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rfc:rfc4006

Network Working Group H. Hakala Request for Comments: 4006 L. Mattila Category: Standards Track Ericsson

                                                         J-P. Koskinen
                                                              M. Stura
                                                           J. Loughney
                                                                 Nokia
                                                           August 2005
               Diameter Credit-Control Application

Status of This Memo

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

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

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

Table of Contents

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

Hakala, et al. Standards Track [Page 1] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 2] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 3] RFC 4006 Diameter Credit-Control Application August 2005

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

1. Introduction

 This document specifies a Diameter application that can be used to
 implement real-time credit-control for a variety of end user services
 such as network access, Session Initiation Protocol (SIP) services,
 messaging services, and download services.  It provides a general
 solution to real-time cost and credit-control.
 The prepaid model has been shown to be very successful, for instance,
 in GSM networks, where network operators offering prepaid services
 have experienced a substantial growth of their customer base and
 revenues.  Prepaid services are now cropping up in many other
 wireless and wire line based networks.
 In next generation wireless networks, additional functionality is
 required beyond that specified in the Diameter base protocol.  For
 example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
 that an application must be able to rate service information in
 real-time.  In addition, it is necessary to check that the end user's
 account provides coverage for the requested service prior to
 initiation of that service.  When an account is exhausted or expired,
 the user must be denied the ability to compile additional chargeable
 events.
 A mechanism has to be provided to allow the user to be informed of
 the charges to be levied for a requested service.  In addition, there
 are services such as gaming and advertising that may credit as well
 as debit a user account.
 The other Diameter applications provide service specific
 authorization, and they do not provide credit authorization for
 prepaid users.  The credit authorization shall be generic and
 applicable to all the service environments required to support
 prepaid services.

Hakala, et al. Standards Track [Page 4] RFC 4006 Diameter Credit-Control Application August 2005

 To fulfill these requirements, it is necessary to facilitate credit-
 control communication between the network element providing the
 service (e.g., Network Access Server, SIP Proxy, and Application
 Server) and a credit-control server.
 The scope of this specification is the credit authorization.  Service
 specific authorization and authentication is out of the scope.

1.1. Requirements Language

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

1.2. Terminology

 AAA
 Authentication, Authorization, and Accounting
 AA answer
 AA answer generically refers to a service specific authorization and
 authentication answer.  AA answer commands are defined in service
 specific authorization applications, e.g., [NASREQ] and [DIAMMIP].
 AA request
 AA request generically refers to a service specific authorization and
 authentication request.  AA request commands are defined in service
 specific authorization applications e.g., [NASREQ] and [DIAMMIP].
 Credit-control
 Credit-control is a mechanism that directly interacts in real-time
 with an account and controls or monitors the charges related to the
 service usage.  Credit-control is a process of checking whether
 credit is available, credit-reservation, deduction of credit from the
 end user account when service is completed and refunding of reserved
 credit that is not used.
 Diameter Credit-control Server
 A Diameter credit-control server acts as a prepaid server, performing
 real-time rating and credit-control.  It is located in the home
 domain and is accessed by service elements or Diameter AAA servers in

Hakala, et al. Standards Track [Page 5] RFC 4006 Diameter Credit-Control Application August 2005

 real-time for purpose of price determination and credit-control
 before the service event is delivered to the end-user.  It may also
 interact with business support systems.
 Diameter Credit-control Client
 A Diameter credit-control client is an entity that interacts with a
 credit-control server.  It monitors the usage of the granted quota
 according to instructions returned by credit-control server.
 Interrogation
 The Diameter credit-control client uses interrogation to initiate a
 session based credit-control process.  During the credit-control
 process, it is used to report the used quota and request a new one.
 An interrogation maps to a request/answer transaction.
 One-time event
 Basically, a request/answer transaction of type event.
 Rating
 The act of determining the cost of the service event.
 Service
 A type of task performed by a service element for an end user.
 Service Element
 A network element that provides a service to the end users.  The
 Service Element may include the Diameter credit-control client, or
 another entity (e.g., RADIUS AAA server) that can act as a Credit-
 control client on behalf of the Service Element.  In the latter case,
 the interface between the Service Element and the Diameter credit-
 control client is outside the scope of this specification.  Examples
 of the Service Elements include Network Access Server (NAS), SIP
 Proxy, and Application Servers such as messaging server, content
 server, and gaming server.
 Service Event
 An event relating to a service provided to the end user.

Hakala, et al. Standards Track [Page 6] RFC 4006 Diameter Credit-Control Application August 2005

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

1.3. Advertising Application Support

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

2. Architecture Models

 The current accounting models specified in the Radius Accounting
 [RFC2866] and Diameter base [DIAMBASE] are not sufficient for real-
 time credit-control, where credit-worthiness is to be determined
 prior to service initiation.  Also, the existing Diameter
 authorization applications, [NASREQ] and [DIAMMIP], only provide
 service authorization, but do not provide credit authorization for
 prepaid users.  In order to support real-time credit-control, a new
 type of server is needed in the AAA infrastructure: Diameter credit-
 control server.  The Diameter credit-control server is the entity
 responsible for credit authorization for prepaid subscribers.
 A service element may authenticate and authorize the end user with
 the AAA server by using AAA protocols; e.g., RADIUS or a Diameter
 base protocol with a possible Diameter application.
 Accounting protocols such as RADIUS accounting and the Diameter base
 accounting protocol can be used to provide accounting data to the
 accounting server after service is initiated, and to provide possible
 interim reports until service completion.  However, for real-time
 credit-control, these authorization and accounting models are not
 sufficient.
 When real-time credit-control is required, the credit-control client
 contacts the credit-control server with information about a possible
 service event.  The credit-control process is performed to determine
 potential charges and to verify whether the end user's account
 balance is sufficient to cover the cost of the service being
 rendered.

Hakala, et al. Standards Track [Page 7] RFC 4006 Diameter Credit-Control Application August 2005

 Figure 1 illustrates the typical credit-control architecture, which
 consists of a Service Element with an embedded Diameter credit-
 control client, a Diameter credit-control server, and an AAA server.
 A Business Support System is usually deployed; it includes at least
 the billing functionality.  The credit-control server and AAA server
 in this architecture model are logical entities.  The real
 configuration can combine them into a single host.  The credit-
 control protocol is the Diameter base protocol with the Diameter
 credit-control application.
 When an end user requests services such as SIP or messaging, the
 request is typically forwarded to a service element (e.g., SIP Proxy)
 in the user's home domain.  In some cases it might be possible that
 the service element in the visited domain can offer services to the
 end user; however, a commercial agreement must exist between the
 visited domain and the home domain.  Network access is an example of
 a service offered in the visited domain where the NAS, through an AAA
 infrastructure, authenticates and authorizes the user with the user's
 home network.
                 Service Element   AAA and CC
 +----------+      +---------+     Protocols+-----------+  +--------+
 |  End     |<---->|+-------+|<------------>|    AAA    |  |Business|
 |  User    |   +->|| CC    ||              |   Server  |->|Support |
 |          |   |  || Client||<-----+       |           |  |System  |
 +----------+   |  |+-------+|      |       +-----------+  |        |
                |  +---------+      |             ^        +--------+
 +----------+   |                   | CC Protocol |             ^
 |  End     |<--+                   |       +-----v----+        |
 |  User    |                       +------>|Credit-   |        |
 +----------+                Credit-Control |Control   |--------+
                             Protocol       |Server    |
                                            +----------+
            Figure 1: Typical credit-control architecture
 There can be multiple credit-control servers in the system for
 redundancy and load balancing.  The system can also contain separate
 rating server(s), and accounts can be located in a centralized
 database.  To ensure that the end user's account is not debited or
 credited multiple times for the same service event, only one place in
 the credit-control system should perform duplicate detection.  System
 internal interfaces can exist to relay messages between servers and
 an account manager.  However, the detailed architecture of the
 credit-control system and its interfaces are implementation specific
 and are out of scope of this specification.

Hakala, et al. Standards Track [Page 8] RFC 4006 Diameter Credit-Control Application August 2005

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

3. Credit-Control Messages

 This section defines new Diameter message Command-Code values that
 MUST be supported by all Diameter implementations that conform to
 this specification.  The Command Codes are as follows:
 Command-Name                  Abbrev.    Code     Reference
 -----------------------------------------------------------
 Credit-Control-Request        CCR        272      3.1
 Credit-Control-Answer         CCA        272      3.2
 Diameter Base [DIAMBASE] defines in the section 3.2 the Command Code
 ABNF specification.  These formats are observed in Credit-Control
 messages.

3.1. Credit-Control-Request (CCR) Command

 The Credit-Control-Request message (CCR) is indicated by the
 command-code field being set to 272 and the 'R' bit being set in the
 Command Flags field.  It is used between the Diameter credit-control
 client and the credit-control server to request credit authorization
 for a given service.
 The Auth-Application-Id MUST be set to the value 4, indicating the
 Diameter credit-control application.

Hakala, et al. Standards Track [Page 9] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 10] RFC 4006 Diameter Credit-Control Application August 2005

3.2. Credit-Control-Answer (CCA) Command

 The Credit-Control-Answer message (CCA) is indicated by the command-
 code field being set to 272 and the 'R' bit being cleared in the
 Command Flags field.  It is used between the credit-control server
 and the Diameter credit-control client to acknowledge a Credit-
 Control-Request command.
 Message Format
    <Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
                                < Session-Id >
                                { Result-Code }
                                { Origin-Host }
                                { Origin-Realm }
                                { Auth-Application-Id }
                                { CC-Request-Type }
                                { CC-Request-Number }
                                [ User-Name ]
                                [ CC-Session-Failover ]
                                [ CC-Sub-Session-Id ]
                                [ Acct-Multi-Session-Id ]
                                [ Origin-State-Id ]
                                [ Event-Timestamp ]
                                [ Granted-Service-Unit ]
                               *[ Multiple-Services-Credit-Control ]
                                [ Cost-Information]
                                [ Final-Unit-Indication ]
                                [ Check-Balance-Result ]
                                [ Credit-Control-Failure-Handling ]
                                [ Direct-Debiting-Failure-Handling ]
                                [ Validity-Time]
                               *[ Redirect-Host]
                                [ Redirect-Host-Usage ]
                                [ Redirect-Max-Cache-Time ]
                               *[ Proxy-Info ]
                               *[ Route-Record ]
                               *[ Failed-AVP ]
                               *[ AVP ]

4. Credit-Control Application Overview

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

Hakala, et al. Standards Track [Page 11] RFC 4006 Diameter Credit-Control Application August 2005

 authorization with direct debiting.  In both models, the credit-
 control client requests credit authorization from the credit-control
 server prior to allowing any service to be delivered to the end user.
 In the first model, the credit-control server rates the request,
 reserves a suitable amount of money from the user's account, and
 returns the corresponding amount of credit resources.  Note that
 credit resources may not imply actual monetary credit; credit
 resources may be granted to the credit control client in the form of
 units (e.g., data volume or time) to be metered.
 Upon receipt of a successful credit authorization answer with a
 certain amount of credit resources, the credit-control client allows
 service delivery to the end user and starts monitoring the usage of
 the granted resources.  When the credit resources granted to the user
 have been consumed or the service has been successfully delivered or
 terminated, the credit-control client reports back to the server the
 used amount.  The credit-control server deducts the used amount from
 the end user's account; it may perform rating and make a new credit
 reservation if the service delivery is continuing.  This process is
 accomplished with session based credit-control that includes the
 first interrogation, possible intermediate interrogations, and the
 final interrogation.  For session based credit-control, both the
 credit control client and the credit-control server are required to
 maintain credit-control session state.  Session based credit-control
 is described in more detail, with more variations, in section 5.
 In contrast, credit authorization with direct debiting is a single
 transaction process wherein the credit-control server directly
 deducts a suitable amount of money from the user's account as soon as
 the credit authorization request is received.  Upon receipt of a
 successful credit authorization answer, the credit-control client
 allows service delivery to the end user.  This process is
 accomplished with the one-time event.  Session state is not
 maintained.
 In a multi-service environment, an end user can issue an additional
 service request (e.g., data service) during an ongoing service (e.g.,
 voice call) toward the same account.  Alternatively, during an active
 multimedia session, an additional media type is added to the session,
 causing a new simultaneous request toward same account.
 Consequently, this needs to be considered when credit resources are
 granted to the services.
 The credit-control application also supports operations such as
 service price enquiry, user's balance check, and refund of credit on
 the user's account.  These operations are accomplished with the one-
 time event.  Session state is not maintained.

Hakala, et al. Standards Track [Page 12] RFC 4006 Diameter Credit-Control Application August 2005

 A flexible credit-control application specific failure handling is
 defined in which the home service provider can model the credit-
 control client behavior according to its own credit risk management
 policy.
 The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
 Failure-Handling AVP are defined to determine what is done if the
 sending of credit-control messages to the credit-control server has
 been temporarily prevented.  The usage of the Credit-Control-
 Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP
 allows flexibility, as failure handling for the credit-control
 session and one time event direct debiting may be different.

4.1. Service-Specific Rating Input and Interoperability

 The Diameter credit-control application defines the framework for
 credit-control; it provides generic credit-control mechanisms
 supporting multiple service applications.  The credit-control
 application, therefore, does not define AVPs that could be used as
 input in the rating process.  Listing the possible services that
 could use this Diameter application is out of scope for this generic
 mechanism.
 It is reasonable to expect that a service level agreement will exist
 between providers of the credit-control client and the credit-control
 server covering the charging, services offered, roaming agreements,
 agreed rating input (i.e., AVPs), and so on.
 Therefore, it is assumed that a Diameter credit-control server will
 provide service only for Diameter credit-control clients that have
 agreed beforehand as to the content of credit-control messages.
 Naturally, it is possible that any arbitrary Diameter credit-control
 client can interchange credit-control messages with any Diameter
 credit-control server, but with a higher likelihood that unsupported
 services/AVPs could be present in the credit-control message, causing
 the server to reject the request with an appropriate result-code.

4.1.1. Specifying Rating Input AVPs

 There are two ways to provide rating input to the credit-control
 server: either by using AVPs or by including them in the Service-
 Parameter-Info AVP.  The general principles for sending rating
 parameters are as follows:
 1a. The service SHOULD re-use existing AVPs if it can use AVPs
 defined in existing Diameter applications (e.g., NASREQ for network
 access services).  Re-use of existing AVPs is strongly recommended in
 [DIAMBASE].

Hakala, et al. Standards Track [Page 13] RFC 4006 Diameter Credit-Control Application August 2005

 For AVPs of type Enumerated, the service may require a new value to
 be defined.  Allocation of new AVP values is done as specified in
 [DIAMBASE], section 1.2.
 1b. New AVPs can be defined if the existing AVPs do not provide
 sufficient rating information.  In this case, the procedures defined
 in [DIAMBASE] for creating new AVPs MUST be followed.
 1c. For services specific only to one vendor's implementation, a
 Vendor-Specific AVP code for Private use can be used.  Where a
 Vendor-Specific AVP is implemented by more than one vendor,
 allocation of global AVPs is encouraged instead; refer to [DIAMBASE].
 2. The Service-Parameter-Info AVP MAY be used as a container to pass
 legacy rating information in its original encoded form (e.g., ASN.1
 BER).  This method can be used to avoid unnecessary conversions from
 an existing data format to an AVP format.  In this case, the rating
 input is embedded in the Service-Parameter-Info AVP as defined in
 section 8.43.
 New service applications SHOULD favor the use of explicitly defined
 AVPs as described in items 1a and 1b, to simplify interoperability.

4.1.2. Service-Specific Documentation

 The service specific rating input AVPs, the contents of the Service-
 Parameter-Info AVP or Service-Context-Id AVP (defined in section
 8.42) are not within the scope of this document.  To facilitate
 interoperability, it is RECOMMENDED that the rating input and the
 values of the Service-Context-Id be coordinated via an informational
 RFC or other permanent and readily available reference.  The
 specification of another cooperative standardization body (e.g.,
 3GPP, OMA, and 3GPP2) SHOULD be used.  However, private services may
 be deployed that are subject to agreements between providers of the
 credit-control server and client.  In this case, vendor specific AVPs
 can be used.
 This specification, together with the above service specific
 documents, governs the credit-control message.  Service specific
 documents define which existing AVPs or new AVPs are used as input to
 the rating process (i.e., those that do not define new credit-control
 applications), and thus have to be included in the Credit-Control-
 Request command by a Diameter credit-control client supporting a
 given service as *[AVP].  Should Service-Parameter-Info be used, then
 the service specific document MUST specify the exact content of this
 grouped AVP.

Hakala, et al. Standards Track [Page 14] RFC 4006 Diameter Credit-Control Application August 2005

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

4.1.3. Handling of Unsupported/Incorrect Rating Input

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

4.1.4. RADIUS Vendor-Specific Rating Attributes

 When service specific documents include RADIUS vendor specific
 attributes that could be used as input in the rating process, the
 rules described in [NASREQ] for formatting the Diameter AVP MUST be
 followed.
 For example, if the AVP code used is the vendor attribute type code,
 the Vendor-Specific flag MUST be set to 1 and the Vendor-ID MUST be
 set to the IANA Vendor identification value.  The Diameter AVP data
 field contains only the attribute value of the RADIUS attribute.

5. Session Based Credit-Control

5.1. General Principles

 For a session-based credit-control, several interrogations are
 needed: the first, intermediate (optional) and the final
 interrogations.  This is illustrated in Figures 2 and 3.
 If the credit-control client performs credit-reservation before
 granting service to the end user, it MUST use several interrogations
 toward the credit-control server (i.e., session based credit-

Hakala, et al. Standards Track [Page 15] RFC 4006 Diameter Credit-Control Application August 2005

 control).  In this case, the credit-control server MUST maintain the
 credit-control session state.
 Each credit-control session MUST have a globally unique Session-Id as
 defined in [DIAMBASE], which MUST NOT be changed during the lifetime
 of a credit-control session.
 Certain applications require multiple credit-control sub-sessions.
 These applications would send messages with a constant Session-Id
 AVP, but with a different CC-Sub-Session-Id AVP.  If several credit
 sub-sessions will be used, all sub-sessions MUST be closed separately
 before the main session is closed so that units per sub-session may
 be reported.  The absence of this AVP implies that no sub-sessions
 are in use.
 Note that the service element might send a service specific re-
 authorization message to the AAA server due to expiration of the
 authorization-lifetime during an ongoing credit-control session.
 However, the service specific re-authorization does not influence the
 credit authorization that is ongoing between the credit-control
 client and credit-control server, as credit authorization is
 controlled by the burning rate of the granted quota.
 If service specific re-authorization fails, the user will be
 disconnected, and the credit-control client MUST send a final
 interrogation to the credit-control server.
 The Diameter credit-control server may seek to control the validity
 time of the granted quota and/or the production of intermediate
 interrogations.  Thus, it MAY include the Validity-Time AVP in the
 answer message to the credit-control client.  Upon expiration of the
 Validity-Time, the credit-control client MUST generate a credit-
 control update request and report the used quota to the credit-
 control server.  It is up to the credit-control server to determine
 the value of the Validity-Time to be used for consumption of the
 granted service units.  If the Validity-Time is used, its value
 SHOULD be given as input to set the session supervision timer Tcc
 (the session supervision timer MAY be set to two times the value of
 the Validity-Time, as defined in section 13).  Since credit-control
 update requests are also produced at the expiry of granted service
 units and/or for mid-session service events, the omission of
 Validity-Time does not mean that intermediate interrogation for the
 purpose of credit-control is not performed.

Hakala, et al. Standards Track [Page 16] RFC 4006 Diameter Credit-Control Application August 2005

5.1.1. Basic Tariff-Time Change Support

 The Diameter credit-control server and client MAY optionally support
 a tariff change mechanism.  The Diameter credit-control server may
 include a Tariff-Time-Change AVP in the answer message.  Note that
 the granted units should be allocated based on the worst-case
 scenario in case of forthcoming tariff change, so that the overall
 reported used units would never exceed the credit reservation.
 When the Diameter credit-control client reports the used units and a
 tariff change has occurred during the reporting period, the Diameter
 credit-control client MUST separately itemize the units used before
 and after the tariff change.  If the client is unable to distinguish
 whether units straddling the tariff change were used before or after
 the tariff change, the credit-control client MUST itemize those units
 in a third category.
 If a client does not support the tariff change mechanism and it
 receives a CCA message carrying the Tariff-Time-Change AVP, it MUST
 terminate the credit-control session, giving a reason of
 DIAMETER_BAD_ANSWER in the Termination-Cause AVP.
 For time based services, the quota is continuously consumed at the
 regular rate of 60 seconds per minute.  At the time when credit
 resources are allocated, the server already knows how many units will
 be consumed before the tariff time change and how many units will be
 consumed afterward.  Similarly, the server can determine the units
 consumed at the before rate and the units consumed at the rate
 afterward in the event that the end-user closes the session before
 the consumption of the allotted quota.  There is no need for
 additional traffic between client and server in the case of tariff
 time changes for continuous time based service.  Therefore, the
 tariff change mechanism is not used for such services.  For time-
 based services in which the quota is NOT continuously consumed at a
 regular rate, the tariff change mechanism described for volume and
 event units MAY be used.

