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

    AAA Working Group
    Internet Draft                                         Harri Hakala
    Document: draft-ietf-aaa-diameter-cc-01.txt           Leena Mattila
    Expires: April 2004                                        Ericsson
                                                    Juha-Pekka Koskinen
                                                            Marco Stura
                                                          John Loughney
                                                                  Nokia
                                                       October 26, 2003
 
 
                   Diameter Credit-Control Application
 
 
 Status of this memo
 
    This document is an Internet-Draft and is subject to all provisions
    of Section 10 of RFC2026.
 
    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups. Note that other
    groups may also distribute working documents as Internet-Drafts.
 
    Internet-Drafts are draft documents valid for a maximum of six months
    and may be updated, replaced, or obsoleted by other documents at any
    time. It is inappropriate to use Internet-Drafts as reference
    material or cite them other than as "work in progress".
 
    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/lid-abstracts.txt
 
    The list of Internet-Draft Shadow Directories can be accessed at
    http://www.ietf.org/shadow.html
 
    This document is a product of the Authentication, Authorization and
    Accounting (AAA) Working Group of the Internet Engineering Task Force
    (IETF).  Comments are welcome should be submitted to the mailing list
    aaa-wg@merit.edu.
 
 Abstract
 
    This document specifies a DIAMETER application that can be used to
    implement real-time credit-control for a variety of end user services
    such as network access, SIP services, messaging services, download
    services etc.
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
    1. Introduction..................................................5
       1.1 Requirements language.....................................5
       1.2 Terminology...............................................6
       1.3 Advertising application support...........................7
    2. Architecture Models...........................................8
    3. Credit-Control Messages......................................10
       3.1 Credit-Control-Request (CCR) Command.....................10
       3.2 Credit-Control-Answer (CCA) Command......................11
    4. Credit Control Application Overview..........................12
       4.1 Rating Input.............................................13
    5. Session Based Credit-control.................................14
       5.1 First Interrogation......................................15
       5.2 Intermediate Interrogation...............................21
       5.3 Final Interrogation......................................22
       5.4 Server-Initiated Credit Re-Authorization.................24
       5.5 Graceful Service Termination.............................25
       5.6 Failure Procedures.......................................30
    6. One Time Event...............................................33
       6.1 Service Price Enquiry....................................34
       6.2 Balance Check............................................34
       6.3 Direct Debiting..........................................35
       6.4 Refund...................................................36
       6.5 Failure Procedure........................................36
    7. Credit Control Application State Machine.....................38
    8. Credit Control AVPs..........................................48
       8.1 CC-Correlation-Id AVP....................................50
       8.2 CC-Request-Number AVP....................................50
       8.3 CC-Request-Type AVP......................................50
       8.4 CC-Session-Failover AVP..................................51
       8.5 CC-Sub-Session-Id AVP....................................52
       8.6 Check-Balance-Result AVP.................................52
       8.7 Cost-Information AVP.....................................52
       8.8 Cost-Unit AVP............................................53
       8.9 Credit-Control AVP.......................................53
       8.10 Credit-Control-Failure-Handling AVP.....................54
       8.11 Currency-Code AVP.......................................55
       8.12 Direct-Debiting-Failure-Handling AVP....................55
       8.13 Exponent AVP............................................56
       8.14 Final-Unit-Action AVP...................................56
       8.15 Final-Unit-Indication AVP...............................56
       8.16 Granted-Service-Unit AVP................................57
       8.17 Redirect-Address-Type AVP...............................58
       8.18 Redirect-Server AVP.....................................58
       8.19 Redirect-Server-Address AVP.............................59
       8.20 Requested-Action AVP....................................59
       8.21 Requested-Service-Unit AVP..............................60
       8.22 Restriction-Filter-Rule AVP.............................60
       8.23 Service-Parameter-Info AVP..............................61
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       8.24 Service-Parameter-Type AVP..............................61
       8.25 Service-Parameter-Value AVP.............................61
       8.26 Subscription-Id AVP.....................................61
       8.27 Subscription-Id-Data AVP................................62
       8.28 Subscription-Id-Type AVP................................62
       8.29 Unit-Value AVP..........................................62
       8.30 Used-Service-Unit AVP...................................63
       8.31 Value-Digits AVP........................................63
       8.32 Validity-Time AVP.......................................64
       8.33 CC-Input-Octets AVP.....................................64
       8.34 CC-Money AVP............................................64
       8.35 CC-Output-Octets AVP....................................64
       8.36 CC-Service-Specific-Units AVP...........................64
       8.37 CC-Time AVP.............................................65
       8.38 CC-Total-Octets AVP.....................................65
       8.39 Rating-Group AVP........................................65
       8.40 Service-Identifier AVP..................................65
    9. Result Code AVP values.......................................65
       9.1 Transient Failure........................................65
       9.2 Permanent Failures.......................................66
    10. AVP Occurrence Table........................................66
       10.1 Credit Control AVP Table................................67
    11. RADIUS/Diameter Credit-control Interworking.................68
       11.1 Initial RADIUS Access-Request...........................69
       11.2 Subsequent RADIUS Access-Request message................70
       11.3 RADIUS Vendor Specific Attributes for Credit Control....71
    12. IANA Considerations.........................................71
       12.1 Application Identifier..................................72
       12.2 Command Codes...........................................72
       12.3 AVP Codes...............................................72
       12.4 Result-Code AVP Values..................................72
       12.5 CC-Request-Type AVP.....................................72
       12.6 CC-Session-Failover AVP.................................72
       12.7 Check-Balance-Result AVP................................72
       12.8 Credit-Control AVP......................................72
       12.9 Credit-Control-Failure-Handling AVP.....................73
       12.10 Direct-Debiting-Failure-Handling AVP...................73
       12.11 Final-Unit-Action AVP..................................73
       12.12 Redirect-Address-Type AVP..............................73
       12.13 Requested-Action AVP...................................73
       12.14 Subscription-Id-Type AVP...............................73
    13. Credit-control Application Related Parameters...............73
    14. Security Consideration......................................74
       14.1 Direct Connection with Redirects........................75
    15. References..................................................75
       15.1 Normative...............................................75
       15.2 Non-Normative...........................................76
    16. Acknowledgement.............................................77
    17. Author's Address............................................77
 
 
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    18. Full Copyright Statement....................................78
    19. Notices.....................................................78
    20. Expiration Date.............................................79
    Appendix A Credit Control sequences.............................79
       A.1  Flow I..................................................79
       A.2  Flow II.................................................81
       A.3  Flow III................................................82
       A.4  Flow IV.................................................84
       A.5  Flow V..................................................85
       A.6  Flow VI.................................................86
       A.7  Flow VII................................................87
       A.8  Flow VIII...............................................88
       A.9  Flow IX.................................................89
       A.10 Flow X..................................................91
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
 1. Introduction
 
    This document specifies a DIAMETER application that can be used to
    implement real-time credit-control for a variety of end user services
    such as network access, SIP services, messaging services, download
    services etc. It provides a general solution to the real-time cost
    and credit control.
 
    The prepaid model shown to be very successful for instance in GSM
    networks where network operators offering prepaid services have
    experienced a substantial growth of their customer base and revenues,
    prepaid services are now cropping up in many other wireless and wire
    line based networks as well.
 
    In next generation wireless networks, additional functionality is
    required beyond that specified in the Diameter base protocol. For
    example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
    that an application must be able to rate service information in real-
    time. In addition, it is necessary to check that the end user's
    account provides coverage for the requested service, prior to
    initiation of that service. When an account is exhausted or expired,
    the user must be denied the ability to compile additional chargeable
    events.
 
    A mechanism needs to be provided to allow the user to be informed of
    the charges to be levied for a requested service. In addition, there
    are services such as gaming and advertising that may credit as well
    as deduct from a user account.
 
    The currently existing Diameter applications provide service specific
    authorization and they do not provide credit authorization for
    prepaid users. The credit authorization shall be generic and
    applicable to all the service environments required to support
    prepaid services.
 
    To fulfill these requirements, it is necessary to facilitate
    communication between the network element providing the service (e.g.
    NAS, SIP Proxy, Application Server etc.) and a credit-control server,
    in order to minimize financial risk.
 
    The scope of this specification is the credit authorization. Service
    specific authorization and authentication is out of the scope.
 
 1.1 Requirements language
 
    In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
    "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
    described in [KEYWORDS].
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
 1.2 Terminology
 
    AAA
 
    Authentication, Authorization and Accounting
 
    AA answer
 
    AA answer does generically refer to a service specific authorization
    and authentication answer. AA answer commands are defined in service
    specific authorization applications e.g. [NASREQ] and [DiamMip].
 
    AA request
 
    AA request does generically refer to a service specific authorization
    and authentication request. AA request commands are defined in
    service specific authorization applications e.g. [NASREQ] and
    [DiamMip].
 
    Credit-control
 
    Credit-control is a mechanism, which directly interacts in real-time
    with an account and controls or monitors the charges, related to the
    service usage. Credit-control is a process of checking if credit is
    available, credit-reservation, deduction of credit from the end user
    account when service is completed and refunding of reserved credit
    not used.
 
    Diameter Credit-control Server
 
    Diameter Credit-control server acts as a prepaid server, performing
    real-time rating and credit control. It is located in the home domain
    and is accessed by service elements or AAA servers in real-time for
    purpose of price determination and credit-control before the service
    event is delivered to the end-user. It may also interact with
    business support systems.
 
    Diameter Credit-control Client
 
    A Diameter credit-control client is an entity that interacts with a
    credit-control server. It monitors the usage of the granted quota
    according to instructions returned by credit-control server.
 
    Interrogation
 
    The Diameter credit-control client uses interrogation to initiate a
    session based credit-control process and during the credit-control
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    process 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. The credit-
    control server is not required to maintain session state for one-time
    event.
 
    Rating
 
    The act of determining the cost of the service event.
 
    Service
 
    A type of task that is performed by a service element for an end
    user.
 
    Service Element
 
    A network element that provides a service to the end users.  The
    Service Element may include the Credit-control Client, or another
    entity (e.g. RADIUS AAA server) can act as a Credit-control Client on
    behalf of the Service Element. In the latter case the interface
    between the Service Element and the Diameter Credit-control Client is
    outside the scope of this specification. Examples of the Service
    Elements include NAS, Sip Proxy and Application Servers such as
    messaging server, content server and gaming server.
 
    Service Event
 
    An event relating to a service provided to the end user.
 
    Session based credit-control
 
    Credit-control process that makes use of several interrogations: the
    first, possible intermediates and the final interrogation. The first
    interrogation is used to reserve money from the user's account and
    initiate the process. The intermediate interrogations may be needed
    to request new quota while the service is being rendered. The final
    interrogation is used to exit the process. The credit-control server
    is required to maintain session state for session-based credit-
    control.
 
 1.3 Advertising application support
 
    Diameter nodes conforming to this specification MUST advertise
    support by including the value of 4 in the Auth-Application-Id of the
 
 
 
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    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 provides
    service authorization, but do not provide credit authorization for
    prepaid users. In order to support real-time credit control a new
    type of server is needed in the AAA infrastructure; Diameter credit-
    control server. The Diameter credit-control server is the entity
    responsible of credit authorization for prepaid subscribers.
 
    A service element may authenticate and authorize the end user with
    the AAA server using AAA protocols, e.g. RADIUS or a Diameter base
    protocol with a possible Diameter application.
 
    Accounting protocols such as RADIUS accounting and the Diameter base
    accounting protocol can be used to provide accounting data to the
    accounting server after service is initiated, and to provide possible
    interim reports until service completion. However, for real-time
    credit control, these authorization and accounting models are not
    sufficient.
 
    When real-time credit-control is required, the credit-control client
    contacts the credit-control server with possible service event
    information included before the service is provided to the end user.
    This process is performed in order to determine potential charges and
    to verify whether the end user's account balance is sufficient to
    cover the cost of the service being rendered.
 
    Figure 1 illustrates the typical credit-control architecture, which
    consist of a Service Element with embedded Diameter credit-control
    client, a Diameter credit-control server and an AAA server. A
    Business Support System is usually deployed; it includes at least the
    billing functionality. The credit-control server and AAA server in
    this architecture model are logical entities. The real configuration
    can combine them into a single host. The credit-control protocol is
    the Diameter base protocol with the Diameter credit-control
    application.
 
    When an end user requests services such as for instance SIP services
    or messaging services, the request is typically forwarded to a
    service element (e.g. SIP Proxy) in the user's home domain. In some
    cases it might be possible that the service element in the visited
    domain can offer services to the end user, however a commercial
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    agreement must exist between the visited domain and the home domain.
    Network access is an example of a service offered in the visited
    domain where the NAS, through an AAA infrastructure, authenticates
    and authorizes the user with the user's home network.
 
                   Service Element AAA and credit-control
    +----------+      +---------+    protocols +-----------+  +--------+
    |  End     |<---->|+-------+|<------------>|    AAA    |  |Business|
    |  User    |   +->|| CC    ||              |   Server  |->|Support |
    |          |   |  || client||<-----+       |           |  |System  |
    +----------+   |  |+-------+|      |       +-----------+  |        |
                   |  +---------+      |             ^        +--------+
    +----------+   |                   | CC protocol |             ^
    |  End     |<--+                   |       +-----v----+        |
    |  User    |                       +------>|Credit-   |        |
    +----------+                credit-control |control   |--------+
                                protocol       |server    |
                                               +----------+
 
                Figure 1: Typical credit-control architecture
 
   Other entities, such as RADIUS AAA server, may act as a Diameter
   credit-control client towards the Diameter credit-control server for
   service elements that use credit control mechanisms other than
   Diameter credit-control. In this case the AAA server contact the
   Diameter credit-control server as part of the authorization process.
   The interworking architecture is illustrated in Figure 2, the
   interaction between the Diameter credit-control client and the
   service element is outside the scope of this specification.
   Interworking with RADIUS is addressed in section 11 and Annex A.
 
                                      AAA
    +--------+       +---------+    protocol  +------------+   +--------+
    |  End   |<----->| Service |<------------>|    AAA     |   |Business|
    |  User  |       | Element |              |  Server    |   |Support |
    +--------+   +-->|         |              |+----------+|-->|System  |
                 |   +---------+              ||CC client ||   |        |
                 |                            |+----------+|   |        |
    +--------+   |                            +------^-----+   +--------+
    |  End   |<--+                  credit-control   |               ^
    |  User  |                            protocol   |               |
    +--------+                               +-------V------+        |
                                             |Credit-control|--------+
                                             |   Server     |
                                             +--------------+
 
      Figure 2: Credit-control architecture with Service Element not
                 supporting the credit-control protocol
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    There can be multiple credit-control servers in the system for
    reasons of redundancy and load balancing. The system can also contain
    separate rating server(s) and accounts can locate in a centralized
    database. For duplicate detection only one place in the credit-
    control system should perform duplicate detection to ensure that the
    end user's account is not debited or credited multiple times for the
    same service event. System internal interfaces can exist to relay
    messages between servers and an account manager. However the detailed
    architecture of credit-control system and its interfaces are
    implementation specific and are out of scope of this specification.
 
    There can exist protocol transparent Diameter relays and redirect
    agents between credit-control client and credit-control server. Also
    Diameter Redirect agents, which refer credit control clients to
    credit control servers and allow them to communicate directly can
    exist. These agents transparently support the Diameter credit-control
    application.
 
    If Diameter credit-control proxies exist between the credit-control
    client and the credit-control server, they MUST advertise the
    Diameter credit-control application support.
 
 3. Credit-Control Messages
 
    This section defines new Diameter message Command-Code values that
    MUST be supported by all Diameter implementations that conform to
    this specification. The Command Codes are:
 
     Command-Name                  Abbrev.    Code     Reference
     -----------------------------------------------------------
     Credit-Control-Request        CCR        272      3.1
     Credit-Control-Answer         CCA        272      3.2
 
 3.1 Credit-Control-Request (CCR) Command
 
    The Credit-Control-Request message (CCR), indicated by the command-
    code field set to 272 and the 'R' bit set in the Command Flags field,
    is used between the Diameter credit-control client and the credit-
    control server to request credit authorization for a given service.
 
    The Auth-Application-Id MUST be set to the value 4 indicating the
    Diameter credit-control application.
 
    Message Format
 
         <Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
                                      < Session-Id >
                                      { Origin-Host }
                                      { Origin-Realm }
 
 
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                                      { Destination-Realm }
                                      { Auth-Application-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 ]
                                      [ Termination-Cause ]
                                     *[ Requested-Service-Unit ]
                                      [ Requested-Action ]
                                     *[ Used-Service-Unit ]
                                     *[ Service-Parameter-Info ]
                                     *[ CC-Correlation-Id ]
                                     *[ Proxy-Info ]
                                             *[ Route-Record ]
                                     *[ AVP ]
 
 3.2 Credit-Control-Answer (CCA) Command
 
    The Credit-Control-Answer message (CCA), indicated by the command-
    code field set to 272 and the 'R' bit cleared in the Command Flags
    field, is used between the credit-control server and the Diameter
    credit-control client to acknowledge a Credit-Control-Request
    command.
 
    Message Format
 
         <Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
                                     < Session-Id >
                                     { Result-Code }
                                     { Origin-Host }
                                     { Origin-Realm }
                                     { Auth-Application-Id }
                                     { CC-Request-Type }
                                     { CC-Request-Number }
                                     [ User-Name ]
                                     [ CC-Session-Failover ]
                                     [ CC-Sub-Session-Id ]
                                     [ Redirect-Host AVP ]
                                     [ Redirect-Host-Usage AVP ]
                                     [ Redirect-Max-Cache-Time AVP ]
                                     [ Acct-Multi-Session-Id ]
                                     [ Origin-State-Id ]
                                     [ Event-Timestamp ]
                                     [ Subscription-Id ]
 
 
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                                    *[ Granted-Service-Unit ]
                                     [ Cost-Information]
                                     [ Final-Unit-Indication ]
                                     [ Check-Balance-Result ]
                                     [ Credit-Control-Failure-Handling ]
                                     [ Direct-Debiting-Failure-Handling ]
                                     [ Validity-Time]
                                    *[ Proxy-Info ]
                                    *[ Route-Record ]
                                    *[ AVP ]
 
 4. Credit Control Application Overview
 
    The credit authorization process takes place before and during
    service delivery to the end user, it generally requires user's
    authentication and authorization before any request is sent to the
    credit-control server.
 
    The credit control application defined in this specification supports
    for two different credit authorization models: credit authorization
    with money reservation and credit authorization with direct debiting.
    In both the models, the credit control client requests credit
    authorization to the credit control server prior to allow any service
    to be delivered to the end user.
 
    In the first model, the credit control server rates the request,
    reserve a suitable amount of money from the user's account and return
    the corresponding amount of credit resources. Note that credit
    resources may not imply actual monetary credit; credit resources may
    be granted to the credit control client in form of units (e.g. data
    volume or time) to be metered.
 
    Upon reception of a successful credit authorization answer with a
    certain amount of credit resources, the credit control client allows
    service delivery to the end user and start monitoring the usage of
    the granted resources. When the credit resources granted to the user
    have been consumed, or the service has been successfully delivered or
    terminated, the credit control client reports back to the server the
    used amount. The credit control server deducts the used amount from
    the end user's account; it may perform rating and make a new credit
    reservation if the service delivery is continuing. This process is
    accomplished with session based credit control that includes the
    first interrogation, possible intermediate interrogations and the
    final interrogation. For session based credit control, both the
    credit control client and the credit control server are required to
    maintain credit control session state.
 
    In contrast, credit authorization with direct debiting is a single
    transaction process where the credit control server directly deducts
 
 
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    the suitable amount of money from the user's account as soon as the
    credit authorization request is received. Upon reception of a
    successful credit authorization answer, the credit control client
    allows service delivery to the end user. This process is accomplished
    with the one time event. Session state is not maintained.
 
    In a multi-service environment, an end user may issue an additional
    service request (e.g. data service) during an ongoing service (e.g.
    voice call) towards the same account; or during an active multimedia
    session an additional media type is added to the session causing a
    new simultaneous request towards same account. Consequently this
    needs to be considered when credit resources are granted to the
    services.
 
    The credit control application also support for operations such as
    service price enquiry, user's balance check and refund of credit on
    the user's account. These operations are accomplished with the one
    time event. Session state is not maintained.
 
    A flexible Credit control application specific failure handling is
    defined where the home service provider can model the credit control
    client behavior according to own credit risk management policy.
    The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
    Failure-Handling AVP are defined to determine what to do if the
    sending of credit-control messages to the credit-control server has
    been temporarily prevented. The usage of Credit-Control-Failure-
    Handling AVP and the Direct-Debiting-Failure- Handling AVP gives
    flexibility to have different failure handling for credit-control
    session and one time event direct debiting.
 
 4.1 Rating Input
 
    There SHOULD be an agreement between the service providers of the
    credit control client and the credit control server in order to know
    who shall handle the billing of which services, which chargeable
    services are available when roaming etc. Part of this process has to
    cover also the agreed rating input.
 
    There are two ways for providing rating input to the credit control
    server, either by using AVPs or by including them in the Service-
    Parameter-Info AVP. The general principle for sending rating
    parameters is that the service SHOULD re-use existing AVPs, if the
    service can use AVPs defined by some Diameter application.
    Alternatively new AVPs can be defined if the existing AVPs can not be
    re-used. The Service-Parameter-Info AVP MAY be used to pass legacy
    rating information in its original encoded form (e.g. ASN.1 BER). In
    that case the rating input is embedded in the Service-Parameter-Info
    AVP as defined in the Service-Parameter-Info AVP (section 8.23). New
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    applications SHOULD favor the use of explicitly defined AVP's, to
    simplify interoperability.
 
