AAA Working Group
Internet Draft Harri Hakala
Document: draft-ietf-aaa-diameter-cc-02.txt Leena Mattila
Expires: June 2004 Ericsson
Juha-Pekka Koskinen
Marco Stura
John Loughney
Nokia
December 16, 2003
Diameter Credit-Control Application
Status of this memo
This document is an Internet-Draft and is subject to all provisions of
Section 10 of RFC2026.
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This document is a product of the Authentication, Authorization and
Accounting (AAA) Working Group of the Internet Engineering Task Force
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Abstract
This document specifies a DIAMETER application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, SIP services, messaging services, download
services etc.
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1. Introduction...................................................5
1.1 Requirements language......................................5
1.2 Terminology................................................6
1.3 Advertising application support............................7
2. Architecture Models............................................7
3. Credit-Control Messages.......................................10
3.1 Credit-Control-Request (CCR) Command......................10
3.2 Credit-Control-Answer (CCA) Command.......................11
4. Credit Control Application Overview...........................12
4.1 Service-Specific Rating Input and Interoperability........13
5. Session Based Credit-control..................................15
5.1 First Interrogation.......................................16
5.2 Intermediate Interrogation................................21
5.3 Final Interrogation.......................................23
5.4 Server-Initiated Credit Re-Authorization..................24
5.5 Graceful Service Termination..............................25
5.6 Failure Procedures........................................30
6. One Time Event................................................33
6.1 Service Price Enquiry.....................................34
6.2 Balance Check.............................................34
6.3 Direct Debiting...........................................35
6.4 Refund....................................................36
6.5 Failure Procedure.........................................36
7. Credit Control Application State Machine......................38
8. Credit Control AVPs...........................................48
8.1 CC-Correlation-Id AVP.....................................50
8.2 CC-Request-Number AVP.....................................50
8.3 CC-Request-Type AVP.......................................50
8.4 CC-Session-Failover AVP...................................51
8.5 CC-Sub-Session-Id AVP.....................................52
8.6 Check-Balance-Result AVP..................................52
8.7 Cost-Information AVP......................................52
8.8 Cost-Unit AVP.............................................53
8.9 Credit-Control AVP........................................53
8.10 Credit-Control-Failure-Handling AVP......................54
8.11 Currency-Code AVP........................................55
8.12 Direct-Debiting-Failure-Handling AVP.....................55
8.13 Exponent AVP.............................................56
8.14 Final-Unit-Action AVP....................................56
8.15 Final-Unit-Indication AVP................................56
8.16 Granted-Service-Unit AVP.................................57
8.17 Redirect-Address-Type AVP................................58
8.18 Redirect-Server AVP......................................59
8.19 Redirect-Server-Address AVP..............................59
8.20 Requested-Action AVP.....................................59
8.21 Requested-Service-Unit AVP...............................60
8.22 Restriction-Filter-Rule AVP..............................61
8.23 Service-Parameter-Info AVP...............................61
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8.24 Service-Parameter-Type AVP...............................61
8.25 Service-Parameter-Value AVP..............................62
8.26 Subscription-Id AVP......................................62
8.27 Subscription-Id-Data AVP.................................62
8.28 Subscription-Id-Type AVP.................................62
8.29 Unit-Value AVP...........................................63
8.30 Used-Service-Unit AVP....................................63
8.31 Value-Digits AVP.........................................64
8.32 Validity-Time AVP........................................64
8.33 CC-Input-Octets AVP......................................64
8.34 CC-Money AVP.............................................64
8.35 CC-Output-Octets AVP.....................................65
8.36 CC-Service-Specific-Units AVP............................65
8.37 CC-Time AVP..............................................65
8.38 CC-Total-Octets AVP......................................65
8.39 Rating-Group AVP.........................................65
8.40 Service-Identifier AVP...................................65
8.41 Tariff-Time-Change AVP...................................66
8.42 Tariff-Change-Usage AVP..................................66
9. Result Code AVP values........................................67
9.1 Transient Failure.........................................67
9.2 Permanent Failures........................................67
10. AVP Occurrence Table.........................................68
10.1 Credit Control AVP Table.................................68
11. RADIUS/Diameter Credit-control Interworking..................69
11.1 Initial RADIUS Access-Request............................70
11.2 Subsequent RADIUS Access-Request message.................71
11.3 RADIUS Vendor Specific Attributes for Credit Control.....72
12. IANA Considerations..........................................72
12.1 Application Identifier...................................73
12.2 Command Codes............................................73
12.3 AVP Codes................................................73
12.4 Result-Code AVP Values...................................73
12.5 CC-Request-Type AVP......................................73
12.6 CC-Session-Failover AVP..................................73
12.7 Check-Balance-Result AVP.................................73
12.8 Credit-Control AVP.......................................73
12.9 Credit-Control-Failure-Handling AVP......................73
12.10 Direct-Debiting-Failure-Handling AVP....................74
12.11 Final-Unit-Action AVP...................................74
12.12 Redirect-Address-Type AVP...............................74
12.13 Requested-Action AVP....................................74
12.14 Subscription-Id-Type AVP................................74
12.15 Tariff-Change-Usage AVP.................................74
13. Credit-control Application Related Parameters................74
14. Security Consideration.......................................75
14.1 Direct Connection with Redirects.........................76
15. References...................................................77
15.1 Normative................................................77
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15.2 Non-Normative............................................77
16. Acknowledgement..............................................78
17. Author's Address.............................................78
18. Full Copyright Statement.....................................79
19. Notices......................................................79
20. Expiration Date..............................................80
Appendix A Credit Control sequences..............................80
A.1 Flow I...................................................80
A.2 Flow II..................................................82
A.3 Flow III.................................................83
A.4 Flow IV..................................................85
A.5 Flow V...................................................86
A.6 Flow VI..................................................87
A.7 Flow VII.................................................88
A.8 Flow VIII................................................89
A.9 Flow IX..................................................90
A.10 Flow X...................................................92
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1. Introduction
This document specifies a DIAMETER application that can be used to
implement real-time credit-control for a variety of end user services
such as network access, SIP services, messaging services, download
services etc. It provides a general solution to the real-time cost and
credit control.
The prepaid model shown to be very successful for instance in GSM
networks where network operators offering prepaid services have
experienced a substantial growth of their customer base and revenues,
prepaid services are now cropping up in many other wireless and wire
line based networks as well.
In next generation wireless networks, additional functionality is
required beyond that specified in the Diameter base protocol. For
example, the 3GPP Charging and Billing requirements [3GPPCHARG] state
that an application must be able to rate service information in real-
time. In addition, it is necessary to check that the end user's
account provides coverage for the requested service, prior to
initiation of that service. When an account is exhausted or expired,
the user must be denied the ability to compile additional chargeable
events.
A mechanism needs to be provided to allow the user to be informed of
the charges to be levied for a requested service. In addition, there
are services such as gaming and advertising that may credit as well as
deduct from a user account.
The currently existing Diameter applications provide service specific
authorization and they do not provide credit authorization for prepaid
users. The credit authorization shall be generic and applicable to all
the service environments required to support prepaid services.
To fulfill these requirements, it is necessary to facilitate
communication between the network element providing the service (e.g.
NAS, SIP Proxy, Application Server etc.) and a credit-control server,
in order to minimize financial risk.
The scope of this specification is the credit authorization. Service
specific authorization and authentication is out of the scope.
1.1 Requirements language
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
"RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [KEYWORDS].
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1.2 Terminology
AAA
Authentication, Authorization and Accounting
AA answer
AA answer does generically refer to a service specific authorization
and authentication answer. AA answer commands are defined in service
specific authorization applications e.g. [NASREQ] and [DiamMip].
AA request
AA request does generically refer to a service specific authorization
and authentication request. AA request commands are defined in service
specific authorization applications e.g. [NASREQ] and [DiamMip].
Credit-control
Credit-control is a mechanism, which directly interacts in real-time
with an account and controls or monitors the charges, related to the
service usage. Credit-control is a process of checking if credit is
available, credit-reservation, deduction of credit from the end user
account when service is completed and refunding of reserved credit not
used.
Diameter Credit-control Server
Diameter Credit-control server acts as a prepaid server, performing
real-time rating and credit control. It is located in the home domain
and is accessed by service elements or AAA servers in real-time for
purpose of price determination and credit-control before the service
event is delivered to the end-user. It may also interact with business
support systems.
Diameter Credit-control Client
A Diameter credit-control client is an entity that interacts with a
credit-control server. It monitors the usage of the granted quota
according to instructions returned by credit-control server.
Interrogation
The Diameter credit-control client uses interrogation to initiate a
session based credit-control process and during the credit-control
process to report the used quota and request a new one. An
interrogation maps to a request/answer transaction.
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One-time event
Basically a request/answer transaction of type event. The credit-
control server is not required to maintain session state for one-time
event.
Rating
The act of determining the cost of the service event.
Service
A type of task that is performed by a service element for an end user.
Service Element
A network element that provides a service to the end users. The
Service Element may include the Credit-control Client, or another
entity (e.g. RADIUS AAA server) can act as a Credit-control Client on
behalf of the Service Element. In the latter case the interface
between the Service Element and the Diameter Credit-control Client is
outside the scope of this specification. Examples of the Service
Elements include NAS, Sip Proxy and Application Servers such as
messaging server, content server and gaming server.
Service Event
An event relating to a service provided to the end user.
Session based credit-control
Credit-control process that makes use of several interrogations: the
first, possible intermediates and the final interrogation. The first
interrogation is used to reserve money from the user's account and
initiate the process. The intermediate interrogations may be needed to
request new quota while the service is being rendered. The final
interrogation is used to exit the process. The credit-control server
is required to maintain session state for session-based credit-
control.
1.3 Advertising application support
Diameter nodes conforming to this specification MUST advertise support
by including the value of 4 in the Auth-Application-Id of the
Capabilities-Exchange-Request and Capabilities-Exchange-Answer command
[DIAMBASE].
2. Architecture Models
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The current accounting models specified in the Radius Accounting
[RFC2866] and Diameter base [DIAMBASE] are not sufficient for real-
time credit control, where credit-worthiness is to be determined prior
to service initiation. Also, the existing Diameter authorization
applications [NASREQ] and [DIAMMIP] only provides service
authorization, but do not provide credit authorization for prepaid
users. In order to support real-time credit control a new type of
server is needed in the AAA infrastructure; Diameter credit-control
server. The Diameter credit-control server is the entity responsible
of credit authorization for prepaid subscribers.
A service element may authenticate and authorize the end user with the
AAA server using AAA protocols, e.g. RADIUS or a Diameter base
protocol with a possible Diameter application.
Accounting protocols such as RADIUS accounting and the Diameter base
accounting protocol can be used to provide accounting data to the
accounting server after service is initiated, and to provide possible
interim reports until service completion. However, for real-time
credit control, these authorization and accounting models are not
sufficient.
When real-time credit-control is required, the credit-control client
contacts the credit-control server with possible service event
information included before the service is provided to the end user.
This process is performed in order to determine potential charges and
to verify whether the end user's account balance is sufficient to
cover the cost of the service being rendered.
Figure 1 illustrates the typical credit-control architecture, which
consist of a Service Element with embedded Diameter credit-control
client, a Diameter credit-control server and an AAA server. A Business
Support System is usually deployed; it includes at least the billing
functionality. The credit-control server and AAA server in this
architecture model are logical entities. The real configuration can
combine them into a single host. The credit-control protocol is the
Diameter base protocol with the Diameter credit-control application.
When an end user requests services such as for instance SIP services
or messaging services, the request is typically forwarded to a service
element (e.g. SIP Proxy) in the user's home domain. In some cases it
might be possible that the service element in the visited domain can
offer services to the end user, however a commercial agreement must
exist between the visited domain and the home domain. Network access
is an example of a service offered in the visited domain where the
NAS, through an AAA infrastructure, authenticates and authorizes the
user with the user's home network.
Service Element AAA and credit-control
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+----------+ +---------+ protocols +-----------+ +--------+
| End |<---->|+-------+|<------------>| AAA | |Business|
| User | +->|| CC || | Server |->|Support |
| | | || client||<-----+ | | |System |
+----------+ | |+-------+| | +-----------+ | |
| +---------+ | ^ +--------+
+----------+ | | CC protocol | ^
| End |<--+ | +-----v----+ |
| User | +------>|Credit- | |
+----------+ credit-control |control |--------+
protocol |server |
+----------+
Figure 1: Typical credit-control architecture
Other entities, such as RADIUS AAA server, may act as a Diameter
credit-control client towards the Diameter credit-control server for
service elements that use credit control mechanisms other than
Diameter credit-control. In this case the AAA server contact the
Diameter credit-control server as part of the authorization process.
The interworking architecture is illustrated in Figure 2, the
interaction between the Diameter credit-control client and the service
element is outside the scope of this specification. Interworking with
RADIUS is addressed in section 11 and Annex A.
AAA
+--------+ +---------+ protocol +------------+ +--------+
| End |<----->| Service |<------------>| AAA | |Business|
| User | | Element | | Server | |Support |
+--------+ +-->| | |+----------+|-->|System |
| +---------+ ||CC client || | |
| |+----------+| | |
+--------+ | +------^-----+ +--------+
| End |<--+ credit-control | ^
| User | protocol | |
+--------+ +-------V------+ |
|Credit-control|--------+
| Server |
+--------------+
Figure 2: Credit-control architecture with Service Element not
supporting the credit-control protocol
There can be multiple credit-control servers in the system for reasons
of redundancy and load balancing. The system can also contain separate
rating server(s) and accounts can locate in a centralized database.
For duplicate detection only one place in the credit-control system
should perform duplicate detection to ensure that the end user's
account is not debited or credited multiple times for the same service
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event. System internal interfaces can exist to relay messages between
servers and an account manager. However the detailed architecture of
credit-control system and its interfaces are implementation specific
and are out of scope of this specification.
There can exist protocol transparent Diameter relays and redirect
agents between credit-control client and credit-control server. Also
Diameter Redirect agents, which refer credit control clients to credit
control servers and allow them to communicate directly can exist.
These agents transparently support the Diameter credit-control
application.
If Diameter credit-control proxies exist between the credit-control
client and the credit-control server, they MUST advertise the Diameter
credit-control application support.
3. Credit-Control Messages
This section defines new Diameter message Command-Code values that
MUST be supported by all Diameter implementations that conform to this
specification. The Command Codes are:
Command-Name Abbrev. Code Reference
-----------------------------------------------------------
Credit-Control-Request CCR 272 3.1
Credit-Control-Answer CCA 272 3.2
3.1 Credit-Control-Request (CCR) Command
The Credit-Control-Request message (CCR), indicated by the command-
code field set to 272 and the 'R' bit set in the Command Flags field,
is used between the Diameter credit-control client and the credit-
control server to request credit authorization for a given service.
The Auth-Application-Id MUST be set to the value 4 indicating the
Diameter credit-control application.
Message Format
<Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Application-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ Destination-Host ]
[ User-Name ]
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[ 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 ]
*[ Service-Parameter-Info ]
*[ CC-Correlation-Id ]
*[ Proxy-Info ]
[ Redirect-Host AVP ]
[ Redirect-Host-Usage AVP ]
[ Redirect-Max-Cache-Time AVP ]
*[ Route-Record ]
*[ AVP ]
3.2 Credit-Control-Answer (CCA) Command
The Credit-Control-Answer message (CCA), indicated by the command-code
field set to 272 and the 'R' bit cleared in the Command Flags field,
is used between the credit-control server and the Diameter credit-
control client to acknowledge a Credit-Control-Request command.
Message Format
<Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
< Session-Id >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
{ Auth-Application-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ User-Name ]
[ CC-Session-Failover ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
[ Subscription-Id ]
*[ Granted-Service-Unit ]
[ Cost-Information]
[ Final-Unit-Indication ]
[ Check-Balance-Result ]
[ Credit-Control-Failure-Handling ]
[ Direct-Debiting-Failure-Handling ]
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[ Validity-Time]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP ]
4. Credit Control Application Overview
The credit authorization process takes place before and during service
delivery to the end user, it generally requires user's authentication
and authorization before any request is sent to the credit-control
server.
The credit control application defined in this specification supports
for two different credit authorization models: credit authorization
with money reservation and credit authorization with direct debiting.
In both the models, the credit control client requests credit
authorization to the credit control server prior to allow any service
to be delivered to the end user.
In the first model, the credit control server rates the request,
reserve a suitable amount of money from the user's account and return
the corresponding amount of credit resources. Note that credit
resources may not imply actual monetary credit; credit resources may
be granted to the credit control client in form of units (e.g. data
volume or time) to be metered.
Upon reception of a successful credit authorization answer with a
certain amount of credit resources, the credit control client allows
service delivery to the end user and start monitoring the usage of the
granted resources. When the credit resources granted to the user have
been consumed, or the service has been successfully delivered or
terminated, the credit control client reports back to the server the
used amount. The credit control server deducts the used amount from
the end user's account; it may perform rating and make a new credit
reservation if the service delivery is continuing. This process is
accomplished with session based credit control that includes the first
interrogation, possible intermediate interrogations and the final
interrogation. For session based credit control, both the credit
control client and the credit control server are required to maintain
credit control session state.
In contrast, credit authorization with direct debiting is a single
transaction process where the credit control server directly deducts
the suitable amount of money from the user's account as soon as the
credit authorization request is received. Upon reception of a
successful credit authorization answer, the credit control client
allows service delivery to the end user. This process is accomplished
with the one time event. Session state is not maintained.
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In a multi-service environment, an end user may issue an additional
service request (e.g. data service) during an ongoing service (e.g.
voice call) towards the same account; or during an active multimedia
session an additional media type is added to the session causing a new
simultaneous request towards same account. Consequently this needs to
be considered when credit resources are granted to the services.
The credit control application also support for operations such as
service price enquiry, user's balance check and refund of credit on
the user's account. These operations are accomplished with the one
time event. Session state is not maintained.
A flexible Credit control application specific failure handling is
defined where the home service provider can model the credit control
client behavior according to own credit risk management policy.
The Credit-Control-Failure-Handling AVP and the Direct-Debiting-
Failure-Handling AVP are defined to determine what to do if the
sending of credit-control messages to the credit-control server has
been temporarily prevented. The usage of Credit-Control-Failure-
Handling AVP and the Direct-Debiting-Failure- Handling AVP gives
flexibility to have different failure handling for credit-control
session and one time event direct debiting.
4.1 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 seen as out of scope for this generic
mechanisms as well.
It is reasonable to expect that there will exist a service level
agreement between providers of the credit control client and the
credit control server covering the charging, services offered, roaming
agreements, agreed rating input, etc.
There are two ways for providing rating input to the credit control
server, either by using AVPs or by including them in the Service-
Parameter-Info AVP. The general principle for sending rating
parameters is that the service SHOULD re-use existing AVPs, if the
service can use AVPs defined in existing service specific Diameter
applications (e.g. NASREQ for network access services).
Alternatively, new AVPs can be defined if the existing AVPs do not
provide sufficient rating information. 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). In that case the rating input
is embedded in the Service-Parameter-Info AVP as defined in section
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8.23. New service applications SHOULD favor the use of explicitly
defined AVPs, to simplify interoperability.
The service specific rating input AVPs, the contents of the Service-
Parameter-Info AVP or Service-Identifier AVP are not within the scope
of this document. To facilitate interoperability, it is RECOMMENDED
that the rating input and values of service identifiers are
coordinated via an informational RFC or other permanent and readily
available reference such as 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 service specific documents, is
governing the credit control message. The rule is that service
specific documents only define what existing AVPs or new AVPs are used
as input to the rating process (i.e. they do not define new credit
control applications), and thus need to be included in the Credit-
Control-Request command by a Diameter Credit Control Client supporting
a given service as *[AVP]. In order to define new AVPs, service
specific documents MUST follow the practices defined in
[DIAMBASE]. The service SHOULD be identified using the Service-
Identifier AVP at command level. The Service-Identifier AVP SHOULD be
a unique identifier for a given service as defined in section 8.40.
