For example, if a call
originated in the PSTN and was transiting the IMS domain, the P-CSCF may be the
first to receive the request (i.e., an INVITE) and would create the unique ICID for the
session. This ICID is then used in the response and all other requests/responses associated
with the session until the session is terminated.
When a session originates outside of the IMS, say in the GPRS domain, another
parameter is used to correlate CDRs from that domain. The ACCESS NETWORK
CHARGING IDENTIFIER parameter, found in the P-CHARGING-VECTOR header,
provides another unique identifier from the access network.
For example, in the case of GPRS the identifier would be a combination of the GGSN
address and the PDP context identifier. This identifier would then be used along with
the ICID to correlate CDRs from end to end.
Appendix A
3GPP Documentation
IMS-Related Documentation
TS21.133 Security Threats and Requirements
TS21.905 3G Vocabulary
TS22.002 Circuit Bearer Services (BS) Supported by a Public Land Mobile Network
(PLMN)
TS22.003 Circuit Teleservices Supported by a Public Land Mobile Network (PLMN)
TS22.004 General on Supplementary Services
TS22.016 International Mobile Station Equipment Identities (IMEI)
TS22.022 Personalization of Mobile Equipment (ME); Mobile functionality specification
TS22.024 Description of Charge Advice Information (CAI)
TS22.
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