RETRY_AND_TERMINATE            end user.

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

     PendingU  CC update answer               Grant        Idle
               received with result code      service
               equal to credit-control N/A    to end user

     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 CCFH           end user's
               equal to TERMINATE or          service
               equal 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, or temporary               Idle
               error or failed answer

     PendingT  Change in rating condition                  PendingT




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                        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 or failed CC event       service
               answer received, or            error
               Tx expired, requested
               action BALANCE_CHECK or
               PRICE_ENQUIRY

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

     PendingE  CC event answer                Grant         Idle
               received with result code      service
               credit-control N/A, requested  to end
               action DIRECT_DEBITING         user

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

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

     PendingE  Tx expired, requested          Grant         PendingE
               action DIRECT_DEBITING         service


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                                              to end
                                              user

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

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

     PendingE  Failed answer or answer                      Idle
               received with result code
               SERVICE DENIED or USER_UNKNOWN,
               requested action
               DIRECT_DEBITING and 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










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                    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,
                                              debit units

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

     Open      CC update request              Send          Open
               received and successfully      CC answer,
               processed                      debit used
                                              units and
                                              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


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                                              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  Stop Tcc,      Idle
               expired                        release
                                              reserved
                                              units

8. Credit Control AVPs

   This section defines the credit-control AVPs that are specific to
   Diameter Credit-control Application and 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], in case the first interrogation is performed
   as part of the authorization / authentication process as described in
   section 4.

   The following table describes the Diameter AVPs defined in Credit-
   control application, their AVP Code values, types, possible flag
   values and whether the AVP MAY be encrypted.























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                                            +---------------------+
                                            |    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  |    |  V  | Y  |
   CC-Input-Octets   412  8.33   Unsigned64 | M  |  P  |    |  V  | Y  |
   CC-Money          413  8.34   Grouped    | M  |  P  |    |  V  | Y  |
   CC-Output-Octets  414  8.35   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  8.36   OctetString| 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  8.37   Unsigned32 | M  |  P  |    |  V  | Y  |
   CC-Total-Octets   421  8.38   Unsigned64 | 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  8.8    UTF8String | M  |  P  |    |  V  | Y  |
   Currency-Code     425  8.11   Unsigned32 | M  |  P  |    |  V  | Y  |
   Credit-Control    426  8.9    Enumerated | M  |  P  |    |  V  | Y  |
   Credit-Control-   427  8.10   Enumerated | M  |  P  |    |  V  | Y  |
     Failure-Handling                       |    |     |    |     |    |
   Direct-Debiting   428  8.12   Enumerated | M  |  P  |    |  V  | Y  |
     Failure-Handling                       |    |     |    |     |    |
   Exponent          429  8.13   Integer32  | M  |  P  |    |  V  | Y  |
   Final-Unit-Action 449  8.14   Enumerated | M  |  P  |    |  V  | Y  |
   Final-Unit-       430  8.15   Grouped    | M  |  P  |    |  V  | Y  |
     Indication                             |    |     |    |     |    |
   Granted-Service-  431  8.16   Grouped    | M  |  P  |    |  V  | Y  |
     Unit                                   |    |     |    |     |    |
   Rating-Group      432  8.39   Unsigned32 | M  |  P  |    |  V  | Y  |
   Redirect-Address  433  8.17   Enumerated | M  |  P  |    |  V  | Y  |
     -Type                                  |    |     |    |     |    |
   Redirect-Server   434  8.18   Grouped    | M  |  P  |    |  V  | Y  |
   Redirect-Server   435  8.19   UTF8String | M  |  P  |    |  V  | Y  |
     -Address                               |    |     |    |     |    |
   Requested-Action  436  8.20   Enumerated | M  |  P  |    |  V  | Y  |
   Requested-Service 437  8.21   Grouped    | M  |  P  |    |  V  | Y  |
     Unit                                   |    |     |    |     |    |
   Restriction       438  8.22   IPFiltrRule| M  |  P  |    |  V  | Y  |
     -Filter-Rule                           |    |     |    |     |    |
   Service-          439  8.40   UTF8String | M  |  P  |    |  V  | Y  |
     Identifier                             |    |     |    |     |    |
   Service-Parameter 440  8.23   Grouped    | -  |  P  |    |  V  | Y  |


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     Info                                   |    |     |    |     |    |
   Service-          441  8.24   Unsigned32 | -  |  P  |    |  V  | Y  |
     Parameter-Type                         |    |     |    |     |    |
   Service-          442  8.25   UTF8String | -  |  P  |    |  V  | Y  |
     Parameter-Value                        |    |     |    |     |    |
   Subscription-Id   443  8.26   Grouped    | M  |  P  |    |  V  | Y  |
   Subscription-Id   444  8.27   UTF8String | M  |  P  |    |  V  | Y  |
      -Data                                 |    |     |    |     |    |
   Subscription-Id   450  8.28   Enumerated | M  |  P  |    |  V  | Y  |
     -Type                                  |    |     |    |     |    |
   Tariff-Change     452  8.42   Enumerated | M  |  P  |    |  V  | Y  |
     -Usage                               |    |     |    |     |    |
   Tariff-Time       451  8.41   Time       | M  |  P  |    |  V  | Y  |
     -Change                                |    |     |    |     |    |
   Unit-Value        445  8.29   Grouped    | M  |  P  |    |  V  | Y  |
   Used-Service-Unit 446  8.30   Grouped    | M  |  P  |    |  V  | Y  |
   Value-Digits      447  8.31   Unsigned64 | M  |  P  |    |  V  | Y  |
   Validity-Time     448  8.32   Unsigned32 | M  |  P  |    |  V  | Y  |

8.1 CC-Correlation-Id AVP

   The CC-Correlation-Id AVP (AVP Code 411) is type of OctetString and
   contains information to correlate credit control requests generated
   for different components of the service, e.g. transport and service
   level.

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 credit control request of type
   INITIAL_REQUEST and EVENT_REQUEST, and set the value to 1 for the
   first UPDATE_REQUEST, 2 for the second, and so on until the value for
   TERMINATION_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 CC-Request messages. The following values
   are defined for the CC-Request-Type AVP:

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


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            session.

         UPDATE_REQUEST              2
            An Update Credit-control 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 Credit-control Termination Request is sent to terminate a
            credit-control session and contains credit control
            information relevant to the existing session.

