COMPARATIVE STUDY OF TECHNIQUES FOR IMPROVING TCP PERFORMANCE CE OVER WIREELESS NETWORKS

Abstract

TCP (Transmission Control Protocol) is a reliable end to end transport protocol tuned to perform well in traditional wired networks where the packet losses are primarily due to congestion. However, networks with wireless links show a marked increase in losses because of higher BER (Bit Error Rate) and handoffs. If TCP is applied to such networks without any modification it interprets these transmission losses as congestion losses and invokes congestion control mechanisms that unnecessarily decrease the network throughput. Wireless networks violate many of the assumptions made by TCP, causing degraded end to end performance. In this dissertation, we have first compared three existing techniques for improving TCP performance over wireless networks based on a simulation study. These are Snoop Protocol, Transport Unaware Link Improvement Protocol (TULIP), and Delayed Duplicate Acknowledgements Protocol. A generalized simulation framework has been developed to implement the protocols and their performance has been studied. The performance indices used are average delay, packet lost in wireless networks, number of packets received successfully,delay `d' in duplicate acknowledgement scheme, and end to end packet delivery ratio. It is shown that TULIP gives best performance for all these indices. To further reduce the average delay for packets, a new protocol has been proposed which is based on TULIP. It is shown that this new protocol gives substantial improvements over all the other protocols at the cost of slight increase in overhead. The simulation software is developed using C++ and is tested on both Windows (9x and XP) and Linux 9.0 platforms, running on a -2.1 Ghz,Pentium P