Seamless vertical handover of VoIP calls based on SIP Session Border Controllers

High data rate wireless networks enables the provisioning of real time services to mobile devices over IP. At the same time, the different nature of the adopted radio technologies (802.11/WiFi, Bluetooth, 2.5G/3G networks) has introduced the problems of supporting seamless communication across these heterogeneous wireless accesses, which is a goal for 4G network. This paper describes a Session Initiation Protocol (SIP) based solution for mobility management aiming to provide seamless voice service in this heterogeneous scenario. The novelty of the solution is that it relies on the so called "Session Border Controllers" which are currently used in commercial SIP telephony solutions to deal with NAT traversal. A prototype of the proposed solution has been implemented in a test bed where the 802.11 and 3G (UMTS) technologies have been used respectively as typical WLAN and cellurar access networks. Measurements results are reported which analyze the performance of the solution in a real world environment, using commercial WiFi and 3G services.