Network Working Group H. Hakala
Request for Comments: 4006 L. Mattila
Category: Standards Track Ericsson
J-P. Koskinen
M. Stura
J. Loughney
Nokia
August 2005
Diameter Credit-Control Application
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services.
Table of Contents
1. Introduction................................................. 4
1.1. Requirements Language................................. 5
1.2. Terminology........................................... 5
1.3. Advertising Application Support....................... 7
2. Architecture Models.......................................... 7
3. Credit-Control Messages...................................... 9
3.1. Credit-Control-Request (CCR) Command.................. 9
3.2. Credit-Control-Answer (CCA) Command................... 11
4. Credit-Control Application Overview.......................... 11
4.1. Service-Specific Rating Input and Interoperability.... 13
5. Session Based Credit-Control................................. 15
5.1. General Principles.................................... 15
5.2. First Interrogation................................... 21
5.3. Intermediate Interrogation............................ 27
5.4. Final Interrogation................................... 29
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5.5. Server-Initiated Credit Re-Authorization.............. 30
5.6. Graceful Service Termination.......................... 32
5.7. Failure Procedures.................................... 38
6. One Time Event............................................... 41
6.1. Service Price Enquiry................................. 42
6.2. Balance Check......................................... 42
6.3. Direct Debiting....................................... 43
6.4. Refund................................................ 44
6.5. Failure Procedure..................................... 44
7. Credit-Control Application State Machine..................... 46
8. Credit-Control AVPs.......................................... 55
8.1. CC-Correlation-Id AVP................................. 58
8.2. CC-Request-Number AVP................................. 58
8.3. CC-Request-Type AVP................................... 58
8.4. CC-Session-Failover AVP............................... 59
8.5. CC-Sub-Session-Id AVP................................. 59
8.6. Check-Balance-Result AVP.............................. 60
8.7. Cost-Information AVP.................................. 60
8.8. Unit-Value AVP........................................ 61
8.9. Exponent AVP.......................................... 61
8.10. Value-Digits AVP...................................... 61
8.11. Currency-Code AVP..................................... 62
8.12. Cost-Unit AVP......................................... 62
8.13. Credit-Control AVP.................................... 62
8.14. Credit-Control-Failure-Handling AVP................... 62
8.15. Direct-Debiting-Failure-Handling AVP.................. 63
8.16. Multiple-Services-Credit-Control AVP.................. 64
8.17. Granted-Service-Unit AVP.............................. 65
8.18. Requested-Service-Unit AVP............................ 66
8.19. Used-Service-Unit AVP................................. 66
8.20. Tariff-Time-Change AVP................................ 67
8.21. CC-Time AVP........................................... 67
8.22. CC-Money AVP.......................................... 67
8.23. CC-Total-Octets AVP................................... 68
8.24. CC-Input-Octets AVP................................... 68
8.25. CC-Output-Octets AVP.................................. 68
8.26. CC-Service-Specific-Units AVP......................... 68
8.27. Tariff-Change-Usage AVP............................... 68
8.28. Service-Identifier AVP................................ 69
8.29. Rating-Group AVP...................................... 69
8.30. G-S-U-Pool-Reference AVP.............................. 69
8.31. G-S-U-Pool-Identifier AVP............................. 70
8.32. CC-Unit-Type AVP...................................... 70
8.33. Validity-Time AVP..................................... 70
8.34. Final-Unit-Indication AVP............................. 71
8.35. Final-Unit-Action AVP................................. 72
8.36. Restriction-Filter-Rule AVP........................... 72
8.37. Redirect-Server AVP................................... 73
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8.38. Redirect-Address-Type AVP............................. 73
8.39. Redirect-Server-Address AVP........................... 74
8.40. Multiple-Services-Indicator AVP....................... 74
8.41. Requested-Action AVP.................................. 74
8.42. Service-Context-Id AVP................................ 75
8.43. Service-Parameter-Info AVP............................ 76
8.44. Service-Parameter-Type AVP............................ 76
8.45. Service-Parameter-Value AVP........................... 77
8.46. Subscription-Id AVP................................... 77
8.47. Subscription-Id-Type AVP.............................. 77
8.48. Subscription-Id-Data AVP.............................. 78
8.49. User-Equipment-Info AVP............................... 78
8.50. User-Equipment-Info-Type AVP.......................... 78
8.50. User-Equipment-Info-Value AVP......................... 79
9. Result Code AVP Values....................................... 79
9.1. Transient Failures.................................... 79
9.2. Permanent Failures.................................... 80
10. AVP Occurrence Table......................................... 80
10.1. Credit-Control AVP Table.............................. 81
10.2. Re-Auth-Request/Answer AVP Table...................... 82
11. RADIUS/Diameter Credit-Control Interworking Model............ 82
12. IANA Considerations.......................................... 85
12.1. Application Identifier................................ 86
12.2. Command Codes......................................... 86
12.3. AVP Codes............................................. 86
12.4. Result-Code AVP Values................................ 86
12.5. CC-Request-Type AVP................................... 86
12.6. CC-Session-Failover AVP............................... 86
12.7. CC-Unit-Type AVP...................................... 87
12.8. Check-Balance-Result AVP.............................. 87
12.9. Credit-Control AVP.................................... 87
12.10. Credit-Control-Failure-Handling AVP................... 87
12.11. Direct-Debiting-Failure-Handling AVP.................. 87
12.12. Final-Unit-Action AVP................................. 87
12.13. Multiple-Services-Indicator AVP....................... 87
12.14. Redirect-Address-Type AVP............................. 88
12.15. Requested-Action AVP.................................. 88
12.16. Subscription-Id-Type AVP.............................. 88
12.17. Tariff-Change-Usage AVP............................... 88
12.18. User-Equipment-Info-Type AVP.......................... 88
13. Credit-Control Application Related Parameters................ 88
14. Security Considerations...................................... 89
14.1. Direct Connection with Redirects...................... 90
15. References................................................... 91
15.1. Normative References.................................. 91
15.2. Informative References................................ 92
16. Acknowledgements............................................. 93
Appendix A Credit-Control Sequences.............................. 94
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A.1. Flow I................................................ 94
A.2. Flow II............................................... 96
A.3. Flow III.............................................. 98
A.4. Flow IV............................................... 99
A.5. Flow V................................................ 100
A.6. Flow VI............................................... 102
A.7. Flow VII.............................................. 103
A.8. Flow VIII............................................. 105
A.9. Flow IX............................................... 107
Authors' Addresses............................................... 112
Full Copyright Statement......................................... 114
1. Introduction
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services. It provides a general
solution to real-time cost and credit-control.
The prepaid model has been shown to be very successful, for instance,
in GSM networks, where network operators offering prepaid services
have experienced a substantial growth of their customer base and
revenues. Prepaid services are now cropping up in many other
wireless and wire line based networks.
In next generation wireless networks, additional functionality is
required beyond that specified in the Diameter base protocol. For
example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
that an application must be able to rate service information in
real-time. In addition, it is necessary to check that the end user's
account provides coverage for the requested service prior to
initiation of that service. When an account is exhausted or expired,
the user must be denied the ability to compile additional chargeable
events.
A mechanism has to be provided to allow the user to be informed of
the charges to be levied for a requested service. In addition, there
are services such as gaming and advertising that may credit as well
as debit a user account.
The other Diameter applications provide service specific
authorization, and they do not provide credit authorization for
prepaid users. The credit authorization shall be generic and
applicable to all the service environments required to support
prepaid services.
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To fulfill these requirements, it is necessary to facilitate credit-
control communication between the network element providing the
service (e.g., Network Access Server, SIP Proxy, and Application
Server) and a credit-control server.
The scope of this specification is the credit authorization. Service
specific authorization and authentication is out of the scope.
1.1. Requirements Language
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
"RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [KEYWORDS].
1.2. Terminology
AAA
Authentication, Authorization, and Accounting
AA answer
AA answer generically refers to a service specific authorization and
authentication answer. AA answer commands are defined in service
specific authorization applications, e.g., [NASREQ] and [DIAMMIP].
AA request
AA request generically refers to a service specific authorization and
authentication request. AA request commands are defined in service
specific authorization applications e.g., [NASREQ] and [DIAMMIP].
Credit-control
Credit-control is a mechanism that directly interacts in real-time
with an account and controls or monitors the charges related to the
service usage. Credit-control is a process of checking whether
credit is available, credit-reservation, deduction of credit from the
end user account when service is completed and refunding of reserved
credit that is not used.
Diameter Credit-control Server
A Diameter credit-control server acts as a prepaid server, performing
real-time rating and credit-control. It is located in the home
domain and is accessed by service elements or Diameter AAA servers in
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real-time for purpose of price determination and credit-control
before the service event is delivered to the end-user. It may also
interact with business support systems.
Diameter Credit-control Client
A Diameter credit-control client is an entity that interacts with a
credit-control server. It monitors the usage of the granted quota
according to instructions returned by credit-control server.
Interrogation
The Diameter credit-control client uses interrogation to initiate a
session based credit-control process. During the credit-control
process, it is used to report the used quota and request a new one.
An interrogation maps to a request/answer transaction.
One-time event
Basically, a request/answer transaction of type event.
Rating
The act of determining the cost of the service event.
Service
A type of task performed by a service element for an end user.
Service Element
A network element that provides a service to the end users. The
Service Element may include the Diameter credit-control client, or
another entity (e.g., RADIUS AAA server) that can act as a Credit-
control client on behalf of the Service Element. In the latter case,
the interface between the Service Element and the Diameter credit-
control client is outside the scope of this specification. Examples
of the Service Elements include Network Access Server (NAS), SIP
Proxy, and Application Servers such as messaging server, content
server, and gaming server.
Service Event
An event relating to a service provided to the end user.
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Session based credit-control
A credit-control process that makes use of several interrogations:
the first, a possible intermediate, and the final. The first
interrogation is used to reserve money from the user's account and to
initiate the process. The intermediate interrogations may be needed
to request new quota while the service is being rendered. The final
interrogation is used to exit the process. The credit-control server
is required to maintain session state for session-based credit-
control.
1.3. Advertising Application Support
Diameter nodes conforming to this specification MUST advertise
support by including the value of 4 in the Auth-Application-Id of the
Capabilities-Exchange-Request and Capabilities-Exchange-Answer
command [DIAMBASE].
2. Architecture Models
The current accounting models specified in the Radius Accounting
[RFC2866] and Diameter base [DIAMBASE] are not sufficient for real-
time credit-control, where credit-worthiness is to be determined
prior to service initiation. Also, the existing Diameter
authorization applications, [NASREQ] and [DIAMMIP], only provide
service authorization, but do not provide credit authorization for
prepaid users. In order to support real-time credit-control, a new
type of server is needed in the AAA infrastructure: Diameter credit-
control server. The Diameter credit-control server is the entity
responsible for credit authorization for prepaid subscribers.
A service element may authenticate and authorize the end user with
the AAA server by using AAA protocols; e.g., RADIUS or a Diameter
base protocol with a possible Diameter application.
Accounting protocols such as RADIUS accounting and the Diameter base
accounting protocol can be used to provide accounting data to the
accounting server after service is initiated, and to provide possible
interim reports until service completion. However, for real-time
credit-control, these authorization and accounting models are not
sufficient.
When real-time credit-control is required, the credit-control client
contacts the credit-control server with information about a possible
service event. The credit-control process is performed to determine
potential charges and to verify whether the end user's account
balance is sufficient to cover the cost of the service being
rendered.
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Figure 1 illustrates the typical credit-control architecture, which
consists of a Service Element with an embedded Diameter credit-
control client, a Diameter credit-control server, and an AAA server.
A Business Support System is usually deployed; it includes at least
the billing functionality. The credit-control server and AAA server
in this architecture model are logical entities. The real
configuration can combine them into a single host. The credit-
control protocol is the Diameter base protocol with the Diameter
credit-control application.
When an end user requests services such as SIP or messaging, the
request is typically forwarded to a service element (e.g., SIP Proxy)
in the user's home domain. In some cases it might be possible that
the service element in the visited domain can offer services to the
end user; however, a commercial agreement must exist between the
visited domain and the home domain. Network access is an example of
a service offered in the visited domain where the NAS, through an AAA
infrastructure, authenticates and authorizes the user with the user's
home network.
Service Element AAA and CC
+----------+ +---------+ Protocols+-----------+ +--------+
| End |<---->|+-------+|<------------>| AAA | |Business|
| User | +->|| CC || | Server |->|Support |
| | | || Client||<-----+ | | |System |
+----------+ | |+-------+| | +-----------+ | |
| +---------+ | ^ +--------+
+----------+ | | CC Protocol | ^
| End |<--+ | +-----v----+ |
| User | +------>|Credit- | |
+----------+ Credit-Control |Control |--------+
Protocol |Server |
+----------+
Figure 1: Typical credit-control architecture
There can be multiple credit-control servers in the system for
redundancy and load balancing. The system can also contain separate
rating server(s), and accounts can be located in a centralized
database. To ensure that the end user's account is not debited or
credited multiple times for the same service event, only one place in
the credit-control system should perform duplicate detection. System
internal interfaces can exist to relay messages between servers and
an account manager. However, the detailed architecture of the
credit-control system and its interfaces are implementation specific
and are out of scope of this specification.
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Protocol transparent Diameter relays can exist between the credit-
control client and credit-control server. Also, Diameter Redirect
agents that refer credit-control clients to credit-control servers
and allow them to communicate directly can exist. These agents
transparently support the Diameter credit-control application. The
different roles of Diameter Agents are defined in Diameter base
[DIAMBASE], section 2.8.
If Diameter credit-control proxies exist between the credit-control
client and the credit-control server, they MUST advertise the
Diameter credit-control application support.
3. Credit-Control Messages
This section defines new Diameter message Command-Code values that
MUST be supported by all Diameter implementations that conform to
this specification. The Command Codes are as follows:
Command-Name Abbrev. Code Reference
-----------------------------------------------------------
Credit-Control-Request CCR 272 3.1
Credit-Control-Answer CCA 272 3.2
Diameter Base [DIAMBASE] defines in the section 3.2 the Command Code
ABNF specification. These formats are observed in Credit-Control
messages.
3.1. Credit-Control-Request (CCR) Command
The Credit-Control-Request message (CCR) is indicated by the
command-code field being set to 272 and the 'R' bit being set in the
Command Flags field. It is used between the Diameter credit-control
client and the credit-control server to request credit authorization
for a given service.
The Auth-Application-Id MUST be set to the value 4, indicating the
Diameter credit-control application.
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Message Format
<Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Application-Id }
{ Service-Context-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ Destination-Host ]
[ User-Name ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
*[ Subscription-Id ]
[ Service-Identifier ]
[ Termination-Cause ]
[ Requested-Service-Unit ]
[ Requested-Action ]
*[ Used-Service-Unit ]
[ Multiple-Services-Indicator ]
*[ Multiple-Services-Credit-Control ]
*[ Service-Parameter-Info ]
[ CC-Correlation-Id ]
[ User-Equipment-Info ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP ]
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3.2. Credit-Control-Answer (CCA) Command
The Credit-Control-Answer message (CCA) is indicated by the command-
code field being set to 272 and the 'R' bit being cleared in the
Command Flags field. It is used between the credit-control server
and the Diameter credit-control client to acknowledge a Credit-
Control-Request command.
Message Format
<Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
< Session-Id >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
{ Auth-Application-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ User-Name ]
[ CC-Session-Failover ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
[ Granted-Service-Unit ]
*[ Multiple-Services-Credit-Control ]
[ Cost-Information]
[ Final-Unit-Indication ]
[ Check-Balance-Result ]
[ Credit-Control-Failure-Handling ]
[ Direct-Debiting-Failure-Handling ]
[ Validity-Time]
*[ Redirect-Host]
[ Redirect-Host-Usage ]
[ Redirect-Max-Cache-Time ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ Failed-AVP ]
*[ AVP ]
4. Credit-Control Application Overview
The credit authorization process takes place before and during
service delivery to the end user and generally requires the user's
authentication and authorization before any request is sent to the
credit-control server. The credit-control application defined in
this specification supports two different credit authorization
models: credit authorization with money reservation and credit
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authorization with direct debiting. In both models, the credit-
control client requests credit authorization from the credit-control
server prior to allowing any service to be delivered to the end user.
In the first model, the credit-control server rates the request,
reserves a suitable amount of money from the user's account, and
returns the corresponding amount of credit resources. Note that
credit resources may not imply actual monetary credit; credit
resources may be granted to the credit control client in the form of
units (e.g., data volume or time) to be metered.
Upon receipt of a successful credit authorization answer with a
certain amount of credit resources, the credit-control client allows
service delivery to the end user and starts monitoring the usage of
the granted resources. When the credit resources granted to the user
have been consumed or the service has been successfully delivered or
terminated, the credit-control client reports back to the server the
used amount. The credit-control server deducts the used amount from
the end user's account; it may perform rating and make a new credit
reservation if the service delivery is continuing. This process is
accomplished with session based credit-control that includes the
first interrogation, possible intermediate interrogations, and the
final interrogation. For session based credit-control, both the
credit control client and the credit-control server are required to
maintain credit-control session state. Session based credit-control
is described in more detail, with more variations, in section 5.
In contrast, credit authorization with direct debiting is a single
transaction process wherein the credit-control server directly
deducts a suitable amount of money from the user's account as soon as
the credit authorization request is received. Upon receipt of a
successful credit authorization answer, the credit-control client
allows service delivery to the end user. This process is
accomplished with the one-time event. Session state is not
maintained.
In a multi-service environment, an end user can issue an additional
service request (e.g., data service) during an ongoing service (e.g.,
voice call) toward the same account. Alternatively, during an active
multimedia session, an additional media type is added to the session,
causing a new simultaneous request toward same account.
Consequently, this needs to be considered when credit resources are
granted to the services.
The credit-control application also supports operations such as
service price enquiry, user's balance check, and refund of credit on
the user's account. These operations are accomplished with the one-
time event. Session state is not maintained.
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A flexible credit-control application specific failure handling is
defined in which the home service provider can model the credit-
control client behavior according to its own credit risk management
policy.
The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
Failure-Handling AVP are defined to determine what is done if the
sending of credit-control messages to the credit-control server has
been temporarily prevented. The usage of the Credit-Control-
Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP
allows flexibility, as failure handling for the credit-control
session and one time event direct debiting may be different.
4.1. Service-Specific Rating Input and Interoperability
The Diameter credit-control application defines the framework for
credit-control; it provides generic credit-control mechanisms
supporting multiple service applications. The credit-control
application, therefore, does not define AVPs that could be used as
input in the rating process. Listing the possible services that
could use this Diameter application is out of scope for this generic
mechanism.
It is reasonable to expect that a service level agreement will exist
between providers of the credit-control client and the credit-control
server covering the charging, services offered, roaming agreements,
agreed rating input (i.e., AVPs), and so on.
Therefore, it is assumed that a Diameter credit-control server will
provide service only for Diameter credit-control clients that have
agreed beforehand as to the content of credit-control messages.
Naturally, it is possible that any arbitrary Diameter credit-control
client can interchange credit-control messages with any Diameter
credit-control server, but with a higher likelihood that unsupported
services/AVPs could be present in the credit-control message, causing
the server to reject the request with an appropriate result-code.
4.1.1. Specifying Rating Input AVPs
There are two ways to provide rating input to the credit-control
server: either by using AVPs or by including them in the Service-
Parameter-Info AVP. The general principles for sending rating
parameters are as follows:
1a. The service SHOULD re-use existing AVPs if it can use AVPs
defined in existing Diameter applications (e.g., NASREQ for network
access services). Re-use of existing AVPs is strongly recommended in
[DIAMBASE].
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For AVPs of type Enumerated, the service may require a new value to
be defined. Allocation of new AVP values is done as specified in
[DIAMBASE], section 1.2.
1b. New AVPs can be defined if the existing AVPs do not provide
sufficient rating information. In this case, the procedures defined
in [DIAMBASE] for creating new AVPs MUST be followed.
1c. For services specific only to one vendor's implementation, a
Vendor-Specific AVP code for Private use can be used. Where a
Vendor-Specific AVP is implemented by more than one vendor,
allocation of global AVPs is encouraged instead; refer to [DIAMBASE].
2. The Service-Parameter-Info AVP MAY be used as a container to pass
legacy rating information in its original encoded form (e.g., ASN.1
BER). This method can be used to avoid unnecessary conversions from
an existing data format to an AVP format. In this case, the rating
input is embedded in the Service-Parameter-Info AVP as defined in
section 8.43.
New service applications SHOULD favor the use of explicitly defined
AVPs as described in items 1a and 1b, to simplify interoperability.
4.1.2. Service-Specific Documentation
The service specific rating input AVPs, the contents of the Service-
Parameter-Info AVP or Service-Context-Id AVP (defined in section
8.42) are not within the scope of this document. To facilitate
interoperability, it is RECOMMENDED that the rating input and the
values of the Service-Context-Id be coordinated via an informational
RFC or other permanent and readily available reference. The
specification of another cooperative standardization body (e.g.,
3GPP, OMA, and 3GPP2) SHOULD be used. However, private services may
be deployed that are subject to agreements between providers of the
credit-control server and client. In this case, vendor specific AVPs
can be used.
This specification, together with the above service specific
documents, governs the credit-control message. Service specific
documents define which existing AVPs or new AVPs are used as input to
the rating process (i.e., those that do not define new credit-control
applications), and thus have to be included in the Credit-Control-
Request command by a Diameter credit-control client supporting a
given service as *[AVP]. Should Service-Parameter-Info be used, then
the service specific document MUST specify the exact content of this
grouped AVP.
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The Service-Context-Id AVP MUST be included at the command level of a
Credit-Control Request to identify the service specific document that
applies to the request. The specific service or rating group the
request relates to is uniquely identified by the combination of
Service-Context-Id and Service-Identifier or Rating-Group.
4.1.3. Handling of Unsupported/Incorrect Rating Input
Diameter credit-control implementations are required to support the
Mandatory rating AVPs defined in service specific documentation of
the services they support, according to the 'M' bit rules in
[DIAMBASE].
If a rating input required for the rating process is incorrect in the
Credit-control request, or if the credit-control server does not
support the requested service context (identified by the Service-
Context-Id AVP at command level), the Credit-control answer MUST
contain the error code DIAMETER_RATING_FAILED. A CCA message with
this error MUST contain one or more Failed-AVP AVPs containing the
missing and/or unsupported AVPs that caused the failure. A Diameter
credit-control client that receives the error code
DIAMETER_RATING_FAILED in response to a request MUST NOT send similar
requests in the future.
4.1.4. RADIUS Vendor-Specific Rating Attributes
When service specific documents include RADIUS vendor specific
attributes that could be used as input in the rating process, the
rules described in [NASREQ] for formatting the Diameter AVP MUST be
followed.
For example, if the AVP code used is the vendor attribute type code,
the Vendor-Specific flag MUST be set to 1 and the Vendor-ID MUST be
set to the IANA Vendor identification value. The Diameter AVP data
field contains only the attribute value of the RADIUS attribute.
