Selective slow start: a simple algorithm for improving TCP performance in wireless ATM environment

Mobile computing has emerged as an area of significant research and development activities. To support this computing on move, one approach taken by several researchers involves the introduction of the ATM technology in the wireless environment (termed wireless ATM) and the use a suitable transport protocol to support various applications. It is likely that initial implementations will employ TCP (or a modified version of it) as the transport protocol due to the tremendous support it enjoys in the research community. However the problem with existing versions of TCP is a lack of differentiation between segment loss due to the network congestion and due to the handoff in the wireless network. After a segment loss, TCP would initiate a slow start phase to reduce its offered traffic assuming that the network is going through congestion. This may reduce the TCP throughput significantly and will lead to unacceptable performance specially if the underlying wireless ATM network is capable of supporting high data rates. This paper proposes a new algorithm called 'selective slow start', where TCP will attempt to differentiate between segment losses due to the network congestion and due to the handoffs based on the pattern of losses (timeouts). It will initiate the slow start phase in the former case and it will continue to transmit at its current speed in the latter case. Based on the simulation results presented, the SSS algorithm improves the transport layer throughput significantly in a wireless ATM environment.