    The service specific rating input AVPs or the contents of the
    Service-Parameter-Info AVP are not within the scope of this document
    and SHOULD be defined in another Diameter application, standards
    written by other standardization bodies, or service specific
    documentation.
 
    Within a credit control request, setting the "M" bit implies that a
    rating server or the credit control server itself SHOULD understand
    the AVP in order to rate the service. However, since different
    service providers may apply different rating policies a mandatory
    input parameter for one server might be irrelevant for another.
    Therefore, if the AVP is not relevant to the rating process, when the
    AVP is included within a credit-control request, it can be ignored,
    even if the "M" bit is set.
 
    In case a rating input required for rating process is missing from
    the Credit control request, the Credit control answer MUST contain
    error code DIAMETER_RATING_FAILED. A CCR message with this error MUST
    contain one or more Failed-AVP AVPs containing the missing AVPs that
    caused the failure.
 
 5. Session Based Credit-control
 
    For a session-based credit-control, several interrogations are
    needed: the first, intermediate (optional) and the final
    interrogation. This is illustrated in Figure 3 and Figure 4.
 
    If the credit-control client performs credit-reservation before
    granting service to the end user it MUST use several interrogations
    towards the credit-control server (i.e. session based credit-
    control). In this case the credit-control server MUST maintain the
    credit control session state.
 
    Each credit-control session MUST have globally unique Session-Id as
    defined in [DIAMBASE] and it MUST NOT be changed during the lifetime
    of a credit-control session.
 
    There are certain applications that require multiple credit control
    sub-sessions. Such applications would send messages with a constant
    Session-Id AVP, but a different CC-Sub-Session-Id AVP. If several
    credit sub-sessions will be used, all sub-sessions MUST be closed
    separately before the closing the main session to be able to report
    used units per sub-session. The absence of this AVP implies no sub-
    sessions are in use.
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    When multiple services are used within one user session and each
    service or group of services are subject to different cost, making
    use of credit control sub-sessions will result in increased signaling
    load and resources usage in both the credit control client and the
    credit control server. For instance, during one network access
    session the end user may use several http-services subject to
    different access cost. To optimally support these scenarios, the
    credit control application enables for multiple services credit
    control in a single credit control session. It is possible to request
    and allocate multiple quotas as a credit pool that is shared between
    multiple services. The services can be further grouped into rating
    groups in order to achieve even further aggregation of credit
    allocation. It is also possible to request and allocate multiple
    quotas on a per service basis. The mechanism is illustrated in
    Appendix A (Flow X).
 
    It should be noted that the service element might send a service
    specific re-authorization message to the Diameter AAA server due to
    expiration of the authorization-lifetime during an ongoing credit
    control session. However, the service specific re-authorization does
    not influence the credit authorization that is ongoing between
    credit-control client and credit-control server since credit
    authorization is controlled by the burning rate of the granted quota.
    In the event that service specific re-authorization fails the user
    will be disconnected and the credit-control client MUST send a final
    interrogation to the credit-control server.
 
    The Diameter credit-control server may want to control the validity
    time of the granted quota and/or the production of intermediate
    interrogations, thus it MAY include the Validity-Time AVP in the
    answer message to the credit-control client. Upon expiration of the
    Validity-Time, the credit-control client MUST generate a credit-
    control update request and report the used quota to the credit-
    control server. It is up to the credit-control server to determine,
    the value of the Validity-Time to be used for consumption of the
    granted service units. If the Validity-Time is used, its value SHOULD
    be given as input to set the session supervision timer Tcc (the
    session supervision timer MAY be set to two times the value of the
    Validity-Time as defined in section 13). Since credit-control update
    requests are also produced at the expiry of granted service units
    and/or for mid-session service events the omission of Validity-Time
    does not mean that intermediate interrogation for the purpose of
    credit control are not performed.
 
 5.1 First Interrogation
 
    When session based credit-control is required (e.g. the
    authentication server indicated prepaid user), the first
    interrogation MUST be sent before the Diameter credit-control client
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    allows any service event to the end user. The CC-Request-Type is set
    to the value INITIAL_REQUEST in the request message.
 
    If the Diameter credit-control client knows the cost of the service
    event (e.g. a content server delivering ringing tones may know their
    cost) the monetary amount to be charged is included in the Requested-
    Service-Unit AVP. If the Diameter credit-control client does not know
    the cost of the service event, the Requested-Service-Unit AVP MAY
    contain the number of requested service events and the Service-
    Parameter-Info AVP MAY contain the service event information to be
    rated by the credit-control server. The Service-Parameter-Info AVP
    always refers to the requested service units. Alternatively, service
    event information to be rated can be sent as service specific AVPs.
 
    The Event-Timestamp AVP contains the time when the service event is
    requested in the service element.
 
    The credit-control server SHOULD rate the service event and make a
    credit-reservation from the end user's account that covers the cost
    of the service event. If the type of the Requested-Service-Unit AVP
    is money, no rating is needed but the corresponding monetary amount
    is reserved from end user's account.
 
    The credit-control server returns the Granted-Service-Unit AVP in the
    Answer message to the Diameter credit-control client. The Granted-
    Service-Unit AVP contains the amount of service units that the
    Diameter credit-control client can provide to the end user until a
    new Credit-Control-Request MUST be sent to the credit-control server.
    If several unit types are sent in the Answer message the credit-
    control client MUST handle each unit type separately.  There MUST be
    maximum one instance of the same unit type in one Answer message. In
    case multiple quotas are conveyed to the credit control client, there
    MUST be maximum one instance of the same unit type associated to a
    Service-Identifier, or set of Service-Identifiers, or associated to a
    Rating-Group. The type of the Granted-Service-Unit AVP can be time,
    volume, service specific or money depending on the type of service
    event. It is not allowed to change the unit type(s) within the
    session.
 
    If the credit-control server determines that no further control is
    needed for the service it MAY include the result code indicating that
    the credit-control is not applicable (e.g. service is free of charge)
    and terminate the credit-control session.
 
    The Credit-Control-Answer message MAY also include the Final-Unit-
    Indication AVP to indicate that the answer message contains the final
    units for the service session. After the end user has consumed these
    units, the Diameter credit-control-client MUST behave as described in
    section 5.5.
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
    Two different approaches are defined for the first interrogation to
    suit properly in all the possible architectures. The first approach
    uses credit-control messages after user's authorization and
    authentication took place. The second approach uses service specific
    authorization messages to perform the first interrogation during the
    user's authorization/authentication phase, and credit-control
    messages for the intermediate and the final interrogations.
    In case an implementation of the credit-control client supports both
    the methods, it SHOULD be configurable what method to use.
 
    In service environments such as the Network Access Server (NAS) , it
    is desired to perform the first interrogation as part of the
    authorization/authentication process for the sake of protocol
    efficiency. Further credit authorizations after the first
    interrogation took place are performed with credit control commands
    defined in this specification. Implementations of credit-control
    client operating in the mentioned environments SHOULD support this
    method. In case the credit-control server and AAA server are separate
    physical entities the service element send the request messages to
    the AAA server, which then issue an appropriate request or proxy the
    received request forward to the credit-control server.
 
    In other service environments, such as the 3GPP network and some SIP
    scenario, there is a substantial decoupling between
    registration/access to the network and the actual service request
    (i.e. the authentication/authorization is executed once at
    registration/access to the network and is not executed for every
    service event requested by the subscriber). In such environments it
    is more appropriate to perform the first interrogation after the user
    has been authenticated and authorized. The first interrogation, the
    intermediate and final interrogations are executed with credit
    control commands defined in this specification.
 
    Other IETF standards or standards developed by other standardization
    bodies may define what is the most suitable method in their
    architecture.
 
 5.1.1 First Interrogation after Authorization and Authentication
 
    The Diameter credit-control client in the service element may get
    information from the authorization server whether credit-control is
    required based on its knowledge of the end user. If credit-control is
    required the credit-control server needs to be contacted prior to
    initiate the service delivery to the end user. The accounting
    protocol and the credit-control protocol can be used in parallel, the
    authorization server may also drive whether the parallel accounting
    stream is required.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    The following diagram illustrates the case where both protocols are
    used in parallel and the service element sends credit-control
    messages directly to the credit-control server. More credit-control
    sequence examples are given in Annex A.
 
     End-User        Service Element        AAA Server         CC Server
                       (CC Client)
        | Registration      | AA request/answer(accounting,cc or both)|
        |<----------------->|<------------------>|                    |
        |        :          |                    |                    |
        |        :          |                    |                    |
        | Service Request   |                    |                    |
        |------------------>|                    |                    |
        |                   | CCR(Initial,Credit-Control AVPs)        |
        |                  +|---------------------------------------->|
        |         CC stream||                    |  CCA(Granted-Units)|
        |                  +|<----------------------------------------|
        | Service Delivery  |                    |                    |
        |<----------------->| ACR(start,Accounting AVPs)              |
        |         :         |------------------->|+                   |
        |         :         |                ACA || Accounting stream |
        |                   |<-------------------|+                   |
        |         :         |                    |                    |
        |         :         |                    |                    |
        |                   | CCR(Update,Used-Units)                  |
        |                   |---------------------------------------->|
        |                   |                    |  CCA(Granted-Units)|
        |                   |<----------------------------------------|
        |         :         |                    |                    |
        |         :         |                    |                    |
        | End of Service    |                    |                    |
        |------------------>| CCR(Termination, Used-Units)            |
        |                   |---------------------------------------->|
        |                   |                    |               CCA  |
        |                   |<----------------------------------------|
        |                   | ACR(stop)          |                    |
        |                   |------------------->|                    |
        |                   |                ACA |                    |
        |                   |<-------------------|                    |
 
      Figure 3: Protocol example with first interrogation after user's
                        authorization/authentication
 
 5.1.2 Authorization Messages for First Interrogation
 
    The Diameter credit-control client in the service element MUST
    actively contribute with the authorization/authentication client in
    the construction of the AA request by adding appropriate credit
    control AVPs. The credit-control client MUST add the Credit-Control
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    AVP to indicate credit-control capabilities and MAY add other
    relevant credit-control specific AVPs to the proper
    authorization/authentication command to perform the first
    interrogation towards the home Diameter AAA server. The Auth-
    Application-Id is set to the appropriate value as defined in the
    relevant service specific authorization/authentication application
    document (e.g. [NASREQ], [DiamMIP]). The home Diameter AAA server
    authenticate/authorize the subscriber and determine whether or not
    credit-control is required.
 
    If credit-control is not required for the subscriber the home AAA
    will respond as usual with an appropriate AA answer message. If
    credit-control is required for the subscriber and the Credit-Control
    AVP with the value set to CREDIT_AUTHORIZATION was present in the
    authorization request, the home AAA server MUST contact the credit-
    control server to perform the first interrogation. If credit-control
    is required for the subscriber and the Credit-Control AVP was not
    present in the authorization request, the home AAA server MUST send
    an authorization reject answer message.
 
    The Diameter AAA server supporting credit-control is required to send
    the Credit-Control-Request command (CCR) defined in this document to
    the credit-control server. The Diameter AAA server populates the CCR
    based on service specific AVPs used for input to the rating process
    and possibly credit-control AVPs received in the AA request. The
    credit-control server will make money reservation from the user's
    account, will rate the request and will send a credit-control answer
    message to the home Diameter AAA server. The answer message includes
    the Granted-Service-Unit AVP(s) and MAY include other credit-control
    specific AVPs as appropriate. Additionally, the credit-control server
    MAY set the Validity-Time and MAY include the Credit-Control-Failure-
    Handling AVP and the Direct-Debiting-Failure-Handling AVP to
    determine what to do if the sending of credit-control messages to the
    credit-control server has been temporarily prevented.
 
    Upon receiving the credit-control answer message from the credit-
    control server, the home Diameter AAA server will populate the AA
    answer with the received credit-control AVPs and with usual service
    attributes according to the authorization/authentication specific
    application (e.g. [NASREQ], [DiamMIP]) and forward the packet to the
    credit-control client. If the home AAA server receives a credit-
    control reject message, it will simply generate an appropriate
    authorization reject message to the credit-control client including
    the credit-control specific error code.
 
    The credit-control client in this model sends further credit-control
    messages to the credit-control server via the home AAA server.
    Upon receiving successful authorization answer message with the
    Granted-Service-Unit AVP(s), the credit-control client will grant the
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    service to the end user and will generate intermediate credit-control
    request as required by using Credit-Control commands. The CC-Request-
    Number of the first intermediate request MUST be set to 1 (for how to
    produce unique value for the CC-Request-Number AVP see section 8.2).
 
    If service specific re-authorization is performed (i.e.
    authorization-lifetime expires), the credit-control client MUST add
    to the service specific re-authorization request the Credit-Control
    AVP with value set to RE-AUTHORIZATION to indicate that the credit-
    control server MUST NOT be contacted. When session based credit-
    control is used for the subscriber a constant Credit-Control messages
    stream is flowing through the Diameter AAA server. The Diameter AAA
    server can make use of this credit-control messages flow to deduce
    that user's activity is ongoing; hence it is recommended to set the
    authorization-lifetime to a reasonably high value when credit-control
    is used for the subscriber.
 
    In this scenario the home AAA server MUST advertise support for the
    credit-control application to its peers during the capability
    exchange process.
 
    The following diagram illustrates the use of authorization /
    authentication messages to perform the first interrogation. The
    parallel accounting stream is not shown in the figure.
 
    End-User        Service Element        AAA Server           CC Server
                     (CC Client)
       | Service Request   | AA Request (CC AVPs)                    |
       |------------------>|------------------->|                    |
       |                   |                    | CCR(Initial, CC AVPs)
       |                   |                    |------------------->|
       |                   |                    |    CCA(Granted-Units)
       |                   |                    |<-------------------|
       |                   | AA Answer(Granted-Units)                |
       | Service Delivery  |<-------------------|                    |
       |<----------------->|                    |                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |                   |                    |                    |
       |                   | CCR(Update,Used-Units)                  |
       |                   |------------------->| CCR(Update,Used-Units)
       |                   |                    |------------------->|
       |                   |                    |  CCA(Granted-Units)|
       |                   |  CCA(Granted-Units)|<-------------------|
       |                   |<-------------------|                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       | End of Service    |                    |                    |
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       |------------------>| CCR(Termination,Used-Units)             |
       |                   |------------------->| CCR(Term.,Used-Units)
       |                   |                    |------------------->|
       |                   |                    |                CCA |
       |                   |                CCA |<-------------------|
       |                   |<-------------------|                    |
 
                 Figure 4: Protocol example with use of the
             authorization messages for the first interrogation.
 
 
 5.2 Intermediate Interrogation
 
    When all of the granted service units for one unit type are spent by
    the end user or the Validity-Time is expired, the Diameter credit-
    control client MUST send a new Credit-Control-Request to the credit-
    control server. In the event that credit control for multiple
    services in one credit control session is applied (i.e. units are
    granted associated to Service-Identifier(s) or Rating-Group), a new
    Credit-Control-Request MUST be sent to the credit-control server when
    the whole credit reservation has been consumed, or upon expiration of
    the Validity-Time. In the case when the Validity-Time is used, it is
    always up to the Diameter credit-control client to send a new request
    well in advance before the expiration of the previous request in
    order to avoiding interruption in the service element. Even if the
    granted service units reserved by the credit-control server have not
    been spent upon expiration of the Validity-Time, the Diameter credit-
    control client MUST send a new Credit-Control-Request to the credit-
    control server.
 
    There can be also mid-session service events, which might affect the
    rating of the current service events. In this case a spontaneous
    updating (a new Credit-Control-Request) SHOULD be sent including
    information related to the service event even if all the granted
    service units have not been spent or the Validity-Time has not
    expired.
 
    When the used units are reported to the credit-control server the
    credit-control client will not have any units in its possession
    before new granted units are received from the credit-control server.
    When the new granted units are received from the credit-control
    server these units apply from the point where the measurement of the
    reported used units stopped.
 
    The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
    intermediate request message. The Subscription-Id-Data AVP SHOULD be
    included in the intermediate message to identify the end user in the
    credit-control server.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    The Requested-Service-Unit AVP contains the new amount of requested
    service units. The Used-Service-Unit AVP contains the amount of used
    service units measured from the point when the service became active
    or, in case of interim interrogations are used during the session,
    from the point when the previous measurement ended. The same unit
    types that are used in the previous message MUST be used. If several
    unit types were included in the previous answer message the used
    service units for each unit type MUST be reported.
 
    The Event-Timestamp AVP contains the time of the event that triggered
    the sending of the new Credit-Control-Request.
 
    The credit-control server MUST deduct the used amount from the end
    user's account. It MAY rate the new request and make a new credit-
    reservation from the end user's account that covers the cost of the
    requested service event.
 
    The Credit-Control-Answer message with the CC-Request-Type AVP set to
    the value UPDATE_REQUEST MAY include the Cost-Information AVP
    containing the accumulated cost estimation for the session without
    taking any credit-reservation into account.
 
    The Credit-Control-Answer message MAY also include the Final-Unit-
    Indication AVP to indicate that the answer message contains the final
    units for the service session. After the end user has consumed these
    units, the Diameter credit-control-client MUST behave as described in
    section 5.5.
 
    There can be several intermediate interrogations within a session.
 
 5.3 Final Interrogation
 
    When the end user terminates the service session or according to the
    graceful service termination as described in section 5.5, the
    Diameter credit-control client MUST send a final Credit-Control-
    Request message to the credit-control server. The CC-Request-Type AVP
    is set to the value TERMINATION_REQUEST.
 
    The Event-Timestamp AVP MAY contain the time of the session was
    terminated.
 
    The Used-Service-Unit AVP contains the amount of used service units
    measured from the point when the service became active or, in case of
    interim interrogations are used during the session, from the point
    when the previous measurement ended. If several unit types were
    included in the previous answer message the used service units for
    each unit type MUST be reported.
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    After final interrogation the credit-control server MUST refund the
    reserved credit amount not used to the end user's account and deduct
    the used monetary amount from the end user's account.
 
    The Credit-Control-Answer message with the CC-Request-Type set to the
    value TERMINATION_REQUEST MAY include the Cost-Information AVP
    containing the estimated total cost for the session in question.
 
    If the user logoff during an ongoing credit-control session or some
    other reason causes the user to be logged-off (e.g. final-unit
    indication causes user logoff according to local policy) the service
    element, according to application specific policy, may send a
    session-termination-request (STR) to the home Diameter AAA server as
    usual [DIAMBASE]. Figure 5 illustrates the case when the final-unit
    indication causes the user logoff upon consumption of the final
    granted units and STR is generated.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
    End-User        Service Element        AAA Server           CC Server
                     (CC Client)
       | Service Delivery  |                    |                    |
       |<----------------->|                    |                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |                   |                    |                    |
       |                   | CCR(Update,Used-Units)                  |
       |                   |------------------->| CCR(Update,Used-Units)
       |                   |                    |------------------->|
       |                   |                  CCA(Final-Unit, Terminate)
       |              CCA(Final-Unit, Terminate)|<-------------------|
       |                   |<-------------------|                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |  Disconnect user  |                    |                    |
       |<------------------| CCR(Termination,Used-Units)             |
       |                   |------------------->| CCR(Term.,Used-Units)
       |                   |                    |------------------->|
       |                   |                    |                CCA |
       |                   |                CCA |<-------------------|
       |                   |<-------------------|                    |
       |                   | STR                |                    |
       |                   |------------------->|                    |
       |                   |               STA  |                    |
       |                   |<-------------------|                    |
           Figure 5: User disconnected due to account exhausted
 
 5.4 Server-Initiated Credit Re-Authorization
 
    The Diameter Credit Control Application supports the server-initiated
    re-authorization. The credit control server MAY optionally initiate
    the credit re-authorization by issuing a Re-Auth-Request (RAR) as
    defined in the Diameter base protocol [DIAMBASE]. The Auth-
    Application-Id in the RAR message is set to 4 to indicate the
    Diameter Credit Control Application and the Re-Auth-Request-Type is
    set to AUTHORIZE_ONLY.
 
    If a credit re-authorization is not already ongoing (i.e. the credit
    control session is in OPEN state), a credit control client that
    receives such a RAR message with Session-Id equal to a currently
    active credit control session acknowledges the request by sending the
    Re-Auth-Answer (RAA) message and MUST initiate the credit re-
    authorization towards the server by sending a Credit-Control-Request
    message with the CC-Request-Type AVP set to the value UPDATE_REQUEST.
    The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the
    RAA message to indicate an additional message (i.e. CCR[Update]) is
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    required to complete the procedure. If a quota was allocated to the
    session, the credit control client MUST report the used quota in the
    Credit-Control-Request. Note that the end user does not need to be
    prompted for the credit re-authorization, since the credit re-
    authorization is transparent to the user (i.e it takes place
    exclusively between the credit control client and the credit control
    server).
 
    If credit re-authorization is ongoing at the time when the RAR
    message is received (i.e. RAR-CCR collision), the credit control
    client successfully acknowledges the request but it does not initiate
    a new credit re-authorization. The Result-Code 2001
    (DIAMETER_SUCCESS) SHOULD be used in the RAA message to indicate a
    credit re-authorization procedure is already ongoing (i.e. the client
    was in PendingU state when the RAR was received). The credit control
    server SHOULD process the Credit-Control-Request as if it was
    received in answer to the server initiated credit re-authorization,
    and should consider the server initiated credit re-authorization
    process successful upon reception of the Re-Auth-Answer message.
 