5. Session Based Credit-Control
5.1. General Principles
For a session-based credit-control, several interrogations are
needed: the first, intermediate (optional) and the final
interrogations. This is illustrated in Figures 2 and 3.
If the credit-control client performs credit-reservation before
granting service to the end user, it MUST use several interrogations
toward the credit-control server (i.e., session based credit-
Hakala, et al. Standards Track [Page 15]
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control). In this case, the credit-control server MUST maintain the
credit-control session state.
Each credit-control session MUST have a globally unique Session-Id as
defined in [DIAMBASE], which MUST NOT be changed during the lifetime
of a credit-control session.
Certain applications require multiple credit-control sub-sessions.
These applications would send messages with a constant Session-Id
AVP, but with a different CC-Sub-Session-Id AVP. If several credit
sub-sessions will be used, all sub-sessions MUST be closed separately
before the main session is closed so that units per sub-session may
be reported. The absence of this AVP implies that no sub-sessions
are in use.
Note that the service element might send a service specific re-
authorization message to the AAA server due to expiration of the
authorization-lifetime during an ongoing credit-control session.
However, the service specific re-authorization does not influence the
credit authorization that is ongoing between the credit-control
client and credit-control server, as credit authorization is
controlled by the burning rate of the granted quota.
If service specific re-authorization fails, the user will be
disconnected, and the credit-control client MUST send a final
interrogation to the credit-control server.
The Diameter credit-control server may seek to control the validity
time of the granted quota and/or the production of intermediate
interrogations. Thus, it MAY include the Validity-Time AVP in the
answer message to the credit-control client. Upon expiration of the
Validity-Time, the credit-control client MUST generate a credit-
control update request and report the used quota to the credit-
control server. It is up to the credit-control server to determine
the value of the Validity-Time to be used for consumption of the
granted service units. If the Validity-Time is used, its value
SHOULD be given as input to set the session supervision timer Tcc
(the session supervision timer MAY be set to two times the value of
the Validity-Time, as defined in section 13). Since credit-control
update requests are also produced at the expiry of granted service
units and/or for mid-session service events, the omission of
Validity-Time does not mean that intermediate interrogation for the
purpose of credit-control is not performed.
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5.1.1. Basic Tariff-Time Change Support
The Diameter credit-control server and client MAY optionally support
a tariff change mechanism. The Diameter credit-control server may
include a Tariff-Time-Change AVP in the answer message. Note that
the granted units should be allocated based on the worst-case
scenario in case of forthcoming tariff change, so that the overall
reported used units would never exceed the credit reservation.
When the Diameter credit-control client reports the used units and a
tariff change has occurred during the reporting period, the Diameter
credit-control client MUST separately itemize the units used before
and after the tariff change. If the client is unable to distinguish
whether units straddling the tariff change were used before or after
the tariff change, the credit-control client MUST itemize those units
in a third category.
If a client does not support the tariff change mechanism and it
receives a CCA message carrying the Tariff-Time-Change AVP, it MUST
terminate the credit-control session, giving a reason of
DIAMETER_BAD_ANSWER in the Termination-Cause AVP.
For time based services, the quota is continuously consumed at the
regular rate of 60 seconds per minute. At the time when credit
resources are allocated, the server already knows how many units will
be consumed before the tariff time change and how many units will be
consumed afterward. Similarly, the server can determine the units
consumed at the before rate and the units consumed at the rate
afterward in the event that the end-user closes the session before
the consumption of the allotted quota. There is no need for
additional traffic between client and server in the case of tariff
time changes for continuous time based service. Therefore, the
tariff change mechanism is not used for such services. For time-
based services in which the quota is NOT continuously consumed at a
regular rate, the tariff change mechanism described for volume and
event units MAY be used.
5.1.2. Credit-Control for Multiple Services within a (sub-)Session
When multiple services are used within the same user session and each
service or group of services is subject to different cost, it is
necessary to perform credit-control for each service independently.
Making use of credit-control sub-sessions to achieve independent
credit-control will result in increased signaling load and usage of
resources in both the credit-control client and the credit-control
server. For instance, during one network access session the end user
may use several http-services subject to different access cost. The
network access specific attributes such as the quality of service
Hakala, et al. Standards Track [Page 17]
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(QoS) are common to all the services carried within the access
bearer, but the cost of the bearer may vary depending on its content.
To support these scenarios optimally, the credit-control application
enables independent credit-control of multiple services in a single
credit-control (sub-)session. This is achieved by including the
optional Multiple-Services-Credit-Control AVP in Credit-Control-
Request/Answer messages. It is possible to request and allocate
resources as a credit pool shared between multiple services. The
services can be grouped into rating groups in order to achieve even
further aggregation of credit allocation. It is also possible to
request and allocate quotas on a per service basis. Where quotas are
allocated to a pool by means of the Multiple-Services-Credit-Control
AVP, the quotas remain independent objects that can be re-authorized
independently at any time. Quotas can also be given independent
result codes, validity times, and Final-Unit-Indications.
A Rating-Group gathers a set of services, identified by a Service-
Identifier, and subject to the same cost and rating type (e.g.,
$0.1/minute). It is assumed that the service element is provided
with Rating-Groups, Service-Identifiers, and their associated
parameters that define what has to be metered by means outside the
scope of this specification. (Examples of parameters associated to
Service-Identifiers are IP 5-tuple and HTTP URL.) Service-Identifiers
enable authorization on a per-service based credit as well as
itemized reporting of service usage. It is up to the credit-control
server whether to authorize credit for one or more services or for
the whole rating-group. However, the client SHOULD always report
used units at the finest supported level of granularity. Where quota
is allocated to a rating-group, all the services belonging to that
group draw from the allotted quota. The following is a graphical
representation of the relationship between service-identifiers,
rating-groups, credit pools, and credit-control (sub-)session.
DCC (Sub-)Session
|
+------------+-----------+-------------+--------------- +
| | | | |
Service-Id a Service-Id b Service-Id c Service-Id d.....Service-Id z
\ / \ / /
\ / \ / /
\ / Rating-Group 1.......Rating-Group n
\ / | |
Quota ---------------Quota Quota
| / |
| / |
Credit-Pool Credit-Pool
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If independent credit-control of multiple services is used, the
validity-time and final-unit-indication SHOULD be present either in
the Multiple-Services-Credit-Control AVP(s) or at command level as
single AVPs. However, the Result-Code AVP MAY be present both on the
command level and within the Multiple-Services-Credit-Control AVP.
If the Result-Code on the command level indicates a value other than
SUCCESS, then the Result-Code on command level takes precedence over
any included in the Multiple-Services-Credit-Control AVP.
The credit-control client MUST indicate support for independent
credit-control of multiple services within a (sub-)session by
including the Multiple-Services-Indicator AVP in the first
interrogation. A credit-control server not supporting this feature
MUST treat the Multiple-Services-Indicator AVP and any received
Multiple-Services-Credit-Control AVPs as invalid AVPs.
If the client indicated support for independent credit-control of
multiple services, a credit-control server that wishes to use the
feature MUST return the granted units within the Multiple-Services-
Credit-Control AVP associated to the corresponding service-identifier
and/or rating-group.
To avoid a situation where several parallel (and typically also
small) credit reservations must be made on the same account (i.e.,
credit fragmentation), and also to avoid unnecessary load on the
credit-control server, it is possible to provide service units as a
pool that applies to multiple services or rating groups. This is
achieved by providing the service units in the form of a quota for a
particular service or rating group in the Multiple-Services-Credit-
Control AVP, and also by including a reference to a credit pool for
that unit type.
The reference includes a multiplier derived from the rating
parameter, which translates from service units of a specific type to
the abstract service units in the pool. For instance, if the rating
parameter for service 1 is $1/MB and the rating parameter for service
2 is $0.5/MB, the multipliers could be 10 and 5 for services 1 and 2,
respectively.
If S is the total service units within the pool, M1, M2, ..., Mn are
the multipliers provided for services 1, 2, ..., n, and C1, C2, ...,
Cn are the used resources within the session, then the pool credit is
exhausted and re-authorization MUST be sought when:
C1*M1 + C2*M2 + ... + Cn*Mn >= S
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The total credit in the pool, S, is calculated from the quotas, which
are currently allocated to the pool as follows:
S = Q1*M1 + Q2*M2 + ... + Qn*Mn
If services or rating groups are added to or removed from the pool,
then the total credit is adjusted appropriately. Note that when the
total credit is adjusted because services or rating groups are
removed from the pool, the value that need to be removed is the
consumed one (i.e., Cx*Mx).
Re-authorizations for an individual service or rating group may be
sought at any time; for example, if a 'non-pooled' quota is used up
or the Validity-Time expires.
Where multiple G-S-U-Pool-Reference AVPs (section 8.30) with the same
G-S-U-Pool-Identifier are provided within a Multiple-Services-
Credit-Control AVP (section 8.16) along with the Granted-Service-Unit
AVP, then these MUST have different CC-Unit-Type values, and they all
draw from the credit pool separately. For instance, if one
multiplier for time (M1t) and one multiplier for volume (M1v) are
given, then the used resources from the pool is the sum C1t*M1t +
C1v*M1v, where C1t is the time unit and C1v is the volume unit.
Where service units are provided within a Multiple-Services-Credit-
Control AVP without a corresponding G-S-U-Pool-Reference AVP, then
these are handled independently from any credit pool and from any
other services or rating groups within the session.
The credit pool concept is an optimal tool to avoid the over-
reservation effect of the basic single quota tariff time change
mechanism (the mechanism described in section 5.1.1). Therefore,
Diameter credit-control clients and servers implementing the
independent credit-control of multiple services SHOULD leverage the
credit pool concept when supporting the tariff time change. The
Diameter credit-control server SHOULD include both the Tariff-Time-
Change and Tariff-Change-Usage AVPs in two quota allocations in the
answer message (i.e., two instances of the Multiple-Services-Credit-
Control AVP). One of the granted units is allocated to be used
before the potential tariff change, while the second granted units
are for use after a tariff change. Both granted unit quotas MUST
contain the same Service-Identifier and/or Rating-Group. This dual
quota mechanism ensures that the overall reported used units would
never exceed the credit reservation. The Diameter credit-control
client reports both the used units before and after the tariff change
in a single instance of the Multiple-Services-Credit-Control AVP.
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The failure handling for credit-control sessions is defined in
section 5.7 and reflected in the basic credit-control state machine
in section 7. Credit-control clients and servers implementing the
independent credit-control of multiple services in a (sub-)session
functionality MUST ensure failure handling and general behavior fully
consistent with the above mentioned sections, while maintaining the
ability to handle parallel ongoing credit re-authorization within a
(sub-)session. Therefore, it is RECOMMENDED that Diameter credit-
control clients maintain a PendingU message queue and restart the Tx
timer (section 13) every time a CCR message with the value
UPDATE_REQUEST is sent while they are in PendingU state. When
answers to all pending messages are received, the state machine moves
to OPEN state, and Tx is stopped. Naturally, the action performed
when a problem for the session is detected according to section 5.7
affects all the ongoing services (e.g., failover to a backup server
if possible affect all the CCR messages with the value UPDATE_REQUEST
in the PendingU queue).
Since the client may send CCR messages with the value UPDATE_REQUEST
while in PendingU (i.e., without waiting for an answer to ongoing
credit re-authorization), the time space between these requests may
be very short, and the server may not have received the previous
request(s) yet. Therefore, in this situation the server may receive
out of sequence requests and SHOULD NOT consider this an error
condition. A proper answer is to be returned to each of those
requests.
5.2. First Interrogation
When session based credit-control is required (e.g., the
authentication server indicated a prepaid user), the first
interrogation MUST be sent before the Diameter credit-control client
allows any service event to the end user. The CC-Request-Type is set
to the value INITIAL_REQUEST in the request message.
If the Diameter credit-control client knows the cost of the service
event (e.g., a content server delivering ringing tones may know their
cost) the monetary amount to be charged is included in the
Requested-Service-Unit AVP. If the Diameter credit-control client
does not know the cost of the service event, the Requested-Service-
Unit AVP MAY contain the number of requested service events. Where
the Multiple-Services-Credit-Control AVP is used, it MUST contain the
Requested-Service-Unit AVP to indicate that the quota for the
associated service/rating-group is requested. In the case of
multiple services, the Service-Identifier AVP or the Rating-Group AVP
within the Multiple-Services-Credit-Control AVP always indicates the
service concerned. Additional service event information to be rated
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MAY be sent as service specific AVPs or MAY be sent within the
Service-Parameter-Info AVP at command level. The Service-Context-Id
AVP indicates the service specific document applicable to the
request.
The Event-Timestamp AVP SHOULD be included in the request and
contains the time when the service event is requested in the service
element. The Subscription-Id AVP SHOULD be included to identify the
end user in the credit-control server. The credit-control client MAY
include the User-Equipment-Info AVP so that the credit-control server
has some indication of the type and capabilities of the end user
access device. How the credit-control server uses this information
is outside the scope of this document.
The credit-control server SHOULD rate the service event and make a
credit-reservation from the end user's account that covers the cost
of the service event. If the type of the Requested-Service-Unit AVP
is money, no rating is needed, but the corresponding monetary amount
is reserved from the end user's account.
The credit-control server returns the Granted-Service-Unit AVP in the
Answer message to the Diameter credit-control client. The Granted-
Service-Unit AVP contains the amount of service units that the
Diameter credit-control client can provide to the end user until a
new Credit-Control-Request MUST be sent to the credit-control server.
If several unit types are sent in the Answer message, the credit-
control client MUST handle each unit type separately. The type of
the Granted-Service-Unit AVP can be time, volume, service specific,
or money, depending on the type of service event. The unit type(s)
SHOULD NOT be changed within an ongoing credit-control session.
There MUST be a maximum of one instance of the same unit type in one
Answer message. However, if multiple quotas are conveyed to the
credit-control client in the Multiple-Services-Credit-Control AVPs,
it is possible to carry two instances of the same unit type
associated to a service-identifier/rating-group. This is typically
the case when a tariff time change is expected and the credit-control
server wants to make a distinction between the granted quota before
and after tariff change.
If the credit-control server determines that no further control is
needed for the service, it MAY include the result code indicating
that the credit-control is not applicable (e.g., if the service is
free of charge). This result code at command level implies that the
credit-control session is to be terminated.
The Credit-Control-Answer message MAY also include the Final-Unit-
Indication AVP to indicate that the answer message contains the final
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units for the service. After the end user has consumed these units,
the Diameter credit-control-client MUST behave as described in
section 5.6.
This document defines two different approaches to perform the first
interrogation to be used in different network architectures. The
first approach uses credit-control messages after the user's
authorization and authentication takes place. The second approach
uses service specific authorization messages to perform the first
interrogation during the user's authorization/authentication phase,
and credit-control messages for the intermediate and final
interrogations. If an implementation of the credit-control client
supports both the methods, determining which method to use SHOULD be
configurable.
In service environments such as the Network Access Server (NAS), it
is desired to perform the first interrogation as part of the
authorization/authentication process for the sake of protocol
efficiency. Further credit authorizations after the first
interrogation are performed with credit-control commands defined in
this specification. Implementations of credit-control clients
operating in the mentioned environments SHOULD support this method.
If the credit-control server and AAA server are separate physical
entities, the service element sends the request messages to the AAA
server, which then issues an appropriate request or proxies the
received request forward to the credit-control server.
In other service environments, such as the 3GPP network and some SIP
scenarios, there is a substantial decoupling between
registration/access to the network and the actual service request
(i.e., the authentication/authorization is executed once at
registration/access to the network and is not executed for every
service event requested by the subscriber). In these environments,
it is more appropriate to perform the first interrogation after the
user has been authenticated and authorized. The first, the
intermediate, and the final interrogations are executed with credit-
control commands defined in this specification.
Other IETF standards or standards developed by other standardization
bodies may define the most suitable method in their architectures.
5.2.1. First Interrogation after Authorization and Authentication
The Diameter credit-control client in the service element may get
information from the authorization server as to whether credit-
control is required, based on its knowledge of the end user. If
credit-control is required the credit-control server needs to be
contacted prior to initiating service delivery to the end user. The
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accounting protocol and the credit-control protocol can be used in
parallel. The authorization server may also determine whether the
parallel accounting stream is required.
The following diagram illustrates the case where both protocols are
used in parallel and the service element sends credit-control
messages directly to the credit-control server. More credit-control
sequence examples are given in Annex A.
Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Registration | AA request/answer(accounting,cc or both)|
|<----------------->|<------------------>| |
| : | | |
| : | | |
| Service Request | | |
|------------------>| | |
| | CCR(Initial,Credit-Control AVPs) |
| +|---------------------------------------->|
| CC stream|| | CCA(Granted-Units)|
| +|<----------------------------------------|
| Service Delivery | | |
|<----------------->| ACR(start,Accounting AVPs) |
| : |------------------->|+ |
| : | ACA || Accounting stream |
| |<-------------------|+ |
| : | | |
| : | | |
| | CCR(Update,Used-Units) |
| |---------------------------------------->|
| | | CCA(Granted-Units)|
| |<----------------------------------------|
| : | | |
| : | | |
| End of Service | | |
|------------------>| CCR(Termination, Used-Units) |
| |---------------------------------------->|
| | | CCA |
| |<----------------------------------------|
| | ACR(stop) | |
| |------------------->| |
| | ACA | |
| |<-------------------| |
Figure 2: Protocol example with first interrogation after user's
authorization/authentication
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5.2.2. Authorization Messages for First Interrogation
The Diameter credit-control client in the service element MUST
actively co-operate with the authorization/authentication client in
the construction of the AA request by adding appropriate credit-
control AVPs. The credit-control client MUST add the Credit-Control
AVP to indicate credit-control capabilities and MAY add other
relevant credit-control specific AVPs to the proper
authorization/authentication command to perform the first
interrogation toward the home Diameter AAA server. The Auth-
Application-Id is set to the appropriate value, as defined in the
relevant service specific authorization/authentication application
document (e.g., [NASREQ], [DIAMMIP]). The home Diameter AAA server
authenticates/authorizes the subscriber and determines whether
credit-control is required.
If credit-control is not required for the subscriber, the home
Diameter AAA server will respond as usual, with an appropriate AA
answer message. If credit-control is required for the subscriber and
the Credit-Control AVP with the value set to CREDIT_AUTHORIZATION was
present in the authorization request, the home AAA server MUST
contact the credit-control server to perform the first interrogation.
If credit-control is required for the subscriber and the Credit-
Control AVP was not present in the authorization request, the home
AAA server MUST send an authorization reject answer message.
The Diameter AAA server supporting credit-control is required to send
the Credit-Control-Request command (CCR) defined in this document to
the credit-control server. The Diameter AAA server populates the CCR
based on service specific AVPs used for input to the rating process,
and possibly on credit-control AVPs received in the AA request. The
credit-control server will reserve money from the user's account,
will rate the request and will send a Credit-Control-Answer message
to the home Diameter AAA server. The answer message includes the
Granted-Service-Unit AVP(s) and MAY include other credit-control
specific AVPs, as appropriate. Additionally, the credit-control
server MAY set the Validity-Time and MAY include the Credit-Control-
Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP to
determine what to do if the sending of credit-control messages to the
credit-control server has been temporarily prevented.
Upon receiving the Credit-Control-Answer message from the credit-
control server, the home Diameter AAA server will populate the AA
answer with the received credit-control AVPs and with the appropriate
service attributes according to the authorization/authentication
specific application (e.g., [NASREQ], [DIAMMIP]). It will then
forward the packet to the credit-control client. If the home
Diameter AAA server receives a credit-control reject message, it will
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RFC 4006 Diameter Credit-Control Application August 2005
simply generate an appropriate authorization reject message to the
credit-control client, including the credit-control specific error
code.
In this model, the credit-control client sends further credit-control
messages to the credit-control server via the home Diameter AAA
server. Upon receiving a successful authorization answer message
with the Granted-Service-Unit AVP(s), the credit-control client will
grant the service to the end user and will generate an intermediate
credit-control request, as required by using credit-control commands.
The CC-Request-Number of the first UPDATE_REQUEST MUST be set to 1
(for how to produce unique value for the CC-Request-Number AVP, see
section 8.2).
If service specific re-authorization is performed (i.e.,
authorization-lifetime expires), the credit-control client MUST add
to the service specific re-authorization request the Credit-Control
AVP with a value set to RE_AUTHORIZATION to indicate that the
credit-control server MUST NOT be contacted. When session based
credit-control is used for the subscriber, a constant credit-control
message stream flows through the home Diameter AAA server. The home
Diameter AAA server can make use of this credit-control message flow
to deduce that the user's activity is ongoing; therefore, it is
recommended to set the authorization-lifetime to a reasonably high
value when credit-control is used for the subscriber.
In this scenario, the home Diameter AAA server MUST advertise support
for the credit-control application to its peers during the capability
exchange process.
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The following diagram illustrates the use of
authorization/authentication messages to perform the first
interrogation. The parallel accounting stream is not shown in the
figure.
Service Element Diameter
End User (CC Client) AAA Server CC Server
| Service Request | AA Request (CC AVPs) |
|------------------>|------------------->| |
| | | CCR(Initial, CC AVPs)
| | |------------------->|
| | | CCA(Granted-Units)
| | |<-------------------|
| | AA Answer(Granted-Units) |
| Service Delivery |<-------------------| |
|<----------------->| | |
| : | | |
| : | | |
| : | | |
| | | |
| | CCR(Update,Used-Units) |
| |------------------->| CCR(Update,Used-Units)
| | |------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<-------------------|
| |<-------------------| |
| : | | |
| : | | |
| End of Service | | |
|------------------>| CCR(Termination,Used-Units) |
| |------------------->| CCR(Term.,Used-Units)
| | |------------------->|
| | | CCA |
| | CCA |<-------------------|
| |<-------------------| |
Figure 3: Protocol example with use of the
authorization messages for the first interrogation
5.3. Intermediate Interrogation
When all the granted service units for one unit type are spent by the
end user or the Validity-Time is expired, the Diameter credit-control
client MUST send a new Credit-Control-Request to the credit-control
server. In the event that credit-control for multiple services is
applied in one credit-control session (i.e., units associated to
Service-Identifier(s) or Rating-Group are granted), a new Credit-
Control-Request MUST be sent to the credit-control server when the
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credit reservation has been wholly consumed, or upon expiration of
the Validity-Time. It is always up to the Diameter credit-control
client to send a new request well in advance of the expiration of the
previous request in order to avoid interruption in the service
element. Even if the granted service units reserved by the credit-
control server have not been spent upon expiration of the Validity-
Time, the Diameter credit-control client MUST send a new Credit-
Control-Request to the credit-control server.
There can also be mid-session service events, which might affect the
rating of the current service events. In this case, a spontaneous
updating (a new Credit-Control-Request) SHOULD be sent including
information related to the service event even if all the granted
service units have not been spent or the Validity-Time has not
expired.
When the used units are reported to the credit-control server, the
credit-control client will not have any units in its possession
before new granted units are received from the credit-control server.
When the new granted units are received, these units apply from the
point where the measurement of the reported used units stopped.
Where independent credit-control of multiple services is supported,
this process may be executed for one or more services, a single
rating-group, or a pool within the (sub)session.
