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Internet Engineering Task Force (IETF)                     L. Bertz, Ed.Request for Comments: 8506                                        SprintObsoletes:4006                                           D. Dolson, Ed.Category: Standards Track                               Y. Lifshitz, Ed.ISSN: 2070-1721                                                 Sandvine                                                              March 2019Diameter Credit-Control ApplicationAbstract   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.  The Diameter Credit-   Control application as defined in this document obsoletesRFC 4006,   and it must be supported by all new Diameter Credit-Control   application implementations.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8506.Bertz, et al.                Standards Track                    [Page 1]

RFC 8506           Diameter Credit-Control Application        March 2019Copyright Notice   Copyright (c) 2019 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Bertz, et al.                Standards Track                    [Page 2]

RFC 8506           Diameter Credit-Control Application        March 2019Table of Contents1. Introduction ....................................................61.1. Requirements Language ......................................71.2. Terminology ................................................71.3. Advertising Application Support ............................92. Architecture Models .............................................93. Credit-Control Messages ........................................113.1. Credit-Control-Request (CCR) Command ......................113.2. Credit-Control-Answer (CCA) Command .......................124. Credit-Control Application Overview ............................134.1. Service-Specific Rating Input and Interoperability ........144.1.1. Specifying Rating Input AVPs .......................154.1.2. Service-Specific Documentation .....................164.1.3. Handling of Unsupported/Incorrect Rating Input .....164.1.4. RADIUS Vendor-Specific Rating Attributes ...........175. Session-Based Credit-Control ...................................175.1. General Principles ........................................175.1.1. Basic Support for Tariff Time Change ...............18           5.1.2. Credit-Control for Multiple Services within                  a (Sub-)Session ....................................195.2. First Interrogation .......................................23           5.2.1. First Interrogation after Authorization and                  Authentication .....................................25           5.2.2. First Interrogation Included with                  Authorization Messages .............................275.3. Intermediate Interrogation ................................295.4. Final Interrogation .......................................315.5. Server-Initiated Credit Re-authorization ..................325.6. Graceful Service Termination ..............................345.6.1. Terminate Action ...................................375.6.2. Redirect Action ....................................385.6.3. Restrict Access Action .............................40           5.6.4. Usage of the Server-Initiated Credit                  Re-authorization ...................................415.7. Failure Procedures ........................................416. One-Time Event .................................................446.1. Service Price Inquiry .....................................456.2. Balance Checks ............................................466.3. Direct Debiting ...........................................466.4. Refunds ...................................................476.5. Failure Procedure .........................................487. Credit-Control Application State Machines ......................508. Credit-Control AVPs ............................................598.1. CC-Correlation-Id AVP .....................................618.2. CC-Request-Number AVP .....................................628.3. CC-Request-Type AVP .......................................628.4. CC-Session-Failover AVP ...................................63Bertz, et al.                Standards Track                    [Page 3]

RFC 8506           Diameter Credit-Control Application        March 20198.5. CC-Sub-Session-Id AVP .....................................648.6. Check-Balance-Result AVP ..................................648.7. Cost-Information AVP ......................................648.8. Unit-Value AVP ............................................658.9. Exponent AVP ..............................................658.10. Value-Digits AVP .........................................668.11. Currency-Code AVP ........................................668.12. Cost-Unit AVP ............................................668.13. Credit-Control AVP .......................................668.14. Credit-Control-Failure-Handling AVP (CCFH) ...............678.15. Direct-Debiting-Failure-Handling AVP (DDFH) ..............688.16. Multiple-Services-Credit-Control AVP .....................688.17. Granted-Service-Unit AVP .................................708.18. Requested-Service-Unit AVP ...............................718.19. Used-Service-Unit AVP ....................................718.20. Tariff-Time-Change AVP ...................................728.21. CC-Time AVP ..............................................728.22. CC-Money AVP .............................................728.23. CC-Total-Octets AVP ......................................728.24. CC-Input-Octets AVP ......................................728.25. CC-Output-Octets AVP .....................................738.26. CC-Service-Specific-Units AVP ............................738.27. Tariff-Change-Usage AVP ..................................738.28. Service-Identifier AVP ...................................748.29. Rating-Group AVP .........................................748.30. G-S-U-Pool-Reference AVP .................................748.31. G-S-U-Pool-Identifier AVP ................................758.32. CC-Unit-Type AVP .........................................758.33. Validity-Time AVP ........................................758.34. Final-Unit-Indication AVP ................................768.35. Final-Unit-Action AVP ....................................778.36. Restriction-Filter-Rule AVP ..............................788.37. Redirect-Server AVP ......................................788.38. Redirect-Address-Type AVP ................................798.39. Redirect-Server-Address AVP ..............................798.40. Multiple-Services-Indicator AVP ..........................808.41. Requested-Action AVP .....................................808.42. Service-Context-Id AVP ...................................818.43. Service-Parameter-Info AVP ...............................828.44. Service-Parameter-Type AVP ...............................828.45. Service-Parameter-Value AVP ..............................838.46. Subscription-Id AVP ......................................838.47. Subscription-Id-Type AVP .................................838.48. Subscription-Id-Data AVP .................................848.49. User-Equipment-Info AVP ..................................848.50. User-Equipment-Info-Type AVP .............................848.51. User-Equipment-Info-Value AVP ............................858.52. User-Equipment-Info-Extension AVP ........................85Bertz, et al.                Standards Track                    [Page 4]

RFC 8506           Diameter Credit-Control Application        March 20198.53. User-Equipment-Info-IMEISV AVP ...........................868.54. User-Equipment-Info-MAC AVP ..............................868.55. User-Equipment-Info-EUI64 AVP ............................868.56. User-Equipment-Info-ModifiedEUI64 AVP ....................868.57. User-Equipment-Info-IMEI AVP .............................868.58. Subscription-Id-Extension AVP ............................878.59. Subscription-Id-E164 AVP .................................878.60. Subscription-Id-IMSI AVP .................................878.61. Subscription-Id-SIP-URI AVP ..............................888.62. Subscription-Id-NAI AVP ..................................888.63. Subscription-Id-Private AVP ..............................888.64. Redirect-Server-Extension AVP ............................888.65. Redirect-Address-IPAddress AVP ...........................898.66. Redirect-Address-URL AVP .................................898.67. Redirect-Address-SIP-URI AVP .............................898.68. QoS-Final-Unit-Indication AVP ............................899. Result-Code AVP Values .........................................919.1. Transient Failures ........................................919.2. Permanent Failures ........................................9210. AVP Occurrence Table ..........................................9210.1. Credit-Control AVP Table .................................9310.2. Re-Auth-Request/Re-Auth-Answer AVP Table .................9411. RADIUS/Diameter Credit-Control Interworking Model .............9412. IANA Considerations ...........................................9712.1. Application Identifier ...................................9712.2. Command Codes ............................................9712.3. AVP Codes ................................................9712.4. Result-Code AVP Values ...................................9812.5. CC-Request-Type AVP ......................................9812.6. CC-Session-Failover AVP ..................................9812.7. CC-Unit-Type AVP .........................................9912.8. Check-Balance-Result AVP .................................9912.9. Credit-Control AVP .......................................9912.10. Credit-Control-Failure-Handling AVP .....................9912.11. Direct-Debiting-Failure-Handling AVP ....................9912.12. Final-Unit-Action AVP ...................................9912.13. Multiple-Services-Indicator AVP ........................10012.14. Redirect-Address-Type AVP ..............................10012.15. Requested-Action AVP ...................................10012.16. Subscription-Id-Type AVP ...............................10012.17. Tariff-Change-Usage AVP ................................10012.18. User-Equipment-Info-Type AVP ...........................10013. Parameters Related to the Credit-Control Application .........10114. Security Considerations ......................................10114.1. Direct Connection with Redirects ........................10214.2. Application-Level Redirects .............................103Bertz, et al.                Standards Track                    [Page 5]

RFC 8506           Diameter Credit-Control Application        March 201915. Privacy Considerations .......................................10415.1. Privacy-Sensitive AVPs ..................................10415.2. Data Minimization .......................................10615.3. Diameter Agents .........................................10716. References ...................................................10716.1. Normative References ....................................10716.2. Informative References ..................................110Appendix A. Credit-Control Sequences .............................111A.1. Flow I ....................................................111A.2. Flow II ...................................................113A.3. Flow III ..................................................116A.4. Flow IV ...................................................117A.5. Flow V ....................................................119A.6. Flow VI ...................................................120A.7. Flow VII ..................................................121A.8. Flow VIII .................................................123A.9. Flow IX ...................................................124   Acknowledgements .................................................130   Authors' Addresses ...............................................1301.  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.  ("Credit-control" is   sometimes abbreviated as "CC" in figures and tables throughout this   document.)  The Diameter Credit-Control application as defined in   this document obsoletes [RFC4006], and it must be supported by all   new Diameter Credit-Control application implementations.  This   document 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 mobile networks, additional functionality is required beyond that   specified in the Diameter base protocol [RFC6733].  For example, the   3GPP charging and billing requirements document [TGPPCHARG] states   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.Bertz, et al.                Standards Track                    [Page 6]

RFC 8506           Diameter Credit-Control Application        March 2019   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 (NAS), SIP Proxy,   Application Server) and a credit-control server.   The scope of this specification is credit authorization.  Service-   specific authorization and authentication are out of scope.1.1.  Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.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.,      [RFC7155] [RFC4004].   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.,      [RFC7155] [RFC4004].   Credit-control:  "Credit-control" is a mechanism that directly      interacts in real time with an account and controls or monitors      the charges related to service usage.  Credit-control is a      process of (1) checking whether or not credit is available,      (2) credit reservation, (3) deduction of credit from the end-user      account when service is completed, and (4) refunding of reserved      credit that is not used.Bertz, et al.                Standards Track                    [Page 7]

RFC 8506           Diameter Credit-Control Application        March 2019   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 the      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 the 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:  A charging transaction session comprising a single      request and single response.   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., a 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 Service Elements      include NASs, SIP Proxies, and Application Servers such as      messaging servers, content servers, and gaming servers.   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.  Intermediate      interrogations (if any) may be needed to request a 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.Bertz, et al.                Standards Track                    [Page 8]

RFC 8506           Diameter Credit-Control Application        March 20191.3.  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   commands [RFC6733].2.  Architecture Models   The current accounting models specified in the RADIUS accounting and   Diameter base specifications [RFC2866] [RFC6733] are not sufficient   for real-time credit-control, where creditworthiness is to be   determined prior to service initiation.  Also, the existing Diameter   authorization applications [RFC7155] [RFC4004] only provide service   authorization; they 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: the 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 the Diameter   base protocol (possibly extended via a 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 a AAA   server.  A Business Support System is usually deployed; at a minimum,   it includes 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 [RFC6733] with   the Diameter Credit-Control application.Bertz, et al.                Standards Track                    [Page 9]

RFC 8506           Diameter Credit-Control Application        March 2019   When an end user requests services such as SIP or messaging, the   request is typically forwarded to a Service Element (e.g., a SIP   Proxy) in the user's home realm as defined in [RFC6733].  In some   cases, it might be possible that the Service Element in the local   realm [RFC6733] can offer services to the end user; however, a   commercial agreement must exist between the local realm and the home   realm.  Network access is an example of a service offered in the   local realm where the NAS, through a 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 entity   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 is implementation   specific and is out of scope for 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[RFC6733], Section 2.8.   If Diameter Credit-Control proxies exist between the credit-control   client and the credit-control server, they MUST advertise support for   the Diameter Credit-Control application.Bertz, et al.                Standards Track                   [Page 10]

RFC 8506           Diameter Credit-Control Application        March 20193.  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  |Section 3.1 |         | Credit-Control-Answer  | CCA     | 272  |Section 3.2 |         +------------------------+---------+------+-------------+                     Table 1: Credit-Control CommandsSection 3.2 of [RFC6733] (Diameter base) defines the Command Code   Format 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.   The CCR is extensible via the inclusion of one or more   Attribute-Value Pairs (AVPs).   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 ]Bertz, et al.                Standards Track                   [Page 11]

RFC 8506           Diameter Credit-Control Application        March 2019                                [ Origin-State-Id ]                                [ Event-Timestamp ]                               *[ Subscription-Id ]                               *[ Subscription-Id-Extension ]                                [ 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 ]                                [ User-Equipment-Info-Extension ]                               *[ 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 ]                                    [ QoS-Final-Unit-Indication ]Bertz, et al.                Standards Track                   [Page 12]

RFC 8506           Diameter Credit-Control Application        March 2019                                    [ 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 requests are 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 services 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 amount of credit reserved.  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, inSection 5.Bertz, et al.                Standards Track                   [Page 13]

RFC 8506           Diameter Credit-Control Application        March 2019   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 the 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 inquiries, user's balance checks, and refunds of credit   on the user's account.  These operations are accomplished with the   one-time event.  Session state is not maintained.   Flexible failure handling, specific to the credit-control   application, is defined in the application.  This allows the service   provider to control the credit-control client's behavior according to   its own risk management policy.   The Credit-Control-Failure-Handling AVP (also referred to as the   CCFH) and the Direct-Debiting-Failure-Handling AVP (also referred to   as the DDFH) 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 CCFH and the DDFH 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.Bertz, et al.                Standards Track                   [Page 14]

RFC 8506           Diameter Credit-Control Application        March 2019   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-upon 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: by either using AVPs or including the rating input in the   Service-Parameter-Info AVP.  The general principles for sending   rating parameters are as follows:   1.  Using AVPs:       A.  The service SHOULD reuse existing AVPs if it can use AVPs           defined in existing Diameter applications (e.g., [RFC7155]           for network access services).  [RFC6733] strongly recommends           the reuse of existing AVPs.           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[RFC6733], Section 1.3.       B.  New AVPs can be defined if the existing AVPs do not provide           sufficient rating information.  In this case, the procedures           defined in [RFC6733] for creating new AVPs MUST be followed.       C.  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           [RFC6733].   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 inSection 8.43.Bertz, et al.                Standards Track                   [Page 15]

RFC 8506           Diameter Credit-Control Application        March 2019   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, and the contents of the   Service-Parameter-Info AVP or Service-Context-Id AVP (defined inSection 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   (preferably that of another cooperative standardization body, e.g.,   3GPP, the Open Mobile Alliance (OMA), or 3GPP2).  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-mentioned service-   specific documents, governs the credit-control message.  Service-   specific documents (i.e., those documents that do not define new   credit-control applications) define which existing AVPs or new AVPs   are used as input to the rating process; thus, the AVPs in question   have to be included in the Credit-Control-Request command by a   Diameter Credit-Control client supporting a given service as   "* [AVP]".  Should the Service-Parameter-Info AVP be used, 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   mandatory rating-related AVPs defined in service-specific documents   for the services they support, according to the 'M' bit rules in   [RFC6733].   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 the 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 unsupportedBertz, et al.                Standards Track                   [Page 16]

RFC 8506           Diameter Credit-Control Application        March 2019   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 [RFC7155] for formatting the Diameter AVP MUST be   followed.   For example, if the AVP code used is the vendor attribute type code,   the Vendor-Specific flag MUST be set to 1 and the Vendor-Id MUST be   set to the IANA Vendor identification value.  The Diameter AVP Data   field contains only the attribute value of the RADIUS attribute.5.  Session-Based Credit-Control5.1.  General Principles   For session-based credit-control, several interrogations are needed:   the first, the intermediate (optional), and the final.  This is   illustrated in Figures 3 and 4 (Sections5.2.1 and5.2.2).   If the credit-control client performs credit reservation before   granting service to the end user, it MUST use several interrogations   toward the credit-control server (i.e., session-based   credit-control).  In this case, the credit-control server MUST   maintain the credit-control session state.   Each credit-control session MUST have a globally unique Session-Id as   defined in [RFC6733]; this Session-Id MUST NOT be changed during the   lifetime of a credit-control session.   Certain applications require multiple credit-control sub-sessions.   These applications would send messages with a constant Session-Id AVP   but with a different CC-Sub-Session-Id AVP.  If several credit   sub-sessions will be used, all sub-sessions MUST be closed separately   before the main session is closed so that units per sub-session may   be reported.  The absence of the CC-Sub-Session-Id AVP implies that   no sub-sessions are in use.Bertz, et al.                Standards Track                   [Page 17]

RFC 8506           Diameter Credit-Control Application        March 2019   Note that the Service Element might send a service-specific   re-authorization message to the AAA server due to expiration of the   authorization lifetime during an ongoing credit-control session.   However, the service-specific re-authorization does not influence the   credit authorization that is ongoing between the credit-control   client and credit-control server, as credit authorization is   controlled by the burning rate of the granted quota.   If service-specific re-authorization fails, the user will be   disconnected, and the credit-control client MUST send a final   interrogation to the credit-control server.   The Diameter Credit-Control server may seek to control the validity   time of the granted quota and/or the production of intermediate   interrogations.  Thus, it MAY include the Validity-Time AVP in the   Answer message to the credit-control client.  Upon expiration of the   Validity-Time, the credit-control client MUST generate a   credit-control update request and report the used quota to the   credit-control server.  It is up to the credit-control server to   determine the value of the Validity-Time to be used for consumption   of the granted service unit(s) (G-S-U).  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 inSection 13).   Since credit-control update requests are also produced at the expiry   of granted service units and/or for mid-session service events, the   omission of Validity-Time does not mean that intermediate   interrogation for the purpose of credit-control is not performed.5.1.1.  Basic Support for Tariff Time Change   The Diameter Credit-Control server and client MAY optionally support   a tariff change mechanism.  The Diameter Credit-Control server may   include a Tariff-Time-Change AVP in the Answer message.  Note that   the granted units should be allocated based on the worst-case   scenario, so that the overall reported used units would never exceed   the credit reservation.  For example, in the case of a forthcoming   tariff change, in which the new rate is higher, the allocation should   be given so it does not exceed the credit, assuming that all of it is   used after the tariff changed.   When the Diameter Credit-Control client reports the used units and a   tariff change has occurred during the reporting period, the Diameter   Credit-Control client MUST separately itemize the units used before   and after the tariff change.  If the client is unable to distinguish   whether units straddling the tariff change were used before or after   the tariff change, the credit-control client MUST itemize those units   in a third category.Bertz, et al.                Standards Track                   [Page 18]

RFC 8506           Diameter Credit-Control Application        March 2019   If a client does not support the tariff change mechanism and it   receives a CCA message carrying the Tariff-Time-Change AVP, it MUST   terminate the credit-control session, giving a reason of   DIAMETER_BAD_ANSWER in the Termination-Cause AVP.   For time-based services, the quota is consumed at the rate of the   passage of real time (ignoring leap seconds).  That is, precisely   1 second of quota is consumed per second of real time.  At the time   when credit resources are allocated, the server already knows how   many units will be consumed before the tariff time change and how   many units will be consumed afterward.  Similarly, the server can   determine the units consumed at the "before" rate and the units   consumed at the "afterward" rate in the event that the end user   closes the session before the consumption of the allotted quota.   There is no need for additional traffic between the client and server   in the case of tariff time changes for continuous time-based service.   Therefore, the tariff change mechanism is not used for such services.   For time-based services in which the quota is NOT continuously   consumed at a regular rate, the tariff change mechanism described for   volume and event units MAY be used.5.1.2.  Credit-Control for Multiple Services within a (Sub-)Session   When multiple services are used within the same user session and each   service or group of services is subject to different cost, it is   necessary to perform credit-control for each service independently.   Making use of credit-control sub-sessions to achieve independent   credit-control will result in increased signaling load and usage of   resources in both the credit-control client and the credit-control   server.  For instance, during one network access session, the   end user may use several HTTP-based services that could be charged   with different costs.  The network-access-specific attributes, such   as Quality of Service (QoS), are common to all the services carried   within the access bearer, but the cost of the bearer may vary,   depending on its content.   To support these scenarios optimally, the credit-control application   enables independent credit-control of multiple services in a single   credit-control (sub-)session.  This is achieved by including the   optional Multiple-Services-Credit-Control AVP in Credit-Control-   Request/Credit-Control-Answer messages.  It is possible to request   and allocate resources as a credit pool shared between multiple   services.  The services can be grouped into rating-groups in order to   achieve even further aggregation of credit allocation.  It is also   possible to request and allocate quotas on a per-service basis.   Where quotas are allocated to a pool by means of the Multiple-   Services-Credit-Control AVP, the quotas remain independent objectsBertz, et al.                Standards Track                   [Page 19]

RFC 8506           Diameter Credit-Control Application        March 2019   that can be re-authorized independently at any time.  Quotas can also   be given independent result codes, validity times, and Final-Unit-   Indication AVP values or QoS-Final-Unit-Indication AVP values.   A rating-group gathers a set of services, identified by a Service-   Identifier and subject to the same cost and rating type (e.g.,   $0.1/minute).  It is assumed that the Service Element is provided   with rating-groups, service-identifiers, and their associated   parameters that define what has to be metered by means outside the   scope of this specification.  (Examples of parameters associated to   service-identifiers are IP 5-tuples and HTTP URLs.)  Service-   identifiers enable authorization on a per-service-based credit as   well as itemized reporting of service usage.  It is up to the   credit-control server whether to authorize credit for one or more   services or for the whole rating-group.  However, the client SHOULD   always report used units at the finest supported level of   granularity.  Where a quota is allocated to a rating-group, all the   services belonging to that group draw from the allotted quota.   Figure 2 provides a graphical representation of the relationship   between service-identifiers, rating-groups, credit pools, and   credit-control (sub-)sessions.                  Diameter Credit-Control (Sub-)Session                                  |         +------------+-----------+-------------+--------------- +         |            |           |             |                |   Service-Id a Service-Id b Service-Id c Service-Id d.....Service-Id z         \        /                 \         /                /          \      /                   \       /                /           \    /                  Rating-Group 1.......Rating-Group n            \  /                         |                    |           Quota       ---------------Quota                 Quota             |        /                                       |             |       /                                        |          Credit Pool                                    Credit Pool             Figure 2: Multiple-Service (Sub-)Session Example   If independent credit-control of multiple services is used, the   Validity-Time AVP, and the Final-Unit-Indication AVP or   QoS-Final-Unit-Indication AVP, SHOULD be present either in the   Multiple-Services-Credit-Control AVP(s) or at the command level as   single AVPs.  However, the Result-Code AVP MAY be present both at the   command level and within the Multiple-Services-Credit-Control AVP.   If the Result-Code AVP at the command level indicates a value other   than SUCCESS, then the Result-Code AVP at the command level takes   precedence over any other AVPs included in the Multiple-Services-   Credit-Control AVP.Bertz, et al.                Standards Track                   [Page 20]

RFC 8506           Diameter Credit-Control Application        March 2019   The credit-control client MUST indicate support for independent   credit-control of multiple services within a (sub-)session by   including the Multiple-Services-Indicator AVP in the first   interrogation.  A credit-control server not supporting this feature   MUST treat the Multiple-Services-Indicator AVP and any received   Multiple-Services-Credit-Control AVPs as invalid AVPs.   If the client indicated support for independent credit-control of   multiple services, a credit-control server that wishes to use the   feature MUST return the granted units within the Multiple-Services-   Credit-Control AVP associated to the corresponding service-identifier   and/or rating-group.   To avoid a situation where several parallel (and typically also   small) credit reservations must be made on the same account (i.e.,   credit fragmentation), and also to avoid unnecessary load on the   credit-control server, it is possible to provide service units as a   pool that applies to multiple services or rating-groups.  This is   achieved by providing the service units in the form of a quota for a   particular service or rating-group in the Multiple-Services-Credit-   Control AVP, and also by including a reference to a credit pool for   that unit type.   The reference includes a multiplier derived from the rating   parameter, which translates from service units of a specific type to   the abstract service units in the pool.  For instance, if the rating   parameter for service 1 is $1/MB and the rating parameter for   service 2 is $0.5/MB, the multipliers could be 10 and 5 for   services 1 and 2, respectively.   If (1) S is the total service units within the pool, (2) M1, M2, ...,   Mn are the multipliers provided for services 1, 2, ..., n, and   (3) C1, C2, ..., Cn are the used resources within the session, then   the pool's credit is exhausted and re-authorization MUST be sought   when:            C1*M1 + C2*M2 + ... + Cn*Mn >= S   The total credit in the pool, S, is calculated from the quotas, which   are currently allocated to the pool as follows:            S = Q1*M1 + Q2*M2 + ... + Qn*Mn   If services or rating-groups are added to or removed from the pool,   then the total credit is adjusted appropriately.  Note that when the   total credit is adjusted because services or rating-groups are   removed from the pool, the value that needs to be removed is the   consumed one (i.e., Cx*Mx).Bertz, et al.                Standards Track                   [Page 21]

RFC 8506           Diameter Credit-Control Application        March 2019   Re-authorizations for an individual service or rating-group may be   sought at any time -- for example, if a "non-pooled" quota is used up   or the Validity-Time expires.   Where multiple G-S-U-Pool-Reference AVPs (Section 8.30) with the same   G-S-U-Pool-Identifier are provided within a Multiple-Services-Credit-   Control AVP (Section 8.16) along with the Granted-Service-Unit AVP,   these AVPs MUST have different CC-Unit-Type values, and they all draw   from the credit pool separately.  For instance, if one multiplier for   time (M1t) and one multiplier for volume (M1v) are given, then the   used resources from the pool yield the sum of C1t*M1t + C1v*M1v,   where C1t is the time unit and C1v is the volume unit.   Where service units are provided within a Multiple-Services-Credit-   Control AVP without a corresponding G-S-U-Pool-Reference AVP, these   units are handled independently from any credit pools and from any   other services or rating-groups within the session.   The "credit pool" concept is an optimal tool to avoid the   over-reservation effect of the basic single-quota tariff time change   mechanism (Section 5.1.1).  Therefore, Diameter Credit-Control   clients and servers implementing the independent credit-control of   multiple services SHOULD leverage the credit pool concept when   supporting the tariff time change.  The Diameter Credit-Control   server SHOULD include both the Tariff-Time-Change AVP and the   Tariff-Change-Usage AVP in two quota allocations in the Answer   message (i.e., two instances of the Multiple-Services-Credit-Control   AVP).  One of the grants is allocated to be used before the potential   tariff change, while the second grant is for use after a tariff   change.  Both granted unit quotas MUST contain the same Service-   Identifier and/or rating-group.  This dual-quota mechanism ensures   that the overall reported used units would never exceed the credit   reservation.  The Diameter Credit-Control client reports the used   units both before and after the tariff change in a single instance of   the Multiple-Services-Credit-Control AVP.   Failure handling for credit-control sessions is defined inSection 5.7 and reflected in the basic credit-control state machines   defined inSection 7.  Credit-control clients and servers   implementing the functionality of independent credit-control of   multiple services in a (sub-)session MUST ensure failure handling and   general behavior fully consistent with Sections5.7 and7 while   maintaining the ability to handle parallel ongoing credit   re-authorization within a (sub-)session.  Therefore, it is   RECOMMENDED that Diameter Credit-Control clients maintain a PendingU   message queue (Section 7) and restart the Tx timer (Section 13) every   time a CCR message with the value UPDATE_REQUEST is sent while they   are in PendingU state.  When answers to all pending messages areBertz, et al.                Standards Track                   [Page 22]

