[ RFC Index | RFC Search | Usenet FAQs | Web FAQs | Documents | Cities ]
Alternate Formats: rfc4006.txt | rfc4006.txt.pdf
RFC 4006 - Diameter Credit-Control Application
|
 |
RFC4006 - Diameter Credit-Control Application
Network Working Group H. Hakala
Request for Comments: 4006 L. Mattila
Category: Standards Track Ericsson
J-P. Koskinen
M. Stura
J. Loughney
Nokia
August 2005
Diameter Credit-Control Application
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services.
Table of Contents
1. Introduction................................................. 4
1.1. Requirements Language................................. 5
1.2. Terminology........................................... 5
1.3. Advertising Application Support....................... 7
2. Architecture Models.......................................... 7
3. Credit-Control Messages...................................... 9
3.1. Credit-Control-Request (CCR) Command.................. 9
3.2. Credit-Control-Answer (CCA) Command................... 11
4. Credit-Control Application Overview.......................... 11
4.1. Service-Specific Rating Input and Interoperability.... 13
5. Session Based Credit-Control................................. 15
5.1. General Principles.................................... 15
5.2. First Interrogation................................... 21
5.3. Intermediate Interrogation............................ 27
5.4. Final Interrogation................................... 29
5.5. Server-Initiated Credit Re-Authorization.............. 30
5.6. Graceful Service Termination.......................... 32
5.7. Failure Procedures.................................... 38
6. One Time Event............................................... 41
6.1. Service Price Enquiry................................. 42
6.2. Balance Check......................................... 42
6.3. Direct Debiting....................................... 43
6.4. Refund................................................ 44
6.5. Failure Procedure..................................... 44
7. Credit-Control Application State Machine..................... 46
8. Credit-Control AVPs.......................................... 55
8.1. CC-Correlation-Id AVP................................. 58
8.2. CC-Request-Number AVP................................. 58
8.3. CC-Request-Type AVP................................... 58
8.4. CC-Session-Failover AVP............................... 59
8.5. CC-Sub-Session-Id AVP................................. 59
8.6. Check-Balance-Result AVP.............................. 60
8.7. Cost-Information AVP.................................. 60
8.8. Unit-Value AVP........................................ 61
8.9. Exponent AVP.......................................... 61
8.10. Value-Digits AVP...................................... 61
8.11. Currency-Code AVP..................................... 62
8.12. Cost-Unit AVP......................................... 62
8.13. Credit-Control AVP.................................... 62
8.14. Credit-Control-Failure-Handling AVP................... 62
8.15. Direct-Debiting-Failure-Handling AVP.................. 63
8.16. Multiple-Services-Credit-Control AVP.................. 64
8.17. Granted-Service-Unit AVP.............................. 65
8.18. Requested-Service-Unit AVP............................ 66
8.19. Used-Service-Unit AVP................................. 66
8.20. Tariff-Time-Change AVP................................ 67
8.21. CC-Time AVP........................................... 67
8.22. CC-Money AVP.......................................... 67
8.23. CC-Total-Octets AVP................................... 68
8.24. CC-Input-Octets AVP................................... 68
8.25. CC-Output-Octets AVP.................................. 68
8.26. CC-Service-Specific-Units AVP......................... 68
8.27. Tariff-Change-Usage AVP............................... 68
8.28. Service-Identifier AVP................................ 69
8.29. Rating-Group AVP...................................... 69
8.30. G-S-U-Pool-Reference AVP.............................. 69
8.31. G-S-U-Pool-Identifier AVP............................. 70
8.32. CC-Unit-Type AVP...................................... 70
8.33. Validity-Time AVP..................................... 70
8.34. Final-Unit-Indication AVP............................. 71
8.35. Final-Unit-Action AVP................................. 72
8.36. Restriction-Filter-Rule AVP........................... 72
8.37. Redirect-Server AVP................................... 73
8.38. Redirect-Address-Type AVP............................. 73
8.39. Redirect-Server-Address AVP........................... 74
8.40. Multiple-Services-Indicator AVP....................... 74
8.41. Requested-Action AVP.................................. 74
8.42. Service-Context-Id AVP................................ 75
8.43. Service-Parameter-Info AVP............................ 76
8.44. Service-Parameter-Type AVP............................ 76
8.45. Service-Parameter-Value AVP........................... 77
8.46. Subscription-Id AVP................................... 77
8.47. Subscription-Id-Type AVP.............................. 77
8.48. Subscription-Id-Data AVP.............................. 78
8.49. User-Equipment-Info AVP............................... 78
8.50. User-Equipment-Info-Type AVP.......................... 78
8.50. 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
A.1. Flow I................................................ 94
A.2. Flow II............................................... 96
A.3. Flow III.............................................. 98
A.4. Flow IV............................................... 99
A.5. Flow V................................................ 100
A.6. Flow VI............................................... 102
A.7. Flow VII.............................................. 103
A.8. Flow VIII............................................. 105
A.9. Flow IX............................................... 107
Authors' Addresses............................................... 112
Full Copyright Statement......................................... 114
1. Introduction
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services. It provides a general
solution to real-time cost and credit-control.