As a result it is the combination of support of the Diameter Credit
Control Application (DCC) and the service defined in the Service-
Identifier AVP, which defines interoperability between any given DCC
client and server.
Diameter credit control implementations are required to support the
Mandatory rating AVPs defined in service specific documentation of the
services they support. Introducing new credit control mechanisms not
defined in this specification implies the definition of a new version
of the Diameter Credit Control Application and corresponding
Application Identifier.
In case a rating input required for the rating process is missing from
the Credit control request, or the credit control server does not
support the requested service (i.e. does not support one or more
Mandatory rating AVPs included in the request command), the Credit
control answer MUST contain error code DIAMETER_RATING_FAILED. A CCR
message with this error MUST contain one or more Failed-AVP AVPs
containing the missing and/or unsupported AVPs that caused the
failure. A Diameter credit control client receiving error code
DIAMETER_RATING_FAILED in answer to a request MUST NOT send such
similar requests in the future.
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5. Session Based Credit-control
For a session-based credit-control, several interrogations are needed:
the first, intermediate (optional) and the final interrogation. This
is illustrated in Figure 3 and Figure 4.
If the credit-control client performs credit-reservation before
granting service to the end user it MUST use several interrogations
towards the credit-control server (i.e. session based credit-control).
In this case the credit-control server MUST maintain the credit
control session state.
Each credit-control session MUST have globally unique Session-Id as
defined in [DIAMBASE] and it MUST NOT be changed during the lifetime
of a credit-control session.
There are certain applications that require multiple credit control
sub-sessions. Such applications would send messages with a constant
Session-Id AVP, but a different CC-Sub-Session-Id AVP. If several
credit sub-sessions will be used, all sub-sessions MUST be closed
separately before the closing the main session to be able to report
used units per sub-session. The absence of this AVP implies no sub-
sessions are in use.
When multiple services are used within one user session and each
service or group of services are subject to different cost, making use
of credit control sub-sessions will result in increased signaling load
and resources usage in both the credit control client and the credit
control server. For instance, during one network access session the
end user may use several http-services subject to different access
cost. To optimally support these scenarios, the credit control
application enables for multiple services credit control in a single
credit control session. It is possible to request and allocate
multiple quotas as a credit pool that is shared between multiple
services. The services can be further grouped into rating groups in
order to achieve even further aggregation of credit allocation. It is
also possible to request and allocate multiple quotas on a per service
basis. The mechanism is illustrated in Appendix A (Flow X).
It should be noted that the service element might send a service
specific re-authorization message to the Diameter AAA server due to
expiration of the authorization-lifetime during an ongoing credit
control session. However, the service specific re-authorization does
not influence the credit authorization that is ongoing between credit-
control client and credit-control server since credit authorization is
controlled by the burning rate of the granted quota.
In the event that service specific re-authorization fails the user
will be disconnected and the credit-control client MUST send a final
interrogation to the credit-control server.
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The Diameter credit-control server may want to control the validity
time of the granted quota and/or the production of intermediate
interrogations, thus it MAY include the Validity-Time AVP in the
answer message to the credit-control client. Upon expiration of the
Validity-Time, the credit-control client MUST generate a credit-
control update request and report the used quota to the credit-control
server. It is up to the credit-control server to determine, the value
of the Validity-Time to be used for consumption of the granted service
units. If the Validity-Time is used, its value SHOULD be given as
input to set the session supervision timer Tcc (the session
supervision timer MAY be set to two times the value of the Validity-
Time as defined in section 13). Since credit-control update requests
are also produced at the expiry of granted service units and/or for
mid-session service events the omission of Validity-Time does not mean
that intermediate interrogation for the purpose of credit control are
not performed.
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 then the
Diameter credit-control client SHOULD itemize the units used before
and after the tariff change. In case some units straddled the tariff
change, the credit-control client SHOULD itemize those units as well.
5.1 First Interrogation
When session based credit-control is required (e.g. the authentication
server indicated prepaid user), the first interrogation MUST be sent
before the Diameter credit-control client allows any service event to
the end user. The CC-Request-Type is set to the value INITIAL_REQUEST
in the request message.
If the Diameter credit-control client knows the cost of the service
event (e.g. a content server delivering ringing tones may know their
cost) the monetary amount to be charged is included in the Requested-
Service-Unit AVP. If the Diameter credit-control client does not know
the cost of the service event, the Requested-Service-Unit AVP MAY
contain the number of requested service events and the Service-
Parameter-Info AVP MAY contain the service event information to be
rated by the credit-control server. The Service-Parameter-Info AVP
always refers to the requested service units. Alternatively, service
event information to be rated can be sent as service specific AVPs.
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The Event-Timestamp AVP contains the time when the service event is
requested in the service element.
The credit-control server SHOULD rate the service event and make a
credit-reservation from the end user's account that covers the cost of
the service event. If the type of the Requested-Service-Unit AVP is
money, no rating is needed but the corresponding monetary amount is
reserved from end user's account.
The credit-control server returns the Granted-Service-Unit AVP in the
Answer message to the Diameter credit-control client. The Granted-
Service-Unit AVP contains the amount of service units that the
Diameter credit-control client can provide to the end user until a new
Credit-Control-Request MUST be sent to the credit-control server. If
several unit types are sent in the Answer message the credit-control
client MUST handle each unit type separately. There MUST be maximum
one instance of the same unit type in one Answer message. In case
multiple quotas are conveyed to the credit control client, there MUST
be maximum one instance of the same unit type associated to a Service-
Identifier, or set of Service-Identifiers, or associated to a Rating-
Group. The type of the Granted-Service-Unit AVP can be time, volume,
service specific or money depending on the type of service event. It
is not allowed to change the unit type(s) within the session.
If the credit-control server determines that no further control is
needed for the service it MAY include the result code indicating that
the credit-control is not applicable (e.g. service is free of charge)
and terminate the credit-control session.
The Credit-Control-Answer message MAY also include the Final-Unit-
Indication AVP to indicate that the answer message contains the final
units for the service session. After the end user has consumed these
units, the Diameter credit-control-client MUST behave as described in
section 5.5.
Two different approaches are defined for the first interrogation to
suit properly in all the possible architectures. The first approach
uses credit-control messages after user's authorization and
authentication took place. The second approach uses service specific
authorization messages to perform the first interrogation during the
user's authorization/authentication phase, and credit-control messages
for the intermediate and the final interrogations.
In case an implementation of the credit-control client supports both
the methods, it SHOULD be configurable what method to use.
In service environments such as the Network Access Server (NAS) , it
is desired to perform the first interrogation as part of the
authorization/authentication process for the sake of protocol
efficiency. Further credit authorizations after the first
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interrogation took place are performed with credit control commands
defined in this specification. Implementations of credit-control
client operating in the mentioned environments SHOULD support this
method. In case the credit-control server and AAA server are separate
physical entities the service element send the request messages to the
AAA server, which then issue an appropriate request or proxy the
received request forward to the credit-control server.
In other service environments, such as the 3GPP network and some SIP
scenario, there is a substantial decoupling between
registration/access to the network and the actual service request
(i.e. the authentication/authorization is executed once at
registration/access to the network and is not executed for every
service event requested by the subscriber). In such environments it is
more appropriate to perform the first interrogation after the user has
been authenticated and authorized. The first interrogation, the
intermediate and final interrogations are executed with credit control
commands defined in this specification.
Other IETF standards or standards developed by other standardization
bodies may define what is the most suitable method in their
architecture.
5.1.1 First Interrogation after Authorization and Authentication
The Diameter credit-control client in the service element may get
information from the authorization server whether credit-control is
required based on its knowledge of the end user. If credit-control is
required the credit-control server needs to be contacted prior to
initiate the service delivery to the end user. The accounting protocol
and the credit-control protocol can be used in parallel, the
authorization server may also drive whether the parallel accounting
stream is required.
The following diagram illustrates the case where both protocols are
used in parallel and the service element sends credit-control messages
directly to the credit-control server. More credit-control sequence
examples are given in Annex A.
End-User Service Element AAA Server CC Server
(CC Client)
| Registration | AA request/answer(accounting,cc or both)|
|<----------------->|<------------------>| |
| : | | |
| : | | |
| Service Request | | |
|------------------>| | |
| | CCR(Initial,Credit-Control AVPs) |
| +|---------------------------------------->|
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| CC stream|| | CCA(Granted-Units)|
| +|<----------------------------------------|
| Service Delivery | | |
|<----------------->| ACR(start,Accounting AVPs) |
| : |------------------->|+ |
| : | ACA || Accounting stream |
| |<-------------------|+ |
| : | | |
| : | | |
| | CCR(Update,Used-Units) |
| |---------------------------------------->|
| | | CCA(Granted-Units)|
| |<----------------------------------------|
| : | | |
| : | | |
| End of Service | | |
|------------------>| CCR(Termination, Used-Units) |
| |---------------------------------------->|
| | | CCA |
| |<----------------------------------------|
| | ACR(stop) | |
| |------------------->| |
| | ACA | |
| |<-------------------| |
Figure 3: Protocol example with first interrogation after user's
authorization/authentication
5.1.2 Authorization Messages for First Interrogation
The Diameter credit-control client in the service element MUST
actively contribute with the authorization/authentication client in
the construction of the AA request by adding appropriate credit
control AVPs. The credit-control client MUST add the Credit-Control
AVP to indicate credit-control capabilities and MAY add other relevant
credit-control specific AVPs to the proper
authorization/authentication command to perform the first
interrogation towards the home Diameter AAA server. The Auth-
Application-Id is set to the appropriate value as defined in the
relevant service specific authorization/authentication application
document (e.g. [NASREQ], [DiamMIP]). The home Diameter AAA server
authenticate/authorize the subscriber and determine whether or not
credit-control is required.
If credit-control is not required for the subscriber the home AAA
will respond as usual with an appropriate AA answer message. If
credit-control is required for the subscriber and the Credit-Control
AVP with the value set to CREDIT_AUTHORIZATION was present in the
authorization request, the home AAA server MUST contact the credit-
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control server to perform the first interrogation. If credit-control
is required for the subscriber and the Credit-Control AVP was not
present in the authorization request, the home AAA server MUST send an
authorization reject answer message.
The Diameter AAA server supporting credit-control is required to send
the Credit-Control-Request command (CCR) defined in this document to
the credit-control server. The Diameter AAA server populates the CCR
based on service specific AVPs used for input to the rating process
and possibly credit-control AVPs received in the AA request. The
credit-control server will make money reservation from the user's
account, will rate the request and will send a credit-control answer
message to the home Diameter AAA server. The answer message includes
the Granted-Service-Unit AVP(s) and MAY include other credit-control
specific AVPs as appropriate. Additionally, the credit-control server
MAY set the Validity-Time and MAY include the Credit-Control-Failure-
Handling AVP and the Direct-Debiting-Failure-Handling AVP to determine
what to do if the sending of credit-control messages to the credit-
control server has been temporarily prevented.
Upon receiving the credit-control answer message from the credit-
control server, the home Diameter AAA server will populate the AA
answer with the received credit-control AVPs and with usual service
attributes according to the authorization/authentication specific
application (e.g. [NASREQ], [DiamMIP]) and forward the packet to the
credit-control client. If the home AAA server receives a credit-
control reject message, it will simply generate an appropriate
authorization reject message to the credit-control client including
the credit-control specific error code.
The credit-control client in this model sends further credit-control
messages to the credit-control server via the home AAA server.
Upon receiving successful authorization answer message with the
Granted-Service-Unit AVP(s), the credit-control client will grant the
service to the end user and will generate intermediate credit-control
request as required by using Credit-Control commands. The CC-Request-
Number of the first intermediate request MUST be set to 1 (for how to
produce unique value for the CC-Request-Number AVP see section 8.2).
If service specific re-authorization is performed (i.e. authorization-
lifetime expires), the credit-control client MUST add to the service
specific re-authorization request the Credit-Control AVP with value
set to RE-AUTHORIZATION to indicate that the credit-control server
MUST NOT be contacted. When session based credit-control is used for
the subscriber a constant Credit-Control messages stream is flowing
through the Diameter AAA server. The Diameter AAA server can make use
of this credit-control messages flow to deduce that user's activity is
ongoing; hence it is recommended to set the authorization-lifetime to
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a reasonably high value when credit-control is used for the
subscriber.
In this scenario the home AAA server MUST advertise support for the
credit-control application to its peers during the capability exchange
process.
The following diagram illustrates the use of authorization /
authentication messages to perform the first interrogation. The
parallel accounting stream is not shown in the figure.
End-User Service Element AAA Server CC Server
(CC Client)
| Service Request | AA Request (CC AVPs) |
|------------------>|------------------->| |
| | | CCR(Initial, CC AVPs)
| | |------------------->|
| | | CCA(Granted-Units)
| | |<-------------------|
| | AA Answer(Granted-Units) |
| Service Delivery |<-------------------| |
|<----------------->| | |
| : | | |
| : | | |
| : | | |
| | | |
| | CCR(Update,Used-Units) |
| |------------------->| CCR(Update,Used-Units)
| | |------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<-------------------|
| |<-------------------| |
| : | | |
| : | | |
| End of Service | | |
|------------------>| CCR(Termination,Used-Units) |
| |------------------->| CCR(Term.,Used-Units)
| | |------------------->|
| | | CCA |
| | CCA |<-------------------|
| |<-------------------| |
Figure 4: Protocol example with use of the
authorization messages for the first interrogation.
5.2 Intermediate Interrogation
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When all of the granted service units for one unit type are spent by
the end user or the Validity-Time is expired, the Diameter credit-
control client MUST send a new Credit-Control-Request to the credit-
control server. In the event that credit control for multiple services
in one credit control session is applied (i.e. units are granted
associated to Service-Identifier(s) or Rating-Group), a new Credit-
Control-Request MUST be sent to the credit-control server when the
whole credit reservation has been consumed, or upon expiration of the
Validity-Time. In the case when the Validity-Time is used, it is
always up to the Diameter credit-control client to send a new request
well in advance before the expiration of the previous request in order
to avoiding interruption in the service element. Even if the granted
service units reserved by the credit-control server have not been
spent upon expiration of the Validity-Time, the Diameter credit-
control client MUST send a new Credit-Control-Request to the credit-
control server.
There can be also mid-session service events, which might affect the
rating of the current service events. In this case a spontaneous
updating (a new Credit-Control-Request) SHOULD be sent including
information related to the service event even if all the granted
service units have not been spent or the Validity-Time has not
expired.
When the used units are reported to the credit-control server the
credit-control client will not have any units in its possession before
new granted units are received from the credit-control server. When
the new granted units are received from the credit-control server
these units apply from the point where the measurement of the reported
used units stopped.
The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
intermediate request message. The Subscription-Id-Data AVP SHOULD be
included in the intermediate message to identify the end user in the
credit-control server.
The Requested-Service-Unit AVP contains the new amount of requested
service units. The Used-Service-Unit AVP contains the amount of used
service units measured from the point when the service became active
or, in case of interim interrogations are used during the session,
from the point when the previous measurement ended. The same unit
types that are used in the previous message MUST be used. If several
unit types were included in the previous answer message the used
service units for each unit type MUST be reported.
The Event-Timestamp AVP contains the time of the event that triggered
the sending of the new Credit-Control-Request.
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The credit-control server MUST deduct the used amount from the end
user's account. It MAY rate the new request and make a new credit-
reservation from the end user's account that covers the cost of the
requested service event.
The Credit-Control-Answer message with the CC-Request-Type AVP set to
the value UPDATE_REQUEST MAY include the Cost-Information AVP
containing the accumulated cost estimation for the session without
taking any credit-reservation into account.
The Credit-Control-Answer message MAY also include the Final-Unit-
Indication AVP to indicate that the answer message contains the final
units for the service session. After the end user has consumed these
units, the Diameter credit-control-client MUST behave as described in
section 5.5.
There can be several intermediate interrogations within a session.
5.3 Final Interrogation
When the end user terminates the service session or according to the
graceful service termination as described in section 5.5, the Diameter
credit-control client MUST send a final Credit-Control-Request message
to the credit-control server. The CC-Request-Type AVP is set to the
value TERMINATION_REQUEST.
The Event-Timestamp AVP MAY contain the time of the session was
terminated.
The Used-Service-Unit AVP contains the amount of used service units
measured from the point when the service became active or, in case of
interim interrogations are used during the session, from the point
when the previous measurement ended. If several unit types were
included in the previous answer message the used service units for
each unit type MUST be reported.
After final interrogation the credit-control server MUST refund the
reserved credit amount not used to the end user's account and deduct
the used monetary amount from the end user's account.
The Credit-Control-Answer message with the CC-Request-Type set to the
value TERMINATION_REQUEST MAY include the Cost-Information AVP
containing the estimated total cost for the session in question.
If the user logoff during an ongoing credit-control session or some
other reason causes the user to be logged-off (e.g. final-unit
indication causes user logoff according to local policy) the service
element, according to application specific policy, may send a session-
termination-request (STR) to the home Diameter AAA server as usual
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[DIAMBASE]. Figure 5 illustrates the case when the final-unit
indication causes the user logoff upon consumption of the final
granted units and STR is generated.
End-User Service Element AAA Server CC Server
(CC Client)
| Service Delivery | | |
|<----------------->| | |
| : | | |
| : | | |
| : | | |
| | | |
| | CCR(Update,Used-Units) |
| |------------------->| CCR(Update,Used-Units)
| | |------------------->|
| | CCA(Final-Unit, Terminate)
| CCA(Final-Unit, Terminate)|<-------------------|
| |<-------------------| |
| : | | |
| : | | |
| Disconnect user | | |
|<------------------| CCR(Termination,Used-Units) |
| |------------------->| CCR(Term.,Used-Units)
| | |------------------->|
| | | CCA |
| | CCA |<-------------------|
| |<-------------------| |
| | STR | |
| |------------------->| |
| | STA | |
| |<-------------------| |
Figure 5: User disconnected due to account exhausted
5.4 Server-Initiated Credit Re-Authorization
The Diameter Credit Control Application supports the server-initiated
re-authorization. The credit control server MAY optionally initiate
the credit re-authorization by issuing a Re-Auth-Request (RAR) as
defined in the Diameter base protocol [DIAMBASE]. The Auth-
Application-Id in the RAR message is set to 4 to indicate the Diameter
Credit Control Application and the Re-Auth-Request-Type is set to
AUTHORIZE_ONLY.
If a credit re-authorization is not already ongoing (i.e. the credit
control session is in OPEN state), a credit control client that
receives such a RAR message with Session-Id equal to a currently
active credit control session acknowledges the request by sending the
Re-Auth-Answer (RAA) message and MUST initiate the credit re-
authorization towards the server by sending a Credit-Control-Request
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message with the CC-Request-Type AVP set to the value UPDATE_REQUEST.
The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS) SHOULD be used in the
RAA message to indicate an additional message (i.e. CCR[Update]) is
required to complete the procedure. If a quota was allocated to the
session, the credit control client MUST report the used quota in the
Credit-Control-Request. Note that the end user does not need to be
prompted for the credit re-authorization, since the credit re-
authorization is transparent to the user (i.e it takes place
exclusively between the credit control client and the credit control
server).
