IMS based services can be provided with use of PS bearers and CS bearers for the media. When using CS bearer for
media transport of IMS sessions, interworking solutions for IMS Centralized Services (ICS) as specified in TS 23.292
are used. ICS allows IMS sessions using CS bearers to be treated as standard IMS sessions for the purpose of IMS Service Continuity (ISC). ICS defines signalling mechanisms between the UE and IMS for transport of information as needed for service continuity when using CS access for media transport.
Both ICS and ISC specify functions which are provided by a SIP application server.
This TS specifies the architectural requirements and procedures for delivery of IMS Service Continuity (ISC).
The solution is restricted to service continuity using IMS procedures, i.e. mobility mechanisms on the IP-CAN level are not within the scope of this specification.