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

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

Hakala, et al. Standards Track [Page 17] RFC 4006 Diameter Credit-Control Application August 2005

 (QoS) are common to all the services carried within the access
 bearer, but the cost of the bearer may vary depending on its content.
 To support these scenarios optimally, the credit-control application
 enables independent credit-control of multiple services in a single
 credit-control (sub-)session.  This is achieved by including the
 optional Multiple-Services-Credit-Control AVP in Credit-Control-
 Request/Answer messages.  It is possible to request and allocate
 resources as a credit pool shared between multiple services.  The
 services can be grouped into rating groups in order to achieve even
 further aggregation of credit allocation.  It is also possible to
 request and allocate quotas on a per service basis.  Where quotas are
 allocated to a pool by means of the Multiple-Services-Credit-Control
 AVP, the quotas remain independent objects that can be re-authorized
 independently at any time.  Quotas can also be given independent
 result codes, validity times, and Final-Unit-Indications.
 A Rating-Group gathers a set of services, identified by a Service-
 Identifier, and subject to the same cost and rating type (e.g.,
 $0.1/minute).  It is assumed that the service element is provided
 with Rating-Groups, Service-Identifiers, and their associated
 parameters that define what has to be metered by means outside the
 scope of this specification.  (Examples of parameters associated to
 Service-Identifiers are IP 5-tuple and HTTP URL.) Service-Identifiers
 enable authorization on a per-service based credit as well as
 itemized reporting of service usage.  It is up to the credit-control
 server whether to authorize credit for one or more services or for
 the whole rating-group.  However, the client SHOULD always report
 used units at the finest supported level of granularity.  Where quota
 is allocated to a rating-group, all the services belonging to that
 group draw from the allotted quota.  The following is a graphical
 representation of the relationship between service-identifiers,
 rating-groups, credit pools, and credit-control (sub-)session.
                        DCC (Sub-)Session
                                |
       +------------+-----------+-------------+--------------- +
       |            |           |             |                |
 Service-Id a Service-Id b Service-Id c Service-Id d.....Service-Id z
      \        /                 \         /                /
       \      /                   \       /                /
        \    /                  Rating-Group 1.......Rating-Group n
         \  /                         |                    |
        Quota       ---------------Quota                 Quota
          |        /                                       |
          |       /                                        |
       Credit-Pool                                    Credit-Pool

Hakala, et al. Standards Track [Page 18] RFC 4006 Diameter Credit-Control Application August 2005

 If independent credit-control of multiple services is used, the
 validity-time and final-unit-indication SHOULD be present either in
 the Multiple-Services-Credit-Control AVP(s) or at command level as
 single AVPs.  However, the Result-Code AVP MAY be present both on the
 command level and within the Multiple-Services-Credit-Control AVP.
 If the Result-Code on the command level indicates a value other than
 SUCCESS, then the Result-Code on command level takes precedence over
 any included in the Multiple-Services-Credit-Control AVP.
 The credit-control client MUST indicate support for independent
 credit-control of multiple services within a (sub-)session by
 including the Multiple-Services-Indicator AVP in the first
 interrogation.  A credit-control server not supporting this feature
 MUST treat the Multiple-Services-Indicator AVP and any received
 Multiple-Services-Credit-Control AVPs as invalid AVPs.
 If the client indicated support for independent credit-control of
 multiple services, a credit-control server that wishes to use the
 feature MUST return the granted units within the Multiple-Services-
 Credit-Control AVP associated to the corresponding service-identifier
 and/or rating-group.
 To avoid a situation where several parallel (and typically also
 small) credit reservations must be made on the same account (i.e.,
 credit fragmentation), and also to avoid unnecessary load on the
 credit-control server, it is possible to provide service units as a
 pool that applies to multiple services or rating groups.  This is
 achieved by providing the service units in the form of a quota for a
 particular service or rating group in the Multiple-Services-Credit-
 Control AVP, and also by including a reference to a credit pool for
 that unit type.
 The reference includes a multiplier derived from the rating
 parameter, which translates from service units of a specific type to
 the abstract service units in the pool.  For instance, if the rating
 parameter for service 1 is $1/MB and the rating parameter for service
 2 is $0.5/MB, the multipliers could be 10 and 5 for services 1 and 2,
 respectively.
 If S is the total service units within the pool, M1, M2, ..., Mn are
 the multipliers provided for services 1, 2, ..., n, and C1, C2, ...,
 Cn are the used resources within the session, then the pool credit is
 exhausted and re-authorization MUST be sought when:
       C1*M1 + C2*M2 + ... + Cn*Mn >= S

Hakala, et al. Standards Track [Page 19] RFC 4006 Diameter Credit-Control Application August 2005

 The total credit in the pool, S, is calculated from the quotas, which
 are currently allocated to the pool as follows:
       S = Q1*M1 + Q2*M2 + ... + Qn*Mn
 If services or rating groups are added to or removed from the pool,
 then the total credit is adjusted appropriately.  Note that when the
 total credit is adjusted because services or rating groups are
 removed from the pool, the value that need to be removed is the
 consumed one (i.e., Cx*Mx).
 Re-authorizations for an individual service or rating group may be
 sought at any time; for example, if a 'non-pooled' quota is used up
 or the Validity-Time expires.
 Where multiple G-S-U-Pool-Reference AVPs (section 8.30) with the same
 G-S-U-Pool-Identifier are provided within a Multiple-Services-
 Credit-Control AVP (section 8.16) along with the Granted-Service-Unit
 AVP, then these MUST have different CC-Unit-Type values, and they all
 draw from the credit pool separately.  For instance, if one
 multiplier for time (M1t) and one multiplier for volume (M1v) are
 given, then the used resources from the pool is the sum C1t*M1t +
 C1v*M1v, where C1t is the time unit and C1v is the volume unit.
 Where service units are provided within a Multiple-Services-Credit-
 Control AVP without a corresponding G-S-U-Pool-Reference AVP, then
 these are handled independently from any credit pool and from any
 other services or rating groups within the session.
 The credit pool concept is an optimal tool to avoid the over-
 reservation effect of the basic single quota tariff time change
 mechanism (the mechanism described in section 5.1.1).  Therefore,
 Diameter credit-control clients and servers implementing the
 independent credit-control of multiple services SHOULD leverage the
 credit pool concept when supporting the tariff time change.  The
 Diameter credit-control server SHOULD include both the Tariff-Time-
 Change and Tariff-Change-Usage AVPs in two quota allocations in the
 answer message (i.e., two instances of the Multiple-Services-Credit-
 Control AVP).  One of the granted units is allocated to be used
 before the potential tariff change, while the second granted units
 are for use after a tariff change.  Both granted unit quotas MUST
 contain the same Service-Identifier and/or Rating-Group.  This dual
 quota mechanism ensures that the overall reported used units would
 never exceed the credit reservation.  The Diameter credit-control
 client reports both the used units before and after the tariff change
 in a single instance of the Multiple-Services-Credit-Control AVP.

Hakala, et al. Standards Track [Page 20] RFC 4006 Diameter Credit-Control Application August 2005

 The failure handling for credit-control sessions is defined in
 section 5.7 and reflected in the basic credit-control state machine
 in section 7.  Credit-control clients and servers implementing the
 independent credit-control of multiple services in a (sub-)session
 functionality MUST ensure failure handling and general behavior fully
 consistent with the above mentioned sections, while maintaining the
 ability to handle parallel ongoing credit re-authorization within a
 (sub-)session.  Therefore, it is RECOMMENDED that Diameter credit-
 control clients maintain a PendingU message queue and restart the Tx
 timer (section 13) every time a CCR message with the value
 UPDATE_REQUEST is sent while they are in PendingU state.  When
 answers to all pending messages are received, the state machine moves
 to OPEN state, and Tx is stopped.  Naturally, the action performed
 when a problem for the session is detected according to section 5.7
 affects all the ongoing services (e.g., failover to a backup server
 if possible affect all the CCR messages with the value UPDATE_REQUEST
 in the PendingU queue).
 Since the client may send CCR messages with the value UPDATE_REQUEST
 while in PendingU (i.e., without waiting for an answer to ongoing
 credit re-authorization), the time space between these requests may
 be very short, and the server may not have received the previous
 request(s) yet.  Therefore, in this situation the server may receive
 out of sequence requests and SHOULD NOT consider this an error
 condition.  A proper answer is to be returned to each of those
 requests.

5.2. First Interrogation

 When session based credit-control is required (e.g., the
 authentication server indicated a prepaid user), the first
 interrogation MUST be sent before the Diameter credit-control client
 allows any service event to the end user.  The CC-Request-Type is set
 to the value INITIAL_REQUEST in the request message.
 If the Diameter credit-control client knows the cost of the service
 event (e.g., a content server delivering ringing tones may know their
 cost) the monetary amount to be charged is included in the
 Requested-Service-Unit AVP.  If the Diameter credit-control client
 does not know the cost of the service event, the Requested-Service-
 Unit AVP MAY contain the number of requested service events.  Where
 the Multiple-Services-Credit-Control AVP is used, it MUST contain the
 Requested-Service-Unit AVP to indicate that the quota for the
 associated service/rating-group is requested.  In the case of
 multiple services, the Service-Identifier AVP or the Rating-Group AVP
 within the Multiple-Services-Credit-Control AVP always indicates the
 service concerned.  Additional service event information to be rated

Hakala, et al. Standards Track [Page 21] RFC 4006 Diameter Credit-Control Application August 2005

 MAY be sent as service specific AVPs or MAY be sent within the
 Service-Parameter-Info AVP at command level.  The Service-Context-Id
 AVP indicates the service specific document applicable to the
 request.
 The Event-Timestamp AVP SHOULD be included in the request and
 contains the time when the service event is requested in the service
 element.  The Subscription-Id AVP SHOULD be included to identify the
 end user in the credit-control server.  The credit-control client MAY
 include the User-Equipment-Info AVP so that the credit-control server
 has some indication of the type and capabilities of the end user
 access device.  How the credit-control server uses this information
 is outside the scope of this document.
 The credit-control server SHOULD rate the service event and make a
 credit-reservation from the end user's account that covers the cost
 of the service event.  If the type of the Requested-Service-Unit AVP
 is money, no rating is needed, but the corresponding monetary amount
 is reserved from the end user's account.
 The credit-control server returns the Granted-Service-Unit AVP in the
 Answer message to the Diameter credit-control client.  The Granted-
 Service-Unit AVP contains the amount of service units that the
 Diameter credit-control client can provide to the end user until a
 new Credit-Control-Request MUST be sent to the credit-control server.
 If several unit types are sent in the Answer message, the credit-
 control client MUST handle each unit type separately.  The type of
 the Granted-Service-Unit AVP can be time, volume, service specific,
 or money, depending on the type of service event.  The unit type(s)
 SHOULD NOT be changed within an ongoing credit-control session.
 There MUST be a maximum of one instance of the same unit type in one
 Answer message.  However, if multiple quotas are conveyed to the
 credit-control client in the Multiple-Services-Credit-Control AVPs,
 it is possible to carry two instances of the same unit type
 associated to a service-identifier/rating-group.  This is typically
 the case when a tariff time change is expected and the credit-control
 server wants to make a distinction between the granted quota before
 and after tariff change.
 If the credit-control server determines that no further control is
 needed for the service, it MAY include the result code indicating
 that the credit-control is not applicable (e.g., if the service is
 free of charge).  This result code at command level implies that the
 credit-control session is to be terminated.
 The Credit-Control-Answer message MAY also include the Final-Unit-
 Indication AVP to indicate that the answer message contains the final

Hakala, et al. Standards Track [Page 22] RFC 4006 Diameter Credit-Control Application August 2005

 units for the service.  After the end user has consumed these units,
 the Diameter credit-control-client MUST behave as described in
 section 5.6.
 This document defines two different approaches to perform the first
 interrogation to be used in different network architectures.  The
 first approach uses credit-control messages after the user's
 authorization and authentication takes place.  The second approach
 uses service specific authorization messages to perform the first
 interrogation during the user's authorization/authentication phase,
 and credit-control messages for the intermediate and final
 interrogations.  If an implementation of the credit-control client
 supports both the methods, determining which method to use SHOULD be
 configurable.
 In service environments such as the Network Access Server (NAS), it
 is desired to perform the first interrogation as part of the
 authorization/authentication process for the sake of protocol
 efficiency.  Further credit authorizations after the first
 interrogation are performed with credit-control commands defined in
 this specification.  Implementations of credit-control clients
 operating in the mentioned environments SHOULD support this method.
 If the credit-control server and AAA server are separate physical
 entities, the service element sends the request messages to the AAA
 server, which then issues an appropriate request or proxies the
 received request forward to the credit-control server.
 In other service environments, such as the 3GPP network and some SIP
 scenarios, there is a substantial decoupling between
 registration/access to the network and the actual service request
 (i.e., the authentication/authorization is executed once at
 registration/access to the network and is not executed for every
 service event requested by the subscriber).  In these environments,
 it is more appropriate to perform the first interrogation after the
 user has been authenticated and authorized.  The first, the
 intermediate, and the final interrogations are executed with credit-
 control commands defined in this specification.
 Other IETF standards or standards developed by other standardization
 bodies may define the most suitable method in their architectures.

5.2.1. First Interrogation after Authorization and Authentication

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

Hakala, et al. Standards Track [Page 23] RFC 4006 Diameter Credit-Control Application August 2005

 accounting protocol and the credit-control protocol can be used in
 parallel.  The authorization server may also determine whether the
 parallel accounting stream is required.
 The following diagram illustrates the case where both protocols are
 used in parallel and the service element sends credit-control
 messages directly to the credit-control server.  More credit-control
 sequence examples are given in Annex A.
                                         Diameter
 End User        Service Element        AAA Server         CC Server
                   (CC Client)
    | Registration      | AA request/answer(accounting,cc or both)|
    |<----------------->|<------------------>|                    |
    |        :          |                    |                    |
    |        :          |                    |                    |
    | Service Request   |                    |                    |
    |------------------>|                    |                    |
    |                   | CCR(Initial,Credit-Control AVPs)        |
    |                  +|---------------------------------------->|
    |         CC stream||                    |  CCA(Granted-Units)|
    |                  +|<----------------------------------------|
    | Service Delivery  |                    |                    |
    |<----------------->| ACR(start,Accounting AVPs)              |
    |         :         |------------------->|+                   |
    |         :         |                ACA || Accounting stream |
    |                   |<-------------------|+                   |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |                   | CCR(Update,Used-Units)                  |
    |                   |---------------------------------------->|
    |                   |                    |  CCA(Granted-Units)|
    |                   |<----------------------------------------|
    |         :         |                    |                    |
    |         :         |                    |                    |
    | End of Service    |                    |                    |
    |------------------>| CCR(Termination, Used-Units)            |
    |                   |---------------------------------------->|
    |                   |                    |               CCA  |
    |                   |<----------------------------------------|
    |                   | ACR(stop)          |                    |
    |                   |------------------->|                    |
    |                   |                ACA |                    |
    |                   |<-------------------|                    |
  Figure 2: Protocol example with first interrogation after user's
                    authorization/authentication

Hakala, et al. Standards Track [Page 24] RFC 4006 Diameter Credit-Control Application August 2005

5.2.2. Authorization Messages for First Interrogation

 The Diameter credit-control client in the service element MUST
 actively co-operate with the authorization/authentication client in
 the construction of the AA request by adding appropriate credit-
 control AVPs.  The credit-control client MUST add the Credit-Control
 AVP to indicate credit-control capabilities and MAY add other
 relevant credit-control specific AVPs to the proper
 authorization/authentication command to perform the first
 interrogation toward the home Diameter AAA server.  The Auth-
 Application-Id is set to the appropriate value, as defined in the
 relevant service specific authorization/authentication application
 document (e.g., [NASREQ], [DIAMMIP]).  The home Diameter AAA server
 authenticates/authorizes the subscriber and determines whether
 credit-control is required.
 If credit-control is not required for the subscriber, the home
 Diameter AAA server will respond as usual, with an appropriate AA
 answer message.  If credit-control is required for the subscriber and
 the Credit-Control AVP with the value set to CREDIT_AUTHORIZATION was
 present in the authorization request, the home AAA server MUST
 contact the credit-control server to perform the first interrogation.
 If credit-control is required for the subscriber and the Credit-
 Control AVP was not present in the authorization request, the home
 AAA server MUST send an authorization reject answer message.
 The Diameter AAA server supporting credit-control is required to send
 the Credit-Control-Request command (CCR) defined in this document to
 the credit-control server.  The Diameter AAA server populates the CCR
 based on service specific AVPs used for input to the rating process,
 and possibly on credit-control AVPs received in the AA request.  The
 credit-control server will reserve money from the user's account,
 will rate the request and will send a Credit-Control-Answer message
 to the home Diameter AAA server.  The answer message includes the
 Granted-Service-Unit AVP(s) and MAY include other credit-control
 specific AVPs, as appropriate.  Additionally, the credit-control
 server MAY set the Validity-Time and MAY include the Credit-Control-
 Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP to
 determine what to do if the sending of credit-control messages to the
 credit-control server has been temporarily prevented.
 Upon receiving the Credit-Control-Answer message from the credit-
 control server, the home Diameter AAA server will populate the AA
 answer with the received credit-control AVPs and with the appropriate
 service attributes according to the authorization/authentication
 specific application (e.g., [NASREQ], [DIAMMIP]).  It will then
 forward the packet to the credit-control client.  If the home
 Diameter AAA server receives a credit-control reject message, it will

Hakala, et al. Standards Track [Page 25] RFC 4006 Diameter Credit-Control Application August 2005

 simply generate an appropriate authorization reject message to the
 credit-control client, including the credit-control specific error
 code.
 In this model, the credit-control client sends further credit-control
 messages to the credit-control server via the home Diameter AAA
 server.  Upon receiving a successful authorization answer message
 with the Granted-Service-Unit AVP(s), the credit-control client will
 grant the service to the end user and will generate an intermediate
 credit-control request, as required by using credit-control commands.
 The CC-Request-Number of the first UPDATE_REQUEST MUST be set to 1
 (for how to produce unique value for the CC-Request-Number AVP, see
 section 8.2).
 If service specific re-authorization is performed (i.e.,
 authorization-lifetime expires), the credit-control client MUST add
 to the service specific re-authorization request the Credit-Control
 AVP with a value set to RE_AUTHORIZATION to indicate that the
 credit-control server MUST NOT be contacted.  When session based
 credit-control is used for the subscriber, a constant credit-control
 message stream flows through the home Diameter AAA server.  The home
 Diameter AAA server can make use of this credit-control message flow
 to deduce that the user's activity is ongoing; therefore, it is
 recommended to set the authorization-lifetime to a reasonably high
 value when credit-control is used for the subscriber.
 In this scenario, the home Diameter AAA server MUST advertise support
 for the credit-control application to its peers during the capability
 exchange process.

Hakala, et al. Standards Track [Page 26] RFC 4006 Diameter Credit-Control Application August 2005

 The following diagram illustrates the use of
 authorization/authentication messages to perform the first
 interrogation.  The parallel accounting stream is not shown in the
 figure.
                  Service Element         Diameter
 End User          (CC Client)           AAA Server          CC Server
    | Service Request   | AA Request (CC AVPs)                    |
    |------------------>|------------------->|                    |
    |                   |                    | CCR(Initial, CC AVPs)
    |                   |                    |------------------->|
    |                   |                    |    CCA(Granted-Units)
    |                   |                    |<-------------------|
    |                   | AA Answer(Granted-Units)                |
    | Service Delivery  |<-------------------|                    |
    |<----------------->|                    |                    |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |                   |                    |                    |
    |                   | CCR(Update,Used-Units)                  |
    |                   |------------------->| CCR(Update,Used-Units)
    |                   |                    |------------------->|
    |                   |                    |  CCA(Granted-Units)|
    |                   |  CCA(Granted-Units)|<-------------------|
    |                   |<-------------------|                    |
    |         :         |                    |                    |
    |         :         |                    |                    |
    | End of Service    |                    |                    |
    |------------------>| CCR(Termination,Used-Units)             |
    |                   |------------------->| CCR(Term.,Used-Units)
    |                   |                    |------------------->|
    |                   |                    |                CCA |
    |                   |                CCA |<-------------------|
    |                   |<-------------------|                    |
              Figure 3: Protocol example with use of the
         authorization messages for the first interrogation

5.3. Intermediate Interrogation

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

Hakala, et al. Standards Track [Page 27] RFC 4006 Diameter Credit-Control Application August 2005

 credit reservation has been wholly consumed, or upon expiration of
 the Validity-Time.  It is always up to the Diameter credit-control
 client to send a new request well in advance of the expiration of the
 previous request in order to avoid interruption in the service
 element.  Even if the granted service units reserved by the credit-
 control server have not been spent upon expiration of the Validity-
 Time, the Diameter credit-control client MUST send a new Credit-
 Control-Request to the credit-control server.
 There can also be mid-session service events, which might affect the
 rating of the current service events.  In this case, a spontaneous
 updating (a new Credit-Control-Request) SHOULD be sent including
 information related to the service event even if all the granted
 service units have not been spent or the Validity-Time has not
 expired.
 When the used units are reported to the credit-control server, the
 credit-control client will not have any units in its possession
 before new granted units are received from the credit-control server.
 When the new granted units are received, these units apply from the
 point where the measurement of the reported used units stopped.
 Where independent credit-control of multiple services is supported,
 this process may be executed for one or more services, a single
 rating-group, or a pool within the (sub)session.
 The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
 intermediate request message.  The Subscription-Id AVP SHOULD be
 included in the intermediate message to identify the end user in the
 credit-control server.  The Service-Context-Id AVP indicates the
 service specific document applicable to the request.
 The Requested-Service-Unit AVP MAY contain the new amount of
 requested service units.  Where the Multiple-Services-Credit-Control
 AVP is used, it MUST contain the Requested-Service-Unit AVP if a new
 quota is requested for the associated service/rating-group.  The
 Used-Service-Unit AVP contains the amount of used service units
 measured from the point when the service became active or, if interim
 interrogations are used during the session, from the point when the
 previous measurement ended.  The same unit types used in the previous
 message SHOULD be used.  If several unit types were included in the
 previous answer message, the used service units for each unit type
 MUST be reported.
 The Event-Timestamp AVP SHOULD be included in the request and
 contains the time of the event that triggered the sending of the new
 Credit-Control-Request.