RFC 8506           Diameter Credit-Control Application        March 2019   received, the state machine moves to Open state, and the Tx timer is   stopped.  Naturally, when a problem is detected and acted upon perSection 5.7, all of the ongoing services are affected (e.g., failover   to a backup server affects all of the CCR messages in the PendingU   queue).   Since the client may send CCR messages with the value UPDATE_REQUEST   while in PendingU state (i.e., without waiting for an answer to   ongoing credit re-authorization), the time space between these   requests may be very short, and the server may not have received the   previous request(s) yet.  Therefore, in this situation the server may   receive out-of-sequence requests and SHOULD NOT consider this an   error condition.  A proper answer is to be returned to each of those   requests.5.2.  First Interrogation   When session-based credit-control is required (e.g., the   authentication server indicated a prepaid user), the first   interrogation MUST be sent before the Diameter Credit-Control client   allows any service events for the end user.  The CC-Request-Type AVP   is set to the value INITIAL_REQUEST in the request message.   If the Diameter Credit-Control client knows the cost of the service   event (e.g., a content server delivering ringing tones may know their   cost) the monetary amount to be charged is included in the Requested-   Service-Unit AVP.  If the Diameter Credit-Control client does not   know the cost of the service event, the Requested-Service-Unit AVP   MAY contain the number of requested service events.  Where the   Multiple-Services-Credit-Control AVP is used, it MUST contain the   Requested-Service-Unit AVP to indicate that the quota for the   associated service/rating-group is requested.  In the case of   multiple services, the Service-Identifier AVP or the Rating-Group AVP   within the Multiple-Services-Credit-Control AVP always indicates the   service concerned.  Additional service event information to be rated   MAY be sent as service-specific AVPs or MAY be sent within the   Service-Parameter-Info AVP at the command level.  The   Service-Context-Id AVP indicates the service-specific document   applicable to the request.   The Event-Timestamp AVP SHOULD be included in the request and   contains the time when the service event is requested in the Service   Element.  The Subscription-Id AVP or the Subscription-Id-Extension   AVP SHOULD be included to identify the end user in the credit-control   server.  The credit-control client MAY include the User-Equipment-   Info AVP or User-Equipment-Info-Extension AVP so that theBertz, et al.                Standards Track                   [Page 23]

RFC 8506           Diameter Credit-Control Application        March 2019   credit-control server has some indication of the type and   capabilities of the end-user access device.  How the credit-control   server uses this information is outside the scope of this document.   The credit-control server SHOULD rate the service event and make a   credit reservation from the end user's account that covers the cost   of the service event.  If the type of the Requested-Service-Unit AVP   is "money", no rating is needed, but the corresponding monetary   amount is reserved from the end user's account.   The credit-control server returns the Granted-Service-Unit AVP in the   Answer message to the Diameter Credit-Control client.  The Granted-   Service-Unit AVP contains the amount of service units that the   Diameter Credit-Control client can provide to the end user until a   new Credit-Control-Request MUST be sent to the credit-control server.   If several unit types are sent in the Answer message, the   credit-control client MUST handle each unit type separately.  The   type of the Granted-Service-Unit AVP can be time, volume, service-   specific, or money, depending on the type of service event.  The unit   type(s) SHOULD NOT be changed within an ongoing credit-control   session.   There MUST be a maximum of one instance of the same unit type in one   Answer message.  However, if multiple quotas are conveyed to the   credit-control client in the Multiple-Services-Credit-Control AVPs,   it is possible to carry two instances of the same unit type   associated to a service-identifier/rating-group.  This is typically   the case when a tariff time change is expected and the credit-control   server wants to make a distinction between the granted quota before   the tariff change and the granted quota after the tariff change.   If the credit-control server determines that no further control is   needed for the service, it MAY include the result code indicating   that the credit-control is not applicable (e.g., if the service is   free of charge).  This result code, at the command level, implies   that the credit-control session is to be terminated.   The Credit-Control-Answer message MAY also include the Final-Unit-   Indication AVP or the QoS-Final-Unit-Indication AVP to indicate that   the Answer message contains the final units for the service.  After   the end user has consumed these units, the Diameter Credit-Control   client MUST behave as described inSection 5.6.   This document defines two different approaches for performing the   first interrogation to be used in different network architectures.   The first approach uses credit-control messages after the user's   authorization and authentication take place.  The second approach   uses (1) service-specific authorization messages to perform the firstBertz, et al.                Standards Track                   [Page 24]

RFC 8506           Diameter Credit-Control Application        March 2019   interrogation during the user's authorization/authentication phase   and (2) credit-control messages for the intermediate and final   interrogations.  If an implementation of the credit-control client   supports both methods, determining which method to use SHOULD be   configurable.   In service environments such as NAS environments, it is desired to   perform the first interrogation as part of the authorization/   authentication process for the sake of protocol efficiency.  Further   credit authorizations after the first interrogation are performed   with credit-control commands defined in this specification.   Implementations of credit-control clients operating in the   environments mentioned in this document SHOULD support this method.   If the credit-control server and AAA server are separate physical   entities, the Service Element sends the request messages to the AAA   server, which then issues an appropriate request or proxies the   received request forward to the credit-control server.   In other service environments, such as the 3GPP network and some SIP   scenarios, there is a substantial decoupling between registration/   access to the network and the actual service request (i.e., the   authentication/authorization is executed once during registration/   access to the network and is not executed for every service event   requested by the subscriber).  In these environments, it is more   appropriate to perform the first interrogation after the user has   been authenticated and authorized.  The first, 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 the most suitable method in their architectures.5.2.1.  First Interrogation after Authorization and Authentication   The Diameter Credit-Control client in the Service Element may get   information from the authorization server as to whether   credit-control is required, based on its knowledge of the end user.   If credit-control is required, the credit-control server needs to be   contacted prior to initiating service delivery to the end user.  The   accounting protocol and the credit-control protocol can be used in   parallel.  The authorization server may also determine whether the   parallel accounting stream is required.Bertz, et al.                Standards Track                   [Page 25]

RFC 8506           Diameter Credit-Control Application        March 2019   Figure 3 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 inAppendix A.                                          Diameter   End User      Service Element          AAA Server          CC Server                    (CC Client)     | Registration      | AA-Request/Answer(accounting, CC, or both)|     |<----------------->|<------------------>|                      |     |        :          |                    |                      |     |        :          |                    |                      |     | Service Request   |                    |                      |     |------------------>|                    |                      |     |                   | CCR(Initial, Credit-Control AVPs)         |     |                  +|------------------------------------------>|     |         CC stream||                    |    CCA(Granted-Units)|     |                  +|<------------------------------------------|     | Service Delivery  |                    |                      |     |<----------------->| ACR(start, Accounting AVPs)               |     |         :         |------------------->|+                     |     |         :         |                ACA ||  Accounting stream  |     |                   |<-------------------|+                     |     |         :         |                    |                      |     |         :         |                    |                      |     |                   | CCR(Update, Used-Units)                   |     |                   |------------------------------------------>|     |                   |                    |    CCA(Granted-Units)|     |                   |<------------------------------------------|     |         :         |                    |                      |     |         :         |                    |                      |     | End of Service    |                    |                      |     |------------------>| CCR(Termination, Used-Units)              |     |                   |------------------------------------------>|     |                   |                    |                 CCA  |     |                   |<------------------------------------------|     |                   | ACR(stop)          |                      |     |                   |------------------->|                      |     |                   |                ACA |                      |     |                   |<-------------------|                      |     ACR: Accounting-Request     ACA: Accounting-Answer            Figure 3: Protocol Example with First Interrogation                 after User's Authorization/AuthenticationBertz, et al.                Standards Track                   [Page 26]

RFC 8506           Diameter Credit-Control Application        March 20195.2.2.  First Interrogation Included with Authorization Messages   The Diameter Credit-Control client in the Service Element MUST   actively co-operate with the authorization/authentication client in   the construction of the AA-Request by adding appropriate   Credit-Control AVPs.  The credit-control client MUST add the   Credit-Control AVP to indicate credit-control capabilities and MAY   add other relevant credit-control-specific AVPs to the proper   authorization/authentication command to perform the first   interrogation toward the home Diameter AAA server.  The   Auth-Application-Id is set to the appropriate value, as defined in   service-specific authorization/authentication application document   (e.g., [RFC7155] [RFC4004]).  The home Diameter AAA server   authenticates/authorizes the subscriber and determines whether   credit-control is required.   If credit-control is not required for the subscriber, the home   Diameter AAA server will respond as usual, with an appropriate   AA-Answer message.  If credit-control is required for the subscriber   and the Credit-Control AVP with the value set to CREDIT_AUTHORIZATION   was present in the authorization request, the home AAA server MUST   contact the credit-control server to perform the first interrogation.   If credit-control is required for the subscriber and the   Credit-Control AVP was not present in the authorization request, the   home AAA server MUST send an authorization reject Answer message.   The Diameter AAA server supporting credit-control is required to send   the Credit-Control-Request command (CCR) defined in this document to   the credit-control server.  The Diameter AAA server populates the CCR   based on service-specific AVPs used for input to the rating process,   and possibly on Credit-Control AVPs received in the AA-Request.  The   credit-control server will reserve money from the user's account,   will rate the request, and will send a Credit-Control-Answer message   to the home Diameter AAA server.  The Answer message includes the   Granted-Service-Unit AVP(s) and MAY include other credit-control-   specific AVPs, as appropriate.  Additionally, the credit-control   server MAY set the Validity-Time and MAY include the CCFH and the   DDFH to determine what to do if the sending of credit-control   messages to the credit-control server has been temporarily prevented.   Upon receiving the Credit-Control-Answer message from the   credit-control server, the home Diameter AAA server will populate the   AA-Answer with the received Credit-Control AVPs and with the   appropriate service attributes according to the authorization/   authentication-specific application (e.g., [RFC7155] [RFC4004]).  It   will then forward the packet to the credit-control client.  If the   home Diameter AAA server receives a credit-control reject message, itBertz, et al.                Standards Track                   [Page 27]

RFC 8506           Diameter Credit-Control Application        March 2019   will simply generate an appropriate authorization reject message to   the credit-control client, including the credit-control-specific   error code.   In this model, the credit-control client sends further credit-control   messages to the credit-control server via the home Diameter AAA   server.  Upon receiving a successful authorization Answer message   with the Granted-Service-Unit AVP(s), the credit-control client will   grant the service to the end user and will generate an intermediate   Credit-Control-Request, if required, by using credit-control   commands.  The CC-Request-Number of the first UPDATE_REQUEST MUST be   set to 1 (for details regarding how to produce a unique value for the   CC-Request-Number AVP, seeSection 8.2).   If service-specific re-authorization is performed (i.e., the   authorization lifetime expires), the credit-control client MUST add   to the service-specific re-authorization request the Credit-Control   AVP with a value set to RE_AUTHORIZATION to indicate that the   credit-control server MUST NOT be contacted.  When session-based   credit-control is used for the subscriber, a constant credit-control   message stream flows through the home Diameter AAA server.  The home   Diameter AAA server can make use of this credit-control message flow   to deduce that the user's activity is ongoing; therefore, it is   recommended to set the authorization lifetime to a reasonably high   value when credit-control is used for the subscriber.   In this scenario, the home Diameter AAA server MUST advertise support   for the credit-control application to its peers during the capability   exchange process.Bertz, et al.                Standards Track                   [Page 28]

RFC 8506           Diameter Credit-Control Application        March 2019   Figure 4 illustrates the use of authorization/authentication messages   to perform the first interrogation.  The parallel accounting stream   is not shown in the figure.                                            Diameter                  Service Element           AAA Server        CC Server   End User          (CC Client)    | Service Request   | AA-Request (CC AVPs) |                     |    |------------------>|--------------------->|                     |    |                   |                      | CCR(Initial, CC AVPs)    |                   |                      |-------------------->|    |                   |                      |   CCA(Granted-Units)|    |                   |                      |<--------------------|    |                   | AA-Answer(Granted-Units)                   |    | Service Delivery  |<---------------------|                     |    |<----------------->|                      |                     |    |         :         |                      |                     |    |         :         |                      |                     |    |         :         |                      |                     |    |                   |                      |                     |    |                   | CCR(Update, Used-Units)                    |    |                   |--------------------->| CCR(Update, Used-Units)    |                   |                      |-------------------->|    |                   |                      |   CCA(Granted-Units)|    |                   |    CCA(Granted-Units)|<--------------------|    |                   |<---------------------|                     |    |         :         |                      |                     |    |         :         |                      |                     |    | End of Service    |                      |                     |    |------------------>| CCR(Termination, Used-Units)               |    |                   |--------------------->| CCR(Term., Used-Units)    |                   |                      |-------------------->|    |                   |                      |                 CCA |    |                   |                  CCA |<--------------------|    |                   |<---------------------|                     |       Figure 4: Protocol Example with Use of Authorization Messages                        for the First Interrogation5.3.  Intermediate Interrogation   When all the granted service units for one unit type are spent by the   end user or the Validity-Time has expired, the Diameter   Credit-Control client MUST send a new Credit-Control-Request to the   credit-control server.  In the event that credit-control for multiple   services is applied in one credit-control session (i.e., units   associated to Service-Identifier(s) or the rating-group are granted),   a new Credit-Control-Request MUST be sent to the credit-controlBertz, et al.                Standards Track                   [Page 29]

RFC 8506           Diameter Credit-Control Application        March 2019   server when the credit reservation has been wholly consumed or upon   expiration of the Validity-Time.  It is always up to the Diameter   Credit-Control client to send a new request well in advance of the   expiration of the previous request in order to avoid interruption in   the Service Element.  Even if the granted service units reserved by   the credit-control server have not been spent upon expiration of the   Validity-Time, the Diameter Credit-Control client MUST send a new   Credit-Control-Request to the credit-control server.   There can also be mid-session service events, which might affect the   rating of the current service events.  In this case, a spontaneous   update (a new Credit-Control-Request) SHOULD be sent, including   information related to the service event, even if all the granted   service units have not been spent or the Validity-Time has not   expired.   When the used units are reported to the credit-control server, the   credit-control client will not have any units in its possession   before new granted units are received from the credit-control server.   When the new granted units are received, these units apply from the   point where the measurement of the reported used units stopped.   Where independent credit-control of multiple services is supported,   this process may be executed for one or more services, a single   rating-group, or a pool within the (sub-)session.   The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the   intermediate request message.  The Subscription-Id AVP or   Subscription-Id-Extension AVP SHOULD be included in the intermediate   message to identify the end user in the credit-control server.  The   Service-Context-Id AVP indicates the service-specific document   applicable to the request.   The Requested-Service-Unit AVP MAY contain the new amount of   requested service units.  Where the Multiple-Services-Credit-Control   AVP is used, it MUST contain the Requested-Service-Unit AVP if a new   quota is requested for the associated service/rating-group.  The   Used-Service-Unit AVP contains the amount of used service units   measured from the point when the service became active or, if interim   interrogations are used during the session, from the point when the   previous measurement ended.  The same unit types used in the previous   message SHOULD be used.  If several unit types were included in the   previous Answer message, the used service units for each unit type   MUST be reported.   The Event-Timestamp AVP SHOULD be included in the request and   contains the time of the event that triggered the sending of the new   Credit-Control-Request.Bertz, et al.                Standards Track                   [Page 30]

RFC 8506           Diameter Credit-Control Application        March 2019   The credit-control server MUST deduct the used amount from the   end user's account.  It MAY rate the new request and make a new   credit reservation from the end user's account that covers the cost   of the requested service event.   A Credit-Control-Answer message with the CC-Request-Type AVP set to   the value UPDATE_REQUEST MAY include the Cost-Information AVP   containing the accumulated cost estimation for the session, without   taking any credit reservations into account.   The Credit-Control-Answer message MAY also include the Final-Unit-   Indication AVP or the QoS-Final-Unit-Indication AVP to indicate that   the Answer message contains the final units for the service.  After   the end user has consumed these units, the Diameter Credit-Control   client MUST behave as described inSection 5.6.   There can be several intermediate interrogations within a session.5.4.  Final Interrogation   When the end user terminates the service session or when graceful   service termination (described inSection 5.6) takes place, the   Diameter Credit-Control client MUST send a final Credit-Control-   Request message to the credit-control server.  The CC-Request-Type   AVP is set to the value TERMINATION_REQUEST.  The Service-Context-Id   AVP indicates the service-specific document applicable to the   request.   The Event-Timestamp AVP SHOULD be included in the request and   contains the time when the session was terminated.   The Used-Service-Unit AVP contains the amount of used service units   measured from the point when the service became active or, if interim   interrogations are used during the session, from the point when the   previous measurement ended.  If several unit types were included in   the previous Answer message, the used service units for each unit   type MUST be reported.   After final interrogation, the credit-control server MUST refund the   reserved credit amount not used to the end user's account and deduct   the used monetary amount from the end user's account.   A Credit-Control-Answer message with the CC-Request-Type AVP set to   the value TERMINATION_REQUEST MAY include the Cost-Information AVP   containing the estimated total cost for the session in question.Bertz, et al.                Standards Track                   [Page 31]

RFC 8506           Diameter Credit-Control Application        March 2019   If the user logs off during an ongoing credit-control session or if   the user becomes logged off for some other reason (e.g., a 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 [RFC6733].  Figure 5 illustrates the case when the final-unit   indication causes user logoff upon consumption of the final granted   units and the generation of an STR.   The Diameter AAA server responds with a Session-Termination-Answer   (STA).                 Service Element         AAA Server         CC Server   End User        (CC Client)    | Service Delivery  |                     |                     |    |<----------------->|                     |                     |    |         :         |                     |                     |    |         :         |                     |                     |    |         :         |                     |                     |    |                   |                     |                     |    |                   | CCR(Update, Used-Units)                   |    |                   |-------------------->| CCR(Update, Used-Units)    |                   |                     |-------------------->|    |                   |                   CCA(Final-Unit, Terminate)    |               CCA(Final-Unit, Terminate)|<--------------------|    |                   |<--------------------|                     |    |         :         |                     |                     |    |         :         |                     |                     |    |  Disconnect user  |                     |                     |    |<------------------| CCR(Termination, Used-Units)              |    |                   |-------------------->| CCR(Term., Used-Units)    |                   |                     |-------------------->|    |                   |                     |                 CCA |    |                   |                 CCA |<--------------------|    |                   |<--------------------|                     |    |                   | STR                 |                     |    |                   |-------------------->|                     |    |                   |                STA  |                     |    |                   |<--------------------|                     |           Figure 5: User Disconnected Due to Exhausted Account5.5.  Server-Initiated Credit Re-authorization   The Diameter Credit-Control application supports server-initiated   re-authorization.  The credit-control server MAY optionally initiate   the credit re-authorization by issuing a Re-Auth-Request (RAR) as   defined in the Diameter base protocol [RFC6733].  TheBertz, et al.                Standards Track                   [Page 32]

RFC 8506           Diameter Credit-Control Application        March 2019   Auth-Application-Id in the RAR message is set to 4 to indicate   "Diameter Credit Control", and the Re-Auth-Request-Type is set to   AUTHORIZE_ONLY.Section 5.1.2 defines the feature to enable credit-control for   multiple services within a single (sub-)session where the server can   authorize credit usage at a different level of granularity.  Further,   the server may provide credit resources to multiple services or   rating-groups as a pool (seeSection 5.1.2 for details and   definitions).  Therefore, the server, based on its service logic and   its knowledge of the ongoing session, can decide to request credit   re-authorization for a whole (sub-)session, a single credit pool, a   single service, or a single rating-group.  To request credit   re-authorization for a credit pool, the server includes in the RAR   message the G-S-U-Pool-Identifier AVP indicating the affected pool.   To request credit re-authorization for a service or a rating-group,   the server includes in the RAR message the Service-Identifier AVP or   the Rating-Group AVP, respectively.  To request credit   re-authorization for all the ongoing services within the   (sub-)session, the server includes none of the above-mentioned AVPs   in the RAR message.   If a credit re-authorization is not already ongoing (i.e., the   credit-control session is in Open state), a credit-control client   that receives an RAR message with Session-Id equal to a currently   active credit-control session MUST acknowledge the request by sending   the Re-Auth-Answer (RAA) message and MUST initiate the credit   re-authorization toward the server by sending a Credit-Control-   Request message with the CC-Request-Type AVP set to the value   UPDATE_REQUEST.  The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS)   SHOULD be used in the RAA message to indicate that an additional   message (i.e., a CCR message with the value UPDATE_REQUEST) is   required to complete the procedure.  If a quota was allocated to the   service, the credit-control client MUST report the used quota in the   Credit-Control-Request.  Note that the end user does not need to be   prompted for the credit re-authorization, since the credit   re-authorization is transparent to the user (i.e., it takes place   exclusively between the credit-control client and the credit-control   server).   Where multiple services in a user's session are supported, the   procedure in the above paragraph will be executed at the granularity   requested by the server in the RAR message.   If credit re-authorization is ongoing at the time when the RAR   message is received (i.e., an RAR-CCR collision), the credit-control   client successfully acknowledges the request but does not initiate a   new credit re-authorization.  The Result-Code 2001 (DIAMETER_SUCCESS)Bertz, et al.                Standards Track                   [Page 33]

RFC 8506           Diameter Credit-Control Application        March 2019   SHOULD be used in the RAA message to indicate that a credit   re-authorization procedure is already ongoing (i.e., the client was   in PendingU state when the RAR was received).  The credit-control   server SHOULD process the Credit-Control-Request as if it was   received in answer to the server-initiated credit re-authorization   and should consider the server-initiated credit re-authorization   process successful upon reception of the RAA message.   When multiple services are supported in a user's session, the server   may request credit re-authorization for a credit pool (or for the   (sub-)session) while a credit re-authorization is already ongoing for   some of the services or rating-groups.  In this case, the client   acknowledges the server request with an RAA message and MUST send a   new Credit-Control-Request message to perform re-authorization for   the remaining services/rating-groups.  The Result-Code 2002   (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the RAA message to   indicate that an additional message (i.e., a CCR message with the   value UPDATE_REQUEST) is required to complete the procedure.  The   server processes the received requests and returns an appropriate   answer to both requests.   The above-defined procedures are enabled for each of the possibly   active Diameter Credit-Control sub-sessions.  The server MAY request   re-authorization for an active sub-session by including the   CC-Sub-Session-Id AVP in the RAR message in addition to the   Session-Id AVP.5.6.  Graceful Service Termination   When the user's account runs out of money, the user may not be   allowed to compile additional chargeable events.  However, the home   service provider may offer some services -- for instance, access to a   service portal where it is possible to refill the account -- from   which the user is allowed to benefit for a limited time.  The length   of this time is usually dependent on the home service provider   policy.   This section defines the optional graceful service termination   feature.  This feature MAY be supported by the credit-control server.   Credit-control client implementations MUST support the Final-Unit-   Indication AVP or QoS-Final-Unit-Indication AVP with at least the   teardown of the ongoing service session once the subscriber has   consumed all the final granted units.Bertz, et al.                Standards Track                   [Page 34]

RFC 8506           Diameter Credit-Control Application        March 2019   Where independent credit-control of multiple services in a single   credit-control (sub-)session is supported, it is possible to use   graceful service termination for each of the services/rating-groups   independently.  Naturally, the graceful service termination process   defined in the following subsections will apply to the specific   service/rating-group as requested by the server.   In some service environments (e.g., NAS), graceful service   termination may be used to redirect the subscriber to a service   portal for online balance refill or other services offered by the   home service provider.  In this case, the graceful service   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, redirected to the service portal.  The user may also be   sent an appropriate notification as to why the access has been   limited.  These actions may be communicated explicitly from the   server to the client or may be configured "per service" at the   client.  Explicitly signaled redirection or restriction instructions   always take precedence over configured ones.   It is also possible to use graceful service termination to connect   the prepaid user to a top-up server that plays an announcement and   prompts the user to replenish the account.  In this case, the   credit-control server sends only the address of the top-up server   where the prepaid user shall be connected after the final granted   units have been consumed.  An example of this case is given inAppendix A.7.   The credit-control server MAY initiate graceful service termination   by including the Final-Unit-Indication AVP or the   QoS-Final-Unit-Indication AVP in the Credit-Control-Answer to   indicate that the message contains the final units for the service.   When the credit-control client receives the Final-Unit-Indication AVP   or the QoS-Final-Unit-Indication AVP in the answer from the server,   its behavior depends on the value indicated in the Final-Unit-Action   AVP.  The server may request the following actions: TERMINATE,   REDIRECT, or RESTRICT_ACCESS.   Figure 6 illustrates the graceful service termination procedure   described in the following subsections.Bertz, et al.                Standards Track                   [Page 35]

RFC 8506           Diameter Credit-Control Application        March 2019                                            Diameter   End User        Service Element          AAA Server         CC Server                   (CC Client)     |  Service Delivery |                     |                     |     |<----------------->|                     |                     |     |                   |CCR(Update, Used-Units)                    |     |                   |-------------------->|CCR(Update, Used-Units)     |         :         |                     |-------------------->|     |         :         |                     |CCA(Final-Unit, Action)     |         :         |                     |<--------------------|     |                   |CCA(Final-Unit, Action)                    |     |                   |<--------------------|                     |     |                   |                     |                     |     |         :         |                     |                     |     |         :         |                     |                     |     | ///////////////   |CCR(Update, Used-Units)                    |     |/Final Units End/->|-------------------->|CCR(Update, Used-Units)     |/Action and    //  |                     |-------------------->|     |/Restrictions //   |                     |   CCA(Validity-Time)|     |/Start       //    |   CCA(Validity-Time)|<--------------------|     | /////////////     |<--------------------|                     |     |         :         |                     |                     |     |         :         |                     |                     |     |                 Replenish account       |     +-------+       |     |<--------------------------------------------->|Account|       |     |                   |                     |     +-------+       |     |                   |                     |                 RAR |     |                 + |                 RAR |<====================|     |                 | |<====================|                     |     |                 | | RAA                 |                     |     |  /////////////  | |====================>| RAA                 |     | /If supported / | | CCR(Update)         |====================>|     | /by CC Server/  | |====================>| CCR(Update)         |     | /////////////   | |                     |====================>|     |                 | |                     |   CCA(Granted-Units)|     |                 | |   CCA(Granted-Units)|<====================|     |  Restrictions ->+ |<====================|                     |     |  removed          |                     |                     |     |         :         |                     |                     |     |        OR         | CCR(Update)         |                     |     |   Validity-Time ->|-------------------->| CCR(Update)         |     |   expires         |                     |-------------------->|     |                   |                     |   CCA(Granted-Units)|     |                   |   CCA(Granted-Units)|<--------------------|     |    Restrictions ->|<--------------------|                     |     |    removed        |                     |                     |         Figure 6: Optional Graceful Service Termination ProcedureBertz, et al.                Standards Track                   [Page 36]

RFC 8506           Diameter Credit-Control Application        March 2019   In addition, the credit-control server MAY reply with the Final-Unit-   Indication AVP or QoS-Final-Unit-Indication AVP holding a Granted-   Service-Unit (G-S-U) with a zero grant, indicating that the service   SHOULD be terminated immediately, and no further reporting is   required.  Figure 7 illustrates a graceful service termination   procedure that applies immediately after receiving a zero grant.                                             Diameter   End User        Service Element           AAA Server        CC Server                   (CC Client)     |  Service Delivery |                      |                     |     |<----------------->|                      |                     |     |                   |CCR(Update, Used-Units)                     |     |                   |--------------------->|CCR(Update, Used-Units)     |         :         |                      |-------------------->|     |         :         |                      |CCA(Final-Unit, Action,     |         :         |                      |            Zero G-S-U)     |         :         |                      |<--------------------|     |                   |CCA(Final-Unit, Action,                     |     |                   |            Zero G-S-U)                     |     |                   |<---------------------|                     |     | ///////////////   |                      |                     |     |/Action and    //  |                      |                     |     |/Restrictions //   |                      |                     |     |/Start       //    |                      |                     |     | /////////////     |                      |                     |     |         :         |                      |                     |     |         :         |                      |                     |    Figure 7: Optional Immediate Graceful Service Termination Procedure5.6.1.  Terminate Action   The Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP   with Final-Unit-Action set to TERMINATE does not include any other   information.  When the subscriber has consumed the final granted   units, the Service Element MUST terminate the service.  This is the   default handling applicable whenever the credit-control client   receives an unsupported Final-Unit-Action value and MUST be supported   by all the Diameter Credit-Control client implementations conforming   to this specification.  A final Credit-Control-Request message to the   credit-control server MUST be sent if the Final-Unit-Indication AVP   or the QoS-Final-Unit-Indication AVP indicating action TERMINATE was   present at the command level.  The CC-Request-Type AVP in the request   is set to the value TERMINATION_REQUEST.Bertz, et al.                Standards Track                   [Page 37]

