| The satellite communication has become an important part of the Internet for its special superiorities in recent years. Broadband Internet access via satellite system is the tendency of the development of the satellite communication. TCP protocol is the most commonly used transport layer protocol in the Internet. However, when used in the satellite networks, TCP performance will be sharply degraded for the high latency, high bit error and the asymmetry. Therefore, how to enhance the performance of TCP in satellite link has become an important subject for us.This thesis analyses the causes of the performance deterioration of TCP,then details some schemes that addresses the problems of using TCP in the satellite networks, and also evaluates the feasibility and effect of these schemes. This thesis proposes a scheme based on protocol transition gateways, which can enhance TCP performance over the satellite networks. Protocol transition gateways split the end to end TCP connection into three separate parts. TCP is used in two terrestrial segments and a special protocol designed by us runs over the satellite link between two protocol transition gateways. The special protocol for the satellite link employs an error control mechanism based on negative acknowledgement and allocates available bandwidth resources of the satellite link to multiple active connections in a fair and dynamic way.The performance of the protocol transition gateway scheme have been simulated and compared with the TCP Reno by the