        EVENT_REQUEST                4
            A Credit Control 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-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 whether the moving of the credit-control message
   stream to a backup server during an ongoing credit-control session is
   supported. In case of 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 AAA server,
   can be used as an address of the backup server. An implementation is
   not required to support the moving of credit control message stream to
   an alternative server, since it requires also moving of 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
     alternative destination in case of communication failure.



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     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 alternative
     destination in case of communication failure. The moving the credit
     control message stream to backup server MAY require that
     information related to the credit control session should be also
     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 no sub-sessions are in
   use, with the exception of a CC-Request whose CC-Request-Type is set
   to TERMINATION_REQUEST. A TERMINATION_REQUEST message with no CC-Sub-
   Session-Id AVP present will signal the termination of all sub-sessions
   for a given Session-Id.

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 is used
   to return the cost information of a service in the Credit-Control-
   Answer command. The included Unit-Value AVP contains the cost estimate
   (always type of money) of the service in case of price enquiry or the
   accumulated cost estimation in the case of credit- control session.


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   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 has the following ABNF grammar:

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

8.8 Cost-Unit AVP

   The Cost-Unit AVP (AVP Code 424) is of type UTF8String and 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 pe rminute). The Cost-
   Unit can be for instance minute, hour, day, kilobytes, megabytes etc.

8.9 Credit-Control AVP

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

   CREDIT_AUTHORIZATION                                     0

     If the AAA server determines the user is a prepaid user, this value
     indicates that 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 AA request sent to perform the first
     interrogation and initiate a new credit-control session.

   RE_AUTHORIZATION                                         1


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     This value indicates to the Diameter AAA server that a credit-
     control session is ongoing for the subscriber and 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 AA request sent to perform the first
     interrogation.

8.10 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 the sending of 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,
   and then either terminate or grant the service should also the
   alternative connection fail.

      TERMINATE                                                0

      When the Credit-Control-Failure-Handling AVP is set to TERMINATE
     the service MUST only be granted 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
     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 case of transport or temporary failures,
         provided that failover procedure is supported in the credit-
         control server and the credit-control client, and 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


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         request to an alternative server in case of transport or
         temporary failures, provided that failover procedure is
         supported in the credit-control server and the credit-control
         client, and an alternative server is available. Otherwise, the
         service SHOULD not be granted when the credit-control messages
         can't be delivered.

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 using
   the numeric values defined in the ISO 4217 standard.

8.12 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 the sending of 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 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 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 to
         application level non-volatile storage and try to re-send the
         request.  These requests MUST be marked as possible duplicate 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.




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8.13 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.

8.14 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 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 5.5.2.

      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 5.5.3).

8.15 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 5.5).

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



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   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
   immediately execute the specified action. 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
   disconnect the end user and close the credit control session.

   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 allowed to access also other zero-rated services 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
   other means than the Diameter Credit Control Application e.g. locally
   configured or configured by another entity.

   The Final-Unit-Indication AVP has the following ABNF grammar:

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

8.16 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 of the unit types, and must treat unknown or unsupported
   unit types in the answer message as an incorrect CCA answer. In that



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   case the client shall terminate credit control session and indicate in
   the Termination-Cause AVP reason DIAMETER_BAD_ANSWER.

  The Service-Identifier and the Rating-Group AVPs are used to associate
  the granted units to a given service or rating group.
   In case both the Service-Identifier and the Rating-Group AVPs are
   included, the target of the granted units is always the service(s)
   indicated by the value of the Service-Identifier AVP.
   A value of 0 (zero) granted service unit associated to a Service-
   entifier(s) or Rating-Group indicates that the corresponding traffic
   MUST be denied. Note that in case the credit-control server want to
   disconnect the user and close the credit-control session, it SHOULD
   use the appropriate error code in the Credit-Control-Answer message
   rather than including n times the Granted-Service-Units AVPs with the
   value of  0 (zero).
   In contrast, a value of max type granted service unit (e.g. max
   Unsigned 32 is FFFFFFFF) associated to a Service-Identifier(s) or
   Rating-Group indicates that the corresponding traffic is free-of-
   charge. With unit type money, the value of the Exponent AVP is set to
   0 (zero) when free-of-charge is indicated. With unit type service
   specific, the value of the CC-Service-Specific-Units AVP is set to
   FFFFFFFF to indicate free-of-charge.

   The Granted-Service-Unit AVP has the following ABNF grammar:

         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 ]
                                 *[ Service-Identifier ]
                                  [ Rating-Group ]

8.17 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 form of IPv4 address, as defined in [RFC
         791].

      IPv6 Address                                       1


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         The address type is in form of IPv6 address, as defined in [RFC
         2373].

      URL                                                2
         The address type is in form of Uniform Resource Locator, as
         defined in [RFC 1738].

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

8.18 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) where 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 has the following ABNF grammar:

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

8.19 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) where the end user is to be connected when the
   account cannot cover the service cost.

8.20 Requested-Action AVP

   The Requested-Action AVP (AVP Code 436) is type of 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

          Direct debiting indicates that the request is to decrease the
          end user's account according to information specified in the
          Requested-Service-Unit AVP and/or Service-Parameter-Info AVP.
          The Granted-Service Unit AVP in the Credit-Control-Answer
          command contains the debited units.

       REFUND_ACCOUNT                               1



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          Refund account indicates that the request is to increase the
          end user's account according to information specified in the
          Requested-Service-Unit AVP and/or Service-Parameter-Info AVP.
          The Granted-Service Unit AVP in the Credit-Control-Answer
          command contains the refunded units.

       CHECK_BALANCE                                2

          Check balance indicates that the request is 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

          Price Enquiry indicates that the request is 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.

8.21 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 of
   the unit types, and must treat unknown or unsupported unit types as
   invalid AVPs.

  The Service-Identifier and the Rating-Group AVPs are used to request
  units for a given service(s) or rating group when the service element
  supports credit control for multiple services in one credit control
  session.

  If both the AVPs are present, the Rating-Group AVP indicates the
  rating group to which the service(s) specified by the Service-
  Identifier(s) belongs. If only the Rating-Group-Id AVP is present,
  this is a credit authorization request for all the services that
  belongs to the specified rating group.

   A server not implementing the Service-Identifier AVP and the Rating-
   Group AVP must treat them as invalid AVPs.

