Voice call continuity between Circuit Switched (CS) and IP Multimedia Subsystem (IMS) Study
This document contains the results of the feasibility study into the architectural requirements and alternatives for the active voice call continuity between Circuit Switched (CS) domain and the IP Multimedia Subsystem (IMS). Considerations include overall requirements, architectural requirements, evaluation of potential architectural solutions and alternative architectures.
The Feasibility Study considers different solutions for offering real-time voice call continuity when users move between the GSM/UMTS CS Domain and the IP Connectivity Access Network (e.g., WLAN interworking) with home IMS functionality. Voice call related functionality, including the need for Regulatory issues (e.g. Text Tele phone (TTY as defined in TS 26.226)), Emergency Call and support for supplementary services are taken into consideration.
The objective is to identify an architectural solution that allows completely automatic connectivity from the end-user point of view, while minimizing the additional complexity and impacts to the existing system. The feasibility study shall also investigate mechanisms for selecting the most appropriate network domain to serve the user.
Existing solutions developed by the 3GPP (e.g. 3GPP system to Wireless Local Area Network Interworking (I-WLAN)) should be reused as much as possible.
The impact to, and support of service continuity for sessions/calls established following the principles outlined in the combining of CS and IMS sessions (CSI) will also be considered in this study.