RFC 8506           Diameter Credit-Control Application        March 20195.6.2.  Redirect Action   The Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP   with Final-Unit-Action set to REDIRECT indicates to the Service   Element supporting this action that, upon consumption of the final   granted units, the user MUST be redirected to the address specified   in the Redirect-Server AVP or Redirect-Server-Extension AVP as   follows.   The credit-control server sends the Redirect-Server AVP or Redirect-   Server-Extension 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 or Redirect-Server-   Extension AVP, if possible.  When the end user is redirected (by   using protocols other 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 scenario is out of scope for   this specification.   In addition to the Redirect-Server AVP or Redirect-Server-Extension   AVP, the credit-control server MAY include one or more Restriction-   Filter-Rule AVPs, one or more Filter-Rule AVPs, or one or more   Filter-Id AVPs in the Credit-Control-Answer message to enable the   user to access other services (for example, zero-rated services).  In   such a case, the access device MUST treat all packets according to   the Restriction-Filter-Rule AVPs, Filter-Rule AVPs, and the rules   referred to by the Filter-Id AVP.  After treatment is applied   according to these rules, all traffic that has not been dropped or   already forwarded MUST be redirected to the destination specified in   the Redirect-Server AVP or Redirect-Server-Extension AVP.   An entity other than the credit-control server may provision the   access device with appropriate IP packet filters to be used in   conjunction with the Diameter Credit-Control application.  This case   is considered inSection 5.6.3.   When the final granted units have been consumed, the credit-control   client MUST perform an intermediate interrogation.  The purpose of   this interrogation is to indicate to the credit-control server that   the specified action started and to report the used units.  The   credit-control server MUST deduct the used amount from the end user's   account but MUST NOT make a new credit reservation.  The   credit-control client, however, may send intermediate interrogations   before all the final granted units have been consumed for which   rating and money reservation may be needed -- for instance, upon   Validity-Time expiration or upon mid-session service events that   affect the rating of the current service.  Therefore, theBertz, et al.                Standards Track                   [Page 38]

RFC 8506           Diameter Credit-Control Application        March 2019   credit-control client MUST NOT include any rating-related AVPs in the   request sent once all the final granted units have been consumed, as   an indication to the server that (1) the requested final unit action   started and (2) rating and money reservation are not required (when   the Multiple-Services-Credit-Control AVP is used, the Service-   Identifier AVP or the Rating-Group AVP is included to indicate the   services concerned).  Naturally, the Credit-Control-Answer message   does not contain any granted service units and MUST include the   Validity-Time AVP to indicate to the credit-control client how long   the subscriber is allowed to use network resources before a new   intermediate interrogation is sent to the server.   At the expiry of Validity-Time, the credit-control client sends a   Credit-Control-Request (UPDATE_REQUEST) as usual.  This message does   not include the Used-Service-Unit AVP, as there is no allotted quota   to report.  The credit-control server processes the request and MUST   perform the credit reservation.  If during this time the subscriber   did not replenish their account, whether they will be disconnected or   will be granted access to services not controlled by a credit-control   server for an unlimited time is dependent on the home service   provider policy.  (Note: The latter option implies that the Service   Element should not remove the restriction filters upon termination of   the credit-control.)  The server will return the appropriate   Result-Code (seeSection 9.1) in the Credit-Control-Answer message in   order to implement the policy-defined action.  Otherwise, a new quota   will be returned, and the Service Element MUST remove all the   possible restrictions activated by the graceful service termination   process and continue the credit-control session and service session   as usual.   The credit-control client may not wait until the expiration of the   Validity-Time and may send a spontaneous update (a new   Credit-Control-Request) if the Service Element can determine, for   instance, that communication between the end user and the top-up   server took place.  An example of this case is given inAppendix A.8   (Figure 18).   Note that the credit-control server may already have initiated the   above-described process for the first interrogation.  However, the   user's account might be empty when this first interrogation is   performed.  In this case, the subscriber can be offered a chance to   replenish the account and continue the service.  When the   credit-control client receives (at either the session level or a   service-specific level) a Final-Unit-Indication AVP or QoS-Final-   Unit-Indication AVP, together with Validity-Time AVPs, but without a   Granted-Service-Unit AVP, it immediately starts the graceful service   termination process without sending any messages to the server.  An   example of this case is illustrated inAppendix A.8 (Figure 18).Bertz, et al.                Standards Track                   [Page 39]

RFC 8506           Diameter Credit-Control Application        March 20195.6.3.  Restrict Access Action   A Final-Unit-Indication AVP with Final-Unit-Action set to   RESTRICT_ACCESS indicates to the device supporting this action that,   upon consumption of the final granted units, the user's access MUST   be restricted according to the IP packet filters given in the   Restriction-Filter-Rule AVP(s) or according to the IP packet filters   identified by the Filter-Id AVP(s).  The credit-control server SHOULD   include either the Restriction-Filter-Rule AVP or the Filter-Id AVP   in the Final-Unit-Indication group AVP of the Credit-Control-Answer   message.   A QoS-Final-Unit-Indication AVP with Final-Unit-Action set to   RESTRICT_ACCESS indicates to the device supporting this action that,   upon consumption of the final granted units, the actions specified in   Filter-Rule AVP(s) MUST restrict the traffic according to the   classifiers in the Filter-Rule AVP(s).  If one or more Filter-Id AVPs   are provided in the Credit-Control-Answer message, the credit-control   client MUST restrict the traffic according to the IP packet filters   identified by the Filter-Id AVP(s).  The credit-control server SHOULD   include either the Filter-Rule AVP or the Filter-Id AVP in the   QoS-Final-Unit-Indication group AVP of the Credit-Control-Answer   message.   If both the Final-Unit-Indication AVP and the QoS-Final-Unit-   Indication AVP exist in the Credit-Control-Answer message, a   credit-control client that supports the QoS-Final-Unit-Indication AVP   SHOULD follow the directives included in the QoS-Final-Unit-   Indication AVP and SHOULD ignore the Final-Unit-Indication AVP.   An entity other than the credit-control server may provision the   access device with appropriate IP packet filters to be used in   conjunction with the Diameter Credit-Control application.  Such an   entity may, for instance, configure the access device with IP flows   to be passed when the Diameter Credit-Control application indicates   RESTRICT_ACCESS or REDIRECT.  The access device passes IP packets   according to the filter rules that may have been received in the   Credit-Control-Answer message, in addition to those rules that may   have been configured by the other entity.  However, when the user's   account cannot cover the cost of the requested service, the action   taken is the responsibility of the credit-control server that   controls the prepaid subscriber.   If another entity working in conjunction with the Diameter   Credit-Control application already provisions the access device with   all the required filter rules for the end user, the credit-control   server presumably need not send any additional filters.  Therefore,   it is RECOMMENDED that credit-control server implementationsBertz, et al.                Standards Track                   [Page 40]

RFC 8506           Diameter Credit-Control Application        March 2019   supporting graceful service termination be configurable for sending   the Restriction-Filter-Rule AVP, the 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 inSection 5.6.2.   The credit-control server may initiate graceful service termination   when replying with the action RESTRICT_ACCESS for the first   interrogation.  This is similar to the behavior specified inSection 5.6.2.5.6.4.  Usage of the Server-Initiated Credit Re-authorization   Once the subscriber replenishes the account, they presumably expect   all the restrictions applied by the graceful service termination   procedure to be removed immediately and unlimited service access to   be resumed.  For the best user experience, the credit-control server   implementation MAY support the server-initiated credit   re-authorization (seeSection 5.5).  In such a case, upon the   successful account top-up, the credit-control server sends the   Re-Auth-Request (RAR) message to solicit the credit re-authorization.   The credit-control client initiates the credit re-authorization by   sending the Credit-Control-Request message with the CC-Request-Type   AVP set to the value UPDATE_REQUEST.  The Used-Service-Unit AVP is   not included in the request, as there is no allotted quota to report.   The Requested-Service-Unit AVP MAY be included in the request.  After   the credit-control client successfully receives the Credit-Control-   Answer with a new Granted-Service-Unit AVP, all the possible   restrictions activated for the purpose of graceful service   termination MUST be removed in the Service Element.  The   credit-control session and the service session continue as usual.5.7.  Failure Procedures   The CCFH, as described in this section, determines the behavior of   the credit-control client in fault situations.  The CCFH may be   (1) received from the Diameter home AAA server, (2) received from the   credit-control server, or (3) configured locally.  The CCFH value   received from the home AAA server overrides the locally configured   value.  The CCFH value received from the credit-control server in the   Credit-Control-Answer message always overrides any existing values.Bertz, et al.                Standards Track                   [Page 41]

RFC 8506           Diameter Credit-Control Application        March 2019   The authorization server MAY include the Accounting-Realtime-Required   AVP to determine what to do if the sending of accounting records to   the accounting server has been temporarily prevented, as defined in   [RFC6733].  It is RECOMMENDED that the client complement the   credit-control failure procedures with a backup accounting flow   toward an accounting server.  By using different combinations of the   Accounting-Realtime-Required AVP and the CCFH, different safety   levels can be built.  For example, by choosing a CCFH equal to   CONTINUE for the credit-control flow and an Accounting-Realtime-   Required AVP equal to DELIVER_AND_GRANT for the accounting flow, the   service can be granted to the end user even if the connection to the   credit-control server is down, as long as the accounting server is   able to collect the accounting information and information exchange   is taking place between the accounting server and credit-control   server.   As the credit-control application is based on real-time bidirectional   communication between the credit-control client and the   credit-control server, the usage of alternative destinations and the   buffering of messages may not be sufficient in the event of   communication failures.  Because the credit-control server has to   maintain session states, moving the credit-control message stream to   a backup server requires a complex context transfer solution.   Whether the credit-control message stream is moved to a backup   credit-control server during an ongoing credit-control session   depends on the value of the CC-Session-Failover AVP.  However,   failover may occur at any point in the path between the   credit-control client and the credit-control server if a transport   failure is detected with a peer, as described in [RFC6733].  As a   consequence, the credit-control server might receive duplicate   messages.  These duplicate 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 credit-control server indicated   FAILOVER_SUPPORTED in the CC-Session-Failover AVP.  A secondary   credit-control server name, either received from the home Diameter   AAA server or configured locally, can be used as an address of the   backup server.  If the CC-Session-Failover AVP is set to   FAILOVER_NOT_SUPPORTED, the credit-control message stream MUST NOT be   moved to a backup server.Bertz, et al.                Standards Track                   [Page 42]

RFC 8506           Diameter Credit-Control Application        March 2019   For new credit-control sessions, failover to an alternative   credit-control server SHOULD be performed, if possible.  For   instance, if an implementation of the credit-control client can   determine primary credit-control server unavailability, it can   establish the new credit-control sessions with a possibly available   secondary credit-control server.   The AAA transport profile [RFC3539] defines an application-layer   watchdog algorithm that enables failover from a peer that has failed   and is controlled by a watchdog timer (Tw) (defined in [RFC3539]).   The recommended default initial value for Tw (Twinit) is 30 seconds.   Twinit may be set as low as 6 seconds; however, according to   [RFC3539], setting too low a value for Twinit is likely to result in   an increased probability of duplicates, as well as an increase in   spurious failover and failback attempts.  The Diameter base protocol   [RFC6733] is common to several different types of Diameter AAA   applications that may be run in the same Service Element.  Therefore,   tuning the timer for Twinit to a lower value in order to satisfy the   requirements of real-time applications, such as the Diameter   Credit-Control application, will certainly cause the above-mentioned   problems.  For prepaid services, however, the end user expects an   answer from the network in a reasonable time.  Thus, the Diameter   Credit-Control client will react more quickly than would the   underlying base protocol.  Therefore, this specification defines the   Tx timer (as defined inSection 13), which is used by the   credit-control client to supervise communication with the   credit-control server.  When the Tx timer elapses, the credit-control   client takes action for the end user according to the CCFH.   When the Tx timer expires, the Diameter Credit-Control client always   terminates the service if the CCFH is set to the value TERMINATE.   The credit-control session may be moved to an alternative server only   if a protocol error DIAMETER_TOO_BUSY or DIAMETER_UNABLE_TO_DELIVER   is received before the Tx timer expires.  Therefore, the value   TERMINATE is not appropriate if proper failover behavior is desired.   If the CCFH is set to the value CONTINUE or RETRY_AND_TERMINATE, the   service will be granted to the end user when the Tx timer expires.   An Answer message with granted units may arrive later if the base   protocol transport failover occurred in the path to the   credit-control server.  (The Twinit default value is 3 times more   than the recommended Tx timeout value.)  The credit-control client   SHOULD grant the service to the end user, start monitoring 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, theBertz, et al.                Standards Track                   [Page 43]

RFC 8506           Diameter Credit-Control Application        March 2019   credit-control client terminates or continues the service --   depending on the value set in the CCFH -- and MUST free all the   reserved resources for the credit-control session.  If the protocol   error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is received or   the request times out and the CC-Session-Failover AVP is set to   FAILOVER_SUPPORTED, the credit-control client MAY send the request to   a backup server, if possible.  If the credit-control client receives   a successful answer from the backup server, it continues the   credit-control session with such a server.  If the retransmitted   request also fails, the credit-control client terminates or continues   the service -- depending on the value set in the CCFH -- and MUST   free all the reserved resources for the credit-control session.   If a communication failure occurs during the graceful service   termination procedure, the Service Element SHOULD always terminate   the ongoing service session.   If the credit-control server detects a failure during an ongoing   credit-control session, it will terminate the credit-control session   and return the reserved units back to the end user's account.   The supervision session timer Tcc (as defined inSection 13) is used   in the credit-control server to supervise the credit-control session.   In order to support failover between credit-control servers,   information transfer about the credit-control session and account   state SHOULD take place between the primary and secondary   credit-control servers.  Implementations supporting credit-control   session failover MUST also ensure proper detection of duplicate or   out-of-sequence messages.  Communication between the servers is   regarded as an implementation issue and is outside 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, inquiring   about the price of the service.  The use of a one-time event implies   that the user has been authenticated and authorized beforehand.Bertz, et al.                Standards Track                   [Page 44]

RFC 8506           Diameter Credit-Control Application        March 2019   The one-time event can be used when the credit-control client wants   to know the cost of the service event or to check the account balance   without any credit reservations.  It can also be used for refunding   service units on the user's account or for direct debiting without   any credit reservations.  The one-time event is shown in Figure 8.                                          Diameter   End User        Service Element        AAA Server        CC Server                       (CC Client)     | Service Request   |                    |                    |     |------------------>|                    |                    |     |                   | CCR(Event)         |                    |     |                   |------------------->| CCR(Event)         |     |                   |                    |------------------->|     |                   |                    |  CCA(Granted-Units)|     |                   |  CCA(Granted-Units)|<-------------------|     |  Service Delivery |<-------------------|                    |     |<----------------->|                    |                    |                         Figure 8: 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 Inquiry   The credit-control client may need to know the price of the service   event.  Services offered by application service providers whose   prices are not known in the credit-control client might exist.  The   end user might also want to get an estimate 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 in the Service-Identifier AVP in the   Credit-Control-Request message.  Additional service event information   may be sent as service-specific AVPs or within the Service-Parameter-   Info AVP.  The Service-Context-Id AVP indicates the service-specific   document applicable to the request.   The credit-control server calculates the cost of the requested   service event, but it does not perform any account-balance checks or   credit reservations from the account.Bertz, et al.                Standards Track                   [Page 45]

RFC 8506           Diameter Credit-Control Application        March 2019   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 Checks   The Diameter Credit-Control client may only have to verify that the   end user's account balance covers the cost of a certain service   without reserving any units from the account at the time of the   inquiry.  This method does not guarantee that credit would be left   when the Diameter Credit-Control client requests the debiting of the   account with a separate request.   A Diameter Credit-Control client requesting a balance check MUST set   the CC-Request-Type AVP equal to EVENT_REQUEST, include a Requested-   Action AVP set to CHECK_BALANCE, and include the Subscription-Id AVP   or Subscription-Id-Extension AVP in order to identify the end user in   the credit-control server.  The Service-Context-Id AVP indicates the   service-specific document applicable to the request.   The credit-control server makes the balance check, but it does not   make any credit reservations from the account.   The result of the 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 session-based credit-control   would lead to unreasonably long credit-control sessions.  In these   cases, the Diameter Credit-Control client can use the one-time event   scenario for direct debiting.  The Diameter Credit-Control client   SHOULD be sure that the requested service event execution would be   successful when this scenario is used.   In the Credit-Control-Request message, the CC-Request-Type AVP is set   to the value EVENT_REQUEST and the Requested-Action AVP is set to   DIRECT_DEBITING.  The Subscription-Id AVP or Subscription-Id-   Extension AVP SHOULD be included to identify the end user in the   credit-control server.  The Event-Timestamp AVP SHOULD be included in   the request and contain the time when the service event is requested   in the Service Element.  The Service-Context-Id AVP indicates the   service-specific document applicable to the request.Bertz, et al.                Standards Track                   [Page 46]

RFC 8506           Diameter Credit-Control Application        March 2019   If it knows the cost of the service event, the Diameter   Credit-Control client MAY include in the Requested-Service-Unit AVP   the monetary amount to be charged.  If the Diameter Credit-Control   client does not know the cost of the service event, the Requested-   Service-Unit AVP MAY contain the number of requested service events.   The Service-Identifier AVP always indicates the service concerned.   Additional service event information to be rated MAY be sent as   service-specific AVPs or within the Service-Parameter-Info AVP.   The credit-control server SHOULD rate the service event and deduct   the corresponding monetary amount from the end user's account.  If   the type of the Requested-Service-Unit AVP is "money", no rating is   needed, but the corresponding monetary amount is deducted from the   end user's account.   The credit-control server returns the Granted-Service-Unit AVP in the   Credit-Control-Answer message to the Diameter Credit-Control client.   The Granted-Service-Unit AVP contains the amount of service units   that the Diameter Credit-Control client can provide to the end user.   The type of the Granted-Service-Unit can be time, volume, service-   specific, or money, depending on the type of service event.   If the credit-control server determines that no credit-control is   needed for the service, it can include the result code indicating   that the credit-control is not applicable (e.g., the service is free   of charge).   For informative purposes, the Credit-Control-Answer message MAY also   include the Cost-Information AVP containing the estimated total cost   of the requested service.6.4.  Refunds   Some services may refund service units to the end user's account --   for example, gaming services.   The credit-control client MUST set the CC-Request-Type AVP to the   value EVENT_REQUEST and the Requested-Action AVP to REFUND_ACCOUNT in   the Credit-Control-Request message.  The Subscription-Id AVP or   Subscription-Id-Extension AVP SHOULD be included to identify the   end user in the credit-control server.  The Service-Context-Id AVP   indicates the service-specific document applicable to the request.   The Diameter Credit-Control client MAY include the monetary amount to   be refunded in the Requested-Service-Unit AVP.  The Service-   Identifier AVP always indicates the service concerned.  If the   Diameter Credit-Control client does not know the monetary amount toBertz, et al.                Standards Track                   [Page 47]

RFC 8506           Diameter Credit-Control Application        March 2019   be refunded, in addition to the Service-Identifier AVP it MAY send   service-specific AVPs or the Service-Parameter-Info AVP containing   additional service event information to be rated.   For informative purposes, the Credit-Control-Answer message MAY also   include the Cost-Information AVP containing the estimated monetary   amount of refunded units.6.5.  Failure Procedure   Failover to an alternative credit-control server is allowed for a   one-time event, as the server is not maintaining session states.  For   instance, if the credit-control client receives a protocol error   DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY, it can resend the   request to an alternative server, if possible.  There MAY be   protocol-transparent Diameter relays and redirect agents or Diameter   Credit-Control proxies between the credit-control client and   credit-control server.  Failover may occur at any point in the path   between the credit-control client and the credit-control server if a   transport failure is detected with a peer, as described in [RFC6733].   Because there can be duplicate requests for various reasons, the   credit-control server is responsible for real-time duplicate   detection.  Implementation issues for duplicate detection are   discussed in[RFC6733], Appendix C.   When the credit-control client detects a communication failure with   the credit-control server, its behavior depends on the requested   action.  The Tx timer (as defined inSection 13) is used in the   credit-control client to supervise communication with the   credit-control server.   If the requested action is PRICE_ENQUIRY or CHECK_BALANCE and a   communication failure is detected, the credit-control client SHOULD   forward the request messages to an alternative credit-control server,   if possible.  The secondary credit-control server name, if received   from the home Diameter AAA server, can be used as an address of the   backup server.   If the requested action is DIRECT_DEBITING, the DDFH controls the   credit-control client's behavior.  The DDFH may be received from the   home Diameter AAA server or may be locally configured.  The   credit-control server may also send the DDFH in any CCA messages to   be used for direct-debiting events compiled thereafter.  The DDFH   value received from the home Diameter AAA server overrides the   locally configured value, and the DDFH value received from the   credit-control server in a Credit-Control-Answer message always   overrides any existing values.Bertz, et al.                Standards Track                   [Page 48]

RFC 8506           Diameter Credit-Control Application        March 2019   If the DDFH is set to TERMINATE_OR_BUFFER, the credit-control client   SHOULD NOT grant the service if, after a possible retransmission   attempt to an alternative credit-control server, the credit-control   client can eventually determine 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 credit-control application-level non-volatile   storage.  (Note that resending the request at a later time is not a   guarantee that the service will be debited, as the user's account may   be empty when the server successfully processes the request.)  The   credit-control client MUST mark these request messages as possible   duplicates by setting the T flag in the command header as described   in[RFC6733], Section 3.   If the DDFH is set to CONTINUE, the service SHOULD be granted, even   if credit-control messages cannot be delivered and messages are not   buffered.   If the Tx timer expires, the credit-control client MUST continue the   service and wait for a possible late answer.  If the request   times out, the credit-control client retransmits the request (marked   with the T flag) to a backup credit-control server, if possible.  If   the retransmitted request also times out or if a temporary error is   received in answer, the credit-control client buffers the request if   the value of the DDFH is set to TERMINATE_OR_BUFFER.  If a failed   answer is received for the retransmitted request, the credit-control   client frees all the resources reserved for the event message and   deletes the request regardless of the value of the DDFH.   The Credit-Control-Request with the requested action REFUND_ACCOUNT   should always be stored in credit-control application-level   non-volatile storage in case a temporary failure occurs.  The   credit-control client MUST mark the retransmitted request message as   a possible duplicate by setting the T flag in the command header as   described in[RFC6733], Section 3.   For stored requests, the implementation may choose to limit the   number of retransmission attempts and to define a retransmission   interval.   Note that only one entity in the credit-control system SHOULD be   responsible for duplicate detection.  If there is only one   credit-control server within the given realm, the credit-control   server may perform duplicate detection.  If there is more than one   credit-control server in a given realm, only one entity in the   credit-control system should be responsible, to ensure that the   end user's account is not debited or credited multiple times for the   same service event.Bertz, et al.                Standards Track                   [Page 49]

RFC 8506           Diameter Credit-Control Application        March 20197.  Credit-Control Application State Machines   This section defines five credit-control application state machines.   The first four state machines are to be observed by credit-control   clients.   The first state machine describes session-based credit-control where   the first interrogation is executed as part of the authorization/   authentication process.  The second state machine describes   session-based credit-control where the first interrogation is   executed after the authorization/authentication process.  The   requirements regarding what has to be supported for these two state   machines are discussed inSection 5.2.   The third state machine describes session-based credit-control for   the intermediate and final interrogations.  The fourth state machine   describes event-based credit-control.  These two state machines are   to be observed by all implementations that conform to this   specification.   The fifth state machine describes the credit-control session from a   credit-control server's perspective.   Any event not listed in the state machines MUST be considered an   error condition, and a corresponding answer, if applicable, MUST be   returned to the originator of the message.   In Tables 3, 4, and 5, the event "failure to send" means that the   Diameter Credit-Control client is unable to communicate with the   desired destination or, if a failover procedure is supported, with a   possibly defined alternative destination (e.g., the request times out   and the Answer message is not received).  This could be due to   (1) the peer being down or (2) a physical link failure in the path to   or from the credit-control server.   The event "temporary error" means that the Diameter Credit-Control   client received a protocol error notification (DIAMETER_TOO_BUSY,   DIAMETER_UNABLE_TO_DELIVER, or DIAMETER_LOOP_DETECTED) in the   Result-Code AVP of the Credit-Control-Answer command.  This type of   notification may ultimately be received in answer to the   retransmitted request to a defined alternative destination, if   failover is supported.Bertz, et al.                Standards Track                   [Page 50]

RFC 8506           Diameter Credit-Control Application        March 2019   The event "failed answer" means that the Diameter Credit-Control   client received a non-transient failure (permanent failure)   notification in the Credit-Control-Answer command.  This type of   notification may ultimately be received in answer to the   retransmitted request to a defined alternative destination, if   failover is supported.   The action "store request" means that a request is stored in   credit-control application-level non-volatile storage.   The event "not successfully processed" means that the credit-control   server could not process the message, e.g., due to an unknown   end user, an account being empty, or errors defined in [RFC6733].   The event "user service terminated" can be triggered for various   reasons, e.g., normal user termination, network failure, and ASR   (Abort-Session-Request).  The Termination-Cause AVP contains   information about the reason for termination, as specified in   [RFC6733].   The Tx timer, which is used to control the waiting time in the   credit-control client in the Pending state, is stopped upon exit of   the Pending state.  The stopping of the Tx timer is omitted in the   state machine when the new state is Idle, as moving to Idle state   implies the clearing of the session and all the variables associated   to it.   The states PendingI, PendingU, PendingT, PendingE, and PendingB stand   for pending states to wait for an answer to a credit-control request   related to Initial, Update, Termination, Event, or Buffered request,   respectively.   In Table 2, failover to a secondary server upon "temporary error" or   "failure to send" is not explicitly described.  However, moving an   ongoing credit-control message stream to an alternative server is   possible if the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED,   as described inSection 5.7.   Resending a credit-control event to an alternative server is   supported as described inSection 6.5.Bertz, et al.                Standards Track                   [Page 51]

RFC 8506           Diameter Credit-Control Application        March 2019   +----------+-------------------------------+-------------+----------+   | State    | Event                         | Action      | New      |   |          |                               |             | State    |   +----------+-------------------------------+-------------+----------+   | Idle     | Client or device requests     | Send        | PendingI |   |          | access/service                | AA-Request  |          |   |          |                               | with added  |          |   |          |                               | CC AVPs,    |          |   |          |                               | start Tx    |          |   |          |                               | timer       |          |   |          |                               |             |          |   | PendingI | Successful answer to          | Grant       | Open     |   |          | AA-Request received           | service to  |          |   |          |                               | end user,   |          |   |          |                               | stop Tx     |          |   |          |                               | timer       |          |   |          |                               |             |          |   | PendingI | Tx timer expired              | Disconnect  | Idle     |   |          |                               | user/dev    |          |   |          |                               |             |          |   | PendingI | Failed AA-Answer received     | Disconnect  | Idle     |   |          |                               | user/dev    |          |   |          |                               |             |          |   | PendingI | AA-Answer received with       | Grant       | Idle     |   |          | Result-Code equal to          | service to  |          |   |          | CREDIT_CONTROL_NOT_APPLICABLE | end user    |          |   |          |                               |             |          |   | PendingI | User service terminated       | Queue       | PendingI |   |          |                               | termination |          |   |          |                               | event       |          |   |          |                               |             |          |   | PendingI | Change in rating condition    | Queue       | PendingI |   |          |                               | changed     |          |   |          |                               | rating      |          |   |          |                               | condition   |          |   |          |                               | event       |          |   +----------+-------------------------------+-------------+----------+            Table 2: Session-Based Client State Machine for the                    First Interrogation with AA-RequestBertz, et al.                Standards Track                   [Page 52]

