Impacts of handoff on TCP performance in mobile wireless computing

Abstract

The effects of intermittent disconnections due to host motions on the performance of the TCP connections are investigated. Fading and handoff due to host motion cause increased the delay and packet losses to the active transport layer connection. The 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. We present three phenomena observed (long communication pause, slow post-handoff recovery, and successive timeouts) which are the main causes of the TCP performance degradation in the presence of handoff. To alleviate these effects on the TCP, two schemes, PROBE and BUFFER+FREEZE, are proposed. PROBE makes the 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.