    If several credit control sub-sessions are in use, a credit control
    client receiving the RAR command for a given session will trigger
    credit re-authorization for all the sub-session separately.
 
 5.5 Graceful Service Termination
 
    When the user's account runs out of money the user must be denied to
    compile additional chargeable events. However, the home service
    provider may offer free access services, for instance access to a
    service portal where it is possible to top-up the account, for which
    the user is allowed to benefit for a limited amount of time. This
    time is usually dependant on the home service provider policy.
 
    This section defines the graceful service termination optional
    feature that MAY be supported by the credit control server. Credit
    control client implementations MUST support the Final-Unit-Indication
    with at least the tear down of the ongoing service session upon the
    subscriber has consumed all the final granted units.
 
    In some service environments (e.g. NAS) the graceful service
    termination may be used to redirect the subscriber to a service
    portal for online balance top-up or other zero-rated services offered
    by the home service provider. In this case the graceful termination
    process installs a set of packet filters to restrict the user's
    access capability only to/from the specified destinations, all the IP
    packets not matching the filters will be dropped or possibly re-
    directed to the service portal. The user may also be displayed an
    appropriate notification why the access has been limited.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    It is also possible use the graceful service termination to connect
    the prepaid user to a top-up server that play an announcement and
    prompt the user to replenish the account. In such a case the credit
    control server sends only the address of the top-up server where the
    prepaid user shall be connected after the final granted units have
    been consumed. An example of this is given in Appendix A (Flow VIII).
 
    The credit control server MAY initiate the graceful service
    termination by including the Final-Unit-Indication AVP in the Credit
    Control Answer to indicate that the message contains the final units
    for the service session.
    When the credit control client receives the Final-Unit-Indication AVP
    in the answer from the server its behavior depends on the value
    indicated in the Final-Unit-Action AVP. The server may request the
    following actions: TERMINATE, REDIRECT and RESTRICT_ACCESS.
 
    The following Figure illustrates the graceful service termination
    procedure described in the following sub-sections.
 
    End-User        Service Element         AAA Server          CC Server
                     (CC Client)
       |  Service Delivery |                    |                    |
       |<----------------->|                    |                    |
       |                   |CCR(Update,Used-Units)                   |
       |                   |------------------->|CCR(Update,Used-Units)
       |         :         |                    |------------------->|
       |         :         |                    |CCA(Final-Unit,Action)
       |         :         |                    |<-------------------|
       |                   |CCA(Final-Unit,Action)                   |
       |                   |<-------------------|                    |
       |                   |                    |                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       | ///////////////   |CCR(Update,Used-Units)                   |
       |/Final Units End/->|------------------->|CCR(Update,Used-Units)
       |/Action and    //  |                    |------------------->|
       |/Restrictions //   |                    |  CCA(Validity-Time)|
       |/Start       //    |  CCA(Validity-Time)|<-------------------|
       | /////////////     |<-------------------|                    |
       |         :         |                    |                    |
       |         :         |                    |                    |
       |                 Replenish Account            +-------+      |
       |<-------------------------------------------->|Account|      |
       |                   |                    |     +-------+      |
       |                   |                    |                RAR |
       |                 + |                RAR |<===================|
       |                 | |<===================|                    |
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       |                 | | RAA                |                    |
       |  /////////////  | |===================>| RAA                |
       | /If supported / | | CCR(Update)        |===================>|
       | /by CC Server/  | |===================>| CCR(Update)        |
       | /////////////   | |                    |===================>|
       |                 | |                    |   CCA(Granted-Unit)|
       |                 | |   CCA(Granted-Unit)|<===================|
       |  Restrictions ->+ |<===================|                    |
       |  removed          |                    |                    |
       |         :         |                    |                    |
       |        OR         | CCR(Update)        |                    |
       |   Validity-Time ->|------------------->| CCR(Update)        |
       |   expires         |                    |------------------->|
       |                   |                    |   CCA(Granted-Unit)|
       |                   |   CCA(Granted-Unit)|<-------------------|
       |    Restrictions ->|<-------------------|                    |
       |    removed        |                    |                    |
          Figure 6: Optional graceful service termination procedure
 
 5.5.1 Terminate Action
 
    The Final-Unit-Indication AVP with Final-Unit-Action TERMINATE does
    not include any other information. Upon the subscriber has consumed
    the final granted units the service element MUST terminate the
    service session and MUST send a final Credit-Control-Request message
    to the credit control server. The CC-Request-Type AVP in the request
    is set to the value TERMINATION_REQUEST. This is the default handling
    applicable whenever the credit control client receives an unsupported
    Final-Unit-Action value and MUST be supported by all the Diameter
    credit control client implementations conforming to this
    specification.
 
 5.5.2 Redirect Action
 
    The Final-Unit-Indication AVP with Final-Unit-Action REDIRECT
    indicates to the service element supporting this action that, upon
    consumption of the final granted units, the user MUST be re-directed
    to the address specified in the Redirect-Server AVP as follow.
 
    The credit control server sends the Redirect-Server AVP in the
    Credit-Control-Answer message. In such a case the service element
    MUST redirect or connect the user to the destination specified in the
    Redirect-Server AVP, if possible. When the end user is redirected (by
    using other protocols than Diameter) to the specified server or
    connected to the top-up server, an additional authorization (and
    possibly authentication) may be needed before the subscriber can
    replenish the account, however, this is out of the scope of this
    specification.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    In addition to the Redirect-Server AVP, the credit control server MAY
    include one or more Restriction-Filter-Rule AVP or one or more
    Filter-Id AVP in the Credit-Control-Answer message in order to enable
    the user to access other zero-rated services. In such a case the
    access device MUST drop all the packets not matching the IP filters
    specified in the Credit-Control-Answer message and redirect the user
    to the destination specified in the Redirect-Server AVP, if possible.
 
    Another entity than the credit control server may provision the
    access device with appropriate IP packet filters to be used in
    conjunction with the Diameter credit control application. This case
    is considered in section 5.5.3.
 
    When the final granted units have been consumed the credit control
    client MUST perform an intermediate interrogation. The purpose of
    this intermediate interrogation is to indicate to the credit control
    server that the specified action started and to report the used
    units. The credit control server MUST deduct the used amount from the
    end user's account but MUST NOT make a new credit reservation. The
    credit control client, however, may send intermediate interrogations
    before all the final granted units have been consumed for which
    rating and money reservation may be needed, for instance upon
    Validity-Time expires or upon mid-session service event that affect
    the rating of the current service. Therefore, the credit control
    client MUST NOT include any rating related AVP in the request sent
    upon all the final granted units have been consumed as a hint to the
    server that the requested final unit action started, rating and money
    reservation are not required. Naturally, the Credit-Control-Answer
    message does not contain any granted service unit and MUST include
    the Validity-Time AVP to indicate to the credit control client how
    long the subscriber is allowed to use network resources before a new
    intermediate interrogation is sent to the server.
 
    At the expiry of Validity-Time the credit control client sends a
    Credit-Control-Request (UPDATE_REQUEST) as usual. This message does
    not include the Used-Service-Unit AVP since there is no allotted
    quota to report. The credit control server processes the request and
    MUST perform the credit reservation. If during this time the
    subscriber did not replenish his/her account whether he/she will be
    disconnected or will be granted access to zero-rated services for
    unlimited time is dependent on the home service provider policy
    (note: the latter option implies that the service element should not
    remove the restriction filters upon termination of the credit control
    session). The server will return the appropriate Result-Code (see
    section 9.1) in the Credit-Control-Answer message in order to close
    the credit control session and implement the policy-defined action.
    Otherwise new quota will be returned, the service element MUST remove
    all the possible restrictions activated by the graceful service
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    termination process and continue the credit control session and the
    service session as usual.
 
    The credit control client may not wait until the expiration of the
    Validity-Time and may send a spontaneous updating (a new Credit-
    Control-Request) if the service element can determine for instance
    that communication between the end user and the top-up server took
    place. An example of this is given in Appendix A (Figure A.8).
 
    It is worth noting that the credit control server may initiate the
    above-described process already for the first interrogation. However,
    the user's account might be empty at the time when the first
    interrogation is performed. In this case the subscriber can be
    offered a chance to replenish the account and continue the service.
    The credit control client receives a Credit-Control-Answer or service
    specific authorization answer with the Final-Unit-Indication AVP,
    Validity-Time AVP but no Granted-Unit. In such a case it starts
    immediately the graceful service termination without sending any
    message to the server. An example of this case is illustrated in
    Appendix A.
 
 5.5.3 Restrict Access Action
 
    The Final-Unit-Indication AVP with Final-Unit-Action RESTRICT_ACCESS
    indicates to the access device supporting this action that the user
    MUST be restricted access according to the IP packet filters given in
    the Restriction-Filter-Rule AVP(s) or according to the IP packet
    filters identified by the Filter-Id AVP(s). The credit control server
    SHOULD include either the Restriction-Filter-Rule AVP or the Filter-
    Id AVP in the Credit-Control-Answer message.
 
    Another entity than the credit control server may provision the
    access device with appropriate IP packet filters to be used in
    conjunction with the Diameter credit control application. Such an
    entity, for instance, may configure the access device with "zero-
    rated" IP flows that are to be passed when the Diameter credit
    control application indicates RESTRICT_ACCESS or REDIRECT. The access
    device passes IP packets according to the filter rules possibly
    received in the Credit-Control-Answer message in addition to the
    filter rules possibly configured by the other entity. However, the
    action to be taken when the user's account cannot cover the cost of
    the requested service is the responsibility of the credit control
    server that controls the prepaid subscriber.
 
    If another entity working in conjunction with the Diameter Credit
    control application already provisions the access device with all the
    required filter rules for the end user, it is presumably not needed
    for the credit control server to send any additional filter.
    Therefore it is RECOMMENDED that credit control server
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    implementations supporting the graceful service termination can be
    configurable whether to send the Restriction-Filter-Rule AVP, the
    Filter-Id AVP or none of the above.
 
    When the final granted units have been consumed, the credit control
    client MUST perform an intermediate interrogation. The credit control
    client and the credit control server process this intermediate
    interrogation and execute subsequent procedures as specified in the
    previous section for the REDIRECT action.
 
    The credit control server may initiate the graceful service
    termination with action RESTRICT_ACCESS already for the first
    interrogation as specified in the previous section for the REDIRECT
    action.
 
 5.5.4 Usage of the Server-Initiated Credit Re-Authorization
 
    Once the subscriber replenishes the account she presumably expects
    all the restrictions placed by the graceful termination procedure be
    immediately removed and unlimited services' access be resumed. For
    the best user experience the credit control server implementation MAY
    support the server-initiated credit re-authorization (see section
    5.4). In such a case, upon the successful account top-up took place,
    the credit control server sends the Re-Auth-Request (RAR) message to
    solicit the credit re-authorization. The credit control client
    initiates then the credit re-authorization by sending the Credit-
    Control-Request message with the CC-Request-Type AVP set to the value
    UPDATE_REQUEST. The Used-Service-Unit AVP is not included in the
    request since there is no allotted quota to report. The Requested-
    Service-Unit AVP MAY be included in the request. After the credit
    control client successfully receives the Credit-Control-Answer with
    new Granted-Service-Unit all the possible restrictions activated for
    the purpose of the graceful service termination MUST be removed in
    the service element, the credit control session and the service
    session continue as usual.
 
 5.6 Failure Procedures
 
    The Credit-Control-Failure-Handling AVP (CCFH) as described in this
    section determines the behavior of the credit control client in fault
    situations. The CCFH may be received from the Diameter home AAA
    server, from the credit control server or may be locally configured.
    The CCFH value received from the home AAA server overrides the
    locally configured value and the CCFH value received from the credit
    control server in the Credit-Control-Answer message always override
    any already existing value.
 
    The authorization server MAY include the Accounting-Realtime-Required
    AVP to determine what to do if the sending of accounting records to
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    the accounting server has been temporarily prevented as defined in
    [DIAMBASE]. It is RECOMMENDED that the client complement the credit-
    control failure procedures with backup accounting flow towards an
    accounting server. Using different combinations of Accounting-
    Realtime-Required and Credit-Control-Failure-Handling AVPs different
    safety levels can be built. For example by choosing the Credit-
    Control-Failure-Handling AVP equal to CONTINUE for the credit control
    flow and Accounting-Realtime-Required AVP equal to DELIVER_AND_GRANT
    for the accounting flow, the service can be granted to the end user
    even if the connection to the credit-control server is down but the
    accounting server is able to collect the accounting information,
    provided that there is information exchange taking place between the
    accounting server and credit-control server.
 
    Since the credit-control application is based on real-time bi-
    directional communication between the credit-control client and the
    credit-control server, the usage of alternative destinations and the
    buffering of messages MAY NOT be sufficient in the event of
    communication failures. Since the credit-control server has to
    maintain session states, moving the credit-control message stream to
    a backup server requires a complex context transfer solution. Whether
    the credit-control message stream is moved to a backup credit-control
    server during an ongoing credit-control session depends on the value
    of the CC-session-Failover AVP. However, failover may occur at any
    point in the path between credit-control client and credit-control
    server in the event that a transport failure is detected with a peer,
    as described in [DIAMBASE]. As a consequence the credit-control
    server might receive duplicate messages. These duplicates or out of
    sequence messages can be detected in the credit-control server based
    on the credit-control server session state machine (section 7),
    Session-Id AVP and CC-Request-Number AVP.
 
    If a failure occurs during an ongoing credit-control session, the
    credit-control client may move the credit control message stream to
    an alternative server if the CC-server indicated FAILOVER_SUPPORTED
    in the CC-Session-Failover AVP. A secondary credit control server
    name, received from the AAA server or locally configured, can be used
    as an address of the backup server. If the CC-Session-Failover AVP is
    set to FAILOVER_NOT SUPPORTED the credit control message stream MUST
    NOT be moved to backup server.
 
    For new credit control sessions, failover to an alternative credit-
    control server SHOULD be performed if possible. For instance, if an
    implementation of the credit control client can determine primary
    credit control server unavailability it can establish the new credit
    control sessions with a possibly available secondary credit control
    server.
 
 
 
 
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    The AAA client/agent is typically using only a single persistent
    transport connection to the AAA agent or server, but it may have
    connections to multiple AAA agents or servers and treat them as
    primary/secondary or balance load between them. The AAA transport
    profile [AAATRANS] defines the application layer watchdog algorithm
    that enables failover from a peer that has failed and is controlled
    by the timer Twinit. The recommended default value for Twinit is 30
    seconds. Since the AAA infrastructure is common to several different
    types of AAA applications, tuning the timer Twinit to a lower value
    in order to satisfy the requirements of real-time applications, such
    as the Diameter Credit Control application, will certainly increase
    the probability of premature failover significantly and potentially
    cause congestive collapse in heavy loaded networks. For prepaid
    services, however, the end user expects an answer from the network in
    a reasonable time, thus the Diameter credit control client shall
    react faster than the underlying base protocol. Therefore this
    specification defines the timer Tx that is used by the credit-control
    client (as defined in section 13) to supervise the communication with
    the credit-control server. When the timer Tx elapses the credit-
    control client takes an action to the end user according to the
    Credit-Control-Failure-Handling AVP.
 
    When Tx expires, the Diameter credit control client always terminates
    the service if the Credit-Control-Failure-Handling (CCFH) AVP is set
    to the value TERMINATE. The credit control session may be moved to an
    alternative server only in case a protocol error DIAMETER_TOO_BUSY or
    DIAMETER_UNABLE_TO_DELIVER is received before Tx expires, therefore,
    the value TERMINATE is not appropriate if proper failover behavior is
    desired.
 
    If the Credit-Control-Failure-Handling AVP is set to the value
    CONTINUE or RETRY_AND_TERMINATE, the service will be granted to the
    end user upon the timer Tx expires. An answer message with granted-
    units may arrive later on due to the base protocol transport failover
    occurred in the path to the Credit Control Server (Twinit default
    value is 3 times more than the Tx recommended value). The credit
    control client SHOULD grant the service to the end user, start
    monitoring the resource usage and wait for the possible late answer
    until the timeout of the request (e.g. 120 seconds).  If the request
    fails and the CC-Session-Failover AVP is set to FAILOVER_NOT
    SUPPORTED, the credit control client terminates or continues the
    service depending on the value set in the CCFH and MUST free all the
    reserved resources for the credit control session. If a protocol
    error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is received or
    the request timeout and the CC-Session-Failover AVP is set to
    FAILOVER SUPPORTED, the credit control client MAY send the request to
    a backup server if possible. If the credit control client receives a
    successful answer from the backup server, it continues the credit
    control session with such a server. If also the re-transmitted
 
 
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    request fails, the credit control client terminates or continues the
    service depending on the value set in the CCFH and MUST free all the
    reserved resources for the credit control session.
 
    If a communication failure occurs during the graceful service
    termination procedure, the service element SHOULD always terminate
    the ongoing service session.
 
    If the credit-control server detects a failure during an ongoing
    credit-control session, it will terminate the credit-control session
    and return the reserved units back to the end user's account.
 
    The supervision session timer Tcc (as defined in section 13) is used
    in the credit-control server to supervise the credit-control session.
 
    In order to support the failover between credit control servers
    information transfer about the credit control session and account
    state SHOULD take place between the primary and the secondary credit
    control server. Implementations supporting the credit control session
    failover MUST also ensure proper detection of duplicate or out of
    sequence messages. The communication between the servers is regarded
    as an implementation issue and is outside of the scope of this
    specification.
 
 6. One Time Event
 
    The one-time event is used when there is no need to maintain any
    state in the Diameter credit-control server, for example enquiring
    the price of the service. The use of one-time event implies that the
    user has been authenticated and authorized beforehand.
 
    The one time event can be used when the credit-control client wants
    to know the cost of the service event without any credit-reservation
    or to check the account balance without any credit-reservation. It
    can be used also for refunding service units on the user's account or
    direct debiting without any credit-reservation. The one time event is
    shown in Figure 7.
 
    End-User        Service Element        AAA Server           CC Server
                      (CC Client)
       | Service Request   |                    |                    |
       |------------------>|                    |                    |
       |                   | CCR(Event)         |                    |
       |                   |------------------->| CCR(Event)         |
       |                   |                    |------------------->|
       |                   |                    |  CCA(Granted-Units)|
       |                   |  CCA(Granted-Units)|<-------------------|
       |  Service Delivery |<-------------------|                    |
       |<----------------->|                    |                    |
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
                          Figure 7: One time event
 
    In environments such as the 3GPP architecture the one time event can
    be sent from the service element directly to the credit-control
    server.
 
 6.1 Service Price Enquiry
 
    The credit-control client may need to know the price of the service
    event. There might exist services offered by application service
    providers, whose prices are not known in the credit-control client.
    End user might also want to get an estimation of the price of a
    service event before requesting it.
 
    A Diameter credit-control client requesting the cost information MUST
    set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
    Requested-Action AVP set to PRICE_ENQUIRY and set the requested
    service event information into the Service-Parameter-Info AVP in the
    Credit-Control-Request message.
 
    The credit-control server calculates the cost of the requested
    service event, but it does not perform any account balance check or
    credit-reservation from the account.
 
    The estimated cost of the requested service event is returned to the
    credit-control client in the Cost-Information AVP in the Credit-
    Control-Answer message.
 
 6.2 Balance Check
 
    The Diameter credit-control client may need only to verify that the
    end user's account balance covers the cost for a certain service
    without reserving any units from the account at the time of the
    inquiry. This method does not guarantee that there would be credit
    left when the Diameter credit-control client requests the debiting of
    the account with a separate request.
 
    A Diameter credit-control client requesting the balance check MUST
    set the CC-Request-Type AVP equal to EVENT_REQUEST, include
    Requested-Action AVP set to CHECK_BALANCE and include the
    Subscription-Id-Data to identify the End-User in the credit-control
    server.
 
    The credit-control server makes the balance check, but it does not do
    any credit-reservation from the account.
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    The result of balance check (ENOUGH_CREDIT/NO_CREDIT) is returned to
    the credit-control client in the Check-Balance-Result AVP in the
    Credit-Control-Answer message.
 
 6.3 Direct Debiting
 
    There are certain service events for which service execution is
    always successful in the service environment. The delay between the
    service invocation and the actual service delivery to the end user
    can be sufficiently long that the use of the session-based credit-
    control would lead to unreasonable long credit-control sessions. In
    these cases the Diameter credit-control client can use the one-time
    event scenario for direct debiting. The Diameter credit-control
    client SHOULD be sure that the requested service event execution
    would be successful, when this scenario is used.
 
    The CC-Request-Type is set to the value EVENT_REQUEST and the
    Requested-Action AVP set to DIRECT_DEBITING in the Credit-Control-
    Request message. The Subscription-Id-Data AVP SHOULD be included to
    identify the End-User in the credit-control server. The Event-
    Timestamp AVP contains the time when the service event is requested
    in the service element.
 
    The Diameter credit-control client can include the monetary amount to
    be charged in the Request-Service-Unit AVP, if it knows the cost of
    the service event. If the Diameter credit-control client does not
    know the cost of the service event, then the Service-Parameter-Info
    AVP SHOULD contain the service event information to be rated by the
    credit-control server. The Service-Parameter-Info AVP always refers
    to the requested service unit.
 
    The credit-control server SHOULD rate the service event and deduct
    the corresponding monetary amount from end user's account. If the
    type of the Requested-Service-Unit AVP is money, no rating is needed
    but the corresponding monetary amount is deducted from the End User's
    account.
 
    The credit-control server returns the Granted-Service-Unit AVP in the
    Answer message to the Diameter credit-control client. The Granted-
    Service-Unit AVP contains the amount of service units that the
    Diameter credit-control client can provide to the end user. The type
    of the Granted-Service-Unit can be time, volume, service specific or
    money depending on the type of service event.
 