The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
intermediate request message. The Subscription-Id AVP SHOULD be
included in the intermediate message to identify the end user in the
credit-control server. The Service-Context-Id AVP indicates the
service specific document applicable to the request.
The Requested-Service-Unit AVP MAY contain the new amount of
requested service units. Where the Multiple-Services-Credit-Control
AVP is used, it MUST contain the Requested-Service-Unit AVP if a new
quota is requested for the associated service/rating-group. The
Used-Service-Unit AVP contains the amount of used service units
measured from the point when the service became active or, if interim
interrogations are used during the session, from the point when the
previous measurement ended. The same unit types used in the previous
message SHOULD be used. If several unit types were included in the
previous answer message, the used service units for each unit type
MUST be reported.
The Event-Timestamp AVP SHOULD be included in the request and
contains the time of the event that triggered the sending of the new
Credit-Control-Request.
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The credit-control server MUST deduct the used amount from the end
user's account. It MAY rate the new request and make a new credit-
reservation from the end user's account that covers the cost of the
requested service event.
A Credit-Control-Answer message with the CC-Request-Type AVP set to
the value UPDATE_REQUEST MAY include the Cost-Information AVP
containing the accumulated cost estimation for the session, without
taking any credit-reservation into account.
The Credit-Control-Answer message MAY also include the Final-Unit-
Indication AVP to indicate that the answer message contains the final
units for the service. After the end user has consumed these units,
the Diameter credit-control-client MUST behave as described in
section 5.6.
There can be several intermediate interrogations within a session.
5.4. Final Interrogation
When the end user terminates the service session, or when the
graceful service termination described in section 5.6 takes place,
the Diameter credit-control client MUST send a final Credit-Control-
Request message to the credit-control server. The CC-Request-Type
AVP is set to the value TERMINATION_REQUEST. The Service-Context-Id
AVP indicates the service specific document applicable to the
request.
The Event-Timestamp AVP SHOULD be included in the request and
contains the time when the session was terminated.
The Used-Service-Unit AVP contains the amount of used service units
measured from the point when the service became active or, if interim
interrogations are used during the session, from the point when the
previous measurement ended. If several unit types were included in
the previous answer message, the used service units for each unit
type MUST be reported.
After final interrogation, the credit-control server MUST refund the
reserved credit amount not used to the end user's account and deduct
the used monetary amount from the end user's account.
A Credit-Control-Answer message with the CC-Request-Type set to the
value TERMINATION_REQUEST MAY include the Cost-Information AVP
containing the estimated total cost for the session in question.
If the user logs off during an ongoing credit-control session, or if
some other reason causes the user to become logged off (e.g., final-
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RFC 4006 Diameter Credit-Control Application August 2005
unit indication causes user logoff according to local policy), the
service element, according to application specific policy, may send a
Session-Termination-Request (STR) to the home Diameter AAA server as
usual [DIAMBASE]. Figure 4 illustrates the case when the final-unit
indication causes user logoff upon consumption of the final granted
units and the generation of STR.
Service Element AAA Server CC Server
End User (CC Client)
| Service Delivery | | |
|<----------------->| | |
| : | | |
| : | | |
| : | | |
| | | |
| | CCR(Update,Used-Units) |
| |------------------->| CCR(Update,Used-Units)
| | |------------------->|
| | CCA(Final-Unit, Terminate)
| CCA(Final-Unit, Terminate)|<-------------------|
| |<-------------------| |
| : | | |
| : | | |
| Disconnect user | | |
|<------------------| CCR(Termination,Used-Units) |
| |------------------->| CCR(Term.,Used-Units)
| | |------------------->|
| | | CCA |
| | CCA |<-------------------|
| |<-------------------| |
| | STR | |
| |------------------->| |
| | STA | |
| |<-------------------| |
Figure 4: User disconnected due to exhausted account
5.5. Server-Initiated Credit Re-Authorization
The Diameter credit-control application supports server-initiated
re-authorization. The credit-control server MAY optionally initiate
the credit re-authorization by issuing a Re-Auth-Request (RAR) as
defined in the Diameter base protocol [DIAMBASE]. The Auth-
Application-Id in the RAR message is set to 4 to indicate Diameter
Credit Control, and the Re-Auth-Request-Type is set to
AUTHORIZE_ONLY.
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Section 5.1.2 defines the feature to enable credit-control for
multiple services within a single (sub-)session where the server can
authorize credit usage at a different level of granularity. Further,
the server may provide credit resources to multiple services or
rating groups as a pool (see section 5.1.2 for details and
definitions). Therefore, the server, based on its service logic and
its knowledge of the ongoing session, can decide to request credit
re-authorization for a whole (sub-)session, a single credit pool, a
single service, or a single rating-group. To request credit re-
authorization for a credit pool, the server includes in the RAR
message the G-S-U-Pool-Identifier AVP indicating the affected pool.
To request credit re-authorization for a service or a rating-group,
the server includes in the RAR message the Service-Identifier AVP or
the Rating-Group AVP, respectively. To request credit re-
authorization for all the ongoing services within the (sub-)session,
the server includes none of the above mentioned AVPs in the RAR
message.
If a credit re-authorization is not already ongoing (i.e., the
credit-control session is in Open state), a credit control client
that receives an RAR message with Session-Id equal to a currently
active credit-control session MUST acknowledge the request by sending
the Re-Auth-Answer (RAA) message and MUST initiate the credit re-
authorization toward the server by sending a Credit-Control-Request
message with the CC-Request-Type AVP set to the value UPDATE_REQUEST.
The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the
RAA message to indicate that an additional message (i.e., CCR message
with the value UPDATE_REQUEST) is required to complete the procedure.
If a quota was allocated to the service, the credit-control client
MUST report the used quota in the Credit-Control-Request. Note that
the end user does not need to be prompted for the credit re-
authorization, since the credit re-authorization is transparent to
the user (i.e., it takes place exclusively between the credit-control
client and the credit-control server).
Where multiple services in a user's session are supported, the
procedure in the above paragraph will be executed at the granularity
requested by the server in the RAR message.
If credit re-authorization is ongoing at the time when the RAR
message is received (i.e., RAR-CCR collision), the credit-control
client successfully acknowledges the request but does not initiate a
new credit re-authorization. The Result-Code 2001 (DIAMETER_SUCCESS)
SHOULD be used in the RAA message to indicate that a credit re-
authorization procedure is already ongoing (i.e., the client was in
PendingU state when the RAR was received). The credit-control server
SHOULD process the Credit-Control-Request as if it was received in
answer to the server initiated credit re-authorization, and should
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consider the server initiated credit re-authorization process
successful upon reception of the Re-Auth-Answer message.
When multiple services are supported in a user's session, the server
may request credit re-authorization for a credit pool (or for the
(sub-)session) while a credit re-authorization is already ongoing for
some of the services or rating-groups. In this case, the client
acknowledges the server request with an RAA message and MUST send a
new Credit-Control-Request message to perform re-authorization for
the remaining services/rating-groups. The Result-Code 2002
(DIAMETER_LIMITED_SUCCESS) SHOULD be used in the RAA message to
indicate that an additional message (i.e., CCR message with value
UPDATE_REQUEST) is required to complete the procedure. The server
processes the received requests and returns an appropriate answer to
both requests.
The above-defined procedures are enabled for each of the possibly
active Diameter credit-control sub-sessions. The server MAY request
re-authorization for an active sub-session by including the CC-Sub-
Session-Id AVP in the RAR message in addition to the Session-Id AVP.
5.6. Graceful Service Termination
When the user's account runs out of money, the user may not be
allowed to compile additional chargeable events. However, the home
service provider may offer some services; for instance, access to a
service portal where it is possible to refill the account, for which
the user is allowed to benefit for a limited time. The length of
this time is usually dependent on the home service provider policy.
This section defines the optional graceful service termination
feature that MAY be supported by the credit-control server. Credit-
control client implementations MUST support the Final-Unit-Indication
with at least the teardown of the ongoing service session once the
subscriber has consumed all the final granted units.
Where independent credit-control of multiple services in a single
credit-control (sub-)session is supported, it is possible to use the
graceful service termination for each of the services/rating-groups
independently. Naturally, the graceful service termination process
defined in the following sub-sections will apply to the specific
service/rating-group as requested by the server.
In some service environments (e.g., NAS), the graceful service
termination may be used to redirect the subscriber to a service
portal for online balance refill or other services offered by the
home service provider. In this case, the graceful termination
process installs a set of packet filters to restrict the user's
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access capability only to/from the specified destinations. All the
IP packets not matching the filters will be dropped or, possibly,
re-directed to the service portal. The user may also be sent an
appropriate notification as to why the access has been limited.
These actions may be communicated explicitly from the server to the
client or may be configured per-service at the client. Explicitly
signaled redirect or restrict instructions always take precedence
over configured ones.
It is also possible use the graceful service termination to connect
the prepaid user to a top-up server that plays an announcement and
prompts the user to replenish the account. In this case, the
credit-control server sends only the address of the top-up server
where the prepaid user shall be connected after the final granted
units have been consumed. An example of this is given in Appendix A
(Flow VII).
The credit-control server MAY initiate the graceful service
termination by including the Final-Unit-Indication AVP in the
Credit-Control-Answer to indicate that the message contains the final
units for the service.
When the credit-control client receives the Final-Unit-Indication AVP
in the answer from the server, its behavior depends on the value
indicated in the Final-Unit-Action AVP. The server may request the
following actions: TERMINATE, REDIRECT, or RESTRICT_ACCESS.
A following figure illustrates the graceful service termination
procedure described in the following sub-sections.
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Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Service Delivery | | |
|<----------------->| | |
| |CCR(Update,Used-Units) |
| |------------------->|CCR(Update,Used-Units)
| : | |------------------->|
| : | |CCA(Final-Unit,Action)
| : | |<-------------------|
| |CCA(Final-Unit,Action) |
| |<-------------------| |
| | | |
| : | | |
| : | | |
| : | | |
| /////////////// |CCR(Update,Used-Units) |
|/Final Units End/->|------------------->|CCR(Update,Used-Units)
|/Action and // | |------------------->|
|/Restrictions // | | CCA(Validity-Time)|
|/Start // | CCA(Validity-Time)|<-------------------|
| ///////////// |<-------------------| |
| : | | |
| : | | |
| Replenish Account +-------+ |
|<-------------------------------------------->|Account| |
| | | +-------+ |
| | | RAR |
| + | RAR |<===================|
| | |<===================| |
| | | RAA | |
| ///////////// | |===================>| RAA |
| /If supported / | | CCR(Update) |===================>|
| /by CC Server/ | |===================>| CCR(Update) |
| ///////////// | | |===================>|
| | | | CCA(Granted-Unit)|
| | | CCA(Granted-Unit)|<===================|
| Restrictions ->+ |<===================| |
| removed | | |
| : | | |
| OR | CCR(Update) | |
| Validity-Time ->|------------------->| CCR(Update) |
| expires | |------------------->|
| | | CCA(Granted-Unit)|
| | CCA(Granted-Unit)|<-------------------|
| Restrictions ->|<-------------------| |
| removed | | |
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Figure 5: Optional graceful service termination procedure
5.6.1. Terminate Action
The Final-Unit-Indication AVP with Final-Unit-Action TERMINATE does
not include any other information. When the subscriber has consumed
the final granted units, the service element MUST terminate the
service. This is the default handling applicable whenever the
credit-control client receives an unsupported Final-Unit-Action value
and MUST be supported by all the Diameter credit-control client
implementations conforming to this specification. A final Credit-
Control-Request message to the credit-control server MUST be sent if
the Final-Unit-Indication AVP indicating action TERMINATE was present
at command level. The CC-Request-Type AVP in the request is set to
the value TERMINATION_REQUEST.
5.6.2. Redirect Action
The Final-Unit-Indication AVP with Final-Unit-Action REDIRECT
indicates to the service element supporting this action that, upon
consumption of the final granted units, the user MUST be re-directed
to the address specified in the Redirect-Server AVP as follows.
The credit-control server sends the Redirect-Server AVP in the
Credit-Control-Answer message. In such a case, the service element
MUST redirect or connect the user to the destination specified in the
Redirect-Server AVP, if possible. When the end user is redirected
(by using protocols others than Diameter) to the specified server or
connected to the top-up server, an additional authorization (and
possibly authentication) may be needed before the subscriber can
replenish the account; however, this is out of the scope of this
specification.
In addition to the Redirect-Server AVP, the credit-control server MAY
include one or more Restriction-Filter-Rule AVPs or one or more
Filter-Id AVPs in the Credit-Control-Answer message to enable the
user to access other services (for example, zero-rated services). In
such a case, the access device MUST drop all the packets not matching
the IP filters specified in the Credit-Control-Answer message and, if
possible, redirect the user to the destination specified in the
Redirect-Server AVP.
An entity other than the credit-control server may provision the
access device with appropriate IP packet filters to be used in
conjunction with the Diameter credit-control application. This case
is considered in section 5.6.3.
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When the final granted units have been consumed, the credit-control
client MUST perform an intermediate interrogation. The purpose of
this interrogation is to indicate to the credit-control server that
the specified action started and to report the used units. The
credit-control server MUST deduct the used amount from the end user's
account but MUST NOT make a new credit reservation. The credit-
control client, however, may send intermediate interrogations before
all the final granted units have been consumed for which rating and
money reservation may be needed; for instance, upon Validity-Time
expires or upon mid-session service events that affect the rating of
the current service. Therefore, the credit-control client MUST NOT
include any rating related AVP in the request sent once all the final
granted units have been consumed as an indication to the server that
the requested final unit action started, rating and money reservation
are not required (when the Multiple-Services-Credit-Control AVP is
used, the Service-Identifier or Rating-Group AVPs is included to
indicate the concerned services). Naturally, the Credit-Control-
Answer message does not contain any granted service unit and MUST
include the Validity-Time AVP to indicate to the credit-control
client how long the subscriber is allowed to use network resources
before a new intermediate interrogation is sent to the server.
At the expiry of Validity-Time, the credit-control client sends a
Credit-Control-Request (UPDATE_REQUEST) as usual. This message does
not include the Used-Service-Unit AVP, as there is no allotted quota
to report. The credit-control server processes the request and MUST
perform the credit reservation. If during this time the subscriber
did not replenish his/her account, whether he/she will be
disconnected or will be granted access to services not controlled by
a credit-control server for an unlimited time is dependent on the
home service provider policy (note: the latter option implies that
the service element should not remove the restriction filters upon
termination of the credit-control). The server will return the
appropriate Result-Code (see section 9.1) in the Credit-Control-
Answer message in order to implement the policy-defined action.
Otherwise, new quota will be returned, the service element MUST
remove all the possible restrictions activated by the graceful
service termination process and continue the credit-control session
and service session as usual.
The credit-control client may not wait until the expiration of the
Validity-Time and may send a spontaneous update (a new Credit-
Control-Request) if the service element can determine, for instance,
that communication between the end user and the top-up server took
place. An example of this is given in Appendix A (Figure A.8).
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Note that the credit-control server may already have initiated the
above-described process for the first interrogation. However, the
user's account might be empty when this first interrogation is
performed. In this case, the subscriber can be offered a chance to
replenish the account and continue the service. The credit-control
client receives a Credit-Control-Answer or service specific
authorization answer with the Final-Unit-Indication and Validity-Time
AVPs but no Granted-Service-Unit. It immediately starts the graceful
service termination without sending any message to the server. An
example of this case is illustrated in Appendix A.
5.6.3. Restrict Access Action
A Final-Unit-Indication AVP with the Final-Unit-Action
RESTRICT_ACCESS indicates to the device supporting this action that
the user's access MUST be restricted according to the IP packet
filters given in the Restriction-Filter-Rule AVP(s) or according to
the IP packet filters identified by the Filter-Id AVP(s). The
credit-control server SHOULD include either the Restriction-Filter-
Rule AVP or the Filter-Id AVP in the Credit-Control-Answer message.
An entity other than the credit-control server may provision the
access device with appropriate IP packet filters to be used in
conjunction with the Diameter credit-control application. Such an
entity may, for instance, configure the access device with IP flows
to be passed when the Diameter credit-control application indicates
RESTRICT_ACCESS or REDIRECT. The access device passes IP packets
according to the filter rules that may have been received in the
Credit-Control-Answer message in addition to those that may have been
configured by the other entity. However, when the user's account
cannot cover the cost of the requested service, the action taken is
the responsibility of the credit-control server that controls the
prepaid subscriber.
If another entity working in conjunction with the Diameter credit-
control application already provisions the access device with all the
required filter rules for the end user, the credit-control server
presumably need not send any additional filter. Therefore, it is
RECOMMENDED that credit-control server implementations supporting the
graceful service termination be configurable for sending the
Restriction-Filter-Rule AVP, the Filter-Id AVP, or none of the above.
When the final granted units have been consumed, the credit-control
client MUST perform an intermediate interrogation. The credit-
control client and the credit-control server process this
intermediate interrogation and execute subsequent procedures, as
specified in the previous section for the REDIRECT action.
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The credit-control server may initiate the graceful service
termination with action RESTRICT_ACCESS already for the first
interrogation, as specified in the previous section for the REDIRECT
action.
5.6.4. Usage of the Server-Initiated Credit Re-Authorization
Once the subscriber replenishes the account, she presumably expects
all the restrictions placed by the graceful termination procedure to
be removed immediately and unlimited service' access to be resumed.
For the best user experience, the credit-control server
implementation MAY support the server-initiated credit re-
authorization (see section 5.5). In such a case, upon the successful
account top-up, the credit-control server sends the Re-Auth-Request
(RAR) message to solicit the credit re-authorization. The credit-
control client initiates the credit re-authorization by sending the
Credit-Control-Request message with the CC-Request-Type AVP set to
the value UPDATE_REQUEST. The Used-Service-Unit AVP is not included
in the request, as there is no allotted quota to report. The
Requested-Service-Unit AVP MAY be included in the request. After the
credit-control client successfully receives the Credit-Control-Answer
with new Granted-Service-Unit, all the possible restrictions
activated for the purpose of the graceful service termination MUST be
removed in the service element. The credit-control session and the
service session continue as usual.
5.7. Failure Procedures
The Credit-Control-Failure-Handling AVP (CCFH), as described in this
section, determines the behavior of the credit-control client in
fault situations. The CCFH may be received from the Diameter home
AAA server, from the credit-control server, or may be configured
locally. The CCFH value received from the home AAA server overrides
the locally configured value. The CCFH value received from the
credit-control server in the Credit-Control-Answer message always
overrides any existing value.
The authorization server MAY include the Accounting-Realtime-Required
AVP to determine what to do if the sending of accounting records to
the accounting server has been temporarily prevented, as defined in
[DIAMBASE]. It is RECOMMENDED that the client complement the
credit-control failure procedures with backup accounting flow toward
an accounting server. By using different combinations of
Accounting-Realtime-Required and Credit-Control-Failure-Handling
AVPs, different safety levels can be built. For example, by choosing
a Credit-Control-Failure-Handling AVP equal to CONTINUE for the
credit-control flow and a Accounting-Realtime-Required AVP equal to
DELIVER_AND_GRANT for the accounting flow, the service can be granted
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RFC 4006 Diameter Credit-Control Application August 2005
to the end user even if the connection to the credit-control server
is down, as long as the accounting server is able to collect the
accounting information and information exchange is taking place
between the accounting server and credit-control server.
As the credit-control application is based on real-time bi-
directional communication between the credit-control client and the
credit-control server, the usage of alternative destinations and the
buffering of messages may not be sufficient in the event of
communication failures. Because the credit-control server has to
maintain session states, moving the credit-control message stream to
a backup server requires a complex context transfer solution.
Whether the credit-control message stream is moved to a backup
credit-control server during an ongoing credit-control session
depends on the value of the CC-Session-Failover AVP. However,
failover may occur at any point in the path between the credit-
control client and the credit-control server if a transport failure
is detected with a peer, as described in [DIAMBASE]. As a
consequence, the credit-control server might receive duplicate
messages. These duplicates or out of sequence messages can be
detected in the credit-control server based on the credit-control
server session state machine (section 7), Session-Id AVP, and CC-
Request-Number AVP.
If a failure occurs during an ongoing credit-control session, the
credit-control client may move the credit-control message stream to
an alternative server if the CC-server indicated FAILOVER_SUPPORTED
in the CC-Session-Failover AVP. A secondary credit-control server
name, either received from the home Diameter AAA server or configured
locally, can be used as an address of the backup server. If the CC-
Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED, the credit-
control message stream MUST NOT be moved to a backup server.
For new credit-control sessions, failover to an alternative credit-
control server SHOULD be performed if possible. For instance, if an
implementation of the credit-control client can determine primary
credit-control server unavailability, it can establish the new
credit-control sessions with a possibly available secondary credit-
control server.
The AAA transport profile [AAATRANS] defines the application layer
watchdog algorithm that enables failover from a peer that has failed
and is controlled by a watchdog timer (Tw) defined in [AAATRANS].
The recommended default initial value for Tw (Twinit) is 30 seconds.
Twinit may be set as low as 6 seconds; however, according to
[AAATRANS], setting too low a value for Twinit is likely to result in
an increased probability of duplicates, as well as an increase in
spurious failover and failback attempts. The Diameter base protocol
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RFC 4006 Diameter Credit-Control Application August 2005
is common to several different types of Diameter AAA applications
that may be run in the same service element. Therefore, tuning the
timer Twinit to a lower value in order to satisfy the requirements of
real-time applications, such as the Diameter credit-control
application, will certainly cause the above mentioned problems. For
prepaid services, however, the end user expects an answer from the
network in a reasonable time. Thus, the Diameter credit-control
client will react faster than would the underlying base protocol.
Therefore this specification defines the timer Tx that is used by the
credit-control client (as defined in section 13) to supervise the
communication with the credit-control server. When the timer Tx
elapses, the credit-control client takes an action to the end user
according to the Credit-Control-Failure-Handling AVP.
When Tx expires, the Diameter credit-control client always terminates
the service if the Credit-Control-Failure-Handling (CCFH) AVP is set
to the value TERMINATE. The credit-control session may be moved to
an alternative server only if a protocol error DIAMETER_TOO_BUSY or
DIAMETER_UNABLE_TO_DELIVER is received before Tx expires. Therefore,
the value TERMINATE is not appropriate if proper failover behavior is
desired.
If the Credit-Control-Failure-Handling AVP is set to the value
CONTINUE or RETRY_AND_TERMINATE, the service will be granted to the
end user when the timer Tx expires. An answer message with granted-
units may arrive later if the base protocol transport failover
occurred in the path to the credit-control server. (The Twinit
default value is 3 times more than the Tx recommended value.) The
credit-control client SHOULD grant the service to the end user, start
monitoring the resource usage, and wait for the possible late answer
until the timeout of the request (e.g., 120 seconds). If the request
fails and the CC-Session-Failover AVP is set to
FAILOVER_NOT_SUPPORTED, the credit-control client terminates or
continues the service depending on the value set in the CCFH and MUST
free all the reserved resources for the credit-control session. If
the protocol error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is
received or the request times out and the CC-Session-Failover AVP is
set to FAILOVER_SUPPORTED, the credit-control client MAY send the
request to a backup server, if possible. If the credit-control
client receives a successful answer from the backup server, it
continues the credit-control session with such a server. If the re-
transmitted request also fails, the credit-control client terminates
or continues the service depending on the value set in the CCFH and
MUST free all the reserved resources for the credit-control session.
