During the course of Release 7, TS 23.206
(Voice Call Continuity between CS and IMS) was developed to provides the capability to offer VCC (Voice Call Continuity) for a subscriber moving from a CS radio environment into a VoIPcapable IMS radio environment connected by an IP-CAN. However, for a variety of reasons, the TS specifically excludes the capability of allowing emergency calls to be subject to domain transfer. This TR documents alternatives for how to provide such voice call continuity between the CS Domain and IP-CANs for emergency calls.
This TR contains the results of the feasibility study into the architectural requirements and alternatives for the support of active voice call continuity between Circuit Switched (CS) domain and the IP Multimedia Subsystem (IMS) for emergency calls. Considerations include overall requirements, architectural requirements, evaluation of potential architectural solutions and alternative architectures.
The Feasibility Study considers different solutions for offering voice call continuity for emergency calls when users move between the GSM/UMTS CS Domain and the IP Connectivity Access Network (e.g., WLAN interworking) with home IMS functionality. The objective is to identify an architectural solution that allows completely automatic connectivity to the correct PSAP (from the end-user point of view) as specified in TS 23.167
, and allow for the possibility of a domain transfer as specified in TS 23.206
. The study will also identify configuration impacts upon existing networks in order to realize the desired functionality.
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.