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Internet Engineering Task Force (IETF) L. Bertz, Ed.
Request for Comments: 8506 Sprint
Obsoletes: 4006 D. Dolson, Ed.
Category: Standards Track Y. Lifshitz, Ed.
ISSN: 2070-1721 Sandvine
March 2019
Diameter Credit-Control Application
Abstract
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end-user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services. The Diameter Credit-
Control application as defined in this document obsoletes RFC 4006,
and it must be supported by all new Diameter Credit-Control
application implementations.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8506.
Bertz, et al. Standards Track [Page 1]
RFC 8506 Diameter Credit-Control Application March 2019
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Bertz, et al. Standards Track [Page 2]
RFC 8506 Diameter Credit-Control Application March 2019
Table of Contents
1. Introduction ....................................................6
1.1. Requirements Language ......................................7
1.2. Terminology ................................................7
1.3. Advertising Application Support ............................9
2. Architecture Models .............................................9
3. Credit-Control Messages ........................................11
3.1. Credit-Control-Request (CCR) Command ......................11
3.2. Credit-Control-Answer (CCA) Command .......................12
4. Credit-Control Application Overview ............................13
4.1. Service-Specific Rating Input and Interoperability ........14
4.1.1. Specifying Rating Input AVPs .......................15
4.1.2. Service-Specific Documentation .....................16
4.1.3. Handling of Unsupported/Incorrect Rating Input .....16
4.1.4. RADIUS Vendor-Specific Rating Attributes ...........17
5. Session-Based Credit-Control ...................................17
5.1. General Principles ........................................17
5.1.1. Basic Support for Tariff Time Change ...............18
5.1.2. Credit-Control for Multiple Services within
a (Sub-)Session ....................................19
5.2. First Interrogation .......................................23
5.2.1. First Interrogation after Authorization and
Authentication .....................................25
5.2.2. First Interrogation Included with
Authorization Messages .............................27
5.3. Intermediate Interrogation ................................29
5.4. Final Interrogation .......................................31
5.5. Server-Initiated Credit Re-authorization ..................32
5.6. Graceful Service Termination ..............................34
5.6.1. Terminate Action ...................................37
5.6.2. Redirect Action ....................................38
5.6.3. Restrict Access Action .............................40
5.6.4. Usage of the Server-Initiated Credit
Re-authorization ...................................41
5.7. Failure Procedures ........................................41
6. One-Time Event .................................................44
6.1. Service Price Inquiry .....................................45
6.2. Balance Checks ............................................46
6.3. Direct Debiting ...........................................46
6.4. Refunds ...................................................47
6.5. Failure Procedure .........................................48
7. Credit-Control Application State Machines ......................50
8. Credit-Control AVPs ............................................59
8.1. CC-Correlation-Id AVP .....................................61
8.2. CC-Request-Number AVP .....................................62
8.3. CC-Request-Type AVP .......................................62
8.4. CC-Session-Failover AVP ...................................63
Bertz, et al. Standards Track [Page 3]
RFC 8506 Diameter Credit-Control Application March 2019
8.5. CC-Sub-Session-Id AVP .....................................64
8.6. Check-Balance-Result AVP ..................................64
8.7. Cost-Information AVP ......................................64
8.8. Unit-Value AVP ............................................65
8.9. Exponent AVP ..............................................65
8.10. Value-Digits AVP .........................................66
8.11. Currency-Code AVP ........................................66
8.12. Cost-Unit AVP ............................................66
8.13. Credit-Control AVP .......................................66
8.14. Credit-Control-Failure-Handling AVP (CCFH) ...............67
8.15. Direct-Debiting-Failure-Handling AVP (DDFH) ..............68
8.16. Multiple-Services-Credit-Control AVP .....................68
8.17. Granted-Service-Unit AVP .................................70
8.18. Requested-Service-Unit AVP ...............................71
8.19. Used-Service-Unit AVP ....................................71
8.20. Tariff-Time-Change AVP ...................................72
8.21. CC-Time AVP ..............................................72
8.22. CC-Money AVP .............................................72
8.23. CC-Total-Octets AVP ......................................72
8.24. CC-Input-Octets AVP ......................................72
8.25. CC-Output-Octets AVP .....................................73
8.26. CC-Service-Specific-Units AVP ............................73
8.27. Tariff-Change-Usage AVP ..................................73
8.28. Service-Identifier AVP ...................................74
8.29. Rating-Group AVP .........................................74
8.30. G-S-U-Pool-Reference AVP .................................74
8.31. G-S-U-Pool-Identifier AVP ................................75
8.32. CC-Unit-Type AVP .........................................75
8.33. Validity-Time AVP ........................................75
8.34. Final-Unit-Indication AVP ................................76
8.35. Final-Unit-Action AVP ....................................77
8.36. Restriction-Filter-Rule AVP ..............................78
8.37. Redirect-Server AVP ......................................78
8.38. Redirect-Address-Type AVP ................................79
8.39. Redirect-Server-Address AVP ..............................79
8.40. Multiple-Services-Indicator AVP ..........................80
8.41. Requested-Action AVP .....................................80
8.42. Service-Context-Id AVP ...................................81
8.43. Service-Parameter-Info AVP ...............................82
8.44. Service-Parameter-Type AVP ...............................82
8.45. Service-Parameter-Value AVP ..............................83
8.46. Subscription-Id AVP ......................................83
8.47. Subscription-Id-Type AVP .................................83
8.48. Subscription-Id-Data AVP .................................84
8.49. User-Equipment-Info AVP ..................................84
8.50. User-Equipment-Info-Type AVP .............................84
8.51. User-Equipment-Info-Value AVP ............................85
8.52. User-Equipment-Info-Extension AVP ........................85
Bertz, et al. Standards Track [Page 4]
RFC 8506 Diameter Credit-Control Application March 2019
8.53. User-Equipment-Info-IMEISV AVP ...........................86
8.54. User-Equipment-Info-MAC AVP ..............................86
8.55. User-Equipment-Info-EUI64 AVP ............................86
8.56. User-Equipment-Info-ModifiedEUI64 AVP ....................86
8.57. User-Equipment-Info-IMEI AVP .............................86
8.58. Subscription-Id-Extension AVP ............................87
8.59. Subscription-Id-E164 AVP .................................87
8.60. Subscription-Id-IMSI AVP .................................87
8.61. Subscription-Id-SIP-URI AVP ..............................88
8.62. Subscription-Id-NAI AVP ..................................88
8.63. Subscription-Id-Private AVP ..............................88
8.64. Redirect-Server-Extension AVP ............................88
8.65. Redirect-Address-IPAddress AVP ...........................89
8.66. Redirect-Address-URL AVP .................................89
8.67. Redirect-Address-SIP-URI AVP .............................89
8.68. QoS-Final-Unit-Indication AVP ............................89
9. Result-Code AVP Values .........................................91
9.1. Transient Failures ........................................91
9.2. Permanent Failures ........................................92
10. AVP Occurrence Table ..........................................92
10.1. Credit-Control AVP Table .................................93
10.2. Re-Auth-Request/Re-Auth-Answer AVP Table .................94
11. RADIUS/Diameter Credit-Control Interworking Model .............94
12. IANA Considerations ...........................................97
12.1. Application Identifier ...................................97
12.2. Command Codes ............................................97
12.3. AVP Codes ................................................97
12.4. Result-Code AVP Values ...................................98
12.5. CC-Request-Type AVP ......................................98
12.6. CC-Session-Failover AVP ..................................98
12.7. CC-Unit-Type AVP .........................................99
12.8. Check-Balance-Result AVP .................................99
12.9. Credit-Control AVP .......................................99
12.10. Credit-Control-Failure-Handling AVP .....................99
12.11. Direct-Debiting-Failure-Handling AVP ....................99
12.12. Final-Unit-Action AVP ...................................99
12.13. Multiple-Services-Indicator AVP ........................100
12.14. Redirect-Address-Type AVP ..............................100
12.15. Requested-Action AVP ...................................100
12.16. Subscription-Id-Type AVP ...............................100
12.17. Tariff-Change-Usage AVP ................................100
12.18. User-Equipment-Info-Type AVP ...........................100
13. Parameters Related to the Credit-Control Application .........101
14. Security Considerations ......................................101
14.1. Direct Connection with Redirects ........................102
14.2. Application-Level Redirects .............................103
Bertz, et al. Standards Track [Page 5]
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15. Privacy Considerations .......................................104
15.1. Privacy-Sensitive AVPs ..................................104
15.2. Data Minimization .......................................106
15.3. Diameter Agents .........................................107
16. References ...................................................107
16.1. Normative References ....................................107
16.2. Informative References ..................................110
Appendix A. Credit-Control Sequences .............................111
A.1. Flow I ....................................................111
A.2. Flow II ...................................................113
A.3. Flow III ..................................................116
A.4. Flow IV ...................................................117
A.5. Flow V ....................................................119
A.6. Flow VI ...................................................120
A.7. Flow VII ..................................................121
A.8. Flow VIII .................................................123
A.9. Flow IX ...................................................124
Acknowledgements .................................................130
Authors' Addresses ...............................................130
1. Introduction
This document specifies a Diameter application that can be used to
implement real-time credit-control for a variety of end-user services
such as network access, Session Initiation Protocol (SIP) services,
messaging services, and download services. ("Credit-control" is
sometimes abbreviated as "CC" in figures and tables throughout this
document.) The Diameter Credit-Control application as defined in
this document obsoletes [RFC4006], and it must be supported by all
new Diameter Credit-Control application implementations. This
document provides a general solution to real-time cost and
credit-control.
The prepaid model has been shown to be very successful -- for
instance, in GSM networks, where network operators offering prepaid
services have experienced a substantial growth of their customer base
and revenues. Prepaid services are now cropping up in many other
wireless and wire-line-based networks.
In mobile networks, additional functionality is required beyond that
specified in the Diameter base protocol [RFC6733]. For example, the
3GPP charging and billing requirements document [TGPPCHARG] states
that an application must be able to rate service information in
real time. In addition, it is necessary to check that the end user's
account provides coverage for the requested service prior to
initiation of that service. When an account is exhausted or expired,
the user must be denied the ability to compile additional chargeable
events.
Bertz, et al. Standards Track [Page 6]
RFC 8506 Diameter Credit-Control Application March 2019
A mechanism has to be provided to allow the user to be informed of
the charges to be levied for a requested service. In addition, there
are services such as gaming and advertising that may credit as well
as debit a user account.
The other Diameter applications provide service-specific
authorization, and they do not provide credit authorization for
prepaid users. The credit authorization shall be generic and
applicable to all the service environments required to support
prepaid services.
To fulfill these requirements, it is necessary to facilitate
credit-control communication between the network element providing
the service (e.g., Network Access Server (NAS), SIP Proxy,
Application Server) and a credit-control server.
The scope of this specification is credit authorization. Service-
specific authorization and authentication are out of scope.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Terminology
AAA: Authentication, Authorization, and Accounting.
AA-Answer: "AA-Answer" generically refers to a service-specific
authorization and authentication answer. AA-Answer commands are
defined in service-specific authorization applications, e.g.,
[RFC7155] [RFC4004].
AA-Request: "AA-Request" generically refers to a service-specific
authorization and authentication request. AA-Request commands are
defined in service-specific authorization applications, e.g.,
[RFC7155] [RFC4004].
Credit-control: "Credit-control" is a mechanism that directly
interacts in real time with an account and controls or monitors
the charges related to service usage. Credit-control is a
process of (1) checking whether or not credit is available,
(2) credit reservation, (3) deduction of credit from the end-user
account when service is completed, and (4) refunding of reserved
credit that is not used.
Bertz, et al. Standards Track [Page 7]
RFC 8506 Diameter Credit-Control Application March 2019
Diameter Credit-Control server: A Diameter Credit-Control server
acts as a prepaid server, performing real-time rating and
credit-control. It is located in the home domain and is accessed
by Service Elements or Diameter AAA servers in real time, for the
purpose of price determination and credit-control before the
service event is delivered to the end user. It may also interact
with Business Support Systems.
Diameter Credit-Control client: A Diameter Credit-Control client is
an entity that interacts with a credit-control server. It
monitors the usage of the granted quota according to instructions
returned by the credit-control server.
Interrogation: The Diameter Credit-Control client uses interrogation
to initiate a session-based credit-control process. During the
credit-control process, it is used to report the used quota and
request a new one. An interrogation maps to a request/answer
transaction.
One-time event: A charging transaction session comprising a single
request and single response.
Rating: The act of determining the cost of the service event.
Service: A type of task performed by a Service Element for an
end user.
Service Element: A network element that provides a service to the
end users. The Service Element may include the Diameter
Credit-Control client or another entity (e.g., a RADIUS AAA
server) that can act as a credit-control client on behalf of the
Service Element. In the latter case, the interface between the
Service Element and the Diameter Credit-Control client is outside
the scope of this specification. Examples of Service Elements
include NASs, SIP Proxies, and Application Servers such as
messaging servers, content servers, and gaming servers.
Service event: An event relating to a service provided to the
end user.
Session-based credit-control: A credit-control process that makes
use of several interrogations: the first, a possible intermediate,
and the final. The first interrogation is used to reserve money
from the user's account and to initiate the process. Intermediate
interrogations (if any) may be needed to request a new quota while
the service is being rendered. The final interrogation is used to
exit the process. The credit-control server is required to
maintain session state for session-based credit-control.
Bertz, et al. Standards Track [Page 8]
RFC 8506 Diameter Credit-Control Application March 2019
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
commands [RFC6733].
2. Architecture Models
The current accounting models specified in the RADIUS accounting and
Diameter base specifications [RFC2866] [RFC6733] are not sufficient
for real-time credit-control, where creditworthiness is to be
determined prior to service initiation. Also, the existing Diameter
authorization applications [RFC7155] [RFC4004] only provide service
authorization; they do not provide credit authorization for prepaid
users. In order to support real-time credit-control, a new type of
server is needed in the AAA infrastructure: the Diameter
Credit-Control server. The Diameter Credit-Control server is the
entity responsible for credit authorization for prepaid subscribers.
A Service Element may authenticate and authorize the end user with
the AAA server by using AAA protocols, e.g., RADIUS or the Diameter
base protocol (possibly extended via a Diameter application).
Accounting protocols such as RADIUS accounting and the Diameter base
accounting protocol can be used to provide accounting data to the
accounting server after service is initiated and to provide possible
interim reports until service completion. However, for real-time
credit-control, these authorization and accounting models are not
sufficient.
When real-time credit-control is required, the credit-control client
contacts the credit-control server with information about a possible
service event. The credit-control process is performed to determine
potential charges and to verify whether the end user's account
balance is sufficient to cover the cost of the service being
rendered.
Figure 1 illustrates the typical credit-control architecture, which
consists of a Service Element with an embedded Diameter
Credit-Control client, a Diameter Credit-Control server, and a AAA
server. A Business Support System is usually deployed; at a minimum,
it includes billing functionality. The credit-control server and AAA
server in this architecture model are logical entities. The real
configuration can combine them into a single host. The
credit-control protocol is the Diameter base protocol [RFC6733] with
the Diameter Credit-Control application.
Bertz, et al. Standards Track [Page 9]
RFC 8506 Diameter Credit-Control Application March 2019
When an end user requests services such as SIP or messaging, the
request is typically forwarded to a Service Element (e.g., a SIP
Proxy) in the user's home realm as defined in [RFC6733]. In some
cases, it might be possible that the Service Element in the local
realm [RFC6733] can offer services to the end user; however, a
commercial agreement must exist between the local realm and the home
realm. Network access is an example of a service offered in the
local realm where the NAS, through a AAA infrastructure,
authenticates and authorizes the user with the user's home network.
Service Element AAA and CC
+----------+ +---------+ Protocols+-----------+ +--------+
| End |<---->|+-------+|<------------>| AAA | |Business|
| User | +->|| CC || | Server |->|Support |
| | | || Client||<-----+ | | |System |
+----------+ | |+-------+| | +-----------+ | |
| +---------+ | ^ +--------+
+----------+ | | CC Protocol | ^
| End |<--+ | +-----v----+ |
| User | +------>|Credit- | |
+----------+ Credit-Control |Control |--------+
Protocol |Server |
+----------+
Figure 1: Typical Credit-Control Architecture
There can be multiple credit-control servers in the system for
redundancy and load balancing. The system can also contain separate
rating server(s), and accounts can be located in a centralized
database. To ensure that the end user's account is not debited or
credited multiple times for the same service event, only one entity
in the credit-control system should perform duplicate detection.
System-internal interfaces can exist to relay messages between
servers and an account manager. However, the detailed architecture
of the credit-control system and its interfaces is implementation
specific and is out of scope for this specification.
Protocol-transparent Diameter relays can exist between the
credit-control client and credit-control server. Also, Diameter
redirect agents that refer credit-control clients to credit-control
servers and allow them to communicate directly can exist. These
agents transparently support the Diameter Credit-Control application.
The different roles of Diameter agents are defined in Diameter base
[RFC6733], Section 2.8.
If Diameter Credit-Control proxies exist between the credit-control
client and the credit-control server, they MUST advertise support for
the Diameter Credit-Control application.
Bertz, et al. Standards Track [Page 10]
RFC 8506 Diameter Credit-Control Application March 2019
3. Credit-Control Messages
This section defines new Diameter message Command Code values that
MUST be supported by all Diameter implementations that conform to
this specification. The Command Codes are as follows:
+------------------------+---------+------+-------------+
| Command Name | Abbrev. | Code | Reference |
+------------------------+---------+------+-------------+
| Credit-Control-Request | CCR | 272 | Section 3.1 |
| Credit-Control-Answer | CCA | 272 | Section 3.2 |
+------------------------+---------+------+-------------+
Table 1: Credit-Control Commands
Section 3.2 of [RFC6733] (Diameter base) defines the Command Code
Format specification. These formats are observed in credit-control
messages.
3.1. Credit-Control-Request (CCR) Command
The Credit-Control-Request message (CCR) is indicated by the Command
Code field being set to 272 and the 'R' bit being set in the Command
Flags field. It is used between the Diameter Credit-Control client
and the credit-control server to request credit authorization for a
given service.
The Auth-Application-Id MUST be set to the value 4, indicating the
Diameter Credit-Control application.
The CCR is extensible via the inclusion of one or more
Attribute-Value Pairs (AVPs).
Message Format:
<Credit-Control-Request> ::= < Diameter Header: 272, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Application-Id }
{ Service-Context-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ Destination-Host ]
[ User-Name ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
Bertz, et al. Standards Track [Page 11]
RFC 8506 Diameter Credit-Control Application March 2019
[ Origin-State-Id ]
[ Event-Timestamp ]
*[ Subscription-Id ]
*[ Subscription-Id-Extension ]
[ Service-Identifier ]
[ Termination-Cause ]
[ Requested-Service-Unit ]
[ Requested-Action ]
*[ Used-Service-Unit ]
[ Multiple-Services-Indicator ]
*[ Multiple-Services-Credit-Control ]
*[ Service-Parameter-Info ]
[ CC-Correlation-Id ]
[ User-Equipment-Info ]
[ User-Equipment-Info-Extension ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ AVP ]
3.2. Credit-Control-Answer (CCA) Command
The Credit-Control-Answer message (CCA) is indicated by the Command
Code field being set to 272 and the 'R' bit being cleared in the
Command Flags field. It is used between the credit-control server
and the Diameter Credit-Control client to acknowledge a
Credit-Control-Request command.
Message Format:
<Credit-Control-Answer> ::= < Diameter Header: 272, PXY >
< Session-Id >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
{ Auth-Application-Id }
{ CC-Request-Type }
{ CC-Request-Number }
[ User-Name ]
[ CC-Session-Failover ]
[ CC-Sub-Session-Id ]
[ Acct-Multi-Session-Id ]
[ Origin-State-Id ]
[ Event-Timestamp ]
[ Granted-Service-Unit ]
*[ Multiple-Services-Credit-Control ]
[ Cost-Information ]
[ Final-Unit-Indication ]
[ QoS-Final-Unit-Indication ]
Bertz, et al. Standards Track [Page 12]
RFC 8506 Diameter Credit-Control Application March 2019
[ Check-Balance-Result ]
[ Credit-Control-Failure-Handling ]
[ Direct-Debiting-Failure-Handling ]
[ Validity-Time ]
*[ Redirect-Host ]
[ Redirect-Host-Usage ]
[ Redirect-Max-Cache-Time ]
*[ Proxy-Info ]
*[ Route-Record ]
*[ Failed-AVP ]
*[ AVP ]
4. Credit-Control Application Overview
The credit authorization process takes place before and during
service delivery to the end user and generally requires the user's
authentication and authorization before any requests are sent to the
credit-control server. The credit-control application defined in
this specification supports two different credit authorization
models: credit authorization with money reservation and credit
authorization with direct debiting. In both models, the
credit-control client requests credit authorization from the
credit-control server prior to allowing any services to be delivered
to the end user.
In the first model, the credit-control server rates the request,
reserves a suitable amount of money from the user's account, and
returns the amount of credit reserved. Note that credit resources
may not imply actual monetary credit; credit resources may be granted
to the credit-control client in the form of units (e.g., data volume
or time) to be metered.
Upon receipt of a successful credit authorization answer with a
certain amount of credit resources, the credit-control client allows
service delivery to the end user and starts monitoring the usage of
the granted resources. When the credit resources granted to the user
have been consumed or the service has been successfully delivered or
terminated, the credit-control client reports back to the server the
used amount. The credit-control server deducts the used amount from
the end user's account; it may perform rating and make a new credit
reservation if the service delivery is continuing. This process is
accomplished with session-based credit-control that includes the
first interrogation, possible intermediate interrogations, and the
final interrogation. For session-based credit-control, both the
credit-control client and the credit-control server are required to
maintain credit-control session state. Session-based credit-control
is described in more detail, with more variations, in Section 5.
Bertz, et al. Standards Track [Page 13]
RFC 8506 Diameter Credit-Control Application March 2019
In contrast, credit authorization with direct debiting is a
single-transaction process wherein the credit-control server directly
deducts a suitable amount of money from the user's account as soon as
the credit authorization request is received. Upon receipt of a
successful credit authorization answer, the credit-control client
allows service delivery to the end user. This process is
accomplished with the one-time event. Session state is not
maintained.
In a multi-service environment, an end user can issue an additional
service request (e.g., data service) during an ongoing service (e.g.,
voice call) toward the same account. Alternatively, during an active
multimedia session, an additional media type is added to the session,
causing a new simultaneous request toward the same account.
Consequently, this needs to be considered when credit resources are
granted to the services.
The credit-control application also supports operations such as
service price inquiries, user's balance checks, and refunds of credit
on the user's account. These operations are accomplished with the
one-time event. Session state is not maintained.
Flexible failure handling, specific to the credit-control
application, is defined in the application. This allows the service
provider to control the credit-control client's behavior according to
its own risk management policy.
The Credit-Control-Failure-Handling AVP (also referred to as the
CCFH) and the Direct-Debiting-Failure-Handling AVP (also referred to
as the DDFH) are defined to determine what is done if the sending of
credit-control messages to the credit-control server has been
temporarily prevented. The usage of the CCFH and the DDFH allows
flexibility, as failure handling for the credit-control session and
one-time event direct debiting may be different.
4.1. Service-Specific Rating Input and Interoperability
The Diameter Credit-Control application defines the framework for
credit-control; it provides generic credit-control mechanisms
supporting multiple service applications. The credit-control
application therefore does not define AVPs that could be used as
input in the rating process. Listing the possible services that
could use this Diameter application is out of scope for this generic
mechanism.
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It is reasonable to expect that a service level agreement will exist
between providers of the credit-control client and the credit-control
server covering the charging, services offered, roaming agreements,
agreed-upon rating input (i.e., AVPs), and so on.
Therefore, it is assumed that a Diameter Credit-Control server will
provide service only for Diameter Credit-Control clients that have
agreed beforehand as to the content of credit-control messages.
Naturally, it is possible that any arbitrary Diameter Credit-Control
client can interchange credit-control messages with any Diameter
Credit-Control server, but with a higher likelihood that unsupported
services/AVPs could be present in the credit-control message, causing
the server to reject the request with an appropriate Result-Code.
4.1.1. Specifying Rating Input AVPs
There are two ways to provide rating input to the credit-control
server: by either using AVPs or including the rating input in the
Service-Parameter-Info AVP. The general principles for sending
rating parameters are as follows:
1. Using AVPs:
A. The service SHOULD reuse existing AVPs if it can use AVPs
defined in existing Diameter applications (e.g., [RFC7155]
for network access services). [RFC6733] strongly recommends
the reuse of existing AVPs.
For AVPs of type Enumerated, the service may require a new
value to be defined. Allocation of new AVP values is done as
specified in [RFC6733], Section 1.3.
B. New AVPs can be defined if the existing AVPs do not provide
sufficient rating information. In this case, the procedures
defined in [RFC6733] for creating new AVPs MUST be followed.
C. For services specific only to one vendor's implementation, a
vendor-specific AVP code for private use can be used. Where
a vendor-specific AVP is implemented by more than one vendor,
allocation of global AVPs is encouraged instead; refer to
[RFC6733].
2. The Service-Parameter-Info AVP MAY be used as a container to pass
legacy rating information in its original encoded form (e.g.,
ASN.1 BER). This method can be used to avoid unnecessary
conversions from an existing data format to an AVP format. In
this case, the rating input is embedded in the Service-Parameter-
Info AVP as defined in Section 8.43.
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New service applications SHOULD favor the use of explicitly defined
AVPs as described in items 1a and 1b, to simplify interoperability.
4.1.2. Service-Specific Documentation
The service-specific rating input AVPs, and the contents of the
Service-Parameter-Info AVP or Service-Context-Id AVP (defined in
Section 8.42), are not within the scope of this document. To
facilitate interoperability, it is RECOMMENDED that the rating input
and the values of the Service-Context-Id be coordinated via an
informational RFC or other permanent and readily available reference
(preferably that of another cooperative standardization body, e.g.,
3GPP, the Open Mobile Alliance (OMA), or 3GPP2). However, private
services may be deployed that are subject to agreements between
providers of the credit-control server and client. In this case,
vendor-specific AVPs can be used.
This specification, together with the above-mentioned service-
specific documents, governs the credit-control message. Service-
specific documents (i.e., those documents that do not define new
credit-control applications) define which existing AVPs or new AVPs
are used as input to the rating process; thus, the AVPs in question
have to be included in the Credit-Control-Request command by a
Diameter Credit-Control client supporting a given service as
"* [AVP]". Should the Service-Parameter-Info AVP be used, the
service-specific document MUST specify the exact content of this
Grouped AVP.
The Service-Context-Id AVP MUST be included at the command level of a
Credit-Control-Request to identify the service-specific document that
applies to the request. The specific service or rating-group the
request relates to is uniquely identified by the combination of
Service-Context-Id and Service-Identifier or rating-group.
4.1.3. Handling of Unsupported/Incorrect Rating Input
Diameter Credit-Control implementations are required to support
mandatory rating-related AVPs defined in service-specific documents
for the services they support, according to the 'M' bit rules in
[RFC6733].
If a rating input required for the rating process is incorrect in
the Credit-Control-Request or if the credit-control server does not
support the requested service context (identified by the
Service-Context-Id AVP at the command level), the
Credit-Control-Answer MUST contain the error code
DIAMETER_RATING_FAILED. A CCA message with this error MUST contain
one or more Failed-AVP AVPs containing the missing and/or unsupported
Bertz, et al. Standards Track [Page 16]
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AVPs that caused the failure. A Diameter Credit-Control client that
receives the error code DIAMETER_RATING_FAILED in response to a
request MUST NOT send similar requests in the future.
4.1.4. RADIUS Vendor-Specific Rating Attributes
When service-specific documents include RADIUS vendor-specific
attributes that could be used as input in the rating process, the
rules described in [RFC7155] for formatting the Diameter AVP MUST be
followed.
For example, if the AVP code used is the vendor attribute type code,
the Vendor-Specific flag MUST be set to 1 and the Vendor-Id MUST be
set to the IANA Vendor identification value. The Diameter AVP Data
field contains only the attribute value of the RADIUS attribute.
5. Session-Based Credit-Control
5.1. General Principles
For session-based credit-control, several interrogations are needed:
the first, the intermediate (optional), and the final. This is
illustrated in Figures 3 and 4 (Sections 5.2.1 and 5.2.2).
If the credit-control client performs credit reservation before
granting service to the end user, it MUST use several interrogations
toward the credit-control server (i.e., session-based
credit-control). In this case, the credit-control server MUST
maintain the credit-control session state.
