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The decision to anchor media at the ATGW, during the session origination or termination, can occur<br />
either at receipt of SDP before or after a round trip of SIP signaling with the remote party depending on<br />
the method(s) used for determining whether to anchor media or not.<br />
As part of another Rel-10 study, 3GPP is investigating techniques for supporting seamless service<br />
continuity for subsequent hand-back to VoLTE/Voice over HSPA IMS voice sessions initiated in<br />
VoLTE/Voice over HSPA and previously handed over to 2G/3G CS access. Additionally, it is investigating<br />
feasibility of enabling handovers of the voice calls directly initiated in 2G/3G CS with minimum impact to<br />
CS core network and access nodes.<br />
Several solutions are studied in timeframe of 3GPP Rel-10, but because of lack of time, if this study is not<br />
finished in 3GPP Rel-10, it will be continued as a study work item in 3GPP Rel-11.<br />
7.3.6 IMS SERVICE CONTINUITY (ISC) AND IMS CENTRALIZED SERVICES (ICS)<br />
Work on functionality to provide aspects of Service Continuity has been underway in 3GPP for several<br />
releases. Rel-7 saw the definition of Voice Call Continuity (VCC) and Rel-8 and Rel-9 built on this to<br />
define Service Continuity (SC) and VCC for Single Radio systems (SRVCC). Rel-10 has added further<br />
enhancements to these features including:<br />
� The procedures can be supported between devices belonging to different subscriptions<br />
� Initiation of the procedures can come from multiple devices rather than just one controlling device<br />
� Existing media can be replicated onto different devices<br />
For example, one user could be watching a video stream on a mobile device and a second user, sitting<br />
next to them, or even on the other side of the world, could request that they can watch the same video<br />
stream.<br />
Rel-10 provides enhancement to the performance characteristics of SRVCC to reduce the voice break<br />
experienced by users, for example in some roaming scenarios. SRVCC was also enhanced to support<br />
transfer of a call during the alerting phase.<br />
No significant changes to the Rel-8/Rel-9 ICS features were made in Rel-10.<br />
7.3.7 INTERWORKING WITH WI‐FI<br />
Wi-Fi capability is becoming a commonplace feature on high-end smart phones. End-users with a Wi-Fi<br />
capable handset have the potential to experience higher aggregate throughput, and potentially relaxed<br />
usage caps, at a Wi-Fi hotspot. Network operator control of this capability in any form affords the<br />
operator another tool to protect precious licensed spectrum by managing the offload of certain classes of<br />
traffic to unlicensed spectrum.<br />
WLAN (Wi-Fi) access to the 3GPP packet core was introduced in 3GPP Rel-6, but deployment of this<br />
version of the capability was very limited. 3GPP Rel-8 and Rel-9 introduced different solutions for<br />
standard mobility between 3GPP and WLAN access:<br />
� With host-based mobility (DSMIPv6 client in the UE)<br />
� With network-based mobility (PMIPv6 support in ePDG)<br />
www.4gamericas.org February 2011 Page 75
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