Transmission Control Researches Over Heterogeneous Network

During the last decade years, with the globalization of the telecommunication industryand the development of the Internet, new classes of hosts such as mobile devices are gainingpopularity, while the transmission media becomes more heterogeneous. In order to provideend-to-end communication services for mobile hosts, wireless networks are quickly becomingan interior part of the Internet, and the reliable protocols such as TCP must be supported overthem. So challenges are met in providing reliable transport services to all hosts regardless ofthe type of network connectivity. Over the past couple of years, TCP/IP performance overwireless links has been an active area of research and the researchers have been heavilyinvolved in coordinating transport control research on heterogeneous network.Congestion control is a key part of transmission control. This thesis emphasizes theTCP/IP performance over heterogeneous networks so as to provide an efficient transmissioncontrol mechanism in a heterogeneous network.The wireless channel transmission characteristic and the wired channel have the very bigdifference, so when the traditional congestion control mechanism applies under theheterogeneous network environment, its performance drops rapidly because of the wirelesslink high error rate, high delay, limited bandwidth and so on.Two main aspects work have been done in view of the above question this article:At the first aspect: TCP algorithms which exist at present have been conducted theclassified research. The article analysis the whole performance in view of different types, andprovides several kind of common TCP improved algorithm the technical comparison. In thisfoundation, in view of the transmission control characteristic over heterogeneous network, thearticle proposes an improved algorithm WMTCP which can enhance the performance of TCPover heterogeneous network. This strategy maintains the TCP integrity about end-to-end. TheWMTCP algorithm uses two parameters: one-way relative delay and active probe. Through thestatistical analysis about one-way relative delay, it can effectively distinguish the current linkstate of heterogeneous network. AP can solve the issue about packet losses with host mobility.This article describes the WMTCP design goal, the main thought, parameter design andcomputation, the solution question and so on. Finally the simulation experiment proves that itenhances throughput, and has the good fairness and friendliness.At the other aspect: this paper mainly research on AQM mechanisms. In found of thediscussion of active queue manage mechanism, it propose an efficient AQM algorithm that canbe used in the heterogeneous network. The ERQ algorithm unifies the ECN and the AQMthoughts, and improves ECN mechanism. This algorithm can efficiently distinguish thecongestion condition in the router and promptly send the condition information to the sender.This paper describes the main thought, the parameter and so on. Finally the simulationexperiment proves that the ERQ algorithm reduces the parameter sensitivity and enhances thealgorithm stability, the speed of response, the system throughput and so on.NS-2 is one of the most popular network simulators in the world, which is used toanalyze and evaluate network performance, so we choose NS-2 as our simulator tool tosupport all the experiments in this paper.In a word, this paper does some research in the field of transmission control overheterogeneous networks. We hope it could promote the development of transmission controlstrategies over wired-cum-wireless networks.