Each credit-control session MUST have a globally unique Session-Id as
defined in [RFC6733]; this Session-Id MUST NOT be changed during the
lifetime of a credit-control session.
Certain applications require multiple credit-control sub-sessions.
These applications would send messages with a constant Session-Id AVP
but with a different CC-Sub-Session-Id AVP. If several credit
sub-sessions will be used, all sub-sessions MUST be closed separately
before the main session is closed so that units per sub-session may
be reported. The absence of the CC-Sub-Session-Id AVP implies that
no sub-sessions are in use.
Bertz, et al. Standards Track [Page 17]
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Note that the Service Element might send a service-specific
re-authorization message to the AAA server due to expiration of the
authorization lifetime during an ongoing credit-control session.
However, the service-specific re-authorization does not influence the
credit authorization that is ongoing between the credit-control
client and credit-control server, as credit authorization is
controlled by the burning rate of the granted quota.
If service-specific re-authorization fails, the user will be
disconnected, and the credit-control client MUST send a final
interrogation to the credit-control server.
The Diameter Credit-Control server may seek to control the validity
time of the granted quota and/or the production of intermediate
interrogations. Thus, it MAY include the Validity-Time AVP in the
Answer message to the credit-control client. Upon expiration of the
Validity-Time, the credit-control client MUST generate a
credit-control update request and report the used quota to the
credit-control server. It is up to the credit-control server to
determine the value of the Validity-Time to be used for consumption
of the granted service unit(s) (G-S-U). If the Validity-Time is
used, its value SHOULD be given as input to set the session
supervision timer Tcc (the session supervision timer MAY be set to
two times the value of the Validity-Time, as defined in Section 13).
Since credit-control update requests are also produced at the expiry
of granted service units and/or for mid-session service events, the
omission of Validity-Time does not mean that intermediate
interrogation for the purpose of credit-control is not performed.
5.1.1. Basic Support for Tariff Time Change
The Diameter Credit-Control server and client MAY optionally support
a tariff change mechanism. The Diameter Credit-Control server may
include a Tariff-Time-Change AVP in the Answer message. Note that
the granted units should be allocated based on the worst-case
scenario, so that the overall reported used units would never exceed
the credit reservation. For example, in the case of a forthcoming
tariff change, in which the new rate is higher, the allocation should
be given so it does not exceed the credit, assuming that all of it is
used after the tariff changed.
When the Diameter Credit-Control client reports the used units and a
tariff change has occurred during the reporting period, the Diameter
Credit-Control client MUST separately itemize the units used before
and after the tariff change. If the client is unable to distinguish
whether units straddling the tariff change were used before or after
the tariff change, the credit-control client MUST itemize those units
in a third category.
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If a client does not support the tariff change mechanism and it
receives a CCA message carrying the Tariff-Time-Change AVP, it MUST
terminate the credit-control session, giving a reason of
DIAMETER_BAD_ANSWER in the Termination-Cause AVP.
For time-based services, the quota is consumed at the rate of the
passage of real time (ignoring leap seconds). That is, precisely
1 second of quota is consumed per second of real time. At the time
when credit resources are allocated, the server already knows how
many units will be consumed before the tariff time change and how
many units will be consumed afterward. Similarly, the server can
determine the units consumed at the "before" rate and the units
consumed at the "afterward" rate in the event that the end user
closes the session before the consumption of the allotted quota.
There is no need for additional traffic between the client and server
in the case of tariff time changes for continuous time-based service.
Therefore, the tariff change mechanism is not used for such services.
For time-based services in which the quota is NOT continuously
consumed at a regular rate, the tariff change mechanism described for
volume and event units MAY be used.
5.1.2. Credit-Control for Multiple Services within a (Sub-)Session
When multiple services are used within the same user session and each
service or group of services is subject to different cost, it is
necessary to perform credit-control for each service independently.
Making use of credit-control sub-sessions to achieve independent
credit-control will result in increased signaling load and usage of
resources in both the credit-control client and the credit-control
server. For instance, during one network access session, the
end user may use several HTTP-based services that could be charged
with different costs. The network-access-specific attributes, such
as Quality of Service (QoS), are common to all the services carried
within the access bearer, but the cost of the bearer may vary,
depending on its content.
To support these scenarios optimally, the credit-control application
enables independent credit-control of multiple services in a single
credit-control (sub-)session. This is achieved by including the
optional Multiple-Services-Credit-Control AVP in Credit-Control-
Request/Credit-Control-Answer messages. It is possible to request
and allocate resources as a credit pool shared between multiple
services. The services can be grouped into rating-groups in order to
achieve even further aggregation of credit allocation. It is also
possible to request and allocate quotas on a per-service basis.
Where quotas are allocated to a pool by means of the Multiple-
Services-Credit-Control AVP, the quotas remain independent objects
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that can be re-authorized independently at any time. Quotas can also
be given independent result codes, validity times, and Final-Unit-
Indication AVP values or QoS-Final-Unit-Indication AVP values.
A rating-group gathers a set of services, identified by a Service-
Identifier and subject to the same cost and rating type (e.g.,
$0.1/minute). It is assumed that the Service Element is provided
with rating-groups, service-identifiers, and their associated
parameters that define what has to be metered by means outside the
scope of this specification. (Examples of parameters associated to
service-identifiers are IP 5-tuples and HTTP URLs.) Service-
identifiers enable authorization on a per-service-based credit as
well as itemized reporting of service usage. It is up to the
credit-control server whether to authorize credit for one or more
services or for the whole rating-group. However, the client SHOULD
always report used units at the finest supported level of
granularity. Where a quota is allocated to a rating-group, all the
services belonging to that group draw from the allotted quota.
Figure 2 provides a graphical representation of the relationship
between service-identifiers, rating-groups, credit pools, and
credit-control (sub-)sessions.
Diameter Credit-Control (Sub-)Session
|
+------------+-----------+-------------+--------------- +
| | | | |
Service-Id a Service-Id b Service-Id c Service-Id d.....Service-Id z
\ / \ / /
\ / \ / /
\ / Rating-Group 1.......Rating-Group n
\ / | |
Quota ---------------Quota Quota
| / |
| / |
Credit Pool Credit Pool
Figure 2: Multiple-Service (Sub-)Session Example
If independent credit-control of multiple services is used, the
Validity-Time AVP, and the Final-Unit-Indication AVP or
QoS-Final-Unit-Indication AVP, SHOULD be present either in the
Multiple-Services-Credit-Control AVP(s) or at the command level as
single AVPs. However, the Result-Code AVP MAY be present both at the
command level and within the Multiple-Services-Credit-Control AVP.
If the Result-Code AVP at the command level indicates a value other
than SUCCESS, then the Result-Code AVP at the command level takes
precedence over any other AVPs included in the Multiple-Services-
Credit-Control AVP.
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The credit-control client MUST indicate support for independent
credit-control of multiple services within a (sub-)session by
including the Multiple-Services-Indicator AVP in the first
interrogation. A credit-control server not supporting this feature
MUST treat the Multiple-Services-Indicator AVP and any received
Multiple-Services-Credit-Control AVPs as invalid AVPs.
If the client indicated support for independent credit-control of
multiple services, a credit-control server that wishes to use the
feature MUST return the granted units within the Multiple-Services-
Credit-Control AVP associated to the corresponding service-identifier
and/or rating-group.
To avoid a situation where several parallel (and typically also
small) credit reservations must be made on the same account (i.e.,
credit fragmentation), and also to avoid unnecessary load on the
credit-control server, it is possible to provide service units as a
pool that applies to multiple services or rating-groups. This is
achieved by providing the service units in the form of a quota for a
particular service or rating-group in the Multiple-Services-Credit-
Control AVP, and also by including a reference to a credit pool for
that unit type.
The reference includes a multiplier derived from the rating
parameter, which translates from service units of a specific type to
the abstract service units in the pool. For instance, if the rating
parameter for service 1 is $1/MB and the rating parameter for
service 2 is $0.5/MB, the multipliers could be 10 and 5 for
services 1 and 2, respectively.
If (1) S is the total service units within the pool, (2) M1, M2, ...,
Mn are the multipliers provided for services 1, 2, ..., n, and
(3) C1, C2, ..., Cn are the used resources within the session, then
the pool's credit is exhausted and re-authorization MUST be sought
when:
C1*M1 + C2*M2 + ... + Cn*Mn >= S
The total credit in the pool, S, is calculated from the quotas, which
are currently allocated to the pool as follows:
S = Q1*M1 + Q2*M2 + ... + Qn*Mn
If services or rating-groups are added to or removed from the pool,
then the total credit is adjusted appropriately. Note that when the
total credit is adjusted because services or rating-groups are
removed from the pool, the value that needs to be removed is the
consumed one (i.e., Cx*Mx).
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Re-authorizations for an individual service or rating-group may be
sought at any time -- for example, if a "non-pooled" quota is used up
or the Validity-Time expires.
Where multiple G-S-U-Pool-Reference AVPs (Section 8.30) with the same
G-S-U-Pool-Identifier are provided within a Multiple-Services-Credit-
Control AVP (Section 8.16) along with the Granted-Service-Unit AVP,
these AVPs MUST have different CC-Unit-Type values, and they all draw
from the credit pool separately. For instance, if one multiplier for
time (M1t) and one multiplier for volume (M1v) are given, then the
used resources from the pool yield the sum of C1t*M1t + C1v*M1v,
where C1t is the time unit and C1v is the volume unit.
Where service units are provided within a Multiple-Services-Credit-
Control AVP without a corresponding G-S-U-Pool-Reference AVP, these
units are handled independently from any credit pools and from any
other services or rating-groups within the session.
The "credit pool" concept is an optimal tool to avoid the
over-reservation effect of the basic single-quota tariff time change
mechanism (Section 5.1.1). Therefore, Diameter Credit-Control
clients and servers implementing the independent credit-control of
multiple services SHOULD leverage the credit pool concept when
supporting the tariff time change. The Diameter Credit-Control
server SHOULD include both the Tariff-Time-Change AVP and the
Tariff-Change-Usage AVP in two quota allocations in the Answer
message (i.e., two instances of the Multiple-Services-Credit-Control
AVP). One of the grants is allocated to be used before the potential
tariff change, while the second grant is for use after a tariff
change. Both granted unit quotas MUST contain the same Service-
Identifier and/or rating-group. This dual-quota mechanism ensures
that the overall reported used units would never exceed the credit
reservation. The Diameter Credit-Control client reports the used
units both before and after the tariff change in a single instance of
the Multiple-Services-Credit-Control AVP.
Failure handling for credit-control sessions is defined in
Section 5.7 and reflected in the basic credit-control state machines
defined in Section 7. Credit-control clients and servers
implementing the functionality of independent credit-control of
multiple services in a (sub-)session MUST ensure failure handling and
general behavior fully consistent with Sections 5.7 and 7 while
maintaining the ability to handle parallel ongoing credit
re-authorization within a (sub-)session. Therefore, it is
RECOMMENDED that Diameter Credit-Control clients maintain a PendingU
message queue (Section 7) and restart the Tx timer (Section 13) every
time a CCR message with the value UPDATE_REQUEST is sent while they
are in PendingU state. When answers to all pending messages are
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received, the state machine moves to Open state, and the Tx timer is
stopped. Naturally, when a problem is detected and acted upon per
Section 5.7, all of the ongoing services are affected (e.g., failover
to a backup server affects all of the CCR messages in the PendingU
queue).
Since the client may send CCR messages with the value UPDATE_REQUEST
while in PendingU state (i.e., without waiting for an answer to
ongoing credit re-authorization), the time space between these
requests may be very short, and the server may not have received the
previous request(s) yet. Therefore, in this situation the server may
receive out-of-sequence requests and SHOULD NOT consider this an
error condition. A proper answer is to be returned to each of those
requests.
5.2. First Interrogation
When session-based credit-control is required (e.g., the
authentication server indicated a prepaid user), the first
interrogation MUST be sent before the Diameter Credit-Control client
allows any service events for the end user. The CC-Request-Type AVP
is set to the value INITIAL_REQUEST in the request message.
If the Diameter Credit-Control client knows the cost of the service
event (e.g., a content server delivering ringing tones may know their
cost) the monetary amount to be charged is included in the Requested-
Service-Unit AVP. If the Diameter Credit-Control client does not
know the cost of the service event, the Requested-Service-Unit AVP
MAY contain the number of requested service events. Where the
Multiple-Services-Credit-Control AVP is used, it MUST contain the
Requested-Service-Unit AVP to indicate that the quota for the
associated service/rating-group is requested. In the case of
multiple services, the Service-Identifier AVP or the Rating-Group AVP
within the Multiple-Services-Credit-Control AVP always indicates the
service concerned. Additional service event information to be rated
MAY be sent as service-specific AVPs or MAY be sent within the
Service-Parameter-Info AVP at the command level. The
Service-Context-Id AVP indicates the service-specific document
applicable to the request.
The Event-Timestamp AVP SHOULD be included in the request and
contains the time when the service event is requested in the Service
Element. The Subscription-Id AVP or the Subscription-Id-Extension
AVP SHOULD be included to identify the end user in the credit-control
server. The credit-control client MAY include the User-Equipment-
Info AVP or User-Equipment-Info-Extension AVP so that the
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credit-control server has some indication of the type and
capabilities of the end-user access device. How the credit-control
server uses this information is outside the scope of this document.
The credit-control server SHOULD rate the service event and make a
credit reservation from the end user's account that covers the cost
of the service event. If the type of the Requested-Service-Unit AVP
is "money", no rating is needed, but the corresponding monetary
amount is reserved from the end user's account.
The credit-control server returns the Granted-Service-Unit AVP in the
Answer message to the Diameter Credit-Control client. The Granted-
Service-Unit AVP contains the amount of service units that the
Diameter Credit-Control client can provide to the end user until a
new Credit-Control-Request MUST be sent to the credit-control server.
If several unit types are sent in the Answer message, the
credit-control client MUST handle each unit type separately. The
type of the Granted-Service-Unit AVP can be time, volume, service-
specific, or money, depending on the type of service event. The unit
type(s) SHOULD NOT be changed within an ongoing credit-control
session.
There MUST be a maximum of one instance of the same unit type in one
Answer message. However, if multiple quotas are conveyed to the
credit-control client in the Multiple-Services-Credit-Control AVPs,
it is possible to carry two instances of the same unit type
associated to a service-identifier/rating-group. This is typically
the case when a tariff time change is expected and the credit-control
server wants to make a distinction between the granted quota before
the tariff change and the granted quota after the tariff change.
If the credit-control server determines that no further control is
needed for the service, it MAY include the result code indicating
that the credit-control is not applicable (e.g., if the service is
free of charge). This result code, at the command level, implies
that the credit-control session is to be terminated.
The Credit-Control-Answer message MAY also include the Final-Unit-
Indication AVP or the QoS-Final-Unit-Indication AVP to indicate that
the Answer message contains the final units for the service. After
the end user has consumed these units, the Diameter Credit-Control
client MUST behave as described in Section 5.6.
This document defines two different approaches for performing the
first interrogation to be used in different network architectures.
The first approach uses credit-control messages after the user's
authorization and authentication take place. The second approach
uses (1) service-specific authorization messages to perform the first
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interrogation during the user's authorization/authentication phase
and (2) credit-control messages for the intermediate and final
interrogations. If an implementation of the credit-control client
supports both methods, determining which method to use SHOULD be
configurable.
In service environments such as NAS environments, it is desired to
perform the first interrogation as part of the authorization/
authentication process for the sake of protocol efficiency. Further
credit authorizations after the first interrogation are performed
with credit-control commands defined in this specification.
Implementations of credit-control clients operating in the
environments mentioned in this document SHOULD support this method.
If the credit-control server and AAA server are separate physical
entities, the Service Element sends the request messages to the AAA
server, which then issues an appropriate request or proxies the
received request forward to the credit-control server.
In other service environments, such as the 3GPP network and some SIP
scenarios, there is a substantial decoupling between registration/
access to the network and the actual service request (i.e., the
authentication/authorization is executed once during registration/
access to the network and is not executed for every service event
requested by the subscriber). In these environments, it is more
appropriate to perform the first interrogation after the user has
been authenticated and authorized. The first, intermediate, and
final interrogations are executed with credit-control commands
defined in this specification.
Other IETF standards or standards developed by other standardization
bodies may define the most suitable method in their architectures.
5.2.1. First Interrogation after Authorization and Authentication
The Diameter Credit-Control client in the Service Element may get
information from the authorization server as to whether
credit-control is required, based on its knowledge of the end user.
If credit-control is required, the credit-control server needs to be
contacted prior to initiating service delivery to the end user. The
accounting protocol and the credit-control protocol can be used in
parallel. The authorization server may also determine whether the
parallel accounting stream is required.
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Figure 3 illustrates the case where both protocols are used in
parallel and the Service Element sends credit-control messages
directly to the credit-control server. More credit-control sequence
examples are given in Appendix A.
Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Registration | AA-Request/Answer(accounting, CC, or both)|
|<----------------->|<------------------>| |
| : | | |
| : | | |
| Service Request | | |
|------------------>| | |
| | CCR(Initial, Credit-Control AVPs) |
| +|------------------------------------------>|
| CC stream|| | CCA(Granted-Units)|
| +|<------------------------------------------|
| Service Delivery | | |
|<----------------->| ACR(start, Accounting AVPs) |
| : |------------------->|+ |
| : | ACA || Accounting stream |
| |<-------------------|+ |
| : | | |
| : | | |
| | CCR(Update, Used-Units) |
| |------------------------------------------>|
| | | CCA(Granted-Units)|
| |<------------------------------------------|
| : | | |
| : | | |
| End of Service | | |
|------------------>| CCR(Termination, Used-Units) |
| |------------------------------------------>|
| | | CCA |
| |<------------------------------------------|
| | ACR(stop) | |
| |------------------->| |
| | ACA | |
| |<-------------------| |
ACR: Accounting-Request
ACA: Accounting-Answer
Figure 3: Protocol Example with First Interrogation
after User's Authorization/Authentication
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5.2.2. First Interrogation Included with Authorization Messages
The Diameter Credit-Control client in the Service Element MUST
actively co-operate with the authorization/authentication client in
the construction of the AA-Request by adding appropriate
Credit-Control AVPs. The credit-control client MUST add the
Credit-Control AVP to indicate credit-control capabilities and MAY
add other relevant credit-control-specific AVPs to the proper
authorization/authentication command to perform the first
interrogation toward the home Diameter AAA server. The
Auth-Application-Id is set to the appropriate value, as defined in
service-specific authorization/authentication application document
(e.g., [RFC7155] [RFC4004]). The home Diameter AAA server
authenticates/authorizes the subscriber and determines whether
credit-control is required.
If credit-control is not required for the subscriber, the home
Diameter AAA server will respond as usual, with an appropriate
AA-Answer message. If credit-control is required for the subscriber
and the Credit-Control AVP with the value set to CREDIT_AUTHORIZATION
was present in the authorization request, the home AAA server MUST
contact the credit-control server to perform the first interrogation.
If credit-control is required for the subscriber and the
Credit-Control AVP was not present in the authorization request, the
home AAA server MUST send an authorization reject Answer message.
The Diameter AAA server supporting credit-control is required to send
the Credit-Control-Request command (CCR) defined in this document to
the credit-control server. The Diameter AAA server populates the CCR
based on service-specific AVPs used for input to the rating process,
and possibly on Credit-Control AVPs received in the AA-Request. The
credit-control server will reserve money from the user's account,
will rate the request, and will send a Credit-Control-Answer message
to the home Diameter AAA server. The Answer message includes the
Granted-Service-Unit AVP(s) and MAY include other credit-control-
specific AVPs, as appropriate. Additionally, the credit-control
server MAY set the Validity-Time and MAY include the CCFH and the
DDFH to determine what to do if the sending of credit-control
messages to the credit-control server has been temporarily prevented.
Upon receiving the Credit-Control-Answer message from the
credit-control server, the home Diameter AAA server will populate the
AA-Answer with the received Credit-Control AVPs and with the
appropriate service attributes according to the authorization/
authentication-specific application (e.g., [RFC7155] [RFC4004]). It
will then forward the packet to the credit-control client. If the
home Diameter AAA server receives a credit-control reject message, it
Bertz, et al. Standards Track [Page 27]
RFC 8506 Diameter Credit-Control Application March 2019
will simply generate an appropriate authorization reject message to
the credit-control client, including the credit-control-specific
error code.
In this model, the credit-control client sends further credit-control
messages to the credit-control server via the home Diameter AAA
server. Upon receiving a successful authorization Answer message
with the Granted-Service-Unit AVP(s), the credit-control client will
grant the service to the end user and will generate an intermediate
Credit-Control-Request, if required, by using credit-control
commands. The CC-Request-Number of the first UPDATE_REQUEST MUST be
set to 1 (for details regarding how to produce a unique value for the
CC-Request-Number AVP, see Section 8.2).
If service-specific re-authorization is performed (i.e., the
authorization lifetime expires), the credit-control client MUST add
to the service-specific re-authorization request the Credit-Control
AVP with a value set to RE_AUTHORIZATION to indicate that the
credit-control server MUST NOT be contacted. When session-based
credit-control is used for the subscriber, a constant credit-control
message stream flows through the home Diameter AAA server. The home
Diameter AAA server can make use of this credit-control message flow
to deduce that the user's activity is ongoing; therefore, it is
recommended to set the authorization lifetime to a reasonably high
value when credit-control is used for the subscriber.
In this scenario, the home Diameter AAA server MUST advertise support
for the credit-control application to its peers during the capability
exchange process.
Bertz, et al. Standards Track [Page 28]
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Figure 4 illustrates the use of authorization/authentication messages
to perform the first interrogation. The parallel accounting stream
is not shown in the figure.
Diameter
Service Element AAA Server CC Server
End User (CC Client)
| Service Request | AA-Request (CC AVPs) | |
|------------------>|--------------------->| |
| | | CCR(Initial, CC AVPs)
| | |-------------------->|
| | | CCA(Granted-Units)|
| | |<--------------------|
| | AA-Answer(Granted-Units) |
| Service Delivery |<---------------------| |
|<----------------->| | |
| : | | |
| : | | |
| : | | |
| | | |
| | CCR(Update, Used-Units) |
| |--------------------->| CCR(Update, Used-Units)
| | |-------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<--------------------|
| |<---------------------| |
| : | | |
| : | | |
| End of Service | | |
|------------------>| CCR(Termination, Used-Units) |
| |--------------------->| CCR(Term., Used-Units)
| | |-------------------->|
| | | CCA |
| | CCA |<--------------------|
| |<---------------------| |
Figure 4: Protocol Example with Use of Authorization Messages
for the First Interrogation
5.3. Intermediate Interrogation
When all the granted service units for one unit type are spent by the
end user or the Validity-Time has expired, the Diameter
Credit-Control client MUST send a new Credit-Control-Request to the
credit-control server. In the event that credit-control for multiple
services is applied in one credit-control session (i.e., units
associated to Service-Identifier(s) or the rating-group are granted),
a new Credit-Control-Request MUST be sent to the credit-control
Bertz, et al. Standards Track [Page 29]
RFC 8506 Diameter Credit-Control Application March 2019
server when the credit reservation has been wholly consumed or upon
expiration of the Validity-Time. It is always up to the Diameter
Credit-Control client to send a new request well in advance of the
expiration of the previous request in order to avoid interruption in
the Service Element. Even if the granted service units reserved by
the credit-control server have not been spent upon expiration of the
Validity-Time, the Diameter Credit-Control client MUST send a new
Credit-Control-Request to the credit-control server.
There can also be mid-session service events, which might affect the
rating of the current service events. In this case, a spontaneous
update (a new Credit-Control-Request) SHOULD be sent, including
information related to the service event, even if all the granted
service units have not been spent or the Validity-Time has not
expired.
When the used units are reported to the credit-control server, the
credit-control client will not have any units in its possession
before new granted units are received from the credit-control server.
When the new granted units are received, these units apply from the
point where the measurement of the reported used units stopped.
Where independent credit-control of multiple services is supported,
this process may be executed for one or more services, a single
rating-group, or a pool within the (sub-)session.
The CC-Request-Type AVP is set to the value UPDATE_REQUEST in the
intermediate request message. The Subscription-Id AVP or
Subscription-Id-Extension AVP SHOULD be included in the intermediate
message to identify the end user in the credit-control server. The
Service-Context-Id AVP indicates the service-specific document
applicable to the request.
The Requested-Service-Unit AVP MAY contain the new amount of
requested service units. Where the Multiple-Services-Credit-Control
AVP is used, it MUST contain the Requested-Service-Unit AVP if a new
quota is requested for the associated service/rating-group. The
Used-Service-Unit AVP contains the amount of used service units
measured from the point when the service became active or, if interim
interrogations are used during the session, from the point when the
previous measurement ended. The same unit types used in the previous
message SHOULD be used. If several unit types were included in the
previous Answer message, the used service units for each unit type
MUST be reported.
The Event-Timestamp AVP SHOULD be included in the request and
contains the time of the event that triggered the sending of the new
Credit-Control-Request.
Bertz, et al. Standards Track [Page 30]
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The credit-control server MUST deduct the used amount from the
end user's account. It MAY rate the new request and make a new
credit reservation from the end user's account that covers the cost
of the requested service event.
A Credit-Control-Answer message with the CC-Request-Type AVP set to
the value UPDATE_REQUEST MAY include the Cost-Information AVP
containing the accumulated cost estimation for the session, without
taking any credit reservations into account.
The Credit-Control-Answer message MAY also include the Final-Unit-
Indication AVP or the QoS-Final-Unit-Indication AVP to indicate that
the Answer message contains the final units for the service. After
the end user has consumed these units, the Diameter Credit-Control
client MUST behave as described in Section 5.6.
There can be several intermediate interrogations within a session.
5.4. Final Interrogation
When the end user terminates the service session or when graceful
service termination (described in Section 5.6) takes place, the
Diameter Credit-Control client MUST send a final Credit-Control-
Request message to the credit-control server. The CC-Request-Type
AVP is set to the value TERMINATION_REQUEST. The Service-Context-Id
AVP indicates the service-specific document applicable to the
request.
The Event-Timestamp AVP SHOULD be included in the request and
contains the time when the session was terminated.
The Used-Service-Unit AVP contains the amount of used service units
measured from the point when the service became active or, if interim
interrogations are used during the session, from the point when the
previous measurement ended. If several unit types were included in
the previous Answer message, the used service units for each unit
type MUST be reported.
After final interrogation, the credit-control server MUST refund the
reserved credit amount not used to the end user's account and deduct
the used monetary amount from the end user's account.
A Credit-Control-Answer message with the CC-Request-Type AVP set to
the value TERMINATION_REQUEST MAY include the Cost-Information AVP
containing the estimated total cost for the session in question.
Bertz, et al. Standards Track [Page 31]
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If the user logs off during an ongoing credit-control session or if
the user becomes logged off for some other reason (e.g., a final-unit
indication causes user logoff according to local policy), the Service
Element, according to application-specific policy, may send a
Session-Termination-Request (STR) to the home Diameter AAA server as
usual [RFC6733]. Figure 5 illustrates the case when the final-unit
indication causes user logoff upon consumption of the final granted
units and the generation of an STR.
The Diameter AAA server responds with a Session-Termination-Answer
(STA).
Service Element AAA Server CC Server
End User (CC Client)
| Service Delivery | | |
|<----------------->| | |
| : | | |
| : | | |
| : | | |
| | | |
| | CCR(Update, Used-Units) |
| |-------------------->| CCR(Update, Used-Units)
| | |-------------------->|
| | CCA(Final-Unit, Terminate)
| CCA(Final-Unit, Terminate)|<--------------------|
| |<--------------------| |
| : | | |
| : | | |
| Disconnect user | | |
|<------------------| CCR(Termination, Used-Units) |
| |-------------------->| CCR(Term., Used-Units)
| | |-------------------->|
| | | CCA |
| | CCA |<--------------------|
| |<--------------------| |
| | STR | |
| |-------------------->| |
| | STA | |
| |<--------------------| |
Figure 5: User Disconnected Due to Exhausted Account
5.5. Server-Initiated Credit Re-authorization
The Diameter Credit-Control application supports server-initiated
re-authorization. The credit-control server MAY optionally initiate
the credit re-authorization by issuing a Re-Auth-Request (RAR) as
defined in the Diameter base protocol [RFC6733]. The
Bertz, et al. Standards Track [Page 32]
RFC 8506 Diameter Credit-Control Application March 2019
Auth-Application-Id in the RAR message is set to 4 to indicate
"Diameter Credit Control", and the Re-Auth-Request-Type is set to
AUTHORIZE_ONLY.
