Adjusting TCP sending rate after timeouts events in ad hoc networks

Abstract

In multihop ad hoc networks, TCP cannot effectively deal with the problem of packet drops caused by mobility and shared channel contention among wireless nodes. Mistaking these events for congestion degrades TCP performance. Hence we propose a new end-to-end mechanism, called TCP with Adaptive RTO+ (TCP-AR+), to assure faster recovery after non-congestion induced timeouts. TCP-AR+ comes to enhance the TCP-AR mechanism, we proposed previously. TCP-AR+ is a sender side only modification of the standard congestion control algorithm. It relies on three concepts. First, it distinguishes routes failures from network congestion based on transport layer feedbacks. Second, during timeout, it adjusts the RTO's value to network conditions and finally, after route re-establishment, it sets the congestion window's value according to the offered rate of the new path. We evaluate this new technique using different simulations scenarios, to compare its throughput gain, fairness and friendliness to those of TCP New Reno and TCP AR.