If credit re-authorization is ongoing at the time when the RAR message
is received (i.e. RAR-CCR collision), the credit control client
successfully acknowledges the request but it does not initiate a new
credit re-authorization. The Result-Code 2001 (DIAMETER_SUCCESS)
SHOULD be used in the RAA message to indicate a credit re-
authorization procedure is already ongoing (i.e. the client was in
PendingU state when the RAR was received). The credit control server
SHOULD process the Credit-Control-Request as if it was received in
answer to the server initiated credit re-authorization, and should
consider the server initiated credit re-authorization process
successful upon reception of the Re-Auth-Answer message.
If several credit control sub-sessions are in use, a credit control
client receiving the RAR command for a given session will trigger
credit re-authorization for all the sub-session separately.
5.5 Graceful Service Termination
When the user's account runs out of money the user must be denied to
compile additional chargeable events. However, the home service
provider may offer free access services, for instance access to a
service portal where it is possible to top-up the account, for which
the user is allowed to benefit for a limited amount of time. This time
is usually dependant on the home service provider policy.
This section defines the graceful service termination optional feature
that MAY be supported by the credit control server. Credit control
client implementations MUST support the Final-Unit-Indication with at
least the tear down of the ongoing service session upon the subscriber
has consumed all the final granted units.
In some service environments (e.g. NAS) the graceful service
termination may be used to redirect the subscriber to a service portal
for online balance top-up or other zero-rated services offered by the
home service provider. In this case the graceful termination process
installs a set of packet filters to restrict the user's access
capability only to/from the specified destinations, all the IP packets
not matching the filters will be dropped or possibly re-directed to
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the service portal. The user may also be displayed an appropriate
notification why the access has been limited.
It is also possible use the graceful service termination to connect
the prepaid user to a top-up server that play an announcement and
prompt the user to replenish the account. In such a case the credit
control server sends only the address of the top-up server where the
prepaid user shall be connected after the final granted units have
been consumed. An example of this is given in Appendix A (Flow VIII).
The credit control server MAY initiate the graceful service
termination by including the Final-Unit-Indication AVP in the Credit
Control Answer to indicate that the message contains the final units
for the service session.
When the credit control client receives the Final-Unit-Indication AVP
in the answer from the server its behavior depends on the value
indicated in the Final-Unit-Action AVP. The server may request the
following actions: TERMINATE, REDIRECT and RESTRICT_ACCESS.
The following Figure illustrates the graceful service termination
procedure described in the following sub-sections.
End-User Service Element AAA Server CC Server
(CC Client)
| Service Delivery | | |
|<----------------->| | |
| |CCR(Update,Used-Units) |
| |------------------->|CCR(Update,Used-Units)
| : | |------------------->|
| : | |CCA(Final-Unit,Action)
| : | |<-------------------|
| |CCA(Final-Unit,Action) |
| |<-------------------| |
| | | |
| : | | |
| : | | |
| : | | |
| /////////////// |CCR(Update,Used-Units) |
|/Final Units End/->|------------------->|CCR(Update,Used-Units)
|/Action and // | |------------------->|
|/Restrictions // | | CCA(Validity-Time)|
|/Start // | CCA(Validity-Time)|<-------------------|
| ///////////// |<-------------------| |
| : | | |
| : | | |
| Replenish Account +-------+ |
|<-------------------------------------------->|Account| |
| | | +-------+ |
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| | | 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 6: Optional graceful service termination procedure
5.5.1 Terminate Action
The Final-Unit-Indication AVP with Final-Unit-Action TERMINATE does
not include any other information. Upon the subscriber has consumed
the final granted units the service element MUST terminate the service
session and MUST send a final Credit-Control-Request message to the
credit control server. The CC-Request-Type AVP in the request is set
to the value TERMINATION_REQUEST. This is the default handling
applicable whenever the credit control client receives an unsupported
Final-Unit-Action value and MUST be supported by all the Diameter
credit control client implementations conforming to this
specification.
5.5.2 Redirect Action
The Final-Unit-Indication AVP with Final-Unit-Action REDIRECT
indicates to the service element supporting this action that, upon
consumption of the final granted units, the user MUST be re-directed
to the address specified in the Redirect-Server AVP as follow.
The credit control server sends the Redirect-Server AVP in the Credit-
Control-Answer message. In such a case the service element MUST
redirect or connect the user to the destination specified in the
Redirect-Server AVP, if possible. When the end user is redirected (by
using other protocols than Diameter) to the specified server or
connected to the top-up server, an additional authorization (and
possibly authentication) may be needed before the subscriber can
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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 AVP or one or more Filter-
Id AVP in the Credit-Control-Answer message in order to enable the
user to access other zero-rated services. In such a case the access
device MUST drop all the packets not matching the IP filters specified
in the Credit-Control-Answer message and redirect the user to the
destination specified in the Redirect-Server AVP, if possible.
Another entity than the credit control server may provision the access
device with appropriate IP packet filters to be used in conjunction
with the Diameter credit control application. This case is considered
in section 5.5.3.
When the final granted units have been consumed the credit control
client MUST perform an intermediate interrogation. The purpose of this
intermediate interrogation is to indicate to the credit control server
that the specified action started and to report the used units. The
credit control server MUST deduct the used amount from the end user's
account but MUST NOT make a new credit reservation. The credit control
client, however, may send intermediate interrogations before all the
final granted units have been consumed for which rating and money
reservation may be needed, for instance upon Validity-Time expires or
upon mid-session service event that affect the rating of the current
service. Therefore, the credit control client MUST NOT include any
rating related AVP in the request sent upon all the final granted
units have been consumed as a hint to the server that the requested
final unit action started, rating and money reservation are not
required. Naturally, the Credit-Control-Answer message does not
contain any granted service unit and MUST include the Validity-Time
AVP to indicate to the credit control client how long the subscriber
is allowed to use network resources before a new intermediate
interrogation is sent to the server.
At the expiry of Validity-Time the credit control client sends a
Credit-Control-Request (UPDATE_REQUEST) as usual. This message does
not include the Used-Service-Unit AVP since there is no allotted quota
to report. The credit control server processes the request and MUST
perform the credit reservation. If during this time the subscriber did
not replenish his/her account whether he/she will be disconnected or
will be granted access to zero-rated services for unlimited time is
dependent on the home service provider policy (note: the latter option
implies that the service element should not remove the restriction
filters upon termination of the credit control session). The server
will return the appropriate Result-Code (see section 9.1) in the
Credit-Control-Answer message in order to close the credit control
session and implement the policy-defined action. Otherwise new quota
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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 the service session as usual.
The credit control client may not wait until the expiration of the
Validity-Time and may send a spontaneous updating (a new Credit-
Control-Request) if the service element can determine for instance
that communication between the end user and the top-up server took
place. An example of this is given in Appendix A (Figure A.8).
It is worth noting that the credit control server may initiate the
above-described process already for the first interrogation. However,
the user's account might be empty at the time when the first
interrogation is performed. In this case the subscriber can be offered
a chance to replenish the account and continue the service. The credit
control client receives a Credit-Control-Answer or service specific
authorization answer with the Final-Unit-Indication AVP, Validity-Time
AVP but no Granted-Unit. In such a case it starts immediately the
graceful service termination without sending any message to the
server. An example of this case is illustrated in Appendix A.
5.5.3 Restrict Access Action
The Final-Unit-Indication AVP with Final-Unit-Action RESTRICT_ACCESS
indicates to the access device supporting this action that the user
MUST be restricted access according to the IP packet filters given in
the Restriction-Filter-Rule AVP(s) or according to the IP packet
filters identified by the Filter-Id AVP(s). The credit control server
SHOULD include either the Restriction-Filter-Rule AVP or the Filter-Id
AVP in the Credit-Control-Answer message.
Another entity than the credit control server may provision the access
device with appropriate IP packet filters to be used in conjunction
with the Diameter credit control application. Such an entity, for
instance, may configure the access device with "zero-rated" IP flows
that are to be passed when the Diameter credit control application
indicates RESTRICT_ACCESS or REDIRECT. The access device passes IP
packets according to the filter rules possibly received in the Credit-
Control-Answer message in addition to the filter rules possibly
configured by the other entity. However, the action to be taken when
the user's account cannot cover the cost of the requested service is
the responsibility of the credit control server that controls the
prepaid subscriber.
If another entity working in conjunction with the Diameter Credit
control application already provisions the access device with all the
required filter rules for the end user, it is presumably not needed
for the credit control server to send any additional filter. Therefore
it is RECOMMENDED that credit control server implementations
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supporting the graceful service termination can be configurable
whether to send the Restriction-Filter-Rule AVP, the Filter-Id AVP or
none of the above.
When the final granted units have been consumed, the credit control
client MUST perform an intermediate interrogation. The credit control
client and the credit control server process this intermediate
interrogation and execute subsequent procedures as specified in the
previous section for the REDIRECT action.
The credit control server may initiate the graceful service
termination with action RESTRICT_ACCESS already for the first
interrogation as specified in the previous section for the REDIRECT
action.
5.5.4 Usage of the Server-Initiated Credit Re-Authorization
Once the subscriber replenishes the account she presumably expects all
the restrictions placed by the graceful termination procedure be
immediately removed and unlimited services' access be resumed. For the
best user experience the credit control server implementation MAY
support the server-initiated credit re-authorization (see section
5.4). In such a case, upon the successful account top-up took place,
the credit control server sends the Re-Auth-Request (RAR) message to
solicit the credit re-authorization. The credit control client
initiates then the credit re-authorization by sending the Credit-
Control-Request message with the CC-Request-Type AVP set to the value
UPDATE_REQUEST. The Used-Service-Unit AVP is not included in the
request since there is no allotted quota to report. The Requested-
Service-Unit AVP MAY be included in the request. After the credit
control client successfully receives the Credit-Control-Answer with
new Granted-Service-Unit all the possible restrictions activated for
the purpose of the graceful service termination MUST be removed in the
service element, the credit control session and the service session
continue as usual.
5.6 Failure Procedures
The Credit-Control-Failure-Handling AVP (CCFH) as described in this
section determines the behavior of the credit control client in fault
situations. The CCFH may be received from the Diameter home AAA
server, from the credit control server or may be locally configured.
The CCFH value received from the home AAA server overrides the locally
configured value and the CCFH value received from the credit control
server in the Credit-Control-Answer message always override any
already existing value.
The authorization server MAY include the Accounting-Realtime-Required
AVP to determine what to do if the sending of accounting records to
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the accounting server has been temporarily prevented as defined in
[DIAMBASE]. It is RECOMMENDED that the client complement the credit-
control failure procedures with backup accounting flow towards an
accounting server. Using different combinations of Accounting-
Realtime-Required and Credit-Control-Failure-Handling AVPs different
safety levels can be built. For example by choosing the Credit-
Control-Failure-Handling AVP equal to CONTINUE for the credit control
flow and Accounting-Realtime-Required AVP equal to DELIVER_AND_GRANT
for the accounting flow, the service can be granted to the end user
even if the connection to the credit-control server is down but the
accounting server is able to collect the accounting information,
provided that there is information exchange taking place between the
accounting server and credit-control server.
Since the credit-control application is based on real-time bi-
directional communication between the credit-control client and the
credit-control server, the usage of alternative destinations and the
buffering of messages MAY NOT be sufficient in the event of
communication failures. Since the credit-control server has to
maintain session states, moving the credit-control message stream to a
backup server requires a complex context transfer solution. Whether
the credit-control message stream is moved to a backup credit-control
server during an ongoing credit-control session depends on the value
of the CC-session-Failover AVP. However, failover may occur at any
point in the path between credit-control client and credit-control
server in the event that a transport failure is detected with a peer,
as described in [DIAMBASE]. As a consequence the credit-control server
might receive duplicate messages. These duplicates or out of sequence
messages can be detected in the credit-control server based on the
credit-control server session state machine (section 7), Session-Id
AVP and CC-Request-Number AVP.
If a failure occurs during an ongoing credit-control session, the
credit-control client may move the credit control message stream to an
alternative server if the CC-server indicated FAILOVER_SUPPORTED in
the CC-Session-Failover AVP. A secondary credit control server name,
received from the AAA server or locally configured, can be used as an
address of the backup server. If the CC-Session-Failover AVP is set to
FAILOVER_NOT SUPPORTED the credit control message stream MUST NOT be
moved to backup server.
For new credit control sessions, failover to an alternative credit-
control server SHOULD be performed if possible. For instance, if an
implementation of the credit control client can determine primary
credit control server unavailability it can establish the new credit
control sessions with a possibly available secondary credit control
server.
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The AAA client/agent is typically using only a single persistent
transport connection to the AAA agent or server, but it may have
connections to multiple AAA agents or servers and treat them as
primary/secondary or balance load between them. The AAA transport
profile [AAATRANS] defines the application layer watchdog algorithm
that enables failover from a peer that has failed and is controlled by
the timer Twinit. The recommended default value for Twinit is 30
seconds. Since the AAA infrastructure is common to several different
types of AAA applications, tuning the timer Twinit to a lower value in
order to satisfy the requirements of real-time applications, such as
the Diameter Credit Control application, will certainly increase the
probability of premature failover significantly and potentially cause
congestive collapse in heavy loaded networks. For prepaid services,
however, the end user expects an answer from the network in a
reasonable time, thus the Diameter credit control client shall react
faster than the underlying base protocol. Therefore this specification
defines the timer Tx that is used by the credit-control client (as
defined in section 13) to supervise the communication with the credit-
control server. When the timer Tx elapses the credit-control client
takes an action to the end user according to the Credit-Control-
Failure-Handling AVP.
When Tx expires, the Diameter credit control client always terminates
the service if the Credit-Control-Failure-Handling (CCFH) AVP is set
to the value TERMINATE. The credit control session may be moved to an
alternative server only in case a protocol error DIAMETER_TOO_BUSY or
DIAMETER_UNABLE_TO_DELIVER is received before Tx expires, therefore,
the value TERMINATE is not appropriate if proper failover behavior is
desired.
If the Credit-Control-Failure-Handling AVP is set to the value
CONTINUE or RETRY_AND_TERMINATE, the service will be granted to the
end user upon the timer Tx expires. An answer message with granted-
units may arrive later on due to the base protocol transport failover
occurred in the path to the Credit Control Server (Twinit default
value is 3 times more than the Tx recommended value). The credit
control client SHOULD grant the service to the end user, start
monitoring the resource usage and wait for the possible late answer
until the timeout of the request (e.g. 120 seconds). If the request
fails and the CC-Session-Failover AVP is set to FAILOVER_NOT
SUPPORTED, the credit control client terminates or continues the
service depending on the value set in the CCFH and MUST free all the
reserved resources for the credit control session. If a protocol error
DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is received or the
request timeout and the CC-Session-Failover AVP is set to FAILOVER
SUPPORTED, the credit control client MAY send the request to a backup
server if possible. If the credit control client receives a successful
answer from the backup server, it continues the credit control session
with such a server. If also the re-transmitted request fails, the
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credit control client terminates or continues the service depending on
the value set in the CCFH and MUST free all the reserved resources for
the credit control session.
If a communication failure occurs during the graceful service
termination procedure, the service element SHOULD always terminate the
ongoing service session.
If the credit-control server detects a failure during an ongoing
credit-control session, it will terminate the credit-control session
and return the reserved units back to the end user's account.
The supervision session timer Tcc (as defined in section 13) is used
in the credit-control server to supervise the credit-control session.
In order to support the failover between credit control servers
information transfer about the credit control session and account
state SHOULD take place between the primary and the secondary credit
control server. Implementations supporting the credit control session
failover MUST also ensure proper detection of duplicate or out of
sequence messages. The communication between the servers is regarded
as an implementation issue and is outside of the scope of this
specification.
6. One Time Event
The one-time event is used when there is no need to maintain any state
in the Diameter credit-control server, for example enquiring the price
of the service. The use of one-time event implies that the user has
been authenticated and authorized beforehand.
The one time event can be used when the credit-control client wants to
know the cost of the service event without any credit-reservation or
to check the account balance without any credit-reservation. It can be
used also for refunding service units on the user's account or direct
debiting without any credit-reservation. The one time event is shown
in Figure 7.
End-User Service Element AAA Server CC Server
(CC Client)
| Service Request | | |
|------------------>| | |
| | CCR(Event) | |
| |------------------->| CCR(Event) |
| | |------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<-------------------|
| Service Delivery |<-------------------| |
|<----------------->| | |
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Figure 7: One time event
In environments such as the 3GPP architecture the one time event can
be sent from the service element directly to the credit-control
server.
6.1 Service Price Enquiry
The credit-control client may need to know the price of the service
event. There might exist services offered by application service
providers, whose prices are not known in the credit-control client.
End user might also want to get an estimation of the price of a
service event before requesting it.
A Diameter credit-control client requesting the cost information MUST
set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
Requested-Action AVP set to PRICE_ENQUIRY and set the requested
service event information into the Service-Parameter-Info AVP in the
Credit-Control-Request message.
The credit-control server calculates the cost of the requested service
event, but it does not perform any account balance check or credit-
reservation from the account.
The estimated cost of the requested service event is returned to the
credit-control client in the Cost-Information AVP in the Credit-
Control-Answer message.
6.2 Balance Check
The Diameter credit-control client may need only to verify that the
end user's account balance covers the cost for a certain service
without reserving any units from the account at the time of the
inquiry. This method does not guarantee that there would be credit
left when the Diameter credit-control client requests the debiting of
the account with a separate request.
A Diameter credit-control client requesting the balance check MUST set
the CC-Request-Type AVP equal to EVENT_REQUEST, include Requested-
Action AVP set to CHECK_BALANCE and include the Subscription-Id-Data
to identify the End-User in the credit-control server.
The credit-control server makes the balance check, but it does not do
any credit-reservation from the account.
The result of balance check (ENOUGH_CREDIT/NO_CREDIT) is returned to
the credit-control client in the Check-Balance-Result AVP in the
Credit-Control-Answer message.
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6.3 Direct Debiting
There are certain service events for which service execution is always
successful in the service environment. The delay between the service
invocation and the actual service delivery to the end user can be
sufficiently long that the use of the session-based credit-control
would lead to unreasonable long credit-control sessions. In these
cases the Diameter credit-control client can use the one-time event
scenario for direct debiting. The Diameter credit-control client
SHOULD be sure that the requested service event execution would be
successful, when this scenario is used.
The CC-Request-Type is set to the value EVENT_REQUEST and the
Requested-Action AVP set to DIRECT_DEBITING in the Credit-Control-
Request message. The Subscription-Id-Data AVP SHOULD be included to
identify the End-User in the credit-control server. The Event-
Timestamp AVP contains the time when the service event is requested in
the service element.
The Diameter credit-control client can include the monetary amount to
be charged in the Request-Service-Unit AVP, if it knows the cost of
the service event. If the Diameter credit-control client does not know
the cost of the service event, then the Service-Parameter-Info AVP
SHOULD contain the service event information to be rated by the
credit-control server. The Service-Parameter-Info AVP always refers to
the requested service unit.
The credit-control server SHOULD rate the service event and deduct the
corresponding monetary amount from end user's account. If the type of
the Requested-Service-Unit AVP is money, no rating is needed but the
corresponding monetary amount is deducted from the End User's account.
The credit-control server returns the Granted-Service-Unit AVP in the
Answer message to the Diameter credit-control client. The Granted-
Service-Unit AVP contains the amount of service units that the
Diameter credit-control client can provide to the end user. The type
of the Granted-Service-Unit can be time, volume, service specific or
money depending on the type of service event.
If the credit-control server determines that no credit-control is
needed for the service it can include the result code indicating that
the credit-control is not applicable (e.g. service is free of charge).
For informative purposes, the Credit-Control-Answer message MAY also
include the Cost-Information AVP containing the estimated total cost
of the requested service.
