Page "IP Multimedia Subsystem" Paragraph 86

* Offline Charging: All the SIP network entities ( P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS ) involved in the session use the Diameter Rf interface to send accounting information to a CDF located in the same domain.

The CCF will collect all this information, and build a Call Detail Record ( CDR ), which is sent to the billing system ( BS ) of the domain. Each session carries an IMS Charging Identifier ( ICID ) as a unique identifier generated by the first IMS entity involved in a SIP transaction and used for the correlation with CDRs.

Inter Operator Identifier ( IOI ) is a globally unique identifier shared between sending and receiving networks.

Each domain has its own charging network.

Billing systems in different domains will also exchange information, so that roaming charges can be applied.