Section 5.1.2 defines the feature to enable credit-control for
multiple services within a single (sub-)session where the server can
authorize credit usage at a different level of granularity. Further,
the server may provide credit resources to multiple services or
rating-groups as a pool (see Section 5.1.2 for details and
definitions). Therefore, the server, based on its service logic and
its knowledge of the ongoing session, can decide to request credit
re-authorization for a whole (sub-)session, a single credit pool, a
single service, or a single rating-group. To request credit
re-authorization for a credit pool, the server includes in the RAR
message the G-S-U-Pool-Identifier AVP indicating the affected pool.
To request credit re-authorization for a service or a rating-group,
the server includes in the RAR message the Service-Identifier AVP or
the Rating-Group AVP, respectively. To request credit
re-authorization for all the ongoing services within the
(sub-)session, the server includes none of the above-mentioned AVPs
in the RAR message.
If a credit re-authorization is not already ongoing (i.e., the
credit-control session is in Open state), a credit-control client
that receives an RAR message with Session-Id equal to a currently
active credit-control session MUST acknowledge the request by sending
the Re-Auth-Answer (RAA) message and MUST initiate the credit
re-authorization toward the server by sending a Credit-Control-
Request message with the CC-Request-Type AVP set to the value
UPDATE_REQUEST. The Result-Code 2002 (DIAMETER_LIMITED_SUCCESS)
SHOULD be used in the RAA message to indicate that an additional
message (i.e., a CCR message with the value UPDATE_REQUEST) is
required to complete the procedure. If a quota was allocated to the
service, the credit-control client MUST report the used quota in the
Credit-Control-Request. Note that the end user does not need to be
prompted for the credit re-authorization, since the credit
re-authorization is transparent to the user (i.e., it takes place
exclusively between the credit-control client and the credit-control
server).
Where multiple services in a user's session are supported, the
procedure in the above paragraph will be executed at the granularity
requested by the server in the RAR message.
If credit re-authorization is ongoing at the time when the RAR
message is received (i.e., an RAR-CCR collision), the credit-control
client successfully acknowledges the request but does not initiate a
new credit re-authorization. The Result-Code 2001 (DIAMETER_SUCCESS)
Bertz, et al. Standards Track [Page 33]
RFC 8506 Diameter Credit-Control Application March 2019
SHOULD be used in the RAA message to indicate that a credit
re-authorization procedure is already ongoing (i.e., the client was
in PendingU state when the RAR was received). The credit-control
server SHOULD process the Credit-Control-Request as if it was
received in answer to the server-initiated credit re-authorization
and should consider the server-initiated credit re-authorization
process successful upon reception of the RAA message.
When multiple services are supported in a user's session, the server
may request credit re-authorization for a credit pool (or for the
(sub-)session) while a credit re-authorization is already ongoing for
some of the services or rating-groups. In this case, the client
acknowledges the server request with an RAA message and MUST send a
new Credit-Control-Request message to perform re-authorization for
the remaining services/rating-groups. The Result-Code 2002
(DIAMETER_LIMITED_SUCCESS) SHOULD be used in the RAA message to
indicate that an additional message (i.e., a CCR message with the
value UPDATE_REQUEST) is required to complete the procedure. The
server processes the received requests and returns an appropriate
answer to both requests.
The above-defined procedures are enabled for each of the possibly
active Diameter Credit-Control sub-sessions. The server MAY request
re-authorization for an active sub-session by including the
CC-Sub-Session-Id AVP in the RAR message in addition to the
Session-Id AVP.
5.6. Graceful Service Termination
When the user's account runs out of money, the user may not be
allowed to compile additional chargeable events. However, the home
service provider may offer some services -- for instance, access to a
service portal where it is possible to refill the account -- from
which the user is allowed to benefit for a limited time. The length
of this time is usually dependent on the home service provider
policy.
This section defines the optional graceful service termination
feature. This feature MAY be supported by the credit-control server.
Credit-control client implementations MUST support the Final-Unit-
Indication AVP or QoS-Final-Unit-Indication AVP with at least the
teardown of the ongoing service session once the subscriber has
consumed all the final granted units.
Bertz, et al. Standards Track [Page 34]
RFC 8506 Diameter Credit-Control Application March 2019
Where independent credit-control of multiple services in a single
credit-control (sub-)session is supported, it is possible to use
graceful service termination for each of the services/rating-groups
independently. Naturally, the graceful service termination process
defined in the following subsections will apply to the specific
service/rating-group as requested by the server.
In some service environments (e.g., NAS), graceful service
termination may be used to redirect the subscriber to a service
portal for online balance refill or other services offered by the
home service provider. In this case, the graceful service
termination process installs a set of packet filters to restrict the
user's access capability only to/from the specified destinations.
All the IP packets not matching the filters will be dropped or,
possibly, redirected to the service portal. The user may also be
sent an appropriate notification as to why the access has been
limited. These actions may be communicated explicitly from the
server to the client or may be configured "per service" at the
client. Explicitly signaled redirection or restriction instructions
always take precedence over configured ones.
It is also possible to use graceful service termination to connect
the prepaid user to a top-up server that plays an announcement and
prompts the user to replenish the account. In this case, the
credit-control server sends only the address of the top-up server
where the prepaid user shall be connected after the final granted
units have been consumed. An example of this case is given in
Appendix A.7.
The credit-control server MAY initiate graceful service termination
by including the Final-Unit-Indication AVP or the
QoS-Final-Unit-Indication AVP in the Credit-Control-Answer to
indicate that the message contains the final units for the service.
When the credit-control client receives the Final-Unit-Indication AVP
or the QoS-Final-Unit-Indication AVP in the answer from the server,
its behavior depends on the value indicated in the Final-Unit-Action
AVP. The server may request the following actions: TERMINATE,
REDIRECT, or RESTRICT_ACCESS.
Figure 6 illustrates the graceful service termination procedure
described in the following subsections.
Bertz, et al. Standards Track [Page 35]
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Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Service Delivery | | |
|<----------------->| | |
| |CCR(Update, Used-Units) |
| |-------------------->|CCR(Update, Used-Units)
| : | |-------------------->|
| : | |CCA(Final-Unit, Action)
| : | |<--------------------|
| |CCA(Final-Unit, Action) |
| |<--------------------| |
| | | |
| : | | |
| : | | |
| /////////////// |CCR(Update, Used-Units) |
|/Final Units End/->|-------------------->|CCR(Update, Used-Units)
|/Action and // | |-------------------->|
|/Restrictions // | | CCA(Validity-Time)|
|/Start // | CCA(Validity-Time)|<--------------------|
| ///////////// |<--------------------| |
| : | | |
| : | | |
| Replenish account | +-------+ |
|<--------------------------------------------->|Account| |
| | | +-------+ |
| | | RAR |
| + | RAR |<====================|
| | |<====================| |
| | | RAA | |
| ///////////// | |====================>| RAA |
| /If supported / | | CCR(Update) |====================>|
| /by CC Server/ | |====================>| CCR(Update) |
| ///////////// | | |====================>|
| | | | CCA(Granted-Units)|
| | | CCA(Granted-Units)|<====================|
| Restrictions ->+ |<====================| |
| removed | | |
| : | | |
| OR | CCR(Update) | |
| Validity-Time ->|-------------------->| CCR(Update) |
| expires | |-------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<--------------------|
| Restrictions ->|<--------------------| |
| removed | | |
Figure 6: Optional Graceful Service Termination Procedure
Bertz, et al. Standards Track [Page 36]
RFC 8506 Diameter Credit-Control Application March 2019
In addition, the credit-control server MAY reply with the Final-Unit-
Indication AVP or QoS-Final-Unit-Indication AVP holding a Granted-
Service-Unit (G-S-U) with a zero grant, indicating that the service
SHOULD be terminated immediately, and no further reporting is
required. Figure 7 illustrates a graceful service termination
procedure that applies immediately after receiving a zero grant.
Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Service Delivery | | |
|<----------------->| | |
| |CCR(Update, Used-Units) |
| |--------------------->|CCR(Update, Used-Units)
| : | |-------------------->|
| : | |CCA(Final-Unit, Action,
| : | | Zero G-S-U)
| : | |<--------------------|
| |CCA(Final-Unit, Action, |
| | Zero G-S-U) |
| |<---------------------| |
| /////////////// | | |
|/Action and // | | |
|/Restrictions // | | |
|/Start // | | |
| ///////////// | | |
| : | | |
| : | | |
Figure 7: Optional Immediate Graceful Service Termination Procedure
5.6.1. Terminate Action
The Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP
with Final-Unit-Action set to TERMINATE does not include any other
information. When the subscriber has consumed the final granted
units, the Service Element MUST terminate the service. This is the
default handling applicable whenever the credit-control client
receives an unsupported Final-Unit-Action value and MUST be supported
by all the Diameter Credit-Control client implementations conforming
to this specification. A final Credit-Control-Request message to the
credit-control server MUST be sent if the Final-Unit-Indication AVP
or the QoS-Final-Unit-Indication AVP indicating action TERMINATE was
present at the command level. The CC-Request-Type AVP in the request
is set to the value TERMINATION_REQUEST.
Bertz, et al. Standards Track [Page 37]
RFC 8506 Diameter Credit-Control Application March 2019
5.6.2. Redirect Action
The Final-Unit-Indication AVP or the QoS-Final-Unit-Indication AVP
with Final-Unit-Action set to REDIRECT indicates to the Service
Element supporting this action that, upon consumption of the final
granted units, the user MUST be redirected to the address specified
in the Redirect-Server AVP or Redirect-Server-Extension AVP as
follows.
The credit-control server sends the Redirect-Server AVP or Redirect-
Server-Extension AVP in the Credit-Control-Answer message. In such a
case, the Service Element MUST redirect or connect the user to the
destination specified in the Redirect-Server AVP or Redirect-Server-
Extension AVP, if possible. When the end user is redirected (by
using protocols other than Diameter) to the specified server or
connected to the top-up server, an additional authorization (and
possibly authentication) may be needed before the subscriber can
replenish the account; however, this scenario is out of scope for
this specification.
In addition to the Redirect-Server AVP or Redirect-Server-Extension
AVP, the credit-control server MAY include one or more Restriction-
Filter-Rule AVPs, one or more Filter-Rule AVPs, or one or more
Filter-Id AVPs in the Credit-Control-Answer message to enable the
user to access other services (for example, zero-rated services). In
such a case, the access device MUST treat all packets according to
the Restriction-Filter-Rule AVPs, Filter-Rule AVPs, and the rules
referred to by the Filter-Id AVP. After treatment is applied
according to these rules, all traffic that has not been dropped or
already forwarded MUST be redirected to the destination specified in
the Redirect-Server AVP or Redirect-Server-Extension AVP.
An entity other than the credit-control server may provision the
access device with appropriate IP packet filters to be used in
conjunction with the Diameter Credit-Control application. This case
is considered in Section 5.6.3.
When the final granted units have been consumed, the credit-control
client MUST perform an intermediate interrogation. The purpose of
this interrogation is to indicate to the credit-control server that
the specified action started and to report the used units. The
credit-control server MUST deduct the used amount from the end user's
account but MUST NOT make a new credit reservation. The
credit-control client, however, may send intermediate interrogations
before all the final granted units have been consumed for which
rating and money reservation may be needed -- for instance, upon
Validity-Time expiration or upon mid-session service events that
affect the rating of the current service. Therefore, the
Bertz, et al. Standards Track [Page 38]
RFC 8506 Diameter Credit-Control Application March 2019
credit-control client MUST NOT include any rating-related AVPs in the
request sent once all the final granted units have been consumed, as
an indication to the server that (1) the requested final unit action
started and (2) rating and money reservation are not required (when
the Multiple-Services-Credit-Control AVP is used, the Service-
Identifier AVP or the Rating-Group AVP is included to indicate the
services concerned). Naturally, the Credit-Control-Answer message
does not contain any granted service units and MUST include the
Validity-Time AVP to indicate to the credit-control client how long
the subscriber is allowed to use network resources before a new
intermediate interrogation is sent to the server.
At the expiry of Validity-Time, the credit-control client sends a
Credit-Control-Request (UPDATE_REQUEST) as usual. This message does
not include the Used-Service-Unit AVP, as there is no allotted quota
to report. The credit-control server processes the request and MUST
perform the credit reservation. If during this time the subscriber
did not replenish their account, whether they will be disconnected or
will be granted access to services not controlled by a credit-control
server for an unlimited time is dependent on the home service
provider policy. (Note: The latter option implies that the Service
Element should not remove the restriction filters upon termination of
the credit-control.) The server will return the appropriate
Result-Code (see Section 9.1) in the Credit-Control-Answer message in
order to implement the policy-defined action. Otherwise, a new quota
will be returned, and the Service Element MUST remove all the
possible restrictions activated by the graceful service termination
process and continue the credit-control session and service session
as usual.
The credit-control client may not wait until the expiration of the
Validity-Time and may send a spontaneous update (a new
Credit-Control-Request) if the Service Element can determine, for
instance, that communication between the end user and the top-up
server took place. An example of this case is given in Appendix A.8
(Figure 18).
Note that the credit-control server may already have initiated the
above-described process for the first interrogation. However, the
user's account might be empty when this first interrogation is
performed. In this case, the subscriber can be offered a chance to
replenish the account and continue the service. When the
credit-control client receives (at either the session level or a
service-specific level) a Final-Unit-Indication AVP or QoS-Final-
Unit-Indication AVP, together with Validity-Time AVPs, but without a
Granted-Service-Unit AVP, it immediately starts the graceful service
termination process without sending any messages to the server. An
example of this case is illustrated in Appendix A.8 (Figure 18).
Bertz, et al. Standards Track [Page 39]
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5.6.3. Restrict Access Action
A Final-Unit-Indication AVP with Final-Unit-Action set to
RESTRICT_ACCESS indicates to the device supporting this action that,
upon consumption of the final granted units, the user's access MUST
be restricted according to the IP packet filters given in the
Restriction-Filter-Rule AVP(s) or according to the IP packet filters
identified by the Filter-Id AVP(s). The credit-control server SHOULD
include either the Restriction-Filter-Rule AVP or the Filter-Id AVP
in the Final-Unit-Indication group AVP of the Credit-Control-Answer
message.
A QoS-Final-Unit-Indication AVP with Final-Unit-Action set to
RESTRICT_ACCESS indicates to the device supporting this action that,
upon consumption of the final granted units, the actions specified in
Filter-Rule AVP(s) MUST restrict the traffic according to the
classifiers in the Filter-Rule AVP(s). If one or more Filter-Id AVPs
are provided in the Credit-Control-Answer message, the credit-control
client MUST restrict the traffic according to the IP packet filters
identified by the Filter-Id AVP(s). The credit-control server SHOULD
include either the Filter-Rule AVP or the Filter-Id AVP in the
QoS-Final-Unit-Indication group AVP of the Credit-Control-Answer
message.
If both the Final-Unit-Indication AVP and the QoS-Final-Unit-
Indication AVP exist in the Credit-Control-Answer message, a
credit-control client that supports the QoS-Final-Unit-Indication AVP
SHOULD follow the directives included in the QoS-Final-Unit-
Indication AVP and SHOULD ignore the Final-Unit-Indication AVP.
An entity other than the credit-control server may provision the
access device with appropriate IP packet filters to be used in
conjunction with the Diameter Credit-Control application. Such an
entity may, for instance, configure the access device with IP flows
to be passed when the Diameter Credit-Control application indicates
RESTRICT_ACCESS or REDIRECT. The access device passes IP packets
according to the filter rules that may have been received in the
Credit-Control-Answer message, in addition to those rules that may
have been configured by the other entity. However, when the user's
account cannot cover the cost of the requested service, the action
taken is the responsibility of the credit-control server that
controls the prepaid subscriber.
If another entity working in conjunction with the Diameter
Credit-Control application already provisions the access device with
all the required filter rules for the end user, the credit-control
server presumably need not send any additional filters. Therefore,
it is RECOMMENDED that credit-control server implementations
Bertz, et al. Standards Track [Page 40]
RFC 8506 Diameter Credit-Control Application March 2019
supporting graceful service termination be configurable for sending
the Restriction-Filter-Rule AVP, the Filter-Rule AVP, the Filter-Id
AVP, or none of the above.
When the final granted units have been consumed, the credit-control
client MUST perform an intermediate interrogation. The
credit-control client and the credit-control server process this
intermediate interrogation and execute subsequent procedures, as
specified in Section 5.6.2.
The credit-control server may initiate graceful service termination
when replying with the action RESTRICT_ACCESS for the first
interrogation. This is similar to the behavior specified in
Section 5.6.2.
5.6.4. Usage of the Server-Initiated Credit Re-authorization
Once the subscriber replenishes the account, they presumably expect
all the restrictions applied by the graceful service termination
procedure to be removed immediately and unlimited service access to
be resumed. For the best user experience, the credit-control server
implementation MAY support the server-initiated credit
re-authorization (see Section 5.5). In such a case, upon the
successful account top-up, the credit-control server sends the
Re-Auth-Request (RAR) message to solicit the credit re-authorization.
The credit-control client initiates the credit re-authorization by
sending the Credit-Control-Request message with the CC-Request-Type
AVP set to the value UPDATE_REQUEST. The Used-Service-Unit AVP is
not included in the request, as there is no allotted quota to report.
The Requested-Service-Unit AVP MAY be included in the request. After
the credit-control client successfully receives the Credit-Control-
Answer with a new Granted-Service-Unit AVP, all the possible
restrictions activated for the purpose of graceful service
termination MUST be removed in the Service Element. The
credit-control session and the service session continue as usual.
5.7. Failure Procedures
The CCFH, as described in this section, determines the behavior of
the credit-control client in fault situations. The CCFH may be
(1) received from the Diameter home AAA server, (2) received from the
credit-control server, or (3) configured locally. The CCFH value
received from the home AAA server overrides the locally configured
value. The CCFH value received from the credit-control server in the
Credit-Control-Answer message always overrides any existing values.
Bertz, et al. Standards Track [Page 41]
RFC 8506 Diameter Credit-Control Application March 2019
The authorization server MAY include the Accounting-Realtime-Required
AVP to determine what to do if the sending of accounting records to
the accounting server has been temporarily prevented, as defined in
[RFC6733]. It is RECOMMENDED that the client complement the
credit-control failure procedures with a backup accounting flow
toward an accounting server. By using different combinations of the
Accounting-Realtime-Required AVP and the CCFH, different safety
levels can be built. For example, by choosing a CCFH equal to
CONTINUE for the credit-control flow and an Accounting-Realtime-
Required AVP equal to DELIVER_AND_GRANT for the accounting flow, the
service can be granted to the end user even if the connection to the
credit-control server is down, as long as the accounting server is
able to collect the accounting information and information exchange
is taking place between the accounting server and credit-control
server.
As the credit-control application is based on real-time bidirectional
communication between the credit-control client and the
credit-control server, the usage of alternative destinations and the
buffering of messages may not be sufficient in the event of
communication failures. Because the credit-control server has to
maintain session states, moving the credit-control message stream to
a backup server requires a complex context transfer solution.
Whether the credit-control message stream is moved to a backup
credit-control server during an ongoing credit-control session
depends on the value of the CC-Session-Failover AVP. However,
failover may occur at any point in the path between the
credit-control client and the credit-control server if a transport
failure is detected with a peer, as described in [RFC6733]. As a
consequence, the credit-control server might receive duplicate
messages. These duplicate or out-of-sequence messages can be
detected in the credit-control server based on the credit-control
server session state machine (Section 7), Session-Id AVP, and
CC-Request-Number AVP.
If a failure occurs during an ongoing credit-control session, the
credit-control client may move the credit-control message stream to
an alternative server if the credit-control server indicated
FAILOVER_SUPPORTED in the CC-Session-Failover AVP. A secondary
credit-control server name, either received from the home Diameter
AAA server or configured locally, can be used as an address of the
backup server. If the CC-Session-Failover AVP is set to
FAILOVER_NOT_SUPPORTED, the credit-control message stream MUST NOT be
moved to a backup server.
Bertz, et al. Standards Track [Page 42]
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For new credit-control sessions, failover to an alternative
credit-control server SHOULD be performed, if possible. For
instance, if an implementation of the credit-control client can
determine primary credit-control server unavailability, it can
establish the new credit-control sessions with a possibly available
secondary credit-control server.
The AAA transport profile [RFC3539] defines an application-layer
watchdog algorithm that enables failover from a peer that has failed
and is controlled by a watchdog timer (Tw) (defined in [RFC3539]).
The recommended default initial value for Tw (Twinit) is 30 seconds.
Twinit may be set as low as 6 seconds; however, according to
[RFC3539], setting too low a value for Twinit is likely to result in
an increased probability of duplicates, as well as an increase in
spurious failover and failback attempts. The Diameter base protocol
[RFC6733] is common to several different types of Diameter AAA
applications that may be run in the same Service Element. Therefore,
tuning the timer for Twinit to a lower value in order to satisfy the
requirements of real-time applications, such as the Diameter
Credit-Control application, will certainly cause the above-mentioned
problems. For prepaid services, however, the end user expects an
answer from the network in a reasonable time. Thus, the Diameter
Credit-Control client will react more quickly than would the
underlying base protocol. Therefore, this specification defines the
Tx timer (as defined in Section 13), which is used by the
credit-control client to supervise communication with the
credit-control server. When the Tx timer elapses, the credit-control
client takes action for the end user according to the CCFH.
When the Tx timer expires, the Diameter Credit-Control client always
terminates the service if the CCFH is set to the value TERMINATE.
The credit-control session may be moved to an alternative server only
if a protocol error DIAMETER_TOO_BUSY or DIAMETER_UNABLE_TO_DELIVER
is received before the Tx timer expires. Therefore, the value
TERMINATE is not appropriate if proper failover behavior is desired.
If the CCFH is set to the value CONTINUE or RETRY_AND_TERMINATE, the
service will be granted to the end user when the Tx timer expires.
An Answer message with granted units may arrive later if the base
protocol transport failover occurred in the path to the
credit-control server. (The Twinit default value is 3 times more
than the recommended Tx timeout value.) The credit-control client
SHOULD grant the service to the end user, start monitoring resource
usage, and wait for the possible late answer until the timeout of the
request (e.g., 120 seconds). If the request fails and the
CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED, the
Bertz, et al. Standards Track [Page 43]
RFC 8506 Diameter Credit-Control Application March 2019
credit-control client terminates or continues the service --
depending on the value set in the CCFH -- and MUST free all the
reserved resources for the credit-control session. If the protocol
error DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY is received or
the request times out and the CC-Session-Failover AVP is set to
FAILOVER_SUPPORTED, the credit-control client MAY send the request to
a backup server, if possible. If the credit-control client receives
a successful answer from the backup server, it continues the
credit-control session with such a server. If the retransmitted
request also fails, the credit-control client terminates or continues
the service -- depending on the value set in the CCFH -- and MUST
free all the reserved resources for the credit-control session.
If a communication failure occurs during the graceful service
termination procedure, the Service Element SHOULD always terminate
the ongoing service session.
If the credit-control server detects a failure during an ongoing
credit-control session, it will terminate the credit-control session
and return the reserved units back to the end user's account.
The supervision session timer Tcc (as defined in Section 13) is used
in the credit-control server to supervise the credit-control session.
In order to support failover between credit-control servers,
information transfer about the credit-control session and account
state SHOULD take place between the primary and secondary
credit-control servers. Implementations supporting credit-control
session failover MUST also ensure proper detection of duplicate or
out-of-sequence messages. Communication between the servers is
regarded as an implementation issue and is outside the scope of this
specification.
6. One-Time Event
The one-time event is used when there is no need to maintain any
state in the Diameter Credit-Control server -- for example, inquiring
about the price of the service. The use of a one-time event implies
that the user has been authenticated and authorized beforehand.
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The one-time event can be used when the credit-control client wants
to know the cost of the service event or to check the account balance
without any credit reservations. It can also be used for refunding
service units on the user's account or for direct debiting without
any credit reservations. The one-time event is shown in Figure 8.
Diameter
End User Service Element AAA Server CC Server
(CC Client)
| Service Request | | |
|------------------>| | |
| | CCR(Event) | |
| |------------------->| CCR(Event) |
| | |------------------->|
| | | CCA(Granted-Units)|
| | CCA(Granted-Units)|<-------------------|
| Service Delivery |<-------------------| |
|<----------------->| | |
Figure 8: One-Time Event
In environments such as the 3GPP architecture, the one-time event can
be sent from the Service Element directly to the credit-control
server.
6.1. Service Price Inquiry
The credit-control client may need to know the price of the service
event. Services offered by application service providers whose
prices are not known in the credit-control client might exist. The
end user might also want to get an estimate of the price of a service
event before requesting it.
A Diameter Credit-Control client requesting the cost information MUST
set the CC-Request-Type AVP equal to EVENT_REQUEST, include the
Requested-Action AVP set to PRICE_ENQUIRY, and set the requested
service event information in the Service-Identifier AVP in the
Credit-Control-Request message. Additional service event information
may be sent as service-specific AVPs or within the Service-Parameter-
Info AVP. The Service-Context-Id AVP indicates the service-specific
document applicable to the request.
The credit-control server calculates the cost of the requested
service event, but it does not perform any account-balance checks or
credit reservations from the account.
Bertz, et al. Standards Track [Page 45]
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The estimated cost of the requested service event is returned to the
credit-control client in the Cost-Information AVP in the
Credit-Control-Answer message.
6.2. Balance Checks
The Diameter Credit-Control client may only have to verify that the
end user's account balance covers the cost of a certain service
without reserving any units from the account at the time of the
inquiry. This method does not guarantee that credit would be left
when the Diameter Credit-Control client requests the debiting of the
account with a separate request.
A Diameter Credit-Control client requesting a balance check MUST set
the CC-Request-Type AVP equal to EVENT_REQUEST, include a Requested-
Action AVP set to CHECK_BALANCE, and include the Subscription-Id AVP
or Subscription-Id-Extension AVP in order to identify the end user in
the credit-control server. The Service-Context-Id AVP indicates the
service-specific document applicable to the request.
The credit-control server makes the balance check, but it does not
make any credit reservations from the account.
The result of the balance check (ENOUGH_CREDIT/NO_CREDIT) is returned
to the credit-control client in the Check-Balance-Result AVP in the
Credit-Control-Answer message.
6.3. Direct Debiting
There are certain service events for which service execution is
always successful in the service environment. The delay between the
service invocation and the actual service delivery to the end user
can be sufficiently long that the use of session-based credit-control
would lead to unreasonably long credit-control sessions. In these
cases, the Diameter Credit-Control client can use the one-time event
scenario for direct debiting. The Diameter Credit-Control client
SHOULD be sure that the requested service event execution would be
successful when this scenario is used.
In the Credit-Control-Request message, the CC-Request-Type AVP is set
to the value EVENT_REQUEST and the Requested-Action AVP is set to
DIRECT_DEBITING. The Subscription-Id AVP or Subscription-Id-
Extension AVP SHOULD be included to identify the end user in the
credit-control server. The Event-Timestamp AVP SHOULD be included in
the request and contain the time when the service event is requested
in the Service Element. The Service-Context-Id AVP indicates the
service-specific document applicable to the request.
Bertz, et al. Standards Track [Page 46]
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If it knows the cost of the service event, the Diameter
Credit-Control client MAY include in the Requested-Service-Unit AVP
the monetary amount to be charged. If the Diameter Credit-Control
client does not know the cost of the service event, the Requested-
Service-Unit AVP MAY contain the number of requested service events.
The Service-Identifier AVP always indicates the service concerned.
Additional service event information to be rated MAY be sent as
service-specific AVPs or within the Service-Parameter-Info AVP.
The credit-control server SHOULD rate the service event and deduct
the corresponding monetary amount from the end user's account. If
the type of the Requested-Service-Unit AVP is "money", no rating is
needed, but the corresponding monetary amount is deducted from the
end user's account.
The credit-control server returns the Granted-Service-Unit AVP in the
Credit-Control-Answer message to the Diameter Credit-Control client.
The Granted-Service-Unit AVP contains the amount of service units
that the Diameter Credit-Control client can provide to the end user.
The type of the Granted-Service-Unit can be time, volume, service-
specific, or money, depending on the type of service event.
