RFC 4006
Diameter Credit-Control Application
Network Working Group H. Hakala Request for Comments: 4006 L. Mattila Category: Standards Track Ericsson J-P. Koskinen M. Stura J. Loughney Nokia August 2005 Diameter Credit-Control Application Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2005).Abstract
This document specifies a Diameter application that can be used to implement real-time credit-control for a variety of end user services such as network access, Session Initiation Protocol (SIP) services, messaging services, and download services.Table of Contents
1. Introduction................................................. 4 1.1. Requirements Language................................. 5 1.2. Terminology........................................... 5 1.3. Advertising Application Support....................... 7 2. Architecture Models.......................................... 7 3. Credit-Control Messages...................................... 9 3.1. Credit-Control-Request (CCR) Command.................. 9 3.2. Credit-Control-Answer (CCA) Command................... 11 4. Credit-Control Application Overview.......................... 11 4.1. Service-Specific Rating Input and Interoperability.... 13 5. Session Based Credit-Control................................. 15 5.1. General Principles.................................... 15 5.2. First Interrogation................................... 21 5.3. Intermediate Interrogation............................ 27 5.4. Final Interrogation................................... 29
5.5. Server-Initiated Credit Re-Authorization.............. 30
5.6. Graceful Service Termination.......................... 32
5.7. Failure Procedures.................................... 38
6. One Time Event............................................... 41
6.1. Service Price Enquiry................................. 42
6.2. Balance Check......................................... 42
6.3. Direct Debiting....................................... 43
6.4. Refund................................................ 44
6.5. Failure Procedure..................................... 44
7. Credit-Control Application State Machine..................... 46
8. Credit-Control AVPs.......................................... 55
8.1. CC-Correlation-Id AVP................................. 58
8.2. CC-Request-Number AVP................................. 58
8.3. CC-Request-Type AVP................................... 58
8.4. CC-Session-Failover AVP............................... 59
8.5. CC-Sub-Session-Id AVP................................. 59
8.6. Check-Balance-Result AVP.............................. 60
8.7. Cost-Information AVP.................................. 60
8.8. Unit-Value AVP........................................ 61
8.9. Exponent AVP.......................................... 61
8.10. Value-Digits AVP...................................... 61
8.11. Currency-Code AVP..................................... 62
8.12. Cost-Unit AVP......................................... 62
8.13. Credit-Control AVP.................................... 62
8.14. Credit-Control-Failure-Handling AVP................... 62
8.15. Direct-Debiting-Failure-Handling AVP.................. 63
8.16. Multiple-Services-Credit-Control AVP.................. 64
8.17. Granted-Service-Unit AVP.............................. 65
8.18. Requested-Service-Unit AVP............................ 66
8.19. Used-Service-Unit AVP................................. 66
8.20. Tariff-Time-Change AVP................................ 67
8.21. CC-Time AVP........................................... 67
8.22. CC-Money AVP.......................................... 67
8.23. CC-Total-Octets AVP................................... 68
8.24. CC-Input-Octets AVP................................... 68
8.25. CC-Output-Octets AVP.................................. 68
8.26. CC-Service-Specific-Units AVP......................... 68
8.27. Tariff-Change-Usage AVP............................... 68
8.28. Service-Identifier AVP................................ 69
8.29. Rating-Group AVP...................................... 69
8.30. G-S-U-Pool-Reference AVP.............................. 69
8.31. G-S-U-Pool-Identifier AVP............................. 70
8.32. CC-Unit-Type AVP...................................... 70
8.33. Validity-Time AVP..................................... 70
8.34. Final-Unit-Indication AVP............................. 71
8.35. Final-Unit-Action AVP................................. 72
8.36. Restriction-Filter-Rule AVP........................... 72
8.37. Redirect-Server AVP................................... 73
8.38. Redirect-Address-Type AVP............................. 73
8.39. Redirect-Server-Address AVP........................... 74
8.40. Multiple-Services-Indicator AVP....................... 74
8.41. Requested-Action AVP.................................. 74
8.42. Service-Context-Id AVP................................ 75
8.43. Service-Parameter-Info AVP............................ 76