Hakala, et al. Standards Track [Page 28] RFC 4006 Diameter Credit-Control Application August 2005

 The credit-control server MUST deduct the used amount from the end
 user's account.  It MAY rate the new request and make a new credit-
 reservation from the end user's account that covers the cost of the
 requested service event.
 A Credit-Control-Answer message with the CC-Request-Type AVP set to
 the value UPDATE_REQUEST MAY include the Cost-Information AVP
 containing the accumulated cost estimation for the session, without
 taking any credit-reservation into account.
 The Credit-Control-Answer message MAY also include the Final-Unit-
 Indication AVP to indicate that the answer message contains the final
 units for the service.  After the end user has consumed these units,
 the Diameter credit-control-client MUST behave as described in
 section 5.6.
 There can be several intermediate interrogations within a session.

5.4. Final Interrogation

 When the end user terminates the service session, or when the
 graceful service termination described in section 5.6 takes place,
 the Diameter credit-control client MUST send a final Credit-Control-
 Request message to the credit-control server.  The CC-Request-Type
 AVP is set to the value TERMINATION_REQUEST.  The Service-Context-Id
 AVP indicates the service specific document applicable to the
 request.
 The Event-Timestamp AVP SHOULD be included in the request and
 contains the time when the session was terminated.
 The Used-Service-Unit AVP contains the amount of used service units
 measured from the point when the service became active or, if interim
 interrogations are used during the session, from the point when the
 previous measurement ended.  If several unit types were included in
 the previous answer message, the used service units for each unit
 type MUST be reported.
 After final interrogation, the credit-control server MUST refund the
 reserved credit amount not used to the end user's account and deduct
 the used monetary amount from the end user's account.
 A Credit-Control-Answer message with the CC-Request-Type set to the
 value TERMINATION_REQUEST MAY include the Cost-Information AVP
 containing the estimated total cost for the session in question.
 If the user logs off during an ongoing credit-control session, or if
 some other reason causes the user to become logged off (e.g., final-

Hakala, et al. Standards Track [Page 29] RFC 4006 Diameter Credit-Control Application August 2005

 unit indication causes user logoff according to local policy), the
 service element, according to application specific policy, may send a
 Session-Termination-Request (STR) to the home Diameter AAA server as
 usual [DIAMBASE].  Figure 4 illustrates the case when the final-unit
 indication causes user logoff upon consumption of the final granted
 units and the generation of STR.
                 Service Element        AAA Server        CC Server
 End User         (CC Client)
    | Service Delivery  |                    |                    |
    |<----------------->|                    |                    |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |                   |                    |                    |
    |                   | CCR(Update,Used-Units)                  |
    |                   |------------------->| CCR(Update,Used-Units)
    |                   |                    |------------------->|
    |                   |                  CCA(Final-Unit, Terminate)
    |              CCA(Final-Unit, Terminate)|<-------------------|
    |                   |<-------------------|                    |
    |         :         |                    |                    |
    |         :         |                    |                    |
    |  Disconnect user  |                    |                    |
    |<------------------| CCR(Termination,Used-Units)             |
    |                   |------------------->| CCR(Term.,Used-Units)
    |                   |                    |------------------->|
    |                   |                    |                CCA |
    |                   |                CCA |<-------------------|
    |                   |<-------------------|                    |
    |                   | STR                |                    |
    |                   |------------------->|                    |
    |                   |               STA  |                    |
    |                   |<-------------------|                    |
         Figure 4: User disconnected due to exhausted account

5.5. Server-Initiated Credit Re-Authorization

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

Hakala, et al. Standards Track [Page 30] RFC 4006 Diameter Credit-Control Application August 2005

 Section 5.1.2 defines the feature to enable credit-control for
 multiple services within a single (sub-)session where the server can
 authorize credit usage at a different level of granularity.  Further,
 the server may provide credit resources to multiple services or
 rating groups as a pool (see section 5.1.2 for details and
 definitions).  Therefore, the server, based on its service logic and
 its knowledge of the ongoing session, can decide to request credit
 re-authorization for a whole (sub-)session, a single credit pool, a
 single service, or a single rating-group.  To request credit re-
 authorization for a credit pool, the server includes in the RAR
 message the G-S-U-Pool-Identifier AVP indicating the affected pool.
 To request credit re-authorization for a service or a rating-group,
 the server includes in the RAR message the Service-Identifier AVP or
 the Rating-Group AVP, respectively.  To request credit re-
 authorization for all the ongoing services within the (sub-)session,
 the server includes none of the above mentioned AVPs in the RAR
 message.
 If a credit re-authorization is not already ongoing (i.e., the
 credit-control session is in Open state), a credit control client
 that receives an RAR message with Session-Id equal to a currently
 active credit-control session MUST acknowledge the request by sending
 the Re-Auth-Answer (RAA) message and MUST initiate the credit re-
 authorization toward the server by sending a Credit-Control-Request
 message with the CC-Request-Type AVP set to the value UPDATE_REQUEST.
 The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the
 RAA message to indicate that an additional message (i.e., CCR message
 with the value UPDATE_REQUEST) is required to complete the procedure.
 If a quota was allocated to the service, the credit-control client
 MUST report the used quota in the Credit-Control-Request.  Note that
 the end user does not need to be prompted for the credit re-
 authorization, since the credit re-authorization is transparent to
 the user (i.e., it takes place exclusively between the credit-control
 client and the credit-control server).
 Where multiple services in a user's session are supported, the
 procedure in the above paragraph will be executed at the granularity
 requested by the server in the RAR message.
 If credit re-authorization is ongoing at the time when the RAR
 message is received (i.e., RAR-CCR collision), the credit-control
 client successfully acknowledges the request but does not initiate a
 new credit re-authorization.  The Result-Code 2001 (DIAMETER_SUCCESS)
 SHOULD be used in the RAA message to indicate that a credit re-
 authorization procedure is already ongoing (i.e., the client was in
 PendingU state when the RAR was received).  The credit-control server
 SHOULD process the Credit-Control-Request as if it was received in
 answer to the server initiated credit re-authorization, and should

Hakala, et al. Standards Track [Page 31] RFC 4006 Diameter Credit-Control Application August 2005

 consider the server initiated credit re-authorization process
 successful upon reception of the Re-Auth-Answer message.
 When multiple services are supported in a user's session, the server
 may request credit re-authorization for a credit pool (or for the
 (sub-)session) while a credit re-authorization is already ongoing for
 some of the services or rating-groups.  In this case, the client
 acknowledges the server request with an RAA message and MUST send a
 new Credit-Control-Request message to perform re-authorization for
 the remaining services/rating-groups.  The Result-Code 2002
 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the RAA message to
 indicate that an additional message (i.e., CCR message with value
 UPDATE_REQUEST) is required to complete the procedure.  The server
 processes the received requests and returns an appropriate answer to
 both requests.
 The above-defined procedures are enabled for each of the possibly
 active Diameter credit-control sub-sessions.  The server MAY request
 re-authorization for an active sub-session by including the CC-Sub-
 Session-Id AVP in the RAR message in addition to the Session-Id AVP.

5.6. Graceful Service Termination

 When the user's account runs out of money, the user may not be
 allowed to compile additional chargeable events.  However, the home
 service provider may offer some services; for instance, access to a
 service portal where it is possible to refill the account, for which
 the user is allowed to benefit for a limited time.  The length of
 this time is usually dependent on the home service provider policy.
 This section defines the optional graceful service termination
 feature that MAY be supported by the credit-control server.  Credit-
 control client implementations MUST support the Final-Unit-Indication
 with at least the teardown of the ongoing service session once the
 subscriber has consumed all the final granted units.
 Where independent credit-control of multiple services in a single
 credit-control (sub-)session is supported, it is possible to use the
 graceful service termination for each of the services/rating-groups
 independently.  Naturally, the graceful service termination process
 defined in the following sub-sections will apply to the specific
 service/rating-group as requested by the server.
 In some service environments (e.g., NAS), the graceful service
 termination may be used to redirect the subscriber to a service
 portal for online balance refill or other services offered by the
 home service provider.  In this case, the graceful termination
 process installs a set of packet filters to restrict the user's

Hakala, et al. Standards Track [Page 32] RFC 4006 Diameter Credit-Control Application August 2005

 access capability only to/from the specified destinations.  All the
 IP packets not matching the filters will be dropped or, possibly,
 re-directed to the service portal.  The user may also be sent an
 appropriate notification as to why the access has been limited.
 These actions may be communicated explicitly from the server to the
 client or may be configured per-service at the client.  Explicitly
 signaled redirect or restrict instructions always take precedence
 over configured ones.
 It is also possible use the graceful service termination to connect
 the prepaid user to a top-up server that plays an announcement and
 prompts the user to replenish the account.  In this case, the
 credit-control server sends only the address of the top-up server
 where the prepaid user shall be connected after the final granted
 units have been consumed.  An example of this is given in Appendix A
 (Flow VII).
 The credit-control server MAY initiate the graceful service
 termination by including the Final-Unit-Indication AVP in the
 Credit-Control-Answer to indicate that the message contains the final
 units for the service.
 When the credit-control client receives the Final-Unit-Indication AVP
 in the answer from the server, its behavior depends on the value
 indicated in the Final-Unit-Action AVP.  The server may request the
 following actions: TERMINATE, REDIRECT, or RESTRICT_ACCESS.
 A following figure illustrates the graceful service termination
 procedure described in the following sub-sections.

Hakala, et al. Standards Track [Page 33] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 34] RFC 4006 Diameter Credit-Control Application August 2005

       Figure 5: Optional graceful service termination procedure

5.6.1. Terminate Action

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

5.6.2. Redirect Action

 The Final-Unit-Indication AVP with Final-Unit-Action REDIRECT
 indicates to the service element supporting this action that, upon
 consumption of the final granted units, the user MUST be re-directed
 to the address specified in the Redirect-Server AVP as follows.
 The credit-control server sends the Redirect-Server AVP in the
 Credit-Control-Answer message.  In such a case, the service element
 MUST redirect or connect the user to the destination specified in the
 Redirect-Server AVP, if possible.  When the end user is redirected
 (by using protocols others than Diameter) to the specified server or
 connected to the top-up server, an additional authorization (and
 possibly authentication) may be needed before the subscriber can
 replenish the account; however, this is out of the scope of this
 specification.
 In addition to the Redirect-Server AVP, the credit-control server MAY
 include one or more Restriction-Filter-Rule AVPs or one or more
 Filter-Id AVPs in the Credit-Control-Answer message to enable the
 user to access other services (for example, zero-rated services).  In
 such a case, the access device MUST drop all the packets not matching
 the IP filters specified in the Credit-Control-Answer message and, if
 possible, redirect the user to the destination specified in the
 Redirect-Server AVP.
 An entity other than the credit-control server may provision the
 access device with appropriate IP packet filters to be used in
 conjunction with the Diameter credit-control application.  This case
 is considered in section 5.6.3.

Hakala, et al. Standards Track [Page 35] RFC 4006 Diameter Credit-Control Application August 2005

 When the final granted units have been consumed, the credit-control
 client MUST perform an intermediate interrogation.  The purpose of
 this interrogation is to indicate to the credit-control server that
 the specified action started and to report the used units.  The
 credit-control server MUST deduct the used amount from the end user's
 account but MUST NOT make a new credit reservation.  The credit-
 control client, however, may send intermediate interrogations before
 all the final granted units have been consumed for which rating and
 money reservation may be needed; for instance, upon Validity-Time
 expires or upon mid-session service events that affect the rating of
 the current service.  Therefore, the credit-control client MUST NOT
 include any rating related AVP in the request sent once all the final
 granted units have been consumed as an indication to the server that
 the requested final unit action started, rating and money reservation
 are not required (when the Multiple-Services-Credit-Control AVP is
 used, the Service-Identifier or Rating-Group AVPs is included to
 indicate the concerned services).  Naturally, the Credit-Control-
 Answer message does not contain any granted service unit and MUST
 include the Validity-Time AVP to indicate to the credit-control
 client how long the subscriber is allowed to use network resources
 before a new intermediate interrogation is sent to the server.
 At the expiry of Validity-Time, the credit-control client sends a
 Credit-Control-Request (UPDATE_REQUEST) as usual.  This message does
 not include the Used-Service-Unit AVP, as there is no allotted quota
 to report.  The credit-control server processes the request and MUST
 perform the credit reservation.  If during this time the subscriber
 did not replenish his/her account, whether he/she will be
 disconnected or will be granted access to services not controlled by
 a credit-control server for an unlimited time is dependent on the
 home service provider policy (note: the latter option implies that
 the service element should not remove the restriction filters upon
 termination of the credit-control).  The server will return the
 appropriate Result-Code (see section 9.1) in the Credit-Control-
 Answer message in order to implement the policy-defined action.
 Otherwise, new quota will be returned, the service element MUST
 remove all the possible restrictions activated by the graceful
 service termination process and continue the credit-control session
 and service session as usual.
 The credit-control client may not wait until the expiration of the
 Validity-Time and may send a spontaneous update (a new Credit-
 Control-Request) if the service element can determine, for instance,
 that communication between the end user and the top-up server took
 place.  An example of this is given in Appendix A (Figure A.8).

Hakala, et al. Standards Track [Page 36] RFC 4006 Diameter Credit-Control Application August 2005

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

5.6.3. Restrict Access Action

 A Final-Unit-Indication AVP with the Final-Unit-Action
 RESTRICT_ACCESS indicates to the device supporting this action that
 the user's access MUST be restricted according to the IP packet
 filters given in the Restriction-Filter-Rule AVP(s) or according to
 the IP packet filters identified by the Filter-Id AVP(s).  The
 credit-control server SHOULD include either the Restriction-Filter-
 Rule AVP or the Filter-Id AVP in the Credit-Control-Answer message.
 An entity other than the credit-control server may provision the
 access device with appropriate IP packet filters to be used in
 conjunction with the Diameter credit-control application.  Such an
 entity may, for instance, configure the access device with IP flows
 to be passed when the Diameter credit-control application indicates
 RESTRICT_ACCESS or REDIRECT.  The access device passes IP packets
 according to the filter rules that may have been received in the
 Credit-Control-Answer message in addition to those that may have been
 configured by the other entity.  However, when the user's account
 cannot cover the cost of the requested service, the action taken is
 the responsibility of the credit-control server that controls the
 prepaid subscriber.
 If another entity working in conjunction with the Diameter credit-
 control application already provisions the access device with all the
 required filter rules for the end user, the credit-control server
 presumably need not send any additional filter.  Therefore, it is
 RECOMMENDED that credit-control server implementations supporting the
 graceful service termination be configurable for sending the
 Restriction-Filter-Rule AVP, the Filter-Id AVP, or none of the above.
 When the final granted units have been consumed, the credit-control
 client MUST perform an intermediate interrogation.  The credit-
 control client and the credit-control server process this
 intermediate interrogation and execute subsequent procedures, as
 specified in the previous section for the REDIRECT action.

Hakala, et al. Standards Track [Page 37] RFC 4006 Diameter Credit-Control Application August 2005

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

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

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

5.7. Failure Procedures

 The Credit-Control-Failure-Handling AVP (CCFH), as described in this
 section, determines the behavior of the credit-control client in
 fault situations.  The CCFH may be received from the Diameter home
 AAA server, from the credit-control server, or may be configured
 locally.  The CCFH value received from the home AAA server overrides
 the locally configured value.  The CCFH value received from the
 credit-control server in the Credit-Control-Answer message always
 overrides any existing value.
 The authorization server MAY include the Accounting-Realtime-Required
 AVP to determine what to do if the sending of accounting records to
 the accounting server has been temporarily prevented, as defined in
 [DIAMBASE].  It is RECOMMENDED that the client complement the
 credit-control failure procedures with backup accounting flow toward
 an accounting server.  By using different combinations of
 Accounting-Realtime-Required and Credit-Control-Failure-Handling
 AVPs, different safety levels can be built.  For example, by choosing
 a Credit-Control-Failure-Handling AVP equal to CONTINUE for the
 credit-control flow and a Accounting-Realtime-Required AVP equal to
 DELIVER_AND_GRANT for the accounting flow, the service can be granted

Hakala, et al. Standards Track [Page 38] RFC 4006 Diameter Credit-Control Application August 2005

 to the end user even if the connection to the credit-control server
 is down, as long as the accounting server is able to collect the
 accounting information and information exchange is taking place
 between the accounting server and credit-control server.
 As the credit-control application is based on real-time bi-
 directional communication between the credit-control client and the
 credit-control server, the usage of alternative destinations and the
 buffering of messages may not be sufficient in the event of
 communication failures.  Because the credit-control server has to
 maintain session states, moving the credit-control message stream to
 a backup server requires a complex context transfer solution.
 Whether the credit-control message stream is moved to a backup
 credit-control server during an ongoing credit-control session
 depends on the value of the CC-Session-Failover AVP.  However,
 failover may occur at any point in the path between the credit-
 control client and the credit-control server if a transport failure
 is detected with a peer, as described in [DIAMBASE].  As a
 consequence, the credit-control server might receive duplicate
 messages.  These duplicates or out of sequence messages can be
 detected in the credit-control server based on the credit-control
 server session state machine (section 7), Session-Id AVP, and CC-
 Request-Number AVP.
 If a failure occurs during an ongoing credit-control session, the
 credit-control client may move the credit-control message stream to
 an alternative server if the CC-server indicated FAILOVER_SUPPORTED
 in the CC-Session-Failover AVP.  A secondary credit-control server
 name, either received from the home Diameter AAA server or configured
 locally, can be used as an address of the backup server.  If the CC-
 Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED, the credit-
 control message stream MUST NOT be moved to a backup server.
 For new credit-control sessions, failover to an alternative credit-
 control server SHOULD be performed if possible.  For instance, if an
 implementation of the credit-control client can determine primary
 credit-control server unavailability, it can establish the new
 credit-control sessions with a possibly available secondary credit-
 control server.
 The AAA transport profile [AAATRANS] defines the application layer
 watchdog algorithm that enables failover from a peer that has failed
 and is controlled by a watchdog timer (Tw) defined in [AAATRANS].
 The recommended default initial value for Tw (Twinit) is 30 seconds.
 Twinit may be set as low as 6 seconds; however, according to
 [AAATRANS], setting too low a value for Twinit is likely to result in
 an increased probability of duplicates, as well as an increase in
 spurious failover and failback attempts.  The Diameter base protocol

Hakala, et al. Standards Track [Page 39] RFC 4006 Diameter Credit-Control Application August 2005

 is common to several different types of Diameter AAA applications
 that may be run in the same service element.  Therefore, tuning the
 timer Twinit to a lower value in order to satisfy the requirements of
 real-time applications, such as the Diameter credit-control
 application, will certainly cause the above mentioned problems.  For
 prepaid services, however, the end user expects an answer from the
 network in a reasonable time.  Thus, the Diameter credit-control
 client will react faster than would the underlying base protocol.
 Therefore this specification defines the timer Tx that is used by the
 credit-control client (as defined in section 13) to supervise the
 communication with the credit-control server.  When the timer Tx
 elapses, the credit-control client takes an action to the end user
 according to the Credit-Control-Failure-Handling AVP.
 When Tx expires, the Diameter credit-control client always terminates
 the service if the Credit-Control-Failure-Handling (CCFH) AVP is set
 to the value TERMINATE.  The credit-control session may be moved to
 an alternative server only if a protocol error DIAMETER_TOO_BUSY or
 DIAMETER_UNABLE_TO_DELIVER is received before Tx expires.  Therefore,
 the value TERMINATE is not appropriate if proper failover behavior is
 desired.
 If the Credit-Control-Failure-Handling AVP is set to the value
 CONTINUE or RETRY_AND_TERMINATE, the service will be granted to the
 end user when the timer Tx expires.  An answer message with granted-
 units may arrive later if the base protocol transport failover
 occurred in the path to the credit-control server.  (The Twinit
 default value is 3 times more than the Tx recommended value.) The
 credit-control client SHOULD grant the service to the end user, start
 monitoring the resource usage, and wait for the possible late answer
 until the timeout of the request (e.g., 120 seconds).  If the request
 fails and the CC-Session-Failover AVP is set to
 FAILOVER_NOT_SUPPORTED, the credit-control client terminates or
 continues the service depending on the value set in the CCFH and MUST
 free all the reserved resources for the credit-control session.  If
 the protocol error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is
 received or the request times out and the CC-Session-Failover AVP is
 set to FAILOVER_SUPPORTED, the credit-control client MAY send the
 request to a backup server, if possible.  If the credit-control
 client receives a successful answer from the backup server, it
 continues the credit-control session with such a server.  If the re-
 transmitted request also fails, the credit-control client terminates
 or continues the service depending on the value set in the CCFH and
 MUST free all the reserved resources for the credit-control session.
 If a communication failure occurs during the graceful service
 termination procedure, the service element SHOULD always terminate
 the ongoing service session.