If the credit-control server determines that no credit-control is
needed for the service, it can include the result code indicating
that the credit-control is not applicable (e.g., the service is free
of charge).
For informative purposes, the Credit-Control-Answer message MAY also
include the Cost-Information AVP containing the estimated total cost
of the requested service.
6.4. Refunds
Some services may refund service units to the end user's account --
for example, gaming services.
The credit-control client MUST set the CC-Request-Type AVP to the
value EVENT_REQUEST and the Requested-Action AVP to REFUND_ACCOUNT in
the Credit-Control-Request message. The Subscription-Id AVP or
Subscription-Id-Extension AVP SHOULD be included to identify the
end user in the credit-control server. The Service-Context-Id AVP
indicates the service-specific document applicable to the request.
The Diameter Credit-Control client MAY include the monetary amount to
be refunded in the Requested-Service-Unit AVP. The Service-
Identifier AVP always indicates the service concerned. If the
Diameter Credit-Control client does not know the monetary amount to
Bertz, et al. Standards Track [Page 47]
RFC 8506 Diameter Credit-Control Application March 2019
be refunded, in addition to the Service-Identifier AVP it MAY send
service-specific AVPs or the Service-Parameter-Info AVP containing
additional service event information to be rated.
For informative purposes, the Credit-Control-Answer message MAY also
include the Cost-Information AVP containing the estimated monetary
amount of refunded units.
6.5. Failure Procedure
Failover to an alternative credit-control server is allowed for a
one-time event, as the server is not maintaining session states. For
instance, if the credit-control client receives a protocol error
DIAMETER_UNABLE_TO_DELIVER or DIAMETER_TOO_BUSY, it can resend the
request to an alternative server, if possible. There MAY be
protocol-transparent Diameter relays and redirect agents or Diameter
Credit-Control proxies between the credit-control client and
credit-control server. Failover may occur at any point in the path
between the credit-control client and the credit-control server if a
transport failure is detected with a peer, as described in [RFC6733].
Because there can be duplicate requests for various reasons, the
credit-control server is responsible for real-time duplicate
detection. Implementation issues for duplicate detection are
discussed in [RFC6733], Appendix C.
When the credit-control client detects a communication failure with
the credit-control server, its behavior depends on the requested
action. The Tx timer (as defined in Section 13) is used in the
credit-control client to supervise communication with the
credit-control server.
If the requested action is PRICE_ENQUIRY or CHECK_BALANCE and a
communication failure is detected, the credit-control client SHOULD
forward the request messages to an alternative credit-control server,
if possible. The secondary credit-control server name, if received
from the home Diameter AAA server, can be used as an address of the
backup server.
If the requested action is DIRECT_DEBITING, the DDFH controls the
credit-control client's behavior. The DDFH may be received from the
home Diameter AAA server or may be locally configured. The
credit-control server may also send the DDFH in any CCA messages to
be used for direct-debiting events compiled thereafter. The DDFH
value received from the home Diameter AAA server overrides the
locally configured value, and the DDFH value received from the
credit-control server in a Credit-Control-Answer message always
overrides any existing values.
Bertz, et al. Standards Track [Page 48]
RFC 8506 Diameter Credit-Control Application March 2019
If the DDFH is set to TERMINATE_OR_BUFFER, the credit-control client
SHOULD NOT grant the service if, after a possible retransmission
attempt to an alternative credit-control server, the credit-control
client can eventually determine from the result code or error code in
the Answer message that units have not been debited. Otherwise, the
credit-control client SHOULD grant the service to the end user and
store the request in credit-control application-level non-volatile
storage. (Note that resending the request at a later time is not a
guarantee that the service will be debited, as the user's account may
be empty when the server successfully processes the request.) The
credit-control client MUST mark these request messages as possible
duplicates by setting the T flag in the command header as described
in [RFC6733], Section 3.
If the DDFH is set to CONTINUE, the service SHOULD be granted, even
if credit-control messages cannot be delivered and messages are not
buffered.
If the Tx timer expires, the credit-control client MUST continue the
service and wait for a possible late answer. If the request
times out, the credit-control client retransmits the request (marked
with the T flag) to a backup credit-control server, if possible. If
the retransmitted request also times out or if a temporary error is
received in answer, the credit-control client buffers the request if
the value of the DDFH is set to TERMINATE_OR_BUFFER. If a failed
answer is received for the retransmitted request, the credit-control
client frees all the resources reserved for the event message and
deletes the request regardless of the value of the DDFH.
The Credit-Control-Request with the requested action REFUND_ACCOUNT
should always be stored in credit-control application-level
non-volatile storage in case a temporary failure occurs. The
credit-control client MUST mark the retransmitted request message as
a possible duplicate by setting the T flag in the command header as
described in [RFC6733], Section 3.
For stored requests, the implementation may choose to limit the
number of retransmission attempts and to define a retransmission
interval.
Note that only one entity in the credit-control system SHOULD be
responsible for duplicate detection. If there is only one
credit-control server within the given realm, the credit-control
server may perform duplicate detection. If there is more than one
credit-control server in a given realm, only one entity in the
credit-control system should be responsible, to ensure that the
end user's account is not debited or credited multiple times for the
same service event.
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7. Credit-Control Application State Machines
This section defines five credit-control application state machines.
The first four state machines are to be observed by credit-control
clients.
The first state machine describes session-based credit-control where
the first interrogation is executed as part of the authorization/
authentication process. The second state machine describes
session-based credit-control where the first interrogation is
executed after the authorization/authentication process. The
requirements regarding what has to be supported for these two state
machines are discussed in Section 5.2.
The third state machine describes session-based credit-control for
the intermediate and final interrogations. The fourth state machine
describes event-based credit-control. These two state machines are
to be observed by all implementations that conform to this
specification.
The fifth state machine describes the credit-control session from a
credit-control server's perspective.
Any event not listed in the state machines MUST be considered an
error condition, and a corresponding answer, if applicable, MUST be
returned to the originator of the message.
In Tables 3, 4, and 5, the event "failure to send" means that the
Diameter Credit-Control client is unable to communicate with the
desired destination or, if a failover procedure is supported, with a
possibly defined alternative destination (e.g., the request times out
and the Answer message is not received). This could be due to
(1) the peer being down or (2) a physical link failure in the path to
or from the credit-control server.
The event "temporary error" means that the Diameter Credit-Control
client received a protocol error notification (DIAMETER_TOO_BUSY,
DIAMETER_UNABLE_TO_DELIVER, or DIAMETER_LOOP_DETECTED) in the
Result-Code AVP of the Credit-Control-Answer command. This type of
notification may ultimately be received in answer to the
retransmitted request to a defined alternative destination, if
failover is supported.
Bertz, et al. Standards Track [Page 50]
RFC 8506 Diameter Credit-Control Application March 2019
The event "failed answer" means that the Diameter Credit-Control
client received a non-transient failure (permanent failure)
notification in the Credit-Control-Answer command. This type of
notification may ultimately be received in answer to the
retransmitted request to a defined alternative destination, if
failover is supported.
The action "store request" means that a request is stored in
credit-control application-level non-volatile storage.
The event "not successfully processed" means that the credit-control
server could not process the message, e.g., due to an unknown
end user, an account being empty, or errors defined in [RFC6733].
The event "user service terminated" can be triggered for various
reasons, e.g., normal user termination, network failure, and ASR
(Abort-Session-Request). The Termination-Cause AVP contains
information about the reason for termination, as specified in
[RFC6733].
The Tx timer, which is used to control the waiting time in the
credit-control client in the Pending state, is stopped upon exit of
the Pending state. The stopping of the Tx timer is omitted in the
state machine when the new state is Idle, as moving to Idle state
implies the clearing of the session and all the variables associated
to it.
The states PendingI, PendingU, PendingT, PendingE, and PendingB stand
for pending states to wait for an answer to a credit-control request
related to Initial, Update, Termination, Event, or Buffered request,
respectively.
In Table 2, failover to a secondary server upon "temporary error" or
"failure to send" is not explicitly described. However, moving an
ongoing credit-control message stream to an alternative server is
possible if the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED,
as described in Section 5.7.
Resending a credit-control event to an alternative server is
supported as described in Section 6.5.
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RFC 8506 Diameter Credit-Control Application March 2019
+----------+-------------------------------+-------------+----------+
| State | Event | Action | New |
| | | | State |
+----------+-------------------------------+-------------+----------+
| Idle | Client or device requests | Send | PendingI |
| | access/service | AA-Request | |
| | | with added | |
| | | CC AVPs, | |
| | | start Tx | |
| | | timer | |
| | | | |
| PendingI | Successful answer to | Grant | Open |
| | AA-Request received | service to | |
| | | end user, | |
| | | stop Tx | |
| | | timer | |
| | | | |
| PendingI | Tx timer expired | Disconnect | Idle |
| | | user/dev | |
| | | | |
| PendingI | Failed AA-Answer received | Disconnect | Idle |
| | | user/dev | |
| | | | |
| PendingI | AA-Answer received with | Grant | Idle |
| | Result-Code equal to | service to | |
| | CREDIT_CONTROL_NOT_APPLICABLE | end user | |
| | | | |
| PendingI | User service terminated | Queue | PendingI |
| | | termination | |
| | | event | |
| | | | |
| PendingI | Change in rating condition | Queue | PendingI |
| | | changed | |
| | | rating | |
| | | condition | |
| | | event | |
+----------+-------------------------------+-------------+----------+
Table 2: Session-Based Client State Machine for the
First Interrogation with AA-Request
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RFC 8506 Diameter Credit-Control Application March 2019
+----------+-------------------------------+-------------+----------+
| State | Event | Action | New |
| | | | State |
+----------+-------------------------------+-------------+----------+
| Idle | Client or device requests | Send CC | PendingI |
| | access/service | initial | |
| | | req., start | |
| | | Tx timer | |
| | | | |
| PendingI | Successful CC initial answer | Stop Tx | Open |
| | received | timer | |
| | | | |
| PendingI | Failure to send, or temporary | Grant | Idle |
| | error and CCFH equal to | service to | |
| | CONTINUE | end user | |
| | | | |
| PendingI | Failure to send, or temporary | Terminate | Idle |
| | error and CCFH equal to | end user's | |
| | TERMINATE or to | service | |
| | RETRY_AND_TERMINATE | | |
| | | | |
| PendingI | Tx timer expired and CCFH | Terminate | Idle |
| | equal to TERMINATE | end user's | |
| | | service | |
| | | | |
| PendingI | Tx timer expired and CCFH | Grant | PendingI |
| | equal to CONTINUE or to | service to | |
| | RETRY_AND_TERMINATE | end user | |
| | | | |
| PendingI | CC initial answer received | Terminate | Idle |
| | with Result-Code equal to | end user's | |
| | END_USER_SERVICE_DENIED or to | service | |
| | USER_UNKNOWN | | |
| | | | |
| PendingI | CC initial answer received | Grant | Idle |
| | with Result-Code equal to | service to | |
| | CREDIT_CONTROL_NOT_APPLICABLE | end user | |
| | | | |
| PendingI | Failed CC initial answer | Grant | Idle |
| | received and CCFH equal to | service to | |
| | CONTINUE | end user | |
| | | | |
| PendingI | Failed CC initial answer | Terminate | Idle |
| | received and CCFH equal to | end user's | |
| | TERMINATE or to | service | |
| | RETRY_AND_TERMINATE | | |
| | | | |
Bertz, et al. Standards Track [Page 53]
RFC 8506 Diameter Credit-Control Application March 2019
| PendingI | User service terminated | Queue | PendingI |
| | | termination | |
| | | event | |
| | | | |
| PendingI | Change in rating condition | Queue | PendingI |
| | | changed | |
| | | rating | |
| | | condition | |
| | | event | |
+----------+-------------------------------+-------------+----------+
Table 3: Session-Based Client State Machine for the
First Interrogation with CCR
+----------+-------------------------------+-------------+----------+
| State | Event | Action | New |
| | | | State |
+----------+-------------------------------+-------------+----------+
| Open | Granted unit elapses and no | Send CC | PendingU |
| | final-unit indication | update | |
| | received | req., start | |
| | | Tx timer | |
| | | | |
| Open | Granted unit elapses and | Terminate | PendingT |
| | final unit action equal to | end user's | |
| | TERMINATE received | service, | |
| | | send CC | |
| | | termination | |
| | | req. | |
| | | | |
| Open | Change in rating condition in | Send CC | PendingU |
| | queue | update | |
| | | req., start | |
| | | Tx timer | |
| | | | |
| Open | Service terminated in queue | Send CC | PendingT |
| | | termination | |
| | | req. | |
| | | | |
| Open | Change in rating condition or | Send CC | PendingU |
| | Validity-Time elapses | update | |
| | | req., start | |
| | | Tx timer | |
| | | | |
| Open | User service terminated | Send CC | PendingT |
| | | termination | |
| | | req. | |
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RFC 8506 Diameter Credit-Control Application March 2019
| | | | |
| Open | RAR received | Send RAA | PendingU |
| | | followed by | |
| | | CC update | |
| | | req., start | |
| | | Tx timer | |
| | | | |
| PendingU | Successful CC update answer | Stop Tx | Open |
| | received | timer | |
| | | | |
| PendingU | Failure to send, or temporary | Grant | Idle |
| | error and CCFH equal to | service to | |
| | CONTINUE | end user | |
| | | | |
| PendingU | Failure to send, or temporary | Terminate | Idle |
| | error and CCFH equal to | end user's | |
| | TERMINATE or to | service | |
| | RETRY_AND_TERMINATE | | |
| | | | |
| PendingU | Tx timer expired and CCFH | Terminate | Idle |
| | equal to TERMINATE | end user's | |
| | | service | |
| | | | |
| PendingU | Tx timer expired and CCFH | Grant | PendingU |
| | equal to CONTINUE or to | service to | |
| | RETRY_AND_TERMINATE | end user | |
| | | | |
| PendingU | CC update answer received | Terminate | Idle |
| | with Result-Code equal to | end user's | |
| | END_USER_SERVICE_DENIED | service | |
| | | | |
| PendingU | CC update answer received | Grant | Idle |
| | with Result-Code equal to | service to | |
| | CREDIT_CONTROL_NOT_APPLICABLE | end user | |
| | | | |
| PendingU | Failed CC update answer | Grant | Idle |
| | received and CCFH equal to | service to | |
| | CONTINUE | end user | |
| | | | |
| PendingU | Failed CC update answer | Terminate | Idle |
| | received and CCFH equal to | end user's | |
| | TERMINATE or to | service | |
| | RETRY_AND_TERMINATE | | |
| | | | |
| PendingU | User service terminated | Queue | PendingU |
| | | termination | |
| | | event | |
| | | | |
Bertz, et al. Standards Track [Page 55]
RFC 8506 Diameter Credit-Control Application March 2019
| PendingU | Change in rating condition | Queue | PendingU |
| | | changed | |
| | | rating | |
| | | condition | |
| | | event | |
| | | | |
| PendingU | RAR received | Send RAA | PendingU |
| | | | |
| PendingT | Successful CC termination | | Idle |
| | answer received | | |
| | | | |
| PendingT | Failure to send, temporary | | Idle |
| | error, or failed answer | | |
| | | | |
| PendingT | Change in rating condition | | PendingT |
+----------+-------------------------------+-------------+----------+
Table 4: Session-Based Client State Machine for Intermediate and
Final Interrogations
+----------+--------------------------------+------------+----------+
| State | Event | Action | New |
| | | | State |
+----------+--------------------------------+------------+----------+
| Idle | Client or device requests a | Send CC | PendingE |
| | one-time service | event | |
| | | req., | |
| | | start Tx | |
| | | timer | |
| | | | |
| Idle | Request in storage | Send | PendingB |
| | | stored | |
| | | request | |
| | | | |
| PendingE | Successful CC event answer | Grant | Idle |
| | received | service to | |
| | | end user | |
| | | | |
| PendingE | Failure to send, temporary | Indicate | Idle |
| | error, failed CC event answer | service | |
| | received, or Tx timer expired; | error | |
| | requested action CHECK_BALANCE | | |
| | or PRICE_ENQUIRY | | |
| | | | |
Bertz, et al. Standards Track [Page 56]
RFC 8506 Diameter Credit-Control Application March 2019
| PendingE | CC event answer received with | Terminate | Idle |
| | Result-Code equal to | end user's | |
| | END_USER_SERVICE_DENIED or to | service | |
| | USER_UNKNOWN and Tx timer | | |
| | running | | |
| | | | |
| PendingE | CC event answer received with | Grant | Idle |
| | Result-Code equal to | service to | |
| | CREDIT_CONTROL_NOT_APPLICABLE; | end user | |
| | requested action | | |
| | DIRECT_DEBITING | | |
| | | | |
| PendingE | Failure to send, temporary | Grant | Idle |
| | error, or failed CC event | service to | |
| | answer received; requested | end user | |
| | action DIRECT_DEBITING; DDFH | | |
| | equal to CONTINUE | | |
| | | | |
| PendingE | Failed CC event answer | Terminate | Idle |
| | received or temporary error; | end user's | |
| | requested action | service | |
| | DIRECT_DEBITING; DDFH equal to | | |
| | TERMINATE_OR_BUFFER and Tx | | |
| | timer running | | |
| | | | |
| PendingE | Tx timer expired; requested | Grant | PendingE |
| | action DIRECT_DEBITING | service to | |
| | | end user | |
| | | | |
| PendingE | Failure to send; requested | Store | Idle |
| | action DIRECT_DEBITING; DDFH | request | |
| | equal to TERMINATE_OR_BUFFER | with | |
| | | T flag | |
| | | | |
| PendingE | Temporary error; requested | Store | Idle |
| | action DIRECT_DEBITING; DDFH | request | |
| | equal to TERMINATE_OR_BUFFER; | | |
| | Tx timer expired | | |
| | | | |
| PendingE | Failed answer or answer | | Idle |
| | received with Result-Code | | |
| | equal to END_USER_SERVICE | | |
| | DENIED or to USER_UNKNOWN; | | |
| | requested action | | |
| | DIRECT_DEBITING; Tx timer | | |
| | expired | | |
| | | | |
Bertz, et al. Standards Track [Page 57]
RFC 8506 Diameter Credit-Control Application March 2019
| PendingE | Failed CC event answer | Indicate | Idle |
| | received; requested action | service | |
| | REFUND_ACCOUNT | error and | |
| | | delete | |
| | | request | |
| | | | |
| PendingE | Failure to send or Tx timer | Store | Idle |
| | expired; requested action | request | |
| | REFUND_ACCOUNT | with | |
| | | T flag | |
| | | | |
| PendingE | Temporary error; requested | Store | Idle |
| | action REFUND_ACCOUNT | request | |
| | | | |
| PendingB | Successful CC answer received | Delete | Idle |
| | | request | |
| | | | |
| PendingB | Failed CC answer received | Delete | Idle |
| | | request | |
| | | | |
| PendingB | Failure to send or temporary | | Idle |
| | error | | |
+----------+--------------------------------+------------+----------+
Table 5: One-Time Event Client State Machine
+-------+------------------------+--------------------------+-------+
| State | Event | Action | New |
| | | | State |
+-------+------------------------+--------------------------+-------+
| Idle | CC initial request | Send CC initial answer, | Open |
| | received and | reserve units, start Tcc | |
| | successfully processed | | |
| | | | |
| Idle | CC initial request | Send CC initial answer | Idle |
| | received but not | with Result-Code != | |
| | successfully processed | SUCCESS | |
| | | | |
| Idle | CC event request | Send CC event answer | Idle |
| | received and | | |
| | successfully processed | | |
| | | | |
| Idle | CC event request | Send CC event answer | Idle |
| | received but not | with Result-Code != | |
| | successfully processed | SUCCESS | |
| | | | |
Bertz, et al. Standards Track [Page 58]
RFC 8506 Diameter Credit-Control Application March 2019
| Open | CC update request | Send CC update answer, | Open |
| | received and | debit used units, | |
| | successfully processed | reserve new units, | |
| | | restart Tcc | |
| | | | |
| Open | CC update request | Send CC update answer | Idle |
| | received but not | with Result-Code != | |
| | successfully processed | SUCCESS, debit used | |
| | | units | |
| | | | |
| Open | CC termination request | Send CC termin. answer, | Idle |
| | received and | stop Tcc, debit used | |
| | successfully processed | units | |
| | | | |
| Open | CC termination request | Send CC termin. answer | Idle |
| | received but not | with Result-Code != | |
| | successfully processed | SUCCESS, debit used | |
| | | units | |
| | | | |
| Open | Session supervision | Release reserved units | Idle |
| | timer Tcc expired | | |
+-------+------------------------+--------------------------+-------+
Table 6: Session-Based and Event-Based Server State Machine
8. Credit-Control AVPs
This section defines the Credit-Control AVPs that are specific to the
Diameter Credit-Control application and that MAY be included in the
Diameter Credit-Control messages.
The AVPs defined in this section MAY also be included in
authorization commands defined in authorization-specific
applications, such as [RFC7155] and [RFC4004], if the first
interrogation is performed as part of the authorization/
authentication process, as described in Section 5.2.
The Diameter AVP rules are defined in [RFC6733], Section 4. These
AVP rules are observed in AVPs defined in this section.
The following table describes the Diameter AVPs defined in the
credit-control application, their AVP Code values, types, and
possible flag values. The AVP Flag rules ('M', 'V') are explained in
[RFC6733], Section 4.1.
Bertz, et al. Standards Track [Page 59]
RFC 8506 Diameter Credit-Control Application March 2019
+---------------+
|AVP Flag Rules |
Defined |----+-----+----|
AVP in | | |MUST|
Attribute Name Code Section Data Type |MUST| MAY |NOT |
----------------------------------------------------|----+-----+----|
CC-Correlation-Id 411 8.1 OctetString | | M | V |
CC-Input-Octets 412 8.24 Unsigned64 | M | | V |
CC-Money 413 8.22 Grouped | M | | V |
CC-Output-Octets 414 8.25 Unsigned64 | M | | V |
CC-Request-Number 415 8.2 Unsigned32 | M | | V |
CC-Request-Type 416 8.3 Enumerated | M | | V |
CC-Service-Specific- 417 8.26 Unsigned64 | M | | V |
Units | | | |
CC-Session-Failover 418 8.4 Enumerated | M | | V |
CC-Sub-Session-Id 419 8.5 Unsigned64 | M | | V |
CC-Time 420 8.21 Unsigned32 | M | | V |
CC-Total-Octets 421 8.23 Unsigned64 | M | | V |
CC-Unit-Type 454 8.32 Enumerated | M | | V |
Check-Balance-Result 422 8.6 Enumerated | M | | V |
Cost-Information 423 8.7 Grouped | M | | V |
Cost-Unit 424 8.12 UTF8String | M | | V |
Credit-Control 426 8.13 Enumerated | M | | V |
Credit-Control- 427 8.14 Enumerated | M | | V |
Failure-Handling | | | |
Currency-Code 425 8.11 Unsigned32 | M | | V |
Direct-Debiting- 428 8.15 Enumerated | M | | V |
Failure-Handling | | | |
Exponent 429 8.9 Integer32 | M | | V |
Final-Unit-Action 449 8.35 Enumerated | M | | V |
Final-Unit-Indication 430 8.34 Grouped | M | | V |
QoS-Final-Unit-Indication 669 8.68 Grouped | | M | V |
Granted-Service-Unit 431 8.17 Grouped | M | | V |
G-S-U-Pool-Identifier 453 8.31 Unsigned32 | M | | V |
G-S-U-Pool-Reference 457 8.30 Grouped | M | | V |
Multiple-Services- 456 8.16 Grouped | M | | V |
Credit-Control | | | |
Multiple-Services- 455 8.40 Enumerated | M | | V |
Indicator | | | |
Rating-Group 432 8.29 Unsigned32 | M | | V |
Redirect-Address-Type 433 8.38 Enumerated | M | | V |
Redirect-Server 434 8.37 Grouped | M | | V |
Redirect-Server-Address 435 8.39 UTF8String | M | | V |
Redirect-Server-Extension 665 8.64 Grouped | | M | V |
Redirect-Address- 666 8.65 Address | | M | V |
IPAddress | | | |
Redirect-Address-URL 667 8.66 UTF8String | | M | V |
Redirect-Address-SIP-URI 668 8.67 UTF8String | | M | V |
Bertz, et al. Standards Track [Page 60]
RFC 8506 Diameter Credit-Control Application March 2019
Requested-Action 436 8.41 Enumerated | M | | V |
Requested-Service-Unit 437 8.18 Grouped | M | | V |
Restriction-Filter-Rule 438 8.36 IPFilterRule| M | | V |
Service-Context-Id 461 8.42 UTF8String | M | | V |
Service-Identifier 439 8.28 Unsigned32 | M | | V |
Service-Parameter-Info 440 8.43 Grouped | | M | V |
Service-Parameter-Type 441 8.44 Unsigned32 | | M | V |
Service-Parameter-Value 442 8.45 OctetString | | M | V |
Subscription-Id 443 8.46 Grouped | M | | V |
Subscription-Id-Data 444 8.48 UTF8String | M | | V |
Subscription-Id-Type 450 8.47 Enumerated | M | | V |
Subscription-Id-Extension 659 8.58 Grouped | | M | V |
Subscription-Id-E164 660 8.59 UTF8String | | M | V |
Subscription-Id-IMSI 661 8.60 UTF8String | | M | V |
Subscription-Id-SIP-URI 662 8.61 UTF8String | | M | V |
Subscription-Id-NAI 663 8.62 UTF8String | | M | V |
Subscription-Id-Private 664 8.63 UTF8String | | M | V |
Tariff-Change-Usage 452 8.27 Enumerated | M | | V |
Tariff-Time-Change 451 8.20 Time | M | | V |
Unit-Value 445 8.8 Grouped | M | | V |
Used-Service-Unit 446 8.19 Grouped | M | | V |
User-Equipment-Info 458 8.49 Grouped | | M | V |
User-Equipment-Info-Type 459 8.50 Enumerated | | M | V |
User-Equipment-Info-Value 460 8.51 OctetString | | M | V |
User-Equipment-Info- 653 8.52 Grouped | | M | V |
Extension | | | |
User-Equipment-Info- 654 8.53 OctetString | | M | V |
IMEISV | | | |
User-Equipment-Info-MAC 655 8.54 OctetString | | M | V |
User-Equipment-Info-EUI64 656 8.55 OctetString | | M | V |
User-Equipment-Info- 657 8.56 OctetString | | M | V |
ModifiedEUI64 | | | |
User-Equipment-Info-IMEI 658 8.57 OctetString | | M | V |
Value-Digits 447 8.10 Integer64 | M | | V |
Validity-Time 448 8.33 Unsigned32 | M | | V |
8.1. CC-Correlation-Id AVP
The CC-Correlation-Id AVP (AVP Code 411) is of type OctetString and
contains information to correlate credit-control requests generated
for different components of the service, e.g., transport and service
level. Whoever allocates the Service-Context-Id (i.e., a unique
identifier of a service-specific document) is also responsible for
defining the content and encoding of the CC-Correlation-Id AVP.
Bertz, et al. Standards Track [Page 61]
RFC 8506 Diameter Credit-Control Application March 2019
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 the Session-Id AVP and the
CC-Request-Number AVP is also globally unique and can be used in
matching credit-control messages with confirmations. An easy way to
produce unique numbers is to set the value of the CC-Request-Number
AVP to 0 for a credit-control request with a CC-Request-Type AVP of
INITIAL_REQUEST (the initial request in a session). The value of the
CC-Request-Number AVP should be set to 1 for the first
UPDATE_REQUEST, to 2 for the second, and so on until the value for
TERMINATION_REQUEST is one more than the value for the last
UPDATE_REQUEST. In the case of event charging (when the CC-Request-
Type AVP has the value EVENT_REQUEST), the CC-Request-Number AVP
should be set to 0 for a credit-control request.
8.3. CC-Request-Type AVP
The CC-Request-Type AVP (AVP Code 416) is of type Enumerated and
contains the reason for sending the Credit-Control-Request message.
It MUST be present in all Credit-Control-Request messages. The
following values are defined for the CC-Request-Type AVP (the value
of 0 (zero) is reserved):
INITIAL_REQUEST 1
This request is used to initiate a credit-control session. It
contains credit-control information that is relevant to the
initiation.
UPDATE_REQUEST 2
This request contains credit-control information for an existing
credit-control session. Credit-control requests of this type SHOULD
be sent every time a credit-control re-authorization is needed at the
expiry of the allocated quota or validity time. Further, additional
service-specific events MAY trigger a spontaneous UPDATE_REQUEST.