If a communication failure occurs during the graceful service
termination procedure, the service element SHOULD always terminate
the ongoing service session.
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If the credit-control server detects a failure during an ongoing
credit-control session, it will terminate the credit-control session
and return the reserved units back to the end user's account.
The supervision session timer Tcc (as defined in section 13) is used
in the credit-control server to supervise the credit-control session.
In order to support failover between credit-control servers,
information transfer about the credit-control session and account
state SHOULD take place between the primary and the secondary
credit-control server. Implementations supporting the credit-control
session failover MUST also ensure proper detection of duplicate or
out of sequence messages. The communication between the servers is
regarded as an implementation issue and is outside of the scope of
this specification.
6. One Time Event
The one-time event is used when there is no need to maintain any
state in the Diameter credit-control server; for example, enquiring
about the price of the service. The use of a one-time event implies
that the user has been authenticated and authorized beforehand.
The one time event can be used when the credit-control client wants
to know the cost of the service event or to check the account balance
without any credit-reservation. It can also be used for refunding
service units on the user's account or for direct debiting without
any credit-reservation. The one time event is shown in Figure 6.
Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Service Request | | |
|------------------>| | |
| | CCR(Event) | |
| |------------------->| CCR(Event) |
| | |------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<-------------------|
| Service Delivery |<-------------------| |
|<----------------->| | |
Figure 6: One time event
In environments such as the 3GPP architecture, the one time event can
be sent from the service element directly to the credit-control
server.
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6.1. Service Price Enquiry
The credit-control client may need to know the price of the service
event. Services offered by application service providers whose
prices are not known in the credit-control client might exist. The
end user might also want to get an estimation of the price of a
service event before requesting it.
A Diameter credit-control client requesting the cost information MUST
set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
Requested-Action AVP set to PRICE_ENQUIRY, and set the requested
service event information into the Service-Identifier AVP in the
Credit-Control-Request message. Additional service event information
may be sent as service specific AVPs or within the Service-
Parameter-Info AVP. The Service-Context-Id AVP indicates the service
specific document applicable to the request.
The credit-control server calculates the cost of the requested
service event, but it does not perform any account balance check or
credit-reservation from the account.
The estimated cost of the requested service event is returned to the
credit-control client in the Cost-Information AVP in the Credit-
Control-Answer message.
6.2. Balance Check
The Diameter credit-control client may only have to verify that the
end user's account balance covers the cost of a certain service
without reserving any units from the account at the time of the
inquiry. This method does not guarantee that credit would be left
when the Diameter credit-control client requests the debiting of the
account with a separate request.
A Diameter credit-control client requesting the balance check MUST
set the CC-Request-Type AVP equal to EVENT_REQUEST, include a
Requested-Action AVP set to CHECK_BALANCE, and include the
Subscription-Id AVP in order to identify the end user in the credit-
control server. The Service-Context-Id AVP indicates the service
specific document applicable to the request.
The credit-control server makes the balance check, but it does not
make any credit-reservation from the account.
The result of balance check (ENOUGH_CREDIT/NO_CREDIT) is returned to
the credit-control client in the Check-Balance-Result AVP in the
Credit-Control-Answer message.
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6.3. Direct Debiting
There are certain service events for which service execution is
always successful in the service environment. The delay between the
service invocation and the actual service delivery to the end user
can be sufficiently long that the use of the session-based credit-
control would lead to unreasonably long credit-control sessions. In
these cases, the Diameter credit-control client can use the one-time
event scenario for direct debiting. The Diameter credit-control
client SHOULD be sure that the requested service event execution
would be successful when this scenario is used.
In the Credit-Control-Request message, the CC-Request-Type is set to
the value EVENT_REQUEST and the Requested-Action AVP is set to
DIRECT_DEBITING. The Subscription-Id AVP SHOULD be included to
identify the end user in the credit-control server. The Event-
Timestamp AVP SHOULD be included in the request and contain the time
when the service event is requested in the service element. The
Service-Context-Id AVP indicates the service specific document
applicable to the request.
The Diameter credit-control client MAY include the monetary amount to
be charged in the Requested-Service-Unit AVP, if it knows the cost of
the service event. If the Diameter credit-control client does not
know the cost of the service event, the Requested-Service-Unit AVP
MAY contain the number of requested service events. The Service-
Identifier AVP always indicates the service concerned. Additional
service event information to be rated MAY be sent as service specific
AVPs or within the Service-Parameter-Info AVP.
The credit-control server SHOULD rate the service event and deduct
the corresponding monetary amount from the end user's account. If
the type of the Requested-Service-Unit AVP is money, no rating is
needed, but the corresponding monetary amount is deducted from the
end user's account.
The credit-control server returns the Granted-Service-Unit AVP in the
Credit-Control-Answer message to the Diameter credit-control client.
The Granted-Service-Unit AVP contains the amount of service units
that the Diameter credit-control client can provide to the end user.
The type of the Granted-Service-Unit can be time, volume, service
specific, or money, depending on the type of service event.
If the credit-control server determines that no credit-control is
needed for the service, it can include the result code indicating
that the credit-control is not applicable (e.g., service is free of
charge).
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For informative purposes, the Credit-Control-Answer message MAY also
include the Cost-Information AVP containing the estimated total cost
of the requested service.
6.4. Refund
Some services may refund service units to the end user's account; for
example, gaming services.
The credit-control client MUST set CC-Request-Type to the value
EVENT_REQUEST and the Requested-Action AVP to REFUND_ACCOUNT in the
Credit-Control-Request message. The Subscription-Id AVP SHOULD be
included to identify the end user in the credit-control server. The
Service-Context-Id AVP indicates the service specific document
applicable to the request.
The Diameter credit-control client MAY include the monetary amount to
be refunded in the Requested-Service-Unit AVP. The Service-
Identifier AVP always indicates the concerned service. If the
Diameter credit-control client does not know the monetary amount to
be refunded, in addition to the Service-Identifier AVP it MAY send
service specific AVPs or the Service-Parameter-Info AVP containing
additional service event information to be rated.
For informative purposes, the Credit-Control-Answer message MAY also
include the Cost-Information AVP containing the estimated monetary
amount of refunded unit.
6.5. Failure Procedure
Failover to an alternative credit-control server is allowed for a one
time event, as the server is not maintaining session states. For
instance, if the credit-control client receives a protocol error
DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY, it can re-send the
request to an alternative server, if possible. There MAY be protocol
transparent Diameter relays and redirect agents or Diameter credit-
control proxies between the credit-control client and credit-control
server. Failover may occur at any point in the path between the
credit-control client and the credit-control server if a transport
failure is detected with a peer, as described in [DIAMBASE]. Because
there can be duplicate requests for various reasons, the credit-
control server is responsible for real time duplicate detection.
Implementation issues for duplicate detection are discussed in
[DIAMBASE], Appendix C.
When the credit-control client detects a communication failure with
the credit-control server, its behavior depends on the requested
action. The timer Tx (as defined in section 13) is used in the
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credit-control client to supervise the communication with the
credit-control server.
If the requested action is PRICE_ENQUIRY or CHECK_BALANCE and
communication failure is detected, the credit-control client SHOULD
forward the request messages to an alternative credit-control server,
if possible. The secondary credit-control server name, if received
from the home Diameter AAA server, can be used as an address of
backup server.
If the requested action is DIRECT_DEBITING, the Direct-Debiting-
Failure-Handling AVP (DDFH) controls the credit-control client's
behavior. The DDFH may be received from the home Diameter AAA server
or may be locally configured. The credit-control server may also
send the DDFH in any CCA message to be used for direct debiting
events compiled thereafter. The DDFH value received from the home
Diameter AAA server overrides the locally configured value, and the
DDFH value received from the credit-control server in a Credit-
Control-Answer message always overrides any existing value.
If the DDFH is set to TERMINATE_OR_BUFFER, the credit-control client
SHOULD NOT grant the service if it can determine, eventually after a
possible re-transmission attempt to an alternative credit-control
server, from the result code or error code in the answer message that
units have not been debited. Otherwise, the credit-control client
SHOULD grant the service to the end user and store the request in the
credit-control application level non-volatile storage. (Note that
re-sending the request at a later time is not a guarantee that the
service will be debited, as the user's account may be empty when the
server successfully processes the request.) The credit-control
client MUST mark these request messages as possible duplicates by
setting the T-flag in the command header as described in [DIAMBASE],
section 3.
If the Direct-Debiting-Failure-Handling AVP is set to CONTINUE, the
service SHOULD be granted, even if credit-control messages cannot be
delivered and messages are not buffered.
If the timer Tx expires, the credit-control client MUST continue the
service and wait for a possible late answer. If the request times
out, the credit-control client re-transmits the request (marked with
T-flag) to a backup credit-control server, if possible. If the re-
transmitted request also times out, or if a temporary error is
received in answer, the credit-control client buffers the request if
the value of the Direct-Debiting-Failure-Handling AVP is set to
TERMINATE_OR_BUFFER. If a failed answer is received for the
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re-transmitted request, the credit-control client frees all the
resources reserved for the event message and deletes the request
regardless of the value of the DDFH.
The Credit-Control-Request with the requested action REFUND_ACCOUNT
should always be stored in the credit-control application level non-
volatile storage in case of temporary failure. The credit-control
client MUST mark the re-transmitted request message as a possible
duplicate by setting the T-flag in the command header as described in
[DIAMBASE], section 3.
For stored requests, the implementation may choose to limit the
number of re-transmission attempts and to define a re-transmission
interval.
Note that only one place in the credit-control system SHOULD be
responsible for duplicate detection. If there is only one credit-
control server within the given realm, the credit-control server may
perform duplicate detection. If there is more than one credit-
control server in a given realm, only one entity in the credit-
control system should be responsible, to ensure that the end user's
account is not debited or credited multiple times for the same
service event.
7. Credit-Control Application State Machine
This section defines the credit-control application state machine.
The first four state machines are to be observed by credit-control
clients. The first one describes the session-based credit-control
when the first interrogation is executed as part of the
authorization/authentication process. The second describes the
session-based credit-control when the first interrogation is executed
after the authorization/authentication process. The requirements as
to what state machines have to be supported are discussed in section
5.2.
The third state machine describes the session-based credit-control
for the intermediate and final interrogations. The fourth one
describes the event-based credit-control. These latter state
machines are to be observed by all implementations that conform to
this specification.
The fifth state machine describes the credit-control session from a
credit-control server perspective.
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Any event not listed in the state machines MUST be considered an
error condition, and a corresponding answer, if applicable, MUST be
returned to the originator of the message.
In the state table, the event 'Failure to send' means that the
Diameter credit-control client is unable to communicate with the
desired destination or, if failover procedure is supported, with a
possibly defined alternative destination (e.g., the request times out
and the answer message is not received). This could be due to the
peer being down, or due to a physical link failure in the path to or
from the credit-control server.
The event 'Temporary error' means that the Diameter credit-control
client received a protocol error notification (DIAMETER_TOO_BUSY,
DIAMETER_UNABLE_TO_DELIVER, or DIAMETER_LOOP_DETECTED) in the
Result-Code AVP of the Credit-Control-Answer command. The above
protocol error notification may ultimately be received in answer to
the re-transmitted request to a defined alternative destination, if
failover is supported.
The event 'Failed answer' means that the Diameter credit-control
client received non-transient failure (permanent failure)
notification in the Credit-Control-Answer command. The above
permanent failure notification may ultimately be received in answer
to the re-transmitted request to a defined alternative destination,
if failover is supported.
The action 'store request' means that a request is stored in the
credit-control application level non-volatile storage.
The event 'Not successfully processed' means that the credit-control
server could not process the message; e.g., due to an unknown end
user, account being empty, or errors defined in [DIAMBASE].
The event 'User service terminated' can be triggered by various
reasons, e.g., normal user termination, network failure, and ASR
(Abort-Session-Request). The Termination-Cause AVP contains
information about the termination reason, as specified in [DIAMBASE].
The Tx timer, which is used to control the waiting time in the
credit-control client in the Pending state, is stopped upon exit of
the Pending state. The stopping of the Tx timer is omitted in the
state machine when the new state is Idle, as moving to Idle state
implies the clearing of the session and all the variables associated
to it.
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RFC 4006 Diameter Credit-Control Application August 2005
The states PendingI, PendingU, PendingT, PendingE, and PendingB stand
for pending states to wait for an answer to a credit-control request
related to Initial, Update, Termination, Event, or Buffered request,
respectively.
The acronyms CCFH and DDFH stand for Credit-Control-Failure-Handling
and Direct-Debiting-Failure-Handling, respectively.
In the following state machine table, the failover to a secondary
server upon 'Temporary error' or 'Failure to send' is not explicitly
described. Moving an ongoing credit-control message stream to an
alternative server is, however, possible if the CC-Session-Failover
AVP is set to FAILOVER_SUPPORTED, as described in section 5.7.
Re-sending a credit-control event to an alternative server is
supported as described in section 6.5.
CLIENT, SESSION BASED for the first interrogation with AA request
State Event Action New State
---------------------------------------------------------------
Idle Client or device requests Send PendingI
access/service AA request
with added
CC AVPs,
start Tx
PendingI Successful AA req. Grant Open
answer received service to
end user,
stop Tx
PendingI Tx expired Disconnect Idle
user/dev
PendingI Failed AA answer received Disconnect Idle
user/dev
PendingI AA answer Grant Idle
received with result code service
equal to CREDIT_CONTROL_ to end user
NOT_APPLICABLE
PendingI User service terminated Queue PendingI
termination
event
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PendingI Change in rating condition Queue PendingI
changed
rating
condition
event
CLIENT, SESSION BASED for the first interrogation with CCR
State Event Action New State
----------------------------------------------------------------
Idle Client or device requests Send PendingI
access/service CC initial
req.,
start Tx
PendingI Successful CC initial Stop Tx Open
answer received
PendingI Failure to send, or Grant Idle
temporary error and service to
CCFH equal to CONTINUE end user
PendingI Failure to send, or Terminate Idle
temporary error and end user's
CCFH equal to TERMINATE service
or to RETRY_AND_TERMINATE
PendingI Tx expired and CCFH Terminate Idle
equal to TERMINATE end user's
service
PendingI Tx expired and CCFH equal Grant PendingI
to CONTINUE or to service to
RETRY_AND_TERMINATE end user
PendingI CC initial answer Terminate Idle
received with result code end user's
END_USER_SERVICE_DENIED or service
USER_UNKNOWN
PendingI CC initial answer Grant Idle
received with result code service
equal to CREDIT_CONTROL_ to end user
NOT_APPLICABLE
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PendingI Failed CC initial answer Grant Idle
received and CCFH equal to service to
CONTINUE end user
PendingI Failed CC initial answer Terminate Idle
received and CCFH equal end user's
to TERMINATE or to service
RETRY_AND_TERMINATE
PendingI User service terminated Queue PendingI
termination
event
PendingI Change in rating condition Queue PendingI
changed
rating
condition
event
CLIENT, SESSION BASED for intermediate and final interrogations
State Event Action New State
----------------------------------------------------------------
Open Granted unit elapses Send PendingU
and no final unit CC update
indication received req.,
start Tx
Open Granted unit elapses Terminate PendingT
and final unit action end user's
equal to TERMINATE service, send
received CC termination
req.
Open Change in rating condition Send PendingU
in queue CC update
req.,
Start Tx
Open Service terminated in queue Send PendingT
CC termination
req.
Open Change in rating condition Send PendingU
or Validity-Time elapses CC update
req.,
Start Tx
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Open User service terminated Send PendingT
CC termination
req.
Open RAR received Send RAA PendingU
followed by
CC update req.,
start Tx
PendingU Successful CC update Stop Tx Open
answer received
PendingU Failure to send, or Grant Idle
temporary error and service to
CCFH equal to CONTINUE end user
PendingU Failure to send, or Terminate Idle
temporary error and end user's
CCFH equal to TERMINATE service
or to RETRY_AND_TERMINATE
PendingU Tx expired and CCFH Terminate Idle
equal to TERMINATE end user's
service
PendingU Tx expired and CCFH equal Grant PendingU
to CONTINUE or to service to
RETRY_AND_TERMINATE end user
PendingU CC update answer Terminate Idle
received with result code end user's
END_USER_SERVICE_DENIED service
PendingU CC update answer Grant Idle
received with result code service
equal to CREDIT_CONTROL_ to end user
NOT_APPLICABLE
PendingU Failed CC update Grant Idle
answer received and service to
CCFH equal to CONTINUE end user
PendingU Failed CC update Terminate Idle
answer received and CCFH end user's
equal to TERMINATE or service
to RETRY_AND_TERMINATE
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PendingU User service terminated Queue PendingU
termination
event
PendingU Change in rating Queue PendingU
condition changed
rating
condition
event
PendingU RAR received Send RAA PendingU
PendingT Successful CC Idle
termination answer received
PendingT Failure to send, temporary Idle
error, or failed answer
PendingT Change in rating condition PendingT
CLIENT, EVENT BASED
State Event Action New State
----------------------------------------------------------------
Idle Client or device requests Send PendingE
a one-time service CC event
req.,
Start Tx
Idle Request in storage Send PendingB
stored
request
PendingE Successful CC event Grant Idle
answer received service to
end user
PendingE Failure to send, temporary Indicate Idle
error, failed CC event service
answer received, or error
Tx expired; requested
action CHECK_BALANCE or
PRICE_ENQUIRY
PendingE CC event answer Terminate Idle
received with result code end user's
END_USER_SERVICE_DENIED or service
USER_UNKNOWN and Tx running
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PendingE CC event answer Grant Idle
received with result code service
CREDIT_CONTROL_NOT_APPLICABLE; to end
requested action user
DIRECT_DEBITING
PendingE Failure to send, temporary Grant Idle
error, or failed CC event service
answer received; requested to end
action DIRECT_DEBITING; user
DDFH equal to CONTINUE
PendingE Failed CC event Terminate Idle
answer received or temporary end user's
error; requested action service
DIRECT_DEBITING;
DDFH equal to
TERMINATE_OR_BUFFER and
Tx running
PendingE Tx expired; requested Grant PendingE
action DIRECT_DEBITING service
to end
user
PendingE Failure to send; requested Store Idle
action DIRECT_DEBITING; request with
DDFH equal to T-flag
TERMINATE_OR_BUFFER
PendingE Temporary error; requested Store Idle
action DIRECT_DEBITING; request
DDFH equal to
TERMINATE_OR_BUFFER;
Tx expired
PendingE Failed answer or answer Idle
received with result code
END_USER_SERVICE DENIED or
USER_UNKNOWN; requested action
DIRECT_DEBITING; Tx expired
PendingE Failed CC event answer Indicate Idle
received; requested service
action REFUND_ACCOUNT error and
delete request
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PendingE Failure to send or Store Idle
Tx expired; requested request
action REFUND_ACCOUNT with T-flag
PendingE Temporary error, Store Idle
and requested action request
REFUND_ACCOUNT
PendingB Successful CC answer Delete Idle
received request
PendingB Failed CC answer Delete Idle
received request
PendingB Failure to send or Idle
temporary error
SERVER, SESSION AND EVENT BASED
State Event Action New State
----------------------------------------------------------------
Idle CC initial request Send Open
received and successfully CC initial
processed answer,
reserve units,
start Tcc
Idle CC initial request Send Idle
received but not CC initial
successfully processed answer with
Result-Code
!= SUCCESS
Idle CC event request Send Idle
received and successfully CC event
processed answer
Idle CC event request Send Idle
received but not CC event
successfully processed answer with
Result-Code
!= SUCCESS
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Open CC update request Send CC Open
received and successfully update answer,
processed debit used
units,
reserve
new units,
restart Tcc
Open CC update request Send Idle
received but not CC update
successfully processed answer with
Result-Code
!= SUCCESS,
debit used
units
Open CC termination request Send Idle
received and successfully CC termin.
processed answer,
Stop Tcc,
debit used
units
Open CC termination request Send Idle
received but not CC termin.
successfully processed answer with
Result-Code
!= SUCCESS,
debit used
units
Open Session supervision timer Tcc Release Idle
expired reserved
units
8. Credit-Control AVPs
This section defines the credit-control AVPs that are specific to
Diameter credit-control application and that MAY be included in the
Diameter credit-control messages.
The AVPs defined in this section MAY also be included in
authorization commands defined in authorization-specific
applications, such as [NASREQ] and [DIAMMIP], if the first
interrogation is performed as part of the
authorization/authentication process, as described in section 5.2.
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The Diameter AVP rules are defined in the Diameter Base [DIAMBASE],
section 4. These AVP rules are observed in AVPs defined in this
section.
The following table describes the Diameter AVPs defined in the
credit-control application, their AVP Code values, types, possible
flag values, and whether the AVP MAY be encrypted. The Diameter base
[DIAMBASE] specifies the AVP Flag rules for AVPs in section 4.5.