Hakala, et al. Standards Track [Page 40] RFC 4006 Diameter Credit-Control Application August 2005

 If the credit-control server detects a failure during an ongoing
 credit-control session, it will terminate the credit-control session
 and return the reserved units back to the end user's account.
 The supervision session timer Tcc (as defined in section 13) is used
 in the credit-control server to supervise the credit-control session.
 In order to support failover between credit-control servers,
 information transfer about the credit-control session and account
 state SHOULD take place between the primary and the secondary
 credit-control server.  Implementations supporting the credit-control
 session failover MUST also ensure proper detection of duplicate or
 out of sequence messages.  The communication between the servers is
 regarded as an implementation issue and is outside of the scope of
 this specification.

6. One Time Event

 The one-time event is used when there is no need to maintain any
 state in the Diameter credit-control server; for example, enquiring
 about the price of the service.  The use of a one-time event implies
 that the user has been authenticated and authorized beforehand.
 The one time event can be used when the credit-control client wants
 to know the cost of the service event or to check the account balance
 without any credit-reservation.  It can also be used for refunding
 service units on the user's account or for direct debiting without
 any credit-reservation.  The one time event is shown in Figure 6.
                                         Diameter
 End User        Service Element        AAA Server        CC Server
                   (CC Client)
    | Service Request   |                    |                    |
    |------------------>|                    |                    |
    |                   | CCR(Event)         |                    |
    |                   |------------------->| CCR(Event)         |
    |                   |                    |------------------->|
    |                   |                    |  CCA(Granted-Units)|
    |                   |  CCA(Granted-Units)|<-------------------|
    |  Service Delivery |<-------------------|                    |
    |<----------------->|                    |                    |
                       Figure 6: One time event
 In environments such as the 3GPP architecture, the one time event can
 be sent from the service element directly to the credit-control
 server.

Hakala, et al. Standards Track [Page 41] RFC 4006 Diameter Credit-Control Application August 2005

6.1. Service Price Enquiry

 The credit-control client may need to know the price of the service
 event.  Services offered by application service providers whose
 prices are not known in the credit-control client might exist.  The
 end user might also want to get an estimation of the price of a
 service event before requesting it.
 A Diameter credit-control client requesting the cost information MUST
 set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
 Requested-Action AVP set to PRICE_ENQUIRY, and set the requested
 service event information into the Service-Identifier AVP in the
 Credit-Control-Request message.  Additional service event information
 may be sent as service specific AVPs or within the Service-
 Parameter-Info AVP.  The Service-Context-Id AVP indicates the service
 specific document applicable to the request.
 The credit-control server calculates the cost of the requested
 service event, but it does not perform any account balance check or
 credit-reservation from the account.
 The estimated cost of the requested service event is returned to the
 credit-control client in the Cost-Information AVP in the Credit-
 Control-Answer message.

6.2. Balance Check

 The Diameter credit-control client may only have to verify that the
 end user's account balance covers the cost of a certain service
 without reserving any units from the account at the time of the
 inquiry.  This method does not guarantee that credit would be left
 when the Diameter credit-control client requests the debiting of the
 account with a separate request.
 A Diameter credit-control client requesting the balance check MUST
 set the CC-Request-Type AVP equal to EVENT_REQUEST, include a
 Requested-Action AVP set to CHECK_BALANCE, and include the
 Subscription-Id AVP in order to identify the end user in the credit-
 control server.  The Service-Context-Id AVP indicates the service
 specific document applicable to the request.
 The credit-control server makes the balance check, but it does not
 make any credit-reservation from the account.
 The result of balance check (ENOUGH_CREDIT/NO_CREDIT) is returned to
 the credit-control client in the Check-Balance-Result AVP in the
 Credit-Control-Answer message.

Hakala, et al. Standards Track [Page 42] RFC 4006 Diameter Credit-Control Application August 2005

6.3. Direct Debiting

 There are certain service events for which service execution is
 always successful in the service environment.  The delay between the
 service invocation and the actual service delivery to the end user
 can be sufficiently long that the use of the session-based credit-
 control would lead to unreasonably long credit-control sessions.  In
 these cases, the Diameter credit-control client can use the one-time
 event scenario for direct debiting.  The Diameter credit-control
 client SHOULD be sure that the requested service event execution
 would be successful when this scenario is used.
 In the Credit-Control-Request message, the CC-Request-Type is set to
 the value EVENT_REQUEST and the Requested-Action AVP is set to
 DIRECT_DEBITING.  The Subscription-Id AVP SHOULD be included to
 identify the end user in the credit-control server.  The Event-
 Timestamp AVP SHOULD be included in the request and contain the time
 when the service event is requested in the service element.  The
 Service-Context-Id AVP indicates the service specific document
 applicable to the request.
 The Diameter credit-control client MAY include the monetary amount to
 be charged in the Requested-Service-Unit AVP, if it knows the cost of
 the service event.  If the Diameter credit-control client does not
 know the cost of the service event, the Requested-Service-Unit AVP
 MAY contain the number of requested service events.  The Service-
 Identifier AVP always indicates the service concerned.  Additional
 service event information to be rated MAY be sent as service specific
 AVPs or within the Service-Parameter-Info AVP.
 The credit-control server SHOULD rate the service event and deduct
 the corresponding monetary amount from the end user's account.  If
 the type of the Requested-Service-Unit AVP is money, no rating is
 needed, but the corresponding monetary amount is deducted from the
 end user's account.
 The credit-control server returns the Granted-Service-Unit AVP in the
 Credit-Control-Answer message to the Diameter credit-control client.
 The Granted-Service-Unit AVP contains the amount of service units
 that the Diameter credit-control client can provide to the end user.
 The type of the Granted-Service-Unit can be time, volume, service
 specific, or money, depending on the type of service event.
 If the credit-control server determines that no credit-control is
 needed for the service, it can include the result code indicating
 that the credit-control is not applicable (e.g., service is free of
 charge).

Hakala, et al. Standards Track [Page 43] RFC 4006 Diameter Credit-Control Application August 2005

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

6.4. Refund

 Some services may refund service units to the end user's account; for
 example, gaming services.
 The credit-control client MUST set CC-Request-Type to the value
 EVENT_REQUEST and the Requested-Action AVP to REFUND_ACCOUNT in the
 Credit-Control-Request message.  The Subscription-Id AVP SHOULD be
 included to identify the end user in the credit-control server.  The
 Service-Context-Id AVP indicates the service specific document
 applicable to the request.
 The Diameter credit-control client MAY include the monetary amount to
 be refunded in the Requested-Service-Unit AVP.  The Service-
 Identifier AVP always indicates the concerned service.  If the
 Diameter credit-control client does not know the monetary amount to
 be refunded, in addition to the Service-Identifier AVP it MAY send
 service specific AVPs or the Service-Parameter-Info AVP containing
 additional service event information to be rated.
 For informative purposes, the Credit-Control-Answer message MAY also
 include the Cost-Information AVP containing the estimated monetary
 amount of refunded unit.

6.5. Failure Procedure

 Failover to an alternative credit-control server is allowed for a one
 time event, as the server is not maintaining session states.  For
 instance, if the credit-control client receives a protocol error
 DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY, it can re-send the
 request to an alternative server, if possible.  There MAY be protocol
 transparent Diameter relays and redirect agents or Diameter credit-
 control proxies between the credit-control client and credit-control
 server.  Failover may occur at any point in the path between the
 credit-control client and the credit-control server if a transport
 failure is detected with a peer, as described in [DIAMBASE].  Because
 there can be duplicate requests for various reasons, the credit-
 control server is responsible for real time duplicate detection.
 Implementation issues for duplicate detection are discussed in
 [DIAMBASE], Appendix C.
 When the credit-control client detects a communication failure with
 the credit-control server, its behavior depends on the requested
 action.  The timer Tx (as defined in section 13) is used in the

Hakala, et al. Standards Track [Page 44] RFC 4006 Diameter Credit-Control Application August 2005

 credit-control client to supervise the communication with the
 credit-control server.
 If the requested action is PRICE_ENQUIRY or CHECK_BALANCE and
 communication failure is detected, the credit-control client SHOULD
 forward the request messages to an alternative credit-control server,
 if possible.  The secondary credit-control server name, if received
 from the home Diameter AAA server, can be used as an address of
 backup server.
 If the requested action is DIRECT_DEBITING, the Direct-Debiting-
 Failure-Handling AVP (DDFH) controls the credit-control client's
 behavior.  The DDFH may be received from the home Diameter AAA server
 or may be locally configured.  The credit-control server may also
 send the DDFH in any CCA message to be used for direct debiting
 events compiled thereafter.  The DDFH value received from the home
 Diameter AAA server overrides the locally configured value, and the
 DDFH value received from the credit-control server in a Credit-
 Control-Answer message always overrides any existing value.
 If the DDFH is set to TERMINATE_OR_BUFFER, the credit-control client
 SHOULD NOT grant the service if it can determine, eventually after a
 possible re-transmission attempt to an alternative credit-control
 server, from the result code or error code in the answer message that
 units have not been debited.  Otherwise, the credit-control client
 SHOULD grant the service to the end user and store the request in the
 credit-control application level non-volatile storage.  (Note that
 re-sending the request at a later time is not a guarantee that the
 service will be debited, as the user's account may be empty when the
 server successfully processes the request.)  The credit-control
 client MUST mark these request messages as possible duplicates by
 setting the T-flag in the command header as described in [DIAMBASE],
 section 3.
 If the Direct-Debiting-Failure-Handling AVP is set to CONTINUE, the
 service SHOULD be granted, even if credit-control messages cannot be
 delivered and messages are not buffered.
 If the timer Tx expires, the credit-control client MUST continue the
 service and wait for a possible late answer.  If the request times
 out, the credit-control client re-transmits the request (marked with
 T-flag) to a backup credit-control server, if possible.  If the re-
 transmitted request also times out, or if a temporary error is
 received in answer, the credit-control client buffers the request if
 the value of the Direct-Debiting-Failure-Handling AVP is set to
 TERMINATE_OR_BUFFER.  If a failed answer is received for the

Hakala, et al. Standards Track [Page 45] RFC 4006 Diameter Credit-Control Application August 2005

 re-transmitted request, the credit-control client frees all the
 resources reserved for the event message and deletes the request
 regardless of the value of the DDFH.
 The Credit-Control-Request with the requested action REFUND_ACCOUNT
 should always be stored in the credit-control application level non-
 volatile storage in case of temporary failure.  The credit-control
 client MUST mark the re-transmitted request message as a possible
 duplicate by setting the T-flag in the command header as described in
 [DIAMBASE], section 3.
 For stored requests, the implementation may choose to limit the
 number of re-transmission attempts and to define a re-transmission
 interval.
 Note that only one place in the credit-control system SHOULD be
 responsible for duplicate detection.  If there is only one credit-
 control server within the given realm, the credit-control server may
 perform duplicate detection.  If there is more than one credit-
 control server in a given realm, only one entity in the credit-
 control system should be responsible, to ensure that the end user's
 account is not debited or credited multiple times for the same
 service event.

7. Credit-Control Application State Machine

 This section defines the credit-control application state machine.
 The first four state machines are to be observed by credit-control
 clients.  The first one describes the session-based credit-control
 when the first interrogation is executed as part of the
 authorization/authentication process.  The second describes the
 session-based credit-control when the first interrogation is executed
 after the authorization/authentication process.  The requirements as
 to what state machines have to be supported are discussed in section
 5.2.
 The third state machine describes the session-based credit-control
 for the intermediate and final interrogations.  The fourth one
 describes the event-based credit-control.  These latter state
 machines are to be observed by all implementations that conform to
 this specification.
 The fifth state machine describes the credit-control session from a
 credit-control server perspective.

Hakala, et al. Standards Track [Page 46] RFC 4006 Diameter Credit-Control Application August 2005

 Any event not listed in the state machines MUST be considered an
 error condition, and a corresponding answer, if applicable, MUST be
 returned to the originator of the message.
 In the state table, the event 'Failure to send' means that the
 Diameter credit-control client is unable to communicate with the
 desired destination or, if failover procedure is supported, with a
 possibly defined alternative destination (e.g., the request times out
 and the answer message is not received).  This could be due to the
 peer being down, or due to a physical link failure in the path to or
 from the credit-control server.
 The event 'Temporary error' means that the Diameter credit-control
 client received a protocol error notification (DIAMETER_TOO_BUSY,
 DIAMETER_UNABLE_TO_DELIVER, or DIAMETER_LOOP_DETECTED) in the
 Result-Code AVP of the Credit-Control-Answer command.  The above
 protocol error notification may ultimately be received in answer to
 the re-transmitted request to a defined alternative destination, if
 failover is supported.
 The event 'Failed answer' means that the Diameter credit-control
 client received non-transient failure (permanent failure)
 notification in the Credit-Control-Answer command.  The above
 permanent failure notification may ultimately be received in answer
 to the re-transmitted request to a defined alternative destination,
 if failover is supported.
 The action 'store request' means that a request is stored in the
 credit-control application level non-volatile storage.
 The event 'Not successfully processed' means that the credit-control
 server could not process the message; e.g., due to an unknown end
 user, account being empty, or errors defined in [DIAMBASE].
 The event 'User service terminated' can be triggered by various
 reasons, e.g., normal user termination, network failure, and ASR
 (Abort-Session-Request).  The Termination-Cause AVP contains
 information about the termination reason, as specified in [DIAMBASE].
 The Tx timer, which is used to control the waiting time in the
 credit-control client in the Pending state, is stopped upon exit of
 the Pending state.  The stopping of the Tx timer is omitted in the
 state machine when the new state is Idle, as moving to Idle state
 implies the clearing of the session and all the variables associated
 to it.

Hakala, et al. Standards Track [Page 47] RFC 4006 Diameter Credit-Control Application August 2005

 The states PendingI, PendingU, PendingT, PendingE, and PendingB stand
 for pending states to wait for an answer to a credit-control request
 related to Initial, Update, Termination, Event, or Buffered request,
 respectively.
 The acronyms CCFH and DDFH stand for Credit-Control-Failure-Handling
 and Direct-Debiting-Failure-Handling, respectively.
 In the following state machine table, the failover to a secondary
 server upon 'Temporary error' or 'Failure to send' is not explicitly
 described.  Moving an ongoing credit-control message stream to an
 alternative server is, however, possible if the CC-Session-Failover
 AVP is set to FAILOVER_SUPPORTED, as described in section 5.7.
 Re-sending a credit-control event to an alternative server is
 supported as described in section 6.5.
 CLIENT, SESSION BASED for the first interrogation with AA request
  State      Event                         Action       New State
  ---------------------------------------------------------------
  Idle       Client or device requests     Send          PendingI
             access/service                AA request
                                           with added
                                           CC AVPs,
                                           start Tx
  PendingI  Successful AA req.             Grant         Open
            answer received                service to
                                           end user,
                                           stop Tx
  PendingI  Tx expired                     Disconnect    Idle
                                           user/dev
  PendingI  Failed AA answer received      Disconnect    Idle
                                           user/dev
  PendingI  AA answer                      Grant         Idle
            received with result code      service
            equal to CREDIT_CONTROL_       to end user
            NOT_APPLICABLE
  PendingI  User service terminated        Queue         PendingI
                                           termination
                                           event

Hakala, et al. Standards Track [Page 48] RFC 4006 Diameter Credit-Control Application August 2005

  PendingI  Change in rating condition     Queue         PendingI
                                           changed
                                           rating
                                           condition
                                           event
    CLIENT, SESSION BASED for the first interrogation with CCR
  State      Event                          Action       New State
  ----------------------------------------------------------------
  Idle      Client or device requests      Send         PendingI
            access/service                 CC initial
                                           req.,
                                           start Tx
  PendingI  Successful CC initial          Stop Tx      Open
            answer received
  PendingI  Failure to send, or            Grant        Idle
            temporary error and            service to
            CCFH equal to CONTINUE         end user
  PendingI  Failure to send, or            Terminate    Idle
            temporary error and            end user's
            CCFH equal to TERMINATE        service
            or to RETRY_AND_TERMINATE
  PendingI  Tx expired and CCFH            Terminate    Idle
            equal to TERMINATE             end user's
                                           service
  PendingI  Tx expired and CCFH equal      Grant        PendingI
            to CONTINUE or to              service to
            RETRY_AND_TERMINATE            end user
  PendingI  CC initial answer              Terminate    Idle
            received with result code      end user's
            END_USER_SERVICE_DENIED or     service
            USER_UNKNOWN
  PendingI  CC initial answer              Grant        Idle
            received with result code      service
            equal to CREDIT_CONTROL_       to end user
            NOT_APPLICABLE

Hakala, et al. Standards Track [Page 49] RFC 4006 Diameter Credit-Control Application August 2005

  PendingI  Failed CC initial answer       Grant        Idle
            received and CCFH equal to     service to
            CONTINUE                       end user
  PendingI  Failed CC initial answer       Terminate    Idle
            received and CCFH equal        end user's
            to TERMINATE or to             service
            RETRY_AND_TERMINATE
  PendingI  User service terminated        Queue        PendingI
                                           termination
                                           event
  PendingI  Change in rating condition     Queue        PendingI
                                           changed
                                           rating
                                           condition
                                           event
   CLIENT, SESSION BASED for intermediate and final interrogations
  State     Event                          Action       New State
  ----------------------------------------------------------------
  Open      Granted unit elapses           Send         PendingU
            and no final unit              CC update
            indication received            req.,
                                           start Tx
  Open      Granted unit elapses           Terminate    PendingT
            and final unit action          end user's
            equal to TERMINATE             service, send
            received                       CC termination
                                           req.
  Open      Change in rating condition     Send         PendingU
            in queue                       CC update
                                           req.,
                                           Start Tx
  Open      Service terminated in queue    Send         PendingT
                                           CC termination
                                           req.
  Open      Change in rating condition     Send         PendingU
            or Validity-Time elapses       CC update
                                           req.,
                                           Start Tx

Hakala, et al. Standards Track [Page 50] RFC 4006 Diameter Credit-Control Application August 2005

  Open      User service terminated        Send         PendingT
                                           CC termination
                                           req.
  Open      RAR received                   Send RAA     PendingU
                                           followed by
                                           CC update req.,
                                           start Tx
  PendingU  Successful CC update           Stop Tx      Open
            answer received
  PendingU  Failure to send, or            Grant        Idle
            temporary error and            service to
            CCFH equal to CONTINUE         end user
  PendingU  Failure to send, or            Terminate    Idle
            temporary error and            end user's
            CCFH equal to TERMINATE        service
            or to RETRY_AND_TERMINATE
  PendingU  Tx expired and CCFH            Terminate    Idle
            equal to TERMINATE             end user's
                                           service
  PendingU  Tx expired and CCFH equal      Grant        PendingU
            to CONTINUE or to              service to
            RETRY_AND_TERMINATE            end user
  PendingU  CC update answer               Terminate    Idle
            received with result code      end user's
            END_USER_SERVICE_DENIED        service
  PendingU  CC update answer               Grant        Idle
            received with result code      service
            equal to CREDIT_CONTROL_       to end user
            NOT_APPLICABLE
  PendingU  Failed CC update               Grant        Idle
            answer received and            service to
            CCFH equal to CONTINUE         end user
  PendingU  Failed CC update               Terminate    Idle
            answer received and CCFH       end user's
            equal to TERMINATE or          service
            to RETRY_AND_TERMINATE

Hakala, et al. Standards Track [Page 51] RFC 4006 Diameter Credit-Control Application August 2005

  PendingU  User service terminated        Queue        PendingU
                                           termination
                                           event
  PendingU  Change in rating               Queue        PendingU
            condition                      changed
                                           rating
                                           condition
                                           event
  PendingU  RAR received                   Send RAA     PendingU
  PendingT  Successful CC                               Idle
            termination answer received
  PendingT  Failure to send, temporary                  Idle
            error, or failed answer
  PendingT  Change in rating condition                  PendingT
                     CLIENT, EVENT BASED
  State     Event                          Action        New State
  ----------------------------------------------------------------
  Idle      Client or device requests      Send          PendingE
            a one-time service             CC event
                                           req.,
                                           Start Tx
  Idle      Request in storage             Send          PendingB
                                           stored
                                           request
  PendingE  Successful CC event            Grant         Idle
            answer received                service to
                                           end user
  PendingE  Failure to send, temporary     Indicate      Idle
            error, failed CC event         service
            answer received, or            error
            Tx expired; requested
            action CHECK_BALANCE or
            PRICE_ENQUIRY
  PendingE  CC event answer                Terminate     Idle
            received with result code      end user's
            END_USER_SERVICE_DENIED or     service
            USER_UNKNOWN and Tx running

Hakala, et al. Standards Track [Page 52] RFC 4006 Diameter Credit-Control Application August 2005

  PendingE  CC event answer                Grant         Idle
            received with result code      service
            CREDIT_CONTROL_NOT_APPLICABLE; to end
            requested action               user
            DIRECT_DEBITING
  PendingE  Failure to send, temporary     Grant         Idle
            error, or failed CC event      service
            answer received; requested     to end
            action DIRECT_DEBITING;        user
            DDFH equal to CONTINUE
  PendingE  Failed CC event                Terminate     Idle
            answer received or temporary   end user's
            error; requested action        service
            DIRECT_DEBITING;
            DDFH equal to
            TERMINATE_OR_BUFFER and
            Tx running
  PendingE  Tx expired; requested          Grant         PendingE
            action DIRECT_DEBITING         service
                                           to end
                                           user
  PendingE  Failure to send; requested     Store         Idle
            action DIRECT_DEBITING;        request with
            DDFH equal to                  T-flag
            TERMINATE_OR_BUFFER
  PendingE  Temporary error; requested     Store         Idle
            action DIRECT_DEBITING;        request
            DDFH equal to
            TERMINATE_OR_BUFFER;
            Tx expired
  PendingE  Failed answer or answer                      Idle
            received with result code
            END_USER_SERVICE DENIED or
            USER_UNKNOWN; requested action
            DIRECT_DEBITING; Tx expired
  PendingE  Failed CC event answer         Indicate      Idle
            received; requested            service
            action REFUND_ACCOUNT          error and
                                           delete request

Hakala, et al. Standards Track [Page 53] RFC 4006 Diameter Credit-Control Application August 2005

  PendingE  Failure to send or             Store         Idle
            Tx expired; requested          request
            action REFUND_ACCOUNT          with T-flag
  PendingE  Temporary error,               Store         Idle
            and requested action           request
            REFUND_ACCOUNT
  PendingB  Successful CC answer           Delete        Idle
            received                       request
  PendingB  Failed CC answer               Delete        Idle
            received                       request
  PendingB  Failure to send or                           Idle
            temporary error
                 SERVER, SESSION AND EVENT BASED
  State     Event                          Action        New State
  ----------------------------------------------------------------
  Idle      CC initial request             Send          Open
            received and successfully      CC initial
            processed                      answer,
                                           reserve units,
                                           start Tcc
  Idle      CC initial request             Send          Idle
            received but not               CC initial
            successfully processed         answer with
                                           Result-Code
                                           != SUCCESS
  Idle      CC event request               Send          Idle
            received and successfully      CC event
            processed                      answer
  Idle      CC event request               Send          Idle
            received but not               CC event
            successfully processed         answer with
                                           Result-Code
                                           != SUCCESS

Hakala, et al. Standards Track [Page 54] RFC 4006 Diameter Credit-Control Application August 2005

  Open      CC update request              Send CC       Open
            received and successfully      update answer,
            processed                      debit used
                                           units,
                                           reserve
                                           new units,
                                           restart Tcc
  Open      CC update request              Send          Idle
            received but not               CC update
            successfully processed         answer with
                                           Result-Code
                                           != SUCCESS,
                                           debit used
                                           units
  Open      CC termination request         Send          Idle
            received and successfully      CC termin.
            processed                      answer,
                                           Stop Tcc,
                                           debit used
                                           units
  Open      CC termination request         Send          Idle
            received but not               CC termin.
            successfully processed         answer with
                                           Result-Code
                                           != SUCCESS,
                                           debit used
                                           units
  Open      Session supervision timer Tcc  Release       Idle
            expired                        reserved
                                           units

8. Credit-Control AVPs

 This section defines the credit-control AVPs that are specific to
 Diameter credit-control application and that MAY be included in the
 Diameter credit-control messages.
 The AVPs defined in this section MAY also be included in
 authorization commands defined in authorization-specific
 applications, such as [NASREQ] and [DIAMMIP], if the first
 interrogation is performed as part of the
 authorization/authentication process, as described in section 5.2.