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6.4 Refund
Some services may refund service units to the end user's account, for
example gaming services.
The credit-control client MUST set CC-Request-Type to the value
EVENT_REQUEST and the Requested-Action AVP to REFUND in the Credit-
Control-Request message. The Subscription-Id-Data AVP SHOULD be
included to identify the End-User in the credit-control server.
The Diameter credit-control client MAY include the monetary amount to
be refunded in the Requested-Service-Unit AVP. If the Diameter credit-
control client does not know the monetary amount to be refunded, then
the Service-Parameter-Info AVP, or other rating AVPs, SHOULD contain
the service event information to be rated by the credit-control
server.
For informative purposes, the Credit-Control-Answer message MAY also
include the Cost-Information AVP containing the estimated monetary
amount of refunded unit.
6.5 Failure Procedure
Failover to an alternative credit-control server is allowed for one
time event since the server is not maintaining session states, for
instance, if the credit control client receives a protocol error
DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY it can re-send the
request to an alternative server if possible. There MAY exist protocol
transparent Diameter relays and redirect agents or Diameter credit-
control proxies between credit-control client and credit-control
server. Failover may occur at any point in the path between credit-
control client and credit-control server in the event that a transport
failure is detected with a peer, as described in [DIAMBASE]. Because
there can be duplicate requests for various reasons the credit-control
server is therefore responsible for the real time duplicate detection.
Implementation issues for duplicate detection are discussed in
[DIAMBASE] Appendix C.
When the credit-control client detects a communication failure to the
credit-control server, its behavior depends on the requested action.
The timer Tx (as defined in section 13) is used in the credit-control
client to supervise the communication with the credit-control server.
In case the requested action is PRICE_ENQUIRY or BALANCE_CHECK and
communication failure is detected the credit-control client SHOULD
forward the request messages to an alternative credit-control server,
if possible. The secondary Credit control server name, if received
from the AAA server, can be used as an address of backup server.
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If the requested action is DIRECT_DEBITING the Direct-Debiting-
Failure-Handling AVP (DDFH) controls the credit control client
behavior. The DDFH may be received from the Diameter home AAA server
or may be locally configured. The credit control server may also send
the DDFH in any CCA message to be used for direct debiting events
compiled thereafter. The DDFH value received from the home AAA server
overrides the locally configured value and the DDFH value received
from the credit control server in a Credit-Control-Answer message
always override any already existing value. If the DDFH is set to
TERMINATE_OR_BUFFER, the credit-control client SHOULD NOT grant the
service if it can determine, eventually after a possible re-
transmission attempt to an alternative credit control server, from the
result code or error code in the answer message that units have not
been debited. Otherwise the credit-control client SHOULD grant the
service to the end user and store the request in the credit-control
application level non-volatile storage (Note that re-sending the
request at a later time is not a guarantee that the service will be
debited, since the user's account may be empty at the time when the
server successfully processes the request). The credit-control client
MUST mark these request messages as possible duplicate by setting the
T-flag in the command header as described in [DIAMBASE] section 3. If
the Direct-Debiting-Failure-Handling AVP is set to CONTINUE, the
service SHOULD be granted even if credit-control messages cannot be
delivered and messages are not buffered.
If the timer Tx expires the credit-control client MUST continue the
service and wait for a possible late answer. If the request timeout
the credit control client re-transmit the request (marked with T-flag)
to a backup credit control server if possible. In the event that also
the re-transmitted request timeout or a temporary error is received in
answer to such a request, the credit control client buffers the
request if the value of the Direct-Debiting-Failure-Handling AVP is
set to TERMINATE_OR_BUFFER. If a failed answer is received for the re-
transmitted request, the credit control client frees all the resources
reserved for the event message and deletes the request regardless the
value of the DDFH.
The Credit-Control-Request with requested action REFUND should always
be stored in the credit-control application level non-volatile storage
in case of temporary failure. The credit-control client MUST mark the
re-transmitted request message as possible duplicate by setting the T-
flag in the command header as described in [DIAMBASE] section 3.
For stored requests, the implementation may choose to limit the number
of re-transmission attempts and define a re-transmission interval.
It should be noted that only one place in the credit-control system
SHOULD be responsible for duplicate detection. If there is only one
credit-control server within the given realm, the credit-control
server may perform duplicate detection. In case when more than one
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credit-control servers are serving a given realm, only one entity in
the credit control system should be responsible to ensure that the end
user's account is not debited or credited multiple times for the same
service event.
7. Credit Control Application State Machine
This section defines the credit control application state machine.
The first four state machines are to be observed by credit-control
clients. The first one describes the session-based credit-control when
the first interrogation is executed as part of the
authorization/authentication process. The second one describes the
session-based credit-control when the first interrogation is executed
after the authorization/authentication process. The requirements what
state machine need to be supported are discussed in section 5.1.
The third state machine describes the session-based credit-control for
intermediate and final interrogations. The fourth one describes the
event-based credit-control. These latter state machines are to be
observed by all the implementations that conform to this
specification.
The fifth state machine describes the credit-control session from a
credit-control server perspective.
Any event not listed in the state machines MUST be considered as an
error condition, and a corresponding answer, if applicable, MUST be
returned to the originator of the message.
In the state table, the event 'Failure to send' means that the
Diameter credit-control client is unable to communicate with the
desired destination or with a possibly defined alternative destination
in case failover procedure is supported (e.g. the request timeout and
the answer message is not received). This could be due to the peer
being down, or due to a physical link failure in the path to/from the
credit-control server.
The event 'Temporary error' means that the Diameter credit-control
client received a protocol error notification DIAMETER_TOO_BUSY,
DIAMETER_UNABLE_TO_DELIVER or DIAMETER_LOOP_DETECTED in the Result-
Code AVP of the Credit-Control-Answer command. The above protocol
error notification may be ultimately received in answer to the re-
transmitted request to a possibly defined alternative destination if
failover is supported.
The event 'Failed answer' means that the Diameter credit-control
client received non-transient failure (permanent failure) notification
in the Credit-Control-Answer command. The above permanent failure
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notification may be ultimately received in answer to the re-
transmitted request to a possibly defined alternative destination if
failover is supported.
The action 'store request' means that a request is stored in the
credit-control application level non-volatile storage.
The event 'Not successfully processed' means that the credit-control
server could not process the message, e.g. due to unknown end user,
account being empty or due to errors defined in [DIAMBASE].
The states PendingI, PendingU, PendingT PendingE and PendingB stand
for pending states to wait for an answer to a credit control request
related to Initial, Update, Termination, Event or Buffered request
respectively.
The abbreviations CCFH and DDFH stand for Credit-Control-Failure-
Handling and Direct-Debiting-Failure-Handling respectively.
In the following state machine table the failover to a possibly
secondary server upon 'Temporary error' or 'Failure to send' is not
explicitly described. Moving an ongoing credit control message stream
to an alternative server is, however, possible if the CC-Session-
Failover AVP is set to FAILOVER_SUPPORTED as described in section 5.6.
Re-sending a credit control event to an alternative server is
supported as described in section 6.5.
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CLIENT, SESSION BASED for the first interrogation with AA request
State Event Action New State
---------------------------------------------------------------
Idle Client or device requests Send PendingI
access/service AA request
with added
CC AVPs,
start Tx
PendingI Successful AA req. Grant Open
answer received service to
end user,
stop Tx
PendingI Tx expired Disconnect Idle
user/dev
PendingI Failed AA answer received Disconnect Idle
user/dev
PendingI AA answer Grant Idle
received with result code service
equal to credit-control N/A to end user
PendingI User service terminated Queue PendingI
termination
event
PendingI Change in rating condition Queue PendingI
changed
rating
condition
event
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CLIENT, SESSION BASED for the first interrogation with CCR
State Event Action New State
----------------------------------------------------------------
Idle Client or device requests Send PendingI
access/service CC initial
req.,
start Tx.
PendingI Successful CC initial Stop Tx Open
answer received
PendingI Failure to send, or Grant Idle
temporary error and service to
CCFH equal to CONTINUE end user
PendingI Failure to send, or Terminate Idle
temporary error and end user's
CCFH equal to TERMINATE service
or equal to RETRY_AND_TERMINATE
PendingI Tx expired and CCFH Terminate Idle
equal to TERMINATE end user's
service
PendingI Tx expired and CCFH equal Grant PendingI
to CONTINUE or equal to service to
RETRY_AND_TERMINATE end user
PendingI CC initial answer Terminate Idle
received with result code end user's
SERVICE_ DENIED or service
USER_UNKNOWN
PendingI CC initial answer Grant Idle
received with result code service
equal to credit-control N/A to end user
PendingI Failed CC initial answer Grant Idle
received CCFH equal to Service to
CONTINUE end user
PendingI Failed CC initial answer Terminate Idle
received and CCFH equal end user's
to TERMINATE or equal to service
RETRY_AND_TERMINATE
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PendingI User service terminated Queue PendingI
termination
event
PendingI Change in rating condition Queue PendingI
changed
rating
condition
event
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CLIENT, SESSION BASED for intermediate and final interrogations
State Event Action New State
----------------------------------------------------------------
Open Granted unit elapses Send PendingU
and no final unit CC update
indication received req.,
start Tx.
Open Granted unit elapses Terminate PendingT
and final unit action end user's
equal to TERMINATE service, send
received CC termination
req.
Open Change in rating condition Send PendingU
in queue CC update
req.,
Start Tx.
Open Service terminated in queue Send PendingT
CC termination
req.
Open Change in rating condition Send PendingU
or Validity-Time elapses CC update
req.,
Start Tx.
Open User service terminated Send PendingT
CC termination
req.
Open RAR received Send RAA PendingU
followed by
CC update req.,
start Tx
PendingU Successful CC update Stop Tx Open
answer received
PendingU Failure to send, or Grant Idle
temporary error and service to
CCFH equal to CONTINUE end user
PendingU Failure to send, or Terminate Idle
temporary error and end user's
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CCFH equal to TERMINATE service
or equal to RETRY_AND_TERMINATE
PendingU Tx expired and CCFH Terminate Idle
equal to TERMINATE end user's
service
PendingU Tx expired and CCFH equal Grant PendingU
to CONTINUE or equal to service to
RETRY_AND_TERMINATE end user.
PendingU CC update answer Terminate Idle
received with result code end user's
SERVICE_DENIED service
PendingU CC update answer Grant Idle
received with result code service
equal to credit-control N/A to end user
PendingU Failed CC update Grant Idle
answer received and service to
CCFH equal to CONTINUE end user.
PendingU Failed CC update Terminate Idle
answer received CCFH end user's
equal to TERMINATE or service
equal to RETRY_AND_TERMINATE
PendingU User service terminated Queue PendingU
termination
event
PendingU Change in rating Queue PendingU
condition changed
rating
condition
event
PendingU RAR received Send RAA PendingU
PendingT Successful CC Idle
termination answer received
PendingT Failure to send, or temporary Idle
error or failed answer
PendingT Change in rating condition PendingT
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CLIENT, EVENT BASED
State Event Action New State
----------------------------------------------------------------
Idle Client or device requests Send PendingE
a one-time service CC event
req.,
Start Tx.
Idle Request in storage Send PendingB
stored
request
PendingE Successful CC event Grant Idle
answer received service to
end user
PendingE Failure to send, temporary Indicate Idle
error or failed CC event service
answer received, or error
Tx expired, requested
action BALANCE_CHECK or
PRICE_ENQUIRY
PendingE CC event answer Terminate Idle
received with result code end user's
SERVICE_DENIED or service
USER_UNKNOWN and Tx running
PendingE CC event answer Grant Idle
received with result code service
credit-control N/A, requested to end
action DIRECT_DEBITING user
PendingE Failure to send, temporary Grant Idle
error or failed CC event service
answer received, requested to end
action DIRECT_DEBITING and user
DDFH equal to CONTINUE
PendingE Failed CC event Terminate Idle
answer received or temporary end user's
error, requested action service
DIRECT_DEBITING and
DDFH equal to
TERMINATE_OR_BUFFER and
Tx running
PendingE Tx expired, requested Grant PendingE
action DIRECT_DEBITING service
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to end
user
PendingE Failure to send, requested Store Idle
action DIRECT_DEBITING and request with
DDFH equal to T-flag
TERMINATE_OR_BUFFER
PendingE Temporary error, requested Store Idle
action DIRECT_DEBITING and request
DDFH equal to
TERMINATE_OR_BUFFER and
Tx expired
PendingE Failed answer or answer Idle
received with result code
SERVICE DENIED or USER_UNKNOWN,
requested action
DIRECT_DEBITING and Tx expired
PendingE Failed CC event answer Indicate Idle
received, requested service
action REFUND_ACCOUNT error and
delete request
PendingE Failure to send or Store Idle
Tx expired, requested request
action REFUND_ACCOUNT with T-flag
PendingE Temporary error Store Idle
and requested action request
REFUND_ACCOUNT
PendingB Successful CC answer Delete Idle
received request
PendingB Failed CC answer Delete Idle
received request
PendingB Failure to send or Idle
temporary error
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SERVER, SESSION AND EVENT BASED
State Event Action New State
----------------------------------------------------------------
Idle CC initial request Send Open
received and successfully CC initial
processed. answer,
reserve units,
start Tcc
Idle CC initial request Send Idle
received, but not CC initial
successfully processed. answer with
Result-Code
=! SUCCESS
Idle CC event request Send Idle
received and successfully CC event
processed. answer,
debit units
Idle CC event request Send Idle
received, but not CC event
successfully processed. Answer with
Result-Code
!= SUCCESS
Open CC update request Send Open
received and successfully CC answer,
processed debit used
units and
reserve
new units,
Restart Tcc
Open CC update request Send Idle
received, but not CC update
successfully processed. Answer with
Result-Code
!= SUCCESS,
debit used
units
Open CC termination request Send Idle
received, and successfully CC termin.
processed answer,
Stop Tcc,
debit used
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units
Open CC termination request Send Idle
received, but not CC termin.
successfully processed. Answer with
Result-Code
!= SUCCESS,
debit used
units
Open Session supervision timer Tcc Stop Tcc, Idle
expired release
reserved
units
8. Credit Control AVPs
This section defines the credit-control AVPs that are specific to
Diameter Credit-control Application and MAY be included in the
Diameter credit control messages.
The AVPs defined in this section MAY also be included in authorization
commands defined in authorization specific applications, such as
[NASREQ] and [DiamMIP], in case the first interrogation is performed
as part of the authorization / authentication process as described in
section 4.
The following table describes the Diameter AVPs defined in Credit-
control application, their AVP Code values, types, possible flag
values and whether the AVP MAY be encrypted.
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+---------------------+
| AVP Flag rules |
|----+-----+----+-----|----+
AVP Section | | |SHLD| MUST| |
Attribute Name Code Defined Data Type |MUST| MAY | NOT| NOT|Encr|
-----------------------------------------|----+-----+----+-----|----|
CC-Correlation-Id 411 8.1 OctetString| - | P | | V | Y |
CC-Input-Octets 412 8.33 Unsigned64 | M | P | | V | Y |
CC-Money 413 8.34 Grouped | M | P | | V | Y |
CC-Output-Octets 414 8.35 Unsigned64 | M | P | | V | Y |
CC-Request-Number 415 8.2 Unsigned32 | M | P | | V | Y |
CC-Request-Type 416 8.3 Enumerated | M | P | | V | Y |
CC-Service- 417 8.36 OctetString| M | P | | V | Y |
Specific-Units | | | | | |
CC-Session- 418 8.4 Enumerated | M | P | | V | Y |
Failover | | | | | |
CC-Sub-Session-Id 419 8.5 Unsigned64 | M | P | | V | Y |
CC-Time 420 8.37 Unsigned32 | M | P | | V | Y |
CC-Total-Octets 421 8.38 Unsigned64 | M | P | | V | Y |
Check-Balance- 422 8.6 Enumerated | M | P | | V | Y |
Result | | | | | |
Cost-Information 423 8.7 Grouped | M | P | | V | Y |
Cost-Unit 424 8.8 UTF8String | M | P | | V | Y |
Currency-Code 425 8.11 Unsigned32 | M | P | | V | Y |
Credit-Control 426 8.9 Enumerated | M | P | | V | Y |
Credit-Control- 427 8.10 Enumerated | M | P | | V | Y |
Failure-Handling | | | | | |
Direct-Debiting 428 8.12 Enumerated | M | P | | V | Y |
Failure-Handling | | | | | |
Exponent 429 8.13 Integer32 | M | P | | V | Y |
Final-Unit-Action 449 8.14 Enumerated | M | P | | V | Y |
Final-Unit- 430 8.15 Grouped | M | P | | V | Y |
Indication | | | | | |
Granted-Service- 431 8.16 Grouped | M | P | | V | Y |
Unit | | | | | |
Rating-Group 432 8.39 Unsigned32 | M | P | | V | Y |
Redirect-Address 433 8.17 Enumerated | M | P | | V | Y |
-Type | | | | | |
Redirect-Server 434 8.18 Grouped | M | P | | V | Y |
Redirect-Server 435 8.19 UTF8String | M | P | | V | Y |
-Address | | | | | |
Requested-Action 436 8.20 Enumerated | M | P | | V | Y |
Requested-Service 437 8.21 Grouped | M | P | | V | Y |
Unit | | | | | |
Restriction 438 8.22 IPFiltrRule| M | P | | V | Y |
-Filter-Rule | | | | | |
Service- 439 8.40 UTF8String | M | P | | V | Y |
Identifier | | | | | |
Service-Parameter 440 8.23 Grouped | - | P | | V | Y |
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Info | | | | | |
Service- 441 8.24 Unsigned32 | - | P | | V | Y |
Parameter-Type | | | | | |
Service- 442 8.25 UTF8String | - | P | | V | Y |
Parameter-Value | | | | | |
Subscription-Id 443 8.26 Grouped | M | P | | V | Y |
Subscription-Id 444 8.27 UTF8String | M | P | | V | Y |
-Data | | | | | |
Subscription-Id 450 8.28 Enumerated | M | P | | V | Y |
-Type | | | | | |
Tariff-Change 452 8.42 Enumerated | M | P | | V | Y |
-Usage | | | | | |
Tariff-Time 451 8.41 Time | M | P | | V | Y |
-Change | | | | | |
Unit-Value 445 8.29 Grouped | M | P | | V | Y |
Used-Service-Unit 446 8.30 Grouped | M | P | | V | Y |
Value-Digits 447 8.31 Unsigned64 | M | P | | V | Y |
Validity-Time 448 8.32 Unsigned32 | M | P | | V | Y |
8.1 CC-Correlation-Id AVP
The CC-Correlation-Id AVP (AVP Code 411) is type of OctetString and
contains information to correlate credit control requests generated
for different components of the service, e.g. transport and service
level.
8.2 CC-Request-Number AVP
The CC-Request-Number AVP (AVP Code 415) is of type Unsigned32 and
identifies this request within one session. As Session-Id AVPs are
globally unique, the combination of Session-Id and CC-Request-Number
AVPs is also globally unique, and can be used in matching credit
control messages with confirmations. An easy way to produce unique
numbers is to set the value to 0 for credit control request of type
INITIAL_REQUEST and EVENT_REQUEST, and set the value to 1 for the
first UPDATE_REQUEST, 2 for the second, and so on until the value for
TERMINATION_REQUEST.
8.3 CC-Request-Type AVP
The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
contains the reason for sending the Credit-control request message.
It MUST be present in all CC-Request messages. The following values
are defined for the CC-Request-Type AVP:
INITIAL_REQUEST 1
A Credit-control Initial request is used to initiate a
credit control session, and contains credit control
information that is relevant to the initiation of the
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session.