The prepaid model has been shown to be very successful, for instance,
in GSM networks, where network operators offering prepaid services
have experienced a substantial growth of their customer base and
revenues. Prepaid services are now cropping up in many other
wireless and wire line based networks.
In next generation wireless networks, additional functionality is
required beyond that specified in the Diameter base protocol. For
example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
that an application must be able to rate service information in
real-time. In addition, it is necessary to check that the end user's
account provides coverage for the requested service prior to
initiation of that service. When an account is exhausted or expired,
the user must be denied the ability to compile additional chargeable
events.
A mechanism has to be provided to allow the user to be informed of
the charges to be levied for a requested service. In addition, there
are services such as gaming and advertising that may credit as well
as debit a user account.
The other Diameter applications provide service specific
authorization, and they do not provide credit authorization for
prepaid users. The credit authorization shall be generic and
applicable to all the service environments required to support
prepaid services.
To fulfill these requirements, it is necessary to facilitate credit-
control communication between the network element providing the
service (e.g., Network Access Server, SIP Proxy, and Application
Server) and a credit-control server.
The scope of this specification is the credit authorization. Service
specific authorization and authentication is out of the scope.
1.1. Requirements Language
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
"RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [KEYWORDS].
1.2. Terminology
AAA
Authentication, Authorization, and Accounting
AA answer
AA answer generically refers to a service specific authorization and
authentication answer. AA answer commands are defined in service
specific authorization applications, e.g., [NASREQ] and [DIAMMIP].
AA request
AA request generically refers to a service specific authorization and
authentication request. AA request commands are defined in service
specific authorization applications e.g., [NASREQ] and [DIAMMIP].
Credit-control
Credit-control is a mechanism that directly interacts in real-time
with an account and controls or monitors the charges related to the
service usage. Credit-control is a process of checking whether
credit is available, credit-reservation, deduction of credit from the
end user account when service is completed and refunding of reserved
credit that is not used.
Diameter Credit-control Server
A Diameter credit-control server acts as a prepaid server, performing
real-time rating and credit-control. It is located in the home
domain and is accessed by service elements or Diameter AAA servers in
real-time for purpose of price determination and credit-control
before the service event is delivered to the end-user. It may also
interact with business support systems.
Diameter Credit-control Client
A Diameter credit-control client is an entity that interacts with a
credit-control server. It monitors the usage of the granted quota
according to instructions returned by credit-control server.
Interrogation
The Diameter credit-control client uses interrogation to initiate a
session based credit-control process. During the credit-control
process, it is used to report the used quota and request a new one.
An interrogation maps to a request/answer transaction.
One-time event
Basically, a request/answer transaction of type event.
Rating
The act of determining the cost of the service event.
Service
A type of task performed by a service element for an end user.
Service Element
A network element that provides a service to the end users. The
Service Element may include the Diameter credit-control client, or
another entity (e.g., RADIUS AAA server) that can act as a Credit-
control client on behalf of the Service Element. In the latter case,
the interface between the Service Element and the Diameter credit-
control client is outside the scope of this specification. Examples
of the Service Elements include Network Access Server (NAS), SIP
Proxy, and Application Servers such as messaging server, content
server, and gaming server.
Service Event
An event relating to a service provided to the end user.
Session based credit-control
A credit-control process that makes use of several interrogations:
the first, a possible intermediate, and the final. The first
interrogation is used to reserve money from the user's account and to
initiate the process. The intermediate interrogations may be needed
to request new quota while the service is being rendered. The final
interrogation is used to exit the process. The credit-control server
is required to maintain session state for session-based credit-
control.
1.3. Advertising Application Support
Diameter nodes conforming to this specification MUST advertise
support by including the value of 4 in the Auth-Application-Id of the
Capabilities-Exchange-Request and Capabilities-Exchange-Answer
command [DIAMBASE].