RFC 8506           Diameter Credit-Control Application        March 2019   +----------+-------------------------------+-------------+----------+   | State    | Event                         | Action      | New      |   |          |                               |             | State    |   +----------+-------------------------------+-------------+----------+   | Idle     | Client or device requests     | Send CC     | PendingI |   |          | access/service                | initial     |          |   |          |                               | req., start |          |   |          |                               | Tx timer    |          |   |          |                               |             |          |   | PendingI | Successful CC initial answer  | Stop Tx     | Open     |   |          | received                      | timer       |          |   |          |                               |             |          |   | PendingI | Failure to send, or temporary | Grant       | Idle     |   |          | error and CCFH equal to       | service to  |          |   |          | CONTINUE                      | end user    |          |   |          |                               |             |          |   | PendingI | Failure to send, or temporary | Terminate   | Idle     |   |          | error and CCFH equal to       | end user's  |          |   |          | TERMINATE or to               | service     |          |   |          | RETRY_AND_TERMINATE           |             |          |   |          |                               |             |          |   | PendingI | Tx timer expired and CCFH     | Terminate   | Idle     |   |          | equal to TERMINATE            | end user's  |          |   |          |                               | service     |          |   |          |                               |             |          |   | PendingI | Tx timer expired and CCFH     | Grant       | PendingI |   |          | equal to CONTINUE or to       | service to  |          |   |          | RETRY_AND_TERMINATE           | end user    |          |   |          |                               |             |          |   | PendingI | CC initial answer received    | Terminate   | Idle     |   |          | with Result-Code equal to     | end user's  |          |   |          | END_USER_SERVICE_DENIED or to | service     |          |   |          | USER_UNKNOWN                  |             |          |   |          |                               |             |          |   | PendingI | CC initial answer received    | Grant       | Idle     |   |          | with Result-Code equal to     | service to  |          |   |          | CREDIT_CONTROL_NOT_APPLICABLE | end user    |          |   |          |                               |             |          |   | PendingI | Failed CC initial answer      | Grant       | Idle     |   |          | received and CCFH equal to    | service to  |          |   |          | CONTINUE                      | end user    |          |   |          |                               |             |          |   | PendingI | Failed CC initial answer      | Terminate   | Idle     |   |          | received and CCFH equal to    | end user's  |          |   |          | TERMINATE or to               | service     |          |   |          | RETRY_AND_TERMINATE           |             |          |   |          |                               |             |          |Bertz, et al.                Standards Track                   [Page 53]

RFC 8506           Diameter Credit-Control Application        March 2019   | PendingI | User service terminated       | Queue       | PendingI |   |          |                               | termination |          |   |          |                               | event       |          |   |          |                               |             |          |   | PendingI | Change in rating condition    | Queue       | PendingI |   |          |                               | changed     |          |   |          |                               | rating      |          |   |          |                               | condition   |          |   |          |                               | event       |          |   +----------+-------------------------------+-------------+----------+            Table 3: Session-Based Client State Machine for the                       First Interrogation with CCR   +----------+-------------------------------+-------------+----------+   | State    | Event                         | Action      | New      |   |          |                               |             | State    |   +----------+-------------------------------+-------------+----------+   | Open     | Granted unit elapses and no   | Send CC     | PendingU |   |          | final-unit indication         | update      |          |   |          | received                      | req., start |          |   |          |                               | Tx timer    |          |   |          |                               |             |          |   | Open     | Granted unit elapses and      | Terminate   | PendingT |   |          | final unit action equal to    | end user's  |          |   |          | TERMINATE received            | service,    |          |   |          |                               | send CC     |          |   |          |                               | termination |          |   |          |                               | req.        |          |   |          |                               |             |          |   | Open     | Change in rating condition in | Send CC     | PendingU |   |          | queue                         | update      |          |   |          |                               | req., start |          |   |          |                               | Tx timer    |          |   |          |                               |             |          |   | Open     | Service terminated in queue   | Send CC     | PendingT |   |          |                               | termination |          |   |          |                               | req.        |          |   |          |                               |             |          |   | Open     | Change in rating condition or | Send CC     | PendingU |   |          | Validity-Time elapses         | update      |          |   |          |                               | req., start |          |   |          |                               | Tx timer    |          |   |          |                               |             |          |   | Open     | User service terminated       | Send CC     | PendingT |   |          |                               | termination |          |   |          |                               | req.        |          |Bertz, et al.                Standards Track                   [Page 54]

RFC 8506           Diameter Credit-Control Application        March 2019   |          |                               |             |          |   | Open     | RAR received                  | Send RAA    | PendingU |   |          |                               | followed by |          |   |          |                               | CC update   |          |   |          |                               | req., start |          |   |          |                               | Tx timer    |          |   |          |                               |             |          |   | PendingU | Successful CC update answer   | Stop Tx     | Open     |   |          | received                      | timer       |          |   |          |                               |             |          |   | PendingU | Failure to send, or temporary | Grant       | Idle     |   |          | error and CCFH equal to       | service to  |          |   |          | CONTINUE                      | end user    |          |   |          |                               |             |          |   | PendingU | Failure to send, or temporary | Terminate   | Idle     |   |          | error and CCFH equal to       | end user's  |          |   |          | TERMINATE or to               | service     |          |   |          | RETRY_AND_TERMINATE           |             |          |   |          |                               |             |          |   | PendingU | Tx timer expired and CCFH     | Terminate   | Idle     |   |          | equal to TERMINATE            | end user's  |          |   |          |                               | service     |          |   |          |                               |             |          |   | PendingU | Tx timer expired and CCFH     | Grant       | PendingU |   |          | equal to CONTINUE or to       | service to  |          |   |          | RETRY_AND_TERMINATE           | end user    |          |   |          |                               |             |          |   | PendingU | CC update answer received     | Terminate   | Idle     |   |          | with Result-Code equal to     | end user's  |          |   |          | END_USER_SERVICE_DENIED       | service     |          |   |          |                               |             |          |   | PendingU | CC update answer received     | Grant       | Idle     |   |          | with Result-Code equal to     | service to  |          |   |          | CREDIT_CONTROL_NOT_APPLICABLE | end user    |          |   |          |                               |             |          |   | PendingU | Failed CC update answer       | Grant       | Idle     |   |          | received and CCFH equal to    | service to  |          |   |          | CONTINUE                      | end user    |          |   |          |                               |             |          |   | PendingU | Failed CC update answer       | Terminate   | Idle     |   |          | received and CCFH equal to    | end user's  |          |   |          | TERMINATE or to               | service     |          |   |          | RETRY_AND_TERMINATE           |             |          |   |          |                               |             |          |   | PendingU | User service terminated       | Queue       | PendingU |   |          |                               | termination |          |   |          |                               | event       |          |   |          |                               |             |          |Bertz, et al.                Standards Track                   [Page 55]

RFC 8506           Diameter Credit-Control Application        March 2019   | PendingU | Change in rating condition    | Queue       | PendingU |   |          |                               | changed     |          |   |          |                               | rating      |          |   |          |                               | condition   |          |   |          |                               | event       |          |   |          |                               |             |          |   | PendingU | RAR received                  | Send RAA    | PendingU |   |          |                               |             |          |   | PendingT | Successful CC termination     |             | Idle     |   |          | answer received               |             |          |   |          |                               |             |          |   | PendingT | Failure to send, temporary    |             | Idle     |   |          | error, or failed answer       |             |          |   |          |                               |             |          |   | PendingT | Change in rating condition    |             | PendingT |   +----------+-------------------------------+-------------+----------+     Table 4: Session-Based Client State Machine for Intermediate and                           Final Interrogations   +----------+--------------------------------+------------+----------+   | State    | Event                          | Action     | New      |   |          |                                |            | State    |   +----------+--------------------------------+------------+----------+   | Idle     | Client or device requests a    | Send CC    | PendingE |   |          | one-time service               | event      |          |   |          |                                | req.,      |          |   |          |                                | start Tx   |          |   |          |                                | timer      |          |   |          |                                |            |          |   | Idle     | Request in storage             | Send       | PendingB |   |          |                                | stored     |          |   |          |                                | request    |          |   |          |                                |            |          |   | PendingE | Successful CC event answer     | Grant      | Idle     |   |          | received                       | service to |          |   |          |                                | end user   |          |   |          |                                |            |          |   | PendingE | Failure to send, temporary     | Indicate   | Idle     |   |          | error, failed CC event answer  | service    |          |   |          | received, or Tx timer expired; | error      |          |   |          | requested action CHECK_BALANCE |            |          |   |          | or PRICE_ENQUIRY               |            |          |   |          |                                |            |          |Bertz, et al.                Standards Track                   [Page 56]

RFC 8506           Diameter Credit-Control Application        March 2019   | PendingE | CC event answer received with  | Terminate  | Idle     |   |          | Result-Code equal to           | end user's |          |   |          | END_USER_SERVICE_DENIED or to  | service    |          |   |          | USER_UNKNOWN and Tx timer      |            |          |   |          | running                        |            |          |   |          |                                |            |          |   | PendingE | CC event answer received with  | Grant      | Idle     |   |          | Result-Code equal to           | service to |          |   |          | CREDIT_CONTROL_NOT_APPLICABLE; | end user   |          |   |          | requested action               |            |          |   |          | DIRECT_DEBITING                |            |          |   |          |                                |            |          |   | PendingE | Failure to send, temporary     | Grant      | Idle     |   |          | error, or failed CC event      | service to |          |   |          | answer received; requested     | end user   |          |   |          | action DIRECT_DEBITING; DDFH   |            |          |   |          | equal to CONTINUE              |            |          |   |          |                                |            |          |   | PendingE | Failed CC event answer         | Terminate  | Idle     |   |          | received or temporary error;   | end user's |          |   |          | requested action               | service    |          |   |          | DIRECT_DEBITING; DDFH equal to |            |          |   |          | TERMINATE_OR_BUFFER and Tx     |            |          |   |          | timer running                  |            |          |   |          |                                |            |          |   | PendingE | Tx timer expired; requested    | Grant      | PendingE |   |          | action DIRECT_DEBITING         | service to |          |   |          |                                | end user   |          |   |          |                                |            |          |   | PendingE | Failure to send; requested     | Store      | Idle     |   |          | action DIRECT_DEBITING; DDFH   | request    |          |   |          | equal to TERMINATE_OR_BUFFER   | with       |          |   |          |                                | T flag     |          |   |          |                                |            |          |   | PendingE | Temporary error; requested     | Store      | Idle     |   |          | action DIRECT_DEBITING; DDFH   | request    |          |   |          | equal to TERMINATE_OR_BUFFER;  |            |          |   |          | Tx timer expired               |            |          |   |          |                                |            |          |   | PendingE | Failed answer or answer        |            | Idle     |   |          | received with Result-Code      |            |          |   |          | equal to END_USER_SERVICE      |            |          |   |          | DENIED or to USER_UNKNOWN;     |            |          |   |          | requested action               |            |          |   |          | DIRECT_DEBITING; Tx timer      |            |          |   |          | expired                        |            |          |   |          |                                |            |          |Bertz, et al.                Standards Track                   [Page 57]

RFC 8506           Diameter Credit-Control Application        March 2019   | PendingE | Failed CC event answer         | Indicate   | Idle     |   |          | received; requested action     | service    |          |   |          | REFUND_ACCOUNT                 | error and  |          |   |          |                                | delete     |          |   |          |                                | request    |          |   |          |                                |            |          |   | PendingE | Failure to send or Tx timer    | Store      | Idle     |   |          | expired; requested action      | request    |          |   |          | REFUND_ACCOUNT                 | with       |          |   |          |                                | T flag     |          |   |          |                                |            |          |   | PendingE | Temporary error; requested     | Store      | Idle     |   |          | action REFUND_ACCOUNT          | request    |          |   |          |                                |            |          |   | PendingB | Successful CC answer received  | Delete     | Idle     |   |          |                                | request    |          |   |          |                                |            |          |   | PendingB | Failed CC answer received      | Delete     | Idle     |   |          |                                | request    |          |   |          |                                |            |          |   | PendingB | Failure to send or temporary   |            | Idle     |   |          | error                          |            |          |   +----------+--------------------------------+------------+----------+               Table 5: One-Time Event Client State Machine   +-------+------------------------+--------------------------+-------+   | State | Event                  | Action                   | New   |   |       |                        |                          | State |   +-------+------------------------+--------------------------+-------+   | Idle  | CC initial request     | Send CC initial answer,  | Open  |   |       | received and           | reserve units, start Tcc |       |   |       | successfully processed |                          |       |   |       |                        |                          |       |   | Idle  | CC initial request     | Send CC initial answer   | Idle  |   |       | received but not       | with Result-Code !=      |       |   |       | successfully processed | SUCCESS                  |       |   |       |                        |                          |       |   | Idle  | CC event request       | Send CC event answer     | Idle  |   |       | received and           |                          |       |   |       | successfully processed |                          |       |   |       |                        |                          |       |   | Idle  | CC event request       | Send CC event answer     | Idle  |   |       | received but not       | with Result-Code !=      |       |   |       | successfully processed | SUCCESS                  |       |   |       |                        |                          |       |Bertz, et al.                Standards Track                   [Page 58]

RFC 8506           Diameter Credit-Control Application        March 2019   | Open  | CC update request      | Send CC update answer,   | Open  |   |       | received and           | debit used units,        |       |   |       | successfully processed | reserve new units,       |       |   |       |                        | restart Tcc              |       |   |       |                        |                          |       |   | Open  | CC update request      | Send CC update answer    | Idle  |   |       | received but not       | with Result-Code !=      |       |   |       | successfully processed | SUCCESS, debit used      |       |   |       |                        | units                    |       |   |       |                        |                          |       |   | Open  | CC termination request | Send CC termin. answer,  | Idle  |   |       | received and           | stop Tcc, debit used     |       |   |       | successfully processed | units                    |       |   |       |                        |                          |       |   | Open  | CC termination request | Send CC termin. answer   | Idle  |   |       | received but not       | with Result-Code !=      |       |   |       | successfully processed | SUCCESS, debit used      |       |   |       |                        | units                    |       |   |       |                        |                          |       |   | Open  | Session supervision    | Release reserved units   | Idle  |   |       | timer Tcc expired      |                          |       |   +-------+------------------------+--------------------------+-------+        Table 6: Session-Based and Event-Based Server State Machine8.  Credit-Control AVPs   This section defines the Credit-Control AVPs that are specific to the   Diameter Credit-Control application and that MAY be included in the   Diameter Credit-Control messages.   The AVPs defined in this section MAY also be included in   authorization commands defined in authorization-specific   applications, such as [RFC7155] and [RFC4004], if the first   interrogation is performed as part of the authorization/   authentication process, as described inSection 5.2.   The Diameter AVP rules are defined in[RFC6733], Section 4.  These   AVP rules are observed in AVPs defined in this section.   The following table describes the Diameter AVPs defined in the   credit-control application, their AVP Code values, types, and   possible flag values.  The AVP Flag rules ('M', 'V') are explained in[RFC6733], Section 4.1.Bertz, et al.                Standards Track                   [Page 59]

RFC 8506           Diameter Credit-Control Application        March 2019                                                       +---------------+                                                       |AVP Flag Rules |                                   Defined             |----+-----+----|                             AVP   in                  |    |     |MUST|   Attribute Name            Code  Section Data Type   |MUST| MAY |NOT |   ----------------------------------------------------|----+-----+----|   CC-Correlation-Id         411   8.1     OctetString |    |  M  |  V |   CC-Input-Octets           412   8.24    Unsigned64  | M  |     |  V |   CC-Money                  413   8.22    Grouped     | M  |     |  V |   CC-Output-Octets          414   8.25    Unsigned64  | M  |     |  V |   CC-Request-Number         415   8.2     Unsigned32  | M  |     |  V |   CC-Request-Type           416   8.3     Enumerated  | M  |     |  V |   CC-Service-Specific-      417   8.26    Unsigned64  | M  |     |  V |     Units                                             |    |     |    |   CC-Session-Failover       418   8.4     Enumerated  | M  |     |  V |   CC-Sub-Session-Id         419   8.5     Unsigned64  | M  |     |  V |   CC-Time                   420   8.21    Unsigned32  | M  |     |  V |   CC-Total-Octets           421   8.23    Unsigned64  | M  |     |  V |   CC-Unit-Type              454   8.32    Enumerated  | M  |     |  V |   Check-Balance-Result      422   8.6     Enumerated  | M  |     |  V |   Cost-Information          423   8.7     Grouped     | M  |     |  V |   Cost-Unit                 424   8.12    UTF8String  | M  |     |  V |   Credit-Control            426   8.13    Enumerated  | M  |     |  V |   Credit-Control-           427   8.14    Enumerated  | M  |     |  V |     Failure-Handling                                  |    |     |    |   Currency-Code             425   8.11    Unsigned32  | M  |     |  V |   Direct-Debiting-          428   8.15    Enumerated  | M  |     |  V |     Failure-Handling                                  |    |     |    |   Exponent                  429   8.9     Integer32   | M  |     |  V |   Final-Unit-Action         449   8.35    Enumerated  | M  |     |  V |   Final-Unit-Indication     430   8.34    Grouped     | M  |     |  V |   QoS-Final-Unit-Indication 669   8.68    Grouped     |    |  M  |  V |   Granted-Service-Unit      431   8.17    Grouped     | M  |     |  V |   G-S-U-Pool-Identifier     453   8.31    Unsigned32  | M  |     |  V |   G-S-U-Pool-Reference      457   8.30    Grouped     | M  |     |  V |   Multiple-Services-        456   8.16    Grouped     | M  |     |  V |     Credit-Control                                    |    |     |    |   Multiple-Services-        455   8.40    Enumerated  | M  |     |  V |     Indicator                                         |    |     |    |   Rating-Group              432   8.29    Unsigned32  | M  |     |  V |   Redirect-Address-Type     433   8.38    Enumerated  | M  |     |  V |   Redirect-Server           434   8.37    Grouped     | M  |     |  V |   Redirect-Server-Address   435   8.39    UTF8String  | M  |     |  V |   Redirect-Server-Extension 665   8.64    Grouped     |    |  M  |  V |   Redirect-Address-         666   8.65    Address     |    |  M  |  V |     IPAddress                                         |    |     |    |   Redirect-Address-URL      667   8.66    UTF8String  |    |  M  |  V |   Redirect-Address-SIP-URI  668   8.67    UTF8String  |    |  M  |  V |Bertz, et al.                Standards Track                   [Page 60]

RFC 8506           Diameter Credit-Control Application        March 2019   Requested-Action          436   8.41    Enumerated  | M  |     |  V |   Requested-Service-Unit    437   8.18    Grouped     | M  |     |  V |   Restriction-Filter-Rule   438   8.36    IPFilterRule| M  |     |  V |   Service-Context-Id        461   8.42    UTF8String  | M  |     |  V |   Service-Identifier        439   8.28    Unsigned32  | M  |     |  V |   Service-Parameter-Info    440   8.43    Grouped     |    |  M  |  V |   Service-Parameter-Type    441   8.44    Unsigned32  |    |  M  |  V |   Service-Parameter-Value   442   8.45    OctetString |    |  M  |  V |   Subscription-Id           443   8.46    Grouped     | M  |     |  V |   Subscription-Id-Data      444   8.48    UTF8String  | M  |     |  V |   Subscription-Id-Type      450   8.47    Enumerated  | M  |     |  V |   Subscription-Id-Extension 659   8.58    Grouped     |    |  M  |  V |   Subscription-Id-E164      660   8.59    UTF8String  |    |  M  |  V |   Subscription-Id-IMSI      661   8.60    UTF8String  |    |  M  |  V |   Subscription-Id-SIP-URI   662   8.61    UTF8String  |    |  M  |  V |   Subscription-Id-NAI       663   8.62    UTF8String  |    |  M  |  V |   Subscription-Id-Private   664   8.63    UTF8String  |    |  M  |  V |   Tariff-Change-Usage       452   8.27    Enumerated  | M  |     |  V |   Tariff-Time-Change        451   8.20    Time        | M  |     |  V |   Unit-Value                445   8.8     Grouped     | M  |     |  V |   Used-Service-Unit         446   8.19    Grouped     | M  |     |  V |   User-Equipment-Info       458   8.49    Grouped     |    |  M  |  V |   User-Equipment-Info-Type  459   8.50    Enumerated  |    |  M  |  V |   User-Equipment-Info-Value 460   8.51    OctetString |    |  M  |  V |   User-Equipment-Info-      653   8.52    Grouped     |    |  M  |  V |     Extension                                         |    |     |    |   User-Equipment-Info-      654   8.53    OctetString |    |  M  |  V |     IMEISV                                            |    |     |    |   User-Equipment-Info-MAC   655   8.54    OctetString |    |  M  |  V |   User-Equipment-Info-EUI64 656   8.55    OctetString |    |  M  |  V |   User-Equipment-Info-      657   8.56    OctetString |    |  M  |  V |     ModifiedEUI64                                     |    |     |    |   User-Equipment-Info-IMEI  658   8.57    OctetString |    |  M  |  V |   Value-Digits              447   8.10    Integer64   | M  |     |  V |   Validity-Time             448   8.33    Unsigned32  | M  |     |  V |8.1.  CC-Correlation-Id AVP   The CC-Correlation-Id AVP (AVP Code 411) is of type OctetString and   contains information to correlate credit-control requests generated   for different components of the service, e.g., transport and service   level.  Whoever allocates the Service-Context-Id (i.e., a unique   identifier of a service-specific document) is also responsible for   defining the content and encoding of the CC-Correlation-Id AVP.Bertz, et al.                Standards Track                   [Page 61]

RFC 8506           Diameter Credit-Control Application        March 20198.2.  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 the Session-Id AVP and the   CC-Request-Number AVP 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 of the CC-Request-Number   AVP to 0 for a credit-control request with a CC-Request-Type AVP of   INITIAL_REQUEST (the initial request in a session).  The value of the   CC-Request-Number AVP should be set to 1 for the first   UPDATE_REQUEST, to 2 for the second, and so on until the value for   TERMINATION_REQUEST is one more than the value for the last   UPDATE_REQUEST.  In the case of event charging (when the CC-Request-   Type AVP has the value EVENT_REQUEST), the CC-Request-Number AVP   should be set to 0 for a credit-control request.8.3.  CC-Request-Type AVP   The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and   contains the reason for sending the Credit-Control-Request message.   It MUST be present in all Credit-Control-Request messages.  The   following values are defined for the CC-Request-Type AVP (the value   of 0 (zero) is reserved):   INITIAL_REQUEST       1   This request is used to initiate a credit-control session.  It   contains credit-control information that is relevant to the   initiation.   UPDATE_REQUEST        2   This request contains credit-control information for an existing   credit-control session.  Credit-control requests of this type 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   This request is sent to terminate a credit-control session.  It   contains credit-control information relevant to the existing session.Bertz, et al.                Standards Track                   [Page 62]

RFC 8506           Diameter Credit-Control Application        March 2019   EVENT_REQUEST         4   This request is used when there is no need to maintain any   credit-control session state in the credit-control server.  It   contains all information relevant to the service and is the only   request of the service.  The reason for this request is further   detailed in the Requested-Action AVP.  The Requested-Action AVP MUST   be included in the Credit-Control-Request message when CC-Request-   Type is set to EVENT_REQUEST.8.4.  CC-Session-Failover AVP   The CC-Session-Failover AVP (AVP Code 418) is of type Enumerated and   contains information as to whether moving the credit-control message   stream to a backup server during an ongoing credit-control session is   supported.  In the 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 home   Diameter AAA server, can be used as an address of the backup server.   An implementation is not required to support moving a credit-control   message stream to an alternative server, as this also requires moving   information related to the credit-control session to the 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 be moved to an alternative   destination in the case of a communication failure.  This is the   default behavior if the AVP isn't included in the reply from the   authorization or credit-control server.   FAILOVER_SUPPORTED       1   When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the   credit-control message stream SHOULD be moved to an alternative   destination in the case of a communication failure.  Moving the   credit-control message stream to a backup server MAY require that   information related to the credit-control session should also be   forwarded to an alternative server.Bertz, et al.                Standards Track                   [Page 63]

RFC 8506           Diameter Credit-Control Application        March 20198.5.  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 AVP and this AVP MUST be unique per sub-session,   and the value of this AVP MUST be monotonically increased by one for   all new sub-sessions.  The absence of this AVP implies that no   sub-sessions are in use.8.6.  Check-Balance-Result AVP   The Check-Balance-Result AVP (AVP Code 422) is of type Enumerated and   contains the result of the balance check.  This AVP is applicable   only when the Requested-Action AVP indicates CHECK_BALANCE in the   Credit-Control-Request command.  The following values are defined for   the Check-Balance-Result AVP:   ENOUGH_CREDIT   0   There is enough credit in the account to cover the requested service.   NO_CREDIT       1   There isn't enough credit in the account to cover the requested   service.8.7.  Cost-Information AVP   The Cost-Information AVP (AVP Code 423) is of type Grouped, and it is   used to return the cost information of a service, which the   credit-control client can transfer transparently to the end user.   The included Unit-Value AVP contains the cost estimate (always of   type "money") of the service in the case of price inquiries, or the   accumulated cost estimation in the case of a credit-control session.   The Currency-Code AVP specifies in which currency the cost was given.   The Cost-Unit AVP 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 the 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 for the requested service, without any reservations   being made.Bertz, et al.                Standards Track                   [Page 64]

RFC 8506           Diameter Credit-Control Application        March 2019   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 reservations 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.   The Cost-Information AVP is defined as follows (per grouped-avp-def   as defined in [RFC6733]):                   Cost-Information ::= < AVP Header: 423 >                                        { Unit-Value }                                        { Currency-Code }                                        [ Cost-Unit ]8.8.  Unit-Value AVP   The Unit-Value AVP is of type Grouped (AVP Code 445) and specifies   the cost as a floating-point value.  The Unit-Value is a significand   with an exponent; i.e., Unit-Value = Value-Digits AVP * 10^Exponent.   This representation avoids unwanted rounding off.  For example, the   value of 2,3 is represented as Value-Digits = 23 and Exponent = -1.   The absence of the exponent part MUST be interpreted as an exponent   equal to zero.   The Unit-Value AVP is defined as follows (per grouped-avp-def as   defined in [RFC6733]):                       Unit-Value ::= < AVP Header: 445 >                                      { Value-Digits }                                      [ Exponent ]8.9.  Exponent AVP   The Exponent AVP is of type Integer32 (AVP Code 429) and contains the   exponent value to be applied for the Value-Digits AVP within the   Unit-Value AVP.Bertz, et al.                Standards Track                   [Page 65]

RFC 8506           Diameter Credit-Control Application        March 20198.10.  Value-Digits AVP   The Value-Digits AVP is of type Integer64 (AVP Code 447) and contains   the significant digits of the number.  If decimal values are needed   to present the units, the scaling MUST be indicated with the related   Exponent AVP.  For example, for the monetary amount $0.05, the value   of the Value-Digits AVP MUST be set to 5, and the scaling MUST be   indicated with the Exponent AVP set to -2.8.11.  Currency-Code AVP   The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and   contains a currency code that specifies in which currency the values   of AVPs containing monetary units were given.  It is specified by   using the numeric values defined in the ISO 4217 standard [ISO4217].8.12.  Cost-Unit AVP   The Cost-Unit AVP (AVP Code 424) is of type UTF8String, and it is   used to display a human-readable string to the end user.  It   specifies the applicable unit to the Cost-Information AVP when the   service cost is a cost per unit (e.g., cost of the service is $1 per   minute).  The Cost-Unit setting can be minutes, hours, days,   kilobytes, megabytes, etc.8.13.  Credit-Control AVP   The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST   be included in AA-Request messages when the Service Element has   credit-control capabilities.  The following values are defined for   the Credit-Control AVP:   CREDIT_AUTHORIZATION   0   If the home Diameter AAA server determines that the user has a   prepaid subscription, this value indicates that the credit-control   server MUST be contacted to perform the first interrogation.  The   value of the Credit-Control AVP MUST always be set to 0 in an   AA-Request sent to perform the first interrogation and to initiate a   new credit-control session.   RE_AUTHORIZATION       1   This value indicates to the Diameter AAA server that a credit-control   session is ongoing for the subscriber and that the credit-control   server MUST NOT be contacted.  The Credit-Control AVP set to the   value of 1 is to be used only when the first interrogation has been   successfully performed and the credit-control session is ongoingBertz, et al.                Standards Track                   [Page 66]