UPDATE_REQUEST 2
An Update Credit-control request contains credit control
information for an existing credit control session. Update
Credit-control requests SHOULD be sent every time a credit-
control re-authorization is needed at the expiry of the
allocated quota or validity time. Further, additional
service-specific events MAY trigger a spontaneous Update
request.
TERMINATION_REQUEST 3
A Credit-control Termination Request is sent to terminate a
credit-control session and contains credit control
information relevant to the existing session.
EVENT_REQUEST 4
A Credit Control Event Request is used when there is no need
to maintain any credit control session state in the credit-
control server. This request contains all information
relevant to the service, and is the only request of the
service. The reason for the Event request
is further detailed in the Requested-Action AVP. The
Requested-AVP MUST be included in the Credit-Control-Request
message when CC-Request-Type is set to EVENT_REQUEST.
8.4 CC-Session-Failover AVP
The CC-Session-Failover AVP (AVP Code 418) is type of Enumerated and
contains information whether the moving of the credit-control message
stream to a backup server during an ongoing credit-control session is
supported. In case of communication failures, the credit control
message streams can be moved to an alternative destination if the
credit control server supports failover to an alternative server. The
secondary credit control server name, if received from the AAA server,
can be used as an address of the backup server. An implementation is
not required to support the moving of credit control message stream to
an alternative server, since it requires also moving of information
related to the credit control session to backup server.
The following values are defined for the CC-Session-Failover AVP:
FAILOVER_NOT_SUPPORTED 0
When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED
the Credit control message stream MUST NOT to be moved to
alternative destination in case of communication failure.
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This is the default behavior if the AVP isn't included in the reply
from the authorization or credit-control server.
FAILOVER_SUPPORTED 1
When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
Credit control message stream SHOULD be moved to alternative
destination in case of communication failure. The moving the credit
control message stream to backup server MAY require that
information related to the credit control session should be also
forwarded to alternative server.
8.5 CC-Sub-Session-Id AVP
The CC-Sub-Session-Id AVP (AVP Code 419) is of type Unsigned64 and
contains the credit-control sub-session identifier. The combination of
the Session-Id and this AVP MUST be unique per sub-session, and the
value of this AVP MUST be monotonically increased by one for all new
sub-sessions. The absence of this AVP implies no sub-sessions are in
use, with the exception of a CC-Request whose CC-Request-Type is set
to TERMINATION_REQUEST. A TERMINATION_REQUEST message with no CC-Sub-
Session-Id AVP present will signal the termination of all sub-sessions
for a given Session-Id.
8.6 Check-Balance-Result AVP
The Check Balance Result AVP (AVP code 422) is of type Enumerated and
contains the result of the balance check. This AVP is applicable only
when the Requested-Action AVP indicates CHECK_BALANCE in the Credit-
Control-Request command.
The following values are defined for the Check-Balance-Result AVP.
ENOUGH_CREDIT 0
There is enough credit in the account to cover the
requested service.
NO_CREDIT 1
There isn't enough credit in the account to cover the
requested service.
8.7 Cost-Information AVP
The Cost-Information AVP (AVP Code 423) is of type Grouped and is used
to return the cost information of a service in the Credit-Control-
Answer command. The included Unit-Value AVP contains the cost estimate
(always type of money) of the service in case of price enquiry or the
accumulated cost estimation in the case of credit- control session.
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The Currency-Code specifies in which currency the cost was given.
The Cost-Unit specifies the unit when the service cost is a cost per
unit (e.g. cost for the service is $1 per minute).
When the Requested-Action AVP with value PRICE_ENQUIRY is included in
the Credit-Control-Request command the Cost-Information AVP sent in
the succeeding Credit-Control-Answer command contains the cost
estimation of the requested service, without any reservation being
made.
The Cost-Information AVP included in the Credit-Control-Answer command
with the CC-Request-Type set to UPDATE_REQUEST contains the
accumulated cost estimation for the session without taking any credit-
reservation into account.
The Cost-Information AVP included in the Credit-Control-Answer command
with the CC-Request-Type set to EVENT_REQUEST or TERMINATION_REQUEST
contains the estimated total cost for the requested service.
It has the following ABNF grammar:
Cost-Information ::= < AVP Header: 423 >
{ Unit-Value }
{ Currency-Code }
[ Cost-Unit ]
8.8 Cost-Unit AVP
The Cost-Unit AVP (AVP Code 424) is of type UTF8String and specifies
the applicable unit to the Cost-Information when the service cost is a
cost per unit (e.g. cost of the service is $1 pe rminute). The Cost-
Unit can be for instance minute, hour, day, kilobytes, megabytes etc.
8.9 Credit-Control AVP
The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
be included in AA requests when service element has credit control
capabilities.
CREDIT_AUTHORIZATION 0
If the AAA server determines the user is a prepaid user, this value
indicates that credit-control server MUST be contacted to perform
the first interrogation. The value of the Credit-Control AVP MUST
always be set to 0 in AA request sent to perform the first
interrogation and initiate a new credit-control session.
RE_AUTHORIZATION 1
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This value indicates to the Diameter AAA server that a credit-
control session is ongoing for the subscriber and the credit-control
server MUST not be contacted. The Credit-Control AVP set to the
value of 1 is to be used only when the first interrogation has been
successfully performed and the credit-control session is ongoing
(i.e. re-authorization triggered by Authorization-Lifetime). This
value MUST NOT be used in AA request sent to perform the first
interrogation.
8.10 Credit-Control-Failure-Handling AVP
The Credit-Control-Failure-Handling AVP (AVP Code 427) is of type
Enumerated. The credit-control client uses information in this AVP to
decide what to do if the sending of credit-control messages to the
credit-control server has been for instance temporarily prevented due
to a network problem. Depending on the service logic, the credit-
control server can order the client to terminate the service
immediately when there is a reason to believe that the service cannot
be charged, or to try failover to an alternative server, if possible,
and then either terminate or grant the service should also the
alternative connection fail.
TERMINATE 0
When the Credit-Control-Failure-Handling AVP is set to TERMINATE
the service MUST only be granted as long as there is a connection
to the credit-control server. If the credit-control client does not
receive any Credit-Control-Answer message within the Tx timer (as
defined in section 13) the credit-control request is regarded
failed and the end user's service session is terminated.
This is the default behavior if the AVP isn't included in the reply
from the authorization or credit-control server.
CONTINUE 1
When the Credit-Control-Failure-Handling AVP is set to CONTINUE
the credit-control client SHOULD re-send the request to an
alternative server in case of transport or temporary failures,
provided that failover procedure is supported in the credit-
control server and the credit-control client, and an alternative
server is available. Otherwise, the service SHOULD be granted
even if credit-control messages can't be delivered.
RETRY_AND_TERMINATE 2
When the Credit-Control-Failure-Handling AVP is set to
RETRY_AND_TERMINATE the credit-control client SHOULD re-send the
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request to an alternative server in case of transport or
temporary failures, provided that failover procedure is
supported in the credit-control server and the credit-control
client, and an alternative server is available. Otherwise, the
service SHOULD not be granted when the credit-control messages
can't be delivered.
8.11 Currency-Code AVP
The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and
contains a currency code that specifies in which currency the values
of AVPs containing monetary units were given. It is specified using
the numeric values defined in the ISO 4217 standard.
8.12 Direct-Debiting-Failure-Handling AVP
The Direct-Debiting-Failure-Handling AVP (AVP Code 428) is of type
Enumerated. The credit-control client uses information in this AVP to
decide what to do if the sending of credit-control messages
(Requested-Action AVP set to Direct Debiting) to the credit-control
server has been for instance temporarily prevented due to a network
problem.
TERMINATE_OR_BUFFER 0
When the Direct-Debiting-Failure-Handling AVP is set to
TERMINATE_OR_BUFFER the service MUST be granted as long as there
is a connection to the credit-control server. If the credit-
control client does not receive any Credit-Control-Answer
message within the Tx timer (as defined in section 13) the
credit-control request is regarded failed. The client SHOULD
terminate the service if it can determine from the failed answer
that units have not been debited. Otherwise the credit-control
client SHOULD grant the service, store the request to
application level non-volatile storage and try to re-send the
request. These requests MUST be marked as possible duplicate by
setting the T-flag in the command header as described in
[DIAMBASE] section 3.
This is the default behavior if the AVP isn't included in the
reply from the authorization server.
CONTINUE
1
When the Direct-Debiting-Failure-Handling AVP is set to CONTINUE
the service SHOULD be granted even if credit-control messages
can't be delivered and the request should be deleted.
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8.13 Exponent AVP
Exponent AVP is of type Integer32 (AVP code 429) and contains the
exponent value to be applied for the Value-Digit AVP within the Unit-
Value AVP.
8.14 Final-Unit-Action AVP
The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
indicates to the credit-control client the action to be taken when the
user's account cannot cover the service cost.
The Final-Unit-Action can be one of the following:
TERMINATE 0
The credit control client MUST terminate the service session.
This is the default handling applicable whenever the credit
control client receives an unsupported Final-Unit-Action value
and MUST be supported by all the Diameter credit control client
implementations conforming to this specification.
REDIRECT 1
The service element MUST redirect the user to the address
specified in the Redirect-Server-Address AVP. The redirect
action is defined in section 5.5.2.
RESTRICT_ACCESS 2
The access device MUST restrict the user access according to the
IP packet filters defined in the Restriction-Filter-Rule AVP or
according to the IP packet filters identified by the Filter-Id
AVP. All the packets not matching the filters MUST be dropped
(see section 5.5.3).
8.15 Final-Unit-Indication AVP
The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
indicates that the Granted-Service-Unit AVP in the Credit-Control-
Answer, or in the AA answer, contains the final units for the service.
After these units have expired, the Diameter credit-control client is
responsible for executing the action indicated in the Final-Unit-
Action AVP (see section 5.5).
If more than one unit types are received in the Credit-Control-Answer,
the Unit type which first expired SHOULD cause the credit-control
client to execute the specified action.
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In the first interrogation, the Final-Unit-Indication AVP with Final-
Unit-Action REDIRECT or RESTRICT_ACCESS can also be present with no
Granted-Service-Unit AVP in the Credit-Control-Answer or in the AA
answer. This indicates to the Diameter credit-control client to
immediately execute the specified action. If the home service provider
policy is to terminate the service, naturally, the server SHOULD
return the appropriate transient failure (see section 9.1) in order to
disconnect the end user and close the credit control session.
The Final-Unit-Action AVP defines the behavior of the service element
when the user's account cannot cover the cost of the service and MUST
always be present if the Final-Unit-Indication AVP is included in a
command.
If the Final-Unit-Action AVP is set to TERMINATE no other AVPs MUST be
present.
If the Final-Unit-Action AVP is set to REDIRECT at least the Redirect-
Server AVP MUST be present. The Restriction-Filter-Rule AVP or the
Filter-Id AVP MAY be present in the Credit-Control-Answer message if
the user is allowed to access also other zero-rated services not
accessible through the address given in the Redirect-Server AVP.
If the Final-Unit-Action AVP is set to RESTRICT_ACCESS either the
Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
The Filter-Id AVP is defined in [NASREQ]. The Filter-Id AVP can be
used to reference an IP filter list installed in the access device by
other means than the Diameter Credit Control Application e.g. locally
configured or configured by another entity.
The Final-Unit-Indication AVP has the following ABNF grammar:
Final-Unit-Indication ::= < AVP Header: 430 >
{ Final-Unit-Action }
*[ Restriction-Filter-Rule ]
*[ Filter-Id ]
[ Redirect-Server ]
8.16 Granted-Service-Unit AVP
Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
contains the amount of units that the Diameter credit-control client
can provide to the end user until the service must be released or the
new Credit-Control-Request must be sent. A client is not required to
implement all of the unit types, and must treat unknown or unsupported
unit types in the answer message as an incorrect CCA answer. In that
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case the client shall terminate credit control session and indicate in
the Termination-Cause AVP reason DIAMETER_BAD_ANSWER.
The Service-Identifier and the Rating-Group AVPs are used to associate
the granted units to a given service or rating group.
In case both the Service-Identifier and the Rating-Group AVPs are
included, the target of the granted units is always the service(s)
indicated by the value of the Service-Identifier AVP.
A value of 0 (zero) granted service unit associated to a Service-
entifier(s) or Rating-Group indicates that the corresponding traffic
MUST be denied. Note that in case the credit-control server want to
disconnect the user and close the credit-control session, it SHOULD
use the appropriate error code in the Credit-Control-Answer message
rather than including n times the Granted-Service-Units AVPs with the
value of 0 (zero).
In contrast, a value of max type granted service unit (e.g. max
Unsigned 32 is FFFFFFFF) associated to a Service-Identifier(s) or
Rating-Group indicates that the corresponding traffic is free-of-
charge. With unit type money, the value of the Exponent AVP is set to
0 (zero) when free-of-charge is indicated. With unit type service
specific, the value of the CC-Service-Specific-Units AVP is set to
FFFFFFFF to indicate free-of-charge.
The Granted-Service-Unit AVP has the following ABNF grammar:
Granted-Service-Unit ::= < AVP Header: 431 >
[ Tariff-Time-Change ]
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ Service-Identifier ]
[ Rating-Group ]
8.17 Redirect-Address-Type AVP
The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated and
defines the address type of the address given in the Redirect-Server-
Address AVP.
The address type can be one of the following:
IPv4 Address 0
The address type is in form of IPv4 address, as defined in [RFC
791].
IPv6 Address 1
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The address type is in form of IPv6 address, as defined in [RFC
2373].
URL 2
The address type is in form of Uniform Resource Locator, as
defined in [RFC 1738].
SIP URI 3
The address type is in form of SIP Uniform Resource Indicator,
as defined in [SIP].
8.18 Redirect-Server AVP
The Redirect-Server AVP (AVP Code 434) is of type Grouped and contains
the address information of the redirect server (e.g. HTTP redirect
server, SIP Server) where the end user is to be connected when the
account cannot cover the service cost. It MUST be present when the
Final-Unit-Action AVP is set to REDIRECT.
It has the following ABNF grammar:
Redirect-Server ::= < AVP Header: 434 >
{ Redirect-Address-Type }
{ Redirect-Server-Address }
8.19 Redirect-Server-Address AVP
The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String
and defines the address of the redirect server (e.g. HTTP redirect
server, SIP Server) where the end user is to be connected when the
account cannot cover the service cost.
8.20 Requested-Action AVP
The Requested-Action AVP (AVP Code 436) is type of Enumerated and
contains the requested action being sent by Credit-Control-Request
command where the CC-Request-Type is set to EVENT_REQUEST. The
following values are defined for the Requested-Action AVP:
DIRECT_DEBITING 0
Direct debiting indicates that the request is to decrease the
end user's account according to information specified in the
Requested-Service-Unit AVP and/or Service-Parameter-Info AVP.
The Granted-Service Unit AVP in the Credit-Control-Answer
command contains the debited units.
REFUND_ACCOUNT 1
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Refund account indicates that the request is to increase the
end user's account according to information specified in the
Requested-Service-Unit AVP and/or Service-Parameter-Info AVP.
The Granted-Service Unit AVP in the Credit-Control-Answer
command contains the refunded units.
CHECK_BALANCE 2
Check balance indicates that the request is a balance check
request. In this case the checking of the account balance is
done without any credit reservation from the account. The
Check-Balance-Result AVP in the Credit-Control-Answer command
contains the result of the Balance Check.
PRICE_ENQUIRY 3
Price Enquiry indicates that the request is a price enquiry
request. In this case neither checking of the account balance
nor reservation from the account will be done, only the price
of the service will be returned in the Cost-Information AVP in
the Credit-Control-Answer Command.
8.21 Requested-Service-Unit AVP
The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
contains the amount of requested units specified by the Diameter
credit-control client. A server is not required to implement all of
the unit types, and must treat unknown or unsupported unit types as
invalid AVPs.
The Service-Identifier and the Rating-Group AVPs are used to request
units for a given service(s) or rating group when the service element
supports credit control for multiple services in one credit control
session.
If both the AVPs are present, the Rating-Group AVP indicates the
rating group to which the service(s) specified by the Service-
Identifier(s) belongs. If only the Rating-Group-Id AVP is present,
this is a credit authorization request for all the services that
belongs to the specified rating group.
A server not implementing the Service-Identifier AVP and the Rating-
Group AVP must treat them as invalid AVPs.
The Requested-Service-Unit AVP has the following ABNF grammar:
Requested-Service-Unit ::= < AVP Header: 437 >
[ CC-Time ]
[ CC-Money ]
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[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ Service-Identifier ]
[ Rating-Group ]
8.22 Restriction-Filter-Rule AVP
The Restriction-Filter-Rule AVP (AVP Code 438) is of type IPFilterRule
and provides filter rules corresponding to zero-rated services offered
by the home service provider. The access device need to configure the
specified filter rules for the subscriber and MUST drop all the
packets not matching these filters. Zero, one or more such AVPs MAY be
present in a Credit-Control-Answer message or in an AA answer message.
8.23 Service-Parameter-Info AVP
The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
contains a service specific information used for price calculation or
rating. The Service-Parameter-Type AVP defines the service parameter
type and the Service-Parameter-Value AVP contains the parameter value.
The actual contents of these AVPs are not within the scope of this
document and SHOULD be defined in another Diameter application,
standards written by other standardization bodies, or service specific
documentation.
In case of unknown service request (e.g. unknown Service-Parameter-
Type), the corresponding answer message MUST contain error code
DIAMETER_RATING_FAILED. A Credit Control Answer message with this
error MUST contain one or more Failed-AVP AVPs containing the Service-
Parameter-Info AVPs that caused the failure.
It has the following ABNF grammar:
Service-Parameter-Info ::= < AVP Header: 440 >
[ Service-Parameter-Type ]
[ Service-Parameter-Value ]
8.24 Service-Parameter-Type AVP
The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)
and defines the type of the service event specific parameter (e.g. it
can be end-user location, service name). The different parameters and
their types are service specific and the meanings of these parameters
are not defined in this document. The Service-Parameter-Value AVP
contains the service parameter type.
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8.25 Service-Parameter-Value AVP
The Service-Parameter-Value AVP is of type UTF8String (AVP Code 442)
and contains the value of the service parameter type.
8.26 Subscription-Id AVP
The Subscription-Id AVP (AVP Code 443) is used to identify the end
user's subscription and is of type Grouped. The Subscription-Id AVP
includes a Subscription-Id-Data AVP that hold the identifier and a
Subscription-Id-Type AVP that defines the identifier type.
It has the following ABNF grammar:
Subscription-Id ::= < AVP Header: 443 >
{ Subscription-Id-Type }
{ Subscription-Id-Data }
8.27 Subscription-Id-Data AVP
The Subscription-Id-Data AVP (AVP Code 444) is used to identify the
end-user and is of type UTF8String. The Subscription-Id-Type AVP
defines which type of identifier is used.
8.28 Subscription-Id-Type AVP
The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated and
it is used to determine which type of identifier that is carried by
the Subscription-Id AVP. A server is not required to implement all of
the Subscription-Id-Types, and MUST treat unknown or unsupported
Subscription-Id-Types as invalid AVP values.
The identifier can be one of the following:
END_USER_MSISDN 0
The identifier is in international MSISDN format, according
to the ITU-T E.164 numbering plan as defined in [E164] and
[CE164].
END_USER_IMSI 1
The identifier is in international IMSI format, according to
the ITU-T E.212 numbering plan as defined in [E121] and
[CE121].
END_USER_SIP_URL 2
The identifier is in the form of a SIP URL as defined in
[SIP].