TERMINATION_REQUEST 3
This request is sent to terminate a credit-control session. It
contains credit-control information relevant to the existing session.
Bertz, et al. Standards Track [Page 62]
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EVENT_REQUEST 4
This request is used when there is no need to maintain any
credit-control session state in the credit-control server. It
contains all information relevant to the service and is the only
request of the service. The reason for this request is further
detailed in the Requested-Action AVP. The Requested-Action AVP MUST
be included in the Credit-Control-Request message when CC-Request-
Type is set to EVENT_REQUEST.
8.4. CC-Session-Failover AVP
The CC-Session-Failover AVP (AVP Code 418) is of type Enumerated and
contains information as to whether moving the credit-control message
stream to a backup server during an ongoing credit-control session is
supported. In the case of communication failures, the credit-control
message streams can be moved to an alternative destination if the
credit-control server supports failover to an alternative server.
The secondary credit-control server name, if received from the home
Diameter AAA server, can be used as an address of the backup server.
An implementation is not required to support moving a credit-control
message stream to an alternative server, as this also requires moving
information related to the credit-control session to the backup
server.
The following values are defined for the CC-Session-Failover AVP:
FAILOVER_NOT_SUPPORTED 0
When the CC-Session-Failover AVP is set to FAILOVER_NOT_SUPPORTED,
the credit-control message stream MUST NOT be moved to an alternative
destination in the case of a communication failure. This is the
default behavior if the AVP isn't included in the reply from the
authorization or credit-control server.
FAILOVER_SUPPORTED 1
When the CC-Session-Failover AVP is set to FAILOVER_SUPPORTED, the
credit-control message stream SHOULD be moved to an alternative
destination in the case of a communication failure. Moving the
credit-control message stream to a backup server MAY require that
information related to the credit-control session should also be
forwarded to an alternative server.
Bertz, et al. Standards Track [Page 63]
RFC 8506 Diameter Credit-Control Application March 2019
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 AVP and this AVP MUST be unique per sub-session,
and the value of this AVP MUST be monotonically increased by one for
all new sub-sessions. The absence of this AVP implies that no
sub-sessions are in use.
8.6. Check-Balance-Result AVP
The Check-Balance-Result AVP (AVP Code 422) is of type Enumerated and
contains the result of the balance check. This AVP is applicable
only when the Requested-Action AVP indicates CHECK_BALANCE in the
Credit-Control-Request command. The following values are defined for
the Check-Balance-Result AVP:
ENOUGH_CREDIT 0
There is enough credit in the account to cover the requested service.
NO_CREDIT 1
There isn't enough credit in the account to cover the requested
service.
8.7. Cost-Information AVP
The Cost-Information AVP (AVP Code 423) is of type Grouped, and it is
used to return the cost information of a service, which the
credit-control client can transfer transparently to the end user.
The included Unit-Value AVP contains the cost estimate (always of
type "money") of the service in the case of price inquiries, or the
accumulated cost estimation in the case of a credit-control session.
The Currency-Code AVP specifies in which currency the cost was given.
The Cost-Unit AVP specifies the unit when the service cost is a cost
per unit (e.g., cost for the service is $1 per minute).
When the Requested-Action AVP with the value PRICE_ENQUIRY is
included in the Credit-Control-Request command, the Cost-Information
AVP sent in the succeeding Credit-Control-Answer command contains the
cost estimation for the requested service, without any reservations
being made.
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RFC 8506 Diameter Credit-Control Application March 2019
The Cost-Information AVP included in the Credit-Control-Answer
command with the CC-Request-Type set to UPDATE_REQUEST contains the
accumulated cost estimation for the session, without taking any
credit reservations into account.
The Cost-Information AVP included in the Credit-Control-Answer
command with the CC-Request-Type set to EVENT_REQUEST or
TERMINATION_REQUEST contains the estimated total cost for the
requested service.
The Cost-Information AVP is defined as follows (per grouped-avp-def
as defined in [RFC6733]):
Cost-Information ::= < AVP Header: 423 >
{ Unit-Value }
{ Currency-Code }
[ Cost-Unit ]
8.8. Unit-Value AVP
The Unit-Value AVP is of type Grouped (AVP Code 445) and specifies
the cost as a floating-point value. The Unit-Value is a significand
with an exponent; i.e., Unit-Value = Value-Digits AVP * 10^Exponent.
This representation avoids unwanted rounding off. For example, the
value of 2,3 is represented as Value-Digits = 23 and Exponent = -1.
The absence of the exponent part MUST be interpreted as an exponent
equal to zero.
The Unit-Value AVP is defined as follows (per grouped-avp-def as
defined in [RFC6733]):
Unit-Value ::= < AVP Header: 445 >
{ Value-Digits }
[ Exponent ]
8.9. Exponent AVP
The Exponent AVP is of type Integer32 (AVP Code 429) and contains the
exponent value to be applied for the Value-Digits AVP within the
Unit-Value AVP.
Bertz, et al. Standards Track [Page 65]
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8.10. Value-Digits AVP
The Value-Digits AVP is of type Integer64 (AVP Code 447) and contains
the significant digits of the number. If decimal values are needed
to present the units, the scaling MUST be indicated with the related
Exponent AVP. For example, for the monetary amount $0.05, the value
of the Value-Digits AVP MUST be set to 5, and the scaling MUST be
indicated with the Exponent AVP set to -2.
8.11. Currency-Code AVP
The Currency-Code AVP (AVP Code 425) is of type Unsigned32 and
contains a currency code that specifies in which currency the values
of AVPs containing monetary units were given. It is specified by
using the numeric values defined in the ISO 4217 standard [ISO4217].
8.12. Cost-Unit AVP
The Cost-Unit AVP (AVP Code 424) is of type UTF8String, and it is
used to display a human-readable string to the end user. It
specifies the applicable unit to the Cost-Information AVP when the
service cost is a cost per unit (e.g., cost of the service is $1 per
minute). The Cost-Unit setting can be minutes, hours, days,
kilobytes, megabytes, etc.
8.13. Credit-Control AVP
The Credit-Control AVP (AVP Code 426) is of type Enumerated and MUST
be included in AA-Request messages when the Service Element has
credit-control capabilities. The following values are defined for
the Credit-Control AVP:
CREDIT_AUTHORIZATION 0
If the home Diameter AAA server determines that the user has a
prepaid subscription, this value indicates that the credit-control
server MUST be contacted to perform the first interrogation. The
value of the Credit-Control AVP MUST always be set to 0 in an
AA-Request sent to perform the first interrogation and to initiate a
new credit-control session.
RE_AUTHORIZATION 1
This value indicates to the Diameter AAA server that a credit-control
session is ongoing for the subscriber and that the credit-control
server MUST NOT be contacted. The Credit-Control AVP set to the
value of 1 is to be used only when the first interrogation has been
successfully performed and the credit-control session is ongoing
Bertz, et al. Standards Track [Page 66]
RFC 8506 Diameter Credit-Control Application March 2019
(i.e., re-authorization triggered by authorization lifetime). This
value MUST NOT be used in an AA-Request sent to perform the first
interrogation.
8.14. Credit-Control-Failure-Handling AVP (CCFH)
The CCFH (AVP Code 427) is of type Enumerated. The credit-control
client uses information in this AVP to decide what to do if sending
credit-control messages to the credit-control server has been, for
instance, temporarily prevented due to a network problem. Depending
on the service logic, the credit-control server can order the client
to terminate the service immediately when there is a reason to
believe that the service cannot be charged, or to try failover to an
alternative server, if possible. The server could then either
terminate or grant the service, should the alternative connection
also fail.
The following values are defined for the CCFH:
TERMINATE 0
When the CCFH is set to TERMINATE, the service MUST only be granted
for as long as there is a connection to the credit-control server.
If the credit-control client does not receive any Credit-Control-
Answer messages before the Tx timer (as defined in Section 13)
expires, the credit-control request is regarded as failed, and the
end user's service session is terminated.
This is the default behavior if the AVP isn't included in the reply
from the authorization or credit-control server.
CONTINUE 1
When the CCFH is set to CONTINUE, the credit-control client SHOULD
resend the request to an alternative server in the case of transport
or temporary failures, provided that (1) a failover procedure is
supported in the credit-control server and the credit-control client
and (2) an alternative server is available. Otherwise, the service
SHOULD be granted, even if credit-control messages can't be
delivered.
RETRY_AND_TERMINATE 2
When the CCFH is set to RETRY_AND_TERMINATE, the credit-control
client SHOULD resend the request to an alternative server in the case
of transport or temporary failures, provided that (1) a failover
procedure is supported in the credit-control server and the
credit-control client and (2) an alternative server is available.
Bertz, et al. Standards Track [Page 67]
RFC 8506 Diameter Credit-Control Application March 2019
Otherwise, the service SHOULD NOT be granted when the credit-control
messages can't be delivered.
8.15. Direct-Debiting-Failure-Handling AVP (DDFH)
The DDFH (AVP Code 428) is of type Enumerated. The credit-control
client uses information in this AVP to decide what to do if sending
credit-control messages (Requested-Action AVP set to DIRECT_DEBITING)
to the credit-control server has been, for instance, temporarily
prevented due to a network problem.
The following values are defined for the DDFH:
TERMINATE_OR_BUFFER 0
When the DDFH is set to TERMINATE_OR_BUFFER, the service MUST be
granted for as long as there is a connection to the credit-control
server. If the credit-control client does not receive any
Credit-Control-Answer messages before the Tx timer (as defined in
Section 13) expires, the credit-control request is regarded as
failed. The client SHOULD terminate the service if it can determine
from the failed answer that units have not been debited. Otherwise,
the credit-control client SHOULD grant the service, store the request
in application-level non-volatile storage, and try to resend the
request. These requests MUST be marked as possible duplicates by
setting the T flag in the command header as described in [RFC6733],
Section 3. This is the default behavior if the AVP isn't included in
the reply from the authorization server.
CONTINUE 1
When the DDFH is set to CONTINUE, the service SHOULD be granted, even
if credit-control messages can't be delivered, and the request should
be deleted.
8.16. Multiple-Services-Credit-Control AVP
The Multiple-Services-Credit-Control AVP (AVP Code 456) is of type
Grouped and contains the AVPs related to the independent
credit-control of multiple services. Note that each instance of this
AVP carries units related to one or more services or related to a
single rating-group.
The Service-Identifier AVP and the Rating-Group AVP are used to
associate the granted units to a given service or rating-group. If
both the Service-Identifier AVP and the Rating-Group AVP are
included, the target of the service units is always the service(s)
indicated by the value of the Service-Identifier AVP(s). If only the
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Rating-Group AVP is present, the Multiple-Services-Credit-Control AVP
relates to all the services that belong to the specified
rating-group.
The G-S-U-Pool-Reference AVP allows the server to specify a
G-S-U-Pool-Identifier identifying a credit pool within which the
units of the specified type are considered pooled. If a G-S-U-Pool-
Reference AVP is present, then actual service units of the specified
type MUST also be present. For example, if the G-S-U-Pool-Reference
AVP specifies a CC-Unit-Type value of TIME (Section 8.32), then the
CC-Time AVP MUST be present.
The Requested-Service-Unit AVP MAY contain the amount of requested
service units or the requested monetary value. It MUST be present in
the initial interrogation and within the intermediate interrogations
in which a new quota is requested. If the credit-control client does
not include the Requested-Service-Unit AVP in a request command --
because, for instance, it has determined that the end user terminated
the service -- the server MUST debit the used amount from the user's
account but MUST NOT return a new quota in the corresponding answer.
The Validity-Time, Result-Code, and Final-Unit-Indication or
QoS-Final-Unit-Indication AVPs MAY be present in a Credit-Control-
Answer command as defined in Sections 5.1.2 and 5.6 for graceful
service termination.
When both the Tariff-Time-Change AVP and the Tariff-Change-Usage AVP
are present, the server MUST include two separate instances of the
Multiple-Services-Credit-Control AVP with the Granted-Service-Unit
AVP associated to the same service-identifier and/or rating-group.
Where the two quotas are associated to the same pool or to different
pools, the credit-pooling mechanism defined in Section 5.1.2 applies.
When the client is reporting used units before and after the tariff
time change, it MUST use the Tariff-Change-Usage AVP inside the
Used-Service-Unit AVP.
A server not implementing the independent credit-control of multiple
services MUST treat the Multiple-Services-Credit-Control AVP as an
invalid AVP.
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The Multiple-Services-Credit-Control AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Multiple-Services-Credit-Control ::= < AVP Header: 456 >
[ Granted-Service-Unit ]
[ Requested-Service-Unit ]
*[ Used-Service-Unit ]
[ Tariff-Change-Usage ]
*[ Service-Identifier ]
[ Rating-Group ]
*[ G-S-U-Pool-Reference ]
[ Validity-Time ]
[ Result-Code ]
[ Final-Unit-Indication ]
[ QoS-Final-Unit-Indication ]
*[ AVP ]
8.17. Granted-Service-Unit AVP
The Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
contains the amount of units that the Diameter Credit-Control client
can provide to the end user until the service must be released or the
new Credit-Control-Request must be sent. A client is not required to
implement all the unit types, and it must treat unknown or
unsupported unit types in the Answer message as an incorrect CCA. In
this case, the client MUST terminate the credit-control session and
indicate the reason as DIAMETER_BAD_ANSWER in the Termination-Cause
AVP.
The Granted-Service-Unit AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Granted-Service-Unit ::= < AVP Header: 431 >
[ Tariff-Time-Change ]
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ AVP ]
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8.18. Requested-Service-Unit AVP
The Requested-Service-Unit AVP (AVP Code 437) is of type Grouped and
contains the amount of requested units specified by the Diameter
Credit-Control client. A server is not required to implement all the
unit types, and it must treat unknown or unsupported unit types as
invalid AVPs.
The Requested-Service-Unit AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Requested-Service-Unit ::= < AVP Header: 437 >
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ AVP ]
8.19. Used-Service-Unit AVP
The Used-Service-Unit AVP is of type Grouped (AVP Code 446) and
contains the amount of used units measured from the point when the
service became active or, if interim interrogations are used during
the session, from the point when the previous measurement ended.
Note: The value reported in a Used-Service-Unit AVP is not
necessarily related to the grant provided in a Granted-Service-Unit
AVP, e.g., the value in this AVP may exceed the value in the grant.
The Used-Service-Unit AVP is defined as follows (per grouped-avp-def
as defined in [RFC6733]):
Used-Service-Unit ::= < AVP Header: 446 >
[ Tariff-Change-Usage ]
[ CC-Time ]
[ CC-Money ]
[ CC-Total-Octets ]
[ CC-Input-Octets ]
[ CC-Output-Octets ]
[ CC-Service-Specific-Units ]
*[ AVP ]
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8.20. Tariff-Time-Change AVP
The Tariff-Time-Change AVP (AVP Code 451) is of type Time. It is
sent from the server to the client and includes the time in seconds
since January 1, 1900, 00:00 UTC, when the tariff of the service will
be changed.
The tariff change mechanism is optional for the client and server,
and it is not used for time-based services (Section 5). If a client
does not support the tariff time change mechanism, it MUST treat the
Tariff-Time-Change AVP in the Answer message as an incorrect CCA. In
this case, the client terminates the credit-control session and
indicates the reason as DIAMETER_BAD_ANSWER in the Termination-Cause
AVP.
Omission of this AVP means that no tariff change is to be reported.
8.21. CC-Time AVP
The CC-Time AVP (AVP Code 420) is of type Unsigned32 and indicates
the length of the requested, granted, or used time in seconds.
8.22. CC-Money AVP
The CC-Money AVP (AVP Code 413) is of type Grouped and specifies the
monetary amount in the given currency. The Currency-Code AVP SHOULD
be included. The CC-Money AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
CC-Money ::= < AVP Header: 413 >
{ Unit-Value }
[ Currency-Code ]
8.23. CC-Total-Octets AVP
The CC-Total-Octets AVP (AVP Code 421) is of type Unsigned64 and
contains the total number of requested, granted, or used octets
regardless of the direction (sent or received).
8.24. CC-Input-Octets AVP
The CC-Input-Octets AVP (AVP Code 412) is of type Unsigned64 and
contains the number of requested, granted, or used octets that
can be / have been received from the end user.
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8.25. CC-Output-Octets AVP
The CC-Output-Octets AVP (AVP Code 414) is of type Unsigned64 and
contains the number of requested, granted, or used octets that
can be / have been sent to the end user.
8.26. CC-Service-Specific-Units AVP
The CC-Service-Specific-Units AVP (AVP Code 417) is of type
Unsigned64 and specifies the number of service-specific units (e.g.,
number of events, points) given in a selected service. The service-
specific units always refer to the service identified in the Service-
Identifier AVP (or Rating-Group AVP when the Multiple-Services-
Credit-Control AVP is used).
8.27. Tariff-Change-Usage AVP
The Tariff-Change-Usage AVP (AVP Code 452) is of type Enumerated and
defines whether units are used before or after a tariff change, or
whether the units straddled a tariff change during the reporting
period. Omission of this AVP means that no tariff change has
occurred.
In addition, when present in Answer messages as part of the Multiple-
Services-Credit-Control AVP, this AVP defines whether units are
allocated to be used before or after a tariff change event.
When the Tariff-Time-Change AVP is present, omission of this AVP in
Answer messages means that the single-quota mechanism applies.
Tariff-Change-Usage can be set to one of the following values:
UNIT_BEFORE_TARIFF_CHANGE 0
When present in the Multiple-Services-Credit-Control AVP, this value
indicates the amount of units allocated for use before a tariff
change occurs.
When present in the Used-Service-Unit AVP, this value indicates the
amount of resource units used before a tariff change had occurred.
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UNIT_AFTER_TARIFF_CHANGE 1
When present in the Multiple-Services-Credit-Control AVP, this value
indicates the amount of units allocated for use after a tariff change
occurs.
When present in the Used-Service-Unit AVP, this value indicates the
amount of resource units used after a tariff change had occurred.
UNIT_INDETERMINATE 2
This value is to be used only in the Used-Service-Unit AVP and
indicates the amount of resource units that straddle the tariff
change (e.g., the metering process reports to the credit-control
client in blocks of n octets, and one block straddled the tariff
change).
8.28. Service-Identifier AVP
The Service-Identifier AVP is of type Unsigned32 (AVP Code 439) and
contains the identifier of a service. The specific service the
request relates to is uniquely identified by the combination of the
Service-Context-Id AVP and the Service-Identifier AVP.
A usage example of this AVP is illustrated in Appendix A.9.
8.29. Rating-Group AVP
The Rating-Group AVP is of type Unsigned32 (AVP Code 432) and
contains the identifier of a rating-group. All the services subject
to the same rating type are part of the same rating-group. The
specific rating-group the request relates to is uniquely identified
by the combination of the Service-Context-Id AVP and the Rating-Group
AVP.
A usage example of this AVP is illustrated in Appendix A.9.
8.30. G-S-U-Pool-Reference AVP
The G-S-U-Pool-Reference AVP (AVP Code 457) is of type Grouped. It
is used in the Credit-Control-Answer message and associates the
Granted-Service-Unit AVP within which it appears with a credit pool
within the session.
The G-S-U-Pool-Identifier AVP specifies the credit pool from which
credit is drawn for this unit type.
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The CC-Unit-Type AVP specifies the type of units for which credit is
pooled.
The Unit-Value AVP specifies the multiplier, which converts between
service units of type CC-Unit-Type and abstract service units within
the credit pool (and thus to service units of any other services or
rating-groups associated with the same pool).
The G-S-U-Pool-Reference AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
G-S-U-Pool-Reference ::= < AVP Header: 457 >
{ G-S-U-Pool-Identifier }
{ CC-Unit-Type }
{ Unit-Value }
8.31. G-S-U-Pool-Identifier AVP
The G-S-U-Pool-Identifier AVP (AVP Code 453) is of type Unsigned32
and identifies a credit pool within the session.
8.32. CC-Unit-Type AVP
The CC-Unit-Type AVP (AVP Code 454) is of type Enumerated and
specifies the type of units considered to be pooled into a
credit pool.
The following values are defined for the CC-Unit-Type AVP:
TIME 0
MONEY 1
TOTAL-OCTETS 2
INPUT-OCTETS 3
OUTPUT-OCTETS 4
SERVICE-SPECIFIC-UNITS 5
8.33. Validity-Time AVP
The Validity-Time AVP is of type Unsigned32 (AVP Code 448). It is
sent from the credit-control server to the credit-control client.
The Validity-Time AVP contains the validity time of the granted
service units. The measurement of the Validity-Time is started upon
receipt of the Credit-Control-Answer message containing this AVP. If
the granted service units have not been consumed within the validity
time specified in this AVP, the credit-control client MUST send a
Credit-Control-Request message to the server, with CC-Request-Type
set to UPDATE_REQUEST. The value field of the Validity-Time AVP is
given in seconds.
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The Validity-Time AVP is also used for graceful service termination
(see Section 5.6) to indicate to the credit-control client how long
the subscriber is allowed to use network resources after the
specified action (i.e., REDIRECT or RESTRICT_ACCESS) started. When
the Validity-Time elapses, a new intermediate interrogation is sent
to the server.
8.34. Final-Unit-Indication AVP
The Final-Unit-Indication AVP (AVP Code 430) is of type Grouped and
indicates that the Granted-Service-Unit AVP in the Credit-Control-
Answer or in the AA-Answer contains the final units for the service.
After these units have expired, the Diameter Credit-Control client is
responsible for executing the action indicated in the Final-Unit-
Action AVP (see Section 5.6).
If more than one unit type is received in the Credit-Control-Answer,
the unit type that first expired SHOULD cause the credit-control
client to execute the specified action.
In the first interrogation, the Final-Unit-Indication AVP with
Final-Unit-Action set to REDIRECT or RESTRICT_ACCESS can also be
present with no Granted-Service-Unit AVP in the Credit-Control-Answer
or in the AA-Answer. This indicates to the Diameter Credit-Control
client that the client is to execute the specified action
immediately. If the home service provider policy is to terminate the
service, naturally, the server SHOULD return the appropriate
transient failure (see Section 9.1) in order to implement the policy-
defined action.
The Final-Unit-Action AVP defines the behavior of the Service Element
when the user's account cannot cover the cost of the service and MUST
always be present if the Final-Unit-Indication AVP is included in a
command.
If the Final-Unit-Action AVP is set to TERMINATE, the Final-Unit-
Indication group AVP MUST NOT contain any other AVPs.
If the Final-Unit-Action AVP is set to REDIRECT, the Redirect-Server
AVP or the Redirect-Server-Extension AVP (at least one) MUST be
present. The Restriction-Filter-Rule AVP or the Filter-Id AVP MAY be
present in the Credit-Control-Answer message if the user is also
allowed to access other services that are not accessible through the
address given in the Redirect-Server AVP.
If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
Restriction-Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
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The Filter-Id AVP is defined in [RFC7155]. The Filter-Id AVP can be
used to reference an IP filter list installed in the access device by
means other than the Diameter Credit-Control application, e.g.,
locally configured or configured by another entity.
If the Final-Unit-Action AVP is set to REDIRECT and the type of
server is not one of the enumerations in the Redirect-Address-Type
AVP, then the QoS-Final-Unit-Indication AVP SHOULD be used together
with the Redirect-Server-Extension AVP instead of the Final-Unit-
Indication AVP.
If the Final-Unit-Action AVP is set to RESTRICT_ACCESS or REDIRECT
and the classification of the restricted traffic cannot be expressed
using an IPFilterRule, or if actions (e.g., QoS) other than just
allowing traffic need to be enforced, then the QoS-Final-Unit-
Indication AVP SHOULD be used instead of the Final-Unit-Indication
AVP. However, if the credit-control server wants to preserve
backward compatibility with credit-control clients that support only
[RFC4006], the Final-Unit-Indication AVP SHOULD be used together with
the Filter-Id AVP.
The Final-Unit-Indication AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Final-Unit-Indication ::= < AVP Header: 430 >
{ Final-Unit-Action }
*[ Restriction-Filter-Rule ]
*[ Filter-Id ]
[ Redirect-Server ]
8.35. Final-Unit-Action AVP
The Final-Unit-Action AVP (AVP Code 449) is of type Enumerated and
indicates to the credit-control client the action to be taken when
the user's account cannot cover the service cost.
Final-Unit-Action can be set to one of the following values:
TERMINATE 0
The credit-control client MUST terminate the service session. This
is the default handling, applicable whenever the credit-control
client receives an unsupported Final-Unit-Action value, and it MUST
be supported by all the Diameter Credit-Control client
implementations conforming to this specification.
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REDIRECT 1
The Service Element MUST redirect the user to the address specified
in the Redirect-Server-Address AVP or one of the AVPs included in the
Redirect-Server-Extension AVP. The redirect action is defined in
Section 5.6.2.
RESTRICT_ACCESS 2
The access device MUST restrict the user's access according to the
filter AVPs contained in the applied Grouped AVP: according to IP
packet filters defined in the Restriction-Filter-Rule AVP, according
to the packet classifier filters defined in the Filter-Rule AVP, or
according to the packet filters identified by the Filter-Id AVP. All
of the packets not matching any restriction filters (see
Section 5.6.3) MUST be dropped.
8.36. Restriction-Filter-Rule AVP
The Restriction-Filter-Rule AVP (AVP Code 438) is of type
IPFilterRule and provides filter rules corresponding to services that
are to remain accessible even if there are no more service units
granted. The access device has to configure the specified filter
rules for the subscriber and MUST drop all the packets not matching
these filters. Zero, one, or more such AVPs MAY be present in a
Credit-Control-Answer message or in an AA-Answer message.
8.37. Redirect-Server AVP
The Redirect-Server AVP (AVP Code 434) is of type Grouped and
contains the address information of the redirect server (e.g., HTTP
redirect server, SIP Server) with which the end user is to be
connected when the account cannot cover the service cost. It MUST be
present when the Final-Unit-Action AVP is set to REDIRECT.
The Redirect-Server AVP is defined as follows (per grouped-avp-def as
defined in [RFC6733]):
Redirect-Server ::= < AVP Header: 434 >
{ Redirect-Address-Type }
{ Redirect-Server-Address }
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8.38. Redirect-Address-Type AVP
The Redirect-Address-Type AVP (AVP Code 433) is of type Enumerated
and defines the address type of the address given in the Redirect-
Server-Address AVP.
Redirect-Address-Type can be set to one of the following values:
IPv4 Address 0
The address type is in the form of a "dotted-decimal" IPv4 address,
as defined in [RFC791].
IPv6 Address 1
The address type is in the form of an IPv6 address, as defined in
[RFC4291]. The address MUST conform to the textual representation of
the address according to [RFC5952].
Because [RFC5952] is more restrictive than the "RFC 3513" format
required by [RFC4006], some legacy implementations may not be
compliant with the new requirements. Accordingly, implementations
receiving this AVP MAY be liberal in the textual IPv6 representations
that are accepted, without raising an error.
URL 2
The address type is in the form of a Uniform Resource Locator, as
defined in [RFC3986].
SIP URI 3
The address type is in the form of a SIP Uniform Resource Identifier,
as defined in [RFC3261].
8.39. Redirect-Server-Address AVP
The Redirect-Server-Address AVP (AVP Code 435) is of type UTF8String
and defines the address of the redirect server (e.g., HTTP redirect
server, SIP Server) with which the end user is to be connected when
the account cannot cover the service cost.
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8.40. Multiple-Services-Indicator AVP
The Multiple-Services-Indicator AVP (AVP Code 455) is of type
Enumerated and indicates whether the Diameter Credit-Control client
is capable of handling multiple services independently within a
(sub-)session. The absence of this AVP means that independent
credit-control of multiple services is not supported.
A server not implementing the independent credit-control of multiple
services MUST treat the Multiple-Services-Indicator AVP as an
invalid AVP.
The following values are defined for the Multiple-Services-Indicator
AVP:
MULTIPLE_SERVICES_NOT_SUPPORTED 0
The client does not support independent credit-control of multiple
services within a (sub-)session.
MULTIPLE_SERVICES_SUPPORTED 1
The client supports independent credit-control of multiple services
within a (sub-)session.
