P-Charging-Vector

The IMS charging correlation information is encoded in the P-Charging-Vector header of a SIP message. This header is defined in RFC 3455 [IET03b]. Extensions to this header and its usage within the IMS network are described in 3GPP TS 24.299 [3GP07c]. The P-Charging-Vector header includes the following identifiers.

• IMS charging identifier (ICID) identifies an IMS call session (or event service) in the charging/billing system. The charging data generated in different IMS nodes

are correlated with the ICID shared among IMS network nodes involved in the IMS session. This identity is globally unique across all 3GPP IMS networks for a time period of at least one month. Expiration of an ICID can be detected by using IMS node-specific information, e.g., high-granularity time information and location information. At each SIP session establishment, a new ICID is generated at the first IMS node (e.g., P-CSCF) that processes the SIP INVITE message. This ICID is then used in all subsequent SIP messages for that session (e.g., SIP 200 OK and BYE messages) until the session is terminated. The ICID is generated by an IMS node in the UTF8String format (e.g., 1234bc9876e) [3GP06c].

• Access network charging identifier specifies the corresponding IP-based bearer that transports the IMS media flows on the originating or the terminating side.

This information is used to correlate the access network charging data with the IMS charging data. Examples for access network charging identifiers are GPRS Charging Identifier (GCID) for GPRS and PDG charging identifier for WLAN services [3GP05b, 3GP06e]. At PDP context activation, the GCID is generated by the GGSN in the UTF8String format [3GP06c].

• Inter-operator identifier (IOI) identifies both originating and terminating networks involved in a SIP session. This identifier is inserted by the S-CSCF and will be removed by the P-CSCF when the SIP request goes outside the IMS network.

In a SIP call establishment, the P-CSCF is typically the first IMS node that processes the SIP request. The P-CSCF includes the P-Charging-Vector header in the SIP request.

In Figure 5.4, the P-Charging-Vector for a SIP request issued from MS1 is P-Charging-Vector: icid-value = 1234bc9876e;

gcid = 3069882;

orig-ioi = home1.net.tw;

term-ioi = home2.net.hk

5.7 Concluding Remarks

This chapter described how CAMEL, RADIUS and Diameter are used to implement charging functionalities in mobile telecommunications networks. We introduced the CAMEL functional architecture and the CAMEL subscription information. We briefly described the RADIUS protocol, and then elaborated on how the Diameter charging protocol is utilized in next generation all-IP networks. Specifically, we described the Diameter message formats and the message flows for offline and online charging.

At the end of this chapter, we also described the SIP headers that are used for IMS charging.

Several commercial Diameter software tools are available for developing IMS char-ging. An example is the RADVISION DIAMETER Toolkit for the development of

CONCLUDING REMARKS 89

IMS Diameter-compliant network elements [RAD07]. Designed to ensure maximum flexibility, this toolkit is equipped with API hooks that allow the application layer to control call flows and objects inside the toolkit for enhanced application capabilities.

Implemented in the C language, this toolkit also allows multiple applications to run over it transparently.

Another example is MARBEN Diameter suitable for use in all IMS equipment needing Diameter [MAR07]. In this tool, access to the Rf and Ro interfaces as well as the Diameter Base Protocol is offered through a set of dedicated high-level object-oriented APIs in languages such as C++ or Java. This tool supports extensibility for creation of new AVPs, security by processing of Diameter security AVP, and provision for supporting IPsec and Transport Layer Security (TLS) secure transport layers. It runs on top of any TCP or Stream Control Transmission Protocol (SCTP) layer [IET02b]

offering a socket transport interface with very little work. Similarly, the operation and management interface has been kept simple while providing the functionalities expected for telecom software that runs under strict operational constraints.

An example of a Diameter implementation for Rf/Ro interfaces in SIP application server will be given in Appendix F.

Review Questions

1. Describe gsmSSF, gsmSCF and gsmSRF. How do they interact with each other?

2. Give two examples of mobile services that can be implemented by CAMEL.

3. Describe the CSI types and their usage.

4. Describe the RADIUS header format.

5. Describe the Acct-Status-Type and Acct-Terminate-Cause attrib-utes used in the RADIUS request message.

6. What is the major difference between CCF and CDF?

7. Describe the Diameter header format.

8. Describe the accounting record types for the Diameter accounting messages.

9. Describe the Acct-Interim-Interval AVP used in offline charging.

Is there any similar AVP used in online charging? What is the advantage and disadvantage of using this kind of AVP?