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END_USER_NAI 3
The identifier is in the form of a Network Access Identifier
as defined in [NAI].
END_USER_PRIVATE 4
The Identifier is a credit-control server private identifier.
8.29 Unit-Value AVP
Unit-Value AVP is of type Grouped (AVP Code 445) and specifies the
units as decimal value. The Unit-Value is a value together with an
exponent, i.e. Unit-Value = Value-Digits AVP * 10^Exponent. This
representation avoids unwanted rounding off. For example the value of
2,3 is represented as Value-Digits = 23 and Exponent = -1. The absence
of exponent part MUST be interpreted as exponent being equal to zero.
It has the following ABNF grammar:
Unit-Value ::= < AVP Header: 445 >
{ Value-Digits }
[ Exponent ]
8.30 Used-Service-Unit AVP
The Used-Service-Unit AVP is of type Grouped AVP (AVP Code 446) and
contains the amount of used units measured from the point when the
service became active or, in case of interim interrogations are used
during the session, from the point when the previous measurement
ended.
The Service-Identifier and the Rating-Group AVPs are used to associate
the used units to a given service or rating group.
When granted service units are associated to a service or rating
group, the credit control client MUST report the corresponding used
service units. If the granted units are associated to a rating group,
the units used by each of the Service-Identifier belonging to that
rating group SHOULD be reported if this information is available to
the credit control client. Therefore, multiple instances of the Used-
Service-Unit AVP MAY be present in a request, each associated to the
relevant Rating-Group-Id and to the identifier of the service (i.e.
Service-Identifier) that consumed some of the granted units.
The Used-Service-Unit AVP has the following ABNF grammar:
Used-Service-Unit ::= < AVP Header: 446 >
[ Tariff-Change-Usage ]
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
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[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ Service-Identifier ]
[ Rating-Group ]
8.31 Value-Digits AVP
The Value-Digits AVP is of type Unsigned64 (AVP code 447) and contains
the significant digits of the number. If decimal values are needed to
present the units, the scaling MUST be indicated with the related
Exponent AVP. For example for the monetary amount $ 0.05 the value of
Value-Digits AVP MUST be set to 5 and the scaling MUST be indicated
with the Exponent AVP set to -2.
8.32 Validity-Time AVP
The Validity-Time AVP is of type Unsigned32 (AVP code 448) and is sent
from the credit-control server to the credit-control client. The AVP
contains the validity time of the granted service units. If the
granted service units have not been consumed within the validity time
specified in this AVP, the credit-control client MUST send a Credit-
Control-Request request to the server with CC-Request-Type set to
UPDATE_REQUEST. The value field of the Validity-Time AVP is given in
seconds.
The Validity-Time AVP is also used for the graceful service
termination (see section 5.5) to indicate to the credit control client
how long the subscriber is allowed to use network resources after the
specified action (i.e. REDIRECT or RESTRICT_ACCESS) started. Upon the
Validity-Time elapses a new intermediate interrogation is sent to the
server.
8.33 CC-Input-Octets AVP
The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64, and
contains the number of requested, granted or used octets that can
be/have been received from the end user.
8.34 CC-Money AVP
The CC-Money AVP (AVP Code 413) is of type Grouped, and specifies the
monetary amount in the given currency. The Currency-Code AVP SHOULD be
included. It has the following ABNF grammar:
CC-Money ::= < AVP Header: 413 >
{ Unit-Value }
[ Currency-Code ]
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8.35 CC-Output-Octets AVP
The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64, and
contains the number of requested, granted or used octets that can
be/have been sent to the end user.
8.36 CC-Service-Specific-Units AVP
The CC-Service-Specific-Units AVP (AVP Code 417) is of type
OctetString, and specifies the number of service specific units (e.g.
number of events, points) given in a selected service.
8.37 CC-Time AVP
The CC-Time AVP (AVP Code 420) is of type Unsigned32, and indicates
the length of the requested, granted or used time in seconds.
8.38 CC-Total-Octets AVP
The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64, and
contains the total number of requested, granted or used octets
regardless of the direction (sent or received).
8.39 Rating-Group AVP
The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and contains
the identifier of a rating group. All the services subject to the same
rating type are part of the same rating group. This is an identifier
allocated by the home service provider and MUST be unique within the
home service provider domain.
A usage example of this AVP is illustrated in Appendix A (Flow X).
8.40 Service-Identifier AVP
The Service-Identifier AVP is of type UTF8String (AVP Code 439) and
contains a unique identifier of a service. This is an identifier
allocated by the service provider, by the service element manufacturer
or by a standardization body and MUST uniquely identify a given
service. The format of the service identifier is:
"service-identifier" "@" "domain"
service-identifier = Token
The Token is an arbitrary string of characters
and digits.
domain = represents the entity that allocated the service-identifier.
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It can be ietf.org, 3gpp.org etc. if the identifier is
allocated by a standardization body, or it can be the FQDN
of the service provider (e.g. provider.com) or of the vendor
(e.g. vendor.com) if the identifier is allocated by a
private entity.
Services that are for private use only, i.e. to one provider's own
use, where no interoperability is deemed useful may define private
identifiers without need of coordination. However, when
interoperability is wanted, coordination of the identifiers via e.g.
publication of informational RFC is RECOMMENDED to make Service-
Identifier globally available.
A usage example of this AVP for multiple services in one user session
is illustrated in Appendix A (Flow X).
8.41 Tariff-Time-Change AVP
The Tariff-Time-Change AVP (AVP code 451) is of type Time, and
includes the time in seconds since January 1, 1900 00:00 UTC when the
tariff of the service will be changed.
The tariff change mechanism is optional for client and server and it
is not used for unit type time, since the server has full control of
the time.
If a client does not support the tariff time change mechanism it must
treat Tariff-Time-Change AVP in the answer message as an incorrect
CCA answer. In that case the client shall terminate credit control
session and indicate in the Termination-Cause AVP reason
DIAMETER_BAD_ANSWER.
8.42 Tariff-Change-Usage AVP
The Tariff-Change-Usage AVP (AVP code 452) is of type Enumerated and
defines whether units are used before, after or straddled tariff
change when a tariff change has occurred during the reporting period.
Omission of this AVP means that no tariff change has been occurred.
Tariff-Change-Usage can be one of the following.
UNIT_BEFORE_TARIFF_CHANGE 0
The used units contains the amount of the units before tariff
change, that is units measured from the point when the previous
measurement ended to the point when tariff change occurred.
UNIT_AFTER_TARIFF_CHANGE 1
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The used units contains the amount of the units after tariff change
has been occurred.
UNIT_INDETERMINATE 2
The used units contains the amount of units that straddle the
tariff change (e.g. the metering process reports to the credit-
control client in blocks of n octets and one block straddled the
tariff change).
9. Result Code AVP values
This section defines new Result-Code AVP [DIAMBASE] values that must
be supported by all Diameter implementations that conform to this
specification.
The Credit-Control-Answer message includes the Result-Code AVP, which
MAY indicate that an error was present in the Credit-Control-Request
message. A rejected Credit-Control-Request message SHOULD cause the
user's session to be terminated.
9.1 Transient Failure
Errors that fall within the transient failures category are used to
inform a peer that the request could not be satisfied at the time it
was received, but MAY be able to satisfy the request in the future.
DIAMETER_END_USER_SERVICE_DENIED 4010
The credit-control server denies the service request due to
service restrictions or limitations related to the end-user,
for example the end-user's account could not cover the requested
service. The possibly reported used-service-units with the CCR
are deducted.
DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE 4011
The credit-control server determines that the service can be
granted to the end user but no further credit-control is needed
for the service (e.g. service is free of charge).
9.2 Permanent Failures
Errors that fall within permanent failure category are used to inform
the peer that the request failed, and should not be attempted again.
DIAMETER_USER_UNKNOWN 5030
The specified end user is unknown in the credit-control server.
DIAMETER_RATING_FAILED 5031
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This error code is used to inform the credit-control client
that the credit-control server cannot rate the service request
due to insufficient rating input, incorrect AVP combination or
due to an AVP or an AVP value that is not recognized or
supported in the rating. The Failed-AVP AVP MUST be included
and contain a copy of the entire AVP(s) that could not be
processed successfully or an example of the missing AVP
complete with the Vendor-Id if applicable. The value field of
the missing AVP should be of correct minimum length and contain
zeroes.
10. AVP Occurrence Table
The following table presents the AVPs defined in this document, and
specifies in which Diameter messages they MAY, or MAY NOT be present.
Note that AVPs that can only be present within a Grouped AVP are not
represented in this table.
The table uses the following symbols:
0 The AVP MUST NOT be present in the message.
0+ Zero or more instances of the AVP MAY be present in the
message.
0-1 Zero or one instance of the AVP MAY be present in the
message. It is considered an error if there are more than
once instance of the AVP.
1 One instance of the AVP MUST be present in the message.
1+ At least one instance of the AVP MUST be present in the
message.
10.1 Credit Control AVP Table
The table in this section is used to represent which Credit-control
applications specific AVPs defined in this document are to be present
in the Credit Control messages.
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+-----------+
| Command |
| Code |
|-----+-----+
Attribute Name | CCR | CCA |
------------------------------|-----+-----+
Acct-Multi-Session-Id | 0-1 | 0-1 |
Auth-Application-Id | 1 | 1 |
CC-Correlation-Id | 0-1 | 0 |
CC-Failover-Supported | 0 | 0-1 |
CC-Request-Number | 1 | 1 |
CC-Request-Type | 1 | 1 |
CC-Sub-Session-Id | 0-1 | 0-1 |
Check-Balance-Result | 0 | 0-1 |
Cost-Information | 0 | 0-1 |
Credit-Control-Failure- | 0 | 0-1 |
Handling | | |
Destination-Host | 0-1 | 0 |
Destination-Realm | 1 | 0 |
Direct-Debiting-Failure- | 0 | 0-1 |
Handling | | |
Event-Timestamp | 0-1 | 0-1 |
Final-Unit-Indication | 0 | 0-1 |
Granted-Service-Unit | 0 | 0+ |
Origin-Host | 1 | 1 |
Origin-Realm | 1 | 1 |
Origin-State-Id | 0-1 | 0-1 |
Proxy-Info | 0+ | 0+ |
Redirect-Host | - | 0+ |
Redirect-Host-Usage | - | 0-1 |
Redirect-Max-Cache-Time | - | 0û1 |
Requested-Action | 0-1 | 0 |
Requested-Service-Unit | 0+ | 0 |
Route-Record | 0+ | 0+ |
Service-Identifier | 0-1 | 0 |
Service-Parameter-Info | 0+ | 0 |
Session-Id | 1 | 1 |
Subscription-Id | 0+ | 0+ |
Termination-Cause | 0-1 | 0 |
Used-Service-Unit | 0+ | 0 |
User-Name | 0-1 | 0-1 |
Validity-Time | 0 | 0-1 |
------------------------------|-----+-----+
11. RADIUS/Diameter Credit-control Interworking
This section defines some basic guidelines to provide the Diameter
Credit-control/RADIUS inter-working, that is a protocol translation
between RADIUS [RFC2865] and Diameter Credit-control application. A
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complete description of all protocol translations between RADIUS and
Diameter Credit-control application is beyond the scope of this
document. Note that this document does not restrict implementations
from creating additional methods; it just provides some guiding
principles for protocol translation. Translation makes use of RADIUS
Vendor Specific Attributes (VSAs) for transporting Diameter credit-
control AVPs.
The Diameter NASREQ [NASREQ] application defines how a RADIUS Request
is forwarded as a Diameter Request. Guidelines defined in the Diameter
NASREQ should be followed to the appropriate extent.
A protocol translation between RADIUS and Diameter Credit-control
application is shown in Annex A.
11.1 Initial RADIUS Access-Request
When an AAA server acting as a Translation Agent receives an initial
RADIUS Access-Request message indicating that the service element is
capable of credit-control (e.g. Radius VSA Pre-Paid-Accounting-
Capability), and if the AAA server determines that the subscriber is a
prepaid subscriber then a Diameter Credit control request MUST be sent
towards the credit-control server.
In addition to those steps defined in [NASREQ] the AAA server should
perform the following steps related to the protocol translation
between RADIUS and Diameter Credit-control application:
- The credit control Session-Id should be included in the Session-
Id AVP.
- The CC-Request-Type is set to INITIAL_REQUEST and CC-Request-
Number value is set to 0.
- Subscription-Id should be added using User-Name attribute from
the RADIUS Access-Request message or some AAA server local Id to
identify user's credit control subscription.
- If the Access-Request message contains the Event-Timestamp
attribute it should be included in the Event-Timestamp AVP
The following steps are applied to response the Access-Request message
when successful credit-control answer is received from the Credit-
control server:
- The AAA server shall generate a RADIUS VSA Quota Id to correlate
subsequent RADIUS message with the credit-control session.
- The Termination-Action attribute must be set to be RADIUS-request
to ensure that the used quota is returned by the service element
upon termination of the service.
- If the Granted-Service-Unit AVP including the CC-Time AVP or the
Validity-Time AVP is returned by the credit control server, then
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the smallest value should be included in the RADIUS VSA
Duration-Quota.
- If the Granted-Service-Unit AVP including the CC-Total-Octets AVP
is returned by the credit-control server, then the volume should
be included in the RADIUS VSA Volume-Quota.
- If separate RADIUS VSA Thresholds (volume or duration) are
required by RADIUS implementation, the AAA server shall derive
the threshold values from the Granted-Service-Unit AVPs. The
threshold should be less than the Duration-Quota or Volume-
Quota, except when the Final-Unit-Indication AVP is returned by
the credit control server.
When credit-control answer message includes the Result-Code, which
indicates that credit control authorization is rejected, the AAA
server shall send an Access-Reject message to service element.
11.2 Subsequent RADIUS Access-Request message
When an AAA server receives a RADIUS Access-Request message containing
RADIUS VSA Quota Id, it indicates that the Access-Request message is
subsequent RADIUS Request related to the credit control session. The
AAA server shall use the Quota Id to identify the credit-control
session.
The AAA server's next steps depend on the value of the RADIUS VSA
Update-Reason. If the Update-Reason indicates æThreshold reached' then
the AAA server should perform the following steps related to a new
quota request:
- The CC-Request-Type is set to UPDATE_REQUEST and CC-Request-Number
value is increased by one.
- If the Granted-Service-Unit AVP including the CC-Time AVP or the
Validity-Time AVP is returned by the credit control server, then
the smallest value should be included in the RADIUS VSA Duration-
Quota.
- If the Granted-Service-Unit AVP including the CC-Total-Octets AVP
is returned by the credit-control server, then the volume should
be included in the RADIUS VSA Volume-Quota.
The reply to the RADIUS Access-Request message shall be handled as
described in initial Radius Access-Request.
If the RADIUS VSA Update-Reason indicates that the associated
resources are released at the service element, then the AAA server
shall terminate the credit control session by performing the following
steps:
- The CC-Request-Type is set to TERMINATION_REQUEST and CC-Request-
Number value is increased by one.
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- If the RADIUS VSA Volume-Quota is present, the value shall be
included in the Used-Service-Unit AVP as CC-Total-Octets.
- If the RADIUS VSA Time-Quota is present, the value shall be
included in the Used-Service-Unit AVP as CC-Time.
After the AAA server receives response to the final credit Control
Credit-Control-Request the RADIUS Access-Accept message shall be
return to the service element.
11.3 RADIUS Vendor Specific Attributes for Credit Control
To provide the credit control for RADIUS implementation the RADIUS
Vendor Specific Attributes (VSAs) are used for transporting Diameter
credit-control AVPs. The RADIUS Type 26 (= Vendor-Specific) is used
for RADIUS VSA.
RADIUS Inter-working with the Diameter Credit control uses the
following VSA included with the RADIUS Access Request and Access
Accept messages:
- Pre-Paid-Accounting-Capability; defines that the Service element
in RADIUS implementation is capable of credit-control.
- Quota Id; generated by the AAA server and it is used to correlate
subsequent RADIUS message with the credit-control session.
- Duration-Quota; in RADIUS Access-Request message it indicates the
used Duration and in RADIUS Access-Accept message it indicates
the Duration allocated for the service element.
- Volume-Quota; in RADIUS Access-Request message it indicates the
used Volume and in RADIUS Access-Accept message it indicates the
Volume allocated for the service element.
- Volume-Threshold; If RADIUS implementation requires separate
threshold attribute for Volume, then Volume-Threshold is sent in
RADIUS Access-Accept message and it represents the volume (in
bytes) that shall be used by the service element before
requesting a new Volume quota.
- Duration-Threshold; If RADIUS implementation requires separate
threshold attribute for Duration, then Duration-Threshold is
sent in RADIUS Access-Accept message and it represents the
duration (in seconds) that shall be used by the service element
before requesting a new Duration quota.
- Update-Reason; in RADIUS Access-Request message it indicates the
reason for the initiating the quota update operation.
12. IANA Considerations
This section contains the namespaces that have either been created in
this specification, or the values assigned to existing namespaces
managed by IANA.
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12.1 Application Identifier
This specification assigns the value 4 to the Application Identifier
namespace defined in [DIAMBASE]. See section 1.3 for more information.
12.2 Command Codes
This specification uses the value 272 from the Command code namespace
defined in [DIAMBASE].
12.3 AVP Codes
This specification assigns the values 411 - 450 from the AVP code
namespace defined in [DIAMBASE] See section 8 for the assignment of
the namespace in this specification.
12.4 Result-Code AVP Values
This specification assigns the values 4010, 4011, 5030 and 5031 from
the Result-Code AVP (AVP Code 268) value namespace defined in
[DIAMBASE]. See section 9 for the assignment of the namespace in this
specification.
12.5 CC-Request-Type AVP
As defined in section 8.3, the CC-Request-Type AVP (AVP code 416)
defines the value 1-3. All remaining values are available for
assignment via Designated Expert [IANA].
12.6 CC-Session-Failover AVP
As defined in section 8.4, the CC-Failover-Supported AVP (AVP code
418) defines the value 0-1. All remaining values are available for
assignment via Designated Expert [IANA].
12.7 Check-Balance-Result AVP
As defined in Section 8.6, the Check-Balance-Result AVP (AVP Code 422)
defines the values 0-1. All remaining values are available for
assignment via Designated Expert [IANA].
12.8 Credit-Control AVP
As defined in section 8.9, the Credit-Control AVP (AVP code 426)
defines the value 0-1. All remaining values are available for
assignment via Designated Expert [IANA].
12.9 Credit-Control-Failure-Handling AVP
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As defined in Section 8.10, the Credit-Control-Failure-Handling AVP
(AVP Code 427) defines the values 0-2. All remaining values are
available for assignment via Designated Expert [IANA].
12.10 Direct-Debiting-Failure-Handling AVP
As defined in Section 8.12, the Direct-Debiting-Failure-Handling AVP
(AVP Code 448) defines the values 0-1. All remaining values are
available for assignment via Designated Expert [IANA].
12.11 Final-Unit-Action AVP
As defined in Section 8.14, the Final-Unit-Action AVP (AVP Code 449)
defines the values 0-2. All remaining values are available for
assignment via Designated Expert [IANA].
12.12 Redirect-Address-Type AVP
As defined in Section 8.17, the Redirect-Address-Type AVP (AVP Code
433) defines the values 0-3. All remaining values are available for
assignment via Designated Expert [IANA].
12.13 Requested-Action AVP
As defined in Section 8.20, the Requested-Action AVP (AVP Code 436)
defines the values 0-3. All remaining values are available for
assignment via Designated Expert [IANA].
12.14 Subscription-Id-Type AVP
As defined in Section 8.28, the Subscription-Id-Type AVP (AVP Code
450) defines the values 0-4. All remaining values are available for
assignment via Designated Expert [IANA].
