Performance research and improvement of TCP_SACK in wireless environment

Abstract

The standard transmission control protocol(TCP) can not distinguish between the random packet losses due to high bit error rate(BER) and the packet losses due to network congestion. TCP responds to all losses by invoking congestion control and avoidance algorithms, resulting in degraded end-to-end performance in wireless and lossy systems. Meanwhile, the performance of TCP would be deteriorated very much when it suffered from multi-packets losses in a single transmission window. This paper propose a modification over TCP_SACK version,we called it MSACK. When MSACK cooperates with the router configured with explicit congestion notification(ECN), it is capable of distinguishing the wireless packet losses from the congestion packet losses, and reacting accordingly. At the same time, MSACK adopts available bandwidth algorithm at data sender to optimize cwnd and ssthresh in order to avoiding lower slow start threshold when packet losses occured. On the other hand, the performance of MSACK in wireless environment can be improved by taking advantage of retransmission and restoration in SACK version when TCP encountered multi-packets losses in a single transmission window. The simulations in this paper show that the modification of TCP is feasible, and the performance of TCP is improved actually.