Dynamically Anchored Conferencing Handoff for Dual-Mode Cellular/WLAN Handsets

In this paper we consider vertical handoff for dualmode (DM) cellular/WLAN handsets. When the handset roams out of WLAN coverage, the DM´s cellular interface is used to maintain the call by anchoring it through a PSTN gateway/PBX. Soft handoff can be achieved in this case if the gateway supports basic conference bridging, since a new leg of the call can be established to the conference bridge while the existing media stream path is active. Unfortunately this requires that all intraenterprise calls be routed through the gateway when the call is established. In this paper we consider conferenced dual-mode handoff and propose a much more scalable mechanism whereby active calls are handed off into the conference bridge just prior to the initiation of the vertical handoff. Results are presented which are taken from dual-mode handset simulations which characterize the scalability of the proposed mechanism.