Research And Development Of Adaptive TCP Congestion Window Controlling Technology

Data Communications has dramatically increased in popularity over the last decade.The basic access technology in computer network has been wire based.However the increasing demand for connectivity from anywhere at anytime has led to the develpment of wireless networking technologies.These.new access media pose several problems to the traditionally used communication protocols.This thesis is concerned with the impact of wireless technologies on one of the major protocols used in todays Internet:the Transimission Control Protocol(TCP).Nearly 80%-85%data transmission on internet is carried on the reliable Transmission Control Protocol.After a long period of development,TCP has become a reliable transport protocol tuned to perform well in traditional networks made up of links with low bit-error rates.Networks with higher bit-error rates,such as those with wireless links,violate many of the assumptions made by TCP,causing degraded end-to-end performance.Many researchers have identified the shortcoming and studied the effects of loss rates or link delay on TCP performance in wireless networks.Many TCP variants have been invented to solve such degradation,and various solutions have been proposed to overcome the TCP deficiency for wireless links.But a big part of the improvement solutions are aimed on its particular situation,once that situation has changed the improvement may fail.Adaptive Selection approach is a method that can improve the performance of TCP in hybrid network environment,but it still cann't distinguish the status of networks well.This thesis proposes a ligt weight method to analyze network status,and supports the adaptive selection of congestion window size factor.This method includes three network status indicators:link delay,bandwidth and packet loss number per time unit.A patch for measuring these indicatiors is developed on the NS2 simulation platform.Simulation results show that the new method of Adaptive Selection improved more than 20%than the standar TCP protocol when the TCP connection is under a long connection situation in wireless environment.The rest of this thesis is organized as follows:(1)The TCP protocol internals and the congestion control algorithm are studied and analyze in depth.(2)The performance of TCP variants in hybrid network environment are analyzed in detail on NS2 simulation platform.(4)We propose an adaptive TCP congestion control mechanism and develop it on NS2 platform to improve the performance of TCP in wireless network.