8.41. Requested-Action AVP
The Requested-Action AVP (AVP Code 436) is of type Enumerated and
contains the requested action being sent in a Credit-Control-Request
command where the CC-Request-Type is set to EVENT_REQUEST. The
following values are defined for the Requested-Action AVP:
DIRECT_DEBITING 0
This indicates a request to decrease the end user's account according
to information specified in the Requested-Service-Unit AVP and/or
Service-Identifier AVP (additional rating information may be included
in service-specific AVPs or in the Service-Parameter-Info AVP). The
Granted-Service-Unit AVP in the Credit-Control-Answer command
contains the debited units.
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REFUND_ACCOUNT 1
This indicates a request to increase the end user's account according
to information specified in the Requested-Service-Unit AVP and/or
Service-Identifier AVP (additional rating information may be included
in service-specific AVPs or in the Service-Parameter-Info AVP). The
Granted-Service-Unit AVP in the Credit-Control-Answer command
contains the refunded units.
CHECK_BALANCE 2
This indicates a balance-check request. In this case, the checking
of the account balance is done without any credit reservations from
the account. The Check-Balance-Result AVP in the Credit-Control-
Answer command contains the result of the balance check.
PRICE_ENQUIRY 3
This indicates a price-inquiry request. In this case, neither
checking of the account balance nor reservation from the account will
be done; only the price of the service will be returned in the
Cost-Information AVP in the Credit-Control-Answer command.
8.42. Service-Context-Id AVP
The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and
contains a unique identifier of the Diameter Credit-Control service-
specific document (as defined in Section 4.1.2) that applies to the
request. This is an identifier allocated by the service provider,
the Service Element manufacturer, or a standardization body, and MUST
uniquely identify a given Diameter Credit-Control service-specific
document. The format of the Service-Context-Id is:
"service-context" "@" "domain"
service-context = Token
The Token is an arbitrary string of characters and digits.
"domain" represents the entity that allocated the Service-Context-Id.
It can be ietf.org, 3gpp.org, etc. if the identifier is allocated by
a standardization body, or it can be the Fully Qualified Domain Name
(FQDN) of the service provider (e.g., provider.example.com) or the
vendor (e.g., vendor.example.com) if the identifier is allocated by a
private entity.
This AVP SHOULD be placed as close to the Diameter header as
possible.
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Service-specific documents that are for private use only (i.e., for
one provider's own use, where no interoperability is deemed useful)
may define private identifiers without a need for coordination.
However, when interoperability is desired, coordination of the
identifiers via, for example, publication of an informational RFC is
RECOMMENDED in order to make the Service-Context-Id AVP globally
available.
8.43. Service-Parameter-Info AVP
The Service-Parameter-Info AVP (AVP Code 440) is of type Grouped and
contains service-specific information used for price calculation or
rating. The Service-Parameter-Type AVP defines the service parameter
type, and the Service-Parameter-Value AVP contains the parameter
value. The actual contents of these AVPs are not within the scope of
this document and SHOULD be defined in another Diameter application,
in standards written by other standardization bodies, or in service-
specific documentation.
In the case of an unknown service request (e.g., unknown Service-
Parameter-Type), the corresponding Answer message MUST contain the
error code DIAMETER_RATING_FAILED. A Credit-Control-Answer message
with this error MUST contain one or more Failed-AVP AVPs containing
the Service-Parameter-Info AVPs that caused the failure.
The Service-Parameter-Info AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Service-Parameter-Info ::= < AVP Header: 440 >
{ Service-Parameter-Type }
{ Service-Parameter-Value }
8.44. Service-Parameter-Type AVP
The Service-Parameter-Type AVP is of type Unsigned32 (AVP Code 441)
and defines the type of the service-event-specific parameter (e.g.,
it can be the end-user location or service name). The different
parameters and their types are service specific, and the meanings of
these parameters are not defined in this document. Whoever allocates
the Service-Context-Id (i.e., a unique identifier of a service-
specific document) is also responsible for assigning Service-
Parameter-Type values for the service and ensuring their uniqueness
within the given service. The Service-Parameter-Value AVP contains
the value associated with the service parameter type.
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8.45. Service-Parameter-Value AVP
The Service-Parameter-Value AVP is of type OctetString (AVP Code 442)
and contains the value of the service parameter type.
8.46. Subscription-Id AVP
The Subscription-Id AVP (AVP Code 443) is used to identify the
end user's subscription and is of type Grouped. The Subscription-Id
AVP includes a Subscription-Id-Data AVP that holds the identifier and
a Subscription-Id-Type AVP that defines the identifier type.
The Subscription-Id AVP is defined as follows (per grouped-avp-def as
defined in [RFC6733]):
Subscription-Id ::= < AVP Header: 443 >
{ Subscription-Id-Type }
{ Subscription-Id-Data }
8.47. Subscription-Id-Type AVP
The Subscription-Id-Type AVP (AVP Code 450) is of type Enumerated,
and it is used to determine which type of identifier is carried by
the Subscription-Id AVP.
This specification defines the following subscription identifiers.
However, new Subscription-Id-Type values can be assigned by IANA as
defined in Section 12. A server MUST implement all the Subscription-
Id-Type values required to perform credit authorization for the
services it supports, including possible future values. Unknown or
unsupported Subscription-Id-Type values MUST be treated according to
the 'M' flag rule, as defined in [RFC6733].
END_USER_E164 0
The identifier is in international E.164 format (e.g., MSISDN),
according to the ITU-T E.164 numbering plan defined in [E164] and
[CE164].
END_USER_IMSI 1
The identifier is in IMSI format, according to the ITU-T E.212
identification plan as defined in [E212] and [CE212].
END_USER_SIP_URI 2
The identifier is in the form of a SIP URI, as defined in [RFC3261].
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END_USER_NAI 3
The identifier is in the form of a Network Access Identifier, as
defined in [RFC7542].
END_USER_PRIVATE 4
The identifier is a credit-control server private identifier.
8.48. Subscription-Id-Data AVP
The Subscription-Id-Data AVP (AVP Code 444) is used to identify the
end user and is of type UTF8String. The Subscription-Id-Type AVP
defines which type of identifier is used.
8.49. User-Equipment-Info AVP
The User-Equipment-Info AVP (AVP Code 458) is of type Grouped and
allows the credit-control client to indicate the identity and
capability of the terminal the subscriber is using for the connection
to the network.
The User-Equipment-Info AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
User-Equipment-Info ::= < AVP Header: 458 >
{ User-Equipment-Info-Type }
{ User-Equipment-Info-Value }
8.50. User-Equipment-Info-Type AVP
The User-Equipment-Info-Type AVP is of type Enumerated (AVP Code 459)
and defines the type of user equipment information contained in the
User-Equipment-Info-Value AVP.
This specification defines the following user equipment types.
However, new User-Equipment-Info-Type values can be assigned by IANA
as defined in Section 12.
IMEISV 0
The identifier contains the International Mobile Equipment Identifier
and Software Version (IMEISV) in the IMEISV format according to 3GPP
TS 23.003 [TGPPIMEI].
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MAC 1
The 48-bit Media Access Control (MAC) address is formatted as
described in Section 3.21 of [RFC3580].
EUI64 2
The 64-bit identifier used to identify the hardware instance of the
product, as defined in [EUI64].
MODIFIED_EUI64 3
There are a number of types of terminals that have identifiers other
than the International Mobile Equipment Identifier (IMEI), IEEE 802
MACs, or EUI-64. These identifiers can be converted to modified
EUI-64 format as described in [RFC4291] or by using some other
methods referred to in the service-specific documentation.
8.51. User-Equipment-Info-Value AVP
The User-Equipment-Info-Value AVP (AVP Code 460) is of type
OctetString. The User-Equipment-Info-Type AVP defines which type of
identifier is used.
8.52. User-Equipment-Info-Extension AVP
The User-Equipment-Info-Extension AVP (AVP Code 653) is of type
Grouped and allows the credit-control client to indicate the identity
and capability of the terminal the subscriber is using for the
connection to the network. If the type of the equipment is one of
the enumerated User-Equipment-Info-Type AVP values, then the
credit-control client SHOULD send the information in the
User-Equipment-Info AVP, in addition to or instead of the
User-Equipment-Info-Extension AVP. This is done in order to preserve
backward compatibility with credit-control servers that support only
[RFC4006]. Exactly one AVP MUST be included inside the
User-Equipment-Info-Extension AVP.
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The User-Equipment-Info-Extension AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
User-Equipment-Info-Extension ::= < AVP Header: 653 >
[ User-Equipment-Info-IMEISV ]
[ User-Equipment-Info-MAC ]
[ User-Equipment-Info-EUI64 ]
[ User-Equipment-Info-ModifiedEUI64 ]
[ User-Equipment-Info-IMEI ]
[ AVP ]
8.53. User-Equipment-Info-IMEISV AVP
The User-Equipment-Info-IMEISV AVP (AVP Code 654) is of type
OctetString. The User-Equipment-Info-IMEISV AVP contains the
International Mobile Equipment Identifier and Software Version in the
IMEISV format according to 3GPP TS 23.003 [TGPPIMEI].
8.54. User-Equipment-Info-MAC AVP
The User-Equipment-Info-MAC AVP (AVP Code 655) is of type
OctetString. The User-Equipment-Info-MAC AVP contains the 48-bit MAC
address; the MAC address is formatted as described in Section 4.1.7.8
of [RFC5777].
8.55. User-Equipment-Info-EUI64 AVP
The User-Equipment-Info-EUI64 AVP (AVP Code 656) is of type
OctetString. The User-Equipment-Info-EUI64 AVP contains the 64-bit
identifier used to identify the hardware instance of the product, as
defined in [EUI64].
8.56. User-Equipment-Info-ModifiedEUI64 AVP
The User-Equipment-Info-ModifiedEUI64 AVP (AVP Code 657) is of type
OctetString. There are a number of types of terminals that have
identifiers other than IMEI, IEEE 802 MACs, or EUI-64. These
identifiers can be converted to modified EUI-64 format as described
in [RFC4291] or by using some other methods referred to in the
service-specific documentation. The User-Equipment-Info-
ModifiedEUI64 AVP contains such identifiers.
8.57. User-Equipment-Info-IMEI AVP
The User-Equipment-Info-IMEI AVP (AVP Code 658) is of type
OctetString. The User-Equipment-Info-IMEI AVP contains the
International Mobile Equipment Identifier in the IMEI format
according to 3GPP TS 23.003 [TGPPIMEI].
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8.58. Subscription-Id-Extension AVP
The Subscription-Id-Extension AVP (AVP Code 659) is used to identify
the end user's subscription and is of type Grouped. The
Subscription-Id-Extension group AVP MUST include an AVP holding the
subscription identifier. The type of this included AVP indicates the
type of the subscription identifier. For each of the enumerated
values of the Subscription-Id-Type AVP, there is a corresponding
sub-AVP for use within the Subscription-Id-Extension group AVP. If a
new identifier type is required, a corresponding new sub-AVP SHOULD
be defined for use within the Subscription-Id-Extension group AVP.
If full backward compatibility with [RFC4006] is required, then the
Subscription-Id AVP MUST be used to indicate identifier types
enumerated in the Subscription-Id-Type AVP, whereas the Subscription-
Id-Extension AVP MUST be used only for newly defined identifier
types. If full backward compatibility with [RFC4006] is not
required, then the Subscription-Id-Extension AVP MAY be used to carry
the existing identifier types. In this case, the Subscription-Id-
Extension AVP MAY be sent together with the Subscription-Id AVP.
Exactly one sub-AVP MUST be included inside the Subscription-Id-
Extension AVP.
The Subscription-Id-Extension AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Subscription-Id-Extension ::= < AVP Header: 659 >
[ Subscription-Id-E164 ]
[ Subscription-Id-IMSI ]
[ Subscription-Id-SIP-URI ]
[ Subscription-Id-NAI ]
[ Subscription-Id-Private ]
[ AVP ]
8.59. Subscription-Id-E164 AVP
The Subscription-Id-E164 AVP (AVP Code 660) is of type UTF8String.
The Subscription-Id-E164 AVP contains the international E.164 format
(e.g., MSISDN), according to the ITU-T E.164 numbering plan defined
in [E164] and [CE164].
8.60. Subscription-Id-IMSI AVP
The Subscription-Id-IMSI AVP (AVP Code 661) is of type UTF8String.
The Subscription-Id-IMSI AVP contains the IMSI format, according to
the ITU-T E.212 identification plan as defined in [E212] and [CE212].
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8.61. Subscription-Id-SIP-URI AVP
The Subscription-Id-SIP-URI AVP (AVP Code 662) is of type UTF8String.
The Subscription-Id-SIP-URI AVP contains the identifier in the form
of a SIP URI, as defined in [RFC3261].
8.62. Subscription-Id-NAI AVP
The Subscription-Id-NAI AVP (AVP Code 663) is of type UTF8String.
The Subscription-Id-NAI AVP contains the identifier in the form of a
Network Access Identifier, as defined in [RFC7542].
8.63. Subscription-Id-Private AVP
The Subscription-Id-Private AVP (AVP Code 664) is of type UTF8String.
The Subscription-Id-Private AVP contains a credit-control server
private identifier.
8.64. Redirect-Server-Extension AVP
The Redirect-Server-Extension AVP (AVP Code 665) is of type Grouped
and contains the address information of the redirect server (e.g.,
HTTP redirect server, SIP Server) with which the end user is to be
connected when the account cannot cover the service cost. It MUST be
present inside the QoS-Final-Unit-Indication AVP when the Final-Unit-
Action AVP is set to REDIRECT. If the type of the redirect server is
one of the enumerated values of the Redirect-Address-Type AVP, then
the credit-control server SHOULD send the information in the
Redirect-Server AVP, in addition to or instead of the Redirect-
Server-Extension AVP. This is done in order to preserve backward
compatibility with credit-control clients that support only
[RFC4006]. Exactly one AVP MUST be included inside the Redirect-
Server-Extension AVP.
The Redirect-Server-Extension AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
Redirect-Server-Extension ::= < AVP Header: 665 >
[ Redirect-Address-IPAddress ]
[ Redirect-Address-URL ]
[ Redirect-Address-SIP-URI ]
[ AVP ]
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8.65. Redirect-Address-IPAddress AVP
The Redirect-Address-IPAddress AVP (AVP Code 666) is of type Address
and defines the IPv4 or IPv6 address of the redirect server with
which the end user is to be connected when the account cannot cover
the service cost.
When encoded as an IPv6 address in 16 bytes, the IPv4-mapped IPv6
format [RFC4291] MAY be used to indicate an IPv4 address.
The interpretation of Redirect-Address-IPAddress by the Diameter
Credit-Control client is a matter of local policy.
8.66. Redirect-Address-URL AVP
The Redirect-Address-URL AVP (AVP Code 667) is of type UTF8String and
defines the address of the redirect server with which the end user is
to be connected when the account cannot cover the service cost. The
address type is in the form of a Uniform Resource Locator, as defined
in [RFC3986]. Note that individual URL schemes may restrict the
contents of the UTF8String.
8.67. Redirect-Address-SIP-URI AVP
The Redirect-Address-SIP-URI AVP (AVP Code 668) is of type UTF8String
and defines the address of the redirect server with which the end
user is to be connected when the account cannot cover the service
cost. The address type is in the form of a SIP Uniform Resource
Identifier, as defined in [RFC3261].
8.68. QoS-Final-Unit-Indication AVP
The QoS-Final-Unit-Indication AVP (AVP Code 669) is of type Grouped
and indicates that the Granted-Service-Unit AVP in the
Credit-Control-Answer or in the AA-Answer contains the final units
for the service. After these units have expired, the Diameter
Credit-Control client is responsible for executing the action
indicated in the Final-Unit-Action AVP (see Section 5.6).
If more than one unit type is received in the Credit-Control-Answer,
the unit type that first expired SHOULD cause the credit-control
client to execute the specified action.
In the first interrogation, the QoS-Final-Unit-Indication AVP with
Final-Unit-Action set to REDIRECT or RESTRICT_ACCESS can also be
present with no Granted-Service-Unit AVP in the Credit-Control-Answer
or in the AA-Answer. This indicates to the Diameter Credit-Control
client that the client is to execute the specified action
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immediately. If the home service provider policy is to terminate the
service, naturally, the server SHOULD return the appropriate
transient failure (see Section 9.1) in order to implement the
policy-defined action.
The Final-Unit-Action AVP defines the behavior of the Service Element
when the user's account cannot cover the cost of the service and MUST
always be present if the QoS-Final-Unit-Indication AVP is included in
a command.
If the Final-Unit-Action AVP is set to TERMINATE, the QoS-Final-Unit-
Indication group AVP MUST NOT contain any other AVPs.
If the Final-Unit-Action AVP is set to REDIRECT, then the Redirect-
Server-Extension AVP MUST be present. The Filter-Rule AVP or the
Filter-Id AVP MAY be present in the Credit-Control-Answer message if
the user is also allowed to access other services that are not
accessible through the address given in the Redirect-Server-Extension
AVP or if access to these services needs to be limited in some way
(e.g., QoS).
If the Final-Unit-Action AVP is set to RESTRICT_ACCESS, either the
Filter-Rule AVP or the Filter-Id AVP SHOULD be present.
The Filter-Rule AVP is defined in [RFC5777]. The Filter-Rule AVP can
be used to define a specific combination of a condition and an
action. If used only with traffic conditions, it should define which
traffic should be allowed when no more service units are granted.
However, if QoS or treatment information exists in the AVP, these
actions should be executed, e.g., limiting the allowed traffic with
certain QoS information. When multiple Filter-Rule AVPs exist,
precedence should be determined as defined in [RFC5777].
The Filter-Id AVP is defined in [RFC7155]. The Filter-Id AVP can be
used to reference an IP filter list installed in the access device by
means other than the Diameter Credit-Control application, e.g.,
locally configured or configured by another entity.
If the Final-Unit-Action AVP is (1) set to TERMINATE, (2) set to
RESTRICT_ACCESS and the action required is to allow only traffic that
could be classified using an IPFilterRule, or (3) set to REDIRECT
using a type that is one of the types in the Redirect-Address-Type
AVP, then the credit-control server SHOULD send the information in
the Final-Unit-Indication AVP, in addition to or instead of the
QoS-Final-Unit-Indication AVP. This is done in order to preserve
backward compatibility with credit-control clients that support only
[RFC4006].
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The QoS-Final-Unit-Indication AVP is defined as follows (per
grouped-avp-def as defined in [RFC6733]):
QoS-Final-Unit-Indication ::= < AVP Header: 669 >
{ Final-Unit-Action }
*[ Filter-Rule ]
*[ Filter-Id ]
[ Redirect-Server-Extension ]
*[ AVP ]
9. Result-Code AVP Values
This section defines new Result-Code AVP [RFC6733] values that must
be supported by all Diameter implementations that conform to this
specification.
The Credit-Control-Answer message includes the Result-Code AVP, which
may indicate that an error was present in the Credit-Control-Request
message. A rejected Credit-Control-Request message SHOULD cause the
user's session to be terminated.
9.1. Transient Failures
Errors that fall within the category of transient failures are used
to inform the peer that the request could not be satisfied at the
time it was received but that the request MAY be able to be satisfied
in the future.
DIAMETER_END_USER_SERVICE_DENIED 4010
The credit-control server denies the service request due to service
restrictions. If the CCR contained used service units, they are
deducted, if possible.
DIAMETER_CREDIT_CONTROL_NOT_APPLICABLE 4011
The credit-control server determines that the service can be granted
to the end user but that no further credit-control is needed for the
service (e.g., the service is free of charge).
DIAMETER_CREDIT_LIMIT_REACHED 4012
The credit-control server denies the service request because the
end user's account could not cover the requested service. If the CCR
contained used service units, they are deducted, if possible.
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9.2. Permanent Failures
Errors that fall within the category of permanent failures are used
to inform the peer that the request failed and should not be
attempted again.
DIAMETER_USER_UNKNOWN 5030
The specified end user is unknown in the credit-control server.
DIAMETER_RATING_FAILED 5031
This error code is used to inform the credit-control client that the
credit-control server cannot rate the service request due to
insufficient rating input, an incorrect AVP combination, or an AVP or
AVP value that is not recognized or supported in the rating. The
Failed-AVP AVP MUST be included and contain (1) a copy of the entire
AVP or AVPs that could not be processed successfully or (2) an
example of the missing AVP, complete with the Vendor-Id if
applicable. The value field of the missing AVP should be of correct
minimum length and contain zeros.
10. AVP Occurrence Table
The table in Section 10.1 presents the AVPs defined in this document
and specifies in which Diameter messages they MAY or MUST NOT be
present. Note that AVPs that can only be present within a Grouped
AVP are not represented in the table.
The table uses the following symbols:
0 The AVP MUST NOT be present in the message.
0+ Zero or more instances of the AVP MAY be present in the
message.
0-1 Zero or one instance of the AVP MAY be present in the
message. It is considered an error if there is more
than one instance of the AVP.
1 One instance of the AVP MUST be present in the message.
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10.1. Credit-Control AVP Table
The table in this section is used to represent which credit-control
application-specific AVPs defined in this document are to be present
in the credit-control messages.
+-----------+
| Command |
| Code |
|-----+-----+
Attribute Name | CCR | CCA |
----------------------------------|-----+-----+
Acct-Multi-Session-Id | 0-1 | 0-1 |
Auth-Application-Id | 1 | 1 |
CC-Correlation-Id | 0-1 | 0 |
CC-Session-Failover | 0 | 0-1 |
CC-Request-Number | 1 | 1 |
CC-Request-Type | 1 | 1 |
CC-Sub-Session-Id | 0-1 | 0-1 |
Check-Balance-Result | 0 | 0-1 |
Cost-Information | 0 | 0-1 |
Credit-Control-Failure-Handling | 0 | 0-1 |
Destination-Host | 0-1 | 0 |
Destination-Realm | 1 | 0 |
Direct-Debiting-Failure-Handling | 0 | 0-1 |
Event-Timestamp | 0-1 | 0-1 |
Failed-AVP | 0 | 0+ |
Final-Unit-Indication | 0 | 0-1 |
QoS-Final-Unit-Indication | 0 | 0-1 |
Granted-Service-Unit | 0 | 0-1 |
Multiple-Services-Credit-Control | 0+ | 0+ |
Multiple-Services-Indicator | 0-1 | 0 |
Origin-Host | 1 | 1 |
Origin-Realm | 1 | 1 |
Origin-State-Id | 0-1 | 0-1 |
Proxy-Info | 0+ | 0+ |
Redirect-Host | 0 | 0+ |
Redirect-Host-Usage | 0 | 0-1 |
Redirect-Max-Cache-Time | 0 | 0-1 |
Requested-Action | 0-1 | 0 |
Requested-Service-Unit | 0-1 | 0 |
Route-Record | 0+ | 0+ |
Result-Code | 0 | 1 |
Service-Context-Id | 1 | 0 |
Service-Identifier | 0-1 | 0 |
Service-Parameter-Info | 0+ | 0 |
Session-Id | 1 | 1 |
Subscription-Id | 0+ | 0 |
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Subscription-Id-Extension | 0+ | 0 |
Termination-Cause | 0-1 | 0 |
User-Equipment-Info | 0-1 | 0 |
User-Equipment-Info-Extension | 0-1 | 0 |
Used-Service-Unit | 0+ | 0 |
User-Name | 0-1 | 0-1 |
Validity-Time | 0 | 0-1 |
----------------------------------|-----+-----+
10.2. Re-Auth-Request/Re-Auth-Answer AVP Table
This section defines AVPs that are specific to the Diameter
Credit-Control application and that MAY be included in the Diameter
Re-Auth-Request/Re-Auth-Answer (RAR/RAA) message [RFC6733].
The RAR/RAA command MAY include the following additional AVPs:
+---------------+
| Command Code |
|-------+-------+
Attribute Name | RAR | RAA |
------------------------------+-------+-------+
CC-Sub-Session-Id | 0-1 | 0-1 |
G-S-U-Pool-Identifier | 0-1 | 0-1 |
Service-Identifier | 0-1 | 0-1 |
Rating-Group | 0-1 | 0-1 |
------------------------------+-------+-------+
11. RADIUS/Diameter Credit-Control Interworking Model
This section defines the basic principles for the Diameter
Credit-Control / RADIUS prepaid interworking model -- that is, a
message translation between a RADIUS-based prepaid solution and a
Diameter Credit-Control application. A complete description of the
protocol translations between RADIUS and the Diameter Credit-Control
application is beyond the scope of this specification and SHOULD be
addressed in another appropriate document.
The Diameter Credit-Control architecture may have a Translation Agent
capable of translation between RADIUS prepaid and Diameter
Credit-Control protocols. A AAA server (usually the home AAA server)
may act as a Translation Agent and as a Diameter Credit-Control
client for Service Elements that use credit-control mechanisms other
than Diameter Credit-Control -- for instance, RADIUS prepaid. In
this case, the home AAA server contacts the Diameter Credit-Control
server as part of the authorization process. The interworking
architecture is illustrated in Figure 9, and an interworking flow is
illustrated in Figure 10. In a roaming situation, the Service
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Element (e.g., the NAS) may be located in the visited network, and a
visited AAA server is usually contacted. The visited AAA server then
connects to the home AAA server.
RADIUS Prepaid
+--------+ +---------+ Protocol +------------+ +--------+
| End |<----->| Service |<---------->| Home AAA | |Business|
| User | | Element | | Server | |Support |
+--------+ +-->| | |+----------+|->|System |
| +---------+ ||CC Client || | |
| |+----------+| | |
+--------+ | +------^-----+ +----^---+
| End |<--+ Credit-Control | |
| User | Protocol | |
+--------+ +-------V--------+ |
|Credit-Control |----+
| Server |
+----------------+
Figure 9: Credit-Control Architecture with Service Element
Containing Translation Agent, Translating RADIUS Prepaid
to Diameter Credit-Control Protocol
When the AAA server acting as a Translation Agent receives an initial
RADIUS Access-Request message from a Service Element (e.g., NAS
access), it performs regular authentication and authorization. If
the RADIUS Access-Request message indicates that the Service Element
is capable of credit-control and if the home AAA server finds that
the subscriber is a prepaid subscriber, then a Diameter
Credit-Control-Request SHOULD be sent toward the credit-control
server to perform credit authorization and to establish a
credit-control session. After the Diameter Credit-Control server
checks the end user's account balance, rates the service, and
reserves credit from the end user's account, the reserved quota is
returned to the home AAA server in the Diameter Credit-Control-
Answer. The home AAA server then sends the reserved quota to the
Service Element in the RADIUS Access-Accept.
At the expiry of the allocated quota, the Service Element sends a new
RADIUS Access-Request containing the units used thus far to the home
AAA server. The home AAA server shall map a RADIUS Access-Request
containing the reported units to the Diameter Credit-Control server
in a Diameter Credit-Control-Request (UPDATE_REQUEST). The Diameter
Credit-Control server debits the used units from the end user's
account and allocates a new quota that is returned to the home AAA
server in the Diameter Credit-Control-Answer. The quota is
transferred to the Service Element in the RADIUS Access-Accept. When
the end user terminates the service or when the entire quota has been
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used, the Service Element sends a RADIUS Access-Request. To debit
the used units from the end user's account and to stop the
credit-control session, the home AAA server sends a Diameter
Credit-Control-Request (TERMINATION_REQUEST) to the credit-control
server. The Diameter Credit-Control server acknowledges the session
termination by sending a Diameter Credit-Control-Answer to the home
AAA server. The RADIUS Access-Accept is sent to the NAS.
Figure 10 illustrates a Diameter Credit-Control / RADIUS prepaid
interworking sequence.
Service Element Translation Agent
(e.g., NAS) (CC Client) CC Server
| Access-Request | |
|----------------------->| |
| | CCR (Initial) |
| |----------------------->|
| | CCA (Granted-Units) |
| |<-----------------------|
| Access-Accept | |
| (Granted-Units) | |
|<-----------------------| |
: : :
| Access-Request | |
| (Used-Units) | |
|----------------------->| |
| | CCR (Update, |
| | Used-Units) |
| |----------------------->|
| | CCA (Granted-Units) |
| |<-----------------------|
| Access-Accept | |
| (Granted-Units) | |
|<-----------------------| |
: : :
| Access-Request | |
|----------------------->| |
| | CCR (Terminate, |
| | Used-Units) |
| |----------------------->|
| | CCA |
| |<-----------------------|
| Access-Accept | |
|<-----------------------| |
| | |
Figure 10: Message Flow Example with Diameter
Credit-Control / RADIUS Prepaid Interworking
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12. IANA Considerations
This document uses several registries that were originally created in
[RFC4006] or the values assigned to existing namespaces managed by
IANA. IANA has updated these registries to reference this document.
The registries and their allocation policies are specified below.