8.44. Service-Parameter-Type AVP............................ 76
8.45. Service-Parameter-Value AVP........................... 77
8.46. Subscription-Id AVP................................... 77
8.47. Subscription-Id-Type AVP.............................. 77
8.48. Subscription-Id-Data AVP.............................. 78
8.49. User-Equipment-Info AVP............................... 78
8.50. User-Equipment-Info-Type AVP.......................... 78
8.51. User-Equipment-Info-Value AVP......................... 79
9. Result Code AVP Values....................................... 79
9.1. Transient Failures.................................... 79
9.2. Permanent Failures.................................... 80
10. AVP Occurrence Table......................................... 80
10.1. Credit-Control AVP Table.............................. 81
10.2. Re-Auth-Request/Answer AVP Table...................... 82
11. RADIUS/Diameter Credit-Control Interworking Model............ 82
12. IANA Considerations.......................................... 85
12.1. Application Identifier................................ 86
12.2. Command Codes......................................... 86
12.3. AVP Codes............................................. 86
12.4. Result-Code AVP Values................................ 86
12.5. CC-Request-Type AVP................................... 86
12.6. CC-Session-Failover AVP............................... 86
12.7. CC-Unit-Type AVP...................................... 87
12.8. Check-Balance-Result AVP.............................. 87
12.9. Credit-Control AVP.................................... 87
12.10. Credit-Control-Failure-Handling AVP................... 87
12.11. Direct-Debiting-Failure-Handling AVP.................. 87
12.12. Final-Unit-Action AVP................................. 87
12.13. Multiple-Services-Indicator AVP....................... 87
12.14. Redirect-Address-Type AVP............................. 88
12.15. Requested-Action AVP.................................. 88
12.16. Subscription-Id-Type AVP.............................. 88
12.17. Tariff-Change-Usage AVP............................... 88
12.18. User-Equipment-Info-Type AVP.......................... 88
13. Credit-Control Application Related Parameters................ 88
14. Security Considerations...................................... 89
14.1. Direct Connection with Redirects...................... 90
15. References................................................... 91
15.1. Normative References.................................. 91
15.2. Informative References................................ 92
16. Acknowledgements............................................. 93
Appendix A Credit-Control Sequences.............................. 94
A.1. Flow I................................................ 94
A.2. Flow II............................................... 96
A.3. Flow III.............................................. 98
A.4. Flow IV............................................... 99
A.5. Flow V................................................ 100
A.6. Flow VI............................................... 102
A.7. Flow VII.............................................. 103
A.8. Flow VIII............................................. 105
A.9. Flow IX............................................... 107
Authors' Addresses............................................... 112
Full Copyright Statement......................................... 114
1. Introduction
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services. It provides a general
solution to real-time cost and credit-control.
The prepaid model has been shown to be very successful, for instance,
in GSM networks, where network operators offering prepaid services
have experienced a substantial growth of their customer base and
revenues. Prepaid services are now cropping up in many other
wireless and wire line based networks.
In next generation wireless networks, additional functionality is
required beyond that specified in the Diameter base protocol. For
example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
that an application must be able to rate service information in
real-time. In addition, it is necessary to check that the end user's
account provides coverage for the requested service prior to
initiation of that service. When an account is exhausted or expired,
the user must be denied the ability to compile additional chargeable
events.
A mechanism has to be provided to allow the user to be informed of
the charges to be levied for a requested service. In addition, there
are services such as gaming and advertising that may credit as well
as debit a user account.
The other Diameter applications provide service specific
authorization, and they do not provide credit authorization for
prepaid users. The credit authorization shall be generic and
applicable to all the service environments required to support
prepaid services.