   The Requested-Service-Unit AVP has the following ABNF grammar:

         Requested-Service-Unit ::= < AVP Header: 437 >
                                    [ CC-Time ]
                                    [ CC-Money ]


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                                    [ CC-Total-Octets ]
                                    [ CC-Input-Octets ]
                                    [ CC-Output-Octets ]
                                    [ CC-Service-Specific-Units ]
                                   *[ Service-Identifier ]
                                    [ Rating-Group ]

8.22 Restriction-Filter-Rule AVP

   The Restriction-Filter-Rule AVP (AVP Code 438) is of type IPFilterRule
   and provides filter rules corresponding to zero-rated services offered
   by the home service provider. The access device need 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.

8.23 Service-Parameter-Info AVP

   The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
   contains a 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,
   standards written by other standardization bodies, or service specific
   documentation.

   In case of unknown service request (e.g. unknown Service-Parameter-
   Type), the corresponding answer message MUST contain 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 has the following ABNF grammar:

              Service-Parameter-Info ::= < AVP Header: 440 >
                                         [ Service-Parameter-Type ]
                                         [ Service-Parameter-Value ]

8.24 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 end-user location, service name). The different parameters and
   their types are service specific and the meanings of these parameters
   are not defined in this document. The Service-Parameter-Value AVP
   contains the service parameter type.




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8.25 Service-Parameter-Value AVP

   The Service-Parameter-Value AVP is of type UTF8String (AVP Code 442)
   and contains the value of the service parameter type.

8.26 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 hold the identifier and a
   Subscription-Id-Type AVP that defines the identifier type.

   It has the following ABNF grammar:

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

8.27 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.

8.28 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 that is carried by
   the Subscription-Id AVP. A server is not required to implement all of
   the Subscription-Id-Types, and MUST treat unknown or unsupported
   Subscription-Id-Types as invalid AVP values.

   The identifier can be one of the following:

      END_USER_MSISDN                                              0

           The identifier is in international MSISDN format, according
           to the ITU-T E.164 numbering plan as 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 [E121] and
           [CE121].

       END_USER_SIP_URL                                             2
          The identifier is in the form of a SIP URL as defined in
          [SIP].



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       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.

8.29 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 together 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 exponent part MUST be interpreted as exponent being equal to zero.

   It has the following ABNF grammar:

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

8.30 Used-Service-Unit AVP

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

  The Service-Identifier and the Rating-Group AVPs are used to associate
  the used units to a given service or rating group.
   When granted service units are associated to a service or rating
   group, the credit control client MUST report the corresponding used
   service units. If the granted units are associated to a rating group,
   the units used by each of the Service-Identifier belonging to that
   rating group SHOULD be reported if this information is available to
   the credit control client. Therefore, multiple instances of the Used-
   Service-Unit AVP MAY be present in a request, each associated to the
   relevant Rating-Group-Id and to the identifier of the service (i.e.
   Service-Identifier) that consumed some of the granted units.

   The Used-Service-Unit AVP has the following ABNF grammar:

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


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                               [ CC-Input-Octets ]
                               [ CC-Output-Octets ]
                               [ CC-Service-Specific-Units ]
                              *[ Service-Identifier ]
                               [ Rating-Group ]

8.31 Value-Digits AVP

   The Value-Digits AVP is of type Unsigned64 (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.

8.32 Validity-Time AVP

   The Validity-Time AVP is of type Unsigned32 (AVP code 448) and is sent
   from the credit-control server to the credit-control client. The AVP
   contains the validity time of the granted service units. 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 request 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 5.5) 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. Upon the
   Validity-Time elapses a new intermediate interrogation is sent to the
   server.

8.33 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.

8.34 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 has the following ABNF grammar:

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



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8.35 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.

8.36 CC-Service-Specific-Units AVP

   The CC-Service-Specific-Units AVP (AVP Code 417) is of type
   OctetString, and specifies the number of service specific units (e.g.
   number of events, points) given in a selected service.

8.37 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.

8.38 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).

8.39 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. This is an identifier
   allocated by the home service provider and MUST be unique within the
   home service provider domain.

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

8.40 Service-Identifier AVP

   The Service-Identifier AVP is of type UTF8String (AVP Code 439) and
   contains a unique identifier of a service. 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
   service. The format of the service identifier is:

   "service-identifier" "@" "domain"

   service-identifier = Token
                        The Token is an arbitrary string of characters
                        and digits.

   domain = represents the entity that allocated the service-identifier.



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            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.com) or of the vendor
            (e.g. vendor.com) if the identifier is allocated by a
            private entity.

   Services 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 e.g.
   publication of informational RFC is RECOMMENDED to make Service-
   Identifier globally available.

   A usage example of this AVP for multiple services in one user session
   is illustrated in Appendix A (Flow X).


8.41 Tariff-Time-Change AVP

   The Tariff-Time-Change AVP (AVP code 451) is of type Time, 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 client and server and it
   is not used for unit type time, since the server has full control of
   the time.

   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 that case the client shall terminate credit control
   session and indicate in the Termination-Cause AVP reason
   DIAMETER_BAD_ANSWER.

8.42 Tariff-Change-Usage AVP

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

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

    UNIT_BEFORE_TARIFF_CHANGE                                  0

     The used units contains the amount of the units before tariff
     change, that is units measured from the point when the previous
     measurement ended to the point when tariff change occurred.

    UNIT_AFTER_TARIFF_CHANGE                                   1


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     The used units contains the amount of the units after tariff change
     has been occurred.

    UNIT_INDETERMINATE                                         2

     The used units 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).

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 Failure

   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 MAY be able to satisfy the request in the future.

        DIAMETER_END_USER_SERVICE_DENIED                         4010
        The credit-control server denies the service request due to
        service restrictions or limitations related to the end-user,
        for example the end-user's account could not cover the requested
        service. The possibly reported used-service-units with the CCR
        are deducted.

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

9.2 Permanent Failures

   Errors that fall within 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


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         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, incorrect AVP combination or
         due to 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
         zeroes.

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 are more than
               once 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.

















