RTT Utilization by Detecting Avoidable Timeouts

In general a retransmission timeout (RTO) results from the congestion in the network and reduces TCP flow drastically. TCP may experience RTO even in absence of congestion particularly due to loss of retransmission. In this paper, a simple technique is proposed to identify those timeouts, which are not due to congestion and should be avoided. These avoidable timeouts are typically caused by loss of retransmission due to random channel errors. This type of retransmission timeouts is common in wireless environments in general and satellite links in particular. A TCP sender refrains from transmitting packets for a considerable time i.e., the timeout period. This paper proposes a modification in the original SACK TCP to identify the avoidable timeouts and also to utilize available RTTs before such timeouts. Improved TCP performance of the proposed algorithm to combat channel noise during retransmissions is substantiated with the help of simulations using open source software (ns-2). The simulation approach and its results are also analyzed in this paper