12.1. Application Identifier
This specification assigns the value 4, "Diameter Credit Control", to
the "Application IDs" namespace defined in [RFC6733]. See
Section 1.3 for more information.
12.2. Command Codes
This specification uses the value 272 from the "Command Codes"
namespace defined in [RFC6733] for the Credit-Control-Request (CCR)
and Credit-Control-Answer (CCA) commands.
12.3. AVP Codes
See Section 8 for the assignments in this specification.
This document describes new AVP codes beyond those described in
[RFC4006]. IANA has allocated codes for the AVPs listed in Table 7.
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+-----------------------------------+------+--------------+
| Attribute Name | Code | Defined in |
+-----------------------------------+------+--------------+
| User-Equipment-Info-Extension | 653 | Section 8.52 |
| User-Equipment-Info-IMEISV | 654 | Section 8.53 |
| User-Equipment-Info-MAC | 655 | Section 8.54 |
| User-Equipment-Info-EUI64 | 656 | Section 8.55 |
| User-Equipment-Info-ModifiedEUI64 | 657 | Section 8.56 |
| User-Equipment-Info-IMEI | 658 | Section 8.57 |
| Subscription-Id-Extension | 659 | Section 8.58 |
| Subscription-Id-E164 | 660 | Section 8.59 |
| Subscription-Id-IMSI | 661 | Section 8.60 |
| Subscription-Id-SIP-URI | 662 | Section 8.61 |
| Subscription-Id-NAI | 663 | Section 8.62 |
| Subscription-Id-Private | 664 | Section 8.63 |
| Redirect-Server-Extension | 665 | Section 8.64 |
| Redirect-Address-IPAddress | 666 | Section 8.65 |
| Redirect-Address-URL | 667 | Section 8.66 |
| Redirect-Address-SIP-URI | 668 | Section 8.67 |
| QoS-Final-Unit-Indication | 669 | Section 8.68 |
+-----------------------------------+------+--------------+
Table 7: Requested AVP Assignments
12.4. Result-Code AVP Values
This specification assigns the values 4010, 4011, and 4012 in the
"Result-Code AVP Values (code 268) - Transient Failures" namespace
and values 5030 and 5031 in the "Result-Code AVP Values (code 268) -
Permanent Failure" namespace, both of which were defined by
[RFC6733]. See Section 9 for the assignments in this specification.
12.5. CC-Request-Type AVP
As defined in Section 8.3, the CC-Request-Type AVP includes
Enumerated type values 1-4. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.6. CC-Session-Failover AVP
As defined in Section 8.4, the CC-Session-Failover AVP includes
Enumerated type values 0-1. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
Bertz, et al. Standards Track [Page 98]
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12.7. CC-Unit-Type AVP
As defined in Section 8.32, the CC-Unit-Type AVP includes Enumerated
type values 0-5. IANA has created and is maintaining a namespace for
this AVP. The definition of new values is subject to the
Specification Required policy [RFC8126] and conditions for enumerated
values described in [RFC7423], Section 5.6.
12.8. Check-Balance-Result AVP
As defined in Section 8.6, the Check-Balance-Result AVP includes
Enumerated type values 0-1. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.9. Credit-Control AVP
As defined in Section 8.13, the Credit-Control AVP includes
Enumerated type values 0-1. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.10. Credit-Control-Failure-Handling AVP
As defined in Section 8.14, the Credit-Control-Failure-Handling AVP
includes Enumerated type values 0-2. IANA has created and is
maintaining a namespace for this AVP. The definition of new values
is subject to the Specification Required policy [RFC8126] and
conditions for enumerated values described in [RFC7423], Section 5.6.
12.11. Direct-Debiting-Failure-Handling AVP
As defined in Section 8.15, the Direct-Debiting-Failure-Handling AVP
includes Enumerated type values 0-1. IANA has created and is
maintaining a namespace for this AVP. The definition of new values
is subject to the Specification Required policy [RFC8126] and
conditions for enumerated values described in [RFC7423], Section 5.6.
12.12. Final-Unit-Action AVP
As defined in Section 8.35, the Final-Unit-Action AVP includes
Enumerated type values 0-2. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
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12.13. Multiple-Services-Indicator AVP
As defined in Section 8.40, the Multiple-Services-Indicator AVP
includes Enumerated type values 0-1. IANA has created and is
maintaining a namespace for this AVP. The definition of new values
is subject to the Specification Required policy [RFC8126] and
conditions for enumerated values described in [RFC7423], Section 5.6.
12.14. Redirect-Address-Type AVP
As defined in Section 8.38, the Redirect-Address-Type AVP includes
Enumerated type values 0-3. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.15. Requested-Action AVP
As defined in Section 8.41, the Requested-Action AVP includes
Enumerated type values 0-3. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.16. Subscription-Id-Type AVP
As defined in Section 8.47, the Subscription-Id-Type AVP includes
Enumerated type values 0-4. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.17. Tariff-Change-Usage AVP
As defined in Section 8.27, the Tariff-Change-Usage AVP includes
Enumerated type values 0-2. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
12.18. User-Equipment-Info-Type AVP
As defined in Section 8.50, the User-Equipment-Info-Type AVP includes
Enumerated type values 0-3. IANA has created and is maintaining a
namespace for this AVP. The definition of new values is subject to
the Specification Required policy [RFC8126] and conditions for
enumerated values described in [RFC7423], Section 5.6.
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13. Parameters Related to the Credit-Control Application
Tx timer
When real-time credit-control is required, the credit-control
client contacts the credit-control server before and while the
service is provided to an end user. Due to the real-time nature
of the application, communication delays SHOULD be minimized,
e.g., to avoid an overly long service setup time experienced by
the end user. The Tx timer is introduced to control the waiting
time in the client in the Pending state. When the Tx timer
elapses, the credit-control client takes action for the end user
according to the value of the CCFH or the DDFH. The recommended
value is 10 seconds.
Tcc timer
The Tcc timer supervises an ongoing credit-control session in the
credit-control server. It is RECOMMENDED to use the Validity-Time
as input to set the Tcc timer value. In the case of transient
failures in the network, the Diameter Credit-Control server might
change to Idle state. To avoid this, the Tcc timer MAY be set so
that Tcc is equal to 2 x Validity-Time.
Credit-Control-Failure-Handling and Direct-Debiting-Failure-Handling
Client implementations may offer the possibility of locally
configuring these AVPs. In such a case, their values and behavior
are defined in Sections 5.7 and 6.5, respectively.
14. Security Considerations
Security considerations regarding the Diameter protocol itself are
discussed in [RFC6733]. The use of this application of Diameter MUST
take into consideration the security issues and requirements of the
base protocol.
This application includes a mechanism for application-layer replay
protection by means of (1) the Session-Id AVP as specified in
[RFC6733] and (2) the CC-Request-Number AVP, which is specified in
this document. The Diameter Credit-Control application is often used
within one domain, and there may be a single hop between the peers.
In these environments, the use of TLS/TCP, DTLS/SCTP (Datagram
Transport Layer Security / Stream Control Transmission Protocol), or
IPsec is sufficient. The details of security considerations related
to TLS/TCP, DTLS/SCTP, and IPsec are discussed in [RFC6733].
Bertz, et al. Standards Track [Page 101]
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Because this application handles monetary transactions (directly or
indirectly), it increases interest in various security attacks.
Therefore, all parties communicating with each other MUST be
authenticated, including, for instance, TLS client-side
authentication. In addition, authorization of the client SHOULD be
emphasized, i.e., that the client is allowed to perform
credit-control for a certain user. The specific means of
authorization are outside the scope of this specification but can be,
for instance, manual configuration.
Another kind of threat is malicious modification, injection, or
deletion of AVPs or complete credit-control messages. The
credit-control messages contain sensitive billing-related information
(such as subscription identifiers, granted units, used units, or cost
information) whose malicious modification can have financial
consequences. Sometimes simply delaying the credit-control messages
can cause disturbances in the credit-control client or server.
Even without any modifications to the messages, an adversary that can
eavesdrop on transactions can obtain privacy-sensitive information.
Also, by monitoring the credit-control messages, one can collect
information about the credit-control server's billing models and
business relationships.
When third-party relays or proxies are involved, hop-by-hop security
does not necessarily provide sufficient protection for Diameter user
sessions. In some cases, it may be inappropriate to send Diameter
messages, such as CCR messages and CCA messages, containing sensitive
AVPs via untrusted Diameter proxy agents, as there are no assurances
that third-party proxies will not modify the credit-control commands
or AVP values.
14.1. Direct Connection with Redirects
A Diameter Credit-Control agent cannot always know whether agents
between it and the end user's Diameter Credit-Control server are
reliable. In this case, the Diameter Credit-Control agent doesn't
have a routing entry in its Diameter routing table (defined in
[RFC6733], Section 2.7) for the realm of the credit-control server in
the end user's home realm. The Diameter Credit-Control agent can
have a default route configured to a local redirect agent, and it
redirects the CCR message to the redirect agent. The local redirect
agent then returns a redirect notification (Result-Code 3006,
DIAMETER_REDIRECT_INDICATION) to the credit-control agent, as well as
information about the Diameter Credit-Control server(s) (Redirect-
Host AVP) and information about how the routing entry resulting from
the Redirect-Host is to be used (Redirect-Host-Usage AVP). The
Diameter Credit-Control agent then forwards the CCR message directly
Bertz, et al. Standards Track [Page 102]
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to one of the hosts identified by the CCA message from the redirect
agent. If the value of the Redirect-Host-Usage AVP does not equal
zero, all subsequent messages are sent to the host specified in the
Redirect-Host AVP until the time specified by the Redirect-Max-Cache-
Time AVP has expired.
Even with redirects, there are some authorization issues. There may
be attacks toward nodes that have been properly authorized but that
abuse their authorization or have been compromised. These issues are
discussed more widely in [RFC4072], Section 8.
14.2. Application-Level Redirects
This document includes a redirection feature (Section 5.6.2) whereby
the service provider can redirect (in an application-specific way)
the end user to an alternate location when their credits have
expired. This technique is useful in that it allows the user to
return to normal service quickly, but it also exposes additional
risks and attack surface. In particular, this redirection can
potentially occur at an arbitrary point in a user's session,
potentially without any additional contextual confirmation available
to the user that the redirection is driven by the network. This lack
of confirmation matters because, in many application protocols, the
communication peer is also capable of inducing redirection. When the
peer is an attacker, the redirection can be to an attacker-controlled
site. In particular, such sites may be "phishing" sites designed to
appear similar to legitimate payment sites in an attempt to obtain
users' payment information for fraudulent purposes. When users
become accustomed to such redirections, they may have difficulty
distinguishing such attacks from legitimate redirections.
Because of the potentially harmful consequences of arbitrary
redirection by an attacker (such as to phishing sites), it is
important for service providers to be aware of that risk and ensure
that their users are aware of it as well. Service providers should
follow industry best practices for the specific application-layer
protocol to reduce the chances that such attacks could be mistaken
for legitimate redirections. The details of such a practice are out
of scope for this document.
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15. Privacy Considerations
As the Diameter protocol, and especially the credit-control
application, deal with subscribers and their actions, extra care
should be taken regarding the privacy of the subscribers. Per
terminology used in [RFC6973], both the credit-control client and the
credit-control server are intermediary entities, wherein the
subscribers' privacy may be compromised even if no security issues
exist, and only authorized entities have access to the privacy-
sensitive information.
15.1. Privacy-Sensitive AVPs
The privacy-sensitive AVPs listed in this section MUST NOT be sent
across non-trusted networks or Diameter agents without end-to-end
authentication and confidentiality protection, as described in
[RFC6733], Section 13.3.
The following AVPs contain privacy-sensitive information at different
levels:
1. CC-Correlation-Id AVP: may contain privacy-sensitive
information, as the service provider may encode personal
information that helps it correlate different subscriptions and
access technologies.
2. Check-Balance-Result AVP: contains information on the balance
status of the subscriber.
3. Currency-Code AVP: contains information on the subscriber's
locale.
4. Cost-Unit AVP: contains privacy-sensitive information for the
Cost-Information AVP, in human-readable format.
5. Service-Identifier AVP: may contain privacy-sensitive
information about the subscriber's Internet activity.
6. Rating-Group AVP: may contain privacy-sensitive information
about the subscriber's Internet activity.
7. Restriction-Filter-Rule AVP: the information inside IPFilterRule
may be used to infer services used by the subscriber.
Bertz, et al. Standards Track [Page 104]
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8. Redirect-Server-Address AVP: the service provider might embed
personal information on the subscriber in the URL/URI (e.g., to
create a personalized message). However, the service provider
may instead anonymize the subscriber's identity in the URL/URI
and let the redirect server query the information directly.
Such anonymized information must not allow personal information
or the subscriber's identity to be easily guessed. Furthermore,
the service provider should treat the URL/URI schema itself as
confidential and make sure it cannot be inferred (1) from
observation of the traffic or (2) due to its trivial structure.
A trivial structure could allow an adversary to query/modify
personal information even without knowing the subscriber's
identity. Similar AVPs are Redirect-Address-URL and Redirect-
Address-SIP-URI.
9. Service-Context-Id AVP: depending on how the service provider
uses it, it may contain privacy-sensitive information about the
service (e.g., in a 3GPP network Service-Context-Id AVP, it has
a different value for packet switching, SMS, Multimedia Messages
(MMSs), etc.).
10. Service-Parameter-Info AVP: depending on how the service
provider uses it, it may contain privacy-sensitive information
about the subscriber (e.g., location).
11. Subscription-Id-Data AVP: contains the identity of the
subscriber. Similar AVPs are Subscription-Id-E164,
Subscription-Id-IMSI, Subscription-Id-SIP-URI, Subscription-Id-
NAI, and Subscription-Id-Private.
12. User-Equipment-Info-Value AVP: contains the identity of the
device of the subscriber. Similar AVPs are User-Equipment-Info-
IMEISV, User-Equipment-Info-MAC, User-Equipment-Info-EUI64,
User-Equipment-Info-ModifiedEUI64, and User-Equipment-Info-IMEI.
13. QoS-Final-Unit-Indication AVP: Grouped AVP that may contain
privacy-sensitive information in its sub-AVPs (e.g.,
IPFilterRule, redirect address).
Note that some AVPs that are used in this document are defined in
[RFC6733] and may contain privacy-sensitive information. These AVPs
are not listed above.
Bertz, et al. Standards Track [Page 105]
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15.2. Data Minimization
Due to the nature of the credit-control application, some personal
data and identity information must be stored in both the
credit-control client and the credit-control server. However, this
could be minimized by following these guidelines:
1. Data stored in the credit-control client does not need to persist
across sessions. All data could be deleted once the session ends
and could be reconstructed once a new session is initialized.
Note that while the credit-control server is usually owned by the
service provider with which the subscriber already has some
direct legal or business relationship (where the privacy level
could be agreed upon), this is not always true for a
credit-control client that may be owned by a third party.
2. Some information about the subscriber has to be stored in
persistent storage in the credit-control server (e.g., identity,
balance); however, per-transaction information does not have to
be stored in persistent storage, and per-session information may
be deleted from persistent storage once the session ends.
3. In some cases, per-transaction information has to be stored on
the credit-control server, client, or both, for regulatory,
auditability, or debugging reasons. However, this could be
minimized by following these guidelines:
A. Data retention does not need to exceed the required duration.
B. Transaction information could be aggregated in some cases
(e.g., prefer information per session over information per
rating-group; prefer hourly byte summary over per-transaction
byte counts).
C. If not strictly needed, information that is more sensitive
(e.g., location, equipment type) could be filtered out of
such logs. This information is often used to make rating
decisions, and in this case, the rating decisions should be
logged instead of the data used to make them.
D. Due to the reasons explained in the first guideline, the
credit-control server, rather than the credit-control client,
would be the preferred location for storing such transaction
information.
Bertz, et al. Standards Track [Page 106]
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15.3. Diameter Agents
Diameter agents, as described in [RFC6733], may be owned by
third parties. If end-to-end security is supported between the
credit-control client and the credit-control server, the operator can
use it to encrypt privacy-sensitive AVPs (as listed in Section 15.1)
and prevent such information from leaking into the agent.
In some cases, the Diameter agent needs access to privacy-sensitive
AVPs, in order to make correct routing decisions or even to modify
the content of these AVPs. For example, a proxy agent may need to
look at the Subscription-Id-IMSI AVP, in order to extract the mobile
country and network codes of the user and use them to look up the
destination to which the request should be routed (see Section 2.8.2
in [RFC6733]). In such a case, the credit-control client and
credit-control server may use a mechanism that anonymizes the
identity of the subscriber, as well as a mechanism to encrypt other
AVPs not used by the agent.
16. References
16.1. Normative References
[CE164] International Telecommunication Union, "COMPLEMENT TO
ITU-T RECOMMENDATION E.164 (11/2010): LIST OF ITU-T
RECOMMENDATION E.164 ASSIGNED COUNTRY CODES",
November 2011, <https://www.itu.int/dms_pub/itu-t/opb/sp/
T-SP-E.164D-11-2011-PDF-E.pdf>.
[CE212] International Telecommunication Union, "COMPLEMENT TO
RECOMMENDATION ITU-T E.212 (09/2016): LIST OF MOBILE
COUNTRY OR GEOGRAPHICAL AREA CODES", February 2017,
<https://www.itu.int/dms_pub/itu-t/opb/sp/
T-SP-E.212A-2017-PDF-E.pdf>.
[E164] International Telecommunication Union, "The international
public telecommunication numbering plan", ITU-T
Recommendation E.164, November 2010,
<https://www.itu.int/rec/T-REC-E.164/>.
[E212] International Telecommunication Union, "The international
identification plan for public networks and
subscriptions", ITU-T Recommendation E.212,
September 2016, <https://www.itu.int/rec/T-REC-E.212/en>.
Bertz, et al. Standards Track [Page 107]
RFC 8506 Diameter Credit-Control Application March 2019
[EUI64] IEEE, "Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID (CID)", August 2017,
<https://standards.ieee.org/content/dam/
ieee-standards/standards/web/documents/tutorials/eui.pdf>.
[ISO4217] ISO, "Codes for the representation of currencies",
ISO 4217:2015, 2015, <https://www.iso.org/
iso-4217-currency-codes.html>.
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC3539] Aboba, B. and J. Wood, "Authentication, Authorization and
Accounting (AAA) Transport Profile", RFC 3539,
DOI 10.17487/RFC3539, June 2003,
<https://www.rfc-editor.org/info/rfc3539>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and
J. Loughney, "Diameter Credit-Control Application",
RFC 4006, DOI 10.17487/RFC4006, August 2005,
<https://www.rfc-editor.org/info/rfc4006>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291,
February 2006, <https://www.rfc-editor.org/info/rfc4291>.
Bertz, et al. Standards Track [Page 108]
RFC 8506 Diameter Credit-Control Application March 2019
[RFC5777] Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,
Ed., and A. Lior, "Traffic Classification and Quality of
Service (QoS) Attributes for Diameter", RFC 5777,
DOI 10.17487/RFC5777, February 2010,
<https://www.rfc-editor.org/info/rfc5777>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<https://www.rfc-editor.org/info/rfc6733>.
[RFC7155] Zorn, G., Ed., "Diameter Network Access Server
Application", RFC 7155, DOI 10.17487/RFC7155, April 2014,
<https://www.rfc-editor.org/info/rfc7155>.
[RFC7423] Morand, L., Ed., Fajardo, V., and H. Tschofenig, "Diameter
Applications Design Guidelines", BCP 193, RFC 7423,
DOI 10.17487/RFC7423, November 2014,
<https://www.rfc-editor.org/info/rfc7423>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174,
DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.
[TGPPIMEI] 3rd Generation Partnership Project, Technical
Specification Group Core Network, "Numbering, addressing
and identification (release 15)", 3GPP TS 23.003
version 15.6.0, December 2018.
Bertz, et al. Standards Track [Page 109]
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16.2. Informative References
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866,
DOI 10.17487/RFC2866, June 2000,
<https://www.rfc-editor.org/info/rfc2866>.
[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service
(RADIUS) Usage Guidelines", RFC 3580,
DOI 10.17487/RFC3580, September 2003,
<https://www.rfc-editor.org/info/rfc3580>.
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and
G. Camarillo, "Best Current Practices for Third Party Call
Control (3pcc) in the Session Initiation Protocol (SIP)",
BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004,
<https://www.rfc-editor.org/info/rfc3725>.
[RFC4004] Calhoun, P., Johansson, T., Perkins, C., Hiller, T., Ed.,
and P. McCann, "Diameter Mobile IPv4 Application",
RFC 4004, DOI 10.17487/RFC4004, August 2005,
<https://www.rfc-editor.org/info/rfc4004>.
[RFC4072] Eronen, P., Ed., Hiller, T., and G. Zorn, "Diameter
Extensible Authentication Protocol (EAP) Application",
RFC 4072, DOI 10.17487/RFC4072, August 2005,
<https://www.rfc-editor.org/info/rfc4072>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[TGPPCHARG]
3rd Generation Partnership Project, Technical
Specification Group Services and System Aspects, "Service
aspects; Charging and Billing", 3GPP TS 22.115
version 15.5.0, September 2018.
Bertz, et al. Standards Track [Page 110]
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Appendix A. Credit-Control Sequences
A.1. Flow I
A credit-control flow for Network Access Services prepaid is shown in
Figure 11. The Diameter protocol application is implemented in the
Network Access Server (NAS) per [RFC7155]. The focus of this flow is
on credit authorization.
NAS
End User (CC Client) AAA Server CC Server
|(1)User Logon |(2)AA-Request (CC AVPs) |
|------------------>|-------------------->| |
| | |(3)CCR(Initial, CC AVPs)
| | |-------------------->|
| | |(4)CCA(Granted-Units)|
| | |<--------------------|
| |(5)AA-Answer(Granted-Units) |
|(6)Access granted |<--------------------| |
|<----------------->| | |
| | | |
: : : :
| |(7)CCR(Update, Used-Units) |
| |-------------------->|(8)CCR |
| | | (Update, Used-Units)
| | |-------------------->|
| | |(9)CCA(Granted-Units)|
| |(10)CCA(Granted-Units)<--------------------|
| |<--------------------| |
: : : :
| (Auth. lifetime expires) | |
| |(11)AAR (CC AVP) | |
| |-------------------->| |
| | (12)AAA | |
| |<--------------------| |
: : : :
: : : :
Bertz, et al. Standards Track [Page 111]
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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 11: Flow I
The user logs on to the network (1). The Diameter NAS sends a
Diameter AA-Request (AAR) to the home Diameter AAA server (2). The
credit-control client populates the AAR with the Credit-Control AVP
set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,
as usual [RFC7155]. The home Diameter AAA server performs service-
specific authentication and authorization, as usual. The home
Diameter AAA server determines that the user is a prepaid user and
notices from the Credit-Control AVP that the NAS has credit-control
capabilities. It sends a Diameter Credit-Control-Request with
CC-Request-Type set to INITIAL_REQUEST to the Diameter Credit-Control
server to perform credit authorization (3) and to establish a
credit-control session. (The home Diameter AAA server may forward
service-specific AVPs received from the NAS as input for the rating
process.) The Diameter Credit-Control server checks the end user's
account balance, rates the service, and reserves credit from the
end user's account. The reserved quota is returned to the home
Diameter AAA server in the Diameter Credit-Control-Answer (4). The
home Diameter AAA server sends the reserved quota to the NAS in the
Diameter AA-Answer (AAA). Upon receiving the AA-Answer, the NAS
starts the credit-control session and starts monitoring the granted
units (5). The NAS grants access to the end user (6). At the expiry
of the allocated quota, the NAS sends a Diameter Credit-Control-
Request with CC-Request-Type set to UPDATE_REQUEST to the home
Diameter AAA server (7). This message contains the units used thus
far. The home Diameter AAA server forwards the CCR to the Diameter
Credit-Control server (8). The Diameter Credit-Control server debits
the used units from the end user's account and allocates a new quota
that is returned to the home Diameter AAA server in the Diameter
Credit-Control-Answer (9). The message is forwarded to the NAS (10).
During the ongoing credit-control session, the authorization lifetime
expires, and the authorization/authentication client in the NAS
performs service-specific re-authorization to the home Diameter AAA
server, as usual. The credit-control client populates the AAR with
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RFC 8506 Diameter Credit-Control Application March 2019
the Credit-Control AVP set to RE_AUTHORIZATION, indicating that the
credit-control server shall not be contacted, as the credit
authorization is controlled by the burning rate of the granted units
(11). The home Diameter AAA server performs service-specific
re-authorization as usual and returns the AA-Answer to the NAS (12).
The end user logs off from the network (13). To debit the used units
from the end user's account and to stop the credit-control session,
the NAS sends a Diameter Credit-Control-Request with CC-Request-Type
set to TERMINATION_REQUEST to the home Diameter AAA server (14). The
home Diameter AAA server forwards the CCR to the credit-control
server (15). The Diameter Credit-Control server acknowledges the
session termination by sending a Diameter Credit-Control-Answer to
the home Diameter AAA server (16). The home Diameter AAA server
forwards the answer to the NAS (17). The STR/STA takes place between
the NAS and home Diameter AAA server, as usual (18), (19).
A.2. Flow II
Figure 12 provides an example of Diameter Credit-Control for SIP
sessions. Although the flow focuses on illustrating the usage of
credit-control messages, the SIP signaling is inaccurate, and the
diagram is not by any means an attempt to define a service provider's
SIP network. However, for the sake of this example, some assumptions
are made below.
Bertz, et al. Standards Track [Page 113]
RFC 8506 Diameter Credit-Control Application March 2019
SIP Proxy/Registrar AAA
A (CC Client) Server B CC Server
| (i) REGISTER | | | |
|------------->|(ii) | | |
| |------------->| | |
| |authentication & | |
| |authorization | | |
| |<-------------| | |
|(iii) 200 OK | | |
|<-------------| | |
: : : :
|(1) INVITE | :
|------------->|
| |(2) CCR (Initial, SIP-specific AVP) |
| |------------------------------------------->|
| |(3) CCA (Granted-Units) |
| |<-------------------------------------------|
| |(4) INVITE | |
| |---------------------------->| |
: : : :
| |(5) CCR (Update, Used-Units) |
| |------------------------------------------->|
| |(6) CCA (Granted-Units) |
| |<-------------------------------------------|
: : : :
|(7) BYE | | |
|------------->| | |
| |(8) BYE | |
| |---------------------------->| |
| |(9) CCR (Termination, Used-Units) |
| |------------------------------------------->|
| |(10) CCA () |
| |<-------------------------------------------|
| | | |
Figure 12: Flow II
Typically, prepaid services based, for example, on time usage for SIP
sessions require an entity in the service provider network to
intercept all the requests within the SIP dialog in order to detect
events, such as session establishment and session release, that are
essential for performing credit-control operations with the
credit-control server. Therefore, in this example, it is assumed
that the SIP Proxy adds a Record-Route header in the initial SIP
INVITE to make sure that all the future requests in the created
dialog traverse through it (for the definitions of "Record-Route" and
"dialog", please refer to [RFC3261]). Finally, the degree of
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RFC 8506 Diameter Credit-Control Application March 2019
credit-control measuring of the media by the proxy depends on the
business model design used in setting up the end system and proxies
in the SIP network.
The end user (SIP User Agent A) sends a REGISTER with credentials
(i). The SIP Proxy sends a request to the home AAA server to perform
multimedia authentication and authorization by using, for instance, a
Diameter multimedia application (ii). The home AAA server checks
that the credentials are correct and checks the user profile.
Eventually, a 200 OK response (iii) is sent to the User Agent. Note
that the authentication and authorization are valid for the
registration validity period duration (i.e., until re-registration is
performed). Several SIP sessions may be established without
re-authorization.
User Agent A sends an INVITE (1). The SIP Proxy sends a Diameter
Credit-Control-Request (INITIAL_REQUEST) to the Diameter
Credit-Control server (2). The Credit-Control-Request contains
information obtained from the SIP signaling describing the requested
service (e.g., calling party, called party, Session Description
Protocol (SDP) attributes). The Diameter Credit-Control server
checks the end user's account balance, rates the service, and
reserves credit from the end user's account. The reserved quota is
returned to the SIP Proxy in the Diameter Credit-Control-Answer (3).