    If the credit-control server determines that no credit-control is
    needed for the service it can include the result code indicating that
    the credit-control is not applicable (e.g. service is free of
    charge).
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    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 in the Credit-
    Control-Request message. The Subscription-Id-Data AVP SHOULD be
    included to identify the End-User in the credit-control server.
 
    The Diameter credit-control client MAY include the monetary amount to
    be refunded in the Requested-Service-Unit AVP. If the Diameter
    credit-control client does not know the monetary amount to be
    refunded, then the Service-Parameter-Info AVP, or other rating AVPs,
    SHOULD contain the service event information to be rated by the
    credit-control server.
 
    For informative purposes, the Credit-Control-Answer message MAY also
    include the Cost-Information AVP containing the estimated monetary
    amount of refunded unit.
 
 6.5 Failure Procedure
 
    Failover to an alternative credit-control server is allowed for one
    time event since the server is not maintaining session states, for
    instance, if the credit control client receives a protocol error
    DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY it can re-send the
    request to an alternative server if possible. There MAY exist
    protocol transparent Diameter relays and redirect agents or Diameter
    credit-control proxies between credit-control client and credit-
    control server. Failover may occur at any point in the path between
    credit-control client and credit-control server in the event that a
    transport failure is detected with a peer, as described in
    [DIAMBASE]. Because there can be duplicate requests for various
    reasons the credit-control server is therefore responsible for the
    real time duplicate detection. Implementation issues for duplicate
    detection are discussed in [DIAMBASE] Appendix C.
 
    When the credit-control client detects a communication failure to the
    credit-control server, its behavior depends on the requested action.
    The timer Tx (as defined in section 13) is used in the credit-control
    client to supervise the communication with the credit-control server.
 
    In case the requested action is PRICE_ENQUIRY or BALANCE_CHECK and
    communication failure is detected the credit-control client SHOULD
 
 
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    forward the request messages to an alternative credit-control server,
    if possible. The secondary Credit control server name, if received
    from the AAA server, can be used as an address of backup server.
 
    If the requested action is DIRECT_DEBITING the Direct-Debiting-
    Failure-Handling AVP (DDFH) controls the credit control client
    behavior. The DDFH may be received from the Diameter home AAA server
    or may be locally configured. The credit control server may also send
    the DDFH in any CCA message to be used for direct debiting events
    compiled thereafter. The DDFH value received from the home AAA server
    overrides the locally configured value and the DDFH value received
    from the credit control server in a Credit-Control-Answer message
    always override any already existing value. If the DDFH is set to
    TERMINATE_OR_BUFFER, the credit-control client SHOULD NOT grant the
    service if it can determine, eventually after a possible re-
    transmission attempt to an alternative credit control server, from
    the result code or error code in the answer message that units have
    not been debited. Otherwise the credit-control client SHOULD grant
    the service to the end user and store the request in the credit-
    control application level non-volatile storage (Note that re-sending
    the request at a later time is not a guarantee that the service will
    be debited, since the user's account may be empty at the time when
    the server successfully processes the request). The credit-control
    client MUST mark these request messages as possible duplicate by
    setting the T-flag in the command header as described in [DIAMBASE]
    section 3. If the Direct-Debiting-Failure-Handling AVP is set to
    CONTINUE, the service SHOULD be granted even if credit-control
    messages cannot be delivered and messages are not buffered.
    If the timer Tx expires the credit-control client MUST continue the
    service and wait for a possible late answer. If the request timeout
    the credit control client re-transmit the request (marked with T-
    flag) to a backup credit control server if possible. In the event
    that also the re-transmitted request timeout or a temporary error is
    received in answer to such a request, the credit control client
    buffers the request if the value of the Direct-Debiting-Failure-
    Handling AVP is set to TERMINATE_OR_BUFFER. If a failed answer is
    received for the re-transmitted request, the credit control client
    frees all the resources reserved for the event message and deletes
    the request regardless the value of the DDFH.
 
    The Credit-Control-Request with requested action REFUND should always
    be stored in the credit-control application level non-volatile
    storage in case of temporary failure. The credit-control client MUST
    mark the re-transmitted request message as possible duplicate by
    setting the T-flag in the command header as described in [DIAMBASE]
    section 3.
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    For stored requests, the implementation may choose to limit the
    number of re-transmission attempts and define a re-transmission
    interval.
 
    It should be noted that only one place in the credit-control system
    SHOULD be responsible for duplicate detection. If there is only one
    credit-control server within the given realm, the credit-control
    server may perform duplicate detection. In case when more than one
    credit-control servers are serving a given realm, only one entity in
    the credit control system should be responsible to ensure that the
    end user's account is not debited or credited multiple times for the
    same service event.
 
 7. Credit Control Application State Machine
 
    This section defines the credit control application state machine.
 
    The first four state machines are to be observed by credit-control
    clients. The first one describes the session-based credit-control
    when the first interrogation is executed as part of the
    authorization/authentication process. The second one describes the
    session-based credit-control when the first interrogation is executed
    after the authorization/authentication process. The requirements what
    state machine need to be supported are discussed in section 5.1.
 
    The third state machine describes the session-based credit-control
    for intermediate and final interrogations. The fourth one describes
    the event-based credit-control. These latter state machines are to be
    observed by all the implementations that conform to this
    specification.
 
    The fifth state machine describes the credit-control session from a
    credit-control server perspective.
 
    Any event not listed in the state machines MUST be considered as an
    error condition, and a corresponding answer, if applicable, MUST be
    returned to the originator of the message.
 
    In the state table, the event 'Failure to send' means that the
    Diameter credit-control client is unable to communicate with the
    desired destination or with a possibly defined alternative
    destination in case failover procedure is supported (e.g. the request
    timeout and the answer message is not received). This could be due to
    the peer being down, or due to a physical link failure in the path
    to/from the credit-control server.
 
    The event 'Temporary error' means that the Diameter credit-control
    client received a protocol error notification DIAMETER_TOO_BUSY,
    DIAMETER_UNABLE_TO_DELIVER or DIAMETER_LOOP_DETECTED in the Result-
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    Code AVP of the Credit-Control-Answer command. The above protocol
    error notification may be ultimately received in answer to the re-
    transmitted request to a possibly defined alternative destination if
    failover is supported.
 
    The event 'Failed answer' means that the Diameter credit-control
    client received non-transient failure (permanent failure)
    notification in the Credit-Control-Answer command. The above
    permanent failure notification may be ultimately received in answer
    to the re-transmitted request to a possibly defined alternative
    destination if failover is supported.
    The action 'store request' means that a request is stored in the
    credit-control application level non-volatile storage.
 
    The event 'Not successfully processed' means that the credit-control
    server could not process the message, e.g. due to unknown end user,
    account being empty or due to errors defined in [DIAMBASE].
 
    The states PendingI, PendingU, PendingT PendingE and PendingB stand
    for pending states to wait for an answer to a credit control request
    related to Initial, Update, Termination, Event or Buffered request
    respectively.
 
    The abbreviations CCFH and DDFH stand for Credit-Control-Failure-
    Handling and Direct-Debiting-Failure-Handling respectively.
 
    In the following state machine table the failover to a possibly
    secondary server upon 'Temporary error' or 'Failure to send' is not
    explicitly described. Moving an ongoing credit control message stream
    to an alternative server is, however, possible if the CC-Session-
    Failover AVP is set to FAILOVER_SUPPORTED as described in section
    5.6.
 
    Re-sending a credit control event to an alternative server is
    supported as described in section 6.5.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    CLIENT, SESSION BASED for the first interrogation with AA request
 
      State      Event                         Action       New State
      ---------------------------------------------------------------
      Idle       Client or device requests     Send          PendingI
                 access/service                AA request
                                               with added
                                               CC AVPs,
                                               start Tx
 
      PendingI  Successful AA req.             Grant         Open
                answer received                service to
                                               end user,
                                               stop Tx
 
      PendingI  Tx expired                     Disconnect    Idle
                                               user/dev
 
      PendingI  Failed AA answer received      Disconnect    Idle
                                               user/dev
 
      PendingI  AA answer                      Grant         Idle
                received with result code      service
                equal to credit-control N/A    to end user
 
      PendingI  User service terminated        Queue         PendingI
                                               termination
                                               event
 
      PendingI  Change in rating condition     Queue         PendingI
                                               changed
                                               rating
                                               condition
                                               event
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
        CLIENT, SESSION BASED for the first interrogation with CCR
 
      State      Event                          Action       New State
      ----------------------------------------------------------------
 
 
      Idle      Client or device requests      Send         PendingI
                access/service                 CC initial
                                               req.,
                                               start Tx.
 
      PendingI  Successful CC initial          Stop Tx      Open
                answer received
 
      PendingI  Failure to send, or            Grant        Idle
                temporary error and            service to
                CCFH equal to CONTINUE         end user
 
      PendingI  Failure to send, or            Terminate    Idle
                temporary error and            end user's
                CCFH equal to TERMINATE        service
                or equal to RETRY_AND_TERMINATE
 
      PendingI  Tx expired and CCFH            Terminate    Idle
                equal to TERMINATE             end user's
                                               service
 
      PendingI  Tx expired and CCFH equal      Grant        PendingI
                to CONTINUE or equal to        service to
                RETRY_AND_TERMINATE            end user
 
      PendingI  CC initial answer              Terminate    Idle
                received with result code      end user's
                SERVICE_ DENIED or             service
                USER_UNKNOWN
 
      PendingI  CC initial answer              Grant        Idle
                received with result code      service
                equal to credit-control N/A    to end user
 
      PendingI  Failed CC initial answer       Grant        Idle
                received CCFH equal to         Service to
                CONTINUE                       end user
 
      PendingI  Failed CC initial answer       Terminate    Idle
                received and CCFH equal        end user's
                to TERMINATE or equal to       service
                RETRY_AND_TERMINATE
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
      PendingI  User service terminated        Queue        PendingI
                                               termination
                                               event
 
      PendingI  Change in rating condition     Queue        PendingI
                                               changed
                                               rating
                                               condition
                                               event
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       CLIENT, SESSION BASED for intermediate and final interrogations
      State     Event                          Action       New State
      ----------------------------------------------------------------
 
      Open      Granted unit elapses           Send         PendingU
                and no final unit              CC update
                indication received            req.,
                                               start Tx.
 
      Open      Granted unit elapses           Terminate    PendingT
                and final unit action          end user's
                equal to TERMINATE             service, send
                received                       CC termination
                                               req.
 
      Open      Change in rating condition     Send         PendingU
                in queue                       CC update
                                               req.,
                                               Start Tx.
 
 
 
      Open      Service terminated in queue    Send         PendingT
                                               CC termination
                                               req.
 
      Open      Change in rating condition     Send         PendingU
                or Validity-Time elapses       CC update
                                               req.,
                                               Start Tx.
 
      Open      User service terminated        Send         PendingT
                                               CC termination
                                               req.
 
      Open      RAR received                   Send RAA     PendingU
                                               followed by
                                               CC update req.,
                                               start Tx
 
      PendingU  Successful CC update           Stop Tx      Open
                answer received
 
      PendingU  Failure to send, or            Grant        Idle
                temporary error and            service to
                CCFH equal to CONTINUE         end user
 
      PendingU  Failure to send, or            Terminate    Idle
                temporary error and            end user's
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                CCFH equal to TERMINATE        service
                or equal to RETRY_AND_TERMINATE
 
      PendingU  Tx expired and CCFH            Terminate    Idle
                equal to TERMINATE             end user's
                                               service
 
      PendingU  Tx expired and CCFH equal      Grant        PendingU
                to CONTINUE or equal to        service to
                RETRY_AND_TERMINATE            end user.
 
      PendingU  CC update answer               Terminate    Idle
                received with result code      end user's
                SERVICE_DENIED                 service
 
      PendingU  CC update answer               Grant        Idle
                received with result code      service
                equal to credit-control N/A    to end user
 
      PendingU  Failed CC update               Grant        Idle
                answer received and            service to
                CCFH equal to CONTINUE         end user.
 
      PendingU  Failed CC update               Terminate    Idle
                answer received CCFH           end user's
                equal to TERMINATE or          service
                equal to RETRY_AND_TERMINATE
 
      PendingU  User service terminated        Queue        PendingU
                                               termination
                                               event
 
      PendingU  Change in rating               Queue        PendingU
                condition                      changed
                                               rating
                                               condition
                                               event
 
      PendingU  RAR received                   Send RAA     PendingU
 
      PendingT  Successful CC                               Idle
                termination answer received
 
      PendingT  Failure to send, or temporary               Idle
                error or failed answer
 
      PendingT  Change in rating condition                  PendingT
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                         CLIENT, EVENT BASED
      State     Event                          Action        New State
      ----------------------------------------------------------------
      Idle      Client or device requests      Send          PendingE
                a one-time service             CC event
                                               req.,
                                               Start Tx.
 
      Idle      Request in storage             Send          PendingB
                                               stored
                                               request
 
      PendingE  Successful CC event            Grant         Idle
                answer received                service to
                                               end user
 
      PendingE  Failure to send, temporary     Indicate      Idle
                error or failed CC event       service
                answer received, or            error
                Tx expired, requested
                action BALANCE_CHECK or
                PRICE_ENQUIRY
 
      PendingE  CC event answer                Terminate     Idle
                received with result code      end user's
                SERVICE_DENIED or              service
                USER_UNKNOWN and Tx running
 
      PendingE  CC event answer                Grant         Idle
                received with result code      service
                credit-control N/A, requested  to end
                action DIRECT_DEBITING         user
 
      PendingE  Failure to send, temporary     Grant         Idle
                error or failed CC event       service
                answer received, requested     to end
                action DIRECT_DEBITING and     user
                DDFH equal to CONTINUE
 
      PendingE  Failed CC event                Terminate     Idle
                answer received or temporary   end user's
                error, requested action        service
                DIRECT_DEBITING and
                DDFH equal to
                TERMINATE_OR_BUFFER and
                Tx running
 
      PendingE  Tx expired, requested          Grant         PendingE
                action DIRECT_DEBITING         service
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                                               to end
                                               user
 
      PendingE  Failure to send, requested     Store         Idle
                action DIRECT_DEBITING and     request with
                DDFH equal to                  T-flag
                TERMINATE_OR_BUFFER
 
      PendingE  Temporary error, requested     Store         Idle
                action DIRECT_DEBITING and     request
                DDFH equal to
                TERMINATE_OR_BUFFER and
                Tx expired
 
      PendingE  Failed answer or answer                      Idle
                received with result code
                SERVICE DENIED or USER_UNKNOWN,
                requested action
                DIRECT_DEBITING and Tx expired
 
      PendingE  Failed CC event answer         Indicate      Idle
                received, requested            service
                action REFUND_ACCOUNT          error and
                                               delete request
 
      PendingE  Failure to send or             Store         Idle
                Tx expired, requested          request
                action REFUND_ACCOUNT          with T-flag
 
      PendingE  Temporary error                Store         Idle
                and requested action           request
                REFUND_ACCOUNT
 
      PendingB  Successful CC answer           Delete        Idle
                received                       request
 
      PendingB  Failed CC answer               Delete        Idle
                received                       request
 
      PendingB  Failure to send or                           Idle
                temporary error
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                     SERVER, SESSION AND EVENT BASED
 
      State     Event                          Action        New State
      ----------------------------------------------------------------
 
      Idle      CC initial request             Send          Open
                received and successfully      CC initial
                processed.                     answer,
                                               reserve units,
                                               start Tcc
 
      Idle      CC initial request             Send          Idle
                received, but not              CC initial
                successfully processed.        answer with
                                               Result-Code
                                               =! SUCCESS
 
      Idle      CC event request               Send          Idle
                received and successfully      CC event
                processed.                     answer,
                                               debit units
 
      Idle      CC event request               Send          Idle
                received, but not              CC event
                successfully processed.        Answer with
                                               Result-Code
                                               != SUCCESS
 
      Open      CC update request              Send          Open
                received and successfully      CC answer,
                processed                      debit used
                                               units and
                                               reserve
                                               new units,
                                               Restart Tcc
 
      Open      CC update request              Send          Idle
                received, but not              CC update
                successfully processed.        Answer with
                                               Result-Code
                                               != SUCCESS,
                                               debit used
                                               units
 
      Open      CC termination request         Send          Idle
                received, and successfully     CC termin.
                processed                      answer,
                                               Stop Tcc,
                                               debit used
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                                               units
 
      Open      CC termination request         Send          Idle
                received, but not              CC termin.
                successfully processed.        Answer with
                                               Result-Code
                                               != SUCCESS,
                                               debit used
                                               units
 
      Open      Session supervision timer Tcc  Stop Tcc,      Idle
                expired                        release
                                               reserved
                                               units
 
 8. Credit Control AVPs
 
    This section defines the credit-control AVPs that are specific to
    Diameter Credit-control Application and MAY be included in the
    Diameter credit control messages.
 
    The AVPs defined in this section MAY also be included in
    authorization commands defined in authorization specific
    applications, such as [NASREQ] and [DiamMIP], in case the first
    interrogation is performed as part of the authorization /
    authentication process as described in section 4.
 
    The following table describes the Diameter AVPs defined in Credit-
    control application, their AVP Code values, types, possible flag
    values and whether the AVP MAY be encrypted.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                                             +---------------------+
                                             |    AVP Flag rules   |
                                             |----+-----+----+-----|----+
                      AVP  Section           |    |     |SHLD| MUST|    |
    Attribute Name    Code Defined Data Type |MUST| MAY | NOT|  NOT|Encr|
    -----------------------------------------|----+-----+----+-----|----|
    CC-Correlation-Id 411  8.1    OctetString| -  |  P  |    |  V  | Y  |
    CC-Input-Octets   412  8.33   Unsigned64 | M  |  P  |    |  V  | Y  |
    CC-Money          413  8.34   Grouped    | M  |  P  |    |  V  | Y  |
    CC-Output-Octets  414  8.35   Unsigned64 | M  |  P  |    |  V  | Y  |
    CC-Request-Number 415  8.2    Unsigned32 | M  |  P  |    |  V  | Y  |
    CC-Request-Type   416  8.3    Enumerated | M  |  P  |    |  V  | Y  |
    CC-Service-       417  8.36   OctetString| M  |  P  |    |  V  | Y  |
      Specific-Units                         |    |     |    |     |    |
    CC-Session-       418  8.4    Enumerated | M  |  P  |    |  V  | Y  |
      Failover                               |    |     |    |     |    |
    CC-Sub-Session-Id 419  8.5    Unsigned64 | M  |  P  |    |  V  | Y  |
    CC-Time           420  8.37   Unsigned32 | M  |  P  |    |  V  | Y  |
    CC-Total-Octets   421  8.38   Unsigned64 | M  |  P  |    |  V  | Y  |
    Check-Balance-    422  8.6    Enumerated | M  |  P  |    |  V  | Y  |
      Result                                 |    |     |    |     |    |
    Cost-Information  423  8.7    Grouped    | M  |  P  |    |  V  | Y  |
    Cost-Unit         424  8.8    UTF8String | M  |  P  |    |  V  | Y  |
    Currency-Code     425  8.11   Unsigned32 | M  |  P  |    |  V  | Y  |
    Credit-Control    426  8.9    Enumerated | M  |  P  |    |  V  | Y  |
    Credit-Control-   427  8.10   Enumerated | M  |  P  |    |  V  | Y  |
      Failure-Handling                       |    |     |    |     |    |
    Direct-Debiting   428  8.12   Enumerated | M  |  P  |    |  V  | Y  |
      Failure-Handling                       |    |     |    |     |    |
    Exponent          429  8.13   Integer32  | M  |  P  |    |  V  | Y  |
    Final-Unit-Action 449  8.14   Enumerated | M  |  P  |    |  V  | Y  |
    Final-Unit-       430  8.15   Grouped    | M  |  P  |    |  V  | Y  |
      Indication                             |    |     |    |     |    |
    Granted-Service-  431  8.16   Grouped    | M  |  P  |    |  V  | Y  |
      Unit                                   |    |     |    |     |    |
    Rating-Group      432  8.39   Unsigned32 | M  |  P  |    |  V  | Y  |
    Redirect-Address  433  8.17   Enumerated | M  |  P  |    |  V  | Y  |
      -Type                                  |    |     |    |     |    |
    Redirect-Server   434  8.18   Grouped    | M  |  P  |    |  V  | Y  |
    Redirect-Server   435  8.19   UTF8String | M  |  P  |    |  V  | Y  |
      -Address                               |    |     |    |     |    |
    Requested-Action  436  8.20   Enumerated | M  |  P  |    |  V  | Y  |
    Requested-Service 437  8.21   Grouped    | M  |  P  |    |  V  | Y  |
      Unit                                   |    |     |    |     |    |
    Restriction       438  8.22   IPFiltrRule| M  |  P  |    |  V  | Y  |
      -Filter-Rule                           |    |     |    |     |    |
    Service-          439  8.40   UTF8String | M  |  P  |    |  V  | Y  |
      Identifier                             |    |     |    |     |    |
    Service-Parameter 440  8.23   Grouped    | -  |  P  |    |  V  | Y  |
 
 
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                    Diameter Credit Control Application     October 2003
 
 
      Info                                   |    |     |    |     |    |
    Service-          441  8.24   Unsigned32 | -  |  P  |    |  V  | Y  |
      Parameter-Type                         |    |     |    |     |    |
    Service-          442  8.25   UTF8String | -  |  P  |    |  V  | Y  |
      Parameter-Value                        |    |     |    |     |    |
    Subscription-Id   443  8.26   Grouped    | M  |  P  |    |  V  | Y  |
    Subscription-Id   444  8.27   UTF8String | M  |  P  |    |  V  | Y  |
       -Data                                 |    |     |    |     |    |
    Subscription-Id   450  8.28   Enumerated | M  |  P  |    |  V  | Y  |
      -Type                                  |    |     |    |     |    |
    Unit-Value        445  8.29   Grouped    | M  |  P  |    |  V  | Y  |
    Used-Service-Unit 446  8.30   Grouped    | M  |  P  |    |  V  | Y  |
    Value-Digits      447  8.31   Unsigned64 | M  |  P  |    |  V  | Y  |
    Validity-Time     448  8.32   Unsigned32 | M  |  P  |    |  V  | Y  |
 
 8.1 CC-Correlation-Id AVP
 
    The CC-Correlation-Id AVP (AVP Code 411) is type of OctetString and
    contains information to correlate credit control requests generated
    for different components of the service, e.g. transport and service
    level.
 