To fulfill these requirements, it is necessary to facilitate credit- control communication between the network element providing the service (e.g., Network Access Server, SIP Proxy, and Application Server) and a credit-control server. The scope of this specification is the credit authorization. Service specific authorization and authentication is out of the scope.1.1. Requirements Language
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [KEYWORDS].1.2. Terminology
AAA Authentication, Authorization, and Accounting AA answer AA answer generically refers to a service specific authorization and authentication answer. AA answer commands are defined in service specific authorization applications, e.g., [NASREQ] and [DIAMMIP]. AA request AA request generically refers to a service specific authorization and authentication request. AA request commands are defined in service specific authorization applications e.g., [NASREQ] and [DIAMMIP]. Credit-control Credit-control is a mechanism that directly interacts in real-time with an account and controls or monitors the charges related to the service usage. Credit-control is a process of checking whether credit is available, credit-reservation, deduction of credit from the end user account when service is completed and refunding of reserved credit that is not used. Diameter Credit-control Server A Diameter credit-control server acts as a prepaid server, performing real-time rating and credit-control. It is located in the home domain and is accessed by service elements or Diameter AAA servers in
real-time for purpose of price determination and credit-control before the service event is delivered to the end-user. It may also interact with business support systems. Diameter Credit-control Client A Diameter credit-control client is an entity that interacts with a credit-control server. It monitors the usage of the granted quota according to instructions returned by credit-control server. Interrogation The Diameter credit-control client uses interrogation to initiate a session based credit-control process. During the credit-control process, it is used to report the used quota and request a new one. An interrogation maps to a request/answer transaction. One-time event Basically, a request/answer transaction of type event. Rating The act of determining the cost of the service event. Service A type of task performed by a service element for an end user. Service Element A network element that provides a service to the end users. The Service Element may include the Diameter credit-control client, or another entity (e.g., RADIUS AAA server) that can act as a Credit- control client on behalf of the Service Element. In the latter case, the interface between the Service Element and the Diameter credit- control client is outside the scope of this specification. Examples of the Service Elements include Network Access Server (NAS), SIP Proxy, and Application Servers such as messaging server, content server, and gaming server. Service Event An event relating to a service provided to the end user.
Session based credit-control A credit-control process that makes use of several interrogations: the first, a possible intermediate, and the final. The first interrogation is used to reserve money from the user's account and to initiate the process. The intermediate interrogations may be needed to request new quota while the service is being rendered. The final interrogation is used to exit the process. The credit-control server is required to maintain session state for session-based credit- control.1.3. Advertising Application Support
Diameter nodes conforming to this specification MUST advertise support by including the value of 4 in the Auth-Application-Id of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer command [DIAMBASE].2. Architecture Models
The current accounting models specified in the Radius Accounting [RFC2866] and Diameter base [DIAMBASE] are not sufficient for real- time credit-control, where credit-worthiness is to be determined prior to service initiation. Also, the existing Diameter authorization applications, [NASREQ] and [DIAMMIP], only provide service authorization, but do not provide credit authorization for prepaid users. In order to support real-time credit-control, a new type of server is needed in the AAA infrastructure: Diameter credit- control server. The Diameter credit-control server is the entity responsible for credit authorization for prepaid subscribers. A service element may authenticate and authorize the end user with the AAA server by using AAA protocols; e.g., RADIUS or a Diameter base protocol with a possible Diameter application. Accounting protocols such as RADIUS accounting and the Diameter base accounting protocol can be used to provide accounting data to the accounting server after service is initiated, and to provide possible interim reports until service completion. However, for real-time credit-control, these authorization and accounting models are not sufficient. When real-time credit-control is required, the credit-control client contacts the credit-control server with information about a possible service event. The credit-control process is performed to determine potential charges and to verify whether the end user's account balance is sufficient to cover the cost of the service being rendered.
