4 Overall requirements

23.2793GPPCombining Circuit Switched (CS) and IP Multimedia Subsystem (IMS) servicesRelease 17Stage 2TS

4.1 General description

The "combination of CS and IMS services" (CSI) is essentially a combination of existing CS and IMS services, i.e. mechanisms and procedures for the IMS part of the CSI session apply according to TS 23.228 [2].

The UE presents the CS call and IMS session within one context to the user. To facilitate this, the following capabilities shall be provided:

1. Exchange of information related to the current radio environment;

2. Exchange of terminal capability information;

3. Addition of an IMS session to an ongoing CS call;

4. Addition of a CS call to an ongoing IMS session.

5. Network support for establishing multimedia sessions between a UE that uses IMS origination and a UE that uses CSI termination.

CSI services can be provided:

1. Between two CSI capable UEs that both use CSI origination and CSI termination;

2. Between a UE that uses IMS origination and a UE that uses CSI termination.

4.2 Service requirements

The service requirements of combining IMS and CS services are described in TS 22.279 [13].