 8.2 CC-Request-Number AVP
 
    The CC-Request-Number AVP (AVP Code 415) is of type Unsigned32 and
    identifies this request within one session. As Session-Id AVPs are
    globally unique, the combination of Session-Id and CC-Request-Number
    AVPs is also globally unique, and can be used in matching credit
    control messages with confirmations.  An easy way to produce unique
    numbers is to set the value to 0 for credit control request of type
    INITIAL_REQUEST and EVENT_REQUEST, and set the value to 1 for the
    first UPDATE_REQUEST, 2 for the second, and so on until the value for
    TERMINATION_REQUEST.
 
 8.3 CC-Request-Type AVP
 
    The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
    contains the reason for sending the Credit-control request message.
    It MUST be present in all CC-Request messages. The following values
    are defined for the CC-Request-Type AVP:
 
          INITIAL_REQUEST             1
             A Credit-control Initial request is used to initiate a
             credit control session, and contains credit control
             information that is relevant to the initiation of the
             session.
 
          UPDATE_REQUEST              2
             An Update Credit-control request contains credit control
 
 
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                    Diameter Credit Control Application     October 2003
 
 
             information for an existing credit control session. Update
             Credit-control requests SHOULD be sent every time a credit-
             control re-authorization is needed at the expiry of the
             allocated quota or validity time. Further, additional
             service-specific events MAY trigger a spontaneous Update
             request.
 
          TERMINATION_REQUEST         3
             A Credit-control Termination Request is sent to terminate a
             credit-control session and contains credit control
             information relevant to the existing session.
 
         EVENT_REQUEST                4
             A Credit Control Event Request is used when there is no need
             to maintain any credit control session state in the credit-
             control server. This request contains all information
             relevant to the service, and is the only request of the
             service. The reason for the Event request
             is further detailed in the Requested-Action AVP. The
             Requested-AVP MUST be included in the Credit-Control-Request
             message when CC-Request-Type is set to EVENT_REQUEST.
 
 8.4 CC-Session-Failover AVP
 
    The CC-Session-Failover AVP (AVP Code 418) is type of Enumerated and
    contains information whether the moving of the credit-control message
    stream to a backup server during an ongoing credit-control session is
    supported. In case of communication failures, the credit control
    message streams can be moved to an alternative destination if the
    credit control server supports failover to an alternative server. The
    secondary credit control server name, if received from the AAA
    server, can be used as an address of the backup server. An
    implementation is not required to support the moving of credit
    control message stream to an alternative server, since it requires
    also moving of information related to the credit control session to
    backup server.
 
    The following values are defined for the CC-Session-Failover AVP:
 
    FAILOVER_NOT_SUPPORTED                                  0
 
       When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED
       the Credit control message stream MUST NOT to be moved to
       alternative destination in case of communication failure.
 
       This is the default behavior if the AVP isn't included in the
       reply from the authorization or credit-control server.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    FAILOVER_SUPPORTED                                      1
 
       When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
       Credit control message stream SHOULD be moved to alternative
       destination in case of communication failure. The moving the
       credit control message stream to backup server MAY require that
       information related to the credit control session should be also
       forwarded to alternative server.
 
 8.5 CC-Sub-Session-Id AVP
 
    The CC-Sub-Session-Id AVP (AVP Code 419) is of type Unsigned64 and
    contains the credit-control sub-session identifier. The combination
    of the Session-Id and this AVP MUST be unique per sub-session, and
    the value of this AVP MUST be monotonically increased by one for all
    new sub-sessions. The absence of this AVP implies no sub-sessions are
    in use, with the exception of a CC-Request whose CC-Request-Type is
    set to TERMINATION_REQUEST. A TERMINATION_REQUEST message with no CC-
    Sub-Session-Id AVP present will signal the termination of all sub-
    sessions for a given Session-Id.
 
 8.6 Check-Balance-Result AVP
 
    The Check Balance Result AVP (AVP code 422) is of type Enumerated and
    contains the result of the balance check. This AVP is applicable only
    when the Requested-Action AVP indicates CHECK_BALANCE in the Credit-
    Control-Request command.
 
    The following values are defined for the Check-Balance-Result AVP.
 
          ENOUGH_CREDIT                                       0
               There is enough credit in the account to cover the
               requested service.
 
          NO_CREDIT                                           1
                There isn't enough credit in the account to cover the
                requested service.
 
 8.7 Cost-Information AVP
 
    The Cost-Information AVP (AVP Code 423) is of type Grouped and is
    used to return the cost information of a service in the Credit-
    Control-Answer command. The included Unit-Value AVP contains the cost
    estimate (always type of money) of the service in case of price
    enquiry or the accumulated cost estimation in the case of credit-
    control session.
 
    The Currency-Code specifies in which currency the cost was given.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    The Cost-Unit specifies the unit when the service cost is a cost per
    unit (e.g. cost for the service is $1 per minute).
 
    When the Requested-Action AVP with value PRICE_ENQUIRY is included in
    the Credit-Control-Request command the Cost-Information AVP sent in
    the succeeding Credit-Control-Answer command contains the cost
    estimation of the requested service, without any reservation being
    made.
 
    The Cost-Information AVP included in the Credit-Control-Answer
    command with the CC-Request-Type set to UPDATE_REQUEST contains the
    accumulated cost estimation for the session without taking any
    credit-reservation into account.
 
    The Cost-Information AVP included in the Credit-Control-Answer
    command with the CC-Request-Type set to EVENT_REQUEST or
    TERMINATION_REQUEST contains the estimated total cost for the
    requested service.
 
       It has the following ABNF grammar:
 
                   Cost-Information ::= < AVP Header: 423 >
                                        { Unit-Value }
                                        { Currency-Code }
                                        [ Cost-Unit ]
 
 8.8 Cost-Unit AVP
 
    The Cost-Unit AVP (AVP Code 424) is of type UTF8String and specifies
    the applicable unit to the Cost-Information when the service cost is
    a cost per unit (e.g. cost of the service is $1 pe rminute). The
    Cost-Unit can be for instance minute, hour, day, kilobytes, megabytes
    etc.
 
 8.9 Credit-Control AVP
 
    The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
    be included in AA requests when service element has credit control
    capabilities.
 
    CREDIT_AUTHORIZATION                                     0
 
      If the AAA server determines the user is a prepaid user, this value
      indicates that credit-control server MUST be contacted to perform
      the first interrogation. The value of the Credit-Control AVP MUST
      always be set to 0 in AA request sent to perform the first
      interrogation and initiate a new credit-control session.
 
    RE_AUTHORIZATION                                         1
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
      This value indicates to the Diameter AAA server that a credit-
      control session is ongoing for the subscriber and the credit-
      control server MUST not be contacted. The Credit-Control AVP set to
      the value of 1 is to be used only when the first interrogation has
      been successfully performed and the credit-control session is
      ongoing (i.e. re-authorization triggered by Authorization-
      Lifetime). This value MUST NOT be used in AA request sent to
      perform the first interrogation.
 
 8.10 Credit-Control-Failure-Handling AVP
 
     The Credit-Control-Failure-Handling AVP (AVP Code 427) is of type
     Enumerated. The credit-control client uses information in this AVP
     to decide what to do if the sending of credit-control messages to
     the credit-control server has been for instance temporarily
     prevented due to a network problem. Depending on the service logic,
     the credit-control server can order the client to terminate the
     service immediately when there is a reason to believe that the
     service cannot be charged, or to try failover to an alternative
     server, if possible, and then either terminate or grant the service
     should also the alternative connection fail.
 
       TERMINATE                                                0
 
       When the Credit-Control-Failure-Handling AVP is set to TERMINATE
       the service MUST only be granted as long as there is a connection
       to the credit-control server. If the credit-control client does
       not receive any Credit-Control-Answer message within the Tx timer
       (as defined in section 13) the credit-control request is regarded
       failed and the end user's service session is terminated.
 
       This is the default behavior if the AVP isn't included in the
       reply from the authorization or credit-control server.
 
       CONTINUE                                                 1
 
          When the Credit-Control-Failure-Handling AVP is set to
          CONTINUE the credit-control client SHOULD re-send the request
          to an alternative server in case of transport or temporary
          failures, provided that failover procedure is supported in the
          credit-control server and the credit-control client, and an
          alternative server is available. Otherwise, the service SHOULD
          be granted even if credit-control messages can't be delivered.
 
       RETRY_AND_TERMINATE                                      2
 
          When the Credit-Control-Failure-Handling AVP is set to
          RETRY_AND_TERMINATE the credit-control client SHOULD re-send
 
 
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                    Diameter Credit Control Application     October 2003
 
 
          the request to an alternative server in case of transport or
          temporary failures, provided that failover procedure is
          supported in the credit-control server and the credit-control
          client, and an alternative server is available. Otherwise, the
          service SHOULD not be granted when the credit-control messages
          can't be delivered.
 
 8.11 Currency-Code AVP
 
    The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and
    contains a currency code that specifies in which currency the values
    of AVPs containing monetary units were given. It is specified using
    the numeric values defined in the ISO 4217 standard.
 
 8.12 Direct-Debiting-Failure-Handling AVP
 
    The Direct-Debiting-Failure-Handling AVP (AVP Code 428) is of type
    Enumerated. The credit-control client uses information in this AVP to
    decide what to do if the sending of credit-control messages
    (Requested-Action AVP set to Direct Debiting) to the credit-control
    server has been for instance temporarily prevented due to a network
    problem.
 
        TERMINATE_OR_BUFFER                                   0
 
          When the Direct-Debiting-Failure-Handling AVP is set to
          TERMINATE_OR_BUFFER the service MUST be granted as long as
          there is a connection to the credit-control server. If the
          credit-control client does not receive any Credit-Control-
          Answer message within the Tx timer (as defined in section 13)
          the credit-control request is regarded failed. The client
          SHOULD terminate the service if it can determine from the
          failed answer that units have not been debited. Otherwise the
          credit-control client SHOULD grant the service, store the
          request to application level non-volatile storage and try to
          re-send the request.  These requests MUST be marked as
          possible duplicate by setting the T-flag in the command header
          as described in [DIAMBASE] section 3.
 
          This is the default behavior if the AVP isn't included in the
          reply from the authorization server.
 
        CONTINUE
                                      1
          When the Direct-Debiting-Failure-Handling AVP is set to
          CONTINUE the service SHOULD be granted even if credit-control
          messages can't be delivered and the request should be deleted.
 
 
 
 
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 8.13 Exponent AVP
 
    Exponent AVP is of type Integer32 (AVP code 429) and contains the
    exponent value to be applied for the Value-Digit AVP within the Unit-
    Value AVP.
 
 8.14 Final-Unit-Action AVP
 
    The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
    indicates to the credit-control client the action to be taken when
    the user's account cannot cover the service cost.
 
    The Final-Unit-Action can be one of the following:
 
       TERMINATE                                             0
 
          The credit control client MUST terminate the service session.
          This is the default handling applicable whenever the credit
          control client receives an unsupported Final-Unit-Action value
          and MUST be supported by all the Diameter credit control
          client implementations conforming to this specification.
 
       REDIRECT                                              1
 
          The service element MUST redirect the user to the address
          specified in the Redirect-Server-Address AVP. The redirect
          action is defined in section 5.5.2.
 
       RESTRICT_ACCESS                                       2
 
          The access device MUST restrict the user access according to
          the IP packet filters defined in the Restriction-Filter-Rule
          AVP or according to the IP packet filters identified by the
          Filter-Id AVP. All the packets not matching the filters MUST
          be dropped (see section 5.5.3).
 
 8.15 Final-Unit-Indication AVP
 
    The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
    indicates that the Granted-Service-Unit AVP in the Credit-Control-
    Answer, or in the AA answer, contains the final units for the
    service. After these units have expired, the Diameter credit-control
    client is responsible for executing the action indicated in the
    Final-Unit-Action AVP (see section 5.5).
 
    If more than one unit types are received in the Credit-Control-
    Answer, the Unit type which first expired SHOULD cause the credit-
    control client to execute the specified action.
 
 
 
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    In the first interrogation, the Final-Unit-Indication AVP with Final-
    Unit-Action REDIRECT or RESTRICT_ACCESS can also be present with no
    Granted-Service-Unit AVP in the Credit-Control-Answer or in the AA
    answer. This indicates to the Diameter credit-control client to
    immediately execute the specified action. If the home service
    provider policy is to terminate the service, naturally, the server
    SHOULD return the appropriate transient failure (see section 9.1) in
    order to disconnect the end user and close the credit control
    session.
 
    The Final-Unit-Action AVP defines the behavior of the service element
    when the user's account cannot cover the cost of the service and MUST
    always be present if the Final-Unit-Indication AVP is included in a
    command.
 
    If the Final-Unit-Action AVP is set to TERMINATE no other AVPs MUST
    be present.
 
    If the Final-Unit-Action AVP is set to REDIRECT at least the
    Redirect-Server AVP MUST be present. The Restriction-Filter-Rule AVP
    or the Filter-Id AVP MAY be present in the Credit-Control-Answer
    message if the user is allowed to access also other zero-rated
    services not accessible through the address given in the Redirect-
    Server AVP.
 
    If the Final-Unit-Action AVP is set to RESTRICT_ACCESS either the
    Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
 
    The Filter-Id AVP is defined in [NASREQ]. The Filter-Id AVP can be
    used to reference an IP filter list installed in the access device by
    other means than the Diameter Credit Control Application e.g. locally
    configured or configured by another entity.
 
    The Final-Unit-Indication AVP has the following ABNF grammar:
 
                Final-Unit-Indication ::= < AVP Header: 430 >
                                          { Final-Unit-Action }
                                         *[ Restriction-Filter-Rule ]
                                         *[ Filter-Id ]
                                          [ Redirect-Server ]
 
 8.16 Granted-Service-Unit AVP
 
    Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
    contains the amount of units that the Diameter credit-control client
    can provide to the end user until the service must be released or the
    new Credit-Control-Request must be sent. A client is not required to
    implement all of the unit types, and must treat unknown or
 
 
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    unsupported unit types in the answer message as an incorrect CCA
    answer. In that case the client shall terminate credit control
    session and indicate in the Termination-Cause AVP reason
    DIAMETER_BAD_ANSWER.
 
    The Service-Identifier and the Rating-Group AVPs are used to
    associate the granted units to a given service or rating group.
    In case both the Service-Identifier and the Rating-Group AVPs are
    included, the target of the granted units is always the service(s)
    indicated by the value of the Service-Identifier AVP.
 
    The Granted-Service-Unit AVP has the following ABNF grammar:
 
          Granted-Service-Unit ::= < AVP Header: 431 >
                                   [ CC-Time ]
                                   [ CC-Money ]
                                   [ CC-Total-Octets ]
                                   [ CC-Input-Octets ]
                                   [ CC-Output-Octets ]
                                   [ CC-Service-Specific-Units ]
                                  *[ Service-Identifier ]
                                   [ Rating-Group ]
 
 8.17 Redirect-Address-Type AVP
 
    The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated
    and defines the address type of the address given in the Redirect-
    Server-Address AVP.
 
    The address type can be one of the following:
 
       IPv4 Address                                       0
          The address type is in form of IPv4 address, as defined in
          [RFC 791].
 
       IPv6 Address                                       1
          The address type is in form of IPv6 address, as defined in
          [RFC 2373].
 
       URL                                                2
          The address type is in form of Uniform Resource Locator, as
          defined in [RFC 1738].
 
       SIP URI                                            3
          The address type is in form of SIP Uniform Resource Indicator,
          as defined in [SIP].
 
 8.18 Redirect-Server AVP
 
 
 
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    The Redirect-Server AVP (AVP Code 434) is of type Grouped and
    contains the address information of the redirect server (e.g. HTTP
    redirect server, SIP Server) where the end user is to be connected
    when the account cannot cover the service cost. It MUST be present
    when the Final-Unit-Action AVP is set to REDIRECT.
 
    It has the following ABNF grammar:
 
               Redirect-Server ::= < AVP Header: 434 >
                                   { Redirect-Address-Type }
                                   { Redirect-Server-Address }
 
 8.19 Redirect-Server-Address AVP
 
    The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String
    and defines the address of the redirect server (e.g. HTTP redirect
    server, SIP Server) where the end user is to be connected when the
    account cannot cover the service cost.
 
 8.20 Requested-Action AVP
 
    The Requested-Action AVP (AVP Code 436) is type of Enumerated and
    contains the requested action being sent by Credit-Control-Request
    command where the CC-Request-Type is set to EVENT_REQUEST. The
    following values are defined for the Requested-Action AVP:
 
        DIRECT_DEBITING                              0
 
           Direct debiting indicates that the request is to decrease the
           end user's account according to information specified in the
           Requested-Service-Unit AVP and/or Service-Parameter-Info AVP.
           The Granted-Service Unit AVP in the Credit-Control-Answer
           command contains the debited units.
 
        REFUND_ACCOUNT                               1
 
           Refund account indicates that the request is to increase the
           end user's account according to information specified in the
           Requested-Service-Unit AVP and/or Service-Parameter-Info AVP.
           The Granted-Service Unit AVP in the Credit-Control-Answer
           command contains the refunded units.
 
        CHECK_BALANCE                                2
 
           Check balance indicates that the request is a balance check
           request. In this case the checking of the account balance is
           done without any credit reservation from the account. The
           Check-Balance-Result AVP in the Credit-Control-Answer command
           contains the result of the Balance Check.
 
 
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        PRICE_ENQUIRY                                3
 
           Price Enquiry indicates that the request is a price enquiry
           request. In this case neither checking of the account balance
           nor reservation from the account will be done, only the price
           of the service will be returned in the Cost-Information AVP in
           the Credit-Control-Answer Command.
 
 8.21 Requested-Service-Unit AVP
 
    The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
    contains the amount of requested units specified by the Diameter
    credit-control client. A server is not required to implement all of
    the unit types, and must treat unknown or unsupported unit types as
    invalid AVPs.
 
    The Service-Identifier and the Rating-Group AVPs are used to request
    units for a given service(s) or rating group when the service element
    supports credit control for multiple services in one credit control
    session.
 
    If both the AVPs are present, the Rating-Group AVP indicates the
    rating group to which the service(s) specified by the Service-
    Identifier(s) belongs. If only the Rating-Group-Id AVP is present,
    this is a credit authorization request for all the services that
    belongs to the specified rating group.
 
    A server not implementing the Service-Identifier AVP and the Rating-
    Group AVP must treat them as invalid AVPs.
 
    The Requested-Service-Unit AVP has the following ABNF grammar:
 
          Requested-Service-Unit ::= < AVP Header: 437 >
                                     [ CC-Time ]
                                     [ CC-Money ]
                                     [ CC-Total-Octets ]
                                     [ CC-Input-Octets ]
                                     [ CC-Output-Octets ]
                                     [ CC-Service-Specific-Units ]
                                    *[ Service-Identifier ]
                                     [ Rating-Group ]
 
 8.22 Restriction-Filter-Rule AVP
 
    The Restriction-Filter-Rule AVP (AVP Code 438) is of type
    IPFilterRule and provides filter rules corresponding to zero-rated
    services offered by the home service provider. The access device need
    to configure the specified filter rules for the subscriber and MUST
 
 
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    drop all the packets not matching these filters. Zero, one or more
    such AVPs MAY be present in a Credit-Control-Answer message or in an
    AA answer message.
 
 8.23 Service-Parameter-Info AVP
 
    The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
    contains a service specific information used for price calculation or
    rating. The Service-Parameter-Type AVP defines the service parameter
    type and the Service-Parameter-Value AVP contains the parameter
    value. The actual contents of these AVPs are not within the scope of
    this document and SHOULD be defined in another Diameter application,
    standards written by other standardization bodies, or service
    specific documentation.
 
    In case of unknown service request (e.g. unknown Service-Parameter-
    Type), the corresponding answer message MUST contain error code
    DIAMETER_RATING_FAILED. A Credit Control Answer message with this
    error MUST contain one or more Failed-AVP AVPs containing the
    Service-Parameter-Info AVPs that caused the failure.
 
    It has the following ABNF grammar:
 
               Service-Parameter-Info ::= < AVP Header: 440 >
                                          [ Service-Parameter-Type ]
                                          [ Service-Parameter-Value ]
 
 8.24 Service-Parameter-Type AVP
 
    The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)
    and defines the type of the service event specific parameter (e.g. it
    can be end-user location, service name). The different parameters and
    their types are service specific and the meanings of these parameters
    are not defined in this document. The Service-Parameter-Value AVP
    contains the service parameter type.
 