2. Architecture Models
The current accounting models specified in the Radius Accounting
[RFC2866] and Diameter base [DIAMBASE] are not sufficient for real-
time credit-control, where credit-worthiness is to be determined
prior to service initiation. Also, the existing Diameter
authorization applications, [NASREQ] and [DIAMMIP], only provide
service authorization, but do not provide credit authorization for
prepaid users. In order to support real-time credit-control, a new
type of server is needed in the AAA infrastructure: Diameter credit-
control server. The Diameter credit-control server is the entity
responsible for credit authorization for prepaid subscribers.
A service element may authenticate and authorize the end user with
the AAA server by using AAA protocols; e.g., RADIUS or a Diameter
base protocol with a possible Diameter application.
Accounting protocols such as RADIUS accounting and the Diameter base
accounting protocol can be used to provide accounting data to the
accounting server after service is initiated, and to provide possible
interim reports until service completion. However, for real-time
credit-control, these authorization and accounting models are not
sufficient.
When real-time credit-control is required, the credit-control client
contacts the credit-control server with information about a possible
service event. The credit-control process is performed to determine
potential charges and to verify whether the end user's account
balance is sufficient to cover the cost of the service being
rendered.
Figure 1 illustrates the typical credit-control architecture, which
consists of a Service Element with an embedded Diameter credit-
control client, a Diameter credit-control server, and an AAA server.
A Business Support System is usually deployed; it includes at least
the billing functionality. The credit-control server and AAA server
in this architecture model are logical entities. The real
configuration can combine them into a single host. The credit-
control protocol is the Diameter base protocol with the Diameter
credit-control application.
When an end user requests services such as SIP or messaging, the
request is typically forwarded to a service element (e.g., SIP Proxy)
in the user's home domain. In some cases it might be possible that
the service element in the visited domain can offer services to the
end user; however, a commercial agreement must exist between the
visited domain and the home domain. Network access is an example of
a service offered in the visited domain where the NAS, through an AAA
infrastructure, authenticates and authorizes the user with the user's
home network.
Service Element AAA and CC
+----------+ +---------+ Protocols+-----------+ +--------+
| End |<---->|+-------+|<------------>| AAA | |Business|
| User | +->|| CC || | Server |->|Support |
| | | || Client||<-----+ | | |System |
+----------+ | |+-------+| | +-----------+ | |
| +---------+ | ^ +--------+
+----------+ | | CC Protocol | ^
| End |<--+ | +-----v----+ |
| User | +------>|Credit- | |
+----------+ Credit-Control |Control |--------+
Protocol |Server |
+----------+
Figure 1: Typical credit-control architecture
There can be multiple credit-control servers in the system for
redundancy and load balancing. The system can also contain separate
rating server(s), and accounts can be located in a centralized
database. To ensure that the end user's account is not debited or
credited multiple times for the same service event, only one place in
the credit-control system should perform duplicate detection. System
internal interfaces can exist to relay messages between servers and
an account manager. However, the detailed architecture of the
credit-control system and its interfaces are implementation specific
and are out of scope of this specification.
Protocol transparent Diameter relays can exist between the credit-
control client and credit-control server. Also, Diameter Redirect
agents that refer credit-control clients to credit-control servers
and allow them to communicate directly can exist. These agents
transparently support the Diameter credit-control application. The
different roles of Diameter Agents are defined in Diameter base
[DIAMBASE], section 2.8.
If Diameter credit-control proxies exist between the credit-control
client and the credit-control server, they MUST advertise the
Diameter credit-control application support.
3. Credit-Control Messages
This section defines new Diameter message Command-Code values that
MUST be supported by all Diameter implementations that conform to
this specification. The Command Codes are as follows:
Command-Name Abbrev. Code Reference
-----------------------------------------------------------
Credit-Control-Request CCR 272 3.1
Credit-Control-Answer CCA 272 3.2
Diameter Base [DIAMBASE] defines in the section 3.2 the Command Code
ABNF specification. These formats are observed in Credit-Control
messages.
3.1. Credit-Control-Request (CCR) Command
The Credit-Control-Request message (CCR) is indicated by the
command-code field being set to 272 and the 'R' bit being set in the
Command Flags field. It is used between the Diameter credit-control
client and the credit-control server to request credit authorization
for a given service.
The Auth-Application-Id MUST be set to the value 4, indicating the
Diameter credit-control application.