+--------------------+
| AVP Flag rules |
|----+-----+----+----|----+
AVP Section | | |SHLD|MUST| |
Attribute Name Code Defined Data Type |MUST| MAY | NOT|NOT |Encr|
-----------------------------------------|----+-----+----+----|----|
CC-Correlation-Id 411 8.1 OctetString| | P,M | | V | Y |
CC-Input-Octets 412 8.24 Unsigned64 | M | P | | V | Y |
CC-Money 413 8.22 Grouped | M | P | | V | Y |
CC-Output-Octets 414 8.25 Unsigned64 | M | P | | V | Y |
CC-Request-Number 415 8.2 Unsigned32 | M | P | | V | Y |
CC-Request-Type 416 8.3 Enumerated | M | P | | V | Y |
CC-Service- 417 8.26 Unsigned64 | M | P | | V | Y |
Specific-Units | | | | | |
CC-Session- 418 8.4 Enumerated | M | P | | V | Y |
Failover | | | | | |
CC-Sub-Session-Id 419 8.5 Unsigned64 | M | P | | V | Y |
CC-Time 420 8.21 Unsigned32 | M | P | | V | Y |
CC-Total-Octets 421 8.23 Unsigned64 | M | P | | V | Y |
CC-Unit-Type 454 8.32 Enumerated | M | P | | V | Y |
Check-Balance- 422 8.6 Enumerated | M | P | | V | Y |
Result | | | | | |
Cost-Information 423 8.7 Grouped | M | P | | V | Y |
Cost-Unit 424 8.12 UTF8String | M | P | | V | Y |
Credit-Control 426 8.13 Enumerated | M | P | | V | Y |
Credit-Control- 427 8.14 Enumerated | M | P | | V | Y |
Failure-Handling | | | | | |
Currency-Code 425 8.11 Unsigned32 | M | P | | V | Y |
Direct-Debiting- 428 8.15 Enumerated | M | P | | V | Y |
Failure-Handling | | | | | |
Exponent 429 8.9 Integer32 | M | P | | V | Y |
Final-Unit-Action 449 8.35 Enumerated | M | P | | V | Y |
Final-Unit- 430 8.34 Grouped | M | P | | V | Y |
Indication | | | | | |
Granted-Service- 431 8.17 Grouped | M | P | | V | Y |
Unit | | | | | |
G-S-U-Pool- 453 8.31 Unsigned32 | M | P | | V | Y |
Identifier | | | | | |
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G-S-U-Pool- 457 8.30 Grouped | M | P | | V | Y |
Reference | | | | | |
Multiple-Services 456 8.16 Grouped | M | P | | V | Y |
-Credit-Control | | | | | |
Multiple-Services 455 8.40 Enumerated | M | P | | V | Y |
-Indicator | | | | | |
Rating-Group 432 8.29 Unsigned32 | M | P | | V | Y |
Redirect-Address 433 8.38 Enumerated | M | P | | V | Y |
-Type | | | | | |
Redirect-Server 434 8.37 Grouped | M | P | | V | Y |
Redirect-Server 435 8.39 UTF8String | M | P | | V | Y |
-Address | | | | | |
Requested-Action 436 8.41 Enumerated | M | P | | V | Y |
Requested-Service 437 8.18 Grouped | M | P | | V | Y |
-Unit | | | | | |
Restriction 438 8.36 IPFiltrRule| M | P | | V | Y |
-Filter-Rule | | | | | |
Service-Context 461 8.42 UTF8String | M | P | | V | Y |
-Id | | | | | |
Service- 439 8.28 Unsigned32 | M | P | | V | Y |
Identifier | | | | | |
Service-Parameter 440 8.43 Grouped | | P,M | | V | Y |
-Info | | | | | |
Service- 441 8.44 Unsigned32 | | P,M | | V | Y |
Parameter-Type | | | | | |
Service- 442 8.45 OctetString| | P,M | | V | Y |
Parameter-Value | | | | | |
Subscription-Id 443 8.46 Grouped | M | P | | V | Y |
Subscription-Id 444 8.48 UTF8String | M | P | | V | Y |
-Data | | | | | |
Subscription-Id 450 8.47 Enumerated | M | P | | V | Y |
-Type | | | | | |
Tariff-Change 452 8.27 Enumerated | M | P | | V | Y |
-Usage | | | | | |
Tariff-Time 451 8.20 Time | M | P | | V | Y |
-Change | | | | | |
Unit-Value 445 8.8 Grouped | M | P | | V | Y |
Used-Service-Unit 446 8.19 Grouped | M | P | | V | Y |
User-Equipment 458 8.49 Grouped | | P,M | | V | Y |
-Info | | | | | |
User-Equipment 459 8.50 Enumerated | | P,M | | V | Y |
-Info-Type | | | | | |
User-Equipment 460 8.51 OctetString| | P,M | | V | Y |
-Info-Value | | | | | |
Value-Digits 447 8.10 Integer64 | M | P | | V | Y |
Validity-Time 448 8.33 Unsigned32 | M | P | | V | Y |
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8.1. CC-Correlation-Id AVP
The CC-Correlation-Id AVP (AVP Code 411) is of type OctetString and
contains information to correlate credit-control requests generated
for different components of the service; e.g., transport and service
level. The one who allocates the Service-Context-Id (i.e., unique
identifier of a service specific document) is also responsible for
defining the content and encoding of the CC-Correlation-Id AVP.
8.2. CC-Request-Number AVP
The CC-Request-Number AVP (AVP Code 415) is of type Unsigned32 and
identifies this request within one session. As Session-Id AVPs are
globally unique, the combination of Session-Id and CC-Request-Number
AVPs is also globally unique and can be used in matching credit-
control messages with confirmations. An easy way to produce unique
numbers is to set the value to 0 for a credit-control request of type
INITIAL_REQUEST and EVENT_REQUEST and to set the value to 1 for the
first UPDATE_REQUEST, to 2 for the second, and so on until the value
for TERMINATION_REQUEST is one more than for the last UPDATE_REQUEST.
8.3. CC-Request-Type AVP
The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
contains the reason for sending the credit-control request message.
It MUST be present in all Credit-Control-Request messages. The
following values are defined for the CC-Request-Type AVP:
INITIAL_REQUEST 1
An Initial request is used to initiate a credit-control session,
and contains credit control information that is relevant to the
initiation.
UPDATE_REQUEST 2
An Update request contains credit-control information for an
existing credit-control session. Update credit-control requests
SHOULD be sent every time a credit-control re-authorization is
needed at the expiry of the allocated quota or validity time.
Further, additional service-specific events MAY trigger a
spontaneous Update request.
TERMINATION_REQUEST 3
A Termination request is sent to terminate a credit-control
session and contains credit-control information relevant to the
existing session.
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EVENT_REQUEST 4
An Event request is used when there is no need to maintain any
credit-control session state in the credit-control server. This
request contains all information relevant to the service, and is
the only request of the service. The reason for the Event request
is further detailed in the Requested-Action AVP. The Requested-
Action AVP MUST be included in the Credit-Control-Request message
when CC-Request-Type is set to EVENT_REQUEST.
8.4. CC-Session-Failover AVP
The CC-Session-Failover AVP (AVP Code 418) is type of Enumerated and
contains information as to whether moving the credit-control message
stream to a backup server during an ongoing credit-control session is
supported. In communication failures, the credit-control message
streams can be moved to an alternative destination if the credit-
control server supports failover to an alternative server. The
secondary credit-control server name, if received from the home
Diameter AAA server, can be used as an address of the backup server.
An implementation is not required to support moving a credit-control
message stream to an alternative server, as this also requires moving
information related to the credit-control session to backup server.
The following values are defined for the CC-Session-Failover AVP:
FAILOVER_NOT_SUPPORTED 0
When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED,
the credit-control message stream MUST NOT to be moved to an
alternative destination in the case of communication failure.
This is the default behavior if the AVP isn't included in the
reply from the authorization or credit-control server.
FAILOVER_SUPPORTED 1
When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
credit-control message stream SHOULD be moved to an alternative
destination in the case of communication failure. Moving the
credit-control message stream to a backup server MAY require that
information related to the credit-control session should also be
forwarded to alternative server.
8.5. CC-Sub-Session-Id AVP
The CC-Sub-Session-Id AVP (AVP Code 419) is of type Unsigned64 and
contains the credit-control sub-session identifier. The combination
of the Session-Id and this AVP MUST be unique per sub-session, and
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the value of this AVP MUST be monotonically increased by one for all
new sub-sessions. The absence of this AVP implies that no sub-
sessions are in use.
8.6. Check-Balance-Result AVP
The Check Balance Result AVP (AVP Code 422) is of type Enumerated and
contains the result of the balance check. This AVP is applicable
only when the Requested-Action AVP indicates CHECK_BALANCE in the
Credit-Control-Request command.
The following values are defined for the Check-Balance-Result AVP.
ENOUGH_CREDIT 0
There is enough credit in the account to cover the requested
service.
NO_CREDIT 1
There isn't enough credit in the account to cover the requested
service.
8.7. Cost-Information AVP
The Cost-Information AVP (AVP Code 423) is of type Grouped, and it is
used to return the cost information of a service, which the credit-
control client can transfer transparently to the end user. The
included Unit-Value AVP contains the cost estimate (always type of
money) of the service, in the case of price enquiry, or the
accumulated cost estimation, in the case of credit-control session.
The Currency-Code specifies in which currency the cost was given.
The Cost-Unit specifies the unit when the service cost is a cost per
unit (e.g., cost for the service is $1 per minute).
When the Requested-Action AVP with value PRICE_ENQUIRY is included in
the Credit-Control-Request command, the Cost-Information AVP sent in
the succeeding Credit-Control-Answer command contains the cost
estimation of the requested service, without any reservation being
made.
The Cost-Information AVP included in the Credit-Control-Answer
command with the CC-Request-Type set to UPDATE_REQUEST contains the
accumulated cost estimation for the session, without taking any
credit reservation into account.
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The Cost-Information AVP included in the Credit-Control-Answer
command with the CC-Request-Type set to EVENT_REQUEST or
TERMINATION_REQUEST contains the estimated total cost for the
requested service.
It is defined as follows (per the grouped-avp-def of
RFC 3588 [DIAMBASE]):
Cost-Information ::= < AVP Header: 423 >
{ Unit-Value }
{ Currency-Code }
[ Cost-Unit ]
8.8. Unit-Value AVP
Unit-Value AVP is of type Grouped (AVP Code 445) and specifies the
units as decimal value. The Unit-Value is a value with an exponent;
i.e., Unit-Value = Value-Digits AVP * 10^Exponent. This
representation avoids unwanted rounding off. For example, the value
of 2,3 is represented as Value-Digits = 23 and Exponent = -1. The
absence of the exponent part MUST be interpreted as an exponent equal
to zero.
It is defined as follows (per the grouped-avp-def of
RFC 3588 [DIAMBASE]):
Unit-Value ::= < AVP Header: 445 >
{ Value-Digits }
[ Exponent ]
8.9. Exponent AVP
Exponent AVP is of type Integer32 (AVP Code 429) and contains the
exponent value to be applied for the Value-Digit AVP within the
Unit-Value AVP.
8.10. Value-Digits AVP
The Value-Digits AVP is of type Integer64 (AVP Code 447) and contains
the significant digits of the number. If decimal values are needed
to present the units, the scaling MUST be indicated with the related
Exponent AVP. For example, for the monetary amount $ 0.05 the value
of Value-Digits AVP MUST be set to 5, and the scaling MUST be
indicated with the Exponent AVP set to -2.
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8.11. Currency-Code AVP
The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and
contains a currency code that specifies in which currency the values
of AVPs containing monetary units were given. It is specified by
using the numeric values defined in the ISO 4217 standard [ISO4217].
8.12. Cost-Unit AVP
The Cost-Unit AVP (AVP Code 424) is of type UTF8String, and it is
used to display a human readable string to the end user. It
specifies the applicable unit to the Cost-Information when the
service cost is a cost per unit (e.g., cost of the service is $1 per
minute). The Cost-Unit can be minutes, hours, days, kilobytes,
megabytes, etc.
8.13. Credit-Control AVP
The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
be included in AA requests when the service element has credit-
control capabilities.
CREDIT_AUTHORIZATION 0
If the home Diameter AAA server determines that the user has
prepaid subscription, this value indicates that the credit-control
server MUST be contacted to perform the first interrogation. The
value of the Credit-Control AVP MUST always be set to 0 in an AA
request sent to perform the first interrogation and to initiate a
new credit-control session.
RE_AUTHORIZATION 1
This value indicates to the Diameter AAA server that a credit-
control session is ongoing for the subscriber and that the
credit-control server MUST not be contacted. The Credit-Control
AVP set to the value of 1 is to be used only when the first
interrogation has been successfully performed and the credit-
control session is ongoing (i.e., re-authorization triggered by
Authorization-Lifetime). This value MUST NOT be used in an AA
request sent to perform the first interrogation.
8.14. Credit-Control-Failure-Handling AVP
The Credit-Control-Failure-Handling AVP (AVP Code 427) is of type
Enumerated. The credit-control client uses information in this AVP
to decide what to do if sending credit-control messages to the
credit-control server has been, for instance, temporarily prevented
due to a network problem. Depending on the service logic, the
credit-control server can order the client to terminate the service
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immediately when there is a reason to believe that the service cannot
be charged, or to try failover to an alternative server, if possible.
Then the server could either terminate or grant the service, should
the alternative connection also fail.
TERMINATE 0
When the Credit-Control-Failure-Handling AVP is set to TERMINATE,
the service MUST only be granted for as long as there is a
connection to the credit-control server. If the credit-control
client does not receive any Credit-Control-Answer message within
the Tx timer (as defined in section 13), the credit-control
request is regarded as failed, and the end user's service session
is terminated.
This is the default behavior if the AVP isn't included in the
reply from the authorization or credit-control server.
CONTINUE 1
When the Credit-Control-Failure-Handling AVP is set to CONTINUE,
the credit-control client SHOULD re-send the request to an
alternative server in the case of transport or temporary failures,
provided that a failover procedure is supported in the credit-
control server and the credit-control client, and that an
alternative server is available. Otherwise, the service SHOULD be
granted, even if credit-control messages can't be delivered.
RETRY_AND_TERMINATE 2
When the Credit-Control-Failure-Handling AVP is set to
RETRY_AND_TERMINATE, the credit-control client SHOULD re-send the
request to an alternative server in the case of transport or
temporary failures, provided that a failover procedure is
supported in the credit-control server and the credit-control
client, and that an alternative server is available. Otherwise,
the service SHOULD not be granted when the credit-control messages
can't be delivered.
8.15. Direct-Debiting-Failure-Handling AVP
The Direct-Debiting-Failure-Handling AVP (AVP Code 428) is of type
Enumerated. The credit-control client uses information in this AVP
to decide what to do if sending credit-control messages (Requested-
Action AVP set to DIRECT_DEBITING) to the credit-control server has
been, for instance, temporarily prevented due to a network problem.
TERMINATE_OR_BUFFER 0
When the Direct-Debiting-Failure-Handling AVP is set to
TERMINATE_OR_BUFFER, the service MUST be granted for as long as
there is a connection to the credit-control server. If the
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credit-control client does not receive any Credit-Control-Answer
message within the Tx timer (as defined in section 13) the
credit-control request is regarded as failed. The client SHOULD
terminate the service if it can determine from the failed answer
that units have not been debited. Otherwise the credit-control
client SHOULD grant the service, store the request in application
level non-volatile storage, and try to re-send the request. These
requests MUST be marked as possible duplicates by setting the T-
flag in the command header as described in [DIAMBASE] section 3.
This is the default behavior if the AVP isn't included in the
reply from the authorization server.
CONTINUE 1
When the Direct-Debiting-Failure-Handling AVP is set to CONTINUE,
the service SHOULD be granted, even if credit-control messages
can't be delivered, and the request should be deleted.
8.16. Multiple-Services-Credit-Control AVP
Multiple-Services-Credit-Control AVP (AVP Code 456) is of type
Grouped and contains the AVPs related to the independent credit-
control of multiple services feature. Note that each instance of
this AVP carries units related to one or more services or related to
a single rating group.
The Service-Identifier and the Rating-Group AVPs are used to
associate the granted units to a given service or rating group. If
both the Service-Identifier and the Rating-Group AVPs are included,
the target of the service units is always the service(s) indicated by
the value of the Service-Identifier AVP(s). If only the Rating-
Group-Id AVP is present, the Multiple-Services-Credit-Control AVP
relates to all the services that belong to the specified rating
group.
The G-S-U-Pool-Reference AVP allows the server to specify a G-S-U-
Pool-Identifier identifying a credit pool within which the units of
the specified type are considered pooled. If a G-S-U-Pool-Reference
AVP is present, then actual service units of the specified type MUST
also be present. For example, if the G-S-U-Pool-Reference AVP
specifies Unit-Type TIME, then the CC-Time AVP MUST be present.
The Requested-Service-Unit AVP MAY contain the amount of requested
service units or the requested monetary value. It MUST be present in
the initial interrogation and within the intermediate interrogations
in which new quota is requested. If the credit-control client does
not include the Requested-Service-Unit AVP in a request command,
because for instance, it has determined that the end-user terminated
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the service, the server MUST debit the used amount from the user's
account but MUST NOT return a new quota in the corresponding answer.
The Validity-Time, Result-Code, and Final-Unit-Indication AVPs MAY be
present in an answer command as defined in sections 5.1.2 and 5.6 for
the graceful service termination.
When both the Tariff-Time-Change and Tariff-Change-Usage AVPs are
present, the server MUST include two separate instances of the
Multiple-Services-Credit-Control AVP with the Granted-Service-Unit
AVP associated to the same service-identifier and/or rating-group.
Where the two quotas are associated to the same pool or to different
pools, the credit pooling mechanism defined in section 5.1.2 applies.
The Tariff-Change-Usage AVP MUST NOT be included in request commands
to report used units before, and after tariff time change the Used-
Service-Unit AVP MUST be used.
A server not implementing the independent credit-control of multiple
services functionality MUST treat the Multiple-Services-Credit-
Control AVP as an invalid AVP.
The Multiple-Services-Control AVP is defined as follows (per the
grouped-avp-def of RFC 3588 [DIAMBASE]):
Multiple-Services-Credit-Control ::= < AVP Header: 456 >
[ Granted-Service-Unit ]
[ Requested-Service-Unit ]
*[ Used-Service-Unit ]
[ Tariff-Change-Usage ]
*[ Service-Identifier ]
[ Rating-Group ]
*[ G-S-U-Pool-Reference ]
[ Validity-Time ]
[ Result-Code ]
[ Final-Unit-Indication ]
*[ AVP ]
8.17. Granted-Service-Unit AVP
Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
contains the amount of units that the Diameter credit-control client
can provide to the end user until the service must be released or the
new Credit-Control-Request must be sent. A client is not required to
implement all the unit types, and it must treat unknown or
unsupported unit types in the answer message as an incorrect CCA
answer. In this case, the client MUST terminate the credit-control
session and indicate in the Termination-Cause AVP reason
DIAMETER_BAD_ANSWER.
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The Granted-Service-Unit AVP is defined as follows (per the grouped-
avp-def of RFC 3588 [DIAMBASE]):
Granted-Service-Unit ::= < AVP Header: 431 >
[ Tariff-Time-Change ]
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ AVP ]
8.18. Requested-Service-Unit AVP
The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
contains the amount of requested units specified by the Diameter
credit-control client. A server is not required to implement all the
unit types, and it must treat unknown or unsupported unit types as
invalid AVPs.
The Requested-Service-Unit AVP is defined as follows (per the
grouped-avp-def of RFC 3588 [DIAMBASE]):
Requested-Service-Unit ::= < AVP Header: 437 >
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ AVP ]
8.19. Used-Service-Unit AVP
The Used-Service-Unit AVP is of type Grouped (AVP Code 446) and
contains the amount of used units measured from the point when the
service became active or, if interim interrogations are used during
the session, from the point when the previous measurement ended.
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The Used-Service-Unit AVP is defined as follows (per the grouped-
avp-def of RFC 3588 [DIAMBASE]):
Used-Service-Unit ::= < AVP Header: 446 >
[ Tariff-Change-Usage ]
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ AVP ]
8.20. Tariff-Time-Change AVP
The Tariff-Time-Change AVP (AVP Code 451) is of type Time. It is
sent from the server to the client and includes the time in seconds
since January 1, 1900, 00:00 UTC, when the tariff of the service will
be changed.
The tariff change mechanism is optional for the client and server,
and it is not used for time-based services defined in section 5. If
a client does not support the tariff time change mechanism, it MUST
treat Tariff-Time-Change AVP in the answer message as an incorrect
CCA answer. In this case, the client terminates the credit-control
session and indicates in the Termination-Cause AVP reason
DIAMETER_BAD_ANSWER.
Omission of this AVP means that no tariff change is to be reported.
8.21. CC-Time AVP
The CC-Time AVP (AVP Code 420) is of type Unsigned32 and indicates
the length of the requested, granted, or used time in seconds.
8.22. CC-Money AVP
The CC-Money AVP (AVP Code 413) is of type Grouped and specifies the
monetary amount in the given currency. The Currency-Code AVP SHOULD
be included. It is defined as follows (per the grouped-avp-def of
RFC 3588 [DIAMBASE]):
CC-Money ::= < AVP Header: 413 >
{ Unit-Value }
[ Currency-Code ]
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8.23. CC-Total-Octets AVP
The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64 and
contains the total number of requested, granted, or used octets
regardless of the direction (sent or received).
8.24. CC-Input-Octets AVP
The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64 and
contains the number of requested, granted, or used octets that can
be/have been received from the end user.
8.25. CC-Output-Octets AVP
The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64 and
contains the number of requested, granted, or used octets that can
be/have been sent to the end user.
8.26. CC-Service-Specific-Units AVP
The CC-Service-Specific-Units AVP (AVP Code 417) is of type
Unsigned64 and specifies the number of service-specific units (e.g.,
number of events, points) given in a selected service. The service-
specific units always refer to the service identified in the
Service-Identifier AVP (or Rating-Group AVP when the Multiple-
Services-Credit-Control AVP is used).
8.27. Tariff-Change-Usage AVP
The Tariff-Change-Usage AVP (AVP Code 452) is of type Enumerated and
defines whether units are used before or after a tariff change, or
whether the units straddled a tariff change during the reporting
period. Omission of this AVP means that no tariff change has
occurred.
In addition, when present in answer messages as part of the
Multiple-Services-Credit-Control AVP, this AVP defines whether units
are allocated to be used before or after a tariff change event.
When the Tariff-Time-Change AVP is present, omission of this AVP in
answer messages means that the single quota mechanism applies.
Tariff-Change-Usage can be one of the following:
UNIT_BEFORE_TARIFF_CHANGE 0
When present in the Multiple-Services-Credit-Control AVP, this
value indicates the amount of the units allocated for use before a
tariff change occurs.
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When present in the Used-Service-Unit AVP, this value indicates
the amount of resource units used before a tariff change had
occurred.
UNIT_AFTER_TARIFF_CHANGE 1
When present in the Multiple-Services-Credit-Control AVP, this
value indicates the amount of the units allocated for use after a
tariff change occurs.
When present in the Used-Service-Unit AVP, this value indicates
the amount of resource units used after tariff change had
occurred.
UNIT_INDETERMINATE 2
The used unit contains the amount of units that straddle the
tariff change (e.g., the metering process reports to the credit-
control client in blocks of n octets, and one block straddled the
tariff change). This value is to be used only in the Used-
Service-Unit AVP.
8.28. Service-Identifier AVP
The Service-Identifier AVP is of type Unsigned32 (AVP Code 439) and
contains the identifier of a service. The specific service the
request relates to is uniquely identified by the combination of
Service-Context-Id and Service-Identifier AVPs.
A usage example of this AVP is illustrated in Appendix A (Flow IX).
8.29. Rating-Group AVP
The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and
contains the identifier of a rating group. All the services subject
to the same rating type are part of the same rating group. The
specific rating group the request relates to is uniquely identified
by the combination of Service-Context-Id and Rating-Group AVPs.
A usage example of this AVP is illustrated in Appendix A (Flow IX).
8.30. G-S-U-Pool-Reference AVP
The G-S-U-Pool-Reference AVP (AVP Code 457) is of type Grouped. It
is used in the Credit-Control-Answer message, and associates the
Granted-Service-Unit AVP within which it appears with a credit pool
within the session.
The G-S-U-Pool-Identifier AVP specifies the credit pool from which
credit is drawn for this unit type.
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The CC-Unit-Type AVP specifies the type of units for which credit is
pooled.
The Unit-Value AVP specifies the multiplier, which converts between
service units of type CC-Unit-Type and abstract service units within
the credit pool (and thus to service units of any other service or
rating group associated with the same pool).
The G-S-U-Pool-Reference AVP is defined as follows (per the grouped-
avp-def of RFC 3588 [DIAMBASE]):
G-S-U-Pool-Reference ::= < AVP Header: 457 >
{ G-S-U-Pool-Identifier }
{ CC-Unit-Type }
{ Unit-Value }
8.31. G-S-U-Pool-Identifier AVP
The G-S-U-Pool-Identifier AVP (AVP Code 453) is of type Unsigned32
and identifies a credit pool within the session.
