The charging strategy applied in ICS shall ensure complete and correct charging of the access leg that is used for an ICS call. An ICS subscriber may establish or accept a call through CS access or through an IP access network (IP-CAN). The charge that is levied against an ICS subscriber for a call shall encompass the usage of the access network (CS access or IP-CAN) as well as the usage of the IMS network, further depending on the destination of the call and other call related aspects. The access related charge for an ICS call, i.e. the CS access network related charge or IP-CAN related charge, shall be included in the charging record generated by SCC AS. The charge of a SIP call or session may be adapted when this call or session is subject to a value added service (e.g. number translation, call diversion) or is subject to a supplementary service (e.g. call forwarding, call transfer, conference call). Standard inter-operator reconciliation mechanisms for CS and IMS can and should be used. Additional reconciliation for I1 flows can also be applied, due to such flows being uniquely identifiable from other flows over the same bearer (see clause 5.4.1 for more information).

Charging record generated by the SCC AS may be correlated with charging records generated in the MSC Server or with charging records in the IP-CAN, where applicable. The combination of charging records from SCC AS with charging records from MSC Server or IP-CAN is used for determining access charge for the call or multimedia session. The combination of these charging records may further be correlated with other IMS-based charging records generated by S-CSCF or other functional entities in the IMS network, for the purpose of generating an overall charge for a call or multimedia session, including access related charge. Where PS to CS transfer has occurred, at least in roaming situations, the visited network shall correlate the charging records from MSC Server and any visited network IMS functions. The information used for correlation is described in TS 23.237.

When on-line charging is applied for an ICS subscriber, this on-line charging should be performed strictly in IMS. CS network based on-line charging service (e.g., CAMEL prepaid), for example, shall not be invoked for ICS subscribers.

ICS re-uses the CS domain security described in the detailed access specific specification. Access using MSC Server enhanced for ICS is secured by the combination of the CS access security and the IMS Network Domain Security. The MSC Server enhanced for ICS also performs the trusted node authentication procedures according to TS 33.203.

Network domain security with the MSC server enhanced for ICS shall be provided by NDS/IP according to TS 33.210 for the I2 reference point.