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                                       +-----------+
                                       |  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-Failover-Supported         | 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 |
         Final-Unit-Indication         | 0   | 0-1 |
         Granted-Service-Unit          | 0   | 0+  |
         Origin-Host                   | 1   | 1   |
         Origin-Realm                  | 1   | 1   |
         Origin-State-Id               | 0-1 | 0-1 |
         Proxy-Info                    | 0+  | 0+  |
         Redirect-Host                 | -   | 0+  |
         Redirect-Host-Usage           | -   | 0-1 |
         Redirect-Max-Cache-Time       | -   | 0û1 |
         Requested-Action              | 0-1 | 0   |
         Requested-Service-Unit        | 0+  | 0   |
         Route-Record                  | 0+  | 0+  |
         Service-Identifier            | 0-1 | 0   |
         Service-Parameter-Info        | 0+  | 0   |
         Session-Id                    | 1   | 1   |
         Subscription-Id               | 0+  | 0+  |
         Termination-Cause             | 0-1 | 0   |
         Used-Service-Unit             | 0+  | 0   |
         User-Name                     | 0-1 | 0-1 |
         Validity-Time                 | 0   | 0-1 |
         ------------------------------|-----+-----+

11. RADIUS/Diameter Credit-control Interworking

   This section defines some basic guidelines to provide the Diameter
   Credit-control/RADIUS inter-working, that is a protocol translation
   between RADIUS [RFC2865] and Diameter Credit-control application. A


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   complete description of all protocol translations between RADIUS and
   Diameter Credit-control application is beyond the scope of this
   document. Note that this document does not restrict implementations
   from creating additional methods; it just provides some guiding
   principles for protocol translation. Translation makes use of RADIUS
   Vendor Specific Attributes (VSAs) for transporting Diameter credit-
   control AVPs.

   The Diameter NASREQ [NASREQ] application defines how a RADIUS Request
   is forwarded as a Diameter Request. Guidelines defined in the Diameter
   NASREQ should be followed to the appropriate extent.

   A protocol translation between RADIUS and Diameter Credit-control
   application is shown in Annex A.

11.1 Initial RADIUS Access-Request

   When an AAA server acting as a Translation Agent receives an initial
   RADIUS Access-Request message indicating that the service element is
   capable of credit-control (e.g. Radius VSA Pre-Paid-Accounting-
   Capability), and if the AAA server determines that the subscriber is a
   prepaid subscriber then a Diameter Credit control request MUST be sent
   towards the credit-control server.

   In addition to those steps defined in [NASREQ] the AAA server should
   perform the following steps related to the protocol translation
   between RADIUS and Diameter Credit-control application:

      - The credit control Session-Id should be included in the Session-
        Id AVP.
      - The CC-Request-Type is set to INITIAL_REQUEST and CC-Request-
        Number value is set to 0.
      - Subscription-Id should be added using User-Name attribute from
        the RADIUS Access-Request message or some AAA server local Id to
        identify user's credit control subscription.
      - If the Access-Request message contains the Event-Timestamp
        attribute it should be included in the Event-Timestamp AVP

   The following steps are applied to response the Access-Request message
   when successful credit-control answer is received from the Credit-
   control server:

      - The AAA server shall generate a RADIUS VSA Quota Id to correlate
        subsequent RADIUS message with the credit-control session.
      - The Termination-Action attribute must be set to be RADIUS-request
        to ensure that the used quota is returned by the service element
        upon termination of the service.
      - If the Granted-Service-Unit AVP including the CC-Time AVP or the
        Validity-Time AVP is returned by the credit control server, then


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        the smallest value should be included in the RADIUS VSA
        Duration-Quota.
      - If the Granted-Service-Unit AVP including the CC-Total-Octets AVP
        is returned by the credit-control server, then the volume should
        be included in the RADIUS VSA Volume-Quota.
      - If separate RADIUS VSA Thresholds (volume or duration) are
        required by RADIUS implementation, the AAA server shall derive
        the threshold values from the Granted-Service-Unit AVPs. The
        threshold should be less than the Duration-Quota or Volume-
        Quota, except when the Final-Unit-Indication AVP is returned by
        the credit control server.

   When credit-control answer message includes the Result-Code, which
   indicates that credit control authorization is rejected, the AAA
   server shall send an Access-Reject message to service element.

11.2 Subsequent RADIUS Access-Request message

   When an AAA server receives a RADIUS Access-Request message containing
   RADIUS VSA Quota Id, it indicates that the Access-Request message is
   subsequent RADIUS Request related to the credit control session. The
   AAA server shall use the Quota Id to identify the credit-control
   session.

   The AAA server's next steps depend on the value of the RADIUS VSA
   Update-Reason. If the Update-Reason indicates æThreshold reached' then
   the AAA server should perform the following steps related to a new
   quota request:

     - The CC-Request-Type is set to UPDATE_REQUEST and CC-Request-Number
       value is increased by one.
     - If the Granted-Service-Unit AVP including the CC-Time AVP or the
       Validity-Time AVP is returned by the credit control server, then
       the smallest value should be included in the RADIUS VSA Duration-
       Quota.
     - If the Granted-Service-Unit AVP including the CC-Total-Octets AVP
       is returned by the credit-control server, then the volume should
       be included in the RADIUS VSA Volume-Quota.

   The reply to the RADIUS Access-Request message shall be handled as
   described in initial Radius Access-Request.

   If the RADIUS VSA Update-Reason indicates that the associated
   resources are released at the service element, then the AAA server
   shall terminate the credit control session by performing the following
   steps:

     - The CC-Request-Type is set to TERMINATION_REQUEST and CC-Request-
       Number value is increased by one.


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     - If the RADIUS VSA Volume-Quota is present, the value shall be
       included in the Used-Service-Unit AVP as CC-Total-Octets.
     - If the RADIUS VSA Time-Quota is present, the value shall be
       included in the Used-Service-Unit AVP as CC-Time.

   After the AAA server receives response to the final credit Control
   Credit-Control-Request the RADIUS Access-Accept message shall be
   return to the service element.

11.3 RADIUS Vendor Specific Attributes for Credit Control

   To provide the credit control for RADIUS implementation the RADIUS
   Vendor Specific Attributes (VSAs) are used for transporting Diameter
   credit-control AVPs. The RADIUS Type 26 (= Vendor-Specific) is used
   for RADIUS VSA.