8.32. CC-Unit-Type AVP
The CC-Unit-Type AVP (AVP Code 454) is of type Enumerated and
specifies the type of units considered to be pooled into a credit
pool.
The following values are defined for the CC-Unit-Type AVP:
TIME 0
MONEY 1
TOTAL-OCTETS 2
INPUT-OCTETS 3
OUTPUT-OCTETS 4
SERVICE-SPECIFIC-UNITS 5
8.33. Validity-Time AVP
The Validity-Time AVP is of type Unsigned32 (AVP Code 448). It is
sent from the credit-control server to the credit-control client.
The AVP contains the validity time of the granted service units. The
measurement of the Validity-Time is started upon receipt of the
Credit-Control-Answer Message containing this AVP. If the granted
service units have not been consumed within the validity time
specified in this AVP, the credit-control client MUST send a Credit-
Control-Request message to the server, with CC-Request-Type set to
UPDATE_REQUEST. The value field of the Validity-Time AVP is given in
seconds.
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The Validity-Time AVP is also used for the graceful service
termination (see section 5.6) to indicate to the credit-control
client how long the subscriber is allowed to use network resources
after the specified action (i.e., REDIRECT or RESTRICT_ACCESS)
started. When the Validity-Time elapses, a new intermediate
interrogation is sent to the server.
8.34. Final-Unit-Indication AVP
The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
indicates that the Granted-Service-Unit AVP in the Credit-Control-
Answer, or in the AA answer, contains the final units for the
service. After these units have expired, the Diameter credit-control
client is responsible for executing the action indicated in the
Final-Unit-Action AVP (see section 5.6).
If more than one unit type is received in the Credit-Control-Answer,
the unit type that first expired SHOULD cause the credit-control
client to execute the specified action.
In the first interrogation, the Final-Unit-Indication AVP with
Final-Unit-Action REDIRECT or RESTRICT_ACCESS can also be present
with no Granted-Service-Unit AVP in the Credit-Control-Answer or in
the AA answer. This indicates to the Diameter credit-control client
to execute the specified action immediately. If the home service
provider policy is to terminate the service, naturally, the server
SHOULD return the appropriate transient failure (see section 9.1) in
order to implement the policy-defined action.
The Final-Unit-Action AVP defines the behavior of the service element
when the user's account cannot cover the cost of the service and MUST
always be present if the Final-Unit-Indication AVP is included in a
command.
If the Final-Unit-Action AVP is set to TERMINATE, no other AVPs MUST
be present.
If the Final-Unit-Action AVP is set to REDIRECT at least the
Redirect-Server AVP MUST be present. The Restriction-Filter-Rule AVP
or the Filter-Id AVP MAY be present in the Credit-Control-Answer
message if the user is also allowed to access other services that are
not accessible through the address given in the Redirect-Server AVP.
If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
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The Filter-Id AVP is defined in [NASREQ]. The Filter-Id AVP can be
used to reference an IP filter list installed in the access device by
means other than the Diameter credit-control application, e.g.,
locally configured or configured by another entity.
The Final-Unit-Indication AVP is defined as follows (per the
grouped-avp-def of RFC 3588 [DIAMBASE]):
Final-Unit-Indication ::= < AVP Header: 430 >
{ Final-Unit-Action }
*[ Restriction-Filter-Rule ]
*[ Filter-Id ]
[ Redirect-Server ]
8.35. Final-Unit-Action AVP
The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
indicates to the credit-control client the action to be taken when
the user's account cannot cover the service cost.
The Final-Unit-Action can be one of the following:
TERMINATE 0
The credit-control client MUST terminate the service session.
This is the default handling, applicable whenever the credit-
control client receives an unsupported Final-Unit-Action value,
and it MUST be supported by all the Diameter credit-control client
implementations conforming to this specification.
REDIRECT 1
The service element MUST redirect the user to the address
specified in the Redirect-Server-Address AVP. The redirect action
is defined in section 5.6.2.
RESTRICT_ACCESS 2
The access device MUST restrict the user access according to the
IP packet filters defined in the Restriction-Filter-Rule AVP or
according to the IP packet filters identified by the Filter-Id
AVP. All the packets not matching the filters MUST be dropped
(see section 5.6.3).
8.36. Restriction-Filter-Rule AVP
The Restriction-Filter-Rule AVP (AVP Code 438) is of type
IPFilterRule and provides filter rules corresponding to services that
are to remain accessible even if there are no more service units
granted. The access device has to configure the specified filter
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rules for the subscriber and MUST drop all the packets not matching
these filters. Zero, one, or more such AVPs MAY be present in a
Credit-Control-Answer message or in an AA answer message.
8.37. Redirect-Server AVP
The Redirect-Server AVP (AVP Code 434) is of type Grouped and
contains the address information of the redirect server (e.g., HTTP
redirect server, SIP Server) with which the end user is to be
connected when the account cannot cover the service cost. It MUST be
present when the Final-Unit-Action AVP is set to REDIRECT.
It is defined as follows (per the grouped-avp-def of RFC 3588
[DIAMBASE]):
Redirect-Server ::= < AVP Header: 434 >
{ Redirect-Address-Type }
{ Redirect-Server-Address }
8.38. Redirect-Address-Type AVP
The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated
and defines the address type of the address given in the Redirect-
Server-Address AVP.
The address type can be one of the following:
IPv4 Address 0
The address type is in the form of "dotted-decimal" IPv4 address,
as defined in [IPv4].
IPv6 Address 1
The address type is in the form of IPv6 address, as defined in
[IPv6Addr]. The address is a text representation of the address
in either the preferred or alternate text form [IPv6Addr].
Conformant implementations MUST support the preferred form and
SHOULD support the alternate text form for IPv6 addresses.
URL 2
The address type is in the form of Uniform Resource Locator, as
defined in [URL].
SIP URI 3
The address type is in the form of SIP Uniform Resource
Identifier, as defined in [SIP].
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8.39. Redirect-Server-Address AVP
The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String
and defines the address of the redirect server (e.g., HTTP redirect
server, SIP Server) with which the end user is to be connected when
the account cannot cover the service cost.
8.40. Multiple-Services-Indicator AVP
The Multiple-Services-Indicator AVP (AVP Code 455) is of type
Enumerated and indicates whether the Diameter credit-control client
is capable of handling multiple services independently within a
(sub-) session. The absence of this AVP means that independent
credit-control of multiple services is not supported.
A server not implementing the independent credit-control of multiple
services MUST treat the Multiple-Services-Indicator AVP as an invalid
AVP.
The following values are defined for the Multiple-Services-Indicator
AVP:
MULTIPLE_SERVICES_NOT_SUPPORTED 0
Client does not support independent credit-control of multiple
services within a (sub-)session.
MULTIPLE_SERVICES_SUPPORTED 1
Client supports independent credit-control of multiple services
within a (sub-)session.
8.41. Requested-Action AVP
The Requested-Action AVP (AVP Code 436) is of type Enumerated and
contains the requested action being sent by Credit-Control-Request
command where the CC-Request-Type is set to EVENT_REQUEST. The
following values are defined for the Requested-Action AVP:
DIRECT_DEBITING 0
This indicates a request to decrease the end user's account
according to information specified in the Requested-Service-Unit
AVP and/or Service-Identifier AVP (additional rating information
may be included in service-specific AVPs or in the Service-
Parameter-Info AVP). The Granted-Service-Unit AVP in the Credit-
Control-Answer command contains the debited units.
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REFUND_ACCOUNT 1
This indicates a request to increase the end user's account
according to information specified in the Requested-Service-Unit
AVP and/or Service-Identifier AVP (additional rating information
may be included in service-specific AVPs or in the Service-
Parameter-Info AVP). The Granted-Service-Unit AVP in the Credit-
Control-Answer command contains the refunded units.
CHECK_BALANCE 2
This indicates a balance check request. In this case, the
checking of the account balance is done without any credit
reservation from the account. The Check-Balance-Result AVP in the
Credit-Control-Answer command contains the result of the balance
check.
PRICE_ENQUIRY 3
This indicates a price enquiry request. In this case, neither
checking of the account balance nor reservation from the account
will be done; only the price of the service will be returned in
the Cost-Information AVP in the Credit-Control-Answer Command.
8.42. Service-Context-Id AVP
The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and
contains a unique identifier of the Diameter credit-control service
specific document that applies to the request (as defined in section
4.1.2). This is an identifier allocated by the service provider, by
the service element manufacturer, or by a standardization body, and
MUST uniquely identify a given Diameter credit-control service
specific document. The format of the Service-Context-Id is:
"service-context" "@" "domain"
service-context = Token
The Token is an arbitrary string of characters and digits.
'domain' represents the entity that allocated the Service-Context-Id.
It can be ietf.org, 3gpp.org, etc., if the identifier is allocated by
a standardization body, or it can be the FQDN of the service provider
(e.g., provider.example.com) or of the vendor (e.g.,
vendor.example.com) if the identifier is allocated by a private
entity.
This AVP SHOULD be placed as close to the Diameter header as
possible.
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Service-specific documents that are for private use only (i.e., to
one provider's own use, where no interoperability is deemed useful)
may define private identifiers without need of coordination.
However, when interoperability is wanted, coordination of the
identifiers via, for example, publication of an informational RFC is
RECOMMENDED in order to make Service-Context-Id globally available.
8.43. Service-Parameter-Info AVP
The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
contains service-specific information used for price calculation or
rating. The Service-Parameter-Type AVP defines the service parameter
type, and the Service-Parameter-Value AVP contains the parameter
value. The actual contents of these AVPs are not within the scope of
this document and SHOULD be defined in another Diameter application,
in standards written by other standardization bodies, or in service-
specific documentation.
In the case of an unknown service request (e.g., unknown Service-
Parameter-Type), the corresponding answer message MUST contain the
error code DIAMETER_RATING_FAILED. A Credit-Control-Answer message
with this error MUST contain one or more Failed-AVP AVPs containing
the Service-Parameter-Info AVPs that caused the failure.
It is defined as follows (per the grouped-avp-def of RFC 3588
[DIAMBASE]):
Service-Parameter-Info ::= < AVP Header: 440 >
{ Service-Parameter-Type }
{ Service-Parameter-Value }
8.44. Service-Parameter-Type AVP
The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)
and defines the type of the service event specific parameter (e.g.,
it can be the end-user location or service name). The different
parameters and their types are service specific, and the meanings of
these parameters are not defined in this document. Whoever allocates
the Service-Context-Id (i.e., unique identifier of a service-specific
document) is also responsible for assigning Service-Parameter-Type
values for the service and ensuring their uniqueness within the given
service. The Service-Parameter-Value AVP contains the value
associated with the service parameter type.
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8.45. Service-Parameter-Value AVP
The Service-Parameter-Value AVP is of type OctetString (AVP Code 442)
and contains the value of the service parameter type.
8.46. Subscription-Id AVP
The Subscription-Id AVP (AVP Code 443) is used to identify the end
user's subscription and is of type Grouped. The Subscription-Id AVP
includes a Subscription-Id-Data AVP that holds the identifier and a
Subscription-Id-Type AVP that defines the identifier type.
It is defined as follows (per the grouped-avp-def of RFC 3588
[DIAMBASE]):
Subscription-Id ::= < AVP Header: 443 >
{ Subscription-Id-Type }
{ Subscription-Id-Data }
8.47. Subscription-Id-Type AVP
The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated,
and it is used to determine which type of identifier is carried by
the Subscription-Id AVP.
This specification defines the following subscription identifiers.
However, new Subscription-Id-Type values can be assigned by an IANA
designated expert, as defined in section 12. A server MUST implement
all the Subscription-Id-Types required to perform credit
authorization for the services it supports, including possible future
values. Unknown or unsupported Subscription-Id-Types MUST be treated
according to the 'M' flag rule, as defined in [DIAMBASE].
END_USER_E164 0
The identifier is in international E.164 format (e.g., MSISDN),
according to the ITU-T E.164 numbering plan defined in [E164] and
[CE164].
END_USER_IMSI 1
The identifier is in international IMSI format, according to the
ITU-T E.212 numbering plan as defined in [E212] and [CE212].
END_USER_SIP_URI 2
The identifier is in the form of a SIP URI, as defined in [SIP].
END_USER_NAI 3
The identifier is in the form of a Network Access Identifier, as
defined in [NAI].
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END_USER_PRIVATE 4
The Identifier is a credit-control server private identifier.
8.48. Subscription-Id-Data AVP
The Subscription-Id-Data AVP (AVP Code 444) is used to identify the
end user and is of type UTF8String. The Subscription-Id-Type AVP
defines which type of identifier is used.
8.49. User-Equipment-Info AVP
The User-Equipment-Info AVP (AVP Code 458) is of type Grouped and
allows the credit-control client to indicate the identity and
capability of the terminal the subscriber is using for the connection
to network.
It is defined as follows (per the grouped-avp-def of RFC 3588
[DIAMBASE]):
User-Equipment-Info ::= < AVP Header: 458 >
{ User-Equipment-Info-Type }
{ User-Equipment-Info-Value }
8.50. User-Equipment-Info-Type AVP
The User-Equipment-Info-Type AVP is of type Enumerated (AVP Code
459) and defines the type of user equipment information contained in
the User-Equipment-Info-Value AVP.
This specification defines the following user equipment types.
However, new User-Equipment-Info-Type values can be assigned by an
IANA designated expert, as defined in section 12.
IMEISV 0
The identifier contains the International Mobile Equipment
Identifier and Software Version in the international IMEISV format
according to 3GPP TS 23.003 [3GPPIMEI].
MAC 1
The 48-bit MAC address is formatted as described in [RAD802.1X].
EUI64 2
The 64-bit identifier used to identify hardware instance of the
product, as defined in [EUI64].
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MODIFIED_EUI64 3
There are a number of types of terminals that have identifiers
other than IMEI, IEEE 802 MACs, or EUI-64. These identifiers can
be converted to modified EUI-64 format as described in [IPv6Addr]
or by using some other methods referred to in the service-specific
documentation.
8.51. User-Equipment-Info-Value AVP
The User-Equipment-Info-Value AVP (AVP Code 460) is of type
OctetString. The User-Equipment-Info-Type AVP defines which type of
identifier is used.
9. Result Code AVP Values
This section defines new Result-Code AVP [DIAMBASE] values that must
be supported by all Diameter implementations that conform to this
specification.
The Credit-Control-Answer message includes the Result-Code AVP, which
may indicate that an error was present in the Credit-Control-Request
message. A rejected Credit-Control-Request message SHOULD cause the
user's session to be terminated.
9.1. Transient Failures
Errors that fall within the transient failures category are used to
inform a peer that the request could not be satisfied at the time it
was received, but that the request MAY be able to be satisfied in the
future.
DIAMETER_END_USER_SERVICE_DENIED 4010
The credit-control server denies the service request due to
service restrictions. If the CCR contained used-service-units,
they are deducted, if possible.
DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE 4011
The credit-control server determines that the service can be
granted to the end user but that no further credit-control is
needed for the service (e.g., service is free of charge).
DIAMETER_CREDIT_LIMIT_REACHED 4012
The credit-control server denies the service request because the
end user's account could not cover the requested service. If the
CCR contained used-service-units they are deducted, if possible.
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9.2. Permanent Failures
Errors that fall within the permanent failure category are used to
inform the peer that the request failed and should not be attempted
again.
DIAMETER_USER_UNKNOWN 5030
The specified end user is unknown in the credit-control server.
DIAMETER_RATING_FAILED 5031
This error code is used to inform the credit-control client that
the credit-control server cannot rate the service request due to
insufficient rating input, an incorrect AVP combination, or an AVP
or an AVP value that is not recognized or supported in the rating.
The Failed-AVP AVP MUST be included and contain a copy of the
entire AVP(s) that could not be processed successfully or an
example of the missing AVP complete with the Vendor-Id if
applicable. The value field of the missing AVP should be of
correct minimum length and contain zeros.
10. AVP Occurrence Table
The following table presents the AVPs defined in this document and
specifies in which Diameter messages they MAY or MAY NOT be present.
Note that AVPs that can only be present within a Grouped AVP are not
represented in this table.
The table uses the following symbols:
0 The AVP MUST NOT be present in the message.
0+ Zero or more instances of the AVP MAY be present in the
message.
0-1 Zero or one instance of the AVP MAY be present in the
message. It is considered an error if there is more
than one instance of the AVP.
1 One instance of the AVP MUST be present in the message.
1+ At least one instance of the AVP MUST be present in the
message.
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10.1. Credit-Control AVP Table
The table in this section is used to represent which credit-control
applications specific AVPs defined in this document are to be present
in the credit-control messages.
+-----------+
| Command |
| Code |
|-----+-----+
Attribute Name | CCR | CCA |
------------------------------|-----+-----+
Acct-Multi-Session-Id | 0-1 | 0-1 |
Auth-Application-Id | 1 | 1 |
CC-Correlation-Id | 0-1 | 0 |
CC-Session-Failover | 0 | 0-1 |
CC-Request-Number | 1 | 1 |
CC-Request-Type | 1 | 1 |
CC-Sub-Session-Id | 0-1 | 0-1 |
Check-Balance-Result | 0 | 0-1 |
Cost-Information | 0 | 0-1 |
Credit-Control-Failure- | 0 | 0-1 |
Handling | | |
Destination-Host | 0-1 | 0 |
Destination-Realm | 1 | 0 |
Direct-Debiting-Failure- | 0 | 0-1 |
Handling | | |
Event-Timestamp | 0-1 | 0-1 |
Failed-AVP | 0 | 0+ |
Final-Unit-Indication | 0 | 0-1 |
Granted-Service-Unit | 0 | 0-1 |
Multiple-Services-Credit- | 0+ | 0+ |
Control | | |
Multiple-Services-Indicator | 0-1 | 0 |
Origin-Host | 1 | 1 |
Origin-Realm | 1 | 1 |
Origin-State-Id | 0-1 | 0-1 |
Proxy-Info | 0+ | 0+ |
Redirect-Host | 0 | 0+ |
Redirect-Host-Usage | 0 | 0-1 |
Redirect-Max-Cache-Time | 0 | 0-1 |
Requested-Action | 0-1 | 0 |
Requested-Service-Unit | 0-1 | 0 |
Route-Record | 0+ | 0+ |
Result-Code | 0 | 1 |
Service-Context-Id | 1 | 0 |
Service-Identifier | 0-1 | 0 |
Service-Parameter-Info | 0+ | 0 |
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Session-Id | 1 | 1 |
Subscription-Id | 0+ | 0 |
Termination-Cause | 0-1 | 0 |
User-Equipment-Info | 0-1 | 0 |
Used-Service-Unit | 0+ | 0 |
User-Name | 0-1 | 0-1 |
Validity-Time | 0 | 0-1 |
------------------------------|-----+-----+
10.2. Re-Auth-Request/Answer AVP Table
This section defines AVPs that are specific to the Diameter credit-
control application and that MAY be included in the Diameter Re-
Auth-Request/Answer (RAR/RAA) message [DIAMBASE].
Re-Auth-Request/Answer command MAY include the following additional
AVPs:
+---------------+
| Command Code |
|-------+-------+
Attribute Name | RAR | RAA |
------------------------------+-------+-------+
CC-Sub-Session-Id | 0-1 | 0-1 |
G-S-U-Pool-Identifier | 0-1 | 0-1 |
Service-Identifier | 0-1 | 0-1 |
Rating-Group | 0-1 | 0-1 |
------------------------------+-------+-------+
11. RADIUS/Diameter Credit-Control Interworking Model
This section defines the basic principles for the Diameter credit-
control/RADIUS prepaid inter-working model; that is, a message
translation between a RADIUS based prepaid solution and a Diameter
credit-control application. A complete description of the protocol
translations between RADIUS and the Diameter credit-control
application is beyond the scope of this specification and SHOULD be
addressed in another appropriate document, such as the RADIUS prepaid
specification.
The Diameter credit-control architecture may have a Translation Agent
capable of translation between RADIUS prepaid and Diameter credit-
control protocols. An AAA server (usually the home AAA server) may
act as a Translation Agent and as a Diameter credit-control client
for service elements that use credit-control mechanisms other than
Diameter credit control for instance, RADIUS prepaid. In this case,
the home AAA server contacts the Diameter credit-control server as
part of the authorization process. The interworking architecture is
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illustrated in Figure 7, and interworking flow in Figure 8. In a
roaming situation the service element (e.g., the NAS) may be located
in the visited network, and a visited AAA server is usually
contacted. The visited AAA server connects then to the home AAA
server.
RADIUS Prepaid
+--------+ +---------+ protocol +------------+ +--------+
| End |<----->| Service |<---------->| Home AAA | |Business|
| User | | Element | | Server | |Support |
+--------+ +-->| | |+----------+|->|System |
| +---------+ ||CC Client || | |
| |+----------+| | |
+--------+ | +------^-----+ +----^---+
| End |<--+ Credit-Control | |
| User | Protocol | |
+--------+ +-------V--------+ |
|Credit-Control |----+
| Server |
+----------------+
Figure 7: Credit-control architecture with service element
containing translation agent, translating RADIUS
prepaid to Diameter credit-control protocol
When the AAA server acting as a Translation Agent receives an initial
RADIUS Access-Request message from service element (e.g., NAS
access), it performs regular authentication and authorization. If
the RADIUS Access-Request message indicates that the service element
is capable of credit-control, and if the home AAA server finds that
the subscriber is a prepaid subscriber, then a Diameter credit-
control request SHOULD be sent toward the credit-control server to
perform credit authorization and to establish a credit-control
session. After the Diameter credit-control server checks the end
user's account balance, rates the service, and reserves credit from
the end user's account, the reserved quota is returned to the home
AAA server in the Diameter Credit-Control-Answer. Then the home AAA
server sends the reserved quota to the service element in the RADIUS
Access-Accept.
At the expiry of the allocated quota, the service element sends a new
RADIUS Access-Request containing the units used this far to the home
AAA server. The home AAA server shall map a RADIUS Access-Request
containing the reported units to the Diameter credit-control server
in a Diameter Credit-Control-Request (UPDATE_REQUEST). The Diameter
credit-control server debits the used units from the end user's
account and allocates a new quota that is returned to the home AAA
server in the Diameter Credit-Control-Answer. The quota is
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transferred to the service element in the RADIUS Access-Accept. When
the end user terminates the service, or when the entire quota has
been used, the service element sends a RADIUS Access-Request. To
debit the used units from the end user's account and to stop the
credit-control session, the home AAA server sends a Diameter Credit-
Control-Request (TERMINATION_REQUEST) to the credit-control server.
The Diameter credit-control server acknowledges the session
termination by sending a Diameter Credit-Control-Answer to the home
AAA server. The RADIUS Access-Accept is sent to the NAS.
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A following diagram illustrates a RADIUS prepaid - Diameter credit-
control interworking sequence.
