The goals of this project were to examine the performance of inter-domain handoff between Wi-Fi and 3G networks on smartphones. An increasing number of mobile devices are providing internet access from over both Wi-Fi and 3G. This trend has led to interest in looking at optimum ways to use these networks for a variety of needs. In this project, we wanted to examine the feasibility of using handoff for a VOIP application. We considered the case of two users having internet access on both of these interfaces, with the need to conduct VOIP phone calls. An additional requirement is to provide this capability while preferring Wi-Fi for the session if it is available. The desire to move data services to the Wi-Fi domain from 3G is due to the user wanting to minimize the use of data services over 3G.
For our implementation, we used two HTC Tilt smartphones that are Wi-Fi enabled. The smartphones use Windows Mobile 6.1 for the operating system. Communication between these devices is mediated by a server in the middle. For the server application, a linux machine was used running Ubuntu. This server also has a known public IP address that can receive TCP and UDP packets from the participating clients. A block diagram of the configuration is shown below: