TTAF: TCP Timeout Adaptivity Based on Fast Retransmit over MANET

Abstract

Transmission Control Protocol (TCP) is one of the most widely deployed transport layer protocols. It responds to all packet losses, either due to congestion or link breakages, by invoking various congestion control mechanisms. All these mechanisms imply a reduction in the amount of transmitted data. Computing a proper value of the retransmission timeout (RTO) is a challenge for TCP. In mobile ad hoc networks (MANET), mobility and bit error cause a lot of packet losses which degrades TCP throughput. In this paper we introduce an adaptation of TCP NewReno in order to improve its performance during the fast recovery phase. Our adapted algorithm, which we called TTAF, does not rely only on round trip time samples but also takes into consideration fast retransmit events in tuning the value of RTO. A set of experiments have been conducted to evaluate the effect of TTAF over MANET with various mobility speed, traffic load, and bit error rates. Results have shown an improvement in TTAF throughput compared with that of TCP NewReno.