3GPP Work Item description

This page contains informal descriptive text only.  See master WID page for further details.

Feature: Voice call continuity between CS and IMS (incl. I-WLAN)
 

Technical Specification 23.234 (3GPP system to Wireless Local Area Network (WLAN) interworking: System description) provides the possibility to offer VoIP over WLAN interworking with home IMS. The converged IMS architecture offers the possibility to support the most prevalent GSM service, voice calls, over WLAN when there is coverage. A seamless voice call between CS Domain and the WLAN could provide relief to the GSM/UMTS radio resources and increase service revenue. In addition, wireline operators with VoIP offerings should be able to use the 3GPP IMS architecture to offer converged services.

Seamless session continuity between WLAN and 3GPP access assumes the continuation of a WLAN IP service as a 3GPP IP service (i.e. via the PS domain). This current assumption is not realistic for real-time voice services; in particular those with GSM radio coverage. Ongoing work on WIDs 32066 and 32067 do not consider the aspect of voice call continuity between CS domain and IMS. As such additional work is needed.

Objectives:

This work item studies and intends to implement the necessary enhancements to 3GPP systems so that real-time voice call can be offered seamlessly between the CS Domain and the WLAN interworking with IMS architecture. This will be accomplished through the development of a Technical Report (feasibility study) that will lead to the development of a Technical Specification that defines this functionality as a standard 3GPP feature.

This work item studies and defines real-time voice call continuity when moving between the GSM/UMTS CS Domain and WLAN interworking with home IMS functionality. It also studies the framework in which the continuity takes place, e.g. the following aspects:

    §         Ability for the UE to detect and automatically select the appropriate Access Network (such as GSM/UMTS radio or IP Connectivity Access Network) based on operator policy for real-time voice service.

    §         Mechanism for selecting how to route the terminating voice calls to the UE: either through the GSM/UMTS CS Domain or through the WLAN interworking networks with IMS based on the user registration. Criteria for the routing decision as well as the routing mechanism itself should be covered.

    §         Voice call continuity when the user is moving between GSM/UMTS CS Domain and WLAN interworking with home IMS.

    §         Support of calls to/from roaming subscribers accessing service from I-WLANs connected over the public internet.

Whilst the objectives above assume WLAN as the underlying access for IMS, the solution developed for CS-IMS voice call continuity shall be independent of the use of the underlying IP Connectivity Access Network. E.g. the solution shall be applicable to IMS over GPRS or fixed broadband access.

This work item should reuse the existing features that have been developed for the GSM /UMTS whenever possible. In this study the CS call scenarios should include the traditional GSM/UMTS CS calls and possibly the newly developed Combining CS Bearer with IMS (32066) capability.

Service aspects:

To provide subscribers with seamless access to real-time wireless voice service while operating in the GSM/UMTS CS Domain and a WLAN interworking with home IMS deployment.