   RADIUS Inter-working with the Diameter Credit control uses the
   following VSA included with the RADIUS Access Request and Access
   Accept messages:

      - Pre-Paid-Accounting-Capability; defines that the Service element
        in RADIUS implementation is capable of credit-control.
      - Quota Id; generated by the AAA server and it is used to correlate
        subsequent RADIUS message with the credit-control session.
      - Duration-Quota; in RADIUS Access-Request message it indicates the
        used Duration and in RADIUS Access-Accept message it indicates
        the Duration allocated for the service element.
      - Volume-Quota; in RADIUS Access-Request message it indicates the
        used Volume and in RADIUS Access-Accept message it indicates the
        Volume allocated for the service element.
      - Volume-Threshold; If RADIUS implementation requires separate
        threshold attribute for Volume, then Volume-Threshold is sent in
        RADIUS Access-Accept message and it represents the volume (in
        bytes) that shall be used by the service element before
        requesting a new Volume quota.
      - Duration-Threshold; If RADIUS implementation requires separate
        threshold attribute for Duration, then Duration-Threshold is
        sent in RADIUS Access-Accept message and it represents the
        duration (in seconds) that shall be used by the service element
        before requesting a new Duration quota.
      - Update-Reason; in RADIUS Access-Request message it indicates the
        reason for the initiating the quota update operation.

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.



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12.1 Application Identifier

   This specification assigns the value 4 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].

12.3 AVP Codes

   This specification assigns the values 411 - 450 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, 5030 and 5031 from
   the Result-Code AVP (AVP Code 268) 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 (AVP code 416)
   defines the value 1-3. All remaining values are available for
   assignment via Designated Expert [IANA].

12.6 CC-Session-Failover AVP

   As defined in section 8.4, the CC-Failover-Supported AVP (AVP code
   418) defines the value 0-1. All remaining values are available for
   assignment via Designated Expert [IANA].

12.7 Check-Balance-Result AVP

   As defined in Section 8.6, the Check-Balance-Result AVP (AVP Code 422)
   defines the values 0-1. All remaining values are available for
   assignment via Designated Expert [IANA].

12.8 Credit-Control AVP

   As defined in section 8.9, the Credit-Control AVP (AVP code 426)
   defines the value 0-1. All remaining values are available for
   assignment via Designated Expert [IANA].

12.9 Credit-Control-Failure-Handling AVP



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   As defined in Section 8.10, the Credit-Control-Failure-Handling AVP
   (AVP Code 427) defines the values 0-2. All remaining values are
   available for assignment via Designated Expert [IANA].

12.10 Direct-Debiting-Failure-Handling AVP

   As defined in Section 8.12, the Direct-Debiting-Failure-Handling AVP
   (AVP Code 448) defines the values 0-1. All remaining values are
   available for assignment via Designated Expert [IANA].

12.11 Final-Unit-Action AVP

   As defined in Section 8.14, the Final-Unit-Action AVP (AVP Code 449)
   defines the values 0-2. All remaining values are available for
   assignment via Designated Expert [IANA].

12.12 Redirect-Address-Type AVP

   As defined in Section 8.17, the Redirect-Address-Type AVP (AVP Code
   433) defines the values 0-3. All remaining values are available for
   assignment via Designated Expert [IANA].

12.13 Requested-Action AVP

   As defined in Section 8.20, the Requested-Action AVP (AVP Code 436)
   defines the values 0-3. All remaining values are available for
   assignment via Designated Expert [IANA].

12.14 Subscription-Id-Type AVP

   As defined in Section 8.28, the Subscription-Id-Type AVP (AVP Code
   450) defines the values 0-4. All remaining values are available for
   assignment via Designated Expert [IANA].

12.15 Tariff-Change-Usage AVP

   As defined in Section 8.42, the Tariff-Change-Usage AVP (AVP Code 452)
   defines the values 0-2. All remaining values are available for
   assignment via 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 during the
      service is provided to an end user. Due to real-time nature of
      application the communication delays SHOULD be minimized, e.g. to
      avoid too long service set up time experienced by the end user. The


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      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 according to the value
      of the 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. To avoid the credit control
      session in the Diameter credit control server to change to Idle
      state in case of short transient network failure, Tcc MAY be set to
      two times the value of Validity-Time.

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

      Client implementations may offer the possibility to locally
      configure these AVPs. In such a case their value and behavior is
      defined in section 5.6 for the Credit-Control-Failure-Handling and
      in section 6.5 for the Direct-Debiting-Failure-Handling.

14. Security Consideration

   The Diameter base protocol [DIAMBASE] assumes that each Diameter
   implementation uses underlying security, i.e. IPsec or TLS. These
   mechanisms are believed to provide sufficient protection under the
   normal Internet threat model - that is, assuming the authorized nodes
   engaging in the protocol have not been compromised, but the attacker
   has complete control over the communication channels between them.
   This includes eavesdropping, message modification, insertion, man-in-
   the-middle and replay attacks. Note also that this application
   includes a mechanism for application layer replay protection by the
   means of Session-ID from [DIAMBASE], and CC-Request-Number specified
   in this document. The Diameter credit control application is often
   used within one domain and there may be just 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) this kind of application 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 to this, authorization of the client
   shall be emphasized, i.e. that the client is allowed to perform credit
   control for a certain user. The specific means of authorization are


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   outside of the scope of this specification but can be for instance,
   manual configuration.

   Another kind 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 economical 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, because the transactions contain
   private information about the user. Also by monitoring the credit
   control messages one can collect information about 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. Diameter messages, such as CCR and CCA, containing sensitive
   AVPs may be inappropriate in some cases to be sent via untrusted
   Diameter proxy agents since there are no assurance 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 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 re-directs 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 Diameter Credit control Server(s) information
   (Redirect-Host AVP) and information (Redirect-Host-Usage AVP) how to
   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 than
   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
   have attacks towards nodes that have been properly authorized, but
   abuse their authorization or have been compromised. These issues are
   discussed more widely in [DIAMEAP] section 8.


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15. References

15.1 Normative

   [DIAMBASE]  P. Calhoun, J. Loughney, J. Arkko, E. Guttman, G. Zorn.
               "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]       M. Handley, H. Schulzrinne, E. Schooler, J. Rosenberg, G.
               Camarillo, A. Johnston, J. Peterson, R. Sparks
               "SIP: Session Initiation Protocol", RFC 3261. June 2002.