10. Describe the message flow for the session-based offline charging.

11. Describe the credit control request types for the Diameter credit control messages.

12. Describe the detailed steps of immediate event charging where the unit determination is performed at the network node.

13. What is the major difference between the immediate event charging and event charging with unit reservation?

14. Describe the detailed steps of event charging with unit reserva-tion where both unit determinareserva-tion and rating are performed at the network node.

15. Describe the message flow for the session-based online charging.

16. What is Function-Address? What is P-Charging-Vector?

17. What are ICID and IOI?

18. What is an access network charging identifier? Give two examples.

References

[3GP00] Digital cellular telecommunications system (Phase 2+); Customised Applications for Mobile network Enhanced Logic (CAMEL); CAMEL Application Part (CAP) specification (Release 1997), GSM 09.78 version 6.5.0, (2000-07), 2000.

[3GP05a] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Customized Applications for Mobile network Enhanced Logic (CAMEL); Service description; Stage 1 (Release 5), 3G TS 22.078 version 5.15.0 (2005-03), 2005.

[3GP05b] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Services and Systems Aspects; General Packet Radio Service (GPRS); Service description;

Stage 2 (Release 5), 3G TS 23.060 version 5.13.0 (2006-12), 2006.

[3GP06a] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Service and System Aspects; Telecommunication management; Charging management;

Online Charging System (OCS): Applications and interfaces (Release 6), 3G TS 32.296 version 6.3.0 (2006-09), 2006.

[3GP06b] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network; IP Multimedia Subsystem (IMS); Stage 2 (Release 5), 3G TS 23.228 version 5.15.0 (2006-06), 2006.

[3GP06c] 3GPP, 3GPP. 3rd Generation Partnership Project; Technical Specification Group Service and System Aspects; Telecommunication management; Charging man-agement; Charging data description for the IP Multimedia Subsystem (IMS) (Release 5), 3G TS 32.225 version 5.11.0 (2006-03), 2006.

[3GP06d] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network; Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4; CAMEL Application Part (CAP) specification (Release 6), 3G TS 29.078 version 6.5.0 (2006-06), 2006.

[3GP06e] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Service and System Aspects; Telecommunication management; Charging management;

Wireless Local Area Network (WLAN) charging (Release 6), 3G TS 32.252 version 6.2.0 (2006-09), 2006.

[3GP07a] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Service and System Aspects; Telecommunication management; Charging management;

REFERENCES 91

Diameter charging applications (Release 6), 3G TS 32.299 version 6.12.0 (2007-09), 2007.

[3GP07b] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Telecommunication management; Charging management;

Packet Switched (PS) domain charging (Release 6), 3GPP TS 32.251 version 6.10.0 (2007-06), 2007.

[3GP07c] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; IP Multimedia Call Control Protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3 (Release 6), 3GPP TS 24.229 version 6.17.0 (2007-12), 2007.

[3GP07d] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Rx Interface and Rx/Gx signalling flows (Release 6), 3G TS 29.211 version 6.3.0 (2005-12), 2005.

[3GP07e] 3GPP, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Policy control over Gq interface (Release 6), 3G TS 29.209 version 6.6.0 (2006-09), 2006.

[IET00a] IETF, Remote Authentication Dial In User Service (RADIUS). IETF RFC 2865, 2000.

[IET00b] IETF, RADIUS Accounting. IETF RFC 2866, 2000.

[IET02a] IETF, SIP: Session Initiation Protocol. IETF RFC 3261, 2002.

[IET02b] IETF, An Introduction to the Stream Control Transmission Protocol (SCTP). IETF RFC 3286, 2002.

[IET03a] IETF, Diameter Base Protocol. IETF RFC 3588, 2003.

[IET03b] IETF, Private Header (P-Header) Extensions to the Session Initiation Protocol (SIP) for the 3rd Generation Partnership Project (3GPP). IETF RFC 3455, 2003.

[IET05] IETF, Diameter Credit-Control Application. IETF RFC 4006, 2005.

[Lin01] Lin, Y.-B. and Chlamtac, I., Wireless and Mobile Network Architectures. John Wiley & Sons Ltd., Chichester, UK, 2001.

[MAR07] MARBEN Diameter Product, MARBEAN, 2007.

[RAD07] IMS DIAMETER Toolkit. RADVISION, 2007.

6

UMTS CS/PS Charging