RFC 8506           Diameter Credit-Control Application        March 2019   (i.e., re-authorization triggered by authorization lifetime).  This   value MUST NOT be used in an AA-Request sent to perform the first   interrogation.8.14.  Credit-Control-Failure-Handling AVP (CCFH)   The CCFH (AVP Code 427) is of type Enumerated.  The credit-control   client uses information in this AVP to decide what to do if sending   credit-control messages to the credit-control server has been, for   instance, temporarily prevented due to a network problem.  Depending   on the service logic, the credit-control server can order the client   to terminate the service immediately when there is a reason to   believe that the service cannot be charged, or to try failover to an   alternative server, if possible.  The server could then either   terminate or grant the service, should the alternative connection   also fail.   The following values are defined for the CCFH:   TERMINATE             0   When the CCFH is set to TERMINATE, the service MUST only be granted   for as long as there is a connection to the credit-control server.   If the credit-control client does not receive any Credit-Control-   Answer messages before the Tx timer (as defined inSection 13)   expires, the credit-control request is regarded as failed, and the   end user's service session is terminated.   This is the default behavior if the AVP isn't included in the reply   from the authorization or credit-control server.   CONTINUE              1   When the CCFH is set to CONTINUE, the credit-control client SHOULD   resend the request to an alternative server in the case of transport   or temporary failures, provided that (1) a failover procedure is   supported in the credit-control server and the credit-control client   and (2) 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 CCFH is set to RETRY_AND_TERMINATE, the credit-control   client SHOULD resend the request to an alternative server in the case   of transport or temporary failures, provided that (1) a failover   procedure is supported in the credit-control server and the   credit-control client and (2) an alternative server is available.Bertz, et al.                Standards Track                   [Page 67]

RFC 8506           Diameter Credit-Control Application        March 2019   Otherwise, the service SHOULD NOT be granted when the credit-control   messages can't be delivered.8.15.  Direct-Debiting-Failure-Handling AVP (DDFH)   The DDFH (AVP Code 428) is of type Enumerated.  The credit-control   client uses information in this AVP to decide what to do if sending   credit-control messages (Requested-Action AVP set to DIRECT_DEBITING)   to the credit-control server has been, for instance, temporarily   prevented due to a network problem.   The following values are defined for the DDFH:   TERMINATE_OR_BUFFER   0   When the DDFH is set to TERMINATE_OR_BUFFER, the service MUST be   granted for as long as there is a connection to the credit-control   server.  If the credit-control client does not receive any   Credit-Control-Answer messages before the Tx timer (as defined inSection 13) expires, the credit-control request is regarded as   failed.  The client SHOULD terminate the service if it can determine   from the failed answer that units have not been debited.  Otherwise,   the credit-control client SHOULD grant the service, store the request   in application-level non-volatile storage, and try to resend the   request.  These requests MUST be marked as possible duplicates by   setting the T flag in the command header as described in[RFC6733],   Section 3.  This is the default behavior if the AVP isn't included in   the reply from the authorization server.   CONTINUE              1   When the DDFH is set to CONTINUE, the service SHOULD be granted, even   if credit-control messages can't be delivered, and the request should   be deleted.8.16.  Multiple-Services-Credit-Control AVP   The Multiple-Services-Credit-Control AVP (AVP Code 456) is of type   Grouped and contains the AVPs related to the independent   credit-control of multiple services.  Note that each instance of this   AVP carries units related to one or more services or related to a   single rating-group.   The Service-Identifier AVP and the Rating-Group AVP are used to   associate the granted units to a given service or rating-group.  If   both the Service-Identifier AVP and the Rating-Group AVP are   included, the target of the service units is always the service(s)   indicated by the value of the Service-Identifier AVP(s).  If only theBertz, et al.                Standards Track                   [Page 68]

RFC 8506           Diameter Credit-Control Application        March 2019   Rating-Group AVP is present, the Multiple-Services-Credit-Control AVP   relates to all the services that belong to the specified   rating-group.   The G-S-U-Pool-Reference AVP allows the server to specify a   G-S-U-Pool-Identifier identifying a credit pool within which the   units of the specified type are considered pooled.  If a G-S-U-Pool-   Reference AVP is present, then actual service units of the specified   type MUST also be present.  For example, if the G-S-U-Pool-Reference   AVP specifies a CC-Unit-Type value of TIME (Section 8.32), then the   CC-Time AVP MUST be present.   The Requested-Service-Unit AVP MAY contain the amount of requested   service units or the requested monetary value.  It MUST be present in   the initial interrogation and within the intermediate interrogations   in which a new quota is requested.  If the credit-control client does   not include the Requested-Service-Unit AVP in a request command --   because, for instance, it has determined that the end user terminated   the service -- the server MUST debit the used amount from the user's   account but MUST NOT return a new quota in the corresponding answer.   The Validity-Time, Result-Code, and Final-Unit-Indication or   QoS-Final-Unit-Indication AVPs MAY be present in a Credit-Control-   Answer command as defined in Sections5.1.2 and5.6 for graceful   service termination.   When both the Tariff-Time-Change AVP and the Tariff-Change-Usage AVP   are present, the server MUST include two separate instances of the   Multiple-Services-Credit-Control AVP with the Granted-Service-Unit   AVP associated to the same service-identifier and/or rating-group.   Where the two quotas are associated to the same pool or to different   pools, the credit-pooling mechanism defined inSection 5.1.2 applies.   When the client is reporting used units before and after the tariff   time change, it MUST use the Tariff-Change-Usage AVP inside the   Used-Service-Unit AVP.   A server not implementing the independent credit-control of multiple   services MUST treat the Multiple-Services-Credit-Control AVP as an   invalid AVP.Bertz, et al.                Standards Track                   [Page 69]

RFC 8506           Diameter Credit-Control Application        March 2019   The Multiple-Services-Credit-Control AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):    Multiple-Services-Credit-Control ::= < AVP Header: 456 >                                         [ Granted-Service-Unit ]                                         [ Requested-Service-Unit ]                                        *[ Used-Service-Unit ]                                         [ Tariff-Change-Usage ]                                        *[ Service-Identifier ]                                         [ Rating-Group ]                                        *[ G-S-U-Pool-Reference ]                                         [ Validity-Time ]                                         [ Result-Code ]                                         [ Final-Unit-Indication ]                                         [ QoS-Final-Unit-Indication ]                                        *[ AVP ]8.17.  Granted-Service-Unit AVP   The Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and   contains the amount of units that the Diameter Credit-Control client   can provide to the end user until the service must be released or the   new Credit-Control-Request must be sent.  A client is not required to   implement all the unit types, and it must treat unknown or   unsupported unit types in the Answer message as an incorrect CCA.  In   this case, the client MUST terminate the credit-control session and   indicate the reason as DIAMETER_BAD_ANSWER in the Termination-Cause   AVP.   The Granted-Service-Unit AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         Granted-Service-Unit ::= < AVP Header: 431 >                                  [ Tariff-Time-Change ]                                  [ CC-Time ]                                  [ CC-Money ]                                  [ CC-Total-Octets ]                                  [ CC-Input-Octets ]                                  [ CC-Output-Octets ]                                  [ CC-Service-Specific-Units ]                                 *[ AVP ]Bertz, et al.                Standards Track                   [Page 70]

RFC 8506           Diameter Credit-Control Application        March 20198.18.  Requested-Service-Unit AVP   The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and   contains the amount of requested units specified by the Diameter   Credit-Control client.  A server is not required to implement all the   unit types, and it must treat unknown or unsupported unit types as   invalid AVPs.   The Requested-Service-Unit AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         Requested-Service-Unit ::= < AVP Header: 437 >                                    [ CC-Time ]                                    [ CC-Money ]                                    [ CC-Total-Octets ]                                    [ CC-Input-Octets ]                                    [ CC-Output-Octets ]                                    [ CC-Service-Specific-Units ]                                   *[ AVP ]8.19.  Used-Service-Unit AVP   The Used-Service-Unit AVP is of type Grouped (AVP Code 446) and   contains the amount of used units measured from the point when the   service became active or, if interim interrogations are used during   the session, from the point when the previous measurement ended.   Note: The value reported in a Used-Service-Unit AVP is not   necessarily related to the grant provided in a Granted-Service-Unit   AVP, e.g., the value in this AVP may exceed the value in the grant.   The Used-Service-Unit AVP is defined as follows (per grouped-avp-def   as defined in [RFC6733]):         Used-Service-Unit ::= < AVP Header: 446 >                               [ Tariff-Change-Usage ]                               [ CC-Time ]                               [ CC-Money ]                               [ CC-Total-Octets ]                               [ CC-Input-Octets ]                               [ CC-Output-Octets ]                               [ CC-Service-Specific-Units ]                              *[ AVP ]Bertz, et al.                Standards Track                   [Page 71]

RFC 8506           Diameter Credit-Control Application        March 20198.20.  Tariff-Time-Change AVP   The Tariff-Time-Change AVP (AVP Code 451) is of type Time.  It is   sent from the server to the client and includes the time in seconds   since January 1, 1900, 00:00 UTC, when the tariff of the service will   be changed.   The tariff change mechanism is optional for the client and server,   and it is not used for time-based services (Section 5).  If a client   does not support the tariff time change mechanism, it MUST treat the   Tariff-Time-Change AVP in the Answer message as an incorrect CCA.  In   this case, the client terminates the credit-control session and   indicates the reason as DIAMETER_BAD_ANSWER in the Termination-Cause   AVP.   Omission of this AVP means that no tariff change is to be reported.8.21.  CC-Time AVP   The CC-Time AVP (AVP Code 420) is of type Unsigned32 and indicates   the length of the requested, granted, or used time in seconds.8.22.  CC-Money AVP   The CC-Money AVP (AVP Code 413) is of type Grouped and specifies the   monetary amount in the given currency.  The Currency-Code AVP SHOULD   be included.  The CC-Money AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         CC-Money ::= < AVP Header: 413 >                      { Unit-Value }                      [ Currency-Code ]8.23.  CC-Total-Octets AVP   The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64 and   contains the total number of requested, granted, or used octets   regardless of the direction (sent or received).8.24.  CC-Input-Octets AVP   The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64 and   contains the number of requested, granted, or used octets that   can be / have been received from the end user.Bertz, et al.                Standards Track                   [Page 72]

RFC 8506           Diameter Credit-Control Application        March 20198.25.  CC-Output-Octets AVP   The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64 and   contains the number of requested, granted, or used octets that   can be / have been sent to the end user.8.26.  CC-Service-Specific-Units AVP   The CC-Service-Specific-Units AVP (AVP Code 417) is of type   Unsigned64 and specifies the number of service-specific units (e.g.,   number of events, points) given in a selected service.  The service-   specific units always refer to the service identified in the Service-   Identifier AVP (or Rating-Group AVP when the Multiple-Services-   Credit-Control AVP is used).8.27.  Tariff-Change-Usage AVP   The Tariff-Change-Usage AVP (AVP Code 452) is of type Enumerated and   defines whether units are used before or after a tariff change, or   whether the units straddled a tariff change during the reporting   period.  Omission of this AVP means that no tariff change has   occurred.   In addition, when present in Answer messages as part of the Multiple-   Services-Credit-Control AVP, this AVP defines whether units are   allocated to be used before or after a tariff change event.   When the Tariff-Time-Change AVP is present, omission of this AVP in   Answer messages means that the single-quota mechanism applies.   Tariff-Change-Usage can be set to one of the following values:   UNIT_BEFORE_TARIFF_CHANGE   0   When present in the Multiple-Services-Credit-Control AVP, this value   indicates the amount of units allocated for use before a tariff   change occurs.   When present in the Used-Service-Unit AVP, this value indicates the   amount of resource units used before a tariff change had occurred.Bertz, et al.                Standards Track                   [Page 73]

RFC 8506           Diameter Credit-Control Application        March 2019   UNIT_AFTER_TARIFF_CHANGE    1   When present in the Multiple-Services-Credit-Control AVP, this value   indicates the amount of units allocated for use after a tariff change   occurs.   When present in the Used-Service-Unit AVP, this value indicates the   amount of resource units used after a tariff change had occurred.   UNIT_INDETERMINATE          2   This value is to be used only in the Used-Service-Unit AVP and   indicates the amount of resource units that straddle the tariff   change (e.g., the metering process reports to the credit-control   client in blocks of n octets, and one block straddled the tariff   change).8.28.  Service-Identifier AVP   The Service-Identifier AVP is of type Unsigned32 (AVP Code 439) and   contains the identifier of a service.  The specific service the   request relates to is uniquely identified by the combination of the   Service-Context-Id AVP and the Service-Identifier AVP.   A usage example of this AVP is illustrated inAppendix A.9.8.29.  Rating-Group AVP   The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and   contains the identifier of a rating-group.  All the services subject   to the same rating type are part of the same rating-group.  The   specific rating-group the request relates to is uniquely identified   by the combination of the Service-Context-Id AVP and the Rating-Group   AVP.   A usage example of this AVP is illustrated inAppendix A.9.8.30.  G-S-U-Pool-Reference AVP   The G-S-U-Pool-Reference AVP (AVP Code 457) is of type Grouped.  It   is used in the Credit-Control-Answer message and associates the   Granted-Service-Unit AVP within which it appears with a credit pool   within the session.   The G-S-U-Pool-Identifier AVP specifies the credit pool from which   credit is drawn for this unit type.Bertz, et al.                Standards Track                   [Page 74]

RFC 8506           Diameter Credit-Control Application        March 2019   The CC-Unit-Type AVP specifies the type of units for which credit is   pooled.   The Unit-Value AVP specifies the multiplier, which converts between   service units of type CC-Unit-Type and abstract service units within   the credit pool (and thus to service units of any other services or   rating-groups associated with the same pool).   The G-S-U-Pool-Reference AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):           G-S-U-Pool-Reference ::= < AVP Header: 457 >                                    { G-S-U-Pool-Identifier }                                    { CC-Unit-Type }                                    { Unit-Value }8.31.  G-S-U-Pool-Identifier AVP   The G-S-U-Pool-Identifier AVP (AVP Code 453) is of type Unsigned32   and identifies a credit pool within the session.8.32.  CC-Unit-Type AVP   The CC-Unit-Type AVP (AVP Code 454) is of type Enumerated and   specifies the type of units considered to be pooled into a   credit pool.   The following values are defined for the CC-Unit-Type AVP:         TIME                         0         MONEY                        1         TOTAL-OCTETS                 2         INPUT-OCTETS                 3         OUTPUT-OCTETS                4         SERVICE-SPECIFIC-UNITS       58.33.  Validity-Time AVP   The Validity-Time AVP is of type Unsigned32 (AVP Code 448).  It is   sent from the credit-control server to the credit-control client.   The Validity-Time AVP contains the validity time of the granted   service units.  The measurement of the Validity-Time is started upon   receipt of the Credit-Control-Answer message containing this AVP.  If   the granted service units have not been consumed within the validity   time specified in this AVP, the credit-control client MUST send a   Credit-Control-Request message to the server, with CC-Request-Type   set to UPDATE_REQUEST.  The value field of the Validity-Time AVP is   given in seconds.Bertz, et al.                Standards Track                   [Page 75]

RFC 8506           Diameter Credit-Control Application        March 2019   The Validity-Time AVP is also used for graceful service termination   (seeSection 5.6) to indicate to the credit-control client how long   the subscriber is allowed to use network resources after the   specified action (i.e., REDIRECT or RESTRICT_ACCESS) started.  When   the Validity-Time elapses, a new intermediate interrogation is sent   to the server.8.34.  Final-Unit-Indication AVP   The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and   indicates that the Granted-Service-Unit AVP in the Credit-Control-   Answer or in the AA-Answer contains the final units for the service.   After these units have expired, the Diameter Credit-Control client is   responsible for executing the action indicated in the Final-Unit-   Action AVP (seeSection 5.6).   If more than one unit type is received in the Credit-Control-Answer,   the unit type that first expired SHOULD cause the credit-control   client to execute the specified action.   In the first interrogation, the Final-Unit-Indication AVP with   Final-Unit-Action set to 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 that the client is to execute the specified action   immediately.  If the home service provider policy is to terminate the   service, naturally, the server SHOULD return the appropriate   transient failure (seeSection 9.1) in order to implement the policy-   defined action.   The Final-Unit-Action AVP defines the behavior of the Service Element   when the user's account cannot cover the cost of the service and MUST   always be present if the Final-Unit-Indication AVP is included in a   command.   If the Final-Unit-Action AVP is set to TERMINATE, the Final-Unit-   Indication group AVP MUST NOT contain any other AVPs.   If the Final-Unit-Action AVP is set to REDIRECT, the Redirect-Server   AVP or the Redirect-Server-Extension AVP (at least one) MUST be   present.  The Restriction-Filter-Rule AVP or the Filter-Id AVP MAY be   present in the Credit-Control-Answer message if the user is also   allowed to access other services that are not accessible through the   address given in the Redirect-Server AVP.   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the   Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.Bertz, et al.                Standards Track                   [Page 76]

RFC 8506           Diameter Credit-Control Application        March 2019   The Filter-Id AVP is defined in [RFC7155].  The Filter-Id AVP can be   used to reference an IP filter list installed in the access device by   means other than the Diameter Credit-Control application, e.g.,   locally configured or configured by another entity.   If the Final-Unit-Action AVP is set to REDIRECT and the type of   server is not one of the enumerations in the Redirect-Address-Type   AVP, then the QoS-Final-Unit-Indication AVP SHOULD be used together   with the Redirect-Server-Extension AVP instead of the Final-Unit-   Indication AVP.   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS or REDIRECT   and the classification of the restricted traffic cannot be expressed   using an IPFilterRule, or if actions (e.g., QoS) other than just   allowing traffic need to be enforced, then the QoS-Final-Unit-   Indication AVP SHOULD be used instead of the Final-Unit-Indication   AVP.  However, if the credit-control server wants to preserve   backward compatibility with credit-control clients that support only   [RFC4006], the Final-Unit-Indication AVP SHOULD be used together with   the Filter-Id AVP.   The Final-Unit-Indication AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         Final-Unit-Indication ::= < AVP Header: 430 >                                   { Final-Unit-Action }                                  *[ Restriction-Filter-Rule ]                                  *[ Filter-Id ]                                   [ Redirect-Server ]8.35.  Final-Unit-Action AVP   The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and   indicates to the credit-control client the action to be taken when   the user's account cannot cover the service cost.   Final-Unit-Action can be set to one of the following values:   TERMINATE         0   The credit-control client MUST terminate the service session.  This   is the default handling, applicable whenever the credit-control   client receives an unsupported Final-Unit-Action value, and it MUST   be supported by all the Diameter Credit-Control client   implementations conforming to this specification.Bertz, et al.                Standards Track                   [Page 77]

RFC 8506           Diameter Credit-Control Application        March 2019   REDIRECT          1   The Service Element MUST redirect the user to the address specified   in the Redirect-Server-Address AVP or one of the AVPs included in the   Redirect-Server-Extension AVP.  The redirect action is defined inSection 5.6.2.   RESTRICT_ACCESS   2   The access device MUST restrict the user's access according to the   filter AVPs contained in the applied Grouped AVP: according to IP   packet filters defined in the Restriction-Filter-Rule AVP, according   to the packet classifier filters defined in the Filter-Rule AVP, or   according to the packet filters identified by the Filter-Id AVP.  All   of the packets not matching any restriction filters (seeSection 5.6.3) MUST be dropped.8.36.  Restriction-Filter-Rule AVP   The Restriction-Filter-Rule AVP (AVP Code 438) is of type   IPFilterRule and provides filter rules corresponding to services that   are to remain accessible even if there are no more service units   granted.  The access device has to configure the specified filter   rules for the subscriber and MUST drop all the packets not matching   these filters.  Zero, one, or more such AVPs MAY be present in a   Credit-Control-Answer message or in an AA-Answer message.8.37.  Redirect-Server AVP   The Redirect-Server AVP (AVP Code 434) is of type Grouped and   contains the address information of the redirect server (e.g., HTTP   redirect server, SIP Server) with which the end user is to be   connected when the account cannot cover the service cost.  It MUST be   present when the Final-Unit-Action AVP is set to REDIRECT.   The Redirect-Server AVP is defined as follows (per grouped-avp-def as   defined in [RFC6733]):         Redirect-Server ::= < AVP Header: 434 >                             { Redirect-Address-Type }                             { Redirect-Server-Address }Bertz, et al.                Standards Track                   [Page 78]

RFC 8506           Diameter Credit-Control Application        March 20198.38.  Redirect-Address-Type AVP   The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated   and defines the address type of the address given in the Redirect-   Server-Address AVP.   Redirect-Address-Type can be set to one of the following values:   IPv4 Address   0   The address type is in the form of a "dotted-decimal" IPv4 address,   as defined in [RFC791].   IPv6 Address   1   The address type is in the form of an IPv6 address, as defined in   [RFC4291].  The address MUST conform to the textual representation of   the address according to [RFC5952].   Because [RFC5952] is more restrictive than the "RFC 3513" format   required by [RFC4006], some legacy implementations may not be   compliant with the new requirements.  Accordingly, implementations   receiving this AVP MAY be liberal in the textual IPv6 representations   that are accepted, without raising an error.   URL            2   The address type is in the form of a Uniform Resource Locator, as   defined in [RFC3986].   SIP URI        3   The address type is in the form of a SIP Uniform Resource Identifier,   as defined in [RFC3261].8.39.  Redirect-Server-Address AVP   The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String   and defines the address of the redirect server (e.g., HTTP redirect   server, SIP Server) with which the end user is to be connected when   the account cannot cover the service cost.Bertz, et al.                Standards Track                   [Page 79]

RFC 8506           Diameter Credit-Control Application        March 20198.40.  Multiple-Services-Indicator AVP   The Multiple-Services-Indicator AVP (AVP Code 455) is of type   Enumerated and indicates whether the Diameter Credit-Control client   is capable of handling multiple services independently within a   (sub-)session.  The absence of this AVP means that independent   credit-control of multiple services is not supported.   A server not implementing the independent credit-control of multiple   services MUST treat the Multiple-Services-Indicator AVP as an   invalid AVP.   The following values are defined for the Multiple-Services-Indicator   AVP:   MULTIPLE_SERVICES_NOT_SUPPORTED   0   The client does not support independent credit-control of multiple   services within a (sub-)session.   MULTIPLE_SERVICES_SUPPORTED       1   The client supports independent credit-control of multiple services   within a (sub-)session.8.41.  Requested-Action AVP   The Requested-Action AVP (AVP Code 436) is of type Enumerated and   contains the requested action being sent in a Credit-Control-Request   command where the CC-Request-Type is set to EVENT_REQUEST.  The   following values are defined for the Requested-Action AVP:   DIRECT_DEBITING   0   This indicates a request to decrease the end user's account according   to information specified in the Requested-Service-Unit AVP and/or   Service-Identifier AVP (additional rating information may be included   in service-specific AVPs or in the Service-Parameter-Info AVP).  The   Granted-Service-Unit AVP in the Credit-Control-Answer command   contains the debited units.Bertz, et al.                Standards Track                   [Page 80]

RFC 8506           Diameter Credit-Control Application        March 2019   REFUND_ACCOUNT    1   This indicates a request to increase the end user's account according   to information specified in the Requested-Service-Unit AVP and/or   Service-Identifier AVP (additional rating information may be included   in service-specific AVPs or in the Service-Parameter-Info AVP).  The   Granted-Service-Unit AVP in the Credit-Control-Answer command   contains the refunded units.   CHECK_BALANCE     2   This indicates a balance-check request.  In this case, the checking   of the account balance is done without any credit reservations from   the account.  The Check-Balance-Result AVP in the Credit-Control-   Answer command contains the result of the balance check.   PRICE_ENQUIRY     3   This indicates a price-inquiry request.  In this case, neither   checking of the account balance nor reservation from the account will   be done; only the price of the service will be returned in the   Cost-Information AVP in the Credit-Control-Answer command.8.42.  Service-Context-Id AVP   The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and   contains a unique identifier of the Diameter Credit-Control service-   specific document (as defined inSection 4.1.2) that applies to the   request.  This is an identifier allocated by the service provider,   the Service Element manufacturer, or a standardization body, and MUST   uniquely identify a given Diameter Credit-Control service-specific   document.  The format of the Service-Context-Id is:   "service-context" "@" "domain"   service-context = Token   The Token is an arbitrary string of characters and digits.   "domain" represents the entity that allocated the Service-Context-Id.   It can be ietf.org, 3gpp.org, etc. if the identifier is allocated by   a standardization body, or it can be the Fully Qualified Domain Name   (FQDN) of the service provider (e.g., provider.example.com) or the   vendor (e.g., vendor.example.com) if the identifier is allocated by a   private entity.   This AVP SHOULD be placed as close to the Diameter header as   possible.Bertz, et al.                Standards Track                   [Page 81]

RFC 8506           Diameter Credit-Control Application        March 2019   Service-specific documents that are for private use only (i.e., for   one provider's own use, where no interoperability is deemed useful)   may define private identifiers without a need for coordination.   However, when interoperability is desired, coordination of the   identifiers via, for example, publication of an informational RFC is   RECOMMENDED in order to make the Service-Context-Id AVP globally   available.8.43.  Service-Parameter-Info AVP   The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and   contains service-specific information used for price calculation or   rating.  The Service-Parameter-Type AVP defines the service parameter   type, and the Service-Parameter-Value AVP contains the parameter   value.  The actual contents of these AVPs are not within the scope of   this document and SHOULD be defined in another Diameter application,   in standards written by other standardization bodies, or in service-   specific documentation.   In the case of an unknown service request (e.g., unknown Service-   Parameter-Type), the corresponding Answer message MUST contain the   error code DIAMETER_RATING_FAILED.  A Credit-Control-Answer message   with this error MUST contain one or more Failed-AVP AVPs containing   the Service-Parameter-Info AVPs that caused the failure.   The Service-Parameter-Info AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         Service-Parameter-Info ::= < AVP Header: 440 >                                    { Service-Parameter-Type }                                    { Service-Parameter-Value }8.44.  Service-Parameter-Type AVP   The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)   and defines the type of the service-event-specific parameter (e.g.,   it can be the end-user location or service name).  The different   parameters and their types are service specific, and the meanings of   these parameters are not defined in this document.  Whoever allocates   the Service-Context-Id (i.e., a unique identifier of a service-   specific document) is also responsible for assigning Service-   Parameter-Type values for the service and ensuring their uniqueness   within the given service.  The Service-Parameter-Value AVP contains   the value associated with the service parameter type.Bertz, et al.                Standards Track                   [Page 82]

RFC 8506           Diameter Credit-Control Application        March 20198.45.  Service-Parameter-Value AVP   The Service-Parameter-Value AVP is of type OctetString (AVP Code 442)   and contains the value of the service parameter type.8.46.  Subscription-Id AVP   The Subscription-Id AVP (AVP Code 443) is used to identify the   end user's subscription and is of type Grouped.  The Subscription-Id   AVP includes a Subscription-Id-Data AVP that holds the identifier and   a Subscription-Id-Type AVP that defines the identifier type.   The Subscription-Id AVP is defined as follows (per grouped-avp-def as   defined in [RFC6733]):         Subscription-Id ::= < AVP Header: 443 >                             { Subscription-Id-Type }                             { Subscription-Id-Data }8.47.  Subscription-Id-Type AVP   The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated,   and it is used to determine which type of identifier is carried by   the Subscription-Id AVP.   This specification defines the following subscription identifiers.   However, new Subscription-Id-Type values can be assigned by IANA as   defined inSection 12.  A server MUST implement all the Subscription-   Id-Type values required to perform credit authorization for the   services it supports, including possible future values.  Unknown or   unsupported Subscription-Id-Type values MUST be treated according to   the 'M' flag rule, as defined in [RFC6733].   END_USER_E164      0   The identifier is in international E.164 format (e.g., MSISDN),   according to the ITU-T E.164 numbering plan defined in [E164] and   [CE164].   END_USER_IMSI      1   The identifier is in IMSI format, according to the ITU-T E.212   identification plan as defined in [E212] and [CE212].   END_USER_SIP_URI   2   The identifier is in the form of a SIP URI, as defined in [RFC3261].Bertz, et al.                Standards Track                   [Page 83]

RFC 8506           Diameter Credit-Control Application        March 2019   END_USER_NAI       3   The identifier is in the form of a Network Access Identifier, as   defined in [RFC7542].   END_USER_PRIVATE   4   The identifier is a credit-control server private identifier.8.48.  Subscription-Id-Data AVP   The Subscription-Id-Data AVP (AVP Code 444) is used to identify the   end user and is of type UTF8String.  The Subscription-Id-Type AVP   defines which type of identifier is used.8.49.  User-Equipment-Info AVP   The User-Equipment-Info AVP (AVP Code 458) is of type Grouped and   allows the credit-control client to indicate the identity and   capability of the terminal the subscriber is using for the connection   to the network.   The User-Equipment-Info AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         User-Equipment-Info ::= < AVP Header: 458 >                                 { User-Equipment-Info-Type }                                 { User-Equipment-Info-Value }8.50.  User-Equipment-Info-Type AVP   The User-Equipment-Info-Type AVP is of type Enumerated (AVP Code 459)   and defines the type of user equipment information contained in the   User-Equipment-Info-Value AVP.   This specification defines the following user equipment types.   However, new User-Equipment-Info-Type values can be assigned by IANA   as defined inSection 12.   IMEISV           0   The identifier contains the International Mobile Equipment Identifier   and Software Version (IMEISV) in the IMEISV format according to 3GPP   TS 23.003 [TGPPIMEI].Bertz, et al.                Standards Track                   [Page 84]