Service Element Translation Agent
(e.g., NAS) (CC Client) CC Server
| Access-Request | |
|----------------------->| |
| | CCR (initial) |
| |----------------------->|
| | CCA (Granted-Units) |
| |<-----------------------|
| Access-Accept | |
| (Granted-Units) | |
|<-----------------------| |
: : :
| Access-Request | |
| (Used-Units) | |
|----------------------->| |
| | CCR (update, |
| | Used-Units) |
| |----------------------->|
| | CCA (Granted-Units) |
| |<-----------------------|
| Access-Accept | |
| (Granted-Units) | |
|<-----------------------| |
: : :
| Access-Request | |
|----------------------->| |
| | CCR (terminate, |
| | Used-Units) |
| |----------------------->|
| | CCA |
| |<-----------------------|
| Access-Accept | |
|<-----------------------| |
| | |
Figure 8: Message flow example with RADIUS prepaid -
Diameter credit-control interworking
12. IANA Considerations
This section contains the namespaces that have either been created in
this specification, or the values assigned to existing namespaces
managed by IANA.
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In the subsections below, when we speak about review by a Designated
Expert, please note that the designated expert will be assigned by
the IESG. Initially, such Expert discussions take place on the AAA
WG mailing list.
12.1. Application Identifier
This specification assigns the value 4, 'Diameter Credit Control', to
the Application Identifier namespace defined in [DIAMBASE]. See
section 1.3 for more information.
12.2. Command Codes
This specification uses the value 272 from the Command code namespace
defined in [DIAMBASE] for the Credit-Control-Request (CCR) and
Credit-Control-Answer (CCA) commands.
12.3. AVP Codes
This specification assigns the values 411 - 461 from the AVP code
namespace defined in [DIAMBASE]. See section 8 for the assignment of
the namespace in this specification.
12.4. Result-Code AVP Values
This specification assigns the values 4010, 4011, 4012, 5030, 5031
from the Result-Code AVP value namespace defined in [DIAMBASE]. See
section 9 for the assignment of the namespace in this specification.
12.5. CC-Request-Type AVP
As defined in section 8.3, the CC-Request-Type AVP includes
Enumerated type values 1 - 4. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.6. CC-Session-Failover AVP
As defined in section 8.4, the CC-Failover-Supported AVP includes
Enumerated type values 0 - 1. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
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12.7. CC-Unit-Type AVP
As defined in section 8.32, the CC-Unit-Type AVP includes Enumerated
type values 0 - 5. IANA has created and is maintaining a namespace
for this AVP. All remaining values are available for assignment by a
Designated Expert [IANA].
12.8. Check-Balance-Result AVP
As defined in section 8.6, the Check-Balance-Result AVP includes
Enumerated type values 0 - 1. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.9. Credit-Control AVP
As defined in section 8.13, the Credit-Control AVP includes
Enumerated type values 0 - 1. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.10. Credit-Control-Failure-Handling AVP
As defined in section 8.14, the Credit-Control-Failure-Handling AVP
includes Enumerated type values 0 - 2. IANA has created and is
maintaining a namespace for this AVP. All remaining values are
available for assignment by a Designated Expert [IANA].
12.11. Direct-Debiting-Failure-Handling AVP
As defined in section 8.15, the Direct-Debiting-Failure-Handling AVP
includes Enumerated type values 0 - 1. IANA has created and is
maintaining a namespace for this AVP. All remaining values are
available for assignment by a Designated Expert [IANA].
12.12. Final-Unit-Action AVP
As defined in section 8.35, the Final-Unit-Action AVP includes
Enumerated type values 0 - 2. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.13. Multiple-Services-Indicator AVP
As defined in section 8.40, the Multiple-Services-Indicator AVP
includes Enumerated type values 0 - 1. IANA has created and is
maintaining a namespace for this AVP. All remaining values are
available for assignment by a Designated Expert [IANA].
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12.14. Redirect-Address-Type AVP
As defined in section 8.38, the Redirect-Address-Type AVP includes
Enumerated type values 0 - 3. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.15. Requested-Action AVP
As defined in section 8.41, the Requested-Action AVP includes
Enumerated type values 0 - 3. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.16. Subscription-Id-Type AVP
As defined in section 8.47, the Subscription-Id-Type AVP includes
Enumerated type values 0 - 4. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.17. Tariff-Change-Usage AVP
As defined in section 8.27, the Tariff-Change-Usage AVP includes
Enumerated type values 0 - 2. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
12.18. User-Equipment-Info-Type AVP
As defined in section 8.50, the User-Equipment-Info-Type AVP includes
Enumerated type values 0 - 3. IANA has created and is maintaining a
namespace for this AVP. All remaining values are available for
assignment by a Designated Expert [IANA].
13. Credit-Control Application Related Parameters
Tx timer
When real-time credit-control is required, the credit-control
client contacts the credit-control server before and while the
service is provided to an end user. Due to the real-time nature
of the application, the communication delays SHOULD be minimized;
e.g., to avoid an overly long service setup time experienced by
the end user. The Tx timer is introduced to control the waiting
time in the client in the Pending state. When the Tx timer
elapses, the credit-control client takes an action to the end user
according to the value of the Credit-Control-Failure-Handling AVP
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or Direct-Debiting-Failure-Handling AVP. The recommended value is
10 seconds.
Tcc timer
The Tcc timer supervises an ongoing credit-control session in the
credit-control server. It is RECOMMENDED to use the Validity-Time
as input to set the Tcc timer value. In case of transient
failures in the network, the Diameter credit-control server might
change to Idle state. To avoid this, the Tcc timer MAY be set so
that Tcc equals to 2 x Validity-Time.
Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling
Client implementations may offer the possibility of locally
configuring these AVPs. In such a case their value and behavior
is defined in section 5.7 for the Credit-Control-Failure-Handling
and in section 6.5 for the Direct-Debiting-Failure-Handling.
14. Security Considerations
The Diameter base protocol [DIAMBASE] requires that each Diameter
implementation use underlying security; i.e., IPsec or TLS. These
mechanisms are believed to provide sufficient protection under the
normal Internet threat model; that is, assuming that the authorized
nodes engaging in the protocol have not been compromised, but that
the attacker has complete control over the communication channels
between them. This includes eavesdropping, message modification,
insertion, and man-in-the-middle and replay attacks. Note also that
this application includes a mechanism for application layer replay
protection by means of the Session-Id from [DIAMBASE] and CC-
Request-Number, which is specified in this document. The Diameter
credit-control application is often used within one domain, and there
may be a single hop between the peers. In these environments, the
use of TLS or IPsec is sufficient. The details of TLS and IPsec
related security considerations are discussed in the [DIAMBASE].
Because this application handles monetary transactions (directly or
indirectly), it increases the interest for various security attacks.
Therefore, all parties communicating with each other MUST be
authenticated, including, for instance, TLS client-side
authentication. In addition, authorization of the client SHOULD be
emphasized; i.e., that the client is allowed to perform credit-
control for a certain user. The specific means of authorization are
outside of the scope of this specification but can be, for instance,
manual configuration.
Hakala, et al. Standards Track [Page 89]
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Another kind of threat is malicious modification, injection, or
deletion of AVPs or complete credit-control messages. The credit-
control messages contain sensitive billing related information (such
as subscription Id, granted units, used units, cost information)
whose malicious modification can have financial consequences.
Sometimes simply delaying the credit-control messages can cause
disturbances in the credit-control client or server.
Even without any modification to the messages, an adversary can
invite a security threat by eavesdropping, as the transactions
contain private information about the user. Also, by monitoring the
credit-control messages one can collect information about the
credit-control server's billing models and business relationships.
When third-party relays or proxy are involved, the hop-by-hop
security does not necessarily provide sufficient protection for
Diameter user session. In some cases, it may be inappropriate to
send Diameter messages, such as CCR and CCA, containing sensitive
AVPs via untrusted Diameter proxy agents, as there are no assurances
that third-party proxies will not modify the credit-control commands
or AVP values.
14.1. Direct Connection with Redirects
A Diameter credit-control agent cannot always know whether agents
between it and the end user's Diameter credit-control server are
reliable. In this case, the Diameter credit-control agent doesn't
have a routing entry in its Diameter Routing Table (defined in
[DIAMBASE], section 2.7) for the realm of the credit-control server
in the end user's home domain. The Diameter credit-control agent can
have a default route configured to a local Redirect agent, and it
redirects the CCR message to the redirect agent. The local Redirect
agent then returns a redirect notification (Result-code 3006,
DIAMETER_REDIRECT_INDICATION) to the credit-control agent, as well as
Diameter credit-control server(s) information (Redirect-Host AVP) and
information (Redirect-Host-Usage AVP) about how the routing entry
resulting from the Redirect-Host is to be used. The Diameter
credit-control agent then forwards the CCR message directly to one of
the hosts identified by the CCA message from the redirect agent. If
the value of the Redirect-Host-Usage AVP is unequal to zero, all
following messages are sent to the host specified in the Redirect-
Host AVP until the time specified by the Redirect-Max-Cache-Time AVP
is expired.
There are some authorization issues even with redirects. There may
be attacks toward nodes that have been properly authorized, but that
abuse their authorization or have been compromised. These issues are
discussed more widely in [DIAMEAP], section 8.
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15. References
15.1. Normative References
[DIAMBASE] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September
2003.
[3GPPCHARG] 3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects, Service
aspects; Charging and Billing, (release 5), 3GPP TS
22.115 v. 5.2.1, 2002-03.
[SIP] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[NAI] Aboba, B. and M. Beadles, "The Network Access
Identifier", RFC 2486, January 1999.
[E164] Recommendation E.164/I.331 (05/97): The International
Public Telecommunication Numbering Plan. 1997.
[CE164] Complement to ITU-T Recommendation E.164 (05/1997):"List
of ITU-T Recommendation E.164 assigned country codes",
June 2000.
[E212] Recommendation E.212 (11/98): The international
identification plan for mobile terminals and mobile
users. 1998.
[CE212] Complement to ITU-T Recommendation E.212 (11/1997):" List
of mobile country or geographical area codes", February
1999.
[IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[IPv4] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[IPv6Addr] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Hakala, et al. Standards Track [Page 91]
RFC 4006 Diameter Credit-Control Application August 2005
[ISO4217] Codes for the representation of currencies and funds,
International Standard ISO 4217,2001
[NASREQ] Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
"Diameter Network Access Server Application", RFC 4005,
August 2005.
[AAATRANS] Aboba, B. and J. Wood, "Authentication, Authorization and
Accounting (AAA) Transport Profile", RFC 3539, June 2003.
[URL] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
[RAD802.1X] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J.
Roese, "IEEE 802.1X Remote Authentication Dial In User
Service (RADIUS) Usage Guidelines", RFC 3580, September
2003.
[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/regauth/oui/tutorials/
EUI64.html March 1997.
[3GPPIMEI] 3rd Generation Partnership Project; Technical
Specification Group Core Network, Numbering, addressing
and identification, (release 5), 3GPP TS 23.003 v. 5.8.0,
2003-12
15.2. Informative References
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[DIAMMIP] Calhoun, P., Johansson, T., Perkins, C., Hiller, T., and
P. McCann, "Diameter Mobile IPv4 Application", RFC 4004,
August 2005.
[DIAMEAP] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", Work in
Progress.
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
Camarillo, "Best Current Practices for Third Party Call
Control (3pcc) in the Session Initiation Protocol (SIP)",
BCP 85, RFC 3725, April 2004.
Hakala, et al. Standards Track [Page 92]
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16. Acknowledgements
The authors would like to thank Bernard Aboba, Jari Arkko, Robert
Ekblad, Pasi Eronen, Benny Gustafsson, Robert Karlsson, Avi Lior,
Paco Marin, Jussi Maki, Jeff Meyer, Anne Narhi, John Prudhoe,
Christopher Richards, Juha Vallinen, and Mark Watson for their
comments and suggestions.
Hakala, et al. Standards Track [Page 93]
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Appendix A. Credit-Control Sequences
A.1. Flow I
NAS
End User (CC Client) AAA Server CC Server
|(1)User Logon |(2)AA Request (CC AVPs) |
|------------------>|------------------->| |
| | |(3)CCR(initial, CC AVPs)
| | |------------------->|
| | | (4)CCA(Granted-Units)
| | |<-------------------|
| |(5)AA Answer(Granted-Units) |
|(6)Access granted |<-------------------| |
|<----------------->| | |
| | | |
: : : :
| |(7)CCR(update,Used-Units) |
| |------------------->|(8)CCR |
| | | (update,Used-Units)
| | |------------------->|
| | |(9)CCA(Granted-Units)
| |(10)CCA(Granted-Units)<------------------|
| |<-------------------| |
: : : :
| (Auth. lifetime expires) | |
| |(11) AAR (CC AVP) | |
| |------------------->| |
| | (12) AAA | |
| |<-------------------| |
: : : :
: : : :
|(13) User logoff | | |
|------------------>|(14)CCR(term.,Used-Units) |
| |------------------->|(15)CCR |
| | | (term.,Used-Units)
| | |------------------->|
| | | (16)CCA |
| | (17)CCA |<-------------------|
| |<-------------------| |
| |(18)STR | |
| |------------------->| |
| | (19)STA | |
| |<-------------------| |
Figure A.1: Flow I
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A credit-control flow for Network Access Services prepaid is shown in
Figure A.1. The Diameter [NASREQ] is implemented in the Network
Access Server (NAS). The focus of this flow is in the credit
authorization.
The user logs on to the network (1). The Diameter NAS sends a
Diameter AA-Request (AAR) to the home Diameter AAA server. The
credit-control client populates the AAR with the Credit-Control AVP
set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,
as usual [NASREQ]. The home Diameter AAA server performs service-
specific Authentication and Authorization, as usual. The home
Diameter AAA server determines that the user is a prepaid user and
notices from the Credit-Control AVP that the NAS has credit-control
capabilities. It sends a Diameter Credit-Control-Request with CC-
Request-Type set to INITIAL_REQUEST to the Diameter credit-control
server to perform credit authorization (3) and to establish a
credit-control session. (The home Diameter AAA server may forward
service-specific AVPs received from the NAS as input for the rating
process.) The Diameter credit-control server checks the end user's
account balance, rates the service, and reserves credit from the end
user's account. The reserved quota is returned to the home Diameter
AAA server in the Diameter Credit-Control-Answer (4). The home
Diameter AAA server sends the reserved quota to the NAS in the
Diameter AA-Answer (AAA). Upon successful AAA, the NAS starts the
credit-control session and starts monitoring the granted units (5).
The NAS grants access to the end user (6). At the expiry of the
allocated quota, the NAS sends a Diameter Credit-Control-Request with
CC-Request-Type set to UPDATE_REQUEST to the Home Diameter AAA server
(7). This message contains the units used thus far. The home
Diameter AAA server forwards the CCR to the Diameter credit-control
server (8). The Diameter credit-control server debits the used units
from the end user's account and allocates a new quota that is
returned to the home Diameter AAA server in the Diameter Credit-
Control-Answer (9). The message is forwarded to the NAS (10).
During the ongoing credit-control session, the authorization lifetime
expires, and the authorization/authentication client in the NAS
performs service specific re-authorization to the home Diameter AAA
server, as usual. The credit-control client populates the AAR with
the Credit-Control AVP set to RE_AUTHORIZATION, indicating that the
credit-control server shall not be contacted, as the credit
authorization is controlled by the burning rate of the granted units
(11). The home Diameter AAA server performs service-specific re-
authorization as usual and returns the AA-Answer to the NAS (12).
The end user logs off from the network (13). To debit the used units
from the end user's account and to stop the credit-control session,
the NAS sends a Diameter Credit-Control-Request with CC-Request-Type
set to TERMINATION_REQUEST to the home Diameter AAA server (14). The
home Diameter AAA server forwards the CCR to the credit-control
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server (15). The Diameter credit-control server acknowledges the
session termination by sending a Diameter Credit-Control-Answer to
the home Diameter AAA server (16). The home Diameter AAA server
forwards the answer to the NAS (17). STR/STA takes place between the
NAS and home Diameter AAA server, as usual (18-19).
A.2. Flow II
SIP Proxy/Registrar AAA
A (CC Client) Server B CC Server
|(i) REGISTER | | | |
|------------->|(ii) | | |
| |------------->| | |
| |authentication & | |
| |authorization | | |
| |<-------------| | |
|(iii)200 OK | | |
|<-------------| | |
: : : :
|(1) INVITE | :
|------------->|
| |(2) CCR (Initial, SIP specific AVP) |
| |------------------------------------------->|
| |(3) CCA (Granted-Units) |
| |<-------------------------------------------|
| |(4) INVITE | |
| |---------------------------->| |
: : : :
| |(5) CCR (update, Used-Units) |
| |------------------------------------------->|
| |(6) CCA (Granted-Units) |
| |<-------------------------------------------|
: : : :
|(7) BYE | | |
|------------->| | |
| |(8) BYE | |
| |---------------------------->| |
| |(9) CCR (termination, Used-Units) |
| |------------------------------------------->|
| |(10) CCA () |
| |<-------------------------------------------|
| | | |
Figure A.2: Flow II
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This is an example of Diameter credit-control for SIP sessions.
Although the flow focuses on illustrating the usage of credit-control
messages, the SIP signaling is inaccurate, and the diagram is not by
any means an attempt to define a service provider's SIP network.
However, for the sake of this example, some assumptions are made
below.
Typically, prepaid services based, for example, on time usage for SIP
session require an entity in the service provider network to
intercept all the requests within the SIP dialog in order to detect
events, such as session establishment and session release, that are
essential to perform credit-control operations with the credit-
control server. Therefore, in this example, it is assumed that the
SIP Proxy adds a Record-Route header in the initial SIP INVITE to
make sure that all the future requests in the created dialog traverse
through it (for the definitions of 'Record-Route' and 'dialog' please
refer to [SIP]). Finally, the degree of credit-control measuring of
the media by the proxy depends on the business model design used in
setting up the end system and proxies in the SIP network.
The end user (SIP User Agent A) sends REGISTER with credentials (i).
The SIP Proxy sends a request to the home AAA server to perform
Multimedia authentication and authorization by using, for instance,
Diameter Multimedia application (ii). The home AAA server checks
that the credentials are correct and checks the user profile.
Eventually, 200 OK response (iii) is sent to the UA. Note that the
Authentication and Authorization is valid for the registration
validity period duration (i.e., until re-registration is performed).
Several SIP sessions may be established without re-authorization.
UA A sends an INVITE (1). The SIP Proxy sends a Diameter Credit-
Control-Request (INITIAL_REQUEST) to the Diameter credit-control
server (2). The Credit-Control-Request contains information obtained
from the SIP signaling describing the requested service (e.g.,
calling party, called party, Session Description Protocol
attributes). The Diameter credit-control server checks the end
user's account balance, rates the service, and reserves credit from
the end user's account. The reserved quota is returned to the SIP
Proxy in the Diameter Credit-Control-Answer (3). The SIP Proxy
forwards the SIP INVITE to UA B (4). B's phone rings, and B answers.
The media flows between them, and the SIP Proxy starts measuring the
quota. At the expiry of the allocated quota, the SIP Proxy sends a
Diameter Credit-Control-Request (UPDATE_REQUEST) to the Diameter
credit-control server (5). This message contains the units used thus
far. The Diameter credit-control server debits the used units from
the end user's account and allocates new credit that is returned to
the SIP Proxy in the Diameter Credit-Control-Answer (6). The end
user terminates the service by sending a BYE (7). The SIP Proxy
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forwards the BYE message to UA B (8) and sends a Diameter Credit-
Control-Request (TERMINATION_REQUEST) to the credit-control server
(9). The Diameter credit-control server acknowledges the session
termination by sending a Diameter Credit-Control-Answer to the SIP
Proxy (10).
A.3. Flow III
MMS Server
A (CC Client) B CC Server
|(1) Send MMS | | |
|--------------->| | |
| |(2) CCR (event, DIRECT_DEBITING,|
| | MMS specific AVP) |
| |-------------------------------->|
| |(3) CCA (Granted-Units) |
| |<--------------------------------|
|(4) Send MMS Ack| | |
|<---------------| | |
| |(5) Notify MMS | |
| |--------------->| |
: : : :
| |(6) Retrieve MMS| |
| |<---------------| |
| |(7) Retrieve MMS| |
| | Ack | |
| |--------------->| |
| | | |
Figure A.3: Flow III
A credit-control flow for Multimedia Messaging Services is shown in
Figure A.3. The sender is charged as soon as the messaging server
successfully stores the message.
The end user A sends a Multimedia Message (MMS) to the MMS server
(1). The MMS server stores the message and sends a Diameter Credit-
Control-Request (EVENT_REQUEST with Requested-Action DIRECT_DEBITING)
to the Diameter credit-control server (2). The Credit-Control-
Request contains information about the MMS message (e.g., size,
recipient address, image coding type). The Diameter credit-control
server checks the end user's account balance, rates the service, and
debits the service from the end user's account. The granted quota is
returned to the MMS server in the Diameter Credit-Control-Answer (3).
The MMS server acknowledges the successful reception of the MMS
message (4). The MMS Server notifies the recipient about the new MMS
(5), and end user B retrieves the message from the MMS message store
(6),(7).
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A.4. Flow IV
MMS Server
Content Server (CC Client) B CC Server
|(1) Send MMS | | |
|--------------->| | |
| |(2) CCR (event, CHECK_BALANCE, |
| | MMS specific AVP) |
| |-------------------------------->|
| |(3) CCA (ENOUGH_CREDIT) |
| |<--------------------------------|
|(4) Send MMS Ack| | |
|<---------------| | |
| |(5) Notify MMS | |
| |--------------->| |
: : : :
| |(6) Retrieve MMS| |
| |<---------------| |
| |(7) CCR (event, DIRECT_DEBITING,|
| | MMS specific AVP) |
| |-------------------------------->|
| |(8) CCA (Granted-Units) |
| |<--------------------------------|
| |(9) Retrieve MMS| |
| | Ack | |
| |--------------->| |
| | | |
Figure A.4: Flow IV
This is an example of Diameter credit-control for direct debiting
using the Multimedia Messaging Service environment. Although the
flow focuses on illustrating the usage of credit-control messages,
the MMS signaling is inaccurate, and the diagram is not by any means
an attempt to define any service provider's MMS configuration or
billing model.
A credit-control flow for Multimedia Messaging Service is shown in
Figure A.4. The recipient is charged at the message delivery.
A content server sends a Multimedia Message (MMS) to the MMS server
(1) that stores the message. The message recipient will be charged
for the MMS message in this case. As there can be a substantially
long time between the receipt of the message at the MMS server and
the actual retrieval of the message, the MMS server does not
establish any credit-control session to the Diameter credit-control
server but performs first only a balance check (without any credit
reservation) by sending a Diameter Credit-Control-Request
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(EVENT_REQUEST with Requested-Action CHECK_BALANCE) to verify that
end user B can cover the cost for the MMS (2). The Diameter credit-
control server checks the end user's account balance and returns the
answer to the MMS server in the Diameter Credit-Control-Answer (3).
