TCP for seamless vertical handoff in hybrid mobile data networks

Current trends show that 3G cellular network and WLAN will coexist and work together to support more users with higher data rate services over a wider area. In this hybrid mobile network, the WLAN provides high bandwidth data service over a small area while the 3G cellular network provides a higher mobility with lower bandwidth data service. To provide seamless data service to mobile users, vertical handoff between WLAN and 3G cellular network has to be implemented. We present the challenges in the vertical handoff. We propose a TCP scheme for a seamless vertical handoff, and present a performance evaluation. In the proposed scheme, the TCP sender and receiver use the Handoff (HO) option field in TCP header to recognize an impending handoff and a completing handoff. After a vertical handoff, the sender tries to readjust its data rate, since the new network has drastically different characteristics in contrast with horizontal handoff where keeping the same data rate improves performance. The proposed scheme can be implemented incrementally. It is not necessary to change all of the TCP senders for compatibility since it uses an optional field in TCP header.