Using conference servers for sip-based vertical handoff between ip and cellular networks

Abstract

The Session Initiation Protocol (SIP) is the preferred signaling protocol for creating and terminating multimedia sessions in an IP network. Also, voice over IP is becoming the favored means of voice communication mainly because of its low cost when compared to voice communication over traditional networks like cellular and PSTN. Therefore, seamless transfer of calls or handoff between the traditional and IP networks becomes important.We describe a technique to achieve seamless mid-call handoffs in a scenario where a handoff occurs between the cellular network and the IP network. The technique we describe makes use of a network element acting as an ISDN gateway, SIP conference server and SIP proxy server. We have measured handoff delays from IP to ISDN network and vice-versa. When using the proposed soft handoff technique, these delays are 0.10 s and 0.02 s, respectively. Finally, we share the results and some of the challenges we faced while implementing the overall mechanism on a dual-mode handset.