Message Format
<Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Application-Id }
{ Service-Context-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ Destination-Host ]
[ User-Name ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
*[ Subscription-Id ]
[ Service-Identifier ]
[ Termination-Cause ]
[ Requested-Service-Unit ]
[ Requested-Action ]
*[ Used-Service-Unit ]
[ Multiple-Services-Indicator ]
*[ Multiple-Services-Credit-Control ]
*[ Service-Parameter-Info ]
[ CC-Correlation-Id ]
[ User-Equipment-Info ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP ]
3.2. Credit-Control-Answer (CCA) Command
The Credit-Control-Answer message (CCA) is indicated by the command-
code field being set to 272 and the 'R' bit being cleared in the
Command Flags field. It is used between the credit-control server
and the Diameter credit-control client to acknowledge a Credit-
Control-Request command.
Message Format
<Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
< Session-Id >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
{ Auth-Application-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ User-Name ]
[ CC-Session-Failover ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
[ Granted-Service-Unit ]
*[ Multiple-Services-Credit-Control ]
[ Cost-Information]
[ Final-Unit-Indication ]
[ Check-Balance-Result ]
[ Credit-Control-Failure-Handling ]
[ Direct-Debiting-Failure-Handling ]
[ Validity-Time]
*[ Redirect-Host]
[ Redirect-Host-Usage ]
[ Redirect-Max-Cache-Time ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ Failed-AVP ]
*[ AVP ]
4. Credit-Control Application Overview
The credit authorization process takes place before and during
service delivery to the end user and generally requires the user's
authentication and authorization before any request is sent to the
credit-control server. The credit-control application defined in
this specification supports two different credit authorization
models: credit authorization with money reservation and credit
authorization with direct debiting. In both models, the credit-
control client requests credit authorization from the credit-control
server prior to allowing any service to be delivered to the end user.
In the first model, the credit-control server rates the request,
reserves a suitable amount of money from the user's account, and
returns the corresponding amount of credit resources. Note that
credit resources may not imply actual monetary credit; credit
resources may be granted to the credit control client in the form of
units (e.g., data volume or time) to be metered.
Upon receipt of a successful credit authorization answer with a
certain amount of credit resources, the credit-control client allows
service delivery to the end user and starts monitoring the usage of
the granted resources. When the credit resources granted to the user
have been consumed or the service has been successfully delivered or
terminated, the credit-control client reports back to the server the
used amount. The credit-control server deducts the used amount from
the end user's account; it may perform rating and make a new credit
reservation if the service delivery is continuing. This process is
accomplished with session based credit-control that includes the
first interrogation, possible intermediate interrogations, and the
final interrogation. For session based credit-control, both the
credit control client and the credit-control server are required to
maintain credit-control session state. Session based credit-control
is described in more detail, with more variations, in section 5.
In contrast, credit authorization with direct debiting is a single
transaction process wherein the credit-control server directly
deducts a suitable amount of money from the user's account as soon as
the credit authorization request is received. Upon receipt of a
successful credit authorization answer, the credit-control client
allows service delivery to the end user. This process is
accomplished with the one-time event. Session state is not
maintained.
In a multi-service environment, an end user can issue an additional
service request (e.g., data service) during an ongoing service (e.g.,
voice call) toward the same account. Alternatively, during an active
multimedia session, an additional media type is added to the session,
causing a new simultaneous request toward same account.
Consequently, this needs to be considered when credit resources are
granted to the services.
The credit-control application also supports operations such as
service price enquiry, user's balance check, and refund of credit on
the user's account. These operations are accomplished with the one-
time event. Session state is not maintained.
A flexible credit-control application specific failure handling is
defined in which the home service provider can model the credit-
control client behavior according to its own credit risk management
policy.
The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
Failure-Handling AVP are defined to determine what is done if the
sending of credit-control messages to the credit-control server has
been temporarily prevented. The usage of the Credit-Control-
Failure-Handling AVP and the Direct-Debiting-Failure-Handling AVP
allows flexibility, as failure handling for the credit-control
session and one time event direct debiting may be different.
4.1. Service-Specific Rating Input and Interoperability
The Diameter credit-control application defines the framework for
credit-control; it provides generic credit-control mechanisms
supporting multiple service applications. The credit-control
application, therefore, does not define AVPs that could be used as
input in the rating process. Listing the possible services that
could use this Diameter application is out of scope for this generic
mechanism.
It is reasonable to expect that a service level agreement will exist
between providers of the credit-control client and the credit-control
server covering the charging, services offered, roaming agreements,
agreed rating input (i.e., AVPs), and so on.
Therefore, it is assumed that a Diameter credit-control server will
provide service only for Diameter credit-control clients that have
agreed beforehand as to the content of credit-control messages.