The SIP Proxy forwards the SIP INVITE to User Agent B (4). B's phone
rings, and B answers. The media flows between them, and the SIP
Proxy starts measuring the quota. At the expiry of the allocated
quota, the SIP Proxy sends a Diameter Credit-Control-Request
(UPDATE_REQUEST) to the Diameter Credit-Control server (5). This
message contains the units used thus far. The Diameter
Credit-Control server debits the used units from the end user's
account and allocates new credit that is returned to the SIP Proxy in
the Diameter Credit-Control-Answer (6). The end user terminates the
service by sending a BYE message (7). The SIP Proxy forwards the BYE
message to User Agent B (8) and sends a Diameter Credit-Control-
Request (TERMINATION_REQUEST) to the credit-control server (9). The
Diameter Credit-Control server acknowledges the session termination
by sending a Diameter Credit-Control-Answer to the SIP Proxy (10).
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A.3. Flow III
A credit-control flow for Multimedia Messaging Service is shown in
Figure 13. The sender is charged as soon as the messaging server
successfully stores the message.
MMS Server
A (CC Client) B CC Server
|(1) Send MMS | | |
|--------------->| | |
| |(2) CCR (Event, DIRECT_DEBITING, |
| | MMS-specific AVP) |
| |-------------------------------->|
| |(3) CCA (Granted-Units) |
| |<--------------------------------|
|(4) Send MMS Ack| | |
|<---------------| | |
| |(5) Notify MMS | |
| |--------------->| |
: : : :
| |(6) Retrieve MMS| |
| |<---------------| |
| |(7) Retrieve MMS| |
| | Ack | |
| |--------------->| |
| | | |
Figure 13: Flow III
This is an example of Diameter Credit-Control for direct debiting
using the Multimedia Messaging Service environment. Although the
flow focuses on illustrating the usage of credit-control messages,
the MMS signaling is inaccurate, and the diagram is not by any means
an attempt to define a service provider's MMS configuration or
billing model.
End user A sends an MMS to the MMS server (1). The MMS server stores
the message and sends a Diameter Credit-Control-Request
(EVENT_REQUEST with Requested-Action set to DIRECT_DEBITING) to the
Diameter Credit-Control server (2). The Credit-Control-Request
contains information about the MMS message (e.g., size, recipient
address, image coding type). The Diameter Credit-Control server
checks the end user's account balance, rates the service, and debits
the service from the end user's account. The granted quota is
returned to the MMS server in the Diameter Credit-Control-Answer (3).
Bertz, et al. Standards Track [Page 116]
RFC 8506 Diameter Credit-Control Application March 2019
The MMS server acknowledges the successful reception of the MMS
message (4). The MMS server notifies the recipient about the new MMS
(5), and end user B retrieves the message from the MMS message store
(6), (7).
Note that the transfer of the MMS message can take an extended period
of time and can fail, in which case a recovery action is needed. The
MMS server should return the already-debited units to the user's
account by using the REFUND action described in Section 6.4.
A.4. Flow IV
Another credit-control flow for Multimedia Messaging Service is shown
in Figure 14. The recipient is charged at the time of message
delivery.
MMS Server
Content Server (CC Client) B CC Server
|(1) Send MMS | | |
|--------------->| | |
| |(2) CCR (Event, CHECK_BALANCE, |
| | MMS-specific AVP) |
| |-------------------------------->|
| |(3) CCA (ENOUGH_CREDIT) |
| |<--------------------------------|
|(4) Send MMS Ack| | |
|<---------------| | |
| |(5) Notify MMS | |
| |--------------->| |
: : : :
| |(6) Retrieve MMS| |
| |<---------------| |
| |(7) CCR (Event, DIRECT_DEBITING, |
| | MMS-specific AVP) |
| |-------------------------------->|
| |(8) CCA (Granted-Units) |
| |<--------------------------------|
| |(9) Retrieve MMS| |
| | Ack | |
| |--------------->| |
| | | |
Figure 14: Flow IV
Bertz, et al. Standards Track [Page 117]
RFC 8506 Diameter Credit-Control Application March 2019
This is an example of Diameter Credit-Control for direct debiting
using the Multimedia Messaging Service environment. Although the
flow focuses on illustrating the usage of credit-control messages,
the MMS signaling is inaccurate, and the diagram is not by any means
an attempt to define a service provider's MMS configuration or
billing model.
A content server sends an MMS to the MMS server (1), which stores the
message. The message recipient will be charged for the MMS message
in this case. As there can be a substantially long time between the
receipt of the message at the MMS server and the actual retrieval of
the message, the MMS server does not establish any credit-control
sessions to the Diameter Credit-Control server; rather, it first
performs only a balance check (without any credit reservations) by
sending a Diameter Credit-Control-Request (EVENT_REQUEST with
Requested-Action set to CHECK_BALANCE) to verify that end user B can
cover the cost for the MMS (2). The Diameter Credit-Control server
checks the end user's account balance and returns the answer to the
MMS server in the Diameter Credit-Control-Answer (3). The MMS server
acknowledges the successful reception of the MMS message (4). The
MMS server notifies the recipient of the new MMS (5), and after some
time end user B retrieves the message from the MMS message store (6).
The MMS server sends a Diameter Credit-Control-Request (EVENT_REQUEST
with Requested-Action set to DIRECT_DEBITING) to the Diameter
Credit-Control server (7). The Credit-Control-Request contains
information about the MMS message (e.g., size, recipient address,
coding type). The Diameter Credit-Control server checks the
end user's account balance, rates the service, and debits the service
from the end user's account. The granted quota is returned to the
MMS server in the Diameter Credit-Control-Answer (8). The MMS is
transferred to end user B (9).
Note that the transfer of the MMS message can take an extended period
of time and can fail, in which case a recovery action is needed. The
MMS server should return the already-debited units to the user's
account by using the REFUND action described in Section 6.4.
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RFC 8506 Diameter Credit-Control Application March 2019
A.5. Flow V
Figure 15 provides an example of an Advice of Charge (AoC) service
for a SIP call.
SIP Controller
User Agent A (CC Client) User Agent B CC Server
|(1)INVITE | | |
| User Agent B(SDP)| | |
|------------------>| | |
| |(2)CCR (Event, PRICE_ENQUIRY, |
| | SIP-specific AVPs) |
| |------------------------------->|
| |(3)CCA (Cost-Information) |
| |<-------------------------------|
|(4)MESSAGE(URL) | | |
|<------------------| | |
|(5)HTTP GET | | |
|------------------>| | |
|(6)HTTP POST | | |
|------------------>|(7)INVITE(SDP) | |
| |--------------->| |
| | (8)200 OK | |
| (9)200 OK |<---------------| |
|<------------------| | |
Figure 15: Flow V
This is an example of Diameter Credit-Control for SIP sessions.
Although the flow focuses on illustrating the usage of credit-control
messages, the SIP signaling is inaccurate, and the diagram is not by
any means an attempt to define a service provider's SIP network.
User Agent A can be either a postpaid or prepaid subscriber using the
AoC service. It is assumed that the SIP controller also has HTTP
capabilities and delivers an interactive AoC web page with, for
instance, the cost information, the details of the call derived from
the SDP, and a button to accept/not accept the charges. (There may
be many other ways to deliver AoC information; however, this flow
focuses on the use of the credit-control messages.) The user has
been authenticated and authorized prior to initiating the call and
has been subscribed to the AoC service.
User Agent A sends an INVITE with the SDP to User Agent B via the SIP
controller (1). The SIP controller determines that the user is
subscribed to an AoC service and sends a Diameter Credit-Control-
Request (EVENT_REQUEST with Requested-Action set to PRICE_ENQUIRY) to
the Diameter Credit-Control server (2). The Credit-Control-Request
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RFC 8506 Diameter Credit-Control Application March 2019
contains SIP-specific AVPs derived from the SIP signaling, describing
the requested service (e.g., calling party, called party, SDP
attributes). The Diameter Credit-Control server determines the cost
of the service and returns the Credit-Control-Answer, including the
Cost-Information AVP (3). The SIP controller manufactures the AoC
web page with information received in SIP signaling and with the cost
information received from the credit-control server. It then sends a
SIP MESSAGE that contains a URL pointing to the AoC information web
page (4). Upon receipt of the SIP MESSAGE, User Agent A
automatically invokes the web browser that retrieves the AoC
information (5). The user clicks on the appropriate button to accept
the charges (6). The SIP controller continues the session and sends
the INVITE to User Agent B, which accepts the call (7), (8), (9).
A.6. Flow VI
Figure 16 illustrates a credit-control flow for the REFUND case. It
is assumed that there is a trusted relationship and secure connection
between the gaming server and the Diameter Credit-Control server.
The end user may be a prepaid subscriber or a postpaid subscriber.
Gaming Server
End User (CC Client) CC Server
| (1)Service Delivery | |
|<---------------------->| |
: : :
: : :
| |(2)CCR(Event, REFUND,Requested-
| |Service-Unit, Service-Parameter-Info)
| |----------------------->|
| | (3)CCA(Cost-Information)
| |<-----------------------|
| (4)Notification | |
|<-----------------------| |
Figure 16: Flow VI
While the end user is playing the game (1), they enter a new level
that entitles them to a bonus. The gaming server sends a Diameter
Credit-Control-Request (EVENT_REQUEST with Requested-Action set to
REFUND_ACCOUNT) to the Diameter Credit-Control server (2). The
Credit-Control-Request contains the Requested-Service-Unit AVP with
the CC-Service-Specific-Units containing the number of points the
user just won. The Service-Parameter-Info AVP is also included in
the request and specifies the service event to be rated (e.g., Tetris
Bonus). From information received, the Diameter Credit-Control
server determines the amount to be credited, refunds the user's
account, and returns the Credit-Control-Answer, including the
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RFC 8506 Diameter Credit-Control Application March 2019
Cost-Information AVP (3). The Cost-Information AVP indicates the
credited amount. At the first opportunity, the gaming server
notifies the end user of the credited amount (4).
A.7. Flow VII
Figure 17 provides an example of graceful service termination for a
SIP call. It is assumed that the call is set up so that the
controller is in the call as a B2BUA (Back-to-Back User Agent)
performing third-party call control (3PCC). Note that the SIP
signaling is inaccurate, as the focus of this flow is on graceful
service termination and credit-control authorization. Best practices
for 3PCC are defined in [RFC3725].
SIP Controller Top-Up
User Agent A (CC Client) Server User Agent B CC Server
| | | | |
| | (1)CCR(Update, Used-Units) | |
| |------------------------------------------>|
| | (2)CCA(Final-Unit, Redirect)|
| |<------------------------------------------|
: : : : :
: : : : :
| | (3)CCR(Update, Used-Units)| |
| |------------------------------------------>|
| | (3a)INVITE("hold") | |
| |--------------------------->| |
| | | (4)CCA(Validity-Time)|
| |<------------------------------------------|
| (5)INVITE | (6)INVITE | | |
|<---------------|------------->| | |
| (7)RTP | | |
|...............................| | |
| | (8)BYE | | |
| |<-------------| | |
| | (9)CCR(Update) | |
| |------------------------------------------>|
| | (10)CCA(Granted-Units)|
| |<------------------------------------------|
| (12)INVITE | (11)INVITE | |
|<---------------|--------------------------->| |
Figure 17: Flow VII
Bertz, et al. Standards Track [Page 121]
RFC 8506 Diameter Credit-Control Application March 2019
The call is ongoing between User Agents A and B; User Agent A has a
prepaid subscription. At the expiry of the allocated quota, the SIP
controller sends a Diameter Credit-Control-Request (UPDATE_REQUEST)
to the Diameter Credit-Control server (1). This message contains the
units used thus far. The Diameter Credit-Control server debits the
used units from the end user's account and allocates the final quota
returned to the SIP controller in the Diameter Credit-Control-Answer
(2). This message contains the Final-Unit-Indication AVP with
Final-Unit-Action set to REDIRECT, the Redirect-Address-Type set to
SIP URI, and the Redirect-Server-Address set to the top-up server
name (e.g., sip:sip-topup-server@domain.com). At the expiry of the
final allocated quota, the SIP controller sends a Diameter
Credit-Control-Request (UPDATE_REQUEST) to the Diameter
Credit-Control server (3) and places the called party on "hold" by
sending an INVITE with the appropriate connection address in the SDP
(3a). The Credit-Control-Request message contains the units used
thus far. The Diameter Credit-Control server debits the used units
from the end user's account but does not make any credit
reservations. The Credit-Control-Answer message, which contains the
Validity-Time to supervise the graceful service termination process,
is returned to the SIP controller (4). The SIP controller
establishes a SIP session between the prepaid user and the top-up
server (5), (6). The top-up server plays an announcement and prompts
the user to enter a credit card number and the amount of money to be
used to replenish the account (7). The top-up server validates the
credit card number, replenishes the user's account (using some means
outside the scope of this specification), and releases the SIP
session (8). The SIP controller can now assume that communication
between the prepaid user and the top-up server took place. It sends
a spontaneous Credit-Control-Request (UPDATE_REQUEST) to the Diameter
Credit-Control server to check whether the account has been
replenished (9). The Diameter Credit-Control server reserves credit
from the end user's account and returns the reserved quota to the SIP
controller in the Credit-Control-Answer (10). At this point, the SIP
controller reconnects the caller and the called party (11), (12).
Bertz, et al. Standards Track [Page 122]
RFC 8506 Diameter Credit-Control Application March 2019
A.8. Flow VIII
Figure 18 provides an example of graceful service termination
initiated when the first interrogation takes place because the user's
account is empty. In this example, the credit-control server
supports the server-initiated credit re-authorization. The Diameter
protocol application is implemented in the NAS per [RFC7155].
NAS Top-Up CC
End User (CC Client) AAA Server Server Server
|(1)User Logon |(2)AA-Request (CC AVPs) | |
|------------------>|------------------->| | |
| | |(3)CCR(Initial, CC AVPs)
| | |------------------->|
| | |(4)CCA(Final-Unit, |
| | | Validity-Time)|
| | |<-------------------|
| |(5)AA-Answer(Final-Unit, Validity-Time) |
|(6)Limited access |<-------------------| | |
| granted | | | |
|<----------------->| | | |
| | | | |
| (7)TCP/HTTP | (8)TCP/HTTP | |
|<----------------->|<----------------------------->| |
| (9)Replenish account | |
|<------------------------------------------------->| |
| | | (10)RAR |
| |<-------------------|<-------------------|
| |(11)RAA | |
| |------------------->|------------------->|
| |(12)CCR(Update) | |
| |------------------->|(13)CCR(Update) |
| | |------------------->|
| | |(14)CCA(Granted-Units)
| |(15)CCA(Granted-Units)<------------------|
| |<-------------------| |
Figure 18: Flow VIII
The user logs on to the network (1). The Diameter NAS sends a
Diameter AA-Request (AAR) to the home Diameter AAA server (2). The
credit-control client populates the AAR with the Credit-Control AVP
set to CREDIT_AUTHORIZATION, and service-specific AVPs are included,
as usual [RFC7155]. The home Diameter AAA server performs service-
specific authentication and authorization, as usual. The home
Diameter AAA server determines that the user has a prepaid
subscription and notices from the Credit-Control AVP that the NAS has
credit-control capabilities. It sends a Diameter Credit-Control-
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RFC 8506 Diameter Credit-Control Application March 2019
Request with CC-Request-Type set to INITIAL_REQUEST to the Diameter
Credit-Control server to perform credit authorization (3) and to
establish a credit-control session. (The home Diameter AAA server
may forward service-specific AVPs received from the NAS as input for
the rating process.) The Diameter Credit-Control server checks the
end user's account balance, determines that the account cannot cover
the cost of the service, and initiates graceful service termination.
The Credit-Control-Answer is returned to the home Diameter AAA server
(4). This message contains the Final-Unit-Indication AVP and the
Validity-Time AVP set to a reasonable amount of time, to give the
user a chance to replenish their account (e.g., 10 minutes). The
Final-Unit-Indication AVP includes the Final-Unit-Action set to
REDIRECT, the Redirect-Address-Type set to URL, and the Redirect-
Server-Address set to the HTTP top-up server name. The home Diameter
AAA server sends the received Credit-Control AVPs to the NAS in the
Diameter AA-Answer (5). Upon successful AAA, the NAS starts the
credit-control session and immediately starts graceful service
termination, as instructed by the server. The NAS grants limited
access to the user (6). The HTTP client software running in the
user's device opens the transport connection redirected by the NAS to
the top-up server (7), (8). An appropriate web page is provided for
the user where the user can enter the credit card number and the
amount of money to be used to replenish the account, along with a
notification message that they are granted unlimited access if the
replenishment operation will be successfully executed within, for
example, the next 10 minutes. The top-up server validates the credit
card number and replenishes the user's account (using some means
outside the scope of this specification) (9). After successful
account top-up, the credit-control server sends a Re-Auth-Request
message to the NAS (10). The NAS acknowledges the request by
returning the Re-Auth-Answer message (11) and initiates the credit
re-authorization by sending a Credit-Control-Request (UPDATE_REQUEST)
to the Diameter Credit-Control server (12), (13).
The Diameter Credit-Control server reserves credit from the
end user's account and returns the reserved quota to the NAS via the
home Diameter AAA server in the Credit-Control-Answer (14), (15).
The NAS removes the restriction applied by graceful service
termination and starts monitoring the granted units.
A.9. Flow IX
The Diameter Credit-Control application defines the Multiple-
Services-Credit-Control AVP, which can be used to support independent
credit-control of multiple services in a single credit-control
(sub-)session for Service Elements that have such capabilities. It
is possible to request and allocate resources as a credit pool that
is shared between services or rating-groups.
Bertz, et al. Standards Track [Page 124]
RFC 8506 Diameter Credit-Control Application March 2019
Figure 19 illustrates a usage scenario where the credit-control
client and server support independent credit-control of multiple
services, as defined in Section 5.1.2. It is assumed that service-
identifiers, rating-groups, and their associated parameters (e.g., IP
5-tuples) are locally configured in the Service Element or
provisioned by an entity other than the credit-control server.
End User Service Element CC Server
(CC Client)
|(1)User logon | |
|------------------>|(2)CCR(Initial, Service-Id access, |
| | Access-specific AVPs, |
| | Multiple-Services-Indicator) |
| |------------------------------------------->|
| |(3)CCA(Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id access, |
| | Validity-Time, |
| | G-S-U-Pool-Reference(Pool-Id 1, |
| | Multiplier 10))) |
| |<-------------------------------------------|
: : :
|(4)Service-Request (Service 1) |
|------------------>|(5)CCR(Update, Multiple-Services-CC ( |
| | Requested-Units(), Service-Id 1, |
| | Rating-Group 1)) |
| |------------------------------------------->|
| |(6)CCA(Multiple-Services-CC ( |
| | Granted-Units(Time), |
| | Rating-Group 1, |
| | G-S-U-Pool-Reference(Pool-Id 1, |
| | Multiplier 1))) |
| |<-------------------------------------------|
: : :
|(7)Service-Request (Service 2) |
|------------------>| |
: : :
: : :
|(8)Service-Request (Services 3 & 4) |
|------------------>|(9)CCR(Update, Multiple-Services-CC ( |
| | Requested-Units(), Service-Id 3, |
| | Rating-Group 2), |
| | Multiple-Services-CC ( |
| | Requested-Units(), Service-Id 4, |
| | Rating-Group 3)) |
| |------------------------------------------->|
Bertz, et al. Standards Track [Page 125]
RFC 8506 Diameter Credit-Control Application March 2019
| |(10)CCA(Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id 3, Rating-Group 2, |
| | Validity-Time, |
| | G-S-U-Pool-Reference(Pool-Id 2, |
| | Multiplier 2)), |
| | Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id 4, Rating-Group 3 |
| | Validity-Time, |
| | Final-Unit-Ind.(Terminate), |
| | G-S-U-Pool-Reference(Pool-Id 2, |
| | Multiplier 5))) |
| |<-------------------------------------------|
: : :
: : :
| +--------------+ | |
| |Validity time | |(11)CCR(Update, |
| |expires for | | Multiple-Services-CC ( |
| |Service-Id | | Requested-Unit(), |
| | access | | Used-Units(In-Octets, Out-Octets), |
| +--------------+ | Service-Id access)) |
| |------------------------------------------->|
| |(12)CCA(Multiple-Services-CC ( |
| | Granted-Units(Total-Octets), |
| | Service-Id access, |
| | Validity-Time, |
| | G-S-U-Pool-Reference(Pool-Id 1, |
| | Multiplier 10))) |
| |<-------------------------------------------|
: : :
: : :
| +--------------+ | |
| |Total quota | |(13)CCR(Update, |
| |elapses for | | Multiple-Services-CC ( |
| |Pool 2: | | Requested-Unit(), |
| |Service 4 not | | Used-Units(In-Octets, Out-Octets),|
| |allowed, | | Service-Id 3, Rating-Group 2), |
| |Service 3 | | Multiple-Services-CC ( |
| |continues | | Used-Units(In-Octets, Out-Octets),|
| +--------------+ | Service-Id 4, Rating-Group 3)) |
| |------------------------------------------->|
| |(14)CCA(Multiple-Services-CC ( |
| | Result-Code 4011, |
| | Service-Id 3)) |
| |<-------------------------------------------|
: : :
: : :
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RFC 8506 Diameter Credit-Control Application March 2019
|(15)User logoff | |
|------------------>|(16)CCR(Term., |
| | Multiple-Services-CC ( |
| | Used-Units(In-Octets, Out-Octets),|
| | Service-Id access), |
| | Multiple-Services-CC ( |
| | Used-Units(Time), |
| | Service-Id 1, Rating-Group 1), |
| | Multiple-Services-CC ( |
| | Used-Units(Time), |
| | Service-Id 2, Rating-Group 1)) |
| |------------------------------------------->|
| |(17)CCA(Term.) |
| |<-------------------------------------------|
Figure 19: Flow IX: Example of Independent Credit-Control of
Multiple Services in a Credit-Control (Sub-)Session
The user logs on to the network (1). The Service Element sends a
Diameter Credit-Control-Request with CC-Request-Type set to
INITIAL_REQUEST to the Diameter Credit-Control server to perform
credit authorization for the bearer service (e.g., Internet access
service) and to establish a credit-control session (2). In this
message, the credit-control client indicates support for independent
credit-control of multiple services within the session by including
the Multiple-Services-Indicator AVP. The Diameter Credit-Control
server checks the end user's account balance, with rating information
received from the client (i.e., Service-Id and access-specific AVPs);
rates the request; and reserves credit from the end user's account.
Suppose that the server reserves $5 and determines that the cost is
$1/MB. It then returns to the Service Element a Credit-Control-
Answer message that includes the Multiple-Services-Credit-Control AVP
with a quota of 5 MB associated to the Service-Id (access), to a
multiplier value of 10, and to Pool-Id 1 (3).
The user uses service 1 (4). The Service Element sends a Diameter
Credit-Control-Request with CC-Request-Type set to UPDATE_REQUEST to
the credit-control server to perform credit authorization for
service 1 (5). This message includes the Multiple-Services-Credit-
Control AVP to request service units for service 1 that belong to
Rating-Group 1. The Diameter Credit-Control server determines that
service 1 draws credit resources from the same account as the access
service (i.e., pool 1). It rates the request according to
Service-Id/rating-group and updates the existing reservation by
requesting more credit. Suppose that the server reserves $5 more
(now the reservation is $10) and determines that the cost is
$0.1/minute. The server authorizes the whole rating-group. It then
returns to the Service Element a Credit-Control-Answer message that
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RFC 8506 Diameter Credit-Control Application March 2019
includes the Multiple-Services-Credit-Control AVP with a quota of
50 minutes associated to Rating-Group 1, to a multiplier value of 1,
and to Pool-Id 1 (6). The client adjusts the total amount of
resources for pool 1 according to the received quota, which gives S
for pool 1 = 100.
The user uses service 2, which belongs to the authorized rating-group
(Rating-Group 1) (7). Resources are then consumed from pool 1.
The user now requests services 3 and 4 as well, which are not
authorized (8). The Service Element sends a Diameter Credit-Control-
Request with CC-Request-Type set to UPDATE_REQUEST to the
credit-control server in order to perform credit authorization for
services 3 and 4 (9). This message includes two instances of the
Multiple-Services-Credit-Control AVP to request service units for
service 3 that belong to Rating-Group 2 and service units for
service 4 that belong to Rating-Group 3. The Diameter Credit-Control
server determines that services 3 and 4 draw credit resources from
another account (i.e., pool 2). It checks the end user's account
balance and, according to Service-Id/rating-group information, rates
the request. It then reserves credit from pool 2.
For example, the server reserves $5 and determines that service 3
costs $0.2/MB and service 4 costs $0.5/MB. The server authorizes
only services 3 and 4. It returns to the Service Element a
Credit-Control-Answer message that includes two instances of the
Multiple-Services-Credit-Control AVP (10). One instance grants a
quota of 12.5 MB associated to Service-Id 3 to a multiplier value
of 2 and to Pool-Id 2. The other instance grants a quota of 5 MB
associated to Service-Id 4 to a multiplier value of 5 and to
Pool-Id 2.
The server also determines that pool 2 is exhausted and service 4 is
not allowed to continue after these units will be consumed.
Therefore, the Final-Unit-Indication AVP with action TERMINATE is
associated to Service-Id 4. The client calculates the total amount
of resources that can be used for pool 2 according to the received
quotas and multipliers, which gives S for pool 2 = 50.
The Validity-Time for the access service expires. The Service
Element sends a Credit-Control-Request message to the server in order
to perform credit re-authorization for the Service-Id (access) (11).
This message carries one instance of the Multiple-Services-Credit-
Control AVP that includes the units used by this service. Suppose
that the total amount of used units is 4 MB. The client adjusts the
total amount of resources for pool 1 accordingly, which gives S for
pool 1 = 60.
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RFC 8506 Diameter Credit-Control Application March 2019
The server deducts $4 from the user's account and updates the
reservation by requesting more credit. Suppose that the server
reserves $5 more (now the reservation is $11) and already knows the
cost of the Service-Id (access), which is $1/MB. It then returns to
the Service Element a Credit-Control-Answer message that includes the
Multiple-Services-Credit-Control AVP with a quota of 5 MB associated
to the Service-Id (access), to a multiplier value of 10, and to
Pool-Id 1 (12). The client adjusts the total amount of resources for
pool 1 according to the received quota, which gives S for
pool 1 = 110.
Services 3 and 4 consume the total amount of pool 2's credit
resources (i.e., C1*2 + C2*5 >= S). The Service Element immediately
starts the TERMINATE action for service 4 and sends a Credit-Control-
Request message with CC-Request-Type set to UPDATE_REQUEST to the
credit-control server in order to perform credit re-authorization for
service 3 (13). This message contains two instances of the Multiple-
Services-Credit-Control AVP to report the units used by services 3
and 4. The server deducts the last $5 from the user's account
(pool 2) and returns the answer with Result-Code 4011 in the
Multiple-Services-Credit-Control AVP to indicate that service 3 can
continue without credit-control (14).
The end user logs off from the network (15). To debit the used units
from the end user's account and to stop the credit-control session,
the Service Element sends a Diameter Credit-Control-Request with
CC-Request-Type set to TERMINATION_REQUEST to the credit-control
server (16). This message contains the units used by each service in
multiple instances of the Multiple-Services-Credit-Control AVP. The
used units are associated with the relevant Service-Identifier and
rating-group. The Diameter Credit-Control server debits the used
units to the user's account (pool 1) and acknowledges the session
termination by sending a Diameter Credit-Control-Answer to the
Service Element (17).
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RFC 8506 Diameter Credit-Control Application March 2019
Acknowledgements
The original authors of RFC 4006 are Harri Hakala, Leena Mattila,
Juha-Pekka Koskinen, Marco Stura, and John Loughney.
The authors would like to thank Bernard Aboba, Jari Arkko, Robert
Ekblad, Pasi Eronen, Benny Gustafsson, Robert Karlsson, Avi Lior,
Jussi Maki, Paco Marin, Jeff Meyer, Anne Narhi, John Prudhoe,
Christopher Richards, Juha Vallinen, and Mark Watson for their
comments and suggestions.
Authors' Addresses
Lyle Bertz (editor)
Sprint
6220 Sprint Parkway
Overland Park, KS 66251
United States of America
Email: lyleb551144@gmail.com
David Dolson (editor)
Sandvine
408 Albert Street
Waterloo, ON N2L 3V3
Canada
Email: ddolson@acm.org
Yuval Lifshitz (editor)
Sandvine
408 Albert Street
Waterloo, ON N2L 3V3
Canada
Email: yuvalif@yahoo.com
Bertz, et al. Standards Track [Page 130]