RFC 8506           Diameter Credit-Control Application        March 2019   MAC              1   The 48-bit Media Access Control (MAC) address is formatted as   described inSection 3.21 of [RFC3580].   EUI64            2   The 64-bit identifier used to identify the hardware instance of the   product, as defined in [EUI64].   MODIFIED_EUI64   3   There are a number of types of terminals that have identifiers other   than the International Mobile Equipment Identifier (IMEI), IEEE 802   MACs, or EUI-64.  These identifiers can be converted to modified   EUI-64 format as described in [RFC4291] or by using some other   methods referred to in the service-specific documentation.8.51.  User-Equipment-Info-Value AVP   The User-Equipment-Info-Value AVP (AVP Code 460) is of type   OctetString.  The User-Equipment-Info-Type AVP defines which type of   identifier is used.8.52.  User-Equipment-Info-Extension AVP   The User-Equipment-Info-Extension AVP (AVP Code 653) is of type   Grouped and allows the credit-control client to indicate the identity   and capability of the terminal the subscriber is using for the   connection to the network.  If the type of the equipment is one of   the enumerated User-Equipment-Info-Type AVP values, then the   credit-control client SHOULD send the information in the   User-Equipment-Info AVP, in addition to or instead of the   User-Equipment-Info-Extension AVP.  This is done in order to preserve   backward compatibility with credit-control servers that support only   [RFC4006].  Exactly one AVP MUST be included inside the   User-Equipment-Info-Extension AVP.Bertz, et al.                Standards Track                   [Page 85]

RFC 8506           Diameter Credit-Control Application        March 2019   The User-Equipment-Info-Extension AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):    User-Equipment-Info-Extension ::= < AVP Header: 653 >                                  [ User-Equipment-Info-IMEISV ]                                  [ User-Equipment-Info-MAC ]                                  [ User-Equipment-Info-EUI64 ]                                  [ User-Equipment-Info-ModifiedEUI64 ]                                  [ User-Equipment-Info-IMEI ]                                  [ AVP ]8.53.  User-Equipment-Info-IMEISV AVP   The User-Equipment-Info-IMEISV AVP (AVP Code 654) is of type   OctetString.  The User-Equipment-Info-IMEISV AVP contains the   International Mobile Equipment Identifier and Software Version in the   IMEISV format according to 3GPP TS 23.003 [TGPPIMEI].8.54.  User-Equipment-Info-MAC AVP   The User-Equipment-Info-MAC AVP (AVP Code 655) is of type   OctetString.  The User-Equipment-Info-MAC AVP contains the 48-bit MAC   address; the MAC address is formatted as described inSection 4.1.7.8   of [RFC5777].8.55.  User-Equipment-Info-EUI64 AVP   The User-Equipment-Info-EUI64 AVP (AVP Code 656) is of type   OctetString.  The User-Equipment-Info-EUI64 AVP contains the 64-bit   identifier used to identify the hardware instance of the product, as   defined in [EUI64].8.56.  User-Equipment-Info-ModifiedEUI64 AVP   The User-Equipment-Info-ModifiedEUI64 AVP (AVP Code 657) is of type   OctetString.  There are a number of types of terminals that have   identifiers other than IMEI, IEEE 802 MACs, or EUI-64.  These   identifiers can be converted to modified EUI-64 format as described   in [RFC4291] or by using some other methods referred to in the   service-specific documentation.  The User-Equipment-Info-   ModifiedEUI64 AVP contains such identifiers.8.57.  User-Equipment-Info-IMEI AVP   The User-Equipment-Info-IMEI AVP (AVP Code 658) is of type   OctetString.  The User-Equipment-Info-IMEI AVP contains the   International Mobile Equipment Identifier in the IMEI format   according to 3GPP TS 23.003 [TGPPIMEI].Bertz, et al.                Standards Track                   [Page 86]

RFC 8506           Diameter Credit-Control Application        March 20198.58.  Subscription-Id-Extension AVP   The Subscription-Id-Extension AVP (AVP Code 659) is used to identify   the end user's subscription and is of type Grouped.  The   Subscription-Id-Extension group AVP MUST include an AVP holding the   subscription identifier.  The type of this included AVP indicates the   type of the subscription identifier.  For each of the enumerated   values of the Subscription-Id-Type AVP, there is a corresponding   sub-AVP for use within the Subscription-Id-Extension group AVP.  If a   new identifier type is required, a corresponding new sub-AVP SHOULD   be defined for use within the Subscription-Id-Extension group AVP.   If full backward compatibility with [RFC4006] is required, then the   Subscription-Id AVP MUST be used to indicate identifier types   enumerated in the Subscription-Id-Type AVP, whereas the Subscription-   Id-Extension AVP MUST be used only for newly defined identifier   types.  If full backward compatibility with [RFC4006] is not   required, then the Subscription-Id-Extension AVP MAY be used to carry   the existing identifier types.  In this case, the Subscription-Id-   Extension AVP MAY be sent together with the Subscription-Id AVP.   Exactly one sub-AVP MUST be included inside the Subscription-Id-   Extension AVP.   The Subscription-Id-Extension AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         Subscription-Id-Extension ::= < AVP Header: 659 >                                   [ Subscription-Id-E164 ]                                   [ Subscription-Id-IMSI ]                                   [ Subscription-Id-SIP-URI ]                                   [ Subscription-Id-NAI ]                                   [ Subscription-Id-Private ]                                   [ AVP ]8.59.  Subscription-Id-E164 AVP   The Subscription-Id-E164 AVP (AVP Code 660) is of type UTF8String.   The Subscription-Id-E164 AVP contains the international E.164 format   (e.g., MSISDN), according to the ITU-T E.164 numbering plan defined   in [E164] and [CE164].8.60.  Subscription-Id-IMSI AVP   The Subscription-Id-IMSI AVP (AVP Code 661) is of type UTF8String.   The Subscription-Id-IMSI AVP contains the IMSI format, according to   the ITU-T E.212 identification plan as defined in [E212] and [CE212].Bertz, et al.                Standards Track                   [Page 87]

RFC 8506           Diameter Credit-Control Application        March 20198.61.  Subscription-Id-SIP-URI AVP   The Subscription-Id-SIP-URI AVP (AVP Code 662) is of type UTF8String.   The Subscription-Id-SIP-URI AVP contains the identifier in the form   of a SIP URI, as defined in [RFC3261].8.62.  Subscription-Id-NAI AVP   The Subscription-Id-NAI AVP (AVP Code 663) is of type UTF8String.   The Subscription-Id-NAI AVP contains the identifier in the form of a   Network Access Identifier, as defined in [RFC7542].8.63.  Subscription-Id-Private AVP   The Subscription-Id-Private AVP (AVP Code 664) is of type UTF8String.   The Subscription-Id-Private AVP contains a credit-control server   private identifier.8.64.  Redirect-Server-Extension AVP   The Redirect-Server-Extension AVP (AVP Code 665) is of type Grouped   and contains the address information of the redirect server (e.g.,   HTTP redirect server, SIP Server) with which the end user is to be   connected when the account cannot cover the service cost.  It MUST be   present inside the QoS-Final-Unit-Indication AVP when the Final-Unit-   Action AVP is set to REDIRECT.  If the type of the redirect server is   one of the enumerated values of the Redirect-Address-Type AVP, then   the credit-control server SHOULD send the information in the   Redirect-Server AVP, in addition to or instead of the Redirect-   Server-Extension AVP.  This is done in order to preserve backward   compatibility with credit-control clients that support only   [RFC4006].  Exactly one AVP MUST be included inside the Redirect-   Server-Extension AVP.   The Redirect-Server-Extension AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):        Redirect-Server-Extension ::= < AVP Header: 665 >                                  [ Redirect-Address-IPAddress ]                                  [ Redirect-Address-URL ]                                  [ Redirect-Address-SIP-URI ]                                  [ AVP ]Bertz, et al.                Standards Track                   [Page 88]

RFC 8506           Diameter Credit-Control Application        March 20198.65.  Redirect-Address-IPAddress AVP   The Redirect-Address-IPAddress AVP (AVP Code 666) is of type Address   and defines the IPv4 or IPv6 address of the redirect server with   which the end user is to be connected when the account cannot cover   the service cost.   When encoded as an IPv6 address in 16 bytes, the IPv4-mapped IPv6   format [RFC4291] MAY be used to indicate an IPv4 address.   The interpretation of Redirect-Address-IPAddress by the Diameter   Credit-Control client is a matter of local policy.8.66.  Redirect-Address-URL AVP   The Redirect-Address-URL AVP (AVP Code 667) is of type UTF8String and   defines the address of the redirect server with which the end user is   to be connected when the account cannot cover the service cost.  The   address type is in the form of a Uniform Resource Locator, as defined   in [RFC3986].  Note that individual URL schemes may restrict the   contents of the UTF8String.8.67.  Redirect-Address-SIP-URI AVP   The Redirect-Address-SIP-URI AVP (AVP Code 668) is of type UTF8String   and defines the address of the redirect server with which the end   user is to be connected when the account cannot cover the service   cost.  The address type is in the form of a SIP Uniform Resource   Identifier, as defined in [RFC3261].8.68.  QoS-Final-Unit-Indication AVP   The QoS-Final-Unit-Indication AVP (AVP Code 669) 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 (seeSection 5.6).   If more than one unit type is received in the Credit-Control-Answer,   the unit type that first expired SHOULD cause the credit-control   client to execute the specified action.   In the first interrogation, the QoS-Final-Unit-Indication AVP with   Final-Unit-Action set to 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 that the client is to execute the specified actionBertz, et al.                Standards Track                   [Page 89]

RFC 8506           Diameter Credit-Control Application        March 2019   immediately.  If the home service provider policy is to terminate the   service, naturally, the server SHOULD return the appropriate   transient failure (seeSection 9.1) in order to implement the   policy-defined action.   The Final-Unit-Action AVP defines the behavior of the Service Element   when the user's account cannot cover the cost of the service and MUST   always be present if the QoS-Final-Unit-Indication AVP is included in   a command.   If the Final-Unit-Action AVP is set to TERMINATE, the QoS-Final-Unit-   Indication group AVP MUST NOT contain any other AVPs.   If the Final-Unit-Action AVP is set to REDIRECT, then the Redirect-   Server-Extension AVP MUST be present.  The Filter-Rule AVP or the   Filter-Id AVP MAY be present in the Credit-Control-Answer message if   the user is also allowed to access other services that are not   accessible through the address given in the Redirect-Server-Extension   AVP or if access to these services needs to be limited in some way   (e.g., QoS).   If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the   Filter-Rule AVP or the Filter-Id AVP SHOULD be present.   The Filter-Rule AVP is defined in [RFC5777].  The Filter-Rule AVP can   be used to define a specific combination of a condition and an   action.  If used only with traffic conditions, it should define which   traffic should be allowed when no more service units are granted.   However, if QoS or treatment information exists in the AVP, these   actions should be executed, e.g., limiting the allowed traffic with   certain QoS information.  When multiple Filter-Rule AVPs exist,   precedence should be determined as defined in [RFC5777].   The Filter-Id AVP is defined in [RFC7155].  The Filter-Id AVP can be   used to reference an IP filter list installed in the access device by   means other than the Diameter Credit-Control application, e.g.,   locally configured or configured by another entity.   If the Final-Unit-Action AVP is (1) set to TERMINATE, (2) set to   RESTRICT_ACCESS and the action required is to allow only traffic that   could be classified using an IPFilterRule, or (3) set to REDIRECT   using a type that is one of the types in the Redirect-Address-Type   AVP, then the credit-control server SHOULD send the information in   the Final-Unit-Indication AVP, in addition to or instead of the   QoS-Final-Unit-Indication AVP.  This is done in order to preserve   backward compatibility with credit-control clients that support only   [RFC4006].Bertz, et al.                Standards Track                   [Page 90]

RFC 8506           Diameter Credit-Control Application        March 2019   The QoS-Final-Unit-Indication AVP is defined as follows (per   grouped-avp-def as defined in [RFC6733]):         QoS-Final-Unit-Indication ::= < AVP Header: 669 >                                   { Final-Unit-Action }                                  *[ Filter-Rule ]                                  *[ Filter-Id ]                                   [ Redirect-Server-Extension ]                                  *[ AVP ]9.  Result-Code AVP Values   This section defines new Result-Code AVP [RFC6733] values that must   be supported by all Diameter implementations that conform to this   specification.   The Credit-Control-Answer message includes the Result-Code AVP, which   may indicate that an error was present in the Credit-Control-Request   message.  A rejected Credit-Control-Request message SHOULD cause the   user's session to be terminated.9.1.  Transient Failures   Errors that fall within the category of transient failures are used   to inform the peer that the request could not be satisfied at the   time it was received but that the request MAY be able to be satisfied   in the future.   DIAMETER_END_USER_SERVICE_DENIED         4010   The credit-control server denies the service request due to service   restrictions.  If the CCR contained used service units, they are   deducted, if possible.   DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE   4011   The credit-control server determines that the service can be granted   to the end user but that no further credit-control is needed for the   service (e.g., the service is free of charge).   DIAMETER_CREDIT_LIMIT_REACHED            4012   The credit-control server denies the service request because the   end user's account could not cover the requested service.  If the CCR   contained used service units, they are deducted, if possible.Bertz, et al.                Standards Track                   [Page 91]

RFC 8506           Diameter Credit-Control Application        March 20199.2.  Permanent Failures   Errors that fall within the category of permanent failures are used   to inform the peer that the request failed and should not be   attempted again.   DIAMETER_USER_UNKNOWN    5030   The specified end user is unknown in the credit-control server.   DIAMETER_RATING_FAILED   5031   This error code is used to inform the credit-control client that the   credit-control server cannot rate the service request due to   insufficient rating input, an incorrect AVP combination, or an AVP or   AVP value that is not recognized or supported in the rating.  The   Failed-AVP AVP MUST be included and contain (1) a copy of the entire   AVP or AVPs that could not be processed successfully or (2) an   example of the missing AVP, complete with the Vendor-Id if   applicable.  The value field of the missing AVP should be of correct   minimum length and contain zeros.10.  AVP Occurrence Table   The table inSection 10.1 presents the AVPs defined in this document   and specifies in which Diameter messages they MAY or MUST NOT be   present.  Note that AVPs that can only be present within a Grouped   AVP are not represented in the table.   The table uses the following symbols:         0     The AVP MUST NOT be present in the message.         0+    Zero or more instances of the AVP MAY be present in the               message.         0-1   Zero or one instance of the AVP MAY be present in the               message.  It is considered an error if there is more               than one instance of the AVP.         1     One instance of the AVP MUST be present in the message.Bertz, et al.                Standards Track                   [Page 92]

RFC 8506           Diameter Credit-Control Application        March 201910.1.  Credit-Control AVP Table   The table in this section is used to represent which credit-control   application-specific AVPs defined in this document are to be present   in the credit-control messages.                                             +-----------+                                             |  Command  |                                             |   Code    |                                             |-----+-----+           Attribute Name                    | CCR | CCA |           ----------------------------------|-----+-----+           Acct-Multi-Session-Id             | 0-1 | 0-1 |           Auth-Application-Id               | 1   | 1   |           CC-Correlation-Id                 | 0-1 | 0   |           CC-Session-Failover               | 0   | 0-1 |           CC-Request-Number                 | 1   | 1   |           CC-Request-Type                   | 1   | 1   |           CC-Sub-Session-Id                 | 0-1 | 0-1 |           Check-Balance-Result              | 0   | 0-1 |           Cost-Information                  | 0   | 0-1 |           Credit-Control-Failure-Handling   | 0   | 0-1 |           Destination-Host                  | 0-1 | 0   |           Destination-Realm                 | 1   | 0   |           Direct-Debiting-Failure-Handling  | 0   | 0-1 |           Event-Timestamp                   | 0-1 | 0-1 |           Failed-AVP                        | 0   | 0+  |           Final-Unit-Indication             | 0   | 0-1 |           QoS-Final-Unit-Indication         | 0   | 0-1 |           Granted-Service-Unit              | 0   | 0-1 |           Multiple-Services-Credit-Control  | 0+  | 0+  |           Multiple-Services-Indicator       | 0-1 | 0   |           Origin-Host                       | 1   | 1   |           Origin-Realm                      | 1   | 1   |           Origin-State-Id                   | 0-1 | 0-1 |           Proxy-Info                        | 0+  | 0+  |           Redirect-Host                     | 0   | 0+  |           Redirect-Host-Usage               | 0   | 0-1 |           Redirect-Max-Cache-Time           | 0   | 0-1 |           Requested-Action                  | 0-1 | 0   |           Requested-Service-Unit            | 0-1 | 0   |           Route-Record                      | 0+  | 0+  |           Result-Code                       | 0   | 1   |           Service-Context-Id                | 1   | 0   |           Service-Identifier                | 0-1 | 0   |           Service-Parameter-Info            | 0+  | 0   |           Session-Id                        | 1   | 1   |           Subscription-Id                   | 0+  | 0   |Bertz, et al.                Standards Track                   [Page 93]

RFC 8506           Diameter Credit-Control Application        March 2019           Subscription-Id-Extension         | 0+  | 0   |           Termination-Cause                 | 0-1 | 0   |           User-Equipment-Info               | 0-1 | 0   |           User-Equipment-Info-Extension     | 0-1 | 0   |           Used-Service-Unit                 | 0+  | 0   |           User-Name                         | 0-1 | 0-1 |           Validity-Time                     | 0   | 0-1 |           ----------------------------------|-----+-----+10.2.  Re-Auth-Request/Re-Auth-Answer AVP Table   This section defines AVPs that are specific to the Diameter   Credit-Control application and that MAY be included in the Diameter   Re-Auth-Request/Re-Auth-Answer (RAR/RAA) message [RFC6733].   The RAR/RAA command MAY include the following additional AVPs:                                          +---------------+                                          | Command Code  |                                          |-------+-------+            Attribute Name                |  RAR  |  RAA  |            ------------------------------+-------+-------+            CC-Sub-Session-Id             |  0-1  |  0-1  |            G-S-U-Pool-Identifier         |  0-1  |  0-1  |            Service-Identifier            |  0-1  |  0-1  |            Rating-Group                  |  0-1  |  0-1  |            ------------------------------+-------+-------+11.  RADIUS/Diameter Credit-Control Interworking Model   This section defines the basic principles for the Diameter   Credit-Control / RADIUS prepaid interworking model -- that is, a   message translation between a RADIUS-based prepaid solution and a   Diameter Credit-Control application.  A complete description of the   protocol translations between RADIUS and the Diameter Credit-Control   application is beyond the scope of this specification and SHOULD be   addressed in another appropriate document.   The Diameter Credit-Control architecture may have a Translation Agent   capable of translation between RADIUS prepaid and Diameter   Credit-Control protocols.  A AAA server (usually the home AAA server)   may act as a Translation Agent and as a Diameter Credit-Control   client for Service Elements that use credit-control mechanisms other   than Diameter Credit-Control -- for instance, RADIUS prepaid.  In   this case, the home AAA server contacts the Diameter Credit-Control   server as part of the authorization process.  The interworking   architecture is illustrated in Figure 9, and an interworking flow is   illustrated in Figure 10.  In a roaming situation, the ServiceBertz, et al.                Standards Track                   [Page 94]

RFC 8506           Diameter Credit-Control Application        March 2019   Element (e.g., the NAS) may be located in the visited network, and a   visited AAA server is usually contacted.  The visited AAA server then   connects to the home AAA server.                                  RADIUS Prepaid   +--------+       +---------+   Protocol +------------+  +--------+   |  End   |<----->| Service |<---------->| Home AAA   |  |Business|   |  User  |       | Element |            |  Server    |  |Support |   +--------+   +-->|         |            |+----------+|->|System  |                |   +---------+            ||CC Client ||  |        |                |                          |+----------+|  |        |   +--------+   |                          +------^-----+  +----^---+   |  End   |<--+                Credit-Control   |             |   |  User  |                          Protocol   |             |   +--------+                             +-------V--------+    |                                          |Credit-Control  |----+                                          |   Server       |                                          +----------------+        Figure 9: Credit-Control Architecture with Service Element         Containing Translation Agent, Translating RADIUS Prepaid                    to Diameter Credit-Control Protocol   When the AAA server acting as a Translation Agent receives an initial   RADIUS Access-Request message from a Service Element (e.g., NAS   access), it performs regular authentication and authorization.  If   the RADIUS Access-Request message indicates that the Service Element   is capable of credit-control and if the home AAA server finds that   the subscriber is a prepaid subscriber, then a Diameter   Credit-Control-Request SHOULD be sent toward the credit-control   server to perform credit authorization and to establish a   credit-control session.  After the Diameter Credit-Control server   checks the end user's account balance, rates the service, and   reserves credit from the end user's account, the reserved quota is   returned to the home AAA server in the Diameter Credit-Control-   Answer.  The home AAA server then sends the reserved quota to the   Service Element in the RADIUS Access-Accept.   At the expiry of the allocated quota, the Service Element sends a new   RADIUS Access-Request containing the units used thus far to the home   AAA server.  The home AAA server shall map a RADIUS Access-Request   containing the reported units to the Diameter Credit-Control server   in a Diameter Credit-Control-Request (UPDATE_REQUEST).  The Diameter   Credit-Control server debits the used units from the end user's   account and allocates a new quota that is returned to the home AAA   server in the Diameter Credit-Control-Answer.  The quota is   transferred to the Service Element in the RADIUS Access-Accept.  When   the end user terminates the service or when the entire quota has beenBertz, et al.                Standards Track                   [Page 95]

RFC 8506           Diameter Credit-Control Application        March 2019   used, the Service Element sends a RADIUS Access-Request.  To debit   the used units from the end user's account and to stop the   credit-control session, the home AAA server sends a Diameter   Credit-Control-Request (TERMINATION_REQUEST) to the credit-control   server.  The Diameter Credit-Control server acknowledges the session   termination by sending a Diameter Credit-Control-Answer to the home   AAA server.  The RADIUS Access-Accept is sent to the NAS.   Figure 10 illustrates a Diameter Credit-Control / RADIUS prepaid   interworking sequence.   Service Element         Translation Agent     (e.g., NAS)               (CC Client)             CC Server         |     Access-Request     |                        |         |----------------------->|                        |         |                        |    CCR (Initial)       |         |                        |----------------------->|         |                        |    CCA (Granted-Units) |         |                        |<-----------------------|         |     Access-Accept      |                        |         |     (Granted-Units)    |                        |         |<-----------------------|                        |         :                        :                        :         |     Access-Request     |                        |         |     (Used-Units)       |                        |         |----------------------->|                        |         |                        |    CCR (Update,        |         |                        |         Used-Units)    |         |                        |----------------------->|         |                        |    CCA (Granted-Units) |         |                        |<-----------------------|         |     Access-Accept      |                        |         |     (Granted-Units)    |                        |         |<-----------------------|                        |         :                        :                        :         |     Access-Request     |                        |         |----------------------->|                        |         |                        |     CCR (Terminate,    |         |                        |          Used-Units)   |         |                        |----------------------->|         |                        |     CCA                |         |                        |<-----------------------|         |     Access-Accept      |                        |         |<-----------------------|                        |         |                        |                        |               Figure 10: Message Flow Example with Diameter               Credit-Control / RADIUS Prepaid InterworkingBertz, et al.                Standards Track                   [Page 96]

RFC 8506           Diameter Credit-Control Application        March 201912.  IANA Considerations   This document uses several registries that were originally created in   [RFC4006] or the values assigned to existing namespaces managed by   IANA.  IANA has updated these registries to reference this document.   The registries and their allocation policies are specified below.12.1.  Application Identifier   This specification assigns the value 4, "Diameter Credit Control", to   the "Application IDs" namespace defined in [RFC6733].  SeeSection 1.3 for more information.12.2.  Command Codes   This specification uses the value 272 from the "Command Codes"   namespace defined in [RFC6733] for the Credit-Control-Request (CCR)   and Credit-Control-Answer (CCA) commands.12.3.  AVP Codes   SeeSection 8 for the assignments in this specification.   This document describes new AVP codes beyond those described in   [RFC4006].  IANA has allocated codes for the AVPs listed in Table 7.Bertz, et al.                Standards Track                   [Page 97]

RFC 8506           Diameter Credit-Control Application        March 2019        +-----------------------------------+------+--------------+        | Attribute Name                    | Code | Defined in   |        +-----------------------------------+------+--------------+        | User-Equipment-Info-Extension     | 653  |Section 8.52 |        | User-Equipment-Info-IMEISV        | 654  |Section 8.53 |        | User-Equipment-Info-MAC           | 655  |Section 8.54 |        | User-Equipment-Info-EUI64         | 656  |Section 8.55 |        | User-Equipment-Info-ModifiedEUI64 | 657  |Section 8.56 |        | User-Equipment-Info-IMEI          | 658  |Section 8.57 |        | Subscription-Id-Extension         | 659  |Section 8.58 |        | Subscription-Id-E164              | 660  |Section 8.59 |        | Subscription-Id-IMSI              | 661  |Section 8.60 |        | Subscription-Id-SIP-URI           | 662  |Section 8.61 |        | Subscription-Id-NAI               | 663  |Section 8.62 |        | Subscription-Id-Private           | 664  |Section 8.63 |        | Redirect-Server-Extension         | 665  |Section 8.64 |        | Redirect-Address-IPAddress        | 666  |Section 8.65 |        | Redirect-Address-URL              | 667  |Section 8.66 |        | Redirect-Address-SIP-URI          | 668  |Section 8.67 |        | QoS-Final-Unit-Indication         | 669  |Section 8.68 |        +-----------------------------------+------+--------------+                    Table 7: Requested AVP Assignments12.4.  Result-Code AVP Values   This specification assigns the values 4010, 4011, and 4012 in the   "Result-Code AVP Values (code 268) - Transient Failures" namespace   and values 5030 and 5031 in the "Result-Code AVP Values (code 268) -   Permanent Failure" namespace, both of which were defined by   [RFC6733].  SeeSection 9 for the assignments in this specification.12.5.  CC-Request-Type AVP   As defined inSection 8.3, the CC-Request-Type AVP includes   Enumerated type values 1-4.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.6.  CC-Session-Failover AVP   As defined inSection 8.4, the CC-Session-Failover AVP includes   Enumerated type values 0-1.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.Bertz, et al.                Standards Track                   [Page 98]

RFC 8506           Diameter Credit-Control Application        March 201912.7.  CC-Unit-Type AVP   As defined inSection 8.32, the CC-Unit-Type AVP includes Enumerated   type values 0-5.  IANA has created and is maintaining a namespace for   this AVP.  The definition of new values is subject to the   Specification Required policy [RFC8126] and conditions for enumerated   values described in[RFC7423], Section 5.6.12.8.  Check-Balance-Result AVP   As defined inSection 8.6, the Check-Balance-Result AVP includes   Enumerated type values 0-1.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.9.  Credit-Control AVP   As defined inSection 8.13, the Credit-Control AVP includes   Enumerated type values 0-1.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.10.  Credit-Control-Failure-Handling AVP   As defined inSection 8.14, the Credit-Control-Failure-Handling AVP   includes Enumerated type values 0-2.  IANA has created and is   maintaining a namespace for this AVP.  The definition of new values   is subject to the Specification Required policy [RFC8126] and   conditions for enumerated values described in[RFC7423], Section 5.6.12.11.  Direct-Debiting-Failure-Handling AVP   As defined inSection 8.15, the Direct-Debiting-Failure-Handling AVP   includes Enumerated type values 0-1.  IANA has created and is   maintaining a namespace for this AVP.  The definition of new values   is subject to the Specification Required policy [RFC8126] and   conditions for enumerated values described in[RFC7423], Section 5.6.12.12.  Final-Unit-Action AVP   As defined inSection 8.35, the Final-Unit-Action AVP includes   Enumerated type values 0-2.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.Bertz, et al.                Standards Track                   [Page 99]