12.15 Tariff-Change-Usage AVP
As defined in Section 8.42, the Tariff-Change-Usage AVP (AVP Code 452)
defines the values 0-2. All remaining values are available for
assignment via Designated Expert [IANA].
13. Credit-control Application Related Parameters
Tx timer
When real-time credit-control is required, the credit-control
client contacts the credit-control server before and during the
service is provided to an end user. Due to real-time nature of
application the communication delays SHOULD be minimized, e.g. to
avoid too long service set up time experienced by the end user. The
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Tx timer is introduced to control the waiting time in the client in
the PENDING state. When the Tx timer elapses the credit-control
client takes an action to the end user according to the value of
the Credit-Control-Failure-Handling AVP or according to the value
of the Direct-Debiting-Failure-Handling AVP.
The recommended value is 10 seconds.
Tcc timer
The Tcc timer supervises an ongoing credit control session in the
credit control server. It is RECOMMENDED to use the Validity-Time
as input to set the Tcc timer value. To avoid the credit control
session in the Diameter credit control server to change to Idle
state in case of short transient network failure, Tcc MAY be set to
two times the value of Validity-Time.
Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling
Client implementations may offer the possibility to locally
configure these AVPs. In such a case their value and behavior is
defined in section 5.6 for the Credit-Control-Failure-Handling and
in section 6.5 for the Direct-Debiting-Failure-Handling.
14. Security Consideration
The Diameter base protocol [DIAMBASE] assumes that each Diameter
implementation uses underlying security, i.e. IPsec or TLS. These
mechanisms are believed to provide sufficient protection under the
normal Internet threat model - that is, assuming the authorized nodes
engaging in the protocol have not been compromised, but the attacker
has complete control over the communication channels between them.
This includes eavesdropping, message modification, insertion, man-in-
the-middle and replay attacks. Note also that this application
includes a mechanism for application layer replay protection by the
means of Session-ID from [DIAMBASE], and CC-Request-Number specified
in this document. The Diameter credit control application is often
used within one domain and there may be just single hop between the
peers. In these environments the use of TLS or IPsec is sufficient.
The details of TLS and IPsec related security considerations are
discussed in the [DIAMBASE].
Because this application handles monetary transactions (directly or
indirectly) this kind of application increases the interest for
various security attacks. Therefore all parties communicating with
each other must be authenticated, including, for instance, TLS client-
side authentication. In addition to this, authorization of the client
shall be emphasized, i.e. that the client is allowed to perform credit
control for a certain user. The specific means of authorization are
Hakala et al. Expires - June 2004 [Page 75]
Diameter Credit Control Application December 2003
outside of the scope of this specification but can be for instance,
manual configuration.
Another kind threat is malicious modification, injection or deletion
of AVPs or complete credit control messages. The credit control
messages contain sensitive billing related information (such as
subscription Id, granted units, used units, cost information) whose
malicious modification can have economical consequences. Sometimes
simply delaying the credit control messages can cause disturbances in
the credit control client or server.
Even without any modification to the messages an adversary can invite
a security threat by eavesdropping, because the transactions contain
private information about the user. Also by monitoring the credit
control messages one can collect information about credit control
server's billing models and business relationships.
When third party relays or proxy are involved, the hop-by-hop security
does not necessarily provide sufficient protection for Diameter user
session. Diameter messages, such as CCR and CCA, containing sensitive
AVPs may be inappropriate in some cases to be sent via untrusted
Diameter proxy agents since there are no assurance that third party
proxies will not modify the credit control commands or AVP values.
14.1 Direct Connection with Redirects
A Diameter Credit control agent cannot always know whether agents
between it and the end user's Diameter credit control server are
reliable. In this case the Diameter Credit control agent doesn't have
a routing entry in its Diameter Routing Table for the realm of the
Credit Control Server in the end user's home domain. The Diameter
Credit control agent can have a default route configured to a local
Redirect agent and it re-directs the CCR message to the redirect
agent. The local Redirect agent then returns a redirect notification
(Result-code 3006, DIAMETER_REDIRECT_INDICATION) to the Credit control
agent, as well Diameter Credit control Server(s) information
(Redirect-Host AVP) and information (Redirect-Host-Usage AVP) how to
the routing entry resulting from the Redirect-Host is to be used. The
Diameter credit control agent then forwards the CCR message directly
to one of the hosts identified by the CCA message from the redirect
agent. If the value of the Redirect-Host-Usage AVP is unequal than
zero all following messages are sent to the host specified in the
Redirect-Host AVP until the time specified by the Redirect-Max-Cache-
Time AVP is expired.
There are some authorization issues even with redirects. There may
have attacks towards nodes that have been properly authorized, but
abuse their authorization or have been compromised. These issues are
discussed more widely in [DIAMEAP] section 8.
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Diameter Credit Control Application December 2003
15. References
15.1 Normative
[DIAMBASE] P. Calhoun, J. Loughney, J. Arkko, E. Guttman, G. Zorn.
"Diameter Base Protocol", RFC 3588, September 2003.
[3GPPCHARG] 3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects, Service
aspects; Charging and Billing, (release 5), 3GPP TS 22.115
v. 5.2.1, 2002-03
[SIP] M. Handley, H. Schulzrinne, E. Schooler, J. Rosenberg, G.
Camarillo, A. Johnston, J. Peterson, R. Sparks
"SIP: Session Initiation Protocol", RFC 3261. June 2002.
[NAI] Aboba, Beadles "The Network Access Identifier." RFC 2486.
January 1999.
[E164] Recommendation E.164/I.331 (05/97): The International
Public Telecommunication Numbering Plan. 1997.
[CE164] Complement to ITU-T Recommendation E.164 (05/1997):"List
of ITU-T Recommendation E.164 assigned country codes",
June 2000.
[E212] Recommendation E.212 (11/98): The international
identification plan for mobile terminals and mobile users.
1998.
[CE212] Complement to ITU-T Recommendation E.212 (11/1997):" List
of mobile country or geographical area codes ", February
1999.
[IANA] Narten, Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998
15.2 Non-Normative
[KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ACCMGMT] B. Aboba, J.Arkko, D.Harrington. "Introduction to
Accounting Management", RFC 2975, October 2000.
[RFC2866] C. Rigney. "Radius Accounting", RFC 2866, June 2000
Hakala et al. Expires - June 2004 [Page 77]
Diameter Credit Control Application December 2003
[NASREQ] P. Calhoun, G. Zorn, D. Spence, D. Mitton. "Diameter
NASREQ Application", IETF work in progress.
[DIAMMIP] P. Calhoun, T. Johansson, C. Perkins "Diameter Mobile IP
Application", IETF work in progress.
[RFC2865] C. Rigney, S. Willens, A. Rubens, W. Simpson. "Remote
Authentication Dial In User Service (RADIUS), RFC 2865,
June 2000
[DIAMEAP] P. Eronen, T. Hiller, G. Zorn. "Diameter Extensible
Authentication Protocol (EAP) Application", IETF work in
progress.
16. Acknowledgement
The authors would like to thank Bernard Aboba, Robert Ekblad, Benny
Gustafsson, Robert Karlsson, Avi Lior, Paco Marin, Jussi Maki, Jeff
Meyer, Anne Narhi, Juha Vallinen, John Prudhoe, Christopher Richards
and Jari Arkko for their comments and suggestions.
17. Author's Address
Harri Hakala
Oy L M Ericsson Ab
Joukahaisenkatu 1
20520 Turku
Finland
Phone: +358 2 265 3722
EMail: Harri.Hakala@ericsson.com
Leena Mattila
Oy L M Ericsson Ab
Joukahaisenkatu 1
20520 Turku
Finland
Phone: +358 2 265 3731
EMail: Leena.Mattila@ericsson.com
Juha-Pekka Koskinen
Nokia Networks
Hatanpaanvaltatie 30
33100 Tampere
Finland
Phone: +358 7180 74027
Email: juha-pekka.koskinen@nokia.com
Marco Stura
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Diameter Credit Control Application December 2003
Nokia Networks
Hiomotie 32
00380 Helsinki
Finland
Phone: +358 7180 64308
Email: marco.stura@nokia.com
John Loughney
Nokia Research Center
Itamerenkatu 11-13
00180 Helsinki
Finland
Phone: +358 50 483 642
Email: John.Loughney@nokia.com
18. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights defined
in the Internet Standards process must be followed, or as required to
translate it into languages other than English. The limited
permissions granted above are perpetual and will not be revoked by the
Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
19. Notices
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to pertain
to the implementation or use of the technology described in this
document or the extent to which any license under such rights might or
might not be available; neither does it represent that it has made any
effort to identify any such rights. Information on the IETF's
Hakala et al. Expires - June 2004 [Page 79]
Diameter Credit Control Application December 2003
procedures with respect to rights in standards-track and standards-
related documentation can be found in BCP-11. Copies of claims of
rights made available for publication and any assurances of licenses
to be made available, or the result of an attempt made to obtain a
general license or permission for the use of such proprietary rights
by implementors or users of this specification can be obtained from
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The IETF invites any interested party to bring to its attention any
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20. Expiration Date
This memo is filed as <draft-ietf-aaa-diameter-cc-02.txt> and expires
in June 2004.
Appendix A Credit Control sequences
A.1 Flow I
End-User NAS AAA Server CC Server
(CC Client)
|(1)User Logon |(2)AA Request (CC AVPs) |
|------------------>|------------------->| |
| | |(3)CCR(initial, CC AVPs)
| | |------------------->|
| | | (4)CCA(granted Units)
| | |<-------------------|
| |(5)AA Answer(granted Units) |
|(6)Access granted |<-------------------| |
|<----------------->| | |
| | | |
: : : :
| |(7)CCR(update,used Units) |
| |------------------->|(8)CCR |
(update,used units)
| | |------------------->|
| | |(9)CCA(granted Units)
| |(10)CCA(granted Units)<------------------|
| |<-------------------| |
: : : :
| (Auth. lifetime expires) | |
| |(11) AAR (CC AVP) | |
| |------------------->| |
| | (12) AAA | |
| |<-------------------| |
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: : : :
: : : :
|(13) User logoff | | |
|------------------>|(14)CCR(term.,used-Units) |
| |------------------->|(15)CCR |
| | | (term.,used-Units)
| | |------------------->|
| | | (16)CCA |
| | (17)CCA |<-------------------|
| |<-------------------| |
| |(18)STR | |
| |------------------->| |
| | (19)STA | |
| |<-------------------| |
Figure A.1: Flow I
A credit control flow for Network Access Services prepaid is shown in
Figure A.1. The Diameter [NASREQ] is implemented in the Network Access
Server (NAS). The focus of this flow is in the credit authorization.
The user logs onto the network (1). The Diameter NAS first sends a
Diameter Authorization-Authentication-Request to the home AAA Server,
the credit-control client populates the AAR with the Credit-Control
AVP set to CREDIT_AUTHORIZATION and service specific AVPs are
included as usual [NASREQ]. The home AAA server performs service
specific Authentication and Authorization as usual. The AAA server
determines that the user is a prepaid user and notices from the
Credit-Control AVP that the NAS has credit control capabilities, it
sends a Diameter Credit-Control-Request with CC-Request-Type set to
INITIAL_REQUEST to the Diameter credit-control server to perform
credit authorization (3) and to establish a credit control session
(the AAA server may forward service specific AVPs as received from
the NAS as input for the rating process). The Diameter credit-control
server checks the end user's account balance, rates the service and
reserves credit from the end user's account. The reserved quota is
returned to the Home AAA server in the Diameter Credit-Control-Answer
(4). The Home AAA server sends the reserved quota to the NAS in the
Diameter Authorization-Authentication-Answer. Upon successful AAA the
NAS starts the credit-control session and starts monitoring the
granted units (5). The NAS grant access to the end user (6). At the
expiry of the allocated quota, the NAS sends a Diameter Credit-
Control-Request with CC-Request-Type set to UPDATE_REQUEST to the
Home AAA server (7). This message contains the units used this far.
The AAA server forwards the CCR to the Diameter credit-control server
(8). The Diameter credit-control server debits the used units from
the end user's account and allocates a new quota that is returned to
the Home AAA server in the Diameter Credit-Control-Answer (9). The
message is forwarded to the NAS (10). During the ongoing credit-
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control session the authorization-lifetime expires, the
authorization/authentication client in the NAS performs service
specific re-authorization to the Home AAA server as usual. The
credit-control client populate the AAR with the Credit-Control AVP
set to RE_AUTHORIZATION indicating that the credit-control server
shall not be contacted, since the credit authorization is controlled
by the burning rate of the granted units (11). The Home AAA server
performs service specific re-authorization as usual and returns the
Authorization-Authentication-Answer to the NAS (12). The end user
logs off from the network (13). To debit the used units from the end
user's account and to stop the credit control session, the NAS sends
a Diameter Credit-Control-Request with CC-Request-Type set to
TERMINATION_REQUEST to the Home AAA server (14). The AAA server
forwards the CCR to the credit-control server (15). The Diameter
credit-control server acknowledges the session termination by sending
a Diameter Credit-Control-Answer to the Home AAA server (16). The AAA
server forwards the answer to the NAS (17). STR/STA take place
between NAS and Home AAA server as usual (18-19).
A.2 Flow II
AAA Server
NAS (CC Client) CC Server
|(1) Access-Request | |
|----------------------->| |
| |(2) CCR (initial) |
| |----------------------->|
| |(3) CCA (granted_Units) |
| |<-----------------------|
|(4) Access-Accept | |
| (granted Units) | |
|<-----------------------| |
: : :
|(5) Access-Request | |
| (used Units) | |
|----------------------->| |
| |(6) CCR (update, |
| | used Units, |
| |----------------------->|
| |(7) CCA (granted_Units) |
| |<-----------------------|
|(8) Access-Accept | |
| (granted Units) | |
|<-----------------------| |
: : :
|(9) Access-Request | |
|----------------------->| |
| |(10) CCR (termin., |
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| | used Units) |
| |----------------------->|
| |(11) CCA |
| |<-----------------------|
|(12) Access-Accept | |
|<-----------------------| |
| | |
Figure A.2: Flow II
A credit control flow for RADIUS prepaid - Diameter credit control
interworking is shown in Figure A.2. The focus of this flow is in the
AAA Server (Diameter credit-control client) and Diameter credit-
control server interworking.
The NAS first sends a RADIUS Access-Request to the home AAA Server
(1). The home AAA server performs regular Authentication and
Authorization. When the AAA server notices that the user is a prepaid
user it sends a Diameter Credit-Control-Request with CC-Request-Type
set to INITIAL_REQUEST to the Diameter credit-control server to
perform credit authorization (2) and to establish a credit control
session. The Diameter credit-control server checks the end user's
account balance, rates the service and reserves credit from the end
user's account. The reserved quota is returned to the Home AAA server
in the Diameter Credit-Control-Answer (3). The Home AAA server sends
the reserved quota to the NAS in the RADIUS Access-Accept (4). At the
expiry of the allocated quota, the NAS sends a new RADIUS Access-
Request to the Home AAA server (5). This message contains the units
used this far. The units are reported to the Diameter credit-control
server in a Diameter Credit-Control-Request (UPDATE_REQUEST) (6). The
Diameter credit-control server debits the used units from the end
user's account and allocates a new quota that is returned to the Home
AAA server in the Diameter Credit-Control-Answer (7). The quota is
transferred to the NAS in the RADIUS Access-Accept (8). When the end
user terminates the service the NAS sends a RADIUS Access-Request (9).
To debit the used units from the end user's account and to stop the
credit control session, the Home AAA server sends a Diameter Credit-
Control-Request (TERMINATION_REQUEST) to the credit-control server
(10). The Diameter credit-control server acknowledges the session
termination by sending a Diameter Credit-Control-Answer to the Home
AAA server (11). The RADIUS Access-Accept is sent to the NAS (12).
A.3 Flow III
SIP Proxy/Registrar AAA
A (CC Client) Server B CC Server
|(i) REGISTER | | | |
|------------->|(ii) | | |
| |------------->| | |
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| |authentication & | |
| |authorization | | |
| |<-------------| | |
|(iii)200 OK | | |
|<-------------| | |
: : : :
|(1) INVITE | :
|------------->|
| |(2) CCR (Intial, SIP specific AVP) |
| |------------------------------------------->|
| |(3) CCA (granted_Units) |
| |<-------------------------------------------|
| |(4) INVITE | |
| |---------------------------->| |
: : : :
| |(5) CCR (update, used Units) |
| |------------------------------------------->|
| |(6) CCA (granted_Units) |
| |<-------------------------------------------|
: : : :
|(7) BYE | | |
|------------->| | |
| |(8) BYE | |
| |---------------------------->| |
| |(9) CCR (termination, used Units)----------|
| |------------------------------------------->|
| |(10) CCA () |
| |<-------------------------------------------|
| | | |
Figure A.3: Flow III
The end user (SIP User Agent A) sends REGISTER with credentials (i).
The SIP Proxy sends a request to the AAA server to perform Multimedia
authentication and authorization by using for instance Diameter
Multimedia application (ii). The AAA server checks that the
credentials are correct and checks the user profile. Eventually, 200
OK response (iii) is sent to the UA. Note that the Authentication and
Authorization is valid for the registration validity period duration
(i.e. until re-registration is performed), of several SIP sessions may
be established without re-authorization is performed.
UA A sends an INVITE (1). The SIP Proxy sends a Diameter Credit-
Control-Request (INITIAL_REQUEST) to the Diameter credit-control
server (2). The Credit-Control-Request contains information obtained
from the SIP signaling describing the requested service (e.g. calling
party, called party, Session Description Protocol attributes). The
Diameter credit-control server checks the end user's account balance,
rates the service and reserves credit from the end user's account. The
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Diameter Credit Control Application December 2003
reserved quota is returned to the SIP Proxy in the Diameter Credit-
Control-Answer (3). The SIP Proxy forwards the SIP INVITE to UA B (4).
B's phone rings, and B answers. The media flows between them and the
SIP Proxy starts measuring the quota. At the expiry of the allocated
quota, the SIP Proxy sends a Diameter Credit-Control-Request
(UPDATE_REQUEST) to the Diameter credit-control server (5). This
message contains the units used this far. The Diameter credit-control
server debits the used units from the end user's account and allocates
new credit that is returned to the Sip Proxy in the Diameter Credit-
Control-Answer (6). The end user terminates the service by sending a
BYE (7). The SIP Proxy forwards the BYE message to UA B (8) and sends
a Diameter Credit-Control-Request (TERMINATION_REQUEST) to the Credit-
control server (9). The Diameter Credit-control server acknowledges
the session termination by sending a Diameter Credit-Control-Answer to
the SIP Proxy (10).
A.4 Flow IV
MMS Server
A (CC Client) B CC Server
|(1) Send MMS | | |
|--------------->| | |
| |(2) CCR (event, DIRECT_DEBITING,|
| | MMS specific AVP) |
| |-------------------------------->|
| |(3) CCA (granted_Units) |
| |<--------------------------------|
|(4) Send MMS Ack| | |
|<---------------| | |
| |(5) Notify MMS | |
| |--------------->| |
: : : :
| |(6) Retrieve MMS| |
| |<---------------| |
| |(7) Retrieve MMS| |
| | Ack | |
| |--------------->| |
| | | |
Figure A.4: Flow IV
A credit control flow for Multimedia Messaging Services is shown in
Figure A.4. The sender is charged as soon as the messaging server
successfully stores the message.
The end user A sends a Multimedia Message (MMS) to the MMS Server (1).