Figure 1 illustrates the typical credit-control architecture, which consists of a Service Element with an embedded Diameter credit- control client, a Diameter credit-control server, and an AAA server. A Business Support System is usually deployed; it includes at least the billing functionality. The credit-control server and AAA server in this architecture model are logical entities. The real configuration can combine them into a single host. The credit- control protocol is the Diameter base protocol with the Diameter credit-control application. When an end user requests services such as SIP or messaging, the request is typically forwarded to a service element (e.g., SIP Proxy) in the user's home domain. In some cases it might be possible that the service element in the visited domain can offer services to the end user; however, a commercial agreement must exist between the visited domain and the home domain. Network access is an example of a service offered in the visited domain where the NAS, through an AAA infrastructure, authenticates and authorizes the user with the user's home network. Service Element AAA and CC +----------+ +---------+ Protocols+-----------+ +--------+ | End |<---->|+-------+|<------------>| AAA | |Business| | User | +->|| CC || | Server |->|Support | | | | || Client||<-----+ | | |System | +----------+ | |+-------+| | +-----------+ | | | +---------+ | ^ +--------+ +----------+ | | CC Protocol | ^ | End |<--+ | +-----v----+ | | User | +------>|Credit- | | +----------+ Credit-Control |Control |--------+ Protocol |Server | +----------+ Figure 1: Typical credit-control architecture There can be multiple credit-control servers in the system for redundancy and load balancing. The system can also contain separate rating server(s), and accounts can be located in a centralized database. To ensure that the end user's account is not debited or credited multiple times for the same service event, only one place in the credit-control system should perform duplicate detection. System internal interfaces can exist to relay messages between servers and an account manager. However, the detailed architecture of the credit-control system and its interfaces are implementation specific and are out of scope of this specification.
Protocol transparent Diameter relays can exist between the credit- control client and credit-control server. Also, Diameter Redirect agents that refer credit-control clients to credit-control servers and allow them to communicate directly can exist. These agents transparently support the Diameter credit-control application. The different roles of Diameter Agents are defined in Diameter base [DIAMBASE], section 2.8. If Diameter credit-control proxies exist between the credit-control client and the credit-control server, they MUST advertise the Diameter credit-control application support.3. Credit-Control Messages
This section defines new Diameter message Command-Code values that MUST be supported by all Diameter implementations that conform to this specification. The Command Codes are as follows: Command-Name Abbrev. Code Reference ----------------------------------------------------------- Credit-Control-Request CCR 272 3.1 Credit-Control-Answer CCA 272 3.2 Diameter Base [DIAMBASE] defines in the section 3.2 the Command Code ABNF specification. These formats are observed in Credit-Control messages.3.1. Credit-Control-Request (CCR) Command
The Credit-Control-Request message (CCR) is indicated by the command-code field being set to 272 and the 'R' bit being set in the Command Flags field. It is used between the Diameter credit-control client and the credit-control server to request credit authorization for a given service. The Auth-Application-Id MUST be set to the value 4, indicating the Diameter credit-control application.