   [NAI]       Aboba, 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, Alvestrand, "Guidelines for Writing an IANA
               Considerations Section in RFCs", BCP 26, RFC 2434, October
               1998

15.2 Non-Normative

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

   [ACCMGMT]   B. Aboba, J.Arkko, D.Harrington. "Introduction to
               Accounting Management", RFC 2975, October 2000.

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



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                   Diameter Credit Control Application     December 2003


   [NASREQ]    P. Calhoun, G. Zorn, D. Spence, D. Mitton. "Diameter
               NASREQ Application", IETF work in progress.

   [DIAMMIP]   P. Calhoun, T. Johansson, C. Perkins "Diameter Mobile IP
               Application", IETF work in progress.

   [RFC2865]   C. Rigney, S. Willens, A. Rubens, W. Simpson. "Remote
               Authentication Dial In User Service (RADIUS), RFC 2865,
               June 2000

   [DIAMEAP]   P. Eronen, T. Hiller, G. Zorn. "Diameter Extensible
               Authentication Protocol (EAP) Application", IETF work in
               progress.

16. Acknowledgement

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

17. Author's Address

   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


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                   Diameter Credit Control Application     December 2003


   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

18. Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published and
   distributed, in whole or in part, without restriction of any kind,
   provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of developing
   Internet standards in which case the procedures for copyrights defined
   in the Internet Standards process must be followed, or as required to
   translate it into languages other than English. The limited
   permissions granted above are perpetual and will not be revoked by the
   Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
   NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
   WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

19. Notices

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to pertain
   to the implementation or use of the technology described in this
   document or the extent to which any license under such rights might or
   might not be available; neither does it represent that it has made any
   effort to identify any such rights.  Information on the IETF's


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                   Diameter Credit Control Application     December 2003


   procedures with respect to rights in standards-track and standards-
   related documentation can be found in BCP-11.  Copies of claims of
   rights made available for publication and any assurances of licenses
   to be made available, or the result of an attempt made to obtain a
   general license or permission for the use of such proprietary rights
   by implementors or users of this specification can be obtained from
   the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights, which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

20. Expiration Date

   This memo is filed as <draft-ietf-aaa-diameter-cc-02.txt> and expires
   in June 2004.

Appendix A Credit Control sequences

A.1  Flow I

   End-User              NAS             AAA Server           CC Server
                     (CC Client)
      |(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  |                    |
      |                   |<-------------------|                    |


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      :                   :                    :                    :
      :                   :                    :                    :
      |(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 onto the network (1). The Diameter NAS first sends a
   Diameter Authorization-Authentication-Request to the home 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 AAA server performs service
   specific Authentication and Authorization as usual. The 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 AAA server may forward service specific AVPs as 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 AAA server in the Diameter Credit-Control-Answer
   (4). The Home AAA server sends the reserved quota to the NAS in the
   Diameter Authorization-Authentication-Answer. Upon successful AAA the
   NAS starts the credit-control session and starts monitoring the
   granted units (5). The NAS grant 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 AAA server (7). This message contains the units used this far.
   The 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 AAA server in the Diameter Credit-Control-Answer (9). The
   message is forwarded to the NAS (10). During the ongoing credit-


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   control session the authorization-lifetime expires, the
   authorization/authentication client in the NAS performs service
   specific re-authorization to the Home AAA server as usual. The
   credit-control client populate the AAR with the Credit-Control AVP
   set to RE_AUTHORIZATION indicating that the credit-control server
   shall not be contacted, since the credit authorization is controlled
   by the burning rate of the granted units (11). The Home AAA server
   performs service specific re-authorization as usual and returns the
   Authorization-Authentication-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 AAA server (14). The 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 AAA server (16). The AAA
   server forwards the answer to the NAS (17). STR/STA take place
   between NAS and Home AAA server as usual (18-19).

A.2  Flow II


                                 AAA Server
            NAS                  (CC Client)             CC Server
             |(1)  Access-Request     |                        |
             |----------------------->|                        |
             |                        |(2) CCR (initial)       |
             |                        |----------------------->|
             |                        |(3) CCA (granted_Units) |
             |                        |<-----------------------|
             |(4)  Access-Accept      |                        |
             |     (granted Units)    |                        |
             |<-----------------------|                        |
             :                        :                        :
             |(5)  Access-Request     |                        |
             |     (used Units)       |                        |
             |----------------------->|                        |
             |                        |(6) CCR (update,        |
             |                        |         used Units,    |
             |                        |----------------------->|
             |                        |(7) CCA (granted_Units) |
             |                        |<-----------------------|
             |(8)  Access-Accept      |                        |
             |     (granted Units)    |                        |
             |<-----------------------|                        |
             :                        :                        :
             |(9)  Access-Request     |                        |
             |----------------------->|                        |
             |                        |(10) CCR (termin.,      |


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             |                        |          used Units)   |
             |                        |----------------------->|
             |                        |(11) CCA                |
             |                        |<-----------------------|
             |(12) Access-Accept      |                        |
             |<-----------------------|                        |
             |                        |                        |

                            Figure A.2: Flow II

   A credit control flow for RADIUS prepaid - Diameter credit control
   interworking is shown in Figure A.2. The focus of this flow is in the
   AAA Server (Diameter credit-control client) and Diameter credit-
   control server interworking.

   The NAS first sends a RADIUS Access-Request to the home AAA Server
   (1). The home AAA server performs regular Authentication and
   Authorization. When the AAA server notices that the user is a prepaid
   user 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 (2) and to establish a credit control
   session. 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 (3). The Home AAA server sends
   the reserved quota to the NAS in the RADIUS Access-Accept (4). At the
   expiry of the allocated quota, the NAS sends a new RADIUS Access-
   Request to the Home AAA server (5). This message contains the units
   used this far. The units are reported to the Diameter credit-control
   server in a Diameter Credit-Control-Request (UPDATE_REQUEST) (6). 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 (7). The quota is
   transferred to the NAS in the RADIUS Access-Accept (8). When the end
   user terminates the service the NAS sends a RADIUS Access-Request (9).
   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
   (10). The Diameter credit-control server acknowledges the session
   termination by sending a Diameter Credit-Control-Answer to the Home
   AAA server (11). The RADIUS Access-Accept is sent to the NAS (12).