 8.25 Service-Parameter-Value AVP
 
    The Service-Parameter-Value AVP is of type UTF8String (AVP Code 442)
    and contains the value of the service parameter type.
 
 8.26 Subscription-Id AVP
 
    The Subscription-Id AVP (AVP Code 443) is used to identify the end
    user's subscription and is of type Grouped.  The Subscription-Id AVP
    includes a Subscription-Id-Data AVP that hold the identifier and a
    Subscription-Id-Type AVP that defines the identifier type.
 
    It has the following ABNF grammar:
 
 
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                      Subscription-Id ::= < AVP Header: 443 >
                                          { Subscription-Id-Type }
                                          { Subscription-Id-Data }
 
 8.27 Subscription-Id-Data AVP
 
    The Subscription-Id-Data AVP (AVP Code 444) is used to identify the
    end-user and is of type UTF8String. The Subscription-Id-Type AVP
    defines which type of identifier is used.
 
 8.28 Subscription-Id-Type AVP
 
    The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated and
    it is used to determine which type of identifier that is carried by
    the Subscription-Id AVP. A server is not required to implement all of
    the Subscription-Id-Types, and MUST treat unknown or unsupported
    Subscription-Id-Types as invalid AVP values.
 
    The identifier can be one of the following:
 
       END_USER_MSISDN                                              0
 
            The identifier is in international MSISDN format, according
            to the ITU-T E.164 numbering plan as defined in [E164] and
            [CE164].
 
        END_USER_IMSI                                                1
            The identifier is in international IMSI format, according to
            the ITU-T E.212 numbering plan as defined in [E121] and
            [CE121].
 
        END_USER_SIP_URL                                             2
           The identifier is in the form of a SIP URL as defined in
           [SIP].
 
        END_USER_NAI                                                 3
            The identifier is in the form of a Network Access Identifier
            as defined in [NAI].
 
        END_USER_PRIVATE                                             4
            The Identifier is a credit-control server private identifier.
 
 8.29 Unit-Value AVP
 
    Unit-Value AVP is of type Grouped (AVP Code 445) and specifies the
    units as decimal value. The Unit-Value is a value together with an
    exponent, i.e. Unit-Value = Value-Digits AVP * 10^Exponent. This
    representation avoids unwanted rounding off. For example the value of
 
 
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    2,3 is represented as Value-Digits = 23 and Exponent = -1. The
    absence of exponent part MUST be interpreted as exponent being equal
    to zero.
 
    It has the following ABNF grammar:
 
                     Unit-Value ::= < AVP Header: 445 >
                                    { Value-Digits }
                                    [ Exponent ]
 
 8.30 Used-Service-Unit AVP
 
    The Used-Service-Unit AVP is of type Grouped AVP (AVP Code 446) and
    contains the amount of used units measured from the point when the
    service became active or, in case of interim interrogations are used
    during the session, from the point when the previous measurement
    ended.
 
    The Service-Identifier and the Rating-Group AVPs are used to
    associate the used units to a given service or rating group.
    When granted service units are associated to a service or rating
    group, the credit control client MUST report the corresponding used
    service units. If the granted units are associated to a rating group,
    the units used by each of the Service-Identifier belonging to that
    rating group SHOULD be reported if this information is available to
    the credit control client. Therefore, multiple instances of the Used-
    Service-Unit AVP MAY be present in a request, each associated to the
    relevant Rating-Group-Id and to the identifier of the service (i.e.
    Service-Identifier) that consumed some of the granted units.
 
    The Used-Service-Unit AVP has the following ABNF grammar:
 
          Used-Service-Unit ::= < AVP Header: 446 >
                                [ CC-Time ]
                                [ CC-Money ]
                                [ CC-Total-Octets ]
                                [ CC-Input-Octets ]
                                [ CC-Output-Octets ]
                                [ CC-Service-Specific-Units ]
                               *[ Service-Identifier ]
                                [ Rating-Group ]
 
 8.31 Value-Digits AVP
 
    The Value-Digits AVP is of type Unsigned64 (AVP code 447) and
    contains the significant digits of the number. If decimal values are
    needed to present the units, the scaling MUST be indicated with the
    related Exponent AVP. For example for the monetary amount $ 0.05 the
 
 
 
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    value of Value-Digits AVP MUST be set to 5 and the scaling MUST be
    indicated with the Exponent AVP set to -2.
 
 8.32 Validity-Time AVP
 
    The Validity-Time AVP is of type Unsigned32 (AVP code 448) and is
    sent from the credit-control server to the credit-control client. The
    AVP contains the validity time of the granted service units. If the
    granted service units have not been consumed within the validity time
    specified in this AVP, the credit-control client MUST send a Credit-
    Control-Request request to the server with CC-Request-Type set to
    UPDATE_REQUEST. The value field of the Validity-Time AVP is given in
    seconds.
 
    The Validity-Time AVP is also used for the graceful service
    termination (see section 5.5) to indicate to the credit control
    client how long the subscriber is allowed to use network resources
    after the specified action (i.e. REDIRECT or RESTRICT_ACCESS)
    started. Upon the Validity-Time elapses a new intermediate
    interrogation is sent to the server.
 
 8.33 CC-Input-Octets AVP
 
    The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64, and
    contains the number of requested, granted or used octets that can
    be/have been received from the end user.
 
 8.34 CC-Money AVP
 
    The CC-Money AVP (AVP Code 413) is of type Grouped, and specifies the
    monetary amount in the given currency. The Currency-Code AVP SHOULD
    be included. It has the following ABNF grammar:
 
          CC-Money ::= < AVP Header: 413 >
                       { Unit-Value }
                       [ Currency-Code ]
 
 8.35 CC-Output-Octets AVP
 
    The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64, and
    contains the number of requested, granted or used octets that can
    be/have been sent to the end user.
 
 8.36 CC-Service-Specific-Units AVP
 
    The CC-Service-Specific-Units AVP (AVP Code 417) is of type
    OctetString, and specifies the number of service specific units (e.g.
    number of events, points) given in a selected service.
 
 
 
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 8.37 CC-Time AVP
 
    The CC-Time AVP (AVP Code 420) is of type Unsigned32, and indicates
    the length of the requested, granted or used time in seconds.
 
 8.38 CC-Total-Octets AVP
 
    The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64, and
    contains the total number of requested, granted or used octets
    regardless of the direction (sent or received).
 
 8.39 Rating-Group AVP
 
    The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and
    contains the identifier of a rating group. All the services subject
    to the same rating type are part of the same rating group. This is an
    identifier allocated by the home service provider and MUST be unique
    within the home service provider domain.
 
    A usage example of this AVP is illustrated in Appendix A (Flow X).
 
 8.40 Service-Identifier AVP
 
    The Service-Identifier AVP is of type UTF8String (AVP Code 439) and
    contains a unique identifier of a given service. This is an
    identifier allocated by the service provider and MUST uniquely
    identify a given service (e.g. Service 1@example.com).
 
    A usage example of this AVP is illustrated in Appendix A (Flow X).
 
 9. Result Code AVP values
 
    This section defines new Result-Code AVP [DIAMBASE] values that must
    be supported by all Diameter implementations that conform to this
    specification.
 
    The Credit-Control-Answer message includes the Result-Code AVP, which
    MAY indicate that an error was present in the Credit-Control-Request
    message. A rejected Credit-Control-Request message SHOULD cause the
    user's session to be terminated.
 
 9.1 Transient Failure
 
    Errors that fall within the transient failures category are used to
    inform a peer that the request could not be satisfied at the time it
    was received, but MAY be able to satisfy the request in the future.
 
         DIAMETER_END_USER_SERVICE_DENIED                         4010
         The credit-control server denies the service request due to
 
 
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         service restrictions or limitations related to the end-user,
         for example the end-user's account could not cover the requested
         service. The possibly reported used-service-units with the CCR
         are deducted.
 
         DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE                   4011
         The credit-control server determines that the service can be
         granted to the end user but no further credit-control is needed
         for the service (e.g. service is free of charge).
 
 9.2 Permanent Failures
 
    Errors that fall within permanent failure category are used to inform
    the peer that the request failed, and should not be attempted again.
 
          DIAMETER_USER_UNKNOWN                                    5030
          The specified end user is unknown in the credit-control server.
 
          DIAMETER_RATING_FAILED                                   5031
          This error code is used to inform the credit-control client
          that the credit-control server cannot rate the service request
          due to insufficient rating input, incorrect AVP combination or
          due to an AVP or an AVP value that is not recognized or
          supported in the rating. The Failed-AVP AVP MUST be included
          and contain a copy of the entire AVP(s) that could not be
          processed successfully or an example of the missing AVP
          complete with the Vendor-Id if applicable. The value field of
          the missing AVP should be of correct minimum length and contain
          zeroes.
 
 10. AVP Occurrence Table
 
    The following table presents the AVPs defined in this document, and
    specifies in which Diameter messages they MAY, or MAY NOT be present.
    Note that AVPs that can only be present within a Grouped AVP are not
    represented in this table.
 
    The table uses the following symbols:
          0     The AVP MUST NOT be present in the message.
          0+    Zero or more instances of the AVP MAY be present in the
                message.
          0-1   Zero or one instance of the AVP MAY be present in the
                message. It is considered an error if there are more than
                once instance of the AVP.
          1     One instance of the AVP MUST be present in the message.
          1+    At least one instance of the AVP MUST be present in the
                message.
 
 
 
 
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 10.1 Credit Control AVP Table
 
    The table in this section is used to represent which Credit-control
    applications specific AVPs defined in this document are to be present
    in the Credit Control messages.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                                        +-----------+
                                        |  Command  |
                                        |   Code    |
                                        |-----+-----+
          Attribute Name                | CCR | CCA |
          ------------------------------|-----+-----+
          Acct-Multi-Session-Id         | 0-1 | 0-1 |
          Auth-Application-Id           | 1   | 1   |
          CC-Correlation-Id             | 0-1 | 0   |
          CC-Failover-Supported         | 0   | 0-1 |
          CC-Request-Number             | 1   | 1   |
          CC-Request-Type               | 1   | 1   |
          CC-Sub-Session-Id             | 0-1 | 0-1 |
          Check-Balance-Result          | 0   | 0-1 |
          Cost-Information              | 0   | 0-1 |
          Credit-Control-Failure-       | 0   | 0-1 |
             Handling                   |     |     |
          Destination-Host              | 0-1 | 0   |
          Destination-Realm             | 1   | 0   |
          Direct-Debiting-Failure-      | 0   | 0-1 |
             Handling                   |     |     |
          Event-Timestamp               | 0-1 | 0-1 |
          Final-Unit-Indication         | 0   | 0-1 |
          Granted-Service-Unit          | 0   | 0+  |
          Origin-Host                   | 1   | 1   |
          Origin-Realm                  | 1   | 1   |
          Origin-State-Id               | 0-1 | 0-1 |
          Proxy-Info                    | 0+  | 0+  |
          Redirect-Host                 | -   | 0+  |
          Redirect-Host-Usage           | -   | 0-1 |
          Redirect-Max-Cache-Time       | -   | 0û1 |
          Requested-Action              | 0-1 | 0   |
          Requested-Service-Unit        | 0-1 | 0   |
          Route-Record                  | 0+  | 0+  |
          Service-Parameter-Info        | 0+  | 0   |
          Session-Id                    | 1   | 1   |
          Subscription-Id               | 0-1 | 0-1 |
          Termination-Cause             | 0-1 | 0   |
          Used-Service-Unit             | 0+  | 0   |
          User-Name                     | 0-1 | 0-1 |
          Validity-Time                 | 0   | 0-1 |
          ------------------------------|-----+-----+
 
 11. RADIUS/Diameter Credit-control Interworking
 
    This section defines some basic guidelines to provide the Diameter
    Credit-control/RADIUS inter-working, that is a protocol translation
    between RADIUS [RFC2865] and Diameter Credit-control application. A
    complete description of all protocol translations between RADIUS and
 
 
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    Diameter Credit-control application is beyond the scope of this
    document. Note that this document does not restrict implementations
    from creating additional methods; it just provides some guiding
    principles for protocol translation. Translation makes use of RADIUS
    Vendor Specific Attributes (VSAs) for transporting Diameter credit-
    control AVPs.
 
    The Diameter NASREQ [NASREQ] application defines how a RADIUS Request
    is forwarded as a Diameter Request. Guidelines defined in the
    Diameter NASREQ should be followed to the appropriate extent.
 
    A protocol translation between RADIUS and Diameter Credit-control
    application is shown in Annex A.
 
 11.1 Initial RADIUS Access-Request
 
    When an AAA server acting as a Translation Agent receives an initial
    RADIUS Access-Request message indicating that the service element is
    capable of credit-control (e.g. Radius VSA Pre-Paid-Accounting-
    Capability), and if the AAA server determines that the subscriber is
    a prepaid subscriber then a Diameter Credit control request MUST be
    sent towards the credit-control server.
 
    In addition to those steps defined in [NASREQ] the AAA server should
    perform the following steps related to the protocol translation
    between RADIUS and Diameter Credit-control application:
 
       - The credit control Session-Id should be included in the
         Session-Id AVP.
       - The CC-Request-Type is set to INITIAL_REQUEST and CC-Request-
         Number value is set to 0.
       - Subscription-Id should be added using User-Name attribute from
         the RADIUS Access-Request message or some AAA server local Id
         to identify user's credit control subscription.
       - If the Access-Request message contains the Event-Timestamp
         attribute it should be included in the Event-Timestamp AVP
 
    The following steps are applied to response the Access-Request
    message when successful credit-control answer is received from the
    Credit-control server:
 
       - The AAA server shall generate a RADIUS VSA Quota Id to
         correlate subsequent RADIUS message with the credit-control
         session.
       - The Termination-Action attribute must be set to be RADIUS-
         request to ensure that the used quota is returned by the
         service element upon termination of the service.
       - If the Granted-Service-Unit AVP including the CC-Time AVP or
         the Validity-Time AVP is returned by the credit control server,
 
 
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                    Diameter Credit Control Application     October 2003
 
 
         then the smallest value should be included in the RADIUS VSA
         Duration-Quota.
       - If the Granted-Service-Unit AVP including the CC-Total-Octets
         AVP is returned by the credit-control server, then the volume
         should be included in the RADIUS VSA Volume-Quota.
       - If separate RADIUS VSA Thresholds (volume or duration) are
         required by RADIUS implementation, the AAA server shall derive
         the threshold values from the Granted-Service-Unit AVPs. The
         threshold should be less than the Duration-Quota or Volume-
         Quota, except when the Final-Unit-Indication AVP is returned by
         the credit control server.
 
    When credit-control answer message includes the Result-Code, which
    indicates that credit control authorization is rejected, the AAA
    server shall send an Access-Reject message to service element.
 
 11.2 Subsequent RADIUS Access-Request message
 
    When an AAA server receives a RADIUS Access-Request message
    containing RADIUS VSA Quota Id, it indicates that the Access-Request
    message is subsequent RADIUS Request related to the credit control
    session. The AAA server shall use the Quota Id to identify the
    credit-control session.
 
    The AAA server's next steps depend on the value of the RADIUS VSA
    Update-Reason. If the Update-Reason indicates æThreshold reached'
    then the AAA server should perform the following steps related to a
    new quota request:
 
      - The CC-Request-Type is set to UPDATE_REQUEST and CC-Request-
        Number value is increased by one.
      - If the Granted-Service-Unit AVP including the CC-Time AVP or the
        Validity-Time AVP is returned by the credit control server, then
        the smallest value should be included in the RADIUS VSA
        Duration-Quota.
      - If the Granted-Service-Unit AVP including the CC-Total-Octets AVP
        is returned by the credit-control server, then the volume should
        be included in the RADIUS VSA Volume-Quota.
 
    The reply to the RADIUS Access-Request message shall be handled as
    described in initial Radius Access-Request.
 
    If the RADIUS VSA Update-Reason indicates that the associated
    resources are released at the service element, then the AAA server
    shall terminate the credit control session by performing the
    following steps:
 
      - The CC-Request-Type is set to TERMINATION_REQUEST and CC-Request-
        Number value is increased by one.
 
 
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                    Diameter Credit Control Application     October 2003
 
 
      - If the RADIUS VSA Volume-Quota is present, the value shall be
        included in the Used-Service-Unit AVP as CC-Total-Octets.
      - If the RADIUS VSA Time-Quota is present, the value shall be
        included in the Used-Service-Unit AVP as CC-Time.
 
    After the AAA server receives response to the final credit Control
    Credit-Control-Request the RADIUS Access-Accept message shall be
    return to the service element.
 
 11.3 RADIUS Vendor Specific Attributes for Credit Control
 
    To provide the credit control for RADIUS implementation the RADIUS
    Vendor Specific Attributes (VSAs) are used for transporting Diameter
    credit-control AVPs. The RADIUS Type 26 (= Vendor-Specific) is used
    for RADIUS VSA.
 
    RADIUS Inter-working with the Diameter Credit control uses the
    following VSA included with the RADIUS Access Request and Access
    Accept messages:
 
       - Pre-Paid-Accounting-Capability; defines that the Service
         element in RADIUS implementation is capable of credit-control.
       - Quota Id; generated by the AAA server and it is used to
         correlate subsequent RADIUS message with the credit-control
         session.
       - Duration-Quota; in RADIUS Access-Request message it indicates
         the used Duration and in RADIUS Access-Accept message it
         indicates the Duration allocated for the service element.
       - Volume-Quota; in RADIUS Access-Request message it indicates the
         used Volume and in RADIUS Access-Accept message it indicates
         the Volume allocated for the service element.
       - Volume-Threshold; If RADIUS implementation requires separate
         threshold attribute for Volume, then Volume-Threshold is sent
         in RADIUS Access-Accept message and it represents the volume
         (in bytes) that shall be used by the service element before
         requesting a new Volume quota.
       - Duration-Threshold; If RADIUS implementation requires separate
         threshold attribute for Duration, then Duration-Threshold is
         sent in RADIUS Access-Accept message and it represents the
         duration (in seconds) that shall be used by the service element
         before requesting a new Duration quota.
       - Update-Reason; in RADIUS Access-Request message it indicates
         the reason for the initiating the quota update operation.
 
 12. IANA Considerations
 
    This section contains the namespaces that have either been created in
    this specification, or the values assigned to existing namespaces
    managed by IANA.
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 
 12.1 Application Identifier
 
    This specification assigns the value 4 to the Application Identifier
    namespace defined in [DIAMBASE]. See section 1.3 for more
    information.
 
 12.2 Command Codes
 
    This specification uses the value 272 from the Command code namespace
    defined in [DIAMBASE].
 
 12.3 AVP Codes
 
    This specification assigns the values 411 - 450 from the AVP code
    namespace defined in [DIAMBASE] See section 8 for the assignment of
    the namespace in this specification.
 
 12.4 Result-Code AVP Values
 
    This specification assigns the values 4010, 4011, 5030 and 5031 from
    the Result-Code AVP (AVP Code 268) value namespace defined in
    [DIAMBASE]. See section 9 for the assignment of the namespace in this
    specification.
 
 12.5 CC-Request-Type AVP
 
    As defined in section 8.3, the CC-Request-Type AVP (AVP code 416)
    defines the value 1-3. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 12.6 CC-Session-Failover AVP
 
    As defined in section 8.4, the CC-Failover-Supported AVP (AVP code
    418) defines the value 0-1. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 12.7 Check-Balance-Result AVP
 
    As defined in Section 8.6, the Check-Balance-Result AVP (AVP Code
    422) defines the values 0-1. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 12.8 Credit-Control AVP
 
    As defined in section 8.9, the Credit-Control AVP (AVP code 426)
    defines the value 0-1. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
 12.9 Credit-Control-Failure-Handling AVP
 
    As defined in Section 8.10, the Credit-Control-Failure-Handling AVP
    (AVP Code 427) defines the values 0-2. All remaining values are
    available for assignment via Designated Expert [IANA].
 
 12.10 Direct-Debiting-Failure-Handling AVP
 
    As defined in Section 8.12, the Direct-Debiting-Failure-Handling AVP
    (AVP Code 448) defines the values 0-1. All remaining values are
    available for assignment via Designated Expert [IANA].
 
 12.11 Final-Unit-Action AVP
 
    As defined in Section 8.14, the Final-Unit-Action AVP (AVP Code 449)
    defines the values 0-2. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 12.12 Redirect-Address-Type AVP
 
    As defined in Section 8.17, the Redirect-Address-Type AVP (AVP Code
    433) defines the values 0-3. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 12.13 Requested-Action AVP
 
    As defined in Section 8.20, the Requested-Action AVP (AVP Code 436)
    defines the values 0-3. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 12.14 Subscription-Id-Type AVP
 
    As defined in Section 8.28, the Subscription-Id-Type AVP (AVP Code
    450) defines the values 0-4. All remaining values are available for
    assignment via Designated Expert [IANA].
 
 13. Credit-control Application Related Parameters
 
    Tx timer
 
       When real-time credit-control is required, the credit-control
       client contacts the credit-control server before and during the
       service is provided to an end user. Due to real-time nature of
       application the communication delays SHOULD be minimized, e.g. to
       avoid too long service set up time experienced by the end user.
       The Tx timer is introduced to control the waiting time in the
       client in the PENDING state. When the Tx timer elapses the
       credit-control client takes an action to the end user according
       to the value of the Credit-Control-Failure-Handling AVP or
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       according to the value of the Direct-Debiting-Failure-Handling
       AVP.
 
 
       The recommended value is 10 seconds.
 
