scope:

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).

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.

Where possible the present document specifies the requirements for this protocol by reference to specifications produced by the IETF within the scope of SIP, SIP Events and SDP, either directly, or as modified by 3GPP TS 24.229 [8]. Where this is not possible, extensions to SIP are defined within the present document. The document has therefore been structured in order to allow both forms of specification.

Editor's note: If this TS makes no amendment to any of the IETF protocols, then this paragraph will not be included.

The present document is applicable to User Equipment (UEs), Application Servers (AS) and Media Gateway Control Functions (MGCF) providing voice call continuity capabilities.