Hakala, et al. Standards Track [Page 55] RFC 4006 Diameter Credit-Control Application August 2005

 The Diameter AVP rules are defined in the Diameter Base [DIAMBASE],
 section 4.  These AVP rules are observed in AVPs defined in this
 section.
 The following table describes the Diameter AVPs defined in the
 credit-control application, their AVP Code values, types, possible
 flag values, and whether the AVP MAY be encrypted.  The Diameter base
 [DIAMBASE] specifies the AVP Flag rules for AVPs in section 4.5.
                                          +--------------------+
                                          |    AVP Flag rules  |
                                          |----+-----+----+----|----+
                   AVP  Section           |    |     |SHLD|MUST|    |
 Attribute Name    Code Defined Data Type |MUST| MAY | NOT|NOT |Encr|
 -----------------------------------------|----+-----+----+----|----|
 CC-Correlation-Id 411  8.1    OctetString|    | P,M |    |  V | Y  |
 CC-Input-Octets   412  8.24   Unsigned64 | M  |  P  |    |  V | Y  |
 CC-Money          413  8.22   Grouped    | M  |  P  |    |  V | Y  |
 CC-Output-Octets  414  8.25   Unsigned64 | M  |  P  |    |  V | Y  |
 CC-Request-Number 415  8.2    Unsigned32 | M  |  P  |    |  V | Y  |
 CC-Request-Type   416  8.3    Enumerated | M  |  P  |    |  V | Y  |
 CC-Service-       417  8.26   Unsigned64 | M  |  P  |    |  V | Y  |
   Specific-Units                         |    |     |    |    |    |
 CC-Session-       418  8.4    Enumerated | M  |  P  |    |  V | Y  |
   Failover                               |    |     |    |    |    |
 CC-Sub-Session-Id 419  8.5    Unsigned64 | M  |  P  |    |  V | Y  |
 CC-Time           420  8.21   Unsigned32 | M  |  P  |    |  V | Y  |
 CC-Total-Octets   421  8.23   Unsigned64 | M  |  P  |    |  V | Y  |
 CC-Unit-Type      454  8.32   Enumerated | M  |  P  |    |  V | Y  |
 Check-Balance-    422  8.6    Enumerated | M  |  P  |    |  V | Y  |
   Result                                 |    |     |    |    |    |
 Cost-Information  423  8.7    Grouped    | M  |  P  |    |  V | Y  |
 Cost-Unit         424  8.12   UTF8String | M  |  P  |    |  V | Y  |
 Credit-Control    426  8.13   Enumerated | M  |  P  |    |  V | Y  |
 Credit-Control-   427  8.14   Enumerated | M  |  P  |    |  V | Y  |
   Failure-Handling                       |    |     |    |    |    |
 Currency-Code     425  8.11   Unsigned32 | M  |  P  |    |  V | Y  |
 Direct-Debiting-  428  8.15   Enumerated | M  |  P  |    |  V | Y  |
   Failure-Handling                       |    |     |    |    |    |
 Exponent          429  8.9    Integer32  | M  |  P  |    |  V | Y  |
 Final-Unit-Action 449  8.35   Enumerated | M  |  P  |    |  V | Y  |
 Final-Unit-       430  8.34   Grouped    | M  |  P  |    |  V | Y  |
   Indication                             |    |     |    |    |    |
 Granted-Service-  431  8.17   Grouped    | M  |  P  |    |  V | Y  |
   Unit                                   |    |     |    |    |    |
 G-S-U-Pool-       453  8.31   Unsigned32 | M  |  P  |    |  V | Y  |
   Identifier                             |    |     |    |    |    |

Hakala, et al. Standards Track [Page 56] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 57] RFC 4006 Diameter Credit-Control Application August 2005

8.1. CC-Correlation-Id AVP

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

8.2. CC-Request-Number AVP

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

8.3. CC-Request-Type AVP

 The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
 contains the reason for sending the credit-control request message.
 It MUST be present in all Credit-Control-Request messages.  The
 following values are defined for the CC-Request-Type AVP:
 INITIAL_REQUEST                 1
    An Initial request is used to initiate a credit-control session,
    and contains credit control information that is relevant to the
    initiation.
 UPDATE_REQUEST                  2
    An Update request contains credit-control information for an
    existing credit-control session.  Update credit-control requests
    SHOULD be sent every time a credit-control re-authorization is
    needed at the expiry of the allocated quota or validity time.
    Further, additional service-specific events MAY trigger a
    spontaneous Update request.
 TERMINATION_REQUEST             3
    A Termination request is sent to terminate a credit-control
    session and contains credit-control information relevant to the
    existing session.

Hakala, et al. Standards Track [Page 58] RFC 4006 Diameter Credit-Control Application August 2005

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

8.4. CC-Session-Failover AVP

 The CC-Session-Failover AVP (AVP Code 418) is type of Enumerated and
 contains information as to whether moving the credit-control message
 stream to a backup server during an ongoing credit-control session is
 supported.  In communication failures, the credit-control message
 streams can be moved to an alternative destination if the credit-
 control server supports failover to an alternative server.  The
 secondary credit-control server name, if received from the home
 Diameter AAA server, can be used as an address of the backup server.
 An implementation is not required to support moving a credit-control
 message stream to an alternative server, as this also requires moving
 information related to the credit-control session to backup server.
 The following values are defined for the CC-Session-Failover AVP:
 FAILOVER_NOT_SUPPORTED          0
    When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED,
    the credit-control message stream MUST NOT to be moved to an
    alternative destination in the case of communication failure.
    This is the default behavior if the AVP isn't included in the
    reply from the authorization or credit-control server.
 FAILOVER_SUPPORTED              1
    When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
    credit-control message stream SHOULD be moved to an alternative
    destination in the case of communication failure.  Moving the
    credit-control message stream to a backup server MAY require that
    information related to the credit-control session should also be
    forwarded to alternative server.

8.5. CC-Sub-Session-Id AVP

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

Hakala, et al. Standards Track [Page 59] RFC 4006 Diameter Credit-Control Application August 2005

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

8.6. Check-Balance-Result AVP

 The Check Balance Result AVP (AVP Code 422) is of type Enumerated and
 contains the result of the balance check.  This AVP is applicable
 only when the Requested-Action AVP indicates CHECK_BALANCE in the
 Credit-Control-Request command.
 The following values are defined for the Check-Balance-Result AVP.
 ENOUGH_CREDIT                   0
    There is enough credit in the account to cover the requested
    service.
 NO_CREDIT                       1
    There isn't enough credit in the account to cover the requested
    service.

8.7. Cost-Information AVP

 The Cost-Information AVP (AVP Code 423) is of type Grouped, and it is
 used to return the cost information of a service, which the credit-
 control client can transfer transparently to the end user.  The
 included Unit-Value AVP contains the cost estimate (always type of
 money) of the service, in the case of price enquiry, or the
 accumulated cost estimation, in the case of credit-control session.
 The Currency-Code specifies in which currency the cost was given.
 The Cost-Unit specifies the unit when the service cost is a cost per
 unit (e.g., cost for the service is $1 per minute).
 When the Requested-Action AVP with value PRICE_ENQUIRY is included in
 the Credit-Control-Request command, the Cost-Information AVP sent in
 the succeeding Credit-Control-Answer command contains the cost
 estimation of the requested service, without any reservation being
 made.
 The Cost-Information AVP included in the Credit-Control-Answer
 command with the CC-Request-Type set to UPDATE_REQUEST contains the
 accumulated cost estimation for the session, without taking any
 credit reservation into account.

Hakala, et al. Standards Track [Page 60] RFC 4006 Diameter Credit-Control Application August 2005

 The Cost-Information AVP included in the Credit-Control-Answer
 command with the CC-Request-Type set to EVENT_REQUEST or
 TERMINATION_REQUEST contains the estimated total cost for the
 requested service.
 It is defined as follows (per the grouped-avp-def of
 RFC 3588 [DIAMBASE]):
              Cost-Information ::= < AVP Header: 423 >
                                   { Unit-Value }
                                   { Currency-Code }
                                   [ Cost-Unit ]

8.8. Unit-Value AVP

 Unit-Value AVP is of type Grouped (AVP Code 445) and specifies the
 units as decimal value.  The Unit-Value is a value with an exponent;
 i.e., Unit-Value = Value-Digits AVP * 10^Exponent.  This
 representation avoids unwanted rounding off.  For example, the value
 of 2,3 is represented as Value-Digits = 23 and Exponent = -1.  The
 absence of the exponent part MUST be interpreted as an exponent equal
 to zero.
 It is defined as follows (per the grouped-avp-def of
 RFC 3588 [DIAMBASE]):
                  Unit-Value ::= < AVP Header: 445 >
                                 { Value-Digits }
                                 [ Exponent ]

8.9. Exponent AVP

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

8.10. Value-Digits AVP

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

Hakala, et al. Standards Track [Page 61] RFC 4006 Diameter Credit-Control Application August 2005

8.11. Currency-Code AVP

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

8.12. Cost-Unit AVP

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

8.13. Credit-Control AVP

 The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
 be included in AA requests when the service element has credit-
 control capabilities.
 CREDIT_AUTHORIZATION            0
    If the home Diameter AAA server determines that the user has
    prepaid subscription, this value indicates that the credit-control
    server MUST be contacted to perform the first interrogation.  The
    value of the Credit-Control AVP MUST always be set to 0 in an AA
    request sent to perform the first interrogation and to initiate a
    new credit-control session.
 RE_AUTHORIZATION                1
    This value indicates to the Diameter AAA server that a credit-
    control session is ongoing for the subscriber and that the
    credit-control server MUST not be contacted.  The Credit-Control
    AVP set to the value of 1 is to be used only when the first
    interrogation has been successfully performed and the credit-
    control session is ongoing (i.e., re-authorization triggered by
    Authorization-Lifetime).  This value MUST NOT be used in an AA
    request sent to perform the first interrogation.

8.14. Credit-Control-Failure-Handling AVP

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

Hakala, et al. Standards Track [Page 62] RFC 4006 Diameter Credit-Control Application August 2005

 immediately when there is a reason to believe that the service cannot
 be charged, or to try failover to an alternative server, if possible.
 Then the server could either terminate or grant the service, should
 the alternative connection also fail.
 TERMINATE                       0
    When the Credit-Control-Failure-Handling AVP is set to TERMINATE,
    the service MUST only be granted for as long as there is a
    connection to the credit-control server.  If the credit-control
    client does not receive any Credit-Control-Answer message within
    the Tx timer (as defined in section 13), the credit-control
    request is regarded as failed, and the end user's service session
    is terminated.
    This is the default behavior if the AVP isn't included in the
    reply from the authorization or credit-control server.
 CONTINUE                       1
    When the Credit-Control-Failure-Handling AVP is set to CONTINUE,
    the credit-control client SHOULD re-send the request to an
    alternative server in the case of transport or temporary failures,
    provided that a failover procedure is supported in the credit-
    control server and the credit-control client, and that an
    alternative server is available.  Otherwise, the service SHOULD be
    granted, even if credit-control messages can't be delivered.
 RETRY_AND_TERMINATE            2
    When the Credit-Control-Failure-Handling AVP is set to
    RETRY_AND_TERMINATE, the credit-control client SHOULD re-send the
    request to an alternative server in the case of transport or
    temporary failures, provided that a failover procedure is
    supported in the credit-control server and the credit-control
    client, and that an alternative server is available.  Otherwise,
    the service SHOULD not be granted when the credit-control messages
    can't be delivered.

8.15. Direct-Debiting-Failure-Handling AVP

 The Direct-Debiting-Failure-Handling AVP (AVP Code 428) is of type
 Enumerated.  The credit-control client uses information in this AVP
 to decide what to do if sending credit-control messages (Requested-
 Action AVP set to DIRECT_DEBITING) to the credit-control server has
 been, for instance, temporarily prevented due to a network problem.
 TERMINATE_OR_BUFFER             0
    When the Direct-Debiting-Failure-Handling AVP is set to
    TERMINATE_OR_BUFFER, the service MUST be granted for as long as
    there is a connection to the credit-control server.  If the

Hakala, et al. Standards Track [Page 63] RFC 4006 Diameter Credit-Control Application August 2005

    credit-control client does not receive any Credit-Control-Answer
    message within the Tx timer (as defined in section 13) the
    credit-control request is regarded as failed.  The client SHOULD
    terminate the service if it can determine from the failed answer
    that units have not been debited.  Otherwise the credit-control
    client SHOULD grant the service, store the request in application
    level non-volatile storage, and try to re-send the request.  These
    requests MUST be marked as possible duplicates by setting the T-
    flag in the command header as described in [DIAMBASE] section 3.
    This is the default behavior if the AVP isn't included in the
    reply from the authorization server.
 CONTINUE                                              1
    When the Direct-Debiting-Failure-Handling AVP is set to CONTINUE,
    the service SHOULD be granted, even if credit-control messages
    can't be delivered, and the request should be deleted.

8.16. Multiple-Services-Credit-Control AVP

 Multiple-Services-Credit-Control AVP (AVP Code 456) is of type
 Grouped and contains the AVPs related to the independent credit-
 control of multiple services feature.  Note that each instance of
 this AVP carries units related to one or more services or related to
 a single rating group.
 The Service-Identifier and the Rating-Group AVPs are used to
 associate the granted units to a given service or rating group.  If
 both the Service-Identifier and the Rating-Group AVPs are included,
 the target of the service units is always the service(s) indicated by
 the value of the Service-Identifier AVP(s).  If only the Rating-
 Group-Id AVP is present, the Multiple-Services-Credit-Control AVP
 relates to all the services that belong to the specified rating
 group.
 The G-S-U-Pool-Reference AVP allows the server to specify a G-S-U-
 Pool-Identifier identifying a credit pool within which the units of
 the specified type are considered pooled.  If a G-S-U-Pool-Reference
 AVP is present, then actual service units of the specified type MUST
 also be present.  For example, if the G-S-U-Pool-Reference AVP
 specifies Unit-Type TIME, then the CC-Time AVP MUST be present.
 The Requested-Service-Unit AVP MAY contain the amount of requested
 service units or the requested monetary value.  It MUST be present in
 the initial interrogation and within the intermediate interrogations
 in which new quota is requested.  If the credit-control client does
 not include the Requested-Service-Unit AVP in a request command,
 because for instance, it has determined that the end-user terminated

Hakala, et al. Standards Track [Page 64] RFC 4006 Diameter Credit-Control Application August 2005

 the service, the server MUST debit the used amount from the user's
 account but MUST NOT return a new quota in the corresponding answer.
 The Validity-Time, Result-Code, and Final-Unit-Indication AVPs MAY be
 present in an answer command as defined in sections 5.1.2 and 5.6 for
 the graceful service termination.
 When both the Tariff-Time-Change and Tariff-Change-Usage AVPs are
 present, the server MUST include two separate instances of the
 Multiple-Services-Credit-Control AVP with the Granted-Service-Unit
 AVP associated to the same service-identifier and/or rating-group.
 Where the two quotas are associated to the same pool or to different
 pools, the credit pooling mechanism defined in section 5.1.2 applies.
 The Tariff-Change-Usage AVP MUST NOT be included in request commands
 to report used units before, and after tariff time change the Used-
 Service-Unit AVP MUST be used.
 A server not implementing the independent credit-control of multiple
 services functionality MUST treat the Multiple-Services-Credit-
 Control AVP as an invalid AVP.
 The Multiple-Services-Control AVP is defined as follows (per the
 grouped-avp-def of RFC 3588 [DIAMBASE]):
    Multiple-Services-Credit-Control ::= < AVP Header: 456 >
                                         [ Granted-Service-Unit ]
                                         [ Requested-Service-Unit ]
                                        *[ Used-Service-Unit ]
                                         [ Tariff-Change-Usage ]
                                        *[ Service-Identifier ]
                                         [ Rating-Group ]
                                        *[ G-S-U-Pool-Reference ]
                                         [ Validity-Time ]
                                         [ Result-Code ]
                                         [ Final-Unit-Indication ]
                                        *[ AVP ]

8.17. Granted-Service-Unit AVP

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

Hakala, et al. Standards Track [Page 65] RFC 4006 Diameter Credit-Control Application August 2005

 The Granted-Service-Unit AVP is defined as follows (per the grouped-
 avp-def of RFC 3588 [DIAMBASE]):
    Granted-Service-Unit ::= < AVP Header: 431 >
                               [ Tariff-Time-Change ]
                               [ CC-Time ]
                               [ CC-Money ]
                               [ CC-Total-Octets ]
                               [ CC-Input-Octets ]
                               [ CC-Output-Octets ]
                               [ CC-Service-Specific-Units ]
                              *[ AVP ]

8.18. Requested-Service-Unit AVP

 The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
 contains the amount of requested units specified by the Diameter
 credit-control client.  A server is not required to implement all the
 unit types, and it must treat unknown or unsupported unit types as
 invalid AVPs.
 The Requested-Service-Unit AVP is defined as follows (per the
 grouped-avp-def of RFC 3588 [DIAMBASE]):
    Requested-Service-Unit ::= < AVP Header: 437 >
                               [ CC-Time ]
                               [ CC-Money ]
                               [ CC-Total-Octets ]
                               [ CC-Input-Octets ]
                               [ CC-Output-Octets ]
                               [ CC-Service-Specific-Units ]
                              *[ AVP ]

8.19. Used-Service-Unit AVP

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

Hakala, et al. Standards Track [Page 66] RFC 4006 Diameter Credit-Control Application August 2005

 The Used-Service-Unit AVP is defined as follows (per the grouped-
 avp-def of RFC 3588 [DIAMBASE]):
    Used-Service-Unit ::= < AVP Header: 446 >
                          [ Tariff-Change-Usage ]
                          [ CC-Time ]
                          [ CC-Money ]
                          [ CC-Total-Octets ]
                          [ CC-Input-Octets ]
                          [ CC-Output-Octets ]
                          [ CC-Service-Specific-Units ]
                         *[ AVP ]

8.20. Tariff-Time-Change AVP

 The Tariff-Time-Change AVP (AVP Code 451) is of type Time.  It is
 sent from the server to the client and includes the time in seconds
 since January 1, 1900, 00:00 UTC, when the tariff of the service will
 be changed.
 The tariff change mechanism is optional for the client and server,
 and it is not used for time-based services defined in section 5.  If
 a client does not support the tariff time change mechanism, it MUST
 treat Tariff-Time-Change AVP in the answer message as an incorrect
 CCA answer.  In this case, the client terminates the credit-control
 session and indicates in the Termination-Cause AVP reason
 DIAMETER_BAD_ANSWER.
 Omission of this AVP means that no tariff change is to be reported.