RFC 8506           Diameter Credit-Control Application        March 201912.13.  Multiple-Services-Indicator AVP   As defined inSection 8.40, the Multiple-Services-Indicator AVP   includes Enumerated type values 0-1.  IANA has created and is   maintaining a namespace for this AVP.  The definition of new values   is subject to the Specification Required policy [RFC8126] and   conditions for enumerated values described in[RFC7423], Section 5.6.12.14.  Redirect-Address-Type AVP   As defined inSection 8.38, the Redirect-Address-Type AVP includes   Enumerated type values 0-3.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.15.  Requested-Action AVP   As defined inSection 8.41, the Requested-Action AVP includes   Enumerated type values 0-3.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.16.  Subscription-Id-Type AVP   As defined inSection 8.47, the Subscription-Id-Type AVP includes   Enumerated type values 0-4.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.17.  Tariff-Change-Usage AVP   As defined inSection 8.27, the Tariff-Change-Usage AVP includes   Enumerated type values 0-2.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.12.18.  User-Equipment-Info-Type AVP   As defined inSection 8.50, the User-Equipment-Info-Type AVP includes   Enumerated type values 0-3.  IANA has created and is maintaining a   namespace for this AVP.  The definition of new values is subject to   the Specification Required policy [RFC8126] and conditions for   enumerated values described in[RFC7423], Section 5.6.Bertz, et al.                Standards Track                  [Page 100]

RFC 8506           Diameter Credit-Control Application        March 201913.  Parameters Related to the Credit-Control Application   Tx timer      When real-time credit-control is required, the credit-control      client contacts the credit-control server before and while the      service is provided to an end user.  Due to the real-time nature      of the application, communication delays SHOULD be minimized,      e.g., to avoid an overly long service setup time experienced by      the end user.  The Tx timer is introduced to control the waiting      time in the client in the Pending state.  When the Tx timer      elapses, the credit-control client takes action for the end user      according to the value of the CCFH or the DDFH.  The recommended      value is 10 seconds.   Tcc timer      The Tcc timer supervises an ongoing credit-control session in the      credit-control server.  It is RECOMMENDED to use the Validity-Time      as input to set the Tcc timer value.  In the case of transient      failures in the network, the Diameter Credit-Control server might      change to Idle state.  To avoid this, the Tcc timer MAY be set so      that Tcc is equal to 2 x Validity-Time.   Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling      Client implementations may offer the possibility of locally      configuring these AVPs.  In such a case, their values and behavior      are defined in Sections5.7 and6.5, respectively.14.  Security Considerations   Security considerations regarding the Diameter protocol itself are   discussed in [RFC6733].  The use of this application of Diameter MUST   take into consideration the security issues and requirements of the   base protocol.   This application includes a mechanism for application-layer replay   protection by means of (1) the Session-Id AVP as specified in   [RFC6733] and (2) the CC-Request-Number AVP, which is specified in   this document.  The Diameter Credit-Control application is often used   within one domain, and there may be a single hop between the peers.   In these environments, the use of TLS/TCP, DTLS/SCTP (Datagram   Transport Layer Security / Stream Control Transmission Protocol), or   IPsec is sufficient.  The details of security considerations related   to TLS/TCP, DTLS/SCTP, and IPsec are discussed in [RFC6733].Bertz, et al.                Standards Track                  [Page 101]

RFC 8506           Diameter Credit-Control Application        March 2019   Because this application handles monetary transactions (directly or   indirectly), it increases interest in various security attacks.   Therefore, all parties communicating with each other MUST be   authenticated, including, for instance, TLS client-side   authentication.  In addition, authorization of the client SHOULD be   emphasized, i.e., that the client is allowed to perform   credit-control for a certain user.  The specific means of   authorization are outside the scope of this specification but can be,   for instance, manual configuration.   Another kind of threat is malicious modification, injection, or   deletion of AVPs or complete credit-control messages.  The   credit-control messages contain sensitive billing-related information   (such as subscription identifiers, granted units, used units, or cost   information) whose malicious modification can have financial   consequences.  Sometimes simply delaying the credit-control messages   can cause disturbances in the credit-control client or server.   Even without any modifications to the messages, an adversary that can   eavesdrop on transactions can obtain privacy-sensitive information.   Also, by monitoring the credit-control messages, one can collect   information about the credit-control server's billing models and   business relationships.   When third-party relays or proxies are involved, hop-by-hop security   does not necessarily provide sufficient protection for Diameter user   sessions.  In some cases, it may be inappropriate to send Diameter   messages, such as CCR messages and CCA messages, containing sensitive   AVPs via untrusted Diameter proxy agents, as there are no assurances   that third-party proxies will not modify the credit-control commands   or AVP values.14.1.  Direct Connection with Redirects   A Diameter Credit-Control agent cannot always know whether agents   between it and the end user's Diameter Credit-Control server are   reliable.  In this case, the Diameter Credit-Control agent doesn't   have a routing entry in its Diameter routing table (defined in[RFC6733], Section 2.7) for the realm of the credit-control server in   the end user's home realm.  The Diameter Credit-Control agent can   have a default route configured to a local redirect agent, and it   redirects the CCR message to the redirect agent.  The local redirect   agent then returns a redirect notification (Result-Code 3006,   DIAMETER_REDIRECT_INDICATION) to the credit-control agent, as well as   information about the Diameter Credit-Control server(s) (Redirect-   Host AVP) and information about how the routing entry resulting from   the Redirect-Host is to be used (Redirect-Host-Usage AVP).  The   Diameter Credit-Control agent then forwards the CCR message directlyBertz, et al.                Standards Track                  [Page 102]

RFC 8506           Diameter Credit-Control Application        March 2019   to one of the hosts identified by the CCA message from the redirect   agent.  If the value of the Redirect-Host-Usage AVP does not equal   zero, all subsequent messages are sent to the host specified in the   Redirect-Host AVP until the time specified by the Redirect-Max-Cache-   Time AVP has expired.   Even with redirects, there are some authorization issues.  There may   be attacks toward nodes that have been properly authorized but that   abuse their authorization or have been compromised.  These issues are   discussed more widely in[RFC4072], Section 8.14.2.  Application-Level Redirects   This document includes a redirection feature (Section 5.6.2) whereby   the service provider can redirect (in an application-specific way)   the end user to an alternate location when their credits have   expired.  This technique is useful in that it allows the user to   return to normal service quickly, but it also exposes additional   risks and attack surface.  In particular, this redirection can   potentially occur at an arbitrary point in a user's session,   potentially without any additional contextual confirmation available   to the user that the redirection is driven by the network.  This lack   of confirmation matters because, in many application protocols, the   communication peer is also capable of inducing redirection.  When the   peer is an attacker, the redirection can be to an attacker-controlled   site.  In particular, such sites may be "phishing" sites designed to   appear similar to legitimate payment sites in an attempt to obtain   users' payment information for fraudulent purposes.  When users   become accustomed to such redirections, they may have difficulty   distinguishing such attacks from legitimate redirections.   Because of the potentially harmful consequences of arbitrary   redirection by an attacker (such as to phishing sites), it is   important for service providers to be aware of that risk and ensure   that their users are aware of it as well.  Service providers should   follow industry best practices for the specific application-layer   protocol to reduce the chances that such attacks could be mistaken   for legitimate redirections.  The details of such a practice are out   of scope for this document.Bertz, et al.                Standards Track                  [Page 103]

RFC 8506           Diameter Credit-Control Application        March 201915.  Privacy Considerations   As the Diameter protocol, and especially the credit-control   application, deal with subscribers and their actions, extra care   should be taken regarding the privacy of the subscribers.  Per   terminology used in [RFC6973], both the credit-control client and the   credit-control server are intermediary entities, wherein the   subscribers' privacy may be compromised even if no security issues   exist, and only authorized entities have access to the privacy-   sensitive information.15.1.  Privacy-Sensitive AVPs   The privacy-sensitive AVPs listed in this section MUST NOT be sent   across non-trusted networks or Diameter agents without end-to-end   authentication and confidentiality protection, as described in[RFC6733], Section 13.3.   The following AVPs contain privacy-sensitive information at different   levels:   1.   CC-Correlation-Id AVP: may contain privacy-sensitive        information, as the service provider may encode personal        information that helps it correlate different subscriptions and        access technologies.   2.   Check-Balance-Result AVP: contains information on the balance        status of the subscriber.   3.   Currency-Code AVP: contains information on the subscriber's        locale.   4.   Cost-Unit AVP: contains privacy-sensitive information for the        Cost-Information AVP, in human-readable format.   5.   Service-Identifier AVP: may contain privacy-sensitive        information about the subscriber's Internet activity.   6.   Rating-Group AVP: may contain privacy-sensitive information        about the subscriber's Internet activity.   7.   Restriction-Filter-Rule AVP: the information inside IPFilterRule        may be used to infer services used by the subscriber.Bertz, et al.                Standards Track                  [Page 104]

RFC 8506           Diameter Credit-Control Application        March 2019   8.   Redirect-Server-Address AVP: the service provider might embed        personal information on the subscriber in the URL/URI (e.g., to        create a personalized message).  However, the service provider        may instead anonymize the subscriber's identity in the URL/URI        and let the redirect server query the information directly.        Such anonymized information must not allow personal information        or the subscriber's identity to be easily guessed.  Furthermore,        the service provider should treat the URL/URI schema itself as        confidential and make sure it cannot be inferred (1) from        observation of the traffic or (2) due to its trivial structure.        A trivial structure could allow an adversary to query/modify        personal information even without knowing the subscriber's        identity.  Similar AVPs are Redirect-Address-URL and Redirect-        Address-SIP-URI.   9.   Service-Context-Id AVP: depending on how the service provider        uses it, it may contain privacy-sensitive information about the        service (e.g., in a 3GPP network Service-Context-Id AVP, it has        a different value for packet switching, SMS, Multimedia Messages        (MMSs), etc.).   10.  Service-Parameter-Info AVP: depending on how the service        provider uses it, it may contain privacy-sensitive information        about the subscriber (e.g., location).   11.  Subscription-Id-Data AVP: contains the identity of the        subscriber.  Similar AVPs are Subscription-Id-E164,        Subscription-Id-IMSI, Subscription-Id-SIP-URI, Subscription-Id-        NAI, and Subscription-Id-Private.   12.  User-Equipment-Info-Value AVP: contains the identity of the        device of the subscriber.  Similar AVPs are User-Equipment-Info-        IMEISV, User-Equipment-Info-MAC, User-Equipment-Info-EUI64,        User-Equipment-Info-ModifiedEUI64, and User-Equipment-Info-IMEI.   13.  QoS-Final-Unit-Indication AVP: Grouped AVP that may contain        privacy-sensitive information in its sub-AVPs (e.g.,        IPFilterRule, redirect address).   Note that some AVPs that are used in this document are defined in   [RFC6733] and may contain privacy-sensitive information.  These AVPs   are not listed above.Bertz, et al.                Standards Track                  [Page 105]

RFC 8506           Diameter Credit-Control Application        March 201915.2.  Data Minimization   Due to the nature of the credit-control application, some personal   data and identity information must be stored in both the   credit-control client and the credit-control server.  However, this   could be minimized by following these guidelines:   1.  Data stored in the credit-control client does not need to persist       across sessions.  All data could be deleted once the session ends       and could be reconstructed once a new session is initialized.       Note that while the credit-control server is usually owned by the       service provider with which the subscriber already has some       direct legal or business relationship (where the privacy level       could be agreed upon), this is not always true for a       credit-control client that may be owned by a third party.   2.  Some information about the subscriber has to be stored in       persistent storage in the credit-control server (e.g., identity,       balance); however, per-transaction information does not have to       be stored in persistent storage, and per-session information may       be deleted from persistent storage once the session ends.   3.  In some cases, per-transaction information has to be stored on       the credit-control server, client, or both, for regulatory,       auditability, or debugging reasons.  However, this could be       minimized by following these guidelines:       A.  Data retention does not need to exceed the required duration.       B.  Transaction information could be aggregated in some cases           (e.g., prefer information per session over information per           rating-group; prefer hourly byte summary over per-transaction           byte counts).       C.  If not strictly needed, information that is more sensitive           (e.g., location, equipment type) could be filtered out of           such logs.  This information is often used to make rating           decisions, and in this case, the rating decisions should be           logged instead of the data used to make them.       D.  Due to the reasons explained in the first guideline, the           credit-control server, rather than the credit-control client,           would be the preferred location for storing such transaction           information.Bertz, et al.                Standards Track                  [Page 106]

RFC 8506           Diameter Credit-Control Application        March 201915.3.  Diameter Agents   Diameter agents, as described in [RFC6733], may be owned by   third parties.  If end-to-end security is supported between the   credit-control client and the credit-control server, the operator can   use it to encrypt privacy-sensitive AVPs (as listed inSection 15.1)   and prevent such information from leaking into the agent.   In some cases, the Diameter agent needs access to privacy-sensitive   AVPs, in order to make correct routing decisions or even to modify   the content of these AVPs.  For example, a proxy agent may need to   look at the Subscription-Id-IMSI AVP, in order to extract the mobile   country and network codes of the user and use them to look up the   destination to which the request should be routed (seeSection 2.8.2   in [RFC6733]).  In such a case, the credit-control client and   credit-control server may use a mechanism that anonymizes the   identity of the subscriber, as well as a mechanism to encrypt other   AVPs not used by the agent.16.  References16.1.  Normative References   [CE164]    International Telecommunication Union, "COMPLEMENT TO              ITU-T RECOMMENDATION E.164 (11/2010): LIST OF ITU-T              RECOMMENDATION E.164 ASSIGNED COUNTRY CODES",              November 2011, <https://www.itu.int/dms_pub/itu-t/opb/sp/T-SP-E.164D-11-2011-PDF-E.pdf>.   [CE212]    International Telecommunication Union, "COMPLEMENT TO              RECOMMENDATION ITU-T E.212 (09/2016): LIST OF MOBILE              COUNTRY OR GEOGRAPHICAL AREA CODES", February 2017,              <https://www.itu.int/dms_pub/itu-t/opb/sp/T-SP-E.212A-2017-PDF-E.pdf>.   [E164]     International Telecommunication Union, "The international              public telecommunication numbering plan", ITU-T              Recommendation E.164, November 2010,              <https://www.itu.int/rec/T-REC-E.164/>.   [E212]     International Telecommunication Union, "The international              identification plan for public networks and              subscriptions", ITU-T Recommendation E.212,              September 2016, <https://www.itu.int/rec/T-REC-E.212/en>.Bertz, et al.                Standards Track                  [Page 107]

RFC 8506           Diameter Credit-Control Application        March 2019   [EUI64]    IEEE, "Guidelines for Use of Extended Unique Identifier              (EUI), Organizationally Unique Identifier (OUI), and              Company ID (CID)", August 2017,              <https://standards.ieee.org/content/dam/ieee-standards/standards/web/documents/tutorials/eui.pdf>.   [ISO4217]  ISO, "Codes for the representation of currencies",              ISO 4217:2015, 2015, <https://www.iso.org/iso-4217-currency-codes.html>.   [RFC791]   Postel, J., "Internet Protocol", STD 5,RFC 791,              DOI 10.17487/RFC0791, September 1981,              <https://www.rfc-editor.org/info/rfc791>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,              A., Peterson, J., Sparks, R., Handley, M., and E.              Schooler, "SIP: Session Initiation Protocol",RFC 3261,              DOI 10.17487/RFC3261, June 2002,              <https://www.rfc-editor.org/info/rfc3261>.   [RFC3539]  Aboba, B. and J. Wood, "Authentication, Authorization and              Accounting (AAA) Transport Profile",RFC 3539,              DOI 10.17487/RFC3539, June 2003,              <https://www.rfc-editor.org/info/rfc3539>.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC 3986, DOI 10.17487/RFC3986, January 2005,              <https://www.rfc-editor.org/info/rfc3986>.   [RFC4006]  Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and              J. Loughney, "Diameter Credit-Control Application",RFC 4006, DOI 10.17487/RFC4006, August 2005,              <https://www.rfc-editor.org/info/rfc4006>.   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing              Architecture",RFC 4291, DOI 10.17487/RFC4291,              February 2006, <https://www.rfc-editor.org/info/rfc4291>.Bertz, et al.                Standards Track                  [Page 108]

RFC 8506           Diameter Credit-Control Application        March 2019   [RFC5777]  Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,              Ed., and A. Lior, "Traffic Classification and Quality of              Service (QoS) Attributes for Diameter",RFC 5777,              DOI 10.17487/RFC5777, February 2010,              <https://www.rfc-editor.org/info/rfc5777>.   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6              Address Text Representation",RFC 5952,              DOI 10.17487/RFC5952, August 2010,              <https://www.rfc-editor.org/info/rfc5952>.   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,              Ed., "Diameter Base Protocol",RFC 6733,              DOI 10.17487/RFC6733, October 2012,              <https://www.rfc-editor.org/info/rfc6733>.   [RFC7155]  Zorn, G., Ed., "Diameter Network Access Server              Application",RFC 7155, DOI 10.17487/RFC7155, April 2014,              <https://www.rfc-editor.org/info/rfc7155>.   [RFC7423]  Morand, L., Ed., Fajardo, V., and H. Tschofenig, "Diameter              Applications Design Guidelines",BCP 193,RFC 7423,              DOI 10.17487/RFC7423, November 2014,              <https://www.rfc-editor.org/info/rfc7423>.   [RFC7542]  DeKok, A., "The Network Access Identifier",RFC 7542,              DOI 10.17487/RFC7542, May 2015,              <https://www.rfc-editor.org/info/rfc7542>.   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for              Writing an IANA Considerations Section in RFCs",BCP 26,RFC 8126, DOI 10.17487/RFC8126, June 2017,              <https://www.rfc-editor.org/info/rfc8126>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC 2119 Key Words",BCP 14,RFC 8174,              DOI 10.17487/RFC8174, May 2017,              <https://www.rfc-editor.org/info/rfc8174>.   [TGPPIMEI] 3rd Generation Partnership Project, Technical              Specification Group Core Network, "Numbering, addressing              and identification (release 15)", 3GPP TS 23.003              version 15.6.0, December 2018.Bertz, et al.                Standards Track                  [Page 109]

RFC 8506           Diameter Credit-Control Application        March 201916.2.  Informative References   [RFC2866]  Rigney, C., "RADIUS Accounting",RFC 2866,              DOI 10.17487/RFC2866, June 2000,              <https://www.rfc-editor.org/info/rfc2866>.   [RFC3580]  Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,              "IEEE 802.1X Remote Authentication Dial In User Service              (RADIUS) Usage Guidelines",RFC 3580,              DOI 10.17487/RFC3580, September 2003,              <https://www.rfc-editor.org/info/rfc3580>.   [RFC3725]  Rosenberg, J., Peterson, J., Schulzrinne, H., and              G. Camarillo, "Best Current Practices for Third Party Call              Control (3pcc) in the Session Initiation Protocol (SIP)",BCP 85,RFC 3725, DOI 10.17487/RFC3725, April 2004,              <https://www.rfc-editor.org/info/rfc3725>.   [RFC4004]  Calhoun, P., Johansson, T., Perkins, C., Hiller, T., Ed.,              and P. McCann, "Diameter Mobile IPv4 Application",RFC 4004, DOI 10.17487/RFC4004, August 2005,              <https://www.rfc-editor.org/info/rfc4004>.   [RFC4072]  Eronen, P., Ed., Hiller, T., and G. Zorn, "Diameter              Extensible Authentication Protocol (EAP) Application",RFC 4072, DOI 10.17487/RFC4072, August 2005,              <https://www.rfc-editor.org/info/rfc4072>.   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,              Morris, J., Hansen, M., and R. Smith, "Privacy              Considerations for Internet Protocols",RFC 6973,              DOI 10.17487/RFC6973, July 2013,              <https://www.rfc-editor.org/info/rfc6973>.   [TGPPCHARG]              3rd Generation Partnership Project, Technical              Specification Group Services and System Aspects, "Service              aspects; Charging and Billing", 3GPP TS 22.115              version 15.5.0, September 2018.Bertz, et al.                Standards Track                  [Page 110]

RFC 8506           Diameter Credit-Control Application        March 2019Appendix A.  Credit-Control SequencesA.1.  Flow I   A credit-control flow for Network Access Services prepaid is shown in   Figure 11.  The Diameter protocol application is implemented in the   Network Access Server (NAS) per [RFC7155].  The focus of this flow is   on credit authorization.                           NAS   End User          (CC Client)          AAA Server           CC Server     |(1)User Logon      |(2)AA-Request (CC AVPs)                    |     |------------------>|-------------------->|                     |     |                   |                     |(3)CCR(Initial, CC AVPs)     |                   |                     |-------------------->|     |                   |                     |(4)CCA(Granted-Units)|     |                   |                     |<--------------------|     |                   |(5)AA-Answer(Granted-Units)                |     |(6)Access granted  |<--------------------|                     |     |<----------------->|                     |                     |     |                   |                     |                     |     :                   :                     :                     :     |                   |(7)CCR(Update, Used-Units)                 |     |                   |-------------------->|(8)CCR               |     |                   |                     |   (Update, Used-Units)     |                   |                     |-------------------->|     |                   |                     |(9)CCA(Granted-Units)|     |                   |(10)CCA(Granted-Units)<--------------------|     |                   |<--------------------|                     |     :                   :                     :                     :     |         (Auth. lifetime expires)        |                     |     |                   |(11)AAR (CC AVP)     |                     |     |                   |-------------------->|                     |     |                   |            (12)AAA  |                     |     |                   |<--------------------|                     |     :                   :                     :                     :     :                   :                     :                     :Bertz, et al.                Standards Track                  [Page 111]

RFC 8506           Diameter Credit-Control Application        March 2019     |(13)User logoff    |                     |                     |     |------------------>|(14)CCR(Term., Used-Units)                 |     |                   |-------------------->|(15)CCR              |     |                   |                     |   (Term., Used-Units)     |                   |                     |-------------------->|     |                   |                     |             (16)CCA |     |                   |            (17)CCA  |<--------------------|     |                   |<--------------------|                     |     |                   |(18)STR              |                     |     |                   |-------------------->|                     |     |                   |             (19)STA |                     |     |                   |<--------------------|                     |                             Figure 11: Flow I   The user logs on to the network (1).  The Diameter NAS sends a   Diameter AA-Request (AAR) to the home Diameter AAA server (2).  The   credit-control client populates the AAR with the Credit-Control AVP   set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,   as usual [RFC7155].  The home Diameter AAA server performs service-   specific authentication and authorization, as usual.  The home   Diameter AAA server determines that the user is a prepaid user and   notices from the Credit-Control AVP that the NAS has credit-control   capabilities.  It sends a Diameter Credit-Control-Request with   CC-Request-Type set to INITIAL_REQUEST to the Diameter Credit-Control   server to perform credit authorization (3) and to establish a   credit-control session.  (The home Diameter AAA server may forward   service-specific AVPs received from the NAS as input for the rating   process.)  The Diameter Credit-Control server checks the end user's   account balance, rates the service, and reserves credit from the   end user's account.  The reserved quota is returned to the home   Diameter AAA server in the Diameter Credit-Control-Answer (4).  The   home Diameter AAA server sends the reserved quota to the NAS in the   Diameter AA-Answer (AAA).  Upon receiving the AA-Answer, the NAS   starts the credit-control session and starts monitoring the granted   units (5).  The NAS grants access to the end user (6).  At the expiry   of the allocated quota, the NAS sends a Diameter Credit-Control-   Request with CC-Request-Type set to UPDATE_REQUEST to the home   Diameter AAA server (7).  This message contains the units used thus   far.  The home Diameter AAA server forwards the CCR to the Diameter   Credit-Control server (8).  The Diameter Credit-Control server debits   the used units from the end user's account and allocates a new quota   that is returned to the home Diameter AAA server in the Diameter   Credit-Control-Answer (9).  The message is forwarded to the NAS (10).   During the ongoing credit-control session, the authorization lifetime   expires, and the authorization/authentication client in the NAS   performs service-specific re-authorization to the home Diameter AAA   server, as usual.  The credit-control client populates the AAR withBertz, et al.                Standards Track                  [Page 112]

RFC 8506           Diameter Credit-Control Application        March 2019   the Credit-Control AVP set to RE_AUTHORIZATION, indicating that the   credit-control server shall not be contacted, as the credit   authorization is controlled by the burning rate of the granted units   (11).  The home Diameter AAA server performs service-specific   re-authorization as usual and returns the AA-Answer to the NAS (12).   The end user logs off from the network (13).  To debit the used units   from the end user's account and to stop the credit-control session,   the NAS sends a Diameter Credit-Control-Request with CC-Request-Type   set to TERMINATION_REQUEST to the home Diameter AAA server (14).  The   home Diameter AAA server forwards the CCR to the credit-control   server (15).  The Diameter Credit-Control server acknowledges the   session termination by sending a Diameter Credit-Control-Answer to   the home Diameter AAA server (16).  The home Diameter AAA server   forwards the answer to the NAS (17).  The STR/STA takes place between   the NAS and home Diameter AAA server, as usual (18), (19).A.2.  Flow II   Figure 12 provides an example of Diameter Credit-Control for SIP   sessions.  Although the flow focuses on illustrating the usage of   credit-control messages, the SIP signaling is inaccurate, and the   diagram is not by any means an attempt to define a service provider's   SIP network.  However, for the sake of this example, some assumptions   are made below.Bertz, et al.                Standards Track                  [Page 113]

RFC 8506           Diameter Credit-Control Application        March 2019         SIP Proxy/Registrar   AAA   A           (CC Client)     Server           B        CC Server   | (i) REGISTER |              |              |              |   |------------->|(ii)          |              |              |   |              |------------->|              |              |   |              |authentication &             |              |   |              |authorization |              |              |   |              |<-------------|              |              |   |(iii) 200 OK  |                             |              |   |<-------------|                             |              |   :              :                             :              :   |(1)  INVITE   |                                            :   |------------->|   |              |(2)  CCR (Initial, SIP-specific AVP)        |   |              |------------------------------------------->|   |              |(3)  CCA (Granted-Units)                    |   |              |<-------------------------------------------|   |              |(4)  INVITE                  |              |   |              |---------------------------->|              |   :              :                             :              :   |              |(5)  CCR (Update, Used-Units)               |   |              |------------------------------------------->|   |              |(6)  CCA (Granted-Units)                    |   |              |<-------------------------------------------|   :              :                             :              :   |(7)  BYE      |                             |              |   |------------->|                             |              |   |              |(8)  BYE                     |              |   |              |---------------------------->|              |   |              |(9)  CCR (Termination, Used-Units)          |   |              |------------------------------------------->|   |              |(10) CCA ()                                 |   |              |<-------------------------------------------|   |              |                             |              |                            Figure 12: Flow II   Typically, prepaid services based, for example, on time usage for SIP   sessions require an entity in the service provider network to   intercept all the requests within the SIP dialog in order to detect   events, such as session establishment and session release, that are   essential for performing credit-control operations with the   credit-control server.  Therefore, in this example, it is assumed   that the SIP Proxy adds a Record-Route header in the initial SIP   INVITE to make sure that all the future requests in the created   dialog traverse through it (for the definitions of "Record-Route" and   "dialog", please refer to [RFC3261]).  Finally, the degree ofBertz, et al.                Standards Track                  [Page 114]

