scope:

IMS Centralized Services (ICS) enable the delivery of IM CN subsystem based multimedia telephony and supplementary services as defined in 3GPP TS 24.173 [4] to users regardless of the attached access network type; e.g. CS domain access or IP-CAN.

The present document specifies the principles of interworking between the IM CN subsystem and CS domain in order to enable ICS for UEs using CS domain access.

The present document addresses the area of registration procedures interworking between the CS domain and IM CN subsystem.

The present document addresses the areas of control and user plane interworking between the IM CN subsystem and CS domain through an MSC Server enhanced for ICS and CS-MGW respectively. This includes the signalling procedures between the MSC Server and CS-MGW. For the specification of control plane interworking, present document defines the protocol interworking between the 3GPP profile of SIP as described in 3GPP TS 24.229 [2] and NAS signalling as described in 3GPP TS 24.008 [3] required for the support of IM CN subsystem based multimedia telephony and supplementary services.

The present document addresses the area of supplementary service configuration interworking between the CS domain and IM CN subsystem.

The present document is applicable to the MSC Server and CS-MGW.