Message Format
<Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Application-Id }
{ Service-Context-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ Destination-Host ]
[ User-Name ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
*[ Subscription-Id ]
[ Service-Identifier ]
[ Termination-Cause ]
[ Requested-Service-Unit ]
[ Requested-Action ]
*[ Used-Service-Unit ]
[ Multiple-Services-Indicator ]
*[ Multiple-Services-Credit-Control ]
*[ Service-Parameter-Info ]
[ CC-Correlation-Id ]
[ User-Equipment-Info ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP ]
3.2. Credit-Control-Answer (CCA) Command
The Credit-Control-Answer message (CCA) is indicated by the command- code field being set to 272 and the 'R' bit being cleared in the Command Flags field. It is used between the credit-control server and the Diameter credit-control client to acknowledge a Credit- Control-Request command. Message Format <Credit-Control-Answer> ::= < Diameter Header: 272, PXY > < Session-Id > { Result-Code } { Origin-Host } { Origin-Realm } { Auth-Application-Id } { CC-Request-Type } { CC-Request-Number } [ User-Name ] [ CC-Session-Failover ] [ CC-Sub-Session-Id ] [ Acct-Multi-Session-Id ] [ Origin-State-Id ] [ Event-Timestamp ] [ Granted-Service-Unit ] *[ Multiple-Services-Credit-Control ] [ Cost-Information] [ Final-Unit-Indication ] [ Check-Balance-Result ] [ Credit-Control-Failure-Handling ] [ Direct-Debiting-Failure-Handling ] [ Validity-Time] *[ Redirect-Host] [ Redirect-Host-Usage ] [ Redirect-Max-Cache-Time ] *[ Proxy-Info ] *[ Route-Record ] *[ Failed-AVP ] *[ AVP ]4. Credit-Control Application Overview
The credit authorization process takes place before and during service delivery to the end user and generally requires the user's authentication and authorization before any request is sent to the credit-control server. The credit-control application defined in this specification supports two different credit authorization models: credit authorization with money reservation and credit
authorization with direct debiting. In both models, the credit- control client requests credit authorization from the credit-control server prior to allowing any service to be delivered to the end user. In the first model, the credit-control server rates the request, reserves a suitable amount of money from the user's account, and returns the corresponding amount of credit resources. Note that credit resources may not imply actual monetary credit; credit resources may be granted to the credit control client in the form of units (e.g., data volume or time) to be metered. Upon receipt of a successful credit authorization answer with a certain amount of credit resources, the credit-control client allows service delivery to the end user and starts monitoring the usage of the granted resources. When the credit resources granted to the user have been consumed or the service has been successfully delivered or terminated, the credit-control client reports back to the server the used amount. The credit-control server deducts the used amount from the end user's account; it may perform rating and make a new credit reservation if the service delivery is continuing. This process is accomplished with session based credit-control that includes the first interrogation, possible intermediate interrogations, and the final interrogation. For session based credit-control, both the credit control client and the credit-control server are required to maintain credit-control session state. Session based credit-control is described in more detail, with more variations, in section 5. In contrast, credit authorization with direct debiting is a single transaction process wherein the credit-control server directly deducts a suitable amount of money from the user's account as soon as the credit authorization request is received. Upon receipt of a successful credit authorization answer, the credit-control client allows service delivery to the end user. This process is accomplished with the one-time event. Session state is not maintained. In a multi-service environment, an end user can issue an additional service request (e.g., data service) during an ongoing service (e.g., voice call) toward the same account. Alternatively, during an active multimedia session, an additional media type is added to the session, causing a new simultaneous request toward same account. Consequently, this needs to be considered when credit resources are granted to the services. The credit-control application also supports operations such as service price enquiry, user's balance check, and refund of credit on the user's account. These operations are accomplished with the one- time event. Session state is not maintained.
A flexible credit-control application specific failure handling is defined in which the home service provider can model the credit- control client behavior according to its own credit risk management policy. The Credit-Control-Failure-Handling AVP and the Direct-Debiting- Failure-Handling AVP are defined to determine what is done if the sending of credit-control messages to the credit-control server has been temporarily prevented. The usage of the Credit-Control- Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP allows flexibility, as failure handling for the credit-control session and one time event direct debiting may be different.4.1. Service-Specific Rating Input and Interoperability
The Diameter credit-control application defines the framework for credit-control; it provides generic credit-control mechanisms supporting multiple service applications. The credit-control application, therefore, does not define AVPs that could be used as input in the rating process. Listing the possible services that could use this Diameter application is out of scope for this generic mechanism. It is reasonable to expect that a service level agreement will exist between providers of the credit-control client and the credit-control server covering the charging, services offered, roaming agreements, agreed rating input (i.e., AVPs), and so on. Therefore, it is assumed that a Diameter credit-control server will provide service only for Diameter credit-control clients that have agreed beforehand as to the content of credit-control messages. Naturally, it is possible that any arbitrary Diameter credit-control client can interchange credit-control messages with any Diameter credit-control server, but with a higher likelihood that unsupported services/AVPs could be present in the credit-control message, causing the server to reject the request with an appropriate result-code.4.1.1. Specifying Rating Input AVPs
There are two ways to provide rating input to the credit-control server: either by using AVPs or by including them in the Service- Parameter-Info AVP. The general principles for sending rating parameters are as follows: 1a. The service SHOULD re-use existing AVPs if it can use AVPs defined in existing Diameter applications (e.g., NASREQ for network access services). Re-use of existing AVPs is strongly recommended in [DIAMBASE].