Naturally, it is possible that any arbitrary Diameter credit-control
client can interchange credit-control messages with any Diameter
credit-control server, but with a higher likelihood that unsupported
services/AVPs could be present in the credit-control message, causing
the server to reject the request with an appropriate result-code.
4.1.1. Specifying Rating Input AVPs
There are two ways to provide rating input to the credit-control
server: either by using AVPs or by including them in the Service-
Parameter-Info AVP. The general principles for sending rating
parameters are as follows:
1a. The service SHOULD re-use existing AVPs if it can use AVPs
defined in existing Diameter applications (e.g., NASREQ for network
access services). Re-use of existing AVPs is strongly recommended in
[DIAMBASE].
For AVPs of type Enumerated, the service may require a new value to
be defined. Allocation of new AVP values is done as specified in
[DIAMBASE], section 1.2.
1b. New AVPs can be defined if the existing AVPs do not provide
sufficient rating information. In this case, the procedures defined
in [DIAMBASE] for creating new AVPs MUST be followed.
1c. For services specific only to one vendor's implementation, a
Vendor-Specific AVP code for Private use can be used. Where a
Vendor-Specific AVP is implemented by more than one vendor,
allocation of global AVPs is encouraged instead; refer to [DIAMBASE].
2. The Service-Parameter-Info AVP MAY be used as a container to pass
legacy rating information in its original encoded form (e.g., ASN.1
BER). This method can be used to avoid unnecessary conversions from
an existing data format to an AVP format. In this case, the rating
input is embedded in the Service-Parameter-Info AVP as defined in
section 8.43.
New service applications SHOULD favor the use of explicitly defined
AVPs as described in items 1a and 1b, to simplify interoperability.
4.1.2. Service-Specific Documentation
The service specific rating input AVPs, the contents of the Service-
Parameter-Info AVP or Service-Context-Id AVP (defined in section
8.42) are not within the scope of this document. To facilitate
interoperability, it is RECOMMENDED that the rating input and the
values of the Service-Context-Id be coordinated via an informational
RFC or other permanent and readily available reference. The
specification of another cooperative standardization body (e.g.,
3GPP, OMA, and 3GPP2) SHOULD be used. However, private services may
be deployed that are subject to agreements between providers of the
credit-control server and client. In this case, vendor specific AVPs
can be used.
This specification, together with the above service specific
documents, governs the credit-control message. Service specific
documents define which existing AVPs or new AVPs are used as input to
the rating process (i.e., those that do not define new credit-control
applications), and thus have to be included in the Credit-Control-
Request command by a Diameter credit-control client supporting a
given service as *[AVP]. Should Service-Parameter-Info be used, then
the service specific document MUST specify the exact content of this
grouped AVP.
The Service-Context-Id AVP MUST be included at the command level of a
Credit-Control Request to identify the service specific document that
applies to the request. The specific service or rating group the
request relates to is uniquely identified by the combination of
Service-Context-Id and Service-Identifier or Rating-Group.
4.1.3. Handling of Unsupported/Incorrect Rating Input
Diameter credit-control implementations are required to support the
Mandatory rating AVPs defined in service specific documentation of
the services they support, according to the 'M' bit rules in
[DIAMBASE].
If a rating input required for the rating process is incorrect in the
Credit-control request, or if the credit-control server does not
support the requested service context (identified by the Service-
Context-Id AVP at command level), the Credit-control answer MUST
contain the error code DIAMETER_RATING_FAILED. A CCA message with
this error MUST contain one or more Failed-AVP AVPs containing the
missing and/or unsupported AVPs that caused the failure. A Diameter
credit-control client that receives the error code
DIAMETER_RATING_FAILED in response to a request MUST NOT send similar
requests in the future.
4.1.4. RADIUS Vendor-Specific Rating Attributes
When service specific documents include RADIUS vendor specific
attributes that could be used as input in the rating process, the
rules described in [NASREQ] for formatting the Diameter AVP MUST be
followed.
For example, if the AVP code used is the vendor attribute type code,
the Vendor-Specific flag MUST be set to 1 and the Vendor-ID MUST be
set to the IANA Vendor identification value. The Diameter AVP data
field contains only the attribute value of the RADIUS attribute.
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-
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.
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
(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
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
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.
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
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
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
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
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
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.
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
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.
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-
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.
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
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
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.
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 | | |
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.
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).
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.
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
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
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.
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.
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.
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).
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
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
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.
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.
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
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
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 upd