8.21. CC-Time AVP

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

8.22. CC-Money AVP

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

Hakala, et al. Standards Track [Page 67] RFC 4006 Diameter Credit-Control Application August 2005

8.23. CC-Total-Octets AVP

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

8.24. CC-Input-Octets AVP

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

8.25. CC-Output-Octets AVP

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

8.26. CC-Service-Specific-Units AVP

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

8.27. Tariff-Change-Usage AVP

 The Tariff-Change-Usage AVP (AVP Code 452) is of type Enumerated and
 defines whether units are used before or after a tariff change, or
 whether the units straddled a tariff change during the reporting
 period.  Omission of this AVP means that no tariff change has
 occurred.
 In addition, when present in answer messages as part of the
 Multiple-Services-Credit-Control AVP, this AVP defines whether units
 are allocated to be used before or after a tariff change event.
 When the Tariff-Time-Change AVP is present, omission of this AVP in
 answer messages means that the single quota mechanism applies.
 Tariff-Change-Usage can be one of the following:
 UNIT_BEFORE_TARIFF_CHANGE       0
    When present in the Multiple-Services-Credit-Control AVP, this
    value indicates the amount of the units allocated for use before a
    tariff change occurs.

Hakala, et al. Standards Track [Page 68] RFC 4006 Diameter Credit-Control Application August 2005

    When present in the Used-Service-Unit AVP, this value indicates
    the amount of resource units used before a tariff change had
    occurred.
 UNIT_AFTER_TARIFF_CHANGE        1
    When present in the Multiple-Services-Credit-Control AVP, this
    value indicates the amount of the units allocated for use after a
    tariff change occurs.
    When present in the Used-Service-Unit AVP, this value indicates
    the amount of resource units used after tariff change had
    occurred.
 UNIT_INDETERMINATE              2
    The used unit contains the amount of units that straddle the
    tariff change (e.g., the metering process reports to the credit-
    control client in blocks of n octets, and one block straddled the
    tariff change).  This value is to be used only in the Used-
    Service-Unit AVP.

8.28. Service-Identifier AVP

 The Service-Identifier AVP is of type Unsigned32 (AVP Code 439) and
 contains the identifier of a service.  The specific service the
 request relates to is uniquely identified by the combination of
 Service-Context-Id and Service-Identifier AVPs.
 A usage example of this AVP is illustrated in Appendix A (Flow IX).

8.29. Rating-Group AVP

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

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

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

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 The CC-Unit-Type AVP specifies the type of units for which credit is
 pooled.
 The Unit-Value AVP specifies the multiplier, which converts between
 service units of type CC-Unit-Type and abstract service units within
 the credit pool (and thus to service units of any other service or
 rating group associated with the same pool).
 The G-S-U-Pool-Reference AVP is defined as follows (per the grouped-
 avp-def of RFC 3588 [DIAMBASE]):
    G-S-U-Pool-Reference    ::= < AVP Header: 457 >
                                { G-S-U-Pool-Identifier }
                                { CC-Unit-Type }
                                { Unit-Value }

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

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

8.32. CC-Unit-Type AVP

 The CC-Unit-Type AVP (AVP Code 454) is of type Enumerated and
 specifies the type of units considered to be pooled into a credit
 pool.
 The following values are defined for the CC-Unit-Type AVP:
    TIME                         0
    MONEY                        1
    TOTAL-OCTETS                 2
    INPUT-OCTETS                 3
    OUTPUT-OCTETS                4
    SERVICE-SPECIFIC-UNITS       5

8.33. Validity-Time AVP

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

Hakala, et al. Standards Track [Page 70] RFC 4006 Diameter Credit-Control Application August 2005

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

8.34. Final-Unit-Indication AVP

 The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
 indicates that the Granted-Service-Unit AVP in the Credit-Control-
 Answer, or in the AA answer, contains the final units for the
 service.  After these units have expired, the Diameter credit-control
 client is responsible for executing the action indicated in the
 Final-Unit-Action AVP (see section 5.6).
 If more than one unit type is received in the Credit-Control-Answer,
 the unit type that first expired SHOULD cause the credit-control
 client to execute the specified action.
 In the first interrogation, the Final-Unit-Indication AVP with
 Final-Unit-Action REDIRECT or RESTRICT_ACCESS can also be present
 with no Granted-Service-Unit AVP in the Credit-Control-Answer or in
 the AA answer.  This indicates to the Diameter credit-control client
 to execute the specified action immediately.  If the home service
 provider policy is to terminate the service, naturally, the server
 SHOULD return the appropriate transient failure (see section 9.1) in
 order to implement the policy-defined action.
 The Final-Unit-Action AVP defines the behavior of the service element
 when the user's account cannot cover the cost of the service and MUST
 always be present if the Final-Unit-Indication AVP is included in a
 command.
 If the Final-Unit-Action AVP is set to TERMINATE, no other AVPs MUST
 be present.
 If the Final-Unit-Action AVP is set to REDIRECT at least the
 Redirect-Server AVP MUST be present.  The Restriction-Filter-Rule AVP
 or the Filter-Id AVP MAY be present in the Credit-Control-Answer
 message if the user is also allowed to access other services that are
 not accessible through the address given in the Redirect-Server AVP.
 If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
 Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.

Hakala, et al. Standards Track [Page 71] RFC 4006 Diameter Credit-Control Application August 2005

 The Filter-Id AVP is defined in [NASREQ].  The Filter-Id AVP can be
 used to reference an IP filter list installed in the access device by
 means other than the Diameter credit-control application, e.g.,
 locally configured or configured by another entity.
 The Final-Unit-Indication AVP is defined as follows (per the
 grouped-avp-def of RFC 3588 [DIAMBASE]):
    Final-Unit-Indication ::= < AVP Header: 430 >
                              { Final-Unit-Action }
                             *[ Restriction-Filter-Rule ]
                             *[ Filter-Id ]
                              [ Redirect-Server ]

8.35. Final-Unit-Action AVP

 The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
 indicates to the credit-control client the action to be taken when
 the user's account cannot cover the service cost.
 The Final-Unit-Action can be one of the following:
 TERMINATE                       0
    The credit-control client MUST terminate the service session.
    This is the default handling, applicable whenever the credit-
    control client receives an unsupported Final-Unit-Action value,
    and it MUST be supported by all the Diameter credit-control client
    implementations conforming to this specification.
 REDIRECT                        1
    The service element MUST redirect the user to the address
    specified in the Redirect-Server-Address AVP.  The redirect action
    is defined in section 5.6.2.
 RESTRICT_ACCESS                 2
    The access device MUST restrict the user access according to the
    IP packet filters defined in the Restriction-Filter-Rule AVP or
    according to the IP packet filters identified by the Filter-Id
    AVP.  All the packets not matching the filters MUST be dropped
    (see section 5.6.3).

8.36. Restriction-Filter-Rule AVP

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

Hakala, et al. Standards Track [Page 72] RFC 4006 Diameter Credit-Control Application August 2005

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

8.37. Redirect-Server AVP

 The Redirect-Server AVP (AVP Code 434) is of type Grouped and
 contains the address information of the redirect server (e.g., HTTP
 redirect server, SIP Server) with which the end user is to be
 connected when the account cannot cover the service cost.  It MUST be
 present when the Final-Unit-Action AVP is set to REDIRECT.
 It is defined as follows (per the grouped-avp-def of RFC 3588
 [DIAMBASE]):
    Redirect-Server ::= < AVP Header: 434 >
                        { Redirect-Address-Type }
                        { Redirect-Server-Address }

8.38. Redirect-Address-Type AVP

 The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated
 and defines the address type of the address given in the Redirect-
 Server-Address AVP.
 The address type can be one of the following:
 IPv4 Address                    0
    The address type is in the form of "dotted-decimal" IPv4 address,
    as defined in [IPv4].
 IPv6 Address                    1
    The address type is in the form of IPv6 address, as defined in
    [IPv6Addr].  The address is a text representation of the address
    in either the preferred or alternate text form [IPv6Addr].
    Conformant implementations MUST support the preferred form and
    SHOULD support the alternate text form for IPv6 addresses.
 URL                             2
    The address type is in the form of Uniform Resource Locator, as
    defined in [URL].
 SIP URI                         3
    The address type is in the form of SIP Uniform Resource
    Identifier, as defined in [SIP].

Hakala, et al. Standards Track [Page 73] RFC 4006 Diameter Credit-Control Application August 2005

8.39. Redirect-Server-Address AVP

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

8.40. Multiple-Services-Indicator AVP

 The Multiple-Services-Indicator AVP (AVP Code 455) is of type
 Enumerated and indicates whether the Diameter credit-control client
 is capable of handling multiple services independently within a
 (sub-) session.  The absence of this AVP means that independent
 credit-control of multiple services is not supported.
 A server not implementing the independent credit-control of multiple
 services MUST treat the Multiple-Services-Indicator AVP as an invalid
 AVP.
 The following values are defined for the Multiple-Services-Indicator
 AVP:
 MULTIPLE_SERVICES_NOT_SUPPORTED 0
    Client does not support independent credit-control of multiple
    services within a (sub-)session.
 MULTIPLE_SERVICES_SUPPORTED     1
    Client supports independent credit-control of multiple services
    within a (sub-)session.

8.41. Requested-Action AVP

 The Requested-Action AVP (AVP Code 436) is of type Enumerated and
 contains the requested action being sent by Credit-Control-Request
 command where the CC-Request-Type is set to EVENT_REQUEST.  The
 following values are defined for the Requested-Action AVP:
 DIRECT_DEBITING                 0
    This indicates a request to decrease the end user's account
    according to information specified in the Requested-Service-Unit
    AVP and/or Service-Identifier AVP (additional rating information
    may be included in service-specific AVPs or in the Service-
    Parameter-Info AVP).  The Granted-Service-Unit AVP in the Credit-
    Control-Answer command contains the debited units.

Hakala, et al. Standards Track [Page 74] RFC 4006 Diameter Credit-Control Application August 2005

 REFUND_ACCOUNT                  1
    This indicates a request to increase the end user's account
    according to information specified in the Requested-Service-Unit
    AVP and/or Service-Identifier AVP (additional rating information
    may be included in service-specific AVPs or in the Service-
    Parameter-Info AVP).  The Granted-Service-Unit AVP in the Credit-
    Control-Answer command contains the refunded units.
 CHECK_BALANCE                   2
    This indicates a balance check request.  In this case, the
    checking of the account balance is done without any credit
    reservation from the account.  The Check-Balance-Result AVP in the
    Credit-Control-Answer command contains the result of the balance
    check.
 PRICE_ENQUIRY                   3
    This indicates a price enquiry request.  In this case, neither
    checking of the account balance nor reservation from the account
    will be done; only the price of the service will be returned in
    the Cost-Information AVP in the Credit-Control-Answer Command.

8.42. Service-Context-Id AVP

 The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and
 contains a unique identifier of the Diameter credit-control service
 specific document that applies to the request (as defined in section
 4.1.2).  This is an identifier allocated by the service provider, by
 the service element manufacturer, or by a standardization body, and
 MUST uniquely identify a given Diameter credit-control service
 specific document.  The format of the Service-Context-Id is:
 "service-context" "@" "domain"
 service-context = Token
 The Token is an arbitrary string of characters and digits.
 'domain' represents the entity that allocated the Service-Context-Id.
 It can be ietf.org, 3gpp.org, etc., if the identifier is allocated by
 a standardization body, or it can be the FQDN of the service provider
 (e.g., provider.example.com) or of the vendor (e.g.,
 vendor.example.com) if the identifier is allocated by a private
 entity.
 This AVP SHOULD be placed as close to the Diameter header as
 possible.

Hakala, et al. Standards Track [Page 75] RFC 4006 Diameter Credit-Control Application August 2005

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

8.43. Service-Parameter-Info AVP

 The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
 contains service-specific information used for price calculation or
 rating.  The Service-Parameter-Type AVP defines the service parameter
 type, and the Service-Parameter-Value AVP contains the parameter
 value.  The actual contents of these AVPs are not within the scope of
 this document and SHOULD be defined in another Diameter application,
 in standards written by other standardization bodies, or in service-
 specific documentation.
 In the case of an unknown service request (e.g., unknown Service-
 Parameter-Type), the corresponding answer message MUST contain the
 error code DIAMETER_RATING_FAILED.  A Credit-Control-Answer message
 with this error MUST contain one or more Failed-AVP AVPs containing
 the Service-Parameter-Info AVPs that caused the failure.
 It is defined as follows (per the grouped-avp-def of RFC 3588
 [DIAMBASE]):
    Service-Parameter-Info ::= < AVP Header: 440 >
                               { Service-Parameter-Type }
                               { Service-Parameter-Value }

8.44. Service-Parameter-Type AVP

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

Hakala, et al. Standards Track [Page 76] RFC 4006 Diameter Credit-Control Application August 2005

8.45. Service-Parameter-Value AVP

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

8.46. Subscription-Id AVP

 The Subscription-Id AVP (AVP Code 443) is used to identify the end
 user's subscription and is of type Grouped.  The Subscription-Id AVP
 includes a Subscription-Id-Data AVP that holds the identifier and a
 Subscription-Id-Type AVP that defines the identifier type.
 It is defined as follows (per the grouped-avp-def of RFC 3588
 [DIAMBASE]):
    Subscription-Id ::= < AVP Header: 443 >
                        { Subscription-Id-Type }
                        { Subscription-Id-Data }

8.47. Subscription-Id-Type AVP

 The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated,
 and it is used to determine which type of identifier is carried by
 the Subscription-Id AVP.
 This specification defines the following subscription identifiers.
 However, new Subscription-Id-Type values can be assigned by an IANA
 designated expert, as defined in section 12.  A server MUST implement
 all the Subscription-Id-Types required to perform credit
 authorization for the services it supports, including possible future
 values.  Unknown or unsupported Subscription-Id-Types MUST be treated
 according to the 'M' flag rule, as defined in [DIAMBASE].
 END_USER_E164                   0
    The identifier is in international E.164 format (e.g., MSISDN),
    according to the ITU-T E.164 numbering plan defined in [E164] and
    [CE164].
 END_USER_IMSI                   1
    The identifier is in international IMSI format, according to the
    ITU-T E.212 numbering plan as defined in [E212] and [CE212].
 END_USER_SIP_URI                2
    The identifier is in the form of a SIP URI, as defined in [SIP].
 END_USER_NAI                    3
    The identifier is in the form of a Network Access Identifier, as
    defined in [NAI].

Hakala, et al. Standards Track [Page 77] RFC 4006 Diameter Credit-Control Application August 2005

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

8.48. Subscription-Id-Data AVP

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

8.49. User-Equipment-Info AVP

 The User-Equipment-Info AVP (AVP Code 458) is of type Grouped and
 allows the credit-control client to indicate the identity and
 capability of the terminal the subscriber is using for the connection
 to network.
 It is defined as follows (per the grouped-avp-def of RFC 3588
 [DIAMBASE]):
    User-Equipment-Info ::= < AVP Header: 458 >
                            { User-Equipment-Info-Type }
                            { User-Equipment-Info-Value }

8.50. User-Equipment-Info-Type AVP

 The User-Equipment-Info-Type AVP is of type Enumerated  (AVP Code
 459) and defines the type of user equipment information contained in
 the User-Equipment-Info-Value AVP.
 This specification defines the following user equipment types.
 However, new User-Equipment-Info-Type values can be assigned by an
 IANA designated expert, as defined in section 12.
 IMEISV                          0
    The identifier contains the International Mobile Equipment
    Identifier and Software Version in the international IMEISV format
    according to 3GPP TS 23.003 [3GPPIMEI].
 MAC                             1
    The 48-bit MAC address is formatted as described in [RAD802.1X].
 EUI64                           2
    The 64-bit identifier used to identify hardware instance of the
    product, as defined in [EUI64].

Hakala, et al. Standards Track [Page 78] RFC 4006 Diameter Credit-Control Application August 2005

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

8.51. User-Equipment-Info-Value AVP

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

9. Result Code AVP Values

 This section defines new Result-Code AVP [DIAMBASE] values that must
 be supported by all Diameter implementations that conform to this
 specification.
 The Credit-Control-Answer message includes the Result-Code AVP, which
 may indicate that an error was present in the Credit-Control-Request
 message.  A rejected Credit-Control-Request message SHOULD cause the
 user's session to be terminated.

9.1. Transient Failures

 Errors that fall within the transient failures category are used to
 inform a peer that the request could not be satisfied at the time it
 was received, but that the request MAY be able to be satisfied in the
 future.
 DIAMETER_END_USER_SERVICE_DENIED           4010
    The credit-control server denies the service request due to
    service restrictions.  If the CCR contained used-service-units,
    they are deducted, if possible.
 DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE     4011
    The credit-control server determines that the service can be
    granted to the end user but that no further credit-control is
    needed for the service (e.g., service is free of charge).
 DIAMETER_CREDIT_LIMIT_REACHED              4012
    The credit-control server denies the service request because the
    end user's account could not cover the requested service.  If the
    CCR contained used-service-units they are deducted, if possible.

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9.2. Permanent Failures

 Errors that fall within the permanent failure category are used to
 inform the peer that the request failed and should not be attempted
 again.
 DIAMETER_USER_UNKNOWN                      5030
    The specified end user is unknown in the credit-control server.
 DIAMETER_RATING_FAILED                     5031
    This error code is used to inform the credit-control client that
    the credit-control server cannot rate the service request due to
    insufficient rating input, an incorrect AVP combination, or an AVP
    or an AVP value that is not recognized or supported in the rating.
    The Failed-AVP AVP MUST be included and contain a copy of the
    entire AVP(s) that could not be processed successfully or an
    example of the missing AVP complete with the Vendor-Id if
    applicable.  The value field of the missing AVP should be of
    correct minimum length and contain zeros.

10. AVP Occurrence Table

 The following table presents the AVPs defined in this document and
 specifies in which Diameter messages they MAY or MAY NOT be present.
 Note that AVPs that can only be present within a Grouped AVP are not
 represented in this table.
 The table uses the following symbols:
    0     The AVP MUST NOT be present in the message.
    0+    Zero or more instances of the AVP MAY be present in the
          message.
    0-1   Zero or one instance of the AVP MAY be present in the
          message.  It is considered an error if there is more
          than one instance of the AVP.
    1     One instance of the AVP MUST be present in the message.
    1+    At least one instance of the AVP MUST be present in the
          message.

Hakala, et al. Standards Track [Page 80] RFC 4006 Diameter Credit-Control Application August 2005

10.1. Credit-Control AVP Table

 The table in this section is used to represent which credit-control
 applications specific AVPs defined in this document are to be present
 in the credit-control messages.
                                     +-----------+
                                     |  Command  |
                                     |   Code    |
                                     |-----+-----+
       Attribute Name                | CCR | CCA |
       ------------------------------|-----+-----+
       Acct-Multi-Session-Id         | 0-1 | 0-1 |
       Auth-Application-Id           | 1   | 1   |
       CC-Correlation-Id             | 0-1 | 0   |
       CC-Session-Failover           | 0   | 0-1 |
       CC-Request-Number             | 1   | 1   |
       CC-Request-Type               | 1   | 1   |
       CC-Sub-Session-Id             | 0-1 | 0-1 |
       Check-Balance-Result          | 0   | 0-1 |
       Cost-Information              | 0   | 0-1 |
       Credit-Control-Failure-       | 0   | 0-1 |
          Handling                   |     |     |
       Destination-Host              | 0-1 | 0   |
       Destination-Realm             | 1   | 0   |
       Direct-Debiting-Failure-      | 0   | 0-1 |
          Handling                   |     |     |
       Event-Timestamp               | 0-1 | 0-1 |
       Failed-AVP                    | 0   | 0+  |
       Final-Unit-Indication         | 0   | 0-1 |
       Granted-Service-Unit          | 0   | 0-1 |
       Multiple-Services-Credit-     | 0+  | 0+  |
          Control                    |     |     |
       Multiple-Services-Indicator   | 0-1 | 0   |
       Origin-Host                   | 1   | 1   |
       Origin-Realm                  | 1   | 1   |
       Origin-State-Id               | 0-1 | 0-1 |
       Proxy-Info                    | 0+  | 0+  |
       Redirect-Host                 | 0   | 0+  |
       Redirect-Host-Usage           | 0   | 0-1 |
       Redirect-Max-Cache-Time       | 0   | 0-1 |
       Requested-Action              | 0-1 | 0   |
       Requested-Service-Unit        | 0-1 | 0   |
       Route-Record                  | 0+  | 0+  |
       Result-Code                   | 0   | 1   |
       Service-Context-Id            | 1   | 0   |
       Service-Identifier            | 0-1 | 0   |
       Service-Parameter-Info        | 0+  | 0   |

Hakala, et al. Standards Track [Page 81] RFC 4006 Diameter Credit-Control Application August 2005

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

10.2. Re-Auth-Request/Answer AVP Table

 This section defines AVPs that are specific to the Diameter credit-
 control application and that MAY be included in the Diameter Re-
 Auth-Request/Answer (RAR/RAA) message [DIAMBASE].
 Re-Auth-Request/Answer command MAY include the following additional
 AVPs:
                                     +---------------+
                                     | Command Code  |
                                     |-------+-------+
       Attribute Name                |  RAR  |  RAA  |
       ------------------------------+-------+-------+
       CC-Sub-Session-Id             |  0-1  |  0-1  |
       G-S-U-Pool-Identifier         |  0-1  |  0-1  |
       Service-Identifier            |  0-1  |  0-1  |
       Rating-Group                  |  0-1  |  0-1  |
       ------------------------------+-------+-------+