    Tcc timer
 
       The Tcc timer supervises an ongoing credit control session in the
       credit control server. It is RECOMMENDED to use the Validity-Time
       as input to set the Tcc timer value. To avoid the credit control
       session in the Diameter credit control server to change to Idle
       state in case of short transient network failure, Tcc MAY be set
       to two times the value of Validity-Time.
 
    Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling
 
       Client implementations may offer the possibility to locally
       configure these AVPs. In such a case their value and behavior is
       defined in section 5.6 for the Credit-Control-Failure-Handling
       and in section 6.5 for the Direct-Debiting-Failure-Handling.
 
 14. Security Consideration
 
    The Diameter base protocol [DIAMBASE] assumes that each Diameter
    implementation uses underlying security, i.e. IPsec or TLS. These
    mechanisms are believed to provide sufficient protection under the
    normal Internet threat model - that is, assuming the authorized nodes
    engaging in the protocol have not been compromised, but the attacker
    has complete control over the communication channels between them.
    This includes eavesdropping, message modification, insertion, man-in-
    the-middle and replay attacks. Note also that this application
    includes a mechanism for application layer replay protection by the
    means of Session-ID from [DIAMBASE], and CC-Request-Number specified
    in this document. The Diameter credit control application is often
    used within one domain and there may be just single hop between the
    peers. In these environments the use of TLS or IPsec is sufficient.
    The details of TLS and IPsec related security considerations are
    discussed in the  [DIAMBASE].
 
    Because this application handles monetary transactions (directly or
    indirectly) this kind of application increases the interest for
    various security attacks. Therefore extra attention should be paid to
    the authentication of the client and the server, as well as the
    possible proxy and relay agents. In addition to this, authorization
    of the client shall be emphasized, i.e. that the client is allowed to
    perform credit control for a certain user.
 
    Another kind threat is malicious modification, injection or deletion
    of AVPs or complete credit control messages. The credit control
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    messages contain sensitive billing related information (such as
    subscription Id, granted units, used units, cost information) whose
    malicious modification can have economical consequences. Sometimes
    simply delaying the credit control messages can cause disturbances in
    the credit control client or server.
 
    Even without any modification to the messages an adversary can invite
    a security threat by eavesdropping, because the transactions contain
    private information about the user. Also by monitoring the credit
    control messages one can collect information about credit control
    server's billing models and business relationships.
 
    When third party relays or proxy are involved, the hop-by-hop
    security does not necessarily provide sufficient protection for
    Diameter user session. Diameter messages, such as CCR and CCA,
    containing sensitive AVPs are NOT RECOMMENDED to be sent via
    untrusted Diameter proxy agents since there are no assurance that
    third party proxies will not modify the credit control commands or
    AVP values.
 
 14.1 Direct Connection with Redirects
 
    A Diameter Credit control agent cannot always know whether agents
    between it and the end user's Diameter credit control server are
    reliable. In this case the Diameter Credit control agent doesn't have
    a routing entry in its Diameter Routing Table for the realm of the
    Credit Control Server in the end user's home domain. The Diameter
    Credit control agent can have a default route configured to a local
    Redirect agent and it re-directs the CCR message to the redirect
    agent. The local Redirect agent then returns a redirect notification
    (Result-code 3006, DIAMETER_REDIRECT_INDICATION) to the Credit
    control agent, as well Diameter Credit control Server(s) information
    (Redirect-Host AVP) and information (Redirect-Host-Usage AVP) how to
    the routing entry resulting from the Redirect-Host is to be used. The
    Diameter credit control agent then forwards the CCR message directly
    to one of the hosts identified by the CCA message from the redirect
    agent. If the value of the Redirect-Host-Usage AVP is unequal than
    zero all following messages are sent to the host specified in the
    Redirect-Host AVP until the time specified by the Redirect-Max-Cache-
    Time AVP is expired.
 
 15. References
 
 15.1 Normative
 
    [DIAMBASE]  P. Calhoun, J. Loughney, J. Arkko, E. Guttman, G. Zorn.
                "Diameter Base Protocol", RFC 3588, September 2003.
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    [3GPPCHARG] 3rd Generation Partnership Project; Technical
                Specification Group Services and System Aspects, Service
                aspects; Charging and Billing, (release 5), 3GPP TS
                22.115 v. 5.2.1, 2002-03
 
    [SIP]       M. Handley, H. Schulzrinne, E. Schooler, J. Rosenberg, G.
                Camarillo, A. Johnston, J. Peterson, R. Sparks
                "SIP: Session Initiation Protocol", RFC 3261. June 2002.
 
    [NAI]       Aboba, Beadles "The Network Access Identifier." RFC 2486.
                January 1999.
 
    [E164]      Recommendation E.164/I.331 (05/97): The International
                Public Telecommunication Numbering Plan. 1997.
 
    [CE164]     Complement to ITU-T Recommendation E.164 (05/1997):"List
                of ITU-T Recommendation E.164 assigned country codes",
                June 2000.
 
    [E212]      Recommendation E.212 (11/98): The international
                identification plan for mobile terminals and mobile
                users. 1998.
 
    [CE212]     Complement to ITU-T Recommendation E.212 (11/1997):" List
                of mobile country or geographical area codes ", February
                1999.
 
    [IANA]      Narten, Alvestrand, "Guidelines for Writing an IANA
                Considerations Section in RFCs", BCP 26, RFC 2434,
                October
                1998
 
 15.2 Non-Normative
 
    [KEYWORDS]  S. Bradner, "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.
 
    [ACCMGMT]   B. Aboba, J.Arkko, D.Harrington. "Introduction to
                Accounting Management", RFC 2975, October 2000.
 
    [RFC2866]   C. Rigney. "Radius Accounting", RFC 2866, June 2000
 
    [NASREQ]    P. Calhoun, G. Zorn, D. Spence, D. Mitton. "Diameter
                NASREQ Application", IETF work in progress.
 
    [DIAMMIP]   P. Calhoun, T. Johansson, C. Perkins "Diameter Mobile IP
                Application", IETF work in progress.
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    [RFC2865]   C. Rigney, S. Willens, A. Rubens, W. Simpson. "Remote
                Authentication Dial In User Service (RADIUS), RFC 2865,
                June 2000
 
 16. Acknowledgement
 
    The authors would like to thank Bernard Aboba, Robert Ekblad, Benny
    Gustafsson, Robert Karlsson, Avi Lior, Paco Marin, Jussi Maki, Jeff
    Meyer, Anne Narhi and Juha Vallinen for their comments and
    suggestions.
 
 17. Author's Address
 
    Harri Hakala
    Oy L M Ericsson Ab
    Joukahaisenkatu 1
    20520 Turku
    Finland
    Phone: +358 2 265 3722
    EMail: Harri.Hakala@ericsson.com
 
    Leena Mattila
    Oy L M Ericsson Ab
    Joukahaisenkatu 1
    20520 Turku
    Finland
    Phone: +358 2 265 3731
    EMail: Leena.Mattila@ericsson.com
 
    Juha-Pekka Koskinen
    Nokia Networks
    Hatanpaanvaltatie 30
    33100 Tampere
    Finland
 
    Phone: +358 7180 74027
    Email: juha-pekka.koskinen@nokia.com
 
    Marco Stura
    Nokia Networks
    Hiomotie 32
    00380 Helsinki
    Finland
    Phone: +358 7180 64308
    Email: marco.stura@nokia.com
 
    John Loughney
    Nokia Research Center
    Itamerenkatu 11-13
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    00180 Helsinki
    Finland
    Phone: +358 50 483 642
    Email: John.Loughney@nokia.com
 
 18. Full Copyright Statement
 
    Copyright (C) The Internet Society (2003). All Rights Reserved.
 
    This document and translations of it may be copied and furnished to
    others, and derivative works that comment on or otherwise explain it
    or assist in its implementation may be prepared, copied, published
    and distributed, in whole or in part, without restriction of any
    kind, provided that the above copyright notice and this paragraph are
    included on all such copies and derivative works. However, this
    document itself may not be modified in any way, such as by removing
    the copyright notice or references to the Internet Society or other
    Internet organizations, except as needed for the purpose of
    developing Internet standards in which case the procedures for
    copyrights defined in the Internet Standards process must be
    followed, or as required to translate it into languages other than
    English. The limited permissions granted above are perpetual and will
    not be revoked by the Internet Society or its successors or assigns.
 
    This document and the information contained herein is provided on an
    "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
    TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
    BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
    HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
    MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 
 19. Notices
 
    The IETF takes no position regarding the validity or scope of any
    intellectual property or other rights that might be claimed to
    pertain to the implementation or use of the technology described in
    this document or the extent to which any license under such rights
    might or might not be available; neither does it represent that it
    has made any effort to identify any such rights.  Information on the
    IETF's procedures with respect to rights in standards-track and
    standards-related documentation can be found in BCP-11.  Copies of
    claims of rights made available for publication and any assurances of
    licenses to be made available, or the result of an attempt made to
    obtain a general license or permission for the use of such
    proprietary rights by implementors or users of this specification can
    be obtained from the IETF Secretariat.
 
    The IETF invites any interested party to bring to its attention any
    copyrights, patents or patent applications, or other proprietary
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    rights, which may cover technology that may be required to practice
    this standard.  Please address the information to the IETF Executive
    Director.
 
 20. Expiration Date
 
    This memo is filed as <draft-ietf-aaa-diameter-cc-01.txt> and expires
    in April 2004.
 
 Appendix A Credit Control sequences
 
 A.1  Flow I
 
    End-User              NAS             AAA Server           CC Server
                      (CC Client)
       |(1)User Logon      |(2)AA Request (CC AVPs)                  |
       |------------------>|------------------->|                    |
       |                   |                    |(3)CCR(initial, CC AVPs)
       |                   |                    |------------------->|
       |                   |                    | (4)CCA(granted Units)
       |                   |                    |<-------------------|
       |                   |(5)AA Answer(granted Units)              |
       |(6)Access granted  |<-------------------|                    |
       |<----------------->|                    |                    |
       |                   |                    |                    |
       :                   :                    :                    :
       |                   |(7)CCR(update,used Units)                |
       |                   |------------------->|(8)CCR              |
                                                   (update,used units)
       |                   |                    |------------------->|
       |                   |                    |(9)CCA(granted Units)
       |                   |(10)CCA(granted Units)<------------------|
       |                   |<-------------------|                    |
       :                   :                    :                    :
       |         (Auth. lifetime expires)       |                    |
       |                   |(11) AAR (CC AVP)   |                    |
       |                   |------------------->|                    |
       |                   |          (12) AAA  |                    |
       |                   |<-------------------|                    |
       :                   :                    :                    :
       :                   :                    :                    :
       |(13) User logoff   |                    |                    |
       |------------------>|(14)CCR(term.,used-Units)                |
       |                   |------------------->|(15)CCR             |
       |                   |                    |   (term.,used-Units)
       |                   |                    |------------------->|
       |                   |                    |            (16)CCA |
       |                   |            (17)CCA |<-------------------|
       |                   |<-------------------|                    |
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       |                   |(18)STR             |                    |
       |                   |------------------->|                    |
       |                   |            (19)STA |                    |
       |                   |<-------------------|                    |
 
                             Figure A.1: Flow I
 
    A credit control flow for Network Access Services prepaid is shown in
    Figure A.1. The Diameter [NASREQ] is implemented in the Network
    Access Server (NAS). The focus of this flow is in the credit
    authorization.
 
    The user logs onto the network (1). The Diameter NAS first sends a
    Diameter Authorization-Authentication-Request to the home AAA
    Server, the credit-control client populates the AAR with the Credit-
    Control AVP set to CREDIT_AUTHORIZATION and service specific AVPs
    are included as usual [NASREQ]. The home AAA server performs service
    specific Authentication and Authorization as usual. The AAA server
    determines that the user is a prepaid user and notices from the
    Credit-Control AVP that the NAS has credit control capabilities, it
    sends a Diameter Credit-Control-Request with CC-Request-Type set to
    INITIAL_REQUEST to the Diameter credit-control server to perform
    credit authorization (3) and to establish a credit control session
    (the AAA server may forward service specific AVPs as received from
    the NAS as input for the rating process). The Diameter credit-
    control server checks the end user's account balance, rates the
    service and reserves credit from the end user's account. The
    reserved quota is returned to the Home AAA server in the Diameter
    Credit-Control-Answer (4). The Home AAA server sends the reserved
    quota to the NAS in the Diameter Authorization-Authentication-
    Answer. Upon successful AAA the NAS starts the credit-control
    session and starts monitoring the granted units (5). The NAS grant
    access to the end user (6). At the expiry of the allocated quota,
    the NAS sends a Diameter Credit-Control-Request with CC-Request-Type
    set to UPDATE_REQUEST to the Home AAA server (7). This message
    contains the units used this far. The AAA server forwards the CCR to
    the Diameter credit-control server (8). The Diameter credit-control
    server debits the used units from the end user's account and
    allocates a new quota that is returned to the Home AAA server in the
    Diameter Credit-Control-Answer (9). The message is forwarded to the
    NAS (10). During the ongoing credit-control session the
    authorization-lifetime expires, the authorization/authentication
    client in the NAS performs service specific re-authorization to the
    Home AAA server as usual. The credit-control client populate the AAR
    with the Credit-Control AVP set to RE_AUTHORIZATION indicating that
    the credit-control server shall not be contacted, since the credit
    authorization is controlled by the burning rate of the granted units
    (11). The Home AAA server performs service specific re-authorization
    as usual and returns the Authorization-Authentication-Answer to the
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    NAS (12). The end user logs off from the network (13). To debit the
    used units from the end user's account and to stop the credit
    control session, the NAS sends a Diameter Credit-Control-Request
    with CC-Request-Type set to TERMINATION_REQUEST to the Home AAA
    server (14). The AAA server forwards the CCR to the credit-control
    server (15). The Diameter credit-control server acknowledges the
    session termination by sending a Diameter Credit-Control-Answer to
    the Home AAA server (16). The AAA server forwards the answer to the
    NAS (17). STR/STA take place between NAS and Home AAA server as
    usual (18-19).
 
 A.2  Flow II
 
 
                                  AAA Server
             NAS                  (CC Client)             CC Server
              |(1)  Access-Request     |                        |
              |----------------------->|                        |
              |                        |(2) CCR (initial)       |
              |                        |----------------------->|
              |                        |(3) CCA (granted_Units) |
              |                        |<-----------------------|
              |(4)  Access-Accept      |                        |
              |     (granted Units)    |                        |
              |<-----------------------|                        |
              :                        :                        :
              |(5)  Access-Request     |                        |
              |     (used Units)       |                        |
              |----------------------->|                        |
              |                        |(6) CCR (update,        |
              |                        |         used Units,    |
              |                        |----------------------->|
              |                        |(7) CCA (granted_Units) |
              |                        |<-----------------------|
              |(8)  Access-Accept      |                        |
              |     (granted Units)    |                        |
              |<-----------------------|                        |
              :                        :                        :
              |(9)  Access-Request     |                        |
              |----------------------->|                        |
              |                        |(10) CCR (termin.,      |
              |                        |          used Units)   |
              |                        |----------------------->|
              |                        |(11) CCA                |
              |                        |<-----------------------|
              |(12) Access-Accept      |                        |
              |<-----------------------|                        |
              |                        |                        |
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                             Figure A.2: Flow II
 
    A credit control flow for RADIUS prepaid - Diameter credit control
    interworking is shown in Figure A.2. The focus of this flow is in the
    AAA Server (Diameter credit-control client) and Diameter credit-
    control server interworking.
 
    The NAS first sends a RADIUS Access-Request to the home AAA Server
    (1). The home AAA server performs regular Authentication and
    Authorization. When the AAA server notices that the user is a prepaid
    user it sends a Diameter Credit-Control-Request with CC-Request-Type
    set to INITIAL_REQUEST to the Diameter credit-control server to
    perform credit authorization (2) and to establish a credit control
    session. The Diameter credit-control server checks the end user's
    account balance, rates the service and reserves credit from the end
    user's account. The reserved quota is returned to the Home AAA server
    in the Diameter Credit-Control-Answer (3). The Home AAA server sends
    the reserved quota to the NAS in the RADIUS Access-Accept (4). At the
    expiry of the allocated quota, the NAS sends a new RADIUS Access-
    Request to the Home AAA server (5). This message contains the units
    used this far. The units are reported to the Diameter credit-control
    server in a Diameter Credit-Control-Request (UPDATE_REQUEST) (6). The
    Diameter credit-control server debits the used units from the end
    user's account and allocates a new quota that is returned to the Home
    AAA server in the Diameter Credit-Control-Answer (7). The quota is
    transferred to the NAS in the RADIUS Access-Accept (8). When the end
    user terminates the service the NAS sends a RADIUS Access-Request
    (9). To debit the used units from the end user's account and to stop
    the credit control session, the Home AAA server sends a Diameter
    Credit-Control-Request (TERMINATION_REQUEST) to the credit-control
    server (10). The Diameter credit-control server acknowledges the
    session termination by sending a Diameter Credit-Control-Answer to
    the Home AAA server (11). The RADIUS Access-Accept is sent to the NAS
    (12).
 
 A.3  Flow III
 
               SIP Proxy/Registrar   AAA
         A           (CC Client)     Server           B        CC Server
         |(i)  REGISTER |              |              |              |
         |------------->|(ii)          |              |              |
         |              |------------->|              |              |
         |              |authentication &             |              |
         |              |authorization |              |              |
         |              |<-------------|              |              |
         |(iii)200 OK   |                             |              |
         |<-------------|                             |              |
         :              :                             :              :
         |(1)  INVITE   |                                            :
 
 
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                    Diameter Credit Control Application     October 2003
 
 
         |------------->|
         |              |(2)  CCR (Intial, SIP specific AVP)         |
         |              |------------------------------------------->|
         |              |(3)  CCA (granted_Units)                    |
         |              |<-------------------------------------------|
         |              |(4)  INVITE                  |              |
         |              |---------------------------->|              |
         :              :                             :              :
         |              |(5)  CCR (update, used Units)               |
         |              |------------------------------------------->|
         |              |(6)  CCA (granted_Units)                    |
         |              |<-------------------------------------------|
         :              :                             :              :
         |(7)  BYE      |                             |              |
         |------------->|                             |              |
         |              |(8)  BYE                     |              |
         |              |---------------------------->|              |
         |              |(9)  CCR (termination, used Units)----------|
         |              |------------------------------------------->|
         |              |(10) CCA ()                                 |
         |              |<-------------------------------------------|
         |              |                             |              |
 
                            Figure A.3: Flow III
 
    The end user (SIP User Agent A) sends REGISTER with credentials (i).
    The SIP Proxy sends a request to the AAA server to perform Multimedia
    authentication and authorization by using for instance Diameter
    Multimedia application (ii). The AAA server checks that the
    credentials are correct and checks the user profile.  Eventually, 200
    OK response (iii) is sent to the UA. Note that the Authentication and
    Authorization is valid for the registration validity period duration
    (i.e. until re-registration is performed), of several SIP sessions
    may be established without re-authorization is performed.
 
    UA A sends an INVITE (1). The SIP Proxy sends a Diameter Credit-
    Control-Request (INITIAL_REQUEST) to the Diameter credit-control
    server (2). The Credit-Control-Request contains information obtained
    from the SIP signaling describing the requested service (e.g. calling
    party, called party, Session Description Protocol attributes). The
    Diameter credit-control server checks the end user's account balance,
    rates the service and reserves credit from the end user's account.
    The reserved quota is returned to the SIP Proxy in the Diameter
    Credit-Control-Answer (3). The SIP Proxy forwards the SIP INVITE to
    UA B (4). B's phone rings, and B answers. The media flows between
    them and the SIP Proxy starts measuring the quota. At the expiry of
    the allocated quota, the SIP Proxy sends a Diameter Credit-Control-
    Request (UPDATE_REQUEST) to the Diameter credit-control server (5).
    This message contains the units used this far. The Diameter credit-
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    control server debits the used units from the end user's account and
    allocates new credit that is returned to the Sip Proxy in the
    Diameter Credit-Control-Answer (6). The end user terminates the
    service by sending a BYE (7). The SIP Proxy forwards the BYE message
    to UA B (8) and sends a Diameter Credit-Control-Request
    (TERMINATION_REQUEST) to the Credit-control server (9). The Diameter
    Credit-control server acknowledges the session termination by sending
    a Diameter Credit-Control-Answer to the SIP Proxy (10).
 
 A.4  Flow IV
 
                           MMS Server
              A           (CC Client)           B           CC Server
              |(1) Send MMS    |                |                |
              |--------------->|                |                |
              |                |(2)  CCR (event, DIRECT_DEBITING,|
              |                |          MMS specific AVP)      |
              |                |-------------------------------->|
              |                |(3)  CCA (granted_Units)         |
              |                |<--------------------------------|
              |(4) Send MMS Ack|                |                |
              |<---------------|                |                |
              |                |(5) Notify MMS  |                |
              |                |--------------->|                |
              :                :                :                :
              |                |(6) Retrieve MMS|                |
              |                |<---------------|                |
              |                |(7) Retrieve MMS|                |
              |                |    Ack         |                |
              |                |--------------->|                |
              |                |                |                |
 
 
    Figure A.4: Flow IV
 
    A credit control flow for Multimedia Messaging Services is shown in
    Figure A.4. The sender is charged as soon as the messaging server
    successfully stores the message.
 
    The end user A sends a Multimedia Message (MMS) to the MMS Server
    (1). The MMS Server stores the message and sends a Diameter Credit-
    Control-Request (EVENT_REQUEST with Requested-Action:
    DIRECT_DEBITING) to the 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
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    reception of the MMS message (4). The MMS Server notifies the
    recipient about the new MMS (5), and the end user B retrieves the
    message from the MMS message store (6),(7).
 