RFC 8506           Diameter Credit-Control Application        March 2019   credit-control measuring of the media by the proxy depends on the   business model design used in setting up the end system and proxies   in the SIP network.   The end user (SIP User Agent A) sends a REGISTER with credentials   (i).  The SIP Proxy sends a request to the home AAA server to perform   multimedia authentication and authorization by using, for instance, a   Diameter multimedia application (ii).  The home AAA server checks   that the credentials are correct and checks the user profile.   Eventually, a 200 OK response (iii) is sent to the User Agent.  Note   that the authentication and authorization are valid for the   registration validity period duration (i.e., until re-registration is   performed).  Several SIP sessions may be established without   re-authorization.   User Agent 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 (SDP) 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 User Agent B (4).  B's phone   rings, and B answers.  The media flows between them, and the SIP   Proxy starts measuring the quota.  At the expiry of the allocated   quota, the SIP Proxy sends a Diameter Credit-Control-Request   (UPDATE_REQUEST) to the Diameter Credit-Control server (5).  This   message contains the units used thus far.  The Diameter   Credit-Control server debits the used units from the end user's   account and allocates new credit that is returned to the SIP Proxy in   the Diameter Credit-Control-Answer (6).  The end user terminates the   service by sending a BYE message (7).  The SIP Proxy forwards the BYE   message to User Agent 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).Bertz, et al.                Standards Track                  [Page 115]

RFC 8506           Diameter Credit-Control Application        March 2019A.3.  Flow III   A credit-control flow for Multimedia Messaging Service is shown in   Figure 13.  The sender is charged as soon as the messaging server   successfully stores the message.                            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 13: Flow III   This is an example of Diameter Credit-Control for direct debiting   using the Multimedia Messaging Service environment.  Although the   flow focuses on illustrating the usage of credit-control messages,   the MMS signaling is inaccurate, and the diagram is not by any means   an attempt to define a service provider's MMS configuration or   billing model.   End user A sends an MMS to the MMS server (1).  The MMS server stores   the message and sends a Diameter Credit-Control-Request   (EVENT_REQUEST with Requested-Action set to 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).Bertz, et al.                Standards Track                  [Page 116]

RFC 8506           Diameter Credit-Control Application        March 2019   The MMS server acknowledges the successful reception of the MMS   message (4).  The MMS server notifies the recipient about the new MMS   (5), and end user B retrieves the message from the MMS message store   (6), (7).   Note that the transfer of the MMS message can take an extended period   of time and can fail, in which case a recovery action is needed.  The   MMS server should return the already-debited units to the user's   account by using the REFUND action described inSection 6.4.A.4.  Flow IV   Another credit-control flow for Multimedia Messaging Service is shown   in Figure 14.  The recipient is charged at the time of message   delivery.                             MMS Server         Content Server     (CC Client)           B           CC Server                |(1) Send MMS    |                |                |                |--------------->|                |                |                |                |(2) CCR (Event, CHECK_BALANCE,   |                |                |         MMS-specific AVP)       |                |                |-------------------------------->|                |                |(3) CCA (ENOUGH_CREDIT)          |                |                |<--------------------------------|                |(4) Send MMS Ack|                |                |                |<---------------|                |                |                |                |(5) Notify MMS  |                |                |                |--------------->|                |                :                :                :                :                |                |(6) Retrieve MMS|                |                |                |<---------------|                |                |                |(7) CCR (Event, DIRECT_DEBITING, |                |                |          MMS-specific AVP)      |                |                |-------------------------------->|                |                |(8) CCA (Granted-Units)          |                |                |<--------------------------------|                |                |(9) Retrieve MMS|                |                |                |    Ack         |                |                |                |--------------->|                |                |                |                |                |                            Figure 14: Flow IVBertz, et al.                Standards Track                  [Page 117]

RFC 8506           Diameter Credit-Control Application        March 2019   This is an example of Diameter Credit-Control for direct debiting   using the Multimedia Messaging Service environment.  Although the   flow focuses on illustrating the usage of credit-control messages,   the MMS signaling is inaccurate, and the diagram is not by any means   an attempt to define a service provider's MMS configuration or   billing model.   A content server sends an MMS to the MMS server (1), which stores the   message.  The message recipient will be charged for the MMS message   in this case.  As there can be a substantially long time between the   receipt of the message at the MMS server and the actual retrieval of   the message, the MMS server does not establish any credit-control   sessions to the Diameter Credit-Control server; rather, it first   performs only a balance check (without any credit reservations) by   sending a Diameter Credit-Control-Request (EVENT_REQUEST with   Requested-Action set to CHECK_BALANCE) to verify that end user B can   cover the cost for the MMS (2).  The Diameter Credit-Control server   checks the end user's account balance and returns the answer to the   MMS server in the Diameter Credit-Control-Answer (3).  The MMS server   acknowledges the successful reception of the MMS message (4).  The   MMS server notifies the recipient of the new MMS (5), and after some   time end user B retrieves the message from the MMS message store (6).   The MMS server sends a Diameter Credit-Control-Request (EVENT_REQUEST   with Requested-Action set to 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-Answer (8).  The MMS is   transferred to end user B (9).   Note that the transfer of the MMS message can take an extended period   of time and can fail, in which case a recovery action is needed.  The   MMS server should return the already-debited units to the user's   account by using the REFUND action described inSection 6.4.Bertz, et al.                Standards Track                  [Page 118]

RFC 8506           Diameter Credit-Control Application        March 2019A.5.  Flow V   Figure 15 provides an example of an Advice of Charge (AoC) service   for a SIP call.                            SIP Controller         User Agent A        (CC Client)      User Agent B     CC Server              |(1)INVITE          |                |               |              |  User Agent B(SDP)|                |               |              |------------------>|                |               |              |                   |(2)CCR (Event, PRICE_ENQUIRY,   |              |                   |        SIP-specific AVPs)      |              |                   |------------------------------->|              |                   |(3)CCA (Cost-Information)       |              |                   |<-------------------------------|              |(4)MESSAGE(URL)    |                |               |              |<------------------|                |               |              |(5)HTTP GET        |                |               |              |------------------>|                |               |              |(6)HTTP POST       |                |               |              |------------------>|(7)INVITE(SDP)  |               |              |                   |--------------->|               |              |                   |      (8)200 OK |               |              |         (9)200 OK |<---------------|               |              |<------------------|                |               |                             Figure 15: Flow V   This is an example of Diameter Credit-Control for SIP sessions.   Although the flow focuses on illustrating the usage of credit-control   messages, the SIP signaling is inaccurate, and the diagram is not by   any means an attempt to define a service provider's SIP network.   User Agent A can be either a postpaid or prepaid subscriber using the   AoC service.  It is assumed that the SIP controller also has HTTP   capabilities and delivers an interactive AoC web page with, for   instance, the cost information, the details of the call derived from   the SDP, and a button to accept/not accept the charges.  (There may   be many other ways to deliver AoC information; however, this flow   focuses on the use of the credit-control messages.)  The user has   been authenticated and authorized prior to initiating the call and   has been subscribed to the AoC service.   User Agent A sends an INVITE with the SDP to User Agent B via the SIP   controller (1).  The SIP controller determines that the user is   subscribed to an AoC service and sends a Diameter Credit-Control-   Request (EVENT_REQUEST with Requested-Action set to PRICE_ENQUIRY) to   the Diameter Credit-Control server (2).  The Credit-Control-RequestBertz, et al.                Standards Track                  [Page 119]

RFC 8506           Diameter Credit-Control Application        March 2019   contains SIP-specific AVPs derived from the SIP signaling, describing   the requested service (e.g., calling party, called party, SDP   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.  It then sends a   SIP MESSAGE that contains a URL pointing to the AoC information web   page (4).  Upon receipt of the SIP MESSAGE, User Agent A   automatically invokes the web browser that retrieves the AoC   information (5).  The user clicks on the appropriate button to accept   the charges (6).  The SIP controller continues the session and sends   the INVITE to User Agent B, which accepts the call (7), (8), (9).A.6.  Flow VI   Figure 16 illustrates a credit-control flow for the REFUND case.  It   is assumed that there is a trusted relationship and secure connection   between the gaming server and the Diameter Credit-Control server.   The end user may be a prepaid subscriber or a postpaid subscriber.                          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 16: Flow VI   While the end user is playing the game (1), they enter a new level   that entitles them to a bonus.  The gaming server sends a Diameter   Credit-Control-Request (EVENT_REQUEST with Requested-Action set to   REFUND_ACCOUNT) to the Diameter Credit-Control server (2).  The   Credit-Control-Request contains the Requested-Service-Unit AVP with   the CC-Service-Specific-Units containing the number of points the   user just won.  The Service-Parameter-Info AVP is also included in   the request and specifies the service event to be rated (e.g., Tetris   Bonus).  From information received, the Diameter Credit-Control   server determines the amount to be credited, refunds the user's   account, and returns the Credit-Control-Answer, including theBertz, et al.                Standards Track                  [Page 120]

RFC 8506           Diameter Credit-Control Application        March 2019   Cost-Information AVP (3).  The Cost-Information AVP indicates the   credited amount.  At the first opportunity, the gaming server   notifies the end user of the credited amount (4).A.7.  Flow VII   Figure 17 provides an example of graceful service termination for a   SIP call.  It is assumed that the call is set up so that the   controller is in the call as a B2BUA (Back-to-Back User Agent)   performing third-party call control (3PCC).  Note that the SIP   signaling is inaccurate, as the focus of this flow is on graceful   service termination and credit-control authorization.  Best practices   for 3PCC are defined in [RFC3725].                   SIP Controller    Top-Up   User Agent A     (CC Client)      Server      User Agent B  CC Server        |                |              |             |              |        |                | (1)CCR(Update, Used-Units) |              |        |                |------------------------------------------>|        |                |               (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-Units)|        |                |<------------------------------------------|        |     (12)INVITE | (11)INVITE                 |              |        |<---------------|--------------------------->|              |                            Figure 17: Flow VIIBertz, et al.                Standards Track                  [Page 121]

RFC 8506           Diameter Credit-Control Application        March 2019   The call is ongoing between User Agents A and B; User Agent A has a   prepaid subscription.  At the expiry of the allocated quota, the SIP   controller sends a Diameter Credit-Control-Request (UPDATE_REQUEST)   to the Diameter Credit-Control server (1).  This message contains the   units used thus far.  The Diameter Credit-Control server debits the   used units from the end user's account and allocates the final quota   returned to the SIP controller in the Diameter Credit-Control-Answer   (2).  This message contains the Final-Unit-Indication AVP with   Final-Unit-Action set to REDIRECT, the Redirect-Address-Type set to   SIP URI, and the Redirect-Server-Address set to the top-up server   name (e.g., sip:sip-topup-server@domain.com).  At the expiry of the   final allocated quota, the SIP controller sends a Diameter   Credit-Control-Request (UPDATE_REQUEST) to the Diameter   Credit-Control server (3) and places the called party on "hold" by   sending an INVITE with the appropriate connection address in the SDP   (3a).  The Credit-Control-Request message contains the units used   thus far.  The Diameter Credit-Control server debits the used units   from the end user's account but does not make any credit   reservations.  The Credit-Control-Answer message, which contains the   Validity-Time to supervise the graceful service termination process,   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, replenishes the user's account (using some means   outside the scope of this specification), and releases the SIP   session (8).  The SIP controller can now assume that communication   between the prepaid user and the top-up server took place.  It sends   a spontaneous Credit-Control-Request (UPDATE_REQUEST) to the Diameter   Credit-Control server to check whether the account has been   replenished (9).  The Diameter Credit-Control server reserves credit   from the end user's account and returns the reserved quota to the SIP   controller in the Credit-Control-Answer (10).  At this point, the SIP   controller reconnects the caller and the called party (11), (12).Bertz, et al.                Standards Track                  [Page 122]

RFC 8506           Diameter Credit-Control Application        March 2019A.8.  Flow VIII   Figure 18 provides an example of graceful service termination   initiated when the first interrogation takes place because the user's   account is empty.  In this example, the credit-control server   supports the server-initiated credit re-authorization.  The Diameter   protocol application is implemented in the NAS per [RFC7155].                          NAS                          Top-Up      CC   End User         (CC Client)          AAA Server    Server    Server      |(1)User Logon      |(2)AA-Request (CC AVPs)        |         |      |------------------>|------------------->|          |         |      |                   |                    |(3)CCR(Initial, CC AVPs)      |                   |                    |------------------->|      |                   |                    |(4)CCA(Final-Unit,  |      |                   |                    |      Validity-Time)|      |                   |                    |<-------------------|      |                   |(5)AA-Answer(Final-Unit, Validity-Time)  |      |(6)Limited access  |<-------------------|          |         |      |      granted      |                    |          |         |      |<----------------->|                    |          |         |      |                   |                    |          |         |      |   (7)TCP/HTTP     |        (8)TCP/HTTP            |         |      |<----------------->|<----------------------------->|         |      |                  (9)Replenish account             |         |      |<------------------------------------------------->|         |      |                   |                    |            (10)RAR |      |                   |<-------------------|<-------------------|      |                   |(11)RAA             |                    |      |                   |------------------->|------------------->|      |                   |(12)CCR(Update)     |                    |      |                   |------------------->|(13)CCR(Update)     |      |                   |                    |------------------->|      |                   |                    |(14)CCA(Granted-Units)      |                   |(15)CCA(Granted-Units)<------------------|      |                   |<-------------------|                    |                           Figure 18: Flow VIII   The user logs on to the network (1).  The Diameter NAS sends a   Diameter AA-Request (AAR) to the home Diameter AAA server (2).  The   credit-control client populates the AAR with the Credit-Control AVP   set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,   as usual [RFC7155].  The home Diameter AAA server performs service-   specific authentication and authorization, as usual.  The home   Diameter AAA server determines that the user has a prepaid   subscription and notices from the Credit-Control AVP that the NAS has   credit-control capabilities.  It sends a Diameter Credit-Control-Bertz, et al.                Standards Track                  [Page 123]

RFC 8506           Diameter Credit-Control Application        March 2019   Request with CC-Request-Type set to INITIAL_REQUEST to the Diameter   Credit-Control server to perform credit authorization (3) and to   establish a credit-control session.  (The home Diameter AAA server   may forward service-specific AVPs received from the NAS as input for   the rating process.)  The Diameter Credit-Control server checks the   end user's account balance, determines that the account cannot cover   the cost of the service, and initiates graceful service termination.   The Credit-Control-Answer is returned to the home Diameter AAA server   (4).  This message contains the Final-Unit-Indication AVP and the   Validity-Time AVP set to a reasonable amount of time, to give the   user a chance to replenish their account (e.g., 10 minutes).  The   Final-Unit-Indication AVP includes the Final-Unit-Action set to   REDIRECT, the Redirect-Address-Type set to URL, and the Redirect-   Server-Address set to the HTTP top-up server name.  The home Diameter   AAA server sends the received Credit-Control AVPs to the NAS in the   Diameter AA-Answer (5).  Upon successful AAA, the NAS starts the   credit-control session and immediately starts graceful service   termination, as instructed by the server.  The NAS grants limited   access to the user (6).  The HTTP client software running in the   user's device opens the transport connection redirected by the NAS to   the top-up server (7), (8).  An appropriate web page is provided for   the user where the user can enter the credit card number and the   amount of money to be used to replenish the account, along with a   notification message that they are granted unlimited access if the   replenishment operation will be successfully executed within, for   example, the next 10 minutes.  The top-up server validates the credit   card number and replenishes the user's account (using some means   outside the scope of this specification) (9).  After successful   account top-up, the credit-control server sends a Re-Auth-Request   message to the NAS (10).  The NAS acknowledges the request by   returning the Re-Auth-Answer message (11) and initiates the credit   re-authorization by sending a Credit-Control-Request (UPDATE_REQUEST)   to the Diameter Credit-Control server (12), (13).   The Diameter Credit-Control server reserves credit from the   end user's account and returns the reserved quota to the NAS via the   home Diameter AAA server in the Credit-Control-Answer (14), (15).   The NAS removes the restriction applied by graceful service   termination and starts monitoring the granted units.A.9.  Flow IX   The Diameter Credit-Control application defines the Multiple-   Services-Credit-Control AVP, which can be used to support independent   credit-control of multiple services in a single credit-control   (sub-)session for Service Elements that have such capabilities.  It   is possible to request and allocate resources as a credit pool that   is shared between services or rating-groups.Bertz, et al.                Standards Track                  [Page 124]

RFC 8506           Diameter Credit-Control Application        March 2019   Figure 19 illustrates a usage scenario where the credit-control   client and server support independent credit-control of multiple   services, as defined inSection 5.1.2.  It is assumed that service-   identifiers, rating-groups, and their associated parameters (e.g., IP   5-tuples) are locally configured in the Service Element or   provisioned by an entity other than the credit-control server.   End User         Service Element                            CC Server                      (CC Client)     |(1)User logon      |                                            |     |------------------>|(2)CCR(Initial, Service-Id access,          |     |                   |        Access-specific AVPs,               |     |                   |        Multiple-Services-Indicator)        |     |                   |------------------------------------------->|     |                   |(3)CCA(Multiple-Services-CC (               |     |                   |        Granted-Units(Total-Octets),        |     |                   |        Service-Id access,                  |     |                   |        Validity-Time,                      |     |                   |        G-S-U-Pool-Reference(Pool-Id 1,     |     |                   |          Multiplier 10)))                  |     |                   |<-------------------------------------------|     :                   :                                            :     |(4)Service-Request (Service 1)                                  |     |------------------>|(5)CCR(Update, Multiple-Services-CC (       |     |                   |        Requested-Units(), Service-Id 1,    |     |                   |        Rating-Group 1))                    |     |                   |------------------------------------------->|     |                   |(6)CCA(Multiple-Services-CC (               |     |                   |        Granted-Units(Time),                |     |                   |        Rating-Group 1,                     |     |                   |        G-S-U-Pool-Reference(Pool-Id 1,     |     |                   |          Multiplier 1)))                   |     |                   |<-------------------------------------------|     :                   :                                            :     |(7)Service-Request (Service 2)                                  |     |------------------>|                                            |     :                   :                                            :     :                   :                                            :     |(8)Service-Request (Services 3 & 4)                             |     |------------------>|(9)CCR(Update, Multiple-Services-CC (       |     |                   |        Requested-Units(), Service-Id 3,    |     |                   |        Rating-Group 2),                    |     |                   |        Multiple-Services-CC (              |     |                   |        Requested-Units(), Service-Id 4,    |     |                   |        Rating-Group 3))                    |     |                   |------------------------------------------->|Bertz, et al.                Standards Track                  [Page 125]

RFC 8506           Diameter Credit-Control Application        March 2019     |                   |(10)CCA(Multiple-Services-CC (              |     |                   |         Granted-Units(Total-Octets),       |     |                   |         Service-Id 3, Rating-Group 2,      |     |                   |         Validity-Time,                     |     |                   |         G-S-U-Pool-Reference(Pool-Id 2,    |     |                   |           Multiplier 2)),                  |     |                   |         Multiple-Services-CC (             |     |                   |         Granted-Units(Total-Octets),       |     |                   |         Service-Id 4, Rating-Group 3       |     |                   |         Validity-Time,                     |     |                   |         Final-Unit-Ind.(Terminate),        |     |                   |         G-S-U-Pool-Reference(Pool-Id 2,    |     |                   |           Multiplier 5)))                  |     |                   |<-------------------------------------------|     :                   :                                            :     :                   :                                            :     | +--------------+  |                                            |     | |Validity time |  |(11)CCR(Update,                             |     | |expires for   |  |         Multiple-Services-CC (             |     | |Service-Id    |  |         Requested-Unit(),                  |     | | access       |  |         Used-Units(In-Octets, Out-Octets), |     | +--------------+  |         Service-Id access))                |     |                   |------------------------------------------->|     |                   |(12)CCA(Multiple-Services-CC (              |     |                   |         Granted-Units(Total-Octets),       |     |                   |         Service-Id access,                 |     |                   |         Validity-Time,                     |     |                   |         G-S-U-Pool-Reference(Pool-Id 1,    |     |                   |           Multiplier 10)))                 |     |                   |<-------------------------------------------|     :                   :                                            :     :                   :                                            :     | +--------------+  |                                            |     | |Total quota   |  |(13)CCR(Update,                             |     | |elapses for   |  |         Multiple-Services-CC (             |     | |Pool 2:       |  |          Requested-Unit(),                 |     | |Service 4 not |  |          Used-Units(In-Octets, Out-Octets),|     | |allowed,      |  |          Service-Id 3, Rating-Group 2),    |     | |Service 3     |  |         Multiple-Services-CC (             |     | |continues     |  |          Used-Units(In-Octets, Out-Octets),|     | +--------------+  |          Service-Id 4, Rating-Group 3))    |     |                   |------------------------------------------->|     |                   |(14)CCA(Multiple-Services-CC (              |     |                   |         Result-Code 4011,                  |     |                   |         Service-Id 3))                     |     |                   |<-------------------------------------------|     :                   :                                            :     :                   :                                            :Bertz, et al.                Standards Track                  [Page 126]

RFC 8506           Diameter Credit-Control Application        March 2019     |(15)User logoff    |                                            |     |------------------>|(16)CCR(Term.,                              |     |                   |         Multiple-Services-CC (             |     |                   |          Used-Units(In-Octets, Out-Octets),|     |                   |          Service-Id access),               |     |                   |         Multiple-Services-CC (             |     |                   |          Used-Units(Time),                 |     |                   |          Service-Id 1, Rating-Group 1),    |     |                   |         Multiple-Services-CC (             |     |                   |          Used-Units(Time),                 |     |                   |          Service-Id 2, Rating-Group 1))    |     |                   |------------------------------------------->|     |                   |(17)CCA(Term.)                              |     |                   |<-------------------------------------------|       Figure 19: Flow IX: Example of Independent Credit-Control of            Multiple Services in a Credit-Control (Sub-)Session   The user logs on to the network (1).  The Service Element sends a   Diameter Credit-Control-Request with CC-Request-Type set to   INITIAL_REQUEST to the Diameter Credit-Control server to perform   credit authorization for the bearer service (e.g., Internet access   service) and to establish a credit-control session (2).  In this   message, the credit-control client indicates support for independent   credit-control of multiple services within the session by including   the Multiple-Services-Indicator AVP.  The Diameter Credit-Control   server checks the end user's account balance, with rating information   received from the client (i.e., Service-Id and access-specific AVPs);   rates the request; and reserves credit from the end user's account.   Suppose that the server reserves $5 and determines that the cost is   $1/MB.  It then returns to the Service Element a Credit-Control-   Answer message that includes the Multiple-Services-Credit-Control AVP   with a quota of 5 MB associated to the Service-Id (access), to a   multiplier value of 10, and to Pool-Id 1 (3).   The user uses service 1 (4).  The Service Element sends a Diameter   Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to   the credit-control server to perform credit authorization for   service 1 (5).  This message includes the Multiple-Services-Credit-   Control AVP to request service units for service 1 that belong to   Rating-Group 1.  The Diameter Credit-Control server determines that   service 1 draws credit resources from the same account as the access   service (i.e., pool 1).  It rates the request according to   Service-Id/rating-group and updates the existing reservation by   requesting more credit.  Suppose that the server reserves $5 more   (now the reservation is $10) and determines that the cost is   $0.1/minute.  The server authorizes the whole rating-group.  It then   returns to the Service Element a Credit-Control-Answer message thatBertz, et al.                Standards Track                  [Page 127]

RFC 8506           Diameter Credit-Control Application        March 2019   includes the Multiple-Services-Credit-Control AVP with a quota of   50 minutes associated to Rating-Group 1, to a multiplier value of 1,   and to Pool-Id 1 (6).  The client adjusts the total amount of   resources for pool 1 according to the received quota, which gives S   for pool 1 = 100.   The user uses service 2, which belongs to the authorized rating-group   (Rating-Group 1) (7).  Resources are then consumed from pool 1.   The user now requests services 3 and 4 as well, which are not   authorized (8).  The Service Element sends a Diameter Credit-Control-   Request with CC-Request-Type set to UPDATE_REQUEST to the   credit-control server in order to perform credit authorization for   services 3 and 4 (9).  This message includes two instances of the   Multiple-Services-Credit-Control AVP to request service units for   service 3 that belong to Rating-Group 2 and service units for   service 4 that belong to Rating-Group 3.  The Diameter Credit-Control   server determines that services 3 and 4 draw credit resources from   another account (i.e., pool 2).  It checks the end user's account   balance and, according to Service-Id/rating-group information, rates   the request.  It then reserves credit from pool 2.   For example, the server reserves $5 and determines that service 3   costs $0.2/MB and service 4 costs $0.5/MB.  The server authorizes   only services 3 and 4.  It returns to the Service Element a   Credit-Control-Answer message that includes two instances of the   Multiple-Services-Credit-Control AVP (10).  One instance grants a   quota of 12.5 MB associated to Service-Id 3 to a multiplier value   of 2 and to Pool-Id 2.  The other instance grants a quota of 5 MB   associated to Service-Id 4 to a multiplier value of 5 and to   Pool-Id 2.   The server also determines that pool 2 is exhausted and service 4 is   not allowed to continue after these units will be consumed.   Therefore, the Final-Unit-Indication AVP with action TERMINATE is   associated to Service-Id 4.  The client calculates the total amount   of resources that can be used for pool 2 according to the received   quotas and multipliers, which gives S for pool 2 = 50.   The Validity-Time for the access service expires.  The Service   Element sends a Credit-Control-Request message to the server in order   to perform credit re-authorization for the Service-Id (access) (11).   This message carries one instance of the Multiple-Services-Credit-   Control AVP that includes the units used by this service.  Suppose   that the total amount of used units is 4 MB.  The client adjusts the   total amount of resources for pool 1 accordingly, which gives S for   pool 1 = 60.Bertz, et al.                Standards Track                  [Page 128]

RFC 8506           Diameter Credit-Control Application        March 2019   The server deducts $4 from the user's account and updates the   reservation by requesting more credit.  Suppose that the server   reserves $5 more (now the reservation is $11) and already knows the   cost of the Service-Id (access), which is $1/MB.  It then returns to   the Service Element a Credit-Control-Answer message that includes the   Multiple-Services-Credit-Control AVP with a quota of 5 MB associated   to the Service-Id (access), to a multiplier value of 10, and to   Pool-Id 1 (12).  The client adjusts the total amount of resources for   pool 1 according to the received quota, which gives S for   pool 1 = 110.   Services 3 and 4 consume the total amount of pool 2's credit   resources (i.e., C1*2 + C2*5 >= S).  The Service Element immediately   starts the TERMINATE action for service 4 and sends a Credit-Control-   Request message with CC-Request-Type set to UPDATE_REQUEST to the   credit-control server in order to perform credit re-authorization for   service 3 (13).  This message contains two instances of the Multiple-   Services-Credit-Control AVP to report the units used by services 3   and 4.  The server deducts the last $5 from the user's account   (pool 2) and returns the answer with Result-Code 4011 in the   Multiple-Services-Credit-Control AVP to indicate that service 3 can   continue without credit-control (14).   The end user logs off from the network (15).  To debit the used units   from the end user's account and to stop the credit-control session,   the Service Element sends a Diameter Credit-Control-Request with   CC-Request-Type set to TERMINATION_REQUEST to the credit-control   server (16).  This message contains the units used by each service in   multiple instances of the Multiple-Services-Credit-Control AVP.  The   used units are associated with the relevant Service-Identifier and   rating-group.  The Diameter Credit-Control server debits the used   units to the user's account (pool 1) and acknowledges the session   termination by sending a Diameter Credit-Control-Answer to the   Service Element (17).Bertz, et al.                Standards Track                  [Page 129]

RFC 8506           Diameter Credit-Control Application        March 2019Acknowledgements   The original authors ofRFC 4006 are Harri Hakala, Leena Mattila,   Juha-Pekka Koskinen, Marco Stura, and John Loughney.   The authors would like to thank Bernard Aboba, Jari Arkko, Robert   Ekblad, Pasi Eronen, Benny Gustafsson, Robert Karlsson, Avi Lior,   Jussi Maki, Paco Marin, Jeff Meyer, Anne Narhi, John Prudhoe,   Christopher Richards, Juha Vallinen, and Mark Watson for their   comments and suggestions.Authors' Addresses   Lyle Bertz (editor)   Sprint   6220 Sprint Parkway   Overland Park, KS  66251   United States of America   Email: lyleb551144@gmail.com   David Dolson (editor)   Sandvine   408 Albert Street   Waterloo, ON  N2L 3V3   Canada   Email: ddolson@acm.org   Yuval Lifshitz (editor)   Sandvine   408 Albert Street   Waterloo, ON  N2L 3V3   Canada   Email: yuvalif@yahoo.comBertz, et al.                Standards Track                  [Page 130]