Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Combining Circuit Switched (CS) and IP Multimedia Subsystem (IMS) services; Stage 2 (V15.0.0; 3GPP TS 23.279 version 15.0.0 Release 15)
The present document provides architectural details to combine CS services and IMS services for using them in parallel between the same two users in a peer-to-peer context. The document provides a detailed description of how capabilities and identities are exchanged to enable the combination of CS and IMS services between the same two UEs. The present document includes the following capabilities that enable the combination of CS and IMS services: - Radio capability exchange. - SIP based UE terminal capability exchange. - MSISDN number exchange in SIP. - Establishing an IMS session in parallel to an ongoing CS call between the same two UEs. - Establishing a CS call in parallel to an ongoing IMS session between the same two users UEs. - Network support for establishing multimedia sessions between a UE that uses IMS origination and a UE that uses CSI termination. The individual CS call or IMS service that are combined are described in their respective specifications.