The MMS server acknowledges the successful reception of the MMS
message (4). The MMS server notifies the recipient of the new MMS
(5), and after some time end user B retrieves the message from the
MMS message store (6). The MMS server sends a Diameter Credit-
Control-Request (EVENT_REQUEST with Requested-Action:
DIRECT_DEBITING) to the Diameter credit-control server (7). The
Credit-Control-Request contains information about the MMS message
(e.g., size, recipient address, coding type). The Diameter credit-
control server checks the end user's account balance, rates the
service, and debits the service from the end user's account. The
granted quota is returned to the MMS server in the Diameter Credit-
Control-Request (8). The MMS is transferred to end user B (9).
Note that the transfer of the MMS message can take an extended time
and can fail, in which case a recovery action is needed. The MMS
server should return the already debited units to the user's account
by using the REFUND action described in section 6.4.
A.5. Flow V
SIP Controller
A (CC Client) B CC Server
|(1)INVITE B(SDP)| | |
|--------------->| | |
| |(2) CCR (event, PRICE_ENQUIRY, |
| | SIP specific AVPs) |
| |-------------------------------->|
| |(3) CCA (Cost-Information) |
| |<--------------------------------|
| (4)MESSAGE(URL)| | |
|<---------------| | |
|(5)HTTP GET | | |
|--------------->| | |
|(6)HTTP POST | | |
|--------------->|(7)INVITE(SDP) | |
| |--------------->| |
| | (8)200 OK | |
| (9)200 OK |<---------------| |
|<---------------| | |
Figure A.5: Flow V
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This is an example of Diameter credit-control for SIP sessions.
Although the flow focuses on illustrating the usage of credit-control
messages, the SIP signaling is inaccurate, and the diagram is not by
any means an attempt to define a service provider's SIP network.
Figure A.5 is an example of Advice of Charge (AoC) service for SIP
call. User A can be either a postpaid or prepaid subscriber using
the AoC service. It is assumed that the SIP controller also has HTTP
capabilities and delivers an interactive AoC web page with, for
instance, the cost information, the details of the call derived from
the SDP, and a button to accept/not accept the charges. (There may
be many other ways to deliver AoC information; however, this flow
focuses on the use of the credit-control messages.) The user has
been authenticated and authorized prior to initiating the call and
subscribed to AoC service.
UA A sends an INVITE with SDP to B (1). The SIP controller
determines that the user is subscribed to AoC service and sends a
Diameter Credit-Control-Request (EVENT_REQUEST with Requested-Action:
PRICE_ENQUIRY) to the Diameter credit-control server (2). The
Credit-Control-Request contains SIP specific AVPs derived from the
SIP signaling, describing the requested service (e.g., calling party,
called party, Session Description Protocol attributes). The Diameter
credit-control server determines the cost of the service and returns
the Credit-Control-Answer including the Cost-Information AVP (3).
The SIP controller manufactures the AoC web page with information
received in SIP signaling and with the cost information received from
the credit-control server. Then it sends a SIP MESSAGE that contains
a URL pointing to the AoC information web page (4). At the receipt
of the SIP MESSAGE, A's UA automatically invokes the web browser that
retrieves the AoC information (5). The user clicks on a proper
button and accepts the charges (6). The SIP controller continues the
session and sends the INVITE to the B party, which accepts the call
(7,8,9).
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A.6. Flow VI
Gaming Server
End User (CC Client) CC Server
| (1)Service Delivery | |
|<---------------------->| |
: : :
: : :
| |(2)CCR(event,REFUND,Requested-
| |Service-Unit,Service-Parameter-Info)
| |----------------------->|
| | (3)CCA(Cost-Information)
| |<-----------------------|
| (4)Notification | |
|<-----------------------| |
Figure A.6: Flow VI
Figure A.6 illustrates a credit-control flow for the REFUND case. It
is assumed that there is a trusted relationship and secure connection
between the Gaming server and the Diameter credit-control server.
The end user may be a prepaid subscriber or a postpaid subscriber.
While the end user is playing the game (1), she enters a new level
that entitles her to a bonus. The Gaming server sends a Diameter
Credit-Control-Request (EVENT_REQUEST with Requested-Action:
REFUND_ACCOUNT) to the Diameter credit-control server (2). The
Credit-Control-Request Request contains the Requested-Service-Unit
AVP with the CC-Service-Specific-Units containing the number of
points the user just won. The Service-Parameter-Info AVP is also
included in the request and specifies the service event to be rated
(e.g., Tetris Bonus). From information received, the Diameter
credit-control server determines the amount to be credited, refunds
the user's account, and returns the Credit-Control-Answer, including
the Cost-Information AVP (3). The Cost-Information indicates the
credited amount. At the first opportunity, the Gaming server
notifies the end user of the credited amount (4).
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A.7. Flow VII
SIP Controller Top-Up
A (CC Client) Server B CC Server
| | | | |
| | (1) CCR(Update,Used-Unit) | |
| |------------------------------------------>|
| | (2) CCA(Final-Unit, Redirect)|
| |<------------------------------------------|
: : : : :
: : : : :
| | (3) CCR(Update, Used-Units)| |
| |------------------------------------------>|
| | (3a)INVITE("hold") | |
| |--------------------------->| |
| | | (4) CCA(Validity-Time)|
| |<------------------------------------------|
| (5)INVITE | (6)INVITE | | |
|<--------------|------------->| | |
| (7)RTP | | |
|..............................| | |
| | (8)BYE | | |
| |<-------------| | |
| | (9)CCR(Update) | |
| |------------------------------------------>|
| | (10)CCA(Granted-Unit) |
| |<------------------------------------------|
| (12)INVITE | (11)INVITE | |
|<--------------|--------------------------->| |
Figure A.7: Flow VII
Figure A.7 is an example of the graceful service termination for a
SIP call. It is assumed that the call is set up so that the
controller is in the call as a B2BUA (Back to Back User Agent)
performing third-party call control (3PCC). Note that the SIP
signaling is inaccurate, as the focus of this flow is in the graceful
service termination and credit-control authorization. The best
practice for 3PCC is defined in [RFC3725].
The call is ongoing between users A and B; user A has a prepaid
subscription. At the expiry of the allocated quota, the SIP
controller sends a Diameter Credit-Control-Request (UPDATE_REQUEST)
to the Diameter credit-control server (1). This message contains the
units used thus far. The Diameter credit-control server debits the
used units from the end user's account and allocates the final quota
returned to the SIP controller in the Diameter Credit-Control-Answer
(2). This message contains the Final-Unit-Indication AVP with the
Hakala, et al. Standards Track [Page 103]
RFC 4006 Diameter Credit-Control Application August 2005
Final-Unit-Action set to REDIRECT, the Redirect-Address-Type set to
SIP URI, and the Redirect-Server-Address set to the Top-up server
name (e.g., sip:[email protected]). At the expiry of the
final allocated quota, the SIP controller sends a Diameter Credit-
Control-Request (UPDATE_REQUEST) to the Diameter credit-control
server (3) and places the called party on "hold" by sending an INVITE
with the appropriate connection address in the SDP (3a). The
Credit-Control-Request message contains the units used thus far. The
Diameter credit-control server debits the used units from the end
user's account but does not make any credit reservation. The
Credit-Control-Answer message, which contains the Validity-Time to
supervise the graceful service termination, is returned to the SIP
controller (4). The SIP controller establishes a SIP session between
the prepaid user and the Top-up server (5, 6). The Top-up server
plays an announcement and prompts the user to enter a credit card
number and the amount of money to be used to replenish the account
(7). The Top-up server validates the credit card number and
replenishes the user's account (using some means outside the scope of
this specification) and releases the SIP session (8). The SIP
controller can now assume that communication between the prepaid user
and the Top-up server took place. It sends a spontaneous Credit-
Control-Request (UPDATE_REQUEST) to the Diameter credit-control
server to check whether the account has been replenished (9). The
Diameter credit-control server reserves credit from the end user's
account and returns the reserved quota to the SIP controller in the
Credit-Control-Answer (10). At this point, the SIP controller re-
connects the caller and the called party (11,12).
Hakala, et al. Standards Track [Page 104]
RFC 4006 Diameter Credit-Control Application August 2005
A.8. Flow VIII
NAS Top-up CC
End-User (CC Client) AAA Server Server Server
|(1)User Logon |(2)AA Request (CC AVPs) | |
|------------------>|------------------->| | |
| | |(3)CCR(initial, CC AVPs)
| | |------------------->|
| | |(4)CCA(Final-Unit, |
| | | Validity-Time)|
| | |<-------------------|
| |(5)AA Answer(Final-Unit,Validity-Time) |
|(6)Limited Access |<-------------------| | |
| granted | | | |
|<----------------->| | | |
| | | | |
| (7)TCP/HTTP | (8)TCP/HTTP | |
|<----------------->|<----------------------------->| |
| (9) Replenish account | |
|<------------------------------------------------->| |
| | | (10)RAR |
| |<-------------------|<-------------------|
| | (11) RAA | |
| |------------------->|------------------->|
| |(12)CCR(update) | |
| |------------------->|(13)CCR(Update) |
| | |------------------->|
| | |(14)CCA(Granted-Units)
| |(15)CCA(Granted-Units)<------------------|
| |<-------------------| |
Figure A.8: Flow VIII
Figure A.8 is an example of the graceful service termination
initiated when the first interrogation takes place because the user's
account is empty. In this example, the credit-control server
supports the server-initiated credit re-authorization. The Diameter
[NASREQ] is implemented in the Network Access Server (NAS).
The user logs on to the network (1). The Diameter NAS sends a
Diameter AA-Request to the home Diameter AAA server. The credit-
control client populates the AAR with the Credit-Control AVP set to
CREDIT_AUTHORIZATION, and service specific AVPs are included, as
usual [NASREQ]. The home Diameter AAA server performs service
specific Authentication and Authorization, as usual. The home
Diameter AAA server determines that the user has a prepaid
subscription and notices from the Credit-Control AVP that the NAS has
credit-control capabilities. It sends a Diameter Credit-Control-
Hakala, et al. Standards Track [Page 105]
RFC 4006 Diameter Credit-Control Application August 2005
Request with CC-Request-Type set to INITIAL_REQUEST to the Diameter
credit-control server to perform credit authorization (3) and to
establish a credit-control session. (The home Diameter AAA server
may forward service specific AVPs received from the NAS as input for
the rating process.) The Diameter credit-control server checks the
end user's account balance, determines that the account cannot cover
the cost of the service, and initiates the graceful service
termination. The Credit-Control-Answer is returned to the home
Diameter AAA server (4). This message contains the Final-Unit-
Indication AVP and the Validity-Time AVP set to a reasonable amount
of time to give the user a chance to replenish his/her account (e.g.,
10 minutes). The Final-Unit-Indication AVP includes the Final-Unit-
Action set to REDIRECT, the Redirect-Address-Type set to URL, and the
Redirect-Server-Address set to the HTTP Top-up server name. The home
Diameter AAA server sends the received credit-control AVPs to the NAS
in the Diameter AA-Answer (5). Upon successful AAA, the NAS starts
the credit-control session and immediately starts the graceful
service termination, as instructed by the server. The NAS grants
limited access to the user (6). The HTTP client software running in
the user's device opens the transport connection redirected by the
NAS to the Top-up server (7,8). The user is displayed an appropriate
web page on which to enter the credit card number, and the amount of
money to be used to replenish the account, and with a notification
message that she is granted unlimited access if the replenishment
operation will be successfully executed within the next, for example,
10 minutes. The Top-up server validates the credit card number and
replenishes the user's account (using some means outside the scope of
this specification)(9). After successful account top-up, the
credit-control server sends a Re-Auth-Request message to the NAS
(10). The NAS acknowledges the request by returning the Re-Auth-
Answer message (11) and initiates the credit re-authorization by
sending a Credit-Control-request (UPDATE_REQUEST) to the Diameter
credit-control server (12,13).
The Diameter credit-control server reserves credit from the end
user's account and returns the reserved quota to the NAS via the home
Diameter AAA server in the Credit-Control-Answer (14,15). The NAS
removes the restriction placed by the graceful service termination
and starts monitoring the granted units.
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RFC 4006 Diameter Credit-Control Application August 2005
A.9. Flow IX
The Diameter credit-control application defines the Multiple-
Services-Credit-Control AVP that can be used to support independent
credit-control of multiple services in a single credit-control (sub-)
session for service elements that have such capabilities. It is
possible to request and allocate resources as a credit pool that is
shared between services or rating groups.
The flow example hereafter illustrates a usage scenario where the
credit-control client and server support independent credit-control
of multiple services, as defined in section 5.1.2. It is assumed
that Service-Identifiers, Rating-Groups, and their associated
parameters (e.g., IP 5-tuple) are locally configured in the service
element or provisioned by an entity other than the credit-control
server.
End User Service Element CC Server
(CC client)
|(1)User logon | |
|------------------>|(2)CCR(initial, Service-Id access, |
| | Access specific AVPs, |
| | Multiple-Service-Indicator) |
| |---------------------------------------->|
| |(3)CCA(Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id access, |
| | Validity-time, |
| | G-S-U-Pool-Reference(Pool-Id 1, |
| | Multiplier 10))) |
| |<----------------------------------------|
: : :
|(4)Service-Request (Service 1) |
|------------------>|(5)CCR(update, Multiple-Services-CC( |
| | Requested-Units(), Service-Id 1, |
| | Rating-Group 1)) |
| |---------------------------------------->|
| |(6)CCA(Multiple-Services-CC ( |
| | Granted-Units(Time), |
| | Rating-Group 1, |
| | G-S-U-Pool-Reference(Pool-Id 1, |
| | Multiplier 1))) |
| |<----------------------------------------|
: : :
|(7)Service-Request (Service 2) |
|------------------>| |
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RFC 4006 Diameter Credit-Control Application August 2005
: : :
: : :
|(8)Service-Request (Service 3&4) |
|------------------>|(9)CCR(update, Multiple-Services-CC ( |
| | Requested-Units(), Service-Id 3, |
| | Rating-Group 2), |
| | Multiple-Services-CC ( |
| | Requested-Units(), Service-Id 4, |
| | Rating-Group 3)) |
| |---------------------------------------->|
| |(10)CCA(Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id 3, Rating-Group 2, |
| | Validity-time, |
| | G-S-U-Pool-Reference(Pool-Id 2, |
| | Multiplier 2)), |
| | Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id 4, Rating-Group 3 |
| | Validity-Time, |
| | Final-Unit-Ind.(Terminate), |
| | G-S-U-Pool-Reference(Pool-Id 2, |
| | Multiplier 5))) |
| |<----------------------------------------|
: : :
: : :
| +--------------+ | |
| |Validity time | |(11)CCR(update, |
| |expires for | | Multiple-Services-CC ( |
| |Service-Id | | Requested-Unit(), |
| | access | | Used-Units(In-Octets,Out-Octets),|
| +--------------+ | Service-Id access)) |
| |---------------------------------------->|
| |(12)CCA(Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id access, |
| | Validity-Time, |
| | G-S-U-Pool-Reference(Pool-Id 1, |
| | Multiplier 10))) |
| |<----------------------------------------|
: : :
: : :
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RFC 4006 Diameter Credit-Control Application August 2005
| +--------------+ | |
| |Total Quota | |(13)CCR(update, |
| |elapses for | | Multiple-Services-CC ( |
| |pool 2: | | Requested-Unit(), |
| |service 4 not | | Used-Units(In-Octets,Out-Octets),|
| |allowed, | | Service-Id 3, Rating-group 2), |
| |service 3 cont| | Multiple-Services-CC ( |
| +--------------+ | Used-Units(In-Octets,Out-Octets),|
| | Service-Id 4, Rating-Group 3)) |
| |---------------------------------------->|
| |(14)CCA(Multiple-Services-CC ( |
| | Result-Code 4011, |
| | Service-Id 3)) |
| |<----------------------------------------|
: : :
: : :
|(15) User logoff | |
|------------------>|(16)CCR(term, |
| | Multiple-Services-CC ( |
| | Used-Units(In-Octets,Out-Octets),|
| | Service-Id access), |
| | Multiple-Services-CC ( |
| | Used-Units(Time), |
| | Service-Id 1, Rating-Group 1), |
| | Multiple-Services-CC ( |
| | Used-Units(Time), |
| | Service-Id 2, Rating-Group 1)) |
| |---------------------------------------->|
| |(17)CCA(term) |
| |<----------------------------------------|
Figure A.9: Flow example independent credit-control of multiple
services in a credit-control (sub-)Session
The user logs on to the network (1). The service element sends a
Diameter Credit-Control-Request with CC-Request-Type set to
INITIAL_REQUEST to the Diameter credit-control server to perform
credit authorization for the bearer service (e.g., Internet access
service) and to establish a credit-control session (2). In this
message, the credit-control client indicates support for independent
credit-control of multiple services within the session by including
the Multiple-Service-Indicator AVP. The Diameter credit-control
server checks the end user's account balance, with rating information
received from the client (i.e., Service-Id and access specific AVPs),
rates the request, and reserves credit from the end user's account.
Suppose that the server reserves $5 and determines that the cost is
$1/MB. It then returns to the service element a Credit-Control-
Answer message that includes the Multiple-Services-Credit-Control AVP
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RFC 4006 Diameter Credit-Control Application August 2005
with a quota of 5MB associated to the Service-Id (access), to a
multiplier value of 10, and to the Pool-Id 1 (3).
The user uses Service 1 (4). The service element sends a Diameter
Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to
the credit-control server to perform credit authorization for service
1 (5). This message includes the Multiple-Services-Credit-Control
AVP to request service units for Service 1 that belong to Rating-
Group 1. The Diameter credit-control server determines that Service
1 draws credit resources from the same account as the access service
(i.e., pool 1). It rates the request according to Service-
Id/Rating-Group and updates the existing reservation by requesting
more credit. Suppose that the server reserves $5 more (now the
reservation is $10) and determines that the cost is $0.1/minute. The
server authorizes the whole Rating-Group. It then returns to the
service element a Credit-Control-Answer message that includes the
Multiple-Services-Credit-Control AVP with a quota of 50min.
associated to the Rating-Group 1, to a multiplier value of 1, and to
the Pool-Id 1 (6). The client adjusts the total amount of resources
for pool 1 according the received quota, which gives S for Pool 1 =
100.
The user uses Service 2, which belongs to the authorized Rating-
Group, 1 (7). Resources are then consumed from the pool 1.
The user now requests Services 3 and 4 as well, which are not
authorized (8). The service element sends a Diameter Credit-
Control-Request with CC-Request-Type set to UPDATE_REQUEST to the
credit-control server in order to perform credit authorization for
Services 3 and 4 (9). This message includes two instances of the
Multiple-Services-Credit-Control AVP to request service units for
Service 3 that belong to Rating-Group 2 and for Service 4 that belong
to Rating-Group 3. The Diameter credit-control server determines
that Services 3 and 4 draw credit resources from another account
(i.e., pool 2). It checks the end user's account balance and,
according to Service-Ids/Rating-Groups information, rates the
request. Then it reserves credit from pool 2.
For example, the server reserves $5 and determines that Service 3
costs $0.2/MB and Service 4 costs $0.5/MB. The server authorizes
only Services 3 and 4. It returns to the service element a Credit-
Control-Answer message that includes two instances of the Multiple-
Services-Credit-Control AVP (10). One instance grants a quota of
12.5MB associated to the Service-Id 3 to a multiplier value of 2 and
to the Pool-Id 2. The other instance grants a quota of 5 MB
associated to the Service-Id 4 to a multiplier value of 5 and to the
Pool-Id 2.
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RFC 4006 Diameter Credit-Control Application August 2005
The server also determines that pool 2 is exhausted and Service 4 is
not allowed to continue after these units will be consumed.
Therefore the Final-Unit-Indication AVP with action TERMINATE is
associated to the Service-Id 4. The client calculates the total
amount of resources that can be used for pool 2 according the
received quotas and multipliers, which gives S for Pool 2 = 50.
The Validity-Time for the access service expires. The service
element sends a Credit-Control-Request message to the server in order
to perform credit re-authorization for Service-Id (access) (11).
This message carries one instance of the Multiple-Services-Credit-
Control AVP that includes the units used by this service. Suppose
that the total amount of used units is 4MB. The client adjusts the
total amount of resources for pool 1 accordingly, which gives S for
Pool 1 = 60.
The server deducts $4 from the user's account and updates the
reservation by requesting more credit. Suppose that the server
reserves $5 more (now the reservation is $11) and already knows the
cost of the Service-Id (access), which is $1/MB. It then returns to
the service element a Credit-Control-Answer message that includes the
Multiple-Services-Credit-Control AVP with a quota of 5 MB associated
to the Service-Id (access), to a multiplier value of 10, and to the
Pool-Id 1 (12). The client adjusts the total amount of resources for
pool 1 according the received quota, which gives S for Pool 1 = 110.
Services 3 and 4 consume the total amount of pool 2 credit resources
(i.e., C1*2 + C2*5 >= S). The service element immediately starts the
TERMINATE action concerning Service 4 and sends a Credit-Control-
Request message with CC-Request-Type set to UPDATE_REQUEST to the
credit-control server in order to perform credit re-authorization for
Service 3 (13). This message contains two instances of the
Multiple-Services-Credit-Control AVP to report the units used by
Services 3 and 4. The server deducts the last $5 from the user's
account (pool 2) and returns the answer with Result-Code 4011 in the
Multiple-Services-Credit-Control AVP to indicate that Service 3 can
continue without credit-control (14).
The end user logs off from the network (15). To debit the used units
from the end user's account and to stop the credit-control session,
the service element sends a Diameter Credit-Control-Request with CC-
Request-Type set to TERMINATION_REQUEST to the credit-control server
(16). This message contains the units consumed by each of the used
services in multiple instances of the Multiple-Services-Credit-
Control AVP. The used units are associated with the relevant
Service-Identifier and Rating-Group. The Diameter credit-control
Hakala, et al. Standards Track [Page 111]
RFC 4006 Diameter Credit-Control Application August 2005
server debits the used units to the user's account (Pool 1) and
acknowledges the session termination by sending a Diameter Credit-
Control-Answer to the service element (17).
Authors' Addresses
Harri Hakala
Oy L M Ericsson Ab
Joukahaisenkatu 1
20520 Turku
Finland
Phone: +358 2 265 3722
EMail: [email protected]
Leena Mattila
Oy L M Ericsson Ab
Joukahaisenkatu 1
20520 Turku
Finland
Phone: +358 2 265 3731
EMail: [email protected]
Juha-Pekka Koskinen
Nokia Networks
Hatanpaanvaltatie 30
33100 Tampere
Finland
Phone: +358 7180 74027
EMail: [email protected]
Hakala, et al. Standards Track [Page 112]
RFC 4006 Diameter Credit-Control Application August 2005
Marco Stura
Nokia Networks
Hiomotie 32
00380 Helsinki
Finland
Phone: +358 7180 64308
EMail: [email protected]
John Loughney
Nokia Research Center
Itamerenkatu 11-13
00180 Helsinki
Finland
Phone: +358 50 483 642
EMail: [email protected]
Hakala, et al. Standards Track [Page 113]
RFC 4006 Diameter Credit-Control Application August 2005
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Hakala, et al. Standards Track [Page 114]