A.3  Flow III

              SIP Proxy/Registrar   AAA
        A           (CC Client)     Server           B        CC Server
        |(i)  REGISTER |              |              |              |
        |------------->|(ii)          |              |              |
        |              |------------->|              |              |


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        |              |authentication &             |              |
        |              |authorization |              |              |
        |              |<-------------|              |              |
        |(iii)200 OK   |                             |              |
        |<-------------|                             |              |
        :              :                             :              :
        |(1)  INVITE   |                                            :
        |------------->|
        |              |(2)  CCR (Intial, 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.3: Flow III

   The end user (SIP User Agent A) sends REGISTER with credentials (i).
   The SIP Proxy sends a request to the AAA server to perform Multimedia
   authentication and authorization by using for instance Diameter
   Multimedia application (ii). The 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), of several SIP sessions may
   be established without re-authorization is performed.

   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


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   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 this 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.4  Flow IV

                          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.4: Flow IV

   A credit control flow for Multimedia Messaging Services is shown in
   Figure A.4. 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


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   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 the
   end user B retrieves the message from the MMS message store (6),(7).

A.5  Flow V

                          MMS Server
      Content Server     (CC Client)           B           CC Server
             |(1) Send MMS    |                |                |
             |--------------->|                |                |
             |                |(2)  CCR (event, BALANCE_CHECK,  |
             |                |          MMS specific AVP)      |
             |                |-------------------------------->|
             |                |(3)  CCA (OK)                    |
             |                |<--------------------------------|
             |(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.5: Flow V

   A credit control flow for Multimedia Messaging Service is shown in
   Figure A.5. 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. Since there can be substantially long
   time between the reception of the message at the MMS Server and the
   actual retrieval of the message, the MMS Server does not establish any


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   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: BALANCE_CHECK) to verify that the end user B's 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 about the new MMS (5), and after some
   time the 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 the end
   user B (9).

A.6  Flow VI

                        SIP Controller
             A           (CC Client)           B           CC Server
             |(1)INVITE(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.6: Flow VI

   Figure A.6 is an example of Advice of Charge (AoC) service for SIP
   call, the user A can be either 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


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   the SDP and a button to accetp/not accept the charges (there may be
   many other ways to deliver AoC information, however, this flow focus
   on the use of the credit control messages). The user has been
   authenticated and authorized prior to initiate the call and subscribed
   to AoC service.

   UA A sends an INVITE with SDP (1). The SIP controller determines the
   user is subscribed to AoC service and sends a Diameter Credit-Conrol-
   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 sends a SIP MESSAGE that contains a URL pointing
   to the AoC information web page (4). At the reception of the SIP
   MESSAGE the A's UA invokes automatically the web browser that
   retrieves the AoC information (5). The user clicks on a proper button
   and accept the charges (6). The SIP controller continues the session
   and sends the INVITE to the B party that accepts the call (7,8,9).

A.7  Flow VII

                           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.7: Flow VII

   Figure A.7 illustrates a credit control flow for the REFUND case. It
   is assumed that trusted relationship and secure connection between the
   Gaming server and the Diameter credit control server exist. 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 for a bonus. The Gaming server sends a Diameter Credit-


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   Conrol-Request (EVENT_REQUEST with Requested-Action: REFUND) to the
   Diameter credit control server (2). The Credit-Control-Request
   contains the Requested-Service-Unit AVP with Unit-Type set to
   CREDIT_TYPE_SERVICE_SPECIFIC and Unit-Value set to 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). The Diameter credit control server, based on
   received information, 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 notify the end user
   of the credited amount (4).


A.8  Flow VIII

                  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.8: Flow VIII

   Figure A.8 is an example of the graceful service termination for a SIP
   call. It is assumed the call is set up so that the controller is in
   the call as a B2BUA (Back to Back User Agent). Note that the SIP


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   signaling is inaccurate since the focus of this flow is in the
   graceful service termination and credit control authorization.

   The call is ongoing between user A and user B, user A is a prepaid
   user. 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 this
   far. The Diameter credit control server debits the used units from the
   end user's account and allocates the final quota that is 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 this 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, that
   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 and thus sends a
   spontaneous Credit-Control-Request (UPDATE_REQUEST) to the Diameter
   credit control server to check if the account has been replenished
   (9). The Diameter credit control server reserves credit from the end
   user's account and return 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.9  Flow IX

 End-User              NAS             AAA Server    Top-up   CC Server
                     (CC Client)                       Server
      |(1)User Logon      |(2)AA Request (CC AVPs)        |         |
      |------------------>|------------------->|          |         |
      |                   |                    |(3)CCR(initial, CC AVPs)
      |                   |                    |------------------->|
      |                   |                    |(4)CCA(Final-Unit,  |
      |                   |                    |      Validity-Time)|
      |                   |                    |<-------------------|


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      |                   |(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.9: Flow IX

   Figure A.9 is an example of the graceful service termination initiated
   when the first interrogation take place due to 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 onto the network (1). The Diameter NAS first sends a
   Diameter Authorization-Authentication-Request to the home 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 AAA server performs service specific
   Authentication and Authorization as usual. The 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 AAA server may forward
   service specific AVPs as 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 sevice and initiates the graceful service termination. The Credit-
   Control-Answer is returned to the Home AAA server (4). This message
   contains the Final-Unit-Indication AVP and the Validity-Time AVP set
   to a reasonable time to give chance to the user to replenish his/her
   account (e.g. 10 minutes). The Final-Unit-Indication AVP includes: the
   Final-Unit-Actioin set to REDIRECT, the Redirect-Address-Type set to
   ULR and the Redirect-Server-Address set to the HTTP Top-up server


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   name. The Home AAA server sends the received credit control AVPs to
   the NAS in the Diameter Authorization-Authentication-Answer (5). Upon
   successful AAA the NAS starts the credit-control session and starts
   immediately the graceful service termination as instructed by the
   server. The NAS grant limited access to the user (6). The HTTP client
   software running in the user's device opens the transport connection
   that is redirected by the NAS to the Top-up server (7,8). The user is
   displayed an appropriate web page where to enter the credit card
   number, the amount of money to be used to replenish the account and
   with a notification message that she will be granted unlimited access
   if the replenishment operation will be successfully executed within
   the next e.g. 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 return the reserved quota to the NAS via the Home 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.10 Flow X

   The Diameter Credit Control Application defines the Rating-Group and
   Service-Identifier AVPs that can be used to support credit control for
   multiple services in a single credit control session for service
   elements that have such capabilities. The flow example hereafter
   illustrates the usage of these AVPs.