11. RADIUS/Diameter Credit-Control Interworking Model

 This section defines the basic principles for the Diameter credit-
 control/RADIUS prepaid inter-working model; that is, a message
 translation between a RADIUS based prepaid solution and a Diameter
 credit-control application.  A complete description of the protocol
 translations between RADIUS and the Diameter credit-control
 application is beyond the scope of this specification and SHOULD be
 addressed in another appropriate document, such as the RADIUS prepaid
 specification.
 The Diameter credit-control architecture may have a Translation Agent
 capable of translation between RADIUS prepaid and Diameter credit-
 control protocols.  An AAA server (usually the home AAA server) may
 act as a Translation Agent and as a Diameter credit-control client
 for service elements that use credit-control mechanisms other than
 Diameter credit control for instance, RADIUS prepaid.  In this case,
 the home AAA server contacts the Diameter credit-control server as
 part of the authorization process.  The interworking architecture is

Hakala, et al. Standards Track [Page 82] RFC 4006 Diameter Credit-Control Application August 2005

 illustrated in Figure 7, and interworking flow in Figure 8.  In a
 roaming situation the service element (e.g., the NAS) may be located
 in the visited network, and a visited AAA server is usually
 contacted.  The visited AAA server connects then to the home AAA
 server.
                                RADIUS Prepaid
 +--------+       +---------+   protocol +------------+  +--------+
 |  End   |<----->| Service |<---------->| Home AAA   |  |Business|
 |  User  |       | Element |            |  Server    |  |Support |
 +--------+   +-->|         |            |+----------+|->|System  |
              |   +---------+            ||CC Client ||  |        |
              |                          |+----------+|  |        |
 +--------+   |                          +------^-----+  +----^---+
 |  End   |<--+                Credit-Control   |             |
 |  User  |                          Protocol   |             |
 +--------+                             +-------V--------+    |
                                        |Credit-Control  |----+
                                        |   Server       |
                                        +----------------+
      Figure 7: Credit-control architecture with service element
                containing translation agent, translating RADIUS
                prepaid to Diameter credit-control protocol
 When the AAA server acting as a Translation Agent receives an initial
 RADIUS Access-Request message from service element (e.g., NAS
 access), it performs regular authentication and authorization.  If
 the RADIUS Access-Request message indicates that the service element
 is capable of credit-control, and if the home AAA server finds that
 the subscriber is a prepaid subscriber, then a Diameter credit-
 control request SHOULD be sent toward the credit-control server to
 perform credit authorization and to establish a credit-control
 session.  After the Diameter credit-control server checks the end
 user's account balance, rates the service, and reserves credit from
 the end user's account, the reserved quota is returned to the home
 AAA server in the Diameter Credit-Control-Answer.  Then the home AAA
 server sends the reserved quota to the service element in the RADIUS
 Access-Accept.
 At the expiry of the allocated quota, the service element sends a new
 RADIUS Access-Request containing the units used this far to the home
 AAA server.  The home AAA server shall map a RADIUS Access-Request
 containing the reported units to the Diameter credit-control server
 in a Diameter Credit-Control-Request (UPDATE_REQUEST).  The Diameter
 credit-control server debits the used units from the end user's
 account and allocates a new quota that is returned to the home AAA
 server in the Diameter Credit-Control-Answer.  The quota is

Hakala, et al. Standards Track [Page 83] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 84] RFC 4006 Diameter Credit-Control Application August 2005

 A following diagram illustrates a RADIUS prepaid - Diameter credit-
 control interworking sequence.
    Service Element         Translation Agent
      (e.g., NAS)               (CC Client)             CC Server
          |     Access-Request     |                        |
          |----------------------->|                        |
          |                        |    CCR (initial)       |
          |                        |----------------------->|
          |                        |    CCA (Granted-Units) |
          |                        |<-----------------------|
          |     Access-Accept      |                        |
          |     (Granted-Units)    |                        |
          |<-----------------------|                        |
          :                        :                        :
          |     Access-Request     |                        |
          |     (Used-Units)       |                        |
          |----------------------->|                        |
          |                        |    CCR (update,        |
          |                        |         Used-Units)    |
          |                        |----------------------->|
          |                        |    CCA (Granted-Units) |
          |                        |<-----------------------|
          |     Access-Accept      |                        |
          |     (Granted-Units)    |                        |
          |<-----------------------|                        |
          :                        :                        :
          |     Access-Request     |                        |
          |----------------------->|                        |
          |                        |     CCR (terminate,    |
          |                        |          Used-Units)   |
          |                        |----------------------->|
          |                        |     CCA                |
          |                        |<-----------------------|
          |     Access-Accept      |                        |
          |<-----------------------|                        |
          |                        |                        |
         Figure 8: Message flow example with RADIUS prepaid -
                Diameter credit-control interworking

12. IANA Considerations

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

Hakala, et al. Standards Track [Page 85] RFC 4006 Diameter Credit-Control Application August 2005

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

12.1. Application Identifier

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

12.2. Command Codes

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

12.3. AVP Codes

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

12.4. Result-Code AVP Values

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

12.5. CC-Request-Type AVP

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

12.6. CC-Session-Failover AVP

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

Hakala, et al. Standards Track [Page 86] RFC 4006 Diameter Credit-Control Application August 2005

12.7. CC-Unit-Type AVP

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

12.8. Check-Balance-Result AVP

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

12.9. Credit-Control AVP

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

12.10. Credit-Control-Failure-Handling AVP

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

12.11. Direct-Debiting-Failure-Handling AVP

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

12.12. Final-Unit-Action AVP

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

12.13. Multiple-Services-Indicator AVP

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

Hakala, et al. Standards Track [Page 87] RFC 4006 Diameter Credit-Control Application August 2005

12.14. Redirect-Address-Type AVP

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

12.15. Requested-Action AVP

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

12.16. Subscription-Id-Type AVP

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

12.17. Tariff-Change-Usage AVP

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

12.18. User-Equipment-Info-Type AVP

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

13. Credit-Control Application Related Parameters

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

Hakala, et al. Standards Track [Page 88] RFC 4006 Diameter Credit-Control Application August 2005

    or Direct-Debiting-Failure-Handling AVP.  The recommended value is
    10 seconds.
 Tcc timer
    The Tcc timer supervises an ongoing credit-control session in the
    credit-control server.  It is RECOMMENDED to use the Validity-Time
    as input to set the Tcc timer value.  In case of transient
    failures in the network, the Diameter credit-control server might
    change to Idle state.  To avoid this, the Tcc timer MAY be set so
    that Tcc equals to 2 x Validity-Time.
 Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling
    Client implementations may offer the possibility of locally
    configuring these AVPs.  In such a case their value and behavior
    is defined in section 5.7 for the Credit-Control-Failure-Handling
    and in section 6.5 for the Direct-Debiting-Failure-Handling.

14. Security Considerations

 The Diameter base protocol [DIAMBASE] requires that each Diameter
 implementation use underlying security; i.e., IPsec or TLS.  These
 mechanisms are believed to provide sufficient protection under the
 normal Internet threat model; that is, assuming that the authorized
 nodes engaging in the protocol have not been compromised, but that
 the attacker has complete control over the communication channels
 between them.  This includes eavesdropping, message modification,
 insertion, and man-in-the-middle and replay attacks.  Note also that
 this application includes a mechanism for application layer replay
 protection by means of the Session-Id from [DIAMBASE] and CC-
 Request-Number, which is specified in this document.  The Diameter
 credit-control application is often used within one domain, and there
 may be a single hop between the peers.  In these environments, the
 use of TLS or IPsec is sufficient.  The details of TLS and IPsec
 related security considerations are discussed in the [DIAMBASE].
 Because this application handles monetary transactions (directly or
 indirectly), it increases the interest for various security attacks.
 Therefore, all parties communicating with each other MUST be
 authenticated, including, for instance, TLS client-side
 authentication.  In addition, authorization of the client SHOULD be
 emphasized; i.e., that the client is allowed to perform credit-
 control for a certain user.  The specific means of authorization are
 outside of the scope of this specification but can be, for instance,
 manual configuration.

Hakala, et al. Standards Track [Page 89] RFC 4006 Diameter Credit-Control Application August 2005

 Another kind of threat is malicious modification, injection, or
 deletion of AVPs or complete credit-control messages.  The credit-
 control messages contain sensitive billing related information (such
 as subscription Id, granted units, used units, cost information)
 whose malicious modification can have financial consequences.
 Sometimes simply delaying the credit-control messages can cause
 disturbances in the credit-control client or server.
 Even without any modification to the messages, an adversary can
 invite a security threat by eavesdropping, as the transactions
 contain private information about the user.  Also, by monitoring the
 credit-control messages one can collect information about the
 credit-control server's billing models and business relationships.
 When third-party relays or proxy are involved, the hop-by-hop
 security does not necessarily provide sufficient protection for
 Diameter user session.  In some cases, it may be inappropriate to
 send Diameter messages, such as CCR and CCA, containing sensitive
 AVPs via untrusted Diameter proxy agents, as there are no assurances
 that third-party proxies will not modify the credit-control commands
 or AVP values.

14.1. Direct Connection with Redirects

 A Diameter credit-control agent cannot always know whether agents
 between it and the end user's Diameter credit-control server are
 reliable.  In this case, the Diameter credit-control agent doesn't
 have a routing entry in its Diameter Routing Table (defined in
 [DIAMBASE], section 2.7) for the realm of the credit-control server
 in the end user's home domain.  The Diameter credit-control agent can
 have a default route configured to a local Redirect agent, and it
 redirects the CCR message to the redirect agent.  The local Redirect
 agent then returns a redirect notification (Result-code 3006,
 DIAMETER_REDIRECT_INDICATION) to the credit-control agent, as well as
 Diameter credit-control server(s) information (Redirect-Host AVP) and
 information (Redirect-Host-Usage AVP) about how the routing entry
 resulting from the Redirect-Host is to be used.  The Diameter
 credit-control agent then forwards the CCR message directly to one of
 the hosts identified by the CCA message from the redirect agent.  If
 the value of the Redirect-Host-Usage AVP is unequal to zero, all
 following messages are sent to the host specified in the Redirect-
 Host AVP until the time specified by the Redirect-Max-Cache-Time AVP
 is expired.
 There are some authorization issues even with redirects.  There may
 be attacks toward nodes that have been properly authorized, but that
 abuse their authorization or have been compromised.  These issues are
 discussed more widely in [DIAMEAP], section 8.

Hakala, et al. Standards Track [Page 90] RFC 4006 Diameter Credit-Control Application August 2005

15. References

15.1. Normative References

 [DIAMBASE]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
             Arkko, "Diameter Base Protocol", RFC 3588, September
             2003.
 [3GPPCHARG] 3rd Generation Partnership Project; Technical
             Specification Group Services and System Aspects, Service
             aspects; Charging and Billing, (release 5), 3GPP TS
             22.115 v. 5.2.1, 2002-03.
 [SIP]       Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
             A., Peterson, J., Sparks, R., Handley, M., and E.
             Schooler, "SIP:  Session Initiation Protocol", RFC 3261,
             June 2002.
 [NAI]       Aboba, B. and M. Beadles, "The Network Access
             Identifier", RFC 2486, January 1999.
 [E164]      Recommendation E.164/I.331 (05/97): The International
             Public Telecommunication Numbering Plan. 1997.
 [CE164]     Complement to ITU-T Recommendation E.164 (05/1997):"List
             of ITU-T Recommendation E.164 assigned country codes",
             June 2000.
 [E212]      Recommendation E.212 (11/98): The international
             identification plan for mobile terminals and mobile
             users. 1998.
 [CE212]     Complement to ITU-T Recommendation E.212 (11/1997):" List
             of mobile country or geographical area codes", February
             1999.
 [IANA]      Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 2434,
             October 1998.
 [IPv4]      Postel, J., "Internet Protocol", STD 5, RFC 791,
             September 1981.
 [IPv6Addr]  Hinden, R. and S. Deering, "Internet Protocol Version 6
             (IPv6) Addressing Architecture", RFC 3513, April 2003.
 [KEYWORDS]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

Hakala, et al. Standards Track [Page 91] RFC 4006 Diameter Credit-Control Application August 2005

 [ISO4217]   Codes for the representation of currencies and funds,
             International Standard ISO 4217,2001
 [NASREQ]    Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
             "Diameter Network Access Server Application", RFC 4005,
             August 2005.
 [AAATRANS]  Aboba, B. and J. Wood, "Authentication, Authorization and
             Accounting (AAA) Transport Profile", RFC 3539, June 2003.
 [URL]       Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
             Resource Locators (URL)", RFC 1738, December 1994.
 [RAD802.1X] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J.
             Roese, "IEEE 802.1X Remote Authentication Dial In User
             Service (RADIUS) Usage Guidelines", RFC 3580, September
             2003.
 [EUI64]     IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
             Registration Authority",
             http://standards.ieee.org/regauth/oui/tutorials/
             EUI64.html March 1997.
 [3GPPIMEI]  3rd Generation Partnership Project; Technical
             Specification Group Core Network, Numbering, addressing
             and identification, (release 5), 3GPP TS 23.003 v. 5.8.0,
             2003-12

15.2. Informative References

 [RFC2866]   Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
 [DIAMMIP]   Calhoun, P., Johansson, T., Perkins, C., Hiller, T., and
             P. McCann, "Diameter Mobile IPv4 Application", RFC 4004,
             August 2005.
 [DIAMEAP]   Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
             Authentication Protocol (EAP) Application", Work in
             Progress.
 [RFC3725]   Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
             Camarillo, "Best Current Practices for Third Party Call
             Control (3pcc) in the Session Initiation Protocol (SIP)",
             BCP 85, RFC 3725, April 2004.

Hakala, et al. Standards Track [Page 92] RFC 4006 Diameter Credit-Control Application August 2005

16. Acknowledgements

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

Hakala, et al. Standards Track [Page 93] RFC 4006 Diameter Credit-Control Application August 2005

Appendix A. Credit-Control Sequences

A.1. Flow I

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

Hakala, et al. Standards Track [Page 94] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 95] RFC 4006 Diameter Credit-Control Application August 2005

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

A.2. Flow II

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

Hakala, et al. Standards Track [Page 96] RFC 4006 Diameter Credit-Control Application August 2005

 This is an example of Diameter credit-control for SIP sessions.
 Although the flow focuses on illustrating the usage of credit-control
 messages, the SIP signaling is inaccurate, and the diagram is not by
 any means an attempt to define a service provider's SIP network.
 However, for the sake of this example, some assumptions are made
 below.
 Typically, prepaid services based, for example, on time usage for SIP
 session require an entity in the service provider network to
 intercept all the requests within the SIP dialog in order to detect
 events, such as session establishment and session release, that are
 essential to perform credit-control operations with the credit-
 control server.  Therefore, in this example, it is assumed that the
 SIP Proxy adds a Record-Route header in the initial SIP INVITE to
 make sure that all the future requests in the created dialog traverse
 through it (for the definitions of 'Record-Route' and 'dialog' please
 refer to [SIP]).  Finally, the degree of credit-control measuring of
 the media by the proxy depends on the business model design used in
 setting up the end system and proxies in the SIP network.
 The end user (SIP User Agent A) sends REGISTER with credentials (i).
 The SIP Proxy sends a request to the home AAA server to perform
 Multimedia authentication and authorization by using, for instance,
 Diameter Multimedia application (ii).  The home AAA server checks
 that the credentials are correct and checks the user profile.
 Eventually, 200 OK response (iii) is sent to the UA.  Note that the
 Authentication and Authorization is valid for the registration
 validity period duration (i.e., until re-registration is performed).
 Several SIP sessions may be established without re-authorization.
 UA A sends an INVITE (1).  The SIP Proxy sends a Diameter Credit-
 Control-Request (INITIAL_REQUEST) to the Diameter credit-control
 server (2).  The Credit-Control-Request contains information obtained
 from the SIP signaling describing the requested service (e.g.,
 calling party, called party, Session Description Protocol
 attributes).  The Diameter credit-control server checks the end
 user's account balance, rates the service, and reserves credit from
 the end user's account.  The reserved quota is returned to the SIP
 Proxy in the Diameter Credit-Control-Answer (3).  The SIP Proxy
 forwards the SIP INVITE to UA B (4).  B's phone rings, and B answers.
 The media flows between them, and the SIP Proxy starts measuring the
 quota.  At the expiry of the allocated quota, the SIP Proxy sends a
 Diameter Credit-Control-Request (UPDATE_REQUEST) to the Diameter
 credit-control server (5).  This message contains the units used thus
 far.  The Diameter credit-control server debits the used units from
 the end user's account and allocates new credit that is returned to
 the SIP Proxy in the Diameter Credit-Control-Answer (6).  The end
 user terminates the service by sending a BYE (7).  The SIP Proxy

Hakala, et al. Standards Track [Page 97] RFC 4006 Diameter Credit-Control Application August 2005

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

A.3. Flow III

                        MMS Server
           A           (CC Client)           B           CC Server
           |(1) Send MMS    |                |                |
           |--------------->|                |                |
           |                |(2)  CCR (event, DIRECT_DEBITING,|
           |                |          MMS specific AVP)      |
           |                |-------------------------------->|
           |                |(3)  CCA (Granted-Units)         |
           |                |<--------------------------------|
           |(4) Send MMS Ack|                |                |
           |<---------------|                |                |
           |                |(5) Notify MMS  |                |
           |                |--------------->|                |
           :                :                :                :
           |                |(6) Retrieve MMS|                |
           |                |<---------------|                |
           |                |(7) Retrieve MMS|                |
           |                |    Ack         |                |
           |                |--------------->|                |
           |                |                |                |
                           Figure A.3: Flow III
 A credit-control flow for Multimedia Messaging Services is shown in
 Figure A.3.  The sender is charged as soon as the messaging server
 successfully stores the message.
 The end user A sends a Multimedia Message (MMS) to the MMS server
 (1).  The MMS server stores the message and sends a Diameter Credit-
 Control-Request (EVENT_REQUEST with Requested-Action DIRECT_DEBITING)
 to the Diameter credit-control server (2).  The Credit-Control-
 Request contains information about the MMS message (e.g., size,
 recipient address, image coding type).  The Diameter credit-control
 server checks the end user's account balance, rates the service, and
 debits the service from the end user's account.  The granted quota is
 returned to the MMS server in the Diameter Credit-Control-Answer (3).
 The MMS server acknowledges the successful reception of the MMS
 message (4).  The MMS Server notifies the recipient about the new MMS
 (5), and end user B retrieves the message from the MMS message store
 (6),(7).

Hakala, et al. Standards Track [Page 98] RFC 4006 Diameter Credit-Control Application August 2005

A.4. Flow IV

                        MMS Server
    Content Server     (CC Client)           B           CC Server
           |(1) Send MMS    |                |                |
           |--------------->|                |                |
           |                |(2)  CCR (event, CHECK_BALANCE,  |
           |                |          MMS specific AVP)      |
           |                |-------------------------------->|
           |                |(3)  CCA (ENOUGH_CREDIT)         |
           |                |<--------------------------------|
           |(4) Send MMS Ack|                |                |
           |<---------------|                |                |
           |                |(5) Notify MMS  |                |
           |                |--------------->|                |
           :                :                :                :
           |                |(6) Retrieve MMS|                |
           |                |<---------------|                |
           |                |(7)  CCR (event, DIRECT_DEBITING,|
           |                |          MMS specific AVP)      |
           |                |-------------------------------->|
           |                |(8)  CCA (Granted-Units)         |
           |                |<--------------------------------|
           |                |(9) Retrieve MMS|                |
           |                |    Ack         |                |
           |                |--------------->|                |
           |                |                |                |
                            Figure A.4: Flow IV
 This is an example of Diameter credit-control for direct debiting
 using the Multimedia Messaging Service environment.  Although the
 flow focuses on illustrating the usage of credit-control messages,
 the MMS signaling is inaccurate, and the diagram is not by any means
 an attempt to define any service provider's MMS configuration or
 billing model.
 A credit-control flow for Multimedia Messaging Service is shown in
 Figure A.4.  The recipient is charged at the message delivery.
 A content server sends a Multimedia Message (MMS) to the MMS server
 (1) that stores the message.  The message recipient will be charged
 for the MMS message in this case.  As there can be a substantially
 long time between the receipt of the message at the MMS server and
 the actual retrieval of the message, the MMS server does not
 establish any credit-control session to the Diameter credit-control
 server but performs first only a balance check (without any credit
 reservation) by sending a Diameter Credit-Control-Request

Hakala, et al. Standards Track [Page 99] RFC 4006 Diameter Credit-Control Application August 2005

 (EVENT_REQUEST with Requested-Action CHECK_BALANCE) to verify that
 end user B can cover the cost for the MMS (2).  The Diameter credit-
 control server checks the end user's account balance and returns the
 answer to the MMS server in the Diameter Credit-Control-Answer (3).
 The MMS server acknowledges the successful reception of the MMS
 message (4).  The MMS server notifies the recipient of the new MMS
 (5), and after some time end user B retrieves the message from the
 MMS message store (6).  The MMS server sends a Diameter Credit-
 Control-Request (EVENT_REQUEST with Requested-Action:
 DIRECT_DEBITING) to the Diameter credit-control server (7).  The
 Credit-Control-Request contains information about the MMS message
 (e.g., size, recipient address, coding type).  The Diameter credit-
 control server checks the end user's account balance, rates the
 service, and debits the service from the end user's account.  The
 granted quota is returned to the MMS server in the Diameter Credit-
 Control-Request (8).  The MMS is transferred to end user B (9).
 Note that the transfer of the MMS message can take an extended time
 and can fail, in which case a recovery action is needed.  The MMS
 server should return the already debited units to the user's account
 by using the REFUND action described in section 6.4.