The MMS Server stores the message and sends a Diameter Credit-Control-
Request (EVENT_REQUEST with Requested-Action: DIRECT_DEBITING) to the
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Diameter credit-control server (2). The Credit-Control-Request
contains information about the MMS message (e.g. size, recipient
address, image coding type). The Diameter credit-control server checks
the end user's account balance, rates the service and debits the
service from the end user's account. The granted quota is returned to
the MMS Server in the Diameter Credit-Control-Answer (3). The MMS
Server acknowledges the successful reception of the MMS message (4).
The MMS Server notifies the recipient about the new MMS (5), and the
end user B retrieves the message from the MMS message store (6),(7).
A.5 Flow V
MMS Server
Content Server (CC Client) B CC Server
|(1) Send MMS | | |
|--------------->| | |
| |(2) CCR (event, BALANCE_CHECK, |
| | MMS specific AVP) |
| |-------------------------------->|
| |(3) CCA (OK) |
| |<--------------------------------|
|(4) Send MMS Ack| | |
|<---------------| | |
| |(5) Notify MMS | |
| |--------------->| |
: : : :
| |(6) Retrieve MMS| |
| |<---------------| |
| |(7) CCR (event, DIRECT_DEBITING,|
| | MMS specific AVP) |
| |-------------------------------->|
| |(8) CCA (granted_Units) |
| |<--------------------------------|
| |(9) Retrieve MMS| |
| | Ack | |
| |--------------->| |
| | | |
Figure A.5: Flow V
A credit control flow for Multimedia Messaging Service is shown in
Figure A.5. The recipient is charged at the message delivery.
A Content Server sends a Multimedia Message (MMS) to the MMS Server
(1) that stores the message. The message recipient will be charged for
the MMS message in this case. Since there can be substantially long
time between the reception of the message at the MMS Server and the
actual retrieval of the message, the MMS Server does not establish any
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credit control session to the Diameter Credit-Control Server but
performs first only a balance check (without any credit reservation)
by sending a Diameter Credit-Control-Request (EVENT_REQUEST with
Requested-Action: BALANCE_CHECK) to verify that the end user B's can
cover the cost for the MMS (2). The Diameter credit-control server
checks the end user's account balance and returns the answer to the
MMS Server in the Diameter Credit-Control-Answer (3). The MMS Server
acknowledges the successful reception of the MMS message (4). The MMS
Server notifies the recipient about the new MMS (5), and after some
time the end user B retrieves the message from the MMS message store
(6). The MMS Server sends a Diameter Credit-Control-Request
(EVENT_REQUEST with Requested-Action: DIRECT_DEBITING) to the Diameter
Credit-control server (7). The Credit-Control-Request contains
information about the MMS message (e.g. size, recipient address,
coding type). The Diameter credit-control server checks the end user's
account balance, rates the service and debits the service from the end
user's account. The granted quota is returned to the MMS Server in the
Diameter Credit-Control-Request (8). The MMS is transferred to the end
user B (9).
A.6 Flow VI
SIP Controller
A (CC Client) B CC Server
|(1)INVITE(SDP) | | |
|--------------->| | |
| |(2) CCR (event, PRICE_ENQUIRY, |
| | SIP specific AVPs) |
| |-------------------------------->|
| |(3) CCA (Cost-Information) |
| |<--------------------------------|
| (4)MESSAGE(URL)| | |
|<---------------| | |
|(5)HTTP GET | | |
|--------------->| | |
|(6)HTTP POST | | |
|--------------->|(7)INVITE(SDP) | |
| |--------------->| |
| | (8)200 OK | |
| (9)200 OK |<---------------| |
|<---------------| | |
Figure A.6: Flow VI
Figure A.6 is an example of Advice of Charge (AoC) service for SIP
call, the user A can be either postpaid or prepaid subscriber using
the AoC service. It is assumed that the SIP Controller also has HTTP
capabilities and delivers an interactive AoC web page with for
instance the cost information, the details of the call derived from
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the SDP and a button to accetp/not accept the charges (there may be
many other ways to deliver AoC information, however, this flow focus
on the use of the credit control messages). The user has been
authenticated and authorized prior to initiate the call and subscribed
to AoC service.
UA A sends an INVITE with SDP (1). The SIP controller determines the
user is subscribed to AoC service and sends a Diameter Credit-Conrol-
Request (EVENT_REQUEST with Requested-Action: PRICE_ENQUIRY) to the
Diameter credit control server (2). The Credit-Control-Request
contains SIP specific AVPs derived from the SIP signaling describing
the requested service (e.g. calling party, called party, Session
Description Protocol attributes). The Diameter credit control server
determines the cost of the service and returns the Credit-Control-
Answer including the Cost-Information AVP (3). The SIP controller
manufactures the AoC web page with information received in SIP
signaling and with the cost information received from the credit
control server, then sends a SIP MESSAGE that contains a URL pointing
to the AoC information web page (4). At the reception of the SIP
MESSAGE the A's UA invokes automatically the web browser that
retrieves the AoC information (5). The user clicks on a proper button
and accept the charges (6). The SIP controller continues the session
and sends the INVITE to the B party that accepts the call (7,8,9).
A.7 Flow VII
Gaming Server
End-User (CC Client) CC Server
| (1)Service Delivery | |
|<---------------------->| |
: : :
: : :
| |(2)CCR(event,REFUND,Requested-
| |Service-Unit,Service-Parameter-Info)
| |----------------------->|
| | (3)CCA(Cost-Information)
| |<-----------------------|
| (4)Notification | |
|<-----------------------| |
Figure A.7: Flow VII
Figure A.7 illustrates a credit control flow for the REFUND case. It
is assumed that trusted relationship and secure connection between the
Gaming server and the Diameter credit control server exist. The end
user may be a prepaid subscriber or a postpaid subscriber.
While the end user is playing the game (1) she enters a new level that
entitles for a bonus. The Gaming server sends a Diameter Credit-
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Diameter Credit Control Application December 2003
Conrol-Request (EVENT_REQUEST with Requested-Action: REFUND) to the
Diameter credit control server (2). The Credit-Control-Request
contains the Requested-Service-Unit AVP with Unit-Type set to
CREDIT_TYPE_SERVICE_SPECIFIC and Unit-Value set to the number of
points the user just won. The Service-Parameter-Info AVP is also
included in the request and specifies the service event to be rated
(e.g. Tetris Bonus). The Diameter credit control server, based on
received information, determines the amount to be credited, refunds
the user's account and returns the Credit-Control-Answer including the
Cost-Information AVP (3). The Cost-Information indicates the credited
amount. At the first opportunity the Gaming server notify the end user
of the credited amount (4).
A.8 Flow VIII
SIP Controller Top-UP
A (CC Client) Server B CC Server
| | | | |
| | (1) CCR(Update,Used-Unit) | |
| |------------------------------------------>|
| | (2) CCA(Final-Unit, Redirect)|
| |<------------------------------------------|
: : : : :
: : : : :
| | (3) CCR(Update, Used-Units)| |
| |------------------------------------------>|
| | (3a)INVITE("hold") | |
| |--------------------------->| |
| | | (4) CCA(Validity-Time)|
| |<------------------------------------------|
| (5)INVITE | (6)INVITE | | |
|<--------------|------------->| | |
| (7)RTP | | |
|..............................| | |
| | (8)BYE | | |
| |<-------------| | |
| | (9)CCR(Update) | |
| |------------------------------------------>|
| | (10)CCA(Granted-Unit) |
| |<------------------------------------------|
| (12)INVITE | (11)INVITE | |
|<--------------|--------------------------->| |
Figure A.8: Flow VIII
Figure A.8 is an example of the graceful service termination for a SIP
call. It is assumed the call is set up so that the controller is in
the call as a B2BUA (Back to Back User Agent). Note that the SIP
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Diameter Credit Control Application December 2003
signaling is inaccurate since the focus of this flow is in the
graceful service termination and credit control authorization.
The call is ongoing between user A and user B, user A is a prepaid
user. At the expiry of the allocated quota, the SIP controller sends a
Diameter Credit-Control-Request (UPDATE_REQUEST) to the Diameter
credit control server (1). This message contains the units used this
far. The Diameter credit control server debits the used units from the
end user's account and allocates the final quota that is returned to
the SIP controller in the Diameter Credit-Control-Answer (2). This
message contains the Final-Unit-Indication AVP with: the Final-Unit-
Action set to REDIRECT, the Redirect-Address-Type set to SIP URI and
the Redirect-Server-Address set to the Top-up server name (e.g.
sip:sip-topup-server@domain.com). At the expiry of the final allocated
quota, the SIP controller sends a Diameter Credit-Control-Request
(UPDATE_REQUEST) to the Diameter credit control server (3) and places
the called party on "hold" by sending an INVITE with the appropriate
connection address in the SDP (3a). The Credit-Control-Request message
contains the units used this far. The Diameter credit control server
debits the used units from the end user's account but does not make
any credit reservation. The Credit-Control-Answer message, that
contains the Validity-Time to supervise the graceful service
termination, is returned to the SIP controller (4). The SIP controller
establishes a SIP session between the prepaid user and the Top-up
server (5, 6). The Top-up server plays an announcement and prompts the
user to enter a credit card number and the amount of money to be used
to replenish the account (7). The Top-up server validates the credit
card number and replenishes the user's account (using some means
outside the scope of this specification) and releases the SIP session
(8). The SIP controller can now assume that communication between the
prepaid user and the Top-up server took place and thus sends a
spontaneous Credit-Control-Request (UPDATE_REQUEST) to the Diameter
credit control server to check if the account has been replenished
(9). The Diameter credit control server reserves credit from the end
user's account and return the reserved quota to the SIP controller in
the Credit-Control-Answer (10). At this point, the SIP controller re-
connects the caller and the called party (11,12).
A.9 Flow IX
End-User NAS AAA Server Top-up CC Server
(CC Client) Server
|(1)User Logon |(2)AA Request (CC AVPs) | |
|------------------>|------------------->| | |
| | |(3)CCR(initial, CC AVPs)
| | |------------------->|
| | |(4)CCA(Final-Unit, |
| | | Validity-Time)|
| | |<-------------------|
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Diameter Credit Control Application December 2003
| |(5)AA Answer(Final-Unit,Validity-Time) |
|(6)Limited Access |<-------------------| | |
| granted | | | |
|<----------------->| | | |
| | | | |
| (7)TCP/HTTP | (8)TCP/HTTP | |
|<----------------->|<----------------------------->| |
| (9) Replenish account | |
|<------------------------------------------------->| |
| | | (10)RAR |
| |<-------------------|<-------------------|
| | (11) RAA | |
| |------------------->|------------------->|
| |(12)CCR(update) | |
| |------------------->|(13)CCR(Update) |
| | |------------------->|
| | |(14)CCA(granted Units)
| |(15)CCA(granted Units)<------------------|
| |<-------------------| |
Figure A.9: Flow IX
Figure A.9 is an example of the graceful service termination initiated
when the first interrogation take place due to user's account is
empty. In this example the credit control server supports the server
initiated credit re-authorization. The Diameter [NASREQ] is
implemented in the Network Access Server (NAS).
The user logs onto the network (1). The Diameter NAS first sends a
Diameter Authorization-Authentication-Request to the home AAA Server,
the credit-control client populates the AAR with the Credit-Control
AVP set to CREDIT_AUTHORIZATION and service specific AVPs are included
as usual [NASREQ]. The home AAA server performs service specific
Authentication and Authorization as usual. The AAA server determines
that the user is a prepaid user and notices from the Credit-Control
AVP that the NAS has credit control capabilities, it sends a Diameter
Credit-Control-Request with CC-Request-Type set to INITIAL_REQUEST to
the Diameter credit-control server to perform credit authorization (3)
and to establish a credit control session (the AAA server may forward
service specific AVPs as received from the NAS as input for the rating
process). The Diameter credit-control server checks the end user's
account balance, determines that the account cannot cover the cost of
the sevice and initiates the graceful service termination. The Credit-
Control-Answer is returned to the Home AAA server (4). This message
contains the Final-Unit-Indication AVP and the Validity-Time AVP set
to a reasonable time to give chance to the user to replenish his/her
account (e.g. 10 minutes). The Final-Unit-Indication AVP includes: the
Final-Unit-Actioin set to REDIRECT, the Redirect-Address-Type set to
ULR and the Redirect-Server-Address set to the HTTP Top-up server
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Diameter Credit Control Application December 2003
name. The Home AAA server sends the received credit control AVPs to
the NAS in the Diameter Authorization-Authentication-Answer (5). Upon
successful AAA the NAS starts the credit-control session and starts
immediately the graceful service termination as instructed by the
server. The NAS grant limited access to the user (6). The HTTP client
software running in the user's device opens the transport connection
that is redirected by the NAS to the Top-up server (7,8). The user is
displayed an appropriate web page where to enter the credit card
number, the amount of money to be used to replenish the account and
with a notification message that she will be granted unlimited access
if the replenishment operation will be successfully executed within
the next e.g. 10 minutes. The Top-up server validates the credit card
number and replenishes the user's account (using some means outside
the scope of this specification)(9). After successful account top-up
the credit control server sends a Re-Auth-Request message to the NAS
(10). The NAS acknowledges the request by returning the Re-Auth-Answer
message (11) and initiates the credit re-authorization by sending a
Credit-Control-request (UPDATE_REQUEST) to the Diameter credit control
server (12,13).
The Diameter credit control server reserves credit from the end user's
account and return the reserved quota to the NAS via the Home AAA
server in the Credit-Control-Answer (14,15). The NAS removes the
restriction placed by the graceful service termination and starts
monitoring the granted units.
A.10 Flow X
The Diameter Credit Control Application defines the Rating-Group and
Service-Identifier AVPs that can be used to support credit control for
multiple services in a single credit control session for service
elements that have such capabilities. The flow example hereafter
illustrates the usage of these AVPs.
It is assumed that the Service-Identifiers and the Rating-Groups are
locally configured in the Service Element or provisioned by another
entity than the credit control server.
The credit control client may request credit authorization either for
all the possible configured Rating-Groups in one single request,
onwards named all-in-one mode, or for a single Rating-Group upon an
external triggering event, onwards named on-demand mode. The on-demand
mode can be used as well to request individual credit resource limit
for each service.
In this example only the all-in-one mode is shown.
A single credit reservation is kept for the credit control session to
simplify the account management tasks. The credit control server
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Diameter Credit Control Application December 2003
reserves an amount of credit from the user's account and performs
rating for all the requested Rating-Groups and Service-Identifiers
against the reserved credit.
For instance, assume a Credit-Control-Request is received with Rating-
Group-Id 1 and 2. The credit control server queries the rating server
that answers with the following rating parameters: Rating-Group 1
costs $1/Mbyte and Rating-Group 2 costs $1/minute. The credit control
server reserves $20 from the user's account; this gives 20Mbytes for
Rating-Group 1 and 20minutes for Rating-Group 2.
The calculated quotas are conveyed to the credit control client in the
CCA message, each quota associated with the appropriate Rating-Group
or Service-Identifier. At this point the credit control client just
need to track the fraction of reserved credit used by the
corresponding service or Rating-Group, when the sum of the fractions
reaches 100% the credit control client sends an intermediate
interrogation since the whole amount of reserved credit is consumed.
If the credit control client initializes a counter C for each of the
received quota Q (C1 for Q1, C2 for Q2 ... Cn for Qn), the
intermediate interrogation will be sent when (C1/Q1 + C1/Q2 + ... +
Cn/Qn)>= 1.
Continuing the example, the end user uses 10 Mbytes from Rating-Group
1 and 10minutes from Rating-Group 2. This means that Rating-Group 1
consumed 50% of the reservation and Rating-Group 2 consumed the
remaining 50%. 0.5 + 0.5 >=1, so the credit control client sends an
intermediate interrogation to report the used units and request new
ones.
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Diameter Credit Control Application December 2003
Service Element
End-User (CC client) CC Server
|(1)User logon | |
|------------------>|(2)CCR(initial,Requested-Units(Rating-Group 1),
| | Requested-Units(Rating-Group 2)) |
| |---------------------------------------->|
| |(3)CCA(Granted-Units(Rating-Group 1, |
| | Total-Octets)) |
| | Granted-Units(Rating-Group 2, |
| | Time)) |
| |<----------------------------------------|
: : :
|(4)Service-Request (Service 1) |
|------------------>| |
: : :
|(5)Service-Request (Service 2) |
|------------------>| |
: : :
| |(6)CCR(update, Used-Units(Input-Octets, |
| | Output-Octets, |
| | Service-Id 1, |
| | Rating-Group 1),
| | Used-Units(Time, |
| | Service-Id 2, |
| | Rating-Group 2),
| | Requested-Units(Rating-G.1),
| | Requested-Units(Rating-G.2))
| |---------------------------------------->|
| |(7)CCA(Granted-Units(Rating-Group 1, |
| | Total-Octets), |
| | Granted-Units(Rating-Group 2, |
| | Time)) |
| |<----------------------------------------|
: : :
|(8)Service-Request (Service 3) |
|------------------>| |
: : :
|(9) User logoff | |
|------------------>|(10)CCR(term, Used-Units(Input-Octets, |
| | Output-Octets, |
| | Service-Id 1, |
| | Rating-Group 1),|
| | Used-Units(Input-Octets, |
| | Output-Octets, |
| | Service-Id 3, |
| | Rating-Group 1),|
| | Used-Units(Time, |
| | Service-Id 2, |
| | Rating-Group 2),|
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Diameter Credit Control Application December 2003
| |---------------------------------------->|
| |(11)CCA(term) |
| |<----------------------------------------|
Figure A.10: Credit Control for Multiple Services in One Credit
Control Session, flow example
The user logs onto the network (1). The Service Element sends a
Diameter Credit-Control-Request with CC-Request-Type set to
INITIAL_REQUEST to the Diameter credit-control server to perform
credit authorization for multiple rating groups and to establish a
credit control session (2). In this message credit authorization is
requested for Rating-Group 1 and Rating-Group 2 by including two
instances of the Requested-Service-Unit AVP. The Diameter credit-
control server checks the end user's account balance, based on the
Rating-Group information rates the request and reserves credit from
the end user's account. Multiple quotas are returned to the Service
Element, each associated with the relevant Rating-Group (3). The user
uses service 1 and service 2 (4, 5). The service 1 belongs to Rating-
Group 1 and is volume based charged, the service 2 belongs to Rating-
Group 2 and is time based charged. When the user has consumed the
allotted credit, the Service Element sends a Diameter Credit-Control-
Request with CC-Request-Type set to UPDATE_REQUEST to the credit
control server (6). This message contains the units consumed by each
of the used services in the Used-Service-Unit AVPs and two instances
of the Requested-Service-Unit AVP to request credit re-authorization
for the two Rating-Groups. The used units are associated with the
relevant Service-Identifier and Rating-Group.
The Diameter credit-control server debits the used units from the end
user's account and reserves a new amount of credit that is returned in
form of multiple quotas to the Service Element in the Diameter Credit-
Control-Answer (7). Each quota is associated with the relevant Rating-
Group. In addition to service 1 and service 2, the user now starts
using service 3 (8). Service 3 belongs to Rating-Group 1 and is
charged based on volume. The end user logs off from the network (9).
To debit the used units from the end user's account and to stop the
credit control session, the Service Element sends a Diameter Credit-
Control-Request with CC-Request-Type set to TERMINATION_REQUEST to the
credit control server (10).
This message contains the units consumed by each of the used services
in the Used-Service-Unit AVPs. The used units are associated with the
relevant Service-Identifier and Rating-Group. The Diameter credit-
control server debits the used units to the user's account and
acknowledges the session termination by sending a Diameter Credit-
Control-Answer to the Service Element (11).
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