Voice call continuity between Circuit Switched (CS) and IP Multimedia Subsystem (IMS); Stage 3
Voice call continuity allows users to move between the CS domain and the IP Connectivity Access Network (e.g., WLAN interworking) with home IM CN subsystem functionality.
The present document provides the protocol details for voice call continuity between the IP Multimedia (IM) Core Network (CN) subsystem based on the Session Initiation Protocol (SIP) and the Session Description Protocol (SDP) and the protocols of the 3GPP Circuit-Switched (CS) domain (CAP, MAP, ISUP, BICC and the NAS call control protocol for the CS access).
This document makes no VCC specific enhancements to SIP, SIP events or SDP, beyond those specified in 3GPP TS 24.229 [7].
The present document is applicable to User Equipment (UEs), Application Servers (AS) and Media Gateway Control Functions (MGCF) providing voice call continuity capabilities.