A.5. Flow V

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

Hakala, et al. Standards Track [Page 100] RFC 4006 Diameter Credit-Control Application August 2005

 This is an example of Diameter credit-control for SIP sessions.
 Although the flow focuses on illustrating the usage of credit-control
 messages, the SIP signaling is inaccurate, and the diagram is not by
 any means an attempt to define a service provider's SIP network.
 Figure A.5 is an example of Advice of Charge (AoC) service for SIP
 call.  User A can be either a postpaid or prepaid subscriber using
 the AoC service.  It is assumed that the SIP controller also has HTTP
 capabilities and delivers an interactive AoC web page with, for
 instance, the cost information, the details of the call derived from
 the SDP, and a button to accept/not accept the charges.  (There may
 be many other ways to deliver AoC information; however, this flow
 focuses on the use of the credit-control messages.)  The user has
 been authenticated and authorized prior to initiating the call and
 subscribed to AoC service.
 UA A sends an INVITE with SDP to B (1).  The SIP controller
 determines that the user is subscribed to AoC service and sends a
 Diameter Credit-Control-Request (EVENT_REQUEST with Requested-Action:
 PRICE_ENQUIRY) to the Diameter credit-control server (2).  The
 Credit-Control-Request contains SIP specific AVPs derived from the
 SIP signaling, describing the requested service (e.g., calling party,
 called party, Session Description Protocol attributes).  The Diameter
 credit-control server determines the cost of the service and returns
 the Credit-Control-Answer including the Cost-Information AVP (3).
 The SIP controller manufactures the AoC web page with information
 received in SIP signaling and with the cost information received from
 the credit-control server.  Then it sends a SIP MESSAGE that contains
 a URL pointing to the AoC information web page (4).  At the receipt
 of the SIP MESSAGE, A's UA automatically invokes the web browser that
 retrieves the AoC information (5).  The user clicks on a proper
 button and accepts the charges (6).  The SIP controller continues the
 session and sends the INVITE to the B party, which accepts the call
 (7,8,9).

Hakala, et al. Standards Track [Page 101] RFC 4006 Diameter Credit-Control Application August 2005

A.6. Flow VI

                           Gaming Server
    End User                (CC Client)              CC Server
       |  (1)Service Delivery   |                        |
       |<---------------------->|                        |
       :                        :                        :
       :                        :                        :
       |                        |(2)CCR(event,REFUND,Requested-
       |                        |Service-Unit,Service-Parameter-Info)
       |                        |----------------------->|
       |                        |  (3)CCA(Cost-Information)
       |                        |<-----------------------|
       |        (4)Notification |                        |
       |<-----------------------|                        |
                        Figure A.6: Flow VI
 Figure A.6 illustrates a credit-control flow for the REFUND case.  It
 is assumed that there is a trusted relationship and secure connection
 between the Gaming server and the Diameter credit-control server.
 The end user may be a prepaid subscriber or a postpaid subscriber.
 While the end user is playing the game (1), she enters a new level
 that entitles her to a bonus.  The Gaming server sends a Diameter
 Credit-Control-Request (EVENT_REQUEST with Requested-Action:
 REFUND_ACCOUNT) to the Diameter credit-control server (2).  The
 Credit-Control-Request Request contains the Requested-Service-Unit
 AVP with the CC-Service-Specific-Units containing the number of
 points the user just won.  The Service-Parameter-Info AVP is also
 included in the request and specifies the service event to be rated
 (e.g., Tetris Bonus).  From information received, the Diameter
 credit-control server determines the amount to be credited, refunds
 the user's account, and returns the Credit-Control-Answer, including
 the Cost-Information AVP (3).  The Cost-Information indicates the
 credited amount.  At the first opportunity, the Gaming server
 notifies the end user of the credited amount (4).

Hakala, et al. Standards Track [Page 102] RFC 4006 Diameter Credit-Control Application August 2005

A.7. Flow VII

                SIP Controller    Top-Up
      A          (CC Client)      Server           B      CC Server
      |               |              |             |              |
      |               | (1) CCR(Update,Used-Unit)  |              |
      |               |------------------------------------------>|
      |               |              (2) CCA(Final-Unit, Redirect)|
      |               |<------------------------------------------|
      :               :              :             :              :
      :               :              :             :              :
      |               | (3) CCR(Update, Used-Units)|              |
      |               |------------------------------------------>|
      |               | (3a)INVITE("hold")         |              |
      |               |--------------------------->|              |
      |               |              |      (4) CCA(Validity-Time)|
      |               |<------------------------------------------|
      |     (5)INVITE | (6)INVITE    |             |              |
      |<--------------|------------->|             |              |
      |            (7)RTP            |             |              |
      |..............................|             |              |
      |               |       (8)BYE |             |              |
      |               |<-------------|             |              |
      |               | (9)CCR(Update)             |              |
      |               |------------------------------------------>|
      |               |                     (10)CCA(Granted-Unit) |
      |               |<------------------------------------------|
      |    (12)INVITE | (11)INVITE                 |              |
      |<--------------|--------------------------->|              |
                         Figure A.7: Flow VII
 Figure A.7 is an example of the graceful service termination for a
 SIP call.  It is assumed that the call is set up so that the
 controller is in the call as a B2BUA (Back to Back User Agent)
 performing third-party call control (3PCC).  Note that the SIP
 signaling is inaccurate, as the focus of this flow is in the graceful
 service termination and credit-control authorization.  The best
 practice for 3PCC is defined in [RFC3725].
 The call is ongoing between users A and B; user A has a prepaid
 subscription.  At the expiry of the allocated quota, the SIP
 controller sends a Diameter Credit-Control-Request (UPDATE_REQUEST)
 to the Diameter credit-control server (1).  This message contains the
 units used thus far.  The Diameter credit-control server debits the
 used units from the end user's account and allocates the final quota
 returned to the SIP controller in the Diameter Credit-Control-Answer
 (2).  This message contains the Final-Unit-Indication AVP with the

Hakala, et al. Standards Track [Page 103] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 104] RFC 4006 Diameter Credit-Control Application August 2005

A.8. Flow VIII

                       NAS                           Top-up      CC
 End-User         (CC Client)          AAA Server    Server    Server
   |(1)User Logon      |(2)AA Request (CC AVPs)        |         |
   |------------------>|------------------->|          |         |
   |                   |                    |(3)CCR(initial, CC AVPs)
   |                   |                    |------------------->|
   |                   |                    |(4)CCA(Final-Unit,  |
   |                   |                    |      Validity-Time)|
   |                   |                    |<-------------------|
   |                   |(5)AA Answer(Final-Unit,Validity-Time)   |
   |(6)Limited Access  |<-------------------|          |         |
   |      granted      |                    |          |         |
   |<----------------->|                    |          |         |
   |                   |                    |          |         |
   |   (7)TCP/HTTP     |        (8)TCP/HTTP            |         |
   |<----------------->|<----------------------------->|         |
   |                 (9) Replenish account             |         |
   |<------------------------------------------------->|         |
   |                   |                    |            (10)RAR |
   |                   |<-------------------|<-------------------|
   |                   | (11) RAA           |                    |
   |                   |------------------->|------------------->|
   |                   |(12)CCR(update)     |                    |
   |                   |------------------->|(13)CCR(Update)     |
   |                   |                    |------------------->|
   |                   |                    |(14)CCA(Granted-Units)
   |                   |(15)CCA(Granted-Units)<------------------|
   |                   |<-------------------|                    |
                       Figure A.8: Flow VIII
 Figure A.8 is an example of the graceful service termination
 initiated when the first interrogation takes place because the user's
 account is empty.  In this example, the credit-control server
 supports the server-initiated credit re-authorization.  The Diameter
 [NASREQ] is implemented in the Network Access Server (NAS).
 The user logs on to the network (1).  The Diameter NAS sends a
 Diameter AA-Request to the home Diameter AAA server.  The credit-
 control client populates the AAR with the Credit-Control AVP set to
 CREDIT_AUTHORIZATION, and service specific AVPs are included, as
 usual [NASREQ].  The home Diameter AAA server performs service
 specific Authentication and Authorization, as usual.  The home
 Diameter AAA server determines that the user has a prepaid
 subscription and notices from the Credit-Control AVP that the NAS has
 credit-control capabilities.  It sends a Diameter Credit-Control-

Hakala, et al. Standards Track [Page 105] RFC 4006 Diameter Credit-Control Application August 2005

 Request with CC-Request-Type set to INITIAL_REQUEST to the Diameter
 credit-control server to perform credit authorization (3) and to
 establish a credit-control session.  (The home Diameter AAA server
 may forward service specific AVPs received from the NAS as input for
 the rating process.)  The Diameter credit-control server checks the
 end user's account balance, determines that the account cannot cover
 the cost of the service, and initiates the graceful service
 termination.  The Credit-Control-Answer is returned to the home
 Diameter AAA server (4).  This message contains the Final-Unit-
 Indication AVP and the Validity-Time AVP set to a reasonable amount
 of time to give the user a chance to replenish his/her account (e.g.,
 10 minutes).  The Final-Unit-Indication AVP includes the Final-Unit-
 Action set to REDIRECT, the Redirect-Address-Type set to URL, and the
 Redirect-Server-Address set to the HTTP Top-up server name.  The home
 Diameter AAA server sends the received credit-control AVPs to the NAS
 in the Diameter AA-Answer (5).  Upon successful AAA, the NAS starts
 the credit-control session and immediately starts the graceful
 service termination, as instructed by the server.  The NAS grants
 limited access to the user (6).  The HTTP client software running in
 the user's device opens the transport connection redirected by the
 NAS to the Top-up server (7,8).  The user is displayed an appropriate
 web page on which to enter the credit card number, and the amount of
 money to be used to replenish the account, and with a notification
 message that she is granted unlimited access if the replenishment
 operation will be successfully executed within the next, for example,
 10 minutes.  The Top-up server validates the credit card number and
 replenishes the user's account (using some means outside the scope of
 this specification)(9).  After successful account top-up, the
 credit-control server sends a Re-Auth-Request message to the NAS
 (10).  The NAS acknowledges the request by returning the Re-Auth-
 Answer message (11) and initiates the credit re-authorization by
 sending a Credit-Control-request (UPDATE_REQUEST) to the Diameter
 credit-control server (12,13).
 The Diameter credit-control server reserves credit from the end
 user's account and returns the reserved quota to the NAS via the home
 Diameter AAA server in the Credit-Control-Answer (14,15).  The NAS
 removes the restriction placed by the graceful service termination
 and starts monitoring the granted units.

Hakala, et al. Standards Track [Page 106] RFC 4006 Diameter Credit-Control Application August 2005

A.9. Flow IX

 The Diameter credit-control application defines the Multiple-
 Services-Credit-Control AVP that can be used to support independent
 credit-control of multiple services in a single credit-control (sub-)
 session for service elements that have such capabilities.  It is
 possible to request and allocate resources as a credit pool that is
 shared between services or rating groups.
 The flow example hereafter illustrates a usage scenario where the
 credit-control client and server support independent credit-control
 of multiple services, as defined in section 5.1.2.  It is assumed
 that Service-Identifiers, Rating-Groups, and their associated
 parameters (e.g., IP 5-tuple) are locally configured in the service
 element or provisioned by an entity other than the credit-control
 server.
 End User         Service Element                           CC Server
                     (CC client)
    |(1)User logon      |                                         |
    |------------------>|(2)CCR(initial, Service-Id access,       |
    |                   |        Access specific AVPs,            |
    |                   |        Multiple-Service-Indicator)      |
    |                   |---------------------------------------->|
    |                   |(3)CCA(Multiple-Services-CC (            |
    |                   |        Granted-Units(Total-Octets),     |
    |                   |        Service-Id access,               |
    |                   |        Validity-time,                   |
    |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
    |                   |          Multiplier 10)))               |
    |                   |<----------------------------------------|
    :                   :                                         :
    |(4)Service-Request (Service 1)                               |
    |------------------>|(5)CCR(update, Multiple-Services-CC(     |
    |                   |        Requested-Units(), Service-Id 1, |
    |                   |        Rating-Group 1))                 |
    |                   |---------------------------------------->|
    |                   |(6)CCA(Multiple-Services-CC (            |
    |                   |        Granted-Units(Time),             |
    |                   |        Rating-Group 1,                  |
    |                   |        G-S-U-Pool-Reference(Pool-Id 1,  |
    |                   |          Multiplier 1)))                |
    |                   |<----------------------------------------|
    :                   :                                         :
    |(7)Service-Request (Service 2)                               |
    |------------------>|                                         |

Hakala, et al. Standards Track [Page 107] RFC 4006 Diameter Credit-Control Application August 2005

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

Hakala, et al. Standards Track [Page 108] RFC 4006 Diameter Credit-Control Application August 2005

    | +--------------+  |                                         |
    | |Total Quota   |  |(13)CCR(update,                          |
    | |elapses for   |  |       Multiple-Services-CC (            |
    | |pool 2:       |  |        Requested-Unit(),                |
    | |service 4 not |  |        Used-Units(In-Octets,Out-Octets),|
    | |allowed,      |  |        Service-Id 3, Rating-group 2),   |
    | |service 3 cont|  |       Multiple-Services-CC (            |
    | +--------------+  |        Used-Units(In-Octets,Out-Octets),|
    |                   |        Service-Id 4, Rating-Group 3))   |
    |                   |---------------------------------------->|
    |                   |(14)CCA(Multiple-Services-CC (           |
    |                   |        Result-Code 4011,                |
    |                   |        Service-Id 3))                   |
    |                   |<----------------------------------------|
    :                   :                                         :
    :                   :                                         :
    |(15) User logoff   |                                         |
    |------------------>|(16)CCR(term,                            |
    |                   |       Multiple-Services-CC (            |
    |                   |        Used-Units(In-Octets,Out-Octets),|
    |                   |        Service-Id access),              |
    |                   |       Multiple-Services-CC (            |
    |                   |        Used-Units(Time),                |
    |                   |        Service-Id 1, Rating-Group 1),   |
    |                   |       Multiple-Services-CC (            |
    |                   |        Used-Units(Time),                |
    |                   |        Service-Id 2, Rating-Group 1))   |
    |                   |---------------------------------------->|
    |                   |(17)CCA(term)                            |
    |                   |<----------------------------------------|
    Figure A.9: Flow example independent credit-control of multiple
                services in a  credit-control (sub-)Session
 The user logs on to the network (1).  The service element sends a
 Diameter Credit-Control-Request with CC-Request-Type set to
 INITIAL_REQUEST to the Diameter credit-control server to perform
 credit authorization for the bearer service (e.g., Internet access
 service) and to establish a credit-control session (2).  In this
 message, the credit-control client indicates support for independent
 credit-control of multiple services within the session by including
 the Multiple-Service-Indicator AVP.  The Diameter credit-control
 server checks the end user's account balance, with rating information
 received from the client (i.e., Service-Id and access specific AVPs),
 rates the request, and reserves credit from the end user's account.
 Suppose that the server reserves $5 and determines that the cost is
 $1/MB.  It then returns to the service element a Credit-Control-
 Answer message that includes the Multiple-Services-Credit-Control AVP

Hakala, et al. Standards Track [Page 109] RFC 4006 Diameter Credit-Control Application August 2005

 with a quota of 5MB associated to the Service-Id (access), to a
 multiplier value of 10, and to the Pool-Id 1 (3).
 The user uses Service 1 (4).  The service element sends a Diameter
 Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to
 the credit-control server to perform credit authorization for service
 1 (5).  This message includes the Multiple-Services-Credit-Control
 AVP to request service units for Service 1 that belong to Rating-
 Group 1.  The Diameter credit-control server determines that Service
 1 draws credit resources from the same account as the access service
 (i.e., pool 1).  It rates the request according to Service-
 Id/Rating-Group and updates the existing reservation by requesting
 more credit.  Suppose that the server reserves $5 more (now the
 reservation is $10) and determines that the cost is $0.1/minute.  The
 server authorizes the whole Rating-Group.  It then returns to the
 service element a Credit-Control-Answer message that includes the
 Multiple-Services-Credit-Control AVP with a quota of 50min.
 associated to the Rating-Group 1, to a multiplier value of 1, and to
 the Pool-Id 1 (6).  The client adjusts the total amount of resources
 for pool 1 according the received quota, which gives S for Pool 1 =
 100.
 The user uses Service 2, which belongs to the authorized Rating-
 Group, 1 (7).  Resources are then consumed from the pool 1.
 The user now requests Services 3 and 4 as well, which are not
 authorized (8).  The service element sends a Diameter Credit-
 Control-Request with CC-Request-Type set to UPDATE_REQUEST to the
 credit-control server in order to perform credit authorization for
 Services 3 and 4 (9).  This message includes two instances of the
 Multiple-Services-Credit-Control AVP to request service units for
 Service 3 that belong to Rating-Group 2 and for Service 4 that belong
 to Rating-Group 3.  The Diameter credit-control server determines
 that Services 3 and 4 draw credit resources from another account
 (i.e., pool 2).  It checks the end user's account balance and,
 according to Service-Ids/Rating-Groups information, rates the
 request.  Then it reserves credit from pool 2.
 For example, the server reserves $5 and determines that Service 3
 costs $0.2/MB and Service 4 costs $0.5/MB.  The server authorizes
 only Services 3 and 4.  It returns to the service element a Credit-
 Control-Answer message that includes two instances of the Multiple-
 Services-Credit-Control AVP (10).  One instance grants a quota of
 12.5MB associated to the Service-Id 3 to a multiplier value of 2 and
 to the Pool-Id 2.  The other instance grants a quota of 5 MB
 associated to the Service-Id 4 to a multiplier value of 5 and to the
 Pool-Id 2.

Hakala, et al. Standards Track [Page 110] RFC 4006 Diameter Credit-Control Application August 2005

 The server also determines that pool 2 is exhausted and Service 4 is
 not allowed to continue after these units will be consumed.
 Therefore the Final-Unit-Indication AVP with action TERMINATE is
 associated to the Service-Id 4.  The client calculates the total
 amount of resources that can be used for pool 2 according the
 received quotas and multipliers, which gives S for Pool 2 = 50.
 The Validity-Time for the access service expires.  The service
 element sends a Credit-Control-Request message to the server in order
 to perform credit re-authorization for Service-Id (access) (11).
 This message carries one instance of the Multiple-Services-Credit-
 Control AVP that includes the units used by this service.  Suppose
 that the total amount of used units is 4MB.  The client adjusts the
 total amount of resources for pool 1 accordingly, which gives S for
 Pool 1 = 60.
 The server deducts $4 from the user's account and updates the
 reservation by requesting more credit.  Suppose that the server
 reserves $5 more (now the reservation is $11) and already knows the
 cost of the Service-Id (access), which is $1/MB.  It then returns to
 the service element a Credit-Control-Answer message that includes the
 Multiple-Services-Credit-Control AVP with a quota of 5 MB associated
 to the Service-Id (access), to a multiplier value of 10, and to the
 Pool-Id 1 (12).  The client adjusts the total amount of resources for
 pool 1 according the received quota, which gives S for Pool 1 = 110.
 Services 3 and 4 consume the total amount of pool 2 credit resources
 (i.e., C1*2 + C2*5 >= S).  The service element immediately starts the
 TERMINATE action concerning Service 4 and sends a Credit-Control-
 Request message with CC-Request-Type set to UPDATE_REQUEST to the
 credit-control server in order to perform credit re-authorization for
 Service 3 (13).  This message contains two instances of the
 Multiple-Services-Credit-Control AVP to report the units used by
 Services 3 and 4.  The server deducts the last $5 from the user's
 account (pool 2) and returns the answer with Result-Code 4011 in the
 Multiple-Services-Credit-Control AVP to indicate that Service 3 can
 continue without credit-control (14).
 The end user logs off from the network (15).  To debit the used units
 from the end user's account and to stop the credit-control session,
 the service element sends a Diameter Credit-Control-Request with CC-
 Request-Type set to TERMINATION_REQUEST to the credit-control server
 (16).  This message contains the units consumed by each of the used
 services in multiple instances of the Multiple-Services-Credit-
 Control AVP.  The used units are associated with the relevant
 Service-Identifier and Rating-Group.  The Diameter credit-control

Hakala, et al. Standards Track [Page 111] RFC 4006 Diameter Credit-Control Application August 2005

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

Authors' Addresses

 Harri Hakala
 Oy L M Ericsson Ab
 Joukahaisenkatu 1
 20520 Turku
 Finland
 Phone: +358 2 265 3722
 EMail: Harri.Hakala@ericsson.com
 Leena Mattila
 Oy L M Ericsson Ab
 Joukahaisenkatu 1
 20520 Turku
 Finland
 Phone: +358 2 265 3731
 EMail: Leena.Mattila@ericsson.com
 Juha-Pekka Koskinen
 Nokia Networks
 Hatanpaanvaltatie 30
 33100 Tampere
 Finland
 Phone: +358 7180 74027
 EMail: juha-pekka.koskinen@nokia.com

Hakala, et al. Standards Track [Page 112] RFC 4006 Diameter Credit-Control Application August 2005

 Marco Stura
 Nokia Networks
 Hiomotie 32
 00380 Helsinki
 Finland
 Phone: +358 7180 64308
 EMail: marco.stura@nokia.com
 John Loughney
 Nokia Research Center
 Itamerenkatu 11-13
 00180 Helsinki
 Finland
 Phone: +358 50 483 642
 EMail: John.Loughney@nokia.com

Hakala, et al. Standards Track [Page 113] RFC 4006 Diameter Credit-Control Application August 2005

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Hakala, et al. Standards Track [Page 114]

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