Impacts of handoff on TCP performance in mobile wireless computing

The effects of intermittent disconnections due to host motions on the performance of TCP connections are investigated, Fading and handoff due to host motion cause increased delay and packet losses to the active transport layer connection. TCP interprets these as signs of network congestion. As a result, it promptly throttles its transmissions and backoffs its timers, leading to slow post-handoff recovery of the transmission and long idle time, These cause severe end-to-end throughput degradation and unreasonably long interactive delay for human interaction, In this paper, we present three phenomena observed (long communication pause, slow post-handoff recovery, and successive timeouts) which are the main causes for TCP performance degradation in the presence of handoff. To alleviate these effects on TCP, two schemes, PROBE and BUFFER+FREEZE, are proposed, PROBE makes TCP aware of mobility and adapts the protocol to the mobile environment, Whereas, BUFFER+FREEZE tries to hide the effects of motion from TCP by buffering at the basestation and freezing the action of the TCP source.