 A.5  Flow V
 
                           MMS Server
       Content Server     (CC Client)           B           CC Server
              |(1) Send MMS    |                |                |
              |--------------->|                |                |
              |                |(2)  CCR (event, BALANCE_CHECK,  |
              |                |          MMS specific AVP)      |
              |                |-------------------------------->|
              |                |(3)  CCA (OK)                    |
              |                |<--------------------------------|
              |(4) Send MMS Ack|                |                |
              |<---------------|                |                |
              |                |(5) Notify MMS  |                |
              |                |--------------->|                |
              :                :                :                :
              |                |(6) Retrieve MMS|                |
              |                |<---------------|                |
              |                |(7)  CCR (event, DIRECT_DEBITING,|
              |                |          MMS specific AVP)      |
              |                |-------------------------------->|
              |                |(8)  CCA (granted_Units)         |
              |                |<--------------------------------|
              |                |(9) Retrieve MMS|                |
              |                |    Ack         |                |
              |                |--------------->|                |
              |                |                |                |
 
 
                               Figure A.5: Flow V
 
    A credit control flow for Multimedia Messaging Service is shown in
    Figure A.5. The recipient is charged at the message delivery.
 
    A Content Server sends a Multimedia Message (MMS) to the MMS Server
    (1) that stores the message. The message recipient will be charged
    for the MMS message in this case. Since there can be substantially
    long time between the reception of the message at the MMS Server and
    the actual retrieval of the message, the MMS Server does not
    establish any credit control session to the Diameter Credit-Control
    Server but performs first only a balance check (without any credit
    reservation) by sending a Diameter Credit-Control-Request
    (EVENT_REQUEST with Requested-Action: BALANCE_CHECK) to verify that
    the end user B's can cover the cost for the MMS (2). The Diameter
    credit-control server checks the end user's account balance and
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    returns the answer to the MMS Server in the Diameter Credit-Control-
    Answer (3). The MMS Server acknowledges the successful reception of
    the MMS message (4). The MMS Server notifies the recipient about the
    new MMS (5), and after some time the end user B retrieves the message
    from the MMS message store (6). The MMS Server sends a Diameter
    Credit-Control-Request (EVENT_REQUEST with Requested-Action:
    DIRECT_DEBITING) to the Diameter Credit-control server (7). The
    Credit-Control-Request contains information about the MMS message
    (e.g. size, recipient address, coding type). The Diameter credit-
    control server checks the end user's account balance, rates the
    service and debits the service from the end user's account. The
    granted quota is returned to the MMS Server in the Diameter Credit-
    Control-Request (8). The MMS is transferred to the end user B (9).
 
 A.6  Flow VI
 
                         SIP Controller
              A           (CC Client)           B           CC Server
              |(1)INVITE(SDP)  |                |                |
              |--------------->|                |                |
              |                |(2)  CCR (event, PRICE_ENQUIRY,  |
              |                |          SIP specific AVPs)     |
              |                |-------------------------------->|
              |                |(3)  CCA (Cost-Information)      |
              |                |<--------------------------------|
              | (4)MESSAGE(URL)|                |                |
              |<---------------|                |                |
              |(5)HTTP GET     |                |                |
              |--------------->|                |                |
              |(6)HTTP POST    |                |                |
              |--------------->|(7)INVITE(SDP)  |                |
              |                |--------------->|                |
              |                |      (8)200 OK |                |
              |      (9)200 OK |<---------------|                |
              |<---------------|                |                |
 
                             Figure A.6: Flow VI
 
    Figure A.6 is an example of Advice of Charge (AoC) service for SIP
    call, the user A can be either postpaid or prepaid subscriber using
    the AoC service. It is assumed that the SIP Controller also has HTTP
    capabilities and delivers an interactive AoC web page with for
    instance the cost information, the details of the call derived from
    the SDP and a button to accetp/not accept the charges (there may be
    many other ways to deliver AoC information, however, this flow focus
    on the use of the credit control messages).
    The user has been authenticated and authorized prior to initiate the
    call and subscribed to AoC service.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    UA A sends an INVITE with SDP (1). The SIP controller determines the
    user is subscribed to AoC service and sends a Diameter Credit-Conrol-
    Request (EVENT_REQUEST with Requested-Action: PRICE_ENQUIRY) to the
    Diameter credit control server (2). The Credit-Control-Request
    contains SIP specific AVPs derived from the SIP signaling describing
    the requested service (e.g. calling party, called party, Session
    Description Protocol attributes). The Diameter credit control server
    determines the cost of the service and returns the Credit-Control-
    Answer including the Cost-Information AVP (3). The SIP controller
    manufactures the AoC web page with information received in SIP
    signaling and with the cost information received from the credit
    control server, then sends a SIP MESSAGE that contains a URL pointing
    to the AoC information web page (4). At the reception of the SIP
    MESSAGE the A's UA invokes automatically the web browser that
    retrieves the AoC information (5). The user clicks on a proper button
    and accept the charges (6). The SIP controller continues the session
    and sends the INVITE to the B party that accepts the call (7,8,9).
 
 A.7  Flow VII
 
                            Gaming Server
     End-User                (CC Client)              CC Server
        |  (1)Service Delivery   |                        |
        |<---------------------->|                        |
        :                        :                        :
        :                        :                        :
        |                        |(2)CCR(event,REFUND,Requested-
        |                        |Service-Unit,Service-Parameter-Info)
        |                        |----------------------->|
        |                        |  (3)CCA(Cost-Information)
        |                        |<-----------------------|
        |        (4)Notification |                        |
        |<-----------------------|                        |
 
                            Figure A.7: Flow VII
 
    Figure A.7 illustrates a credit control flow for the REFUND case. It
    is assumed that trusted relationship and secure connection between
    the Gaming server and the Diameter credit control server exist. The
    end user may be a prepaid subscriber or a postpaid subscriber.
 
    While the end user is playing the game (1) she enters a new level
    that entitles for a bonus. The Gaming server sends a Diameter Credit-
    Conrol-Request (EVENT_REQUEST with Requested-Action: REFUND) to the
    Diameter credit control server (2). The Credit-Control-Request
    contains the Requested-Service-Unit AVP with Unit-Type set to
    CREDIT_TYPE_SERVICE_SPECIFIC and Unit-Value set to the number of
    points the user just won. The Service-Parameter-Info AVP is also
    included in the request and specifies the service event to be rated
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    (e.g. Tetris Bonus). The Diameter credit control server, based on
    received information, determines the amount to be credited, refunds
    the user's account and returns the Credit-Control-Answer including
    the Cost-Information AVP (3). The Cost-Information indicates the
    credited amount. At the first opportunity the Gaming server notify
    the end user of the credited amount (4).
 
 
 A.8  Flow VIII
 
                   SIP Controller    Top-UP
         A          (CC Client)      Server           B         CC Server
         |               |              |             |              |
         |               | (1) CCR(Update,Used-Unit)  |              |
         |               |------------------------------------------>|
         |               |              (2) CCA(Final-Unit, Redirect)|
         |               |<------------------------------------------|
         :               :              :             :              :
         :               :              :             :              :
         |               | (3) CCR(Update, Used-Units)|              |
         |               |------------------------------------------>|
         |               | (3a)INVITE("hold")         |              |
         |               |--------------------------->|              |
         |               |              |      (4) CCA(Validity-Time)|
         |               |<------------------------------------------|
         |     (5)INVITE | (6)INVITE    |             |              |
         |<--------------|------------->|             |              |
         |            (7)RTP            |             |              |
         |..............................|             |              |
         |               |       (8)BYE |             |              |
         |               |<-------------|             |              |
         |               | (9)CCR(Update)             |              |
         |               |------------------------------------------>|
         |               |                     (10)CCA(Granted-Unit) |
         |               |<------------------------------------------|
         |    (12)INVITE | (11)INVITE                 |              |
         |<--------------|--------------------------->|              |
 
                            Figure A.8: Flow VIII
 
    Figure A.8 is an example of the graceful service termination for a
    SIP call. It is assumed the call is set up so that the controller is
    in the call as a B2BUA (Back to Back User Agent). Note that the SIP
    signaling is inaccurate since the focus of this flow is in the
    graceful service termination and credit control authorization.
 
    The call is ongoing between user A and user B, user A is a prepaid
    user. At the expiry of the allocated quota, the SIP controller sends
    a Diameter Credit-Control-Request (UPDATE_REQUEST) to the Diameter
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    credit control server (1). This message contains the units used this
    far. The Diameter credit control server debits the used units from
    the end user's account and allocates the final quota that is returned
    to the SIP controller in the Diameter Credit-Control-Answer (2). This
    message contains the Final-Unit-Indication AVP with: the Final-Unit-
    Action set to REDIRECT, the Redirect-Address-Type set to SIP URI and
    the Redirect-Server-Address set to the Top-up server name (e.g.
    sip:sip-topup-server@domain.com). At the expiry of the final
    allocated quota, the SIP controller sends a Diameter Credit-Control-
    Request (UPDATE_REQUEST) to the Diameter credit control server (3)
    and places the called party on "hold" by sending an INVITE with the
    appropriate connection address in the SDP (3a). The Credit-Control-
    Request message contains the units used this far. The Diameter credit
    control server debits the used units from the end user's account but
    does not make any credit reservation. The Credit-Control-Answer
    message, that contains the Validity-Time to supervise the graceful
    service termination, is returned to the SIP controller (4). The SIP
    controller establishes a SIP session between the prepaid user and the
    Top-up server (5, 6). The Top-up server plays an announcement and
    prompts the user to enter a credit card number and the amount of
    money to be used to replenish the account (7). The Top-up server
    validates the credit card number and replenishes the user's account
    (using some means outside the scope of this specification) and
    releases the SIP session (8). The SIP controller can now assume that
    communication between the prepaid user and the Top-up server took
    place and thus sends a spontaneous Credit-Control-Request
    (UPDATE_REQUEST) to the Diameter credit control server to check if
    the account has been replenished (9). The Diameter credit control
    server reserves credit from the end user's account and return the
    reserved quota to the SIP controller in the Credit-Control-Answer
    (10). At this point, the SIP controller re-connects the caller and
    the called party (11,12).
 
 A.9  Flow IX
 
   End-User              NAS             AAA Server    Top-up   CC Server
                      (CC Client)                       Server
       |(1)User Logon      |(2)AA Request (CC AVPs)        |         |
       |------------------>|------------------->|          |         |
       |                   |                    |(3)CCR(initial, CC AVPs)
       |                   |                    |------------------->|
       |                   |                    |(4)CCA(Final-Unit,  |
       |                   |                    |      Validity-Time)|
       |                   |                    |<-------------------|
       |                   |(5)AA Answer(Final-Unit,Validity-Time)   |
       |(6)Limited Access  |<-------------------|          |         |
       |      granted      |                    |          |         |
       |<----------------->|                    |          |         |
       |                   |                    |          |         |
 
 
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                    Diameter Credit Control Application     October 2003
 
 
       |   (7)TCP/HTTP     |        (8)TCP/HTTP            |         |
       |<----------------->|<----------------------------->|         |
       |                 (9) Replenish account             |         |
       |<------------------------------------------------->|         |
       |                   |                    |            (10)RAR |
       |                   |<-------------------|<-------------------|
       |                   | (11) RAA           |                    |
       |                   |------------------->|------------------->|
       |                   |(12)CCR(update)     |                    |
       |                   |------------------->|(13)CCR(Update)     |
       |                   |                    |------------------->|
       |                   |                    |(14)CCA(granted Units)
       |                   |(15)CCA(granted Units)<------------------|
       |                   |<-------------------|                    |
 
                             Figure A.9: Flow IX
 
    Figure A.9 is an example of the graceful service termination
    initiated when the first interrogation take place due to user's
    account is empty.  In this example the credit control server supports
    the server initiated credit re-authorization. The Diameter [NASREQ]
    is implemented in the Network Access Server (NAS).
 
    The user logs onto the network (1). The Diameter NAS first sends a
    Diameter Authorization-Authentication-Request to the home AAA Server,
    the credit-control client populates the AAR with the Credit-Control
    AVP set to CREDIT_AUTHORIZATION and service specific AVPs are
    included as usual [NASREQ]. The home AAA server performs service
    specific Authentication and Authorization as usual. The AAA server
    determines that the user is a prepaid user and notices from the
    Credit-Control AVP that the NAS has credit control capabilities, it
    sends a Diameter Credit-Control-Request with CC-Request-Type set to
    INITIAL_REQUEST to the Diameter credit-control server to perform
    credit authorization (3) and to establish a credit control session
    (the AAA server may forward service specific AVPs as received from
    the NAS as input for the rating process). The Diameter credit-control
    server checks the end user's account balance, determines that the
    account cannot cover the cost of the sevice and initiates the
    graceful service termination. The Credit-Control-Answer is returned
    to the Home AAA server (4). This message contains the Final-Unit-
    Indication AVP and the Validity-Time AVP set to a reasonable time to
    give chance to the user to replenish his/her account (e.g. 10
    minutes). The Final-Unit-Indication AVP includes: the Final-Unit-
    Actioin set to REDIRECT, the Redirect-Address-Type set to ULR and the
    Redirect-Server-Address set to the HTTP Top-up server name. The Home
    AAA server sends the received credit control AVPs to the NAS in the
    Diameter Authorization-Authentication-Answer (5). Upon successful AAA
    the NAS starts the credit-control session and starts immediately the
    graceful service termination as instructed by the server. The NAS
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    grant limited access to the user (6). The HTTP client software
    running in the user's device opens the transport connection that is
    redirected by the NAS to the Top-up server (7,8). The user is
    displayed an appropriate web page where to enter the credit card
    number, the amount of money to be used to replenish the account and
    with a notification message that she will be granted unlimited access
    if the replenishment operation will be successfully executed within
    the next e.g. 10 minutes.  The Top-up server validates the credit
    card number and replenishes the user's account (using some means
    outside the scope of this specification)(9). After successful account
    top-up the credit control server sends a Re-Auth-Request message to
    the NAS (10). The NAS acknowledges the request by returning the Re-
    Auth-Answer message (11) and initiates the credit re-authorization by
    sending a Credit-Control-request (UPDATE_REQUEST) to the Diameter
    credit control server (12,13).
 
    The Diameter credit control server reserves credit from the end
    user's account and return the reserved quota to the NAS via the Home
    AAA server in the Credit-Control-Answer (14,15). The NAS removes the
    restriction placed by the graceful service termination and starts
    monitoring the granted units.
 
 A.10 Flow X
 
    The Diameter Credit Control Application defines the Rating-Group and
    Service-Identifier AVPs that can be used to support credit control
    for multiple services in a single credit control session for service
    elements that have such capabilities. The flow example hereafter
    illustrates the usage of these AVPs.
 
    It is assumed that the Service-Identifiers and the Rating-Groups are
    locally configured in the Service Element or provisioned by another
    entity than the credit control server.
 
    The credit control client may request credit authorization either for
    all the possible configured Rating-Groups in one single request,
    onwards named all-in-one mode, or for a single Rating-Group upon an
    external triggering event, onwards named on-demand mode. The on-
    demand mode can be used as well to request individual credit resource
    limit for each service.
 
    In this example only the all-in-one mode is shown.
 
    A single credit reservation is kept for the credit control session to
    simplify the account management tasks. The credit control server
    reserves an amount of credit from the user's account and performs
    rating for all the requested Rating-Groups and Service-Identifiers
    against the reserved credit.
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
    For instance, assume a Credit-Control-Request is received with
    Rating-Group-Id 1 and 2. The credit control server queries the rating
    server that answers with the following rating parameters: Rating-
    Group 1 costs $1/Mbyte and Rating-Group 2 costs $1/minute. The credit
    control server reserves $20 from the user's account; this gives
    20Mbytes for Rating-Group 1 and 20minutes for Rating-Group 2.
 
    The calculated quotas are conveyed to the credit control client in
    the CCA message, each quota associated with the appropriate Rating-
    Group or Service-Identifier. At this point the credit control client
    just need to track the fraction of reserved credit used by the
    corresponding service or Rating-Group, when the sum of the fractions
    reaches 100% the credit control client sends an intermediate
    interrogation since the whole amount of reserved credit is consumed.
 
    If the credit control client initializes a counter C for each of the
    received quota Q (C1 for Q1, C2 for Q2 ... Cn for Qn), the
    intermediate interrogation will be sent when sum(C1/Q1 + C1/Q2 + ...
    + Cn/Qn)>= 1.
 
    Continuing the example, the end user uses 10 Mbytes from Rating-Group
    1 and 10minutes from Rating-Group 2. This means that Rating-Group 1
    consumed 50% of the reservation and Rating-Group 2 consumed the
    remaining 50%. 0.5 + 0.5 >=1, so the credit control client sends an
    intermediate interrogation to report the used units and request new
    ones.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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                    Diameter Credit Control Application     October 2003
 
 
                    Service Element
    End-User         (CC client)                                 CC
    Server
     |(1)User logon      |                                         |
     |------------------>|(2)CCR(initial,Requested-Units(Rating-Group 1),
     |                   |        Requested-Units(Rating-Group 2)) |
     |                   |---------------------------------------->|
     |                   |(3)CCA(Granted-Units(Rating-Group 1,     |
     |                   |                     Total-Octets))      |
     |                   |       Granted-Units(Rating-Group 2,     |
     |                   |                     Time))              |
     |                   |<----------------------------------------|
     :                   :                                         :
     |(4)Service-Request (Service 1)                               |
     |------------------>|                                         |
     :                   :                                         :
     |(5)Service-Request (Service 2)                               |
     |------------------>|                                         |
     :                   :                                         :
     |                   |(6)CCR(update, Used-Units(Input-Octets,  |
     |                   |                          Output-Octets, |
     |                   |                          Service-Id 1,  |
     |                   |                          Rating-Group 1),
     |                   |               Used-Units(Time,          |
     |                   |                          Service-Id 2,  |
     |                   |                          Rating-Group 2),
     |                   |               Requested-Units(Rating-G.1),
     |                   |               Requested-Units(Rating-G.2))
     |                   |---------------------------------------->|
     |                   |(7)CCA(Granted-Units(Rating-Group 1,     |
     |                   |                     Total-Octets),      |
     |                   |       Granted-Units(Rating-Group 2,     |
     |                   |                      Time))             |
     |                   |<----------------------------------------|
     :                   :                                         :
     |(8)Service-Request (Service 3)                               |
     |------------------>|                                         |
     :                   :                                         :
     |(9) User logoff    |                                         |
     |------------------>|(10)CCR(term, Used-Units(Input-Octets,   |
     |                   |                         Output-Octets,  |
     |                   |                         Service-Id 1,   |
     |                   |                         Rating-Group 1),|
     |                   |              Used-Units(Input-Octets,   |
     |                   |                         Output-Octets,  |
     |                   |                         Service-Id 3,   |
     |                   |                         Rating-Group 1),|
     |                   |              Used-Units(Time,           |
     |                   |                         Service-Id 2,   |
 
 
 Hakala et al.             Expires - April 2004             [Page 93]
 

                    Diameter Credit Control Application     October 2003
 
 
     |                   |                         Rating-Group 2),|
     |                   |---------------------------------------->|
     |                   |(11)CCA(term)                            |
     |                   |<----------------------------------------|
 
      Figure A.10: Credit Control for Multiple Services in One Credit
                     Control Session, flow example
 
    The user logs onto the network (1). The Service Element sends a
    Diameter Credit-Control-Request with CC-Request-Type set to
    INITIAL_REQUEST to the Diameter credit-control server to perform
    credit authorization for multiple rating groups and to establish a
    credit control session (2). In this message credit authorization is
    requested for Rating-Group 1 and Rating-Group 2 by including two
    instances of the Requested-Service-Unit AVP. The Diameter credit-
    control server checks the end user's account balance, based on the
    Rating-Group information rates the request and reserves credit from
    the end user's account. Multiple quotas are returned to the Service
    Element, each associated with the relevant Rating-Group (3). The user
    uses service 1 and service 2 (4, 5). The service 1 belongs to Rating-
    Group 1 and is volume based charged, the service 2 belongs to Rating-
    Group 2 and is time based charged. When the user has consumed the
    allotted credit, the Service Element sends a Diameter Credit-Control-
    Request with CC-Request-Type set to UPDATE_REQUEST to the credit
    control server (6). This message contains the units consumed by each
    of the used services in the Used-Service-Unit AVPs and two instances
    of the Requested-Service-Unit AVP to request credit re-authorization
    for the two Rating-Groups. The used units are associated with the
    relevant Service-Identifier and Rating-Group.
 
    The Diameter credit-control server debits the used units from the end
    user's account and reserves a new amount of credit that is returned
    in form of multiple quotas to the Service Element in the Diameter
    Credit-Control-Answer (7). Each quota is associated with the relevant
    Rating-Group. In addition to service 1 and service 2, the user now
    starts using service 3 (8). Service 3 belongs to Rating-Group 1 and
    is charged based on volume. The end user logs off from the network
    (9). To debit the used units from the end user's account and to stop
    the credit control session, the Service Element sends a Diameter
    Credit-Control-Request with CC-Request-Type set to
    TERMINATION_REQUEST to the credit control server (10).
 
    This message contains the units consumed by each of the used services
    in the Used-Service-Unit AVPs. The used units are associated with the
    relevant Service-Identifier and Rating-Group. The Diameter credit-
    control server debits the used units to the user's account and
    acknowledges the session termination by sending a Diameter Credit-
    Control-Answer to the Service Element (11).
 
 
 
 Hakala et al.             Expires - April 2004             [Page 94]
 

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