For AVPs of type Enumerated, the service may require a new value to be defined. Allocation of new AVP values is done as specified in [DIAMBASE], section 1.2. 1b. New AVPs can be defined if the existing AVPs do not provide sufficient rating information. In this case, the procedures defined in [DIAMBASE] for creating new AVPs MUST be followed. 1c. For services specific only to one vendor's implementation, a Vendor-Specific AVP code for Private use can be used. Where a Vendor-Specific AVP is implemented by more than one vendor, allocation of global AVPs is encouraged instead; refer to [DIAMBASE]. 2. The Service-Parameter-Info AVP MAY be used as a container to pass legacy rating information in its original encoded form (e.g., ASN.1 BER). This method can be used to avoid unnecessary conversions from an existing data format to an AVP format. In this case, the rating input is embedded in the Service-Parameter-Info AVP as defined in section 8.43. New service applications SHOULD favor the use of explicitly defined AVPs as described in items 1a and 1b, to simplify interoperability.4.1.2. Service-Specific Documentation
The service specific rating input AVPs, the contents of the Service- Parameter-Info AVP or Service-Context-Id AVP (defined in section 8.42) are not within the scope of this document. To facilitate interoperability, it is RECOMMENDED that the rating input and the values of the Service-Context-Id be coordinated via an informational RFC or other permanent and readily available reference. The specification of another cooperative standardization body (e.g., 3GPP, OMA, and 3GPP2) SHOULD be used. However, private services may be deployed that are subject to agreements between providers of the credit-control server and client. In this case, vendor specific AVPs can be used. This specification, together with the above service specific documents, governs the credit-control message. Service specific documents define which existing AVPs or new AVPs are used as input to the rating process (i.e., those that do not define new credit-control applications), and thus have to be included in the Credit-Control- Request command by a Diameter credit-control client supporting a given service as *[AVP]. Should Service-Parameter-Info be used, then the service specific document MUST specify the exact content of this grouped AVP.
The Service-Context-Id AVP MUST be included at the command level of a Credit-Control Request to identify the service specific document that applies to the request. The specific service or rating group the request relates to is uniquely identified by the combination of Service-Context-Id and Service-Identifier or Rating-Group.4.1.3. Handling of Unsupported/Incorrect Rating Input
Diameter credit-control implementations are required to support the Mandatory rating AVPs defined in service specific documentation of the services they support, according to the 'M' bit rules in [DIAMBASE]. If a rating input required for the rating process is incorrect in the Credit-control request, or if the credit-control server does not support the requested service context (identified by the Service- Context-Id AVP at command level), the Credit-control answer MUST contain the error code DIAMETER_RATING_FAILED. A CCA message with this error MUST contain one or more Failed-AVP AVPs containing the missing and/or unsupported AVPs that caused the failure. A Diameter credit-control client that receives the error code DIAMETER_RATING_FAILED in response to a request MUST NOT send similar requests in the future.4.1.4. RADIUS Vendor-Specific Rating Attributes
When service specific documents include RADIUS vendor specific attributes that could be used as input in the rating process, the rules described in [NASREQ] for formatting the Diameter AVP MUST be followed. For example, if the AVP code used is the vendor attribute type code, the Vendor-Specific flag MUST be set to 1 and the Vendor-ID MUST be set to the IANA Vendor identification value. The Diameter AVP data field contains only the attribute value of the RADIUS attribute.
(page 15 continued on part 2)