   It is assumed that the Service-Identifiers and the Rating-Groups are
   locally configured in the Service Element or provisioned by another
   entity than the credit control server.

   The credit control client may request credit authorization either for
   all the possible configured Rating-Groups in one single request,
   onwards named all-in-one mode, or for a single Rating-Group upon an
   external triggering event, onwards named on-demand mode. The on-demand
   mode can be used as well to request individual credit resource limit
   for each service.

   In this example only the all-in-one mode is shown.

   A single credit reservation is kept for the credit control session to
   simplify the account management tasks. The credit control server


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   reserves an amount of credit from the user's account and performs
   rating for all the requested Rating-Groups and Service-Identifiers
   against the reserved credit.

   For instance, assume a Credit-Control-Request is received with Rating-
   Group-Id 1 and 2. The credit control server queries the rating server
   that answers with the following rating parameters: Rating-Group 1
   costs $1/Mbyte and Rating-Group 2 costs $1/minute. The credit control
   server reserves $20 from the user's account; this gives 20Mbytes for
   Rating-Group 1 and 20minutes for Rating-Group 2.

   The calculated quotas are conveyed to the credit control client in the
   CCA message, each quota associated with the appropriate Rating-Group
   or Service-Identifier. At this point the credit control client just
   need to track the fraction of reserved credit used by the
   corresponding service or Rating-Group, when the sum of the fractions
   reaches 100% the credit control client sends an intermediate
   interrogation since the whole amount of reserved credit is consumed.

   If the credit control client initializes a counter C for each of the
   received quota Q (C1 for Q1, C2 for Q2 ... Cn for Qn), the
   intermediate interrogation will be sent when (C1/Q1 + C1/Q2 + ... +
   Cn/Qn)>= 1.

   Continuing the example, the end user uses 10 Mbytes from Rating-Group
   1 and 10minutes from Rating-Group 2. This means that Rating-Group 1
   consumed 50% of the reservation and Rating-Group 2 consumed the
   remaining 50%. 0.5 + 0.5 >=1, so the credit control client sends an
   intermediate interrogation to report the used units and request new
   ones.





















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                   Service Element
   End-User         (CC client)                                 CC Server
    |(1)User logon      |                                         |
    |------------------>|(2)CCR(initial,Requested-Units(Rating-Group 1),
    |                   |        Requested-Units(Rating-Group 2)) |
    |                   |---------------------------------------->|
    |                   |(3)CCA(Granted-Units(Rating-Group 1,     |
    |                   |                     Total-Octets))      |
    |                   |       Granted-Units(Rating-Group 2,     |
    |                   |                     Time))              |
    |                   |<----------------------------------------|
    :                   :                                         :
    |(4)Service-Request (Service 1)                               |
    |------------------>|                                         |
    :                   :                                         :
    |(5)Service-Request (Service 2)                               |
    |------------------>|                                         |
    :                   :                                         :
    |                   |(6)CCR(update, Used-Units(Input-Octets,  |
    |                   |                          Output-Octets, |
    |                   |                          Service-Id 1,  |
    |                   |                          Rating-Group 1),
    |                   |               Used-Units(Time,          |
    |                   |                          Service-Id 2,  |
    |                   |                          Rating-Group 2),
    |                   |               Requested-Units(Rating-G.1),
    |                   |               Requested-Units(Rating-G.2))
    |                   |---------------------------------------->|
    |                   |(7)CCA(Granted-Units(Rating-Group 1,     |
    |                   |                     Total-Octets),      |
    |                   |       Granted-Units(Rating-Group 2,     |
    |                   |                      Time))             |
    |                   |<----------------------------------------|
    :                   :                                         :
    |(8)Service-Request (Service 3)                               |
    |------------------>|                                         |
    :                   :                                         :
    |(9) User logoff    |                                         |
    |------------------>|(10)CCR(term, Used-Units(Input-Octets,   |
    |                   |                         Output-Octets,  |
    |                   |                         Service-Id 1,   |
    |                   |                         Rating-Group 1),|
    |                   |              Used-Units(Input-Octets,   |
    |                   |                         Output-Octets,  |
    |                   |                         Service-Id 3,   |
    |                   |                         Rating-Group 1),|
    |                   |              Used-Units(Time,           |
    |                   |                         Service-Id 2,   |
    |                   |                         Rating-Group 2),|


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                   Diameter Credit Control Application     December 2003


    |                   |---------------------------------------->|
    |                   |(11)CCA(term)                            |
    |                   |<----------------------------------------|

     Figure A.10: Credit Control for Multiple Services in One Credit
                    Control Session, flow example

   The user logs onto 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 multiple rating groups and to establish a
   credit control session (2). In this message credit authorization is
   requested for Rating-Group 1 and Rating-Group 2 by including two
   instances of the Requested-Service-Unit AVP. The Diameter credit-
   control server checks the end user's account balance, based on the
   Rating-Group information rates the request and reserves credit from
   the end user's account. Multiple quotas are returned to the Service
   Element, each associated with the relevant Rating-Group (3). The user
   uses service 1 and service 2 (4, 5). The service 1 belongs to Rating-
   Group 1 and is volume based charged, the service 2 belongs to Rating-
   Group 2 and is time based charged. When the user has consumed the
   allotted credit, the Service Element sends a Diameter Credit-Control-
   Request with CC-Request-Type set to UPDATE_REQUEST to the credit
   control server (6). This message contains the units consumed by each
   of the used services in the Used-Service-Unit AVPs and two instances
   of the Requested-Service-Unit AVP to request credit re-authorization
   for the two Rating-Groups. The used units are associated with the
   relevant Service-Identifier and Rating-Group.

   The Diameter credit-control server debits the used units from the end
   user's account and reserves a new amount of credit that is returned in
   form of multiple quotas to the Service Element in the Diameter Credit-
   Control-Answer (7). Each quota is associated with the relevant Rating-
   Group. In addition to service 1 and service 2, the user now starts
   using service 3 (8). Service 3 belongs to Rating-Group 1 and is
   charged based on volume. The end user logs off from the network (9).
   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 (10).

   This message contains the units consumed by each of the used services
   in the Used-Service-Unit AVPs. 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 and
   acknowledges the session termination by sending a Diameter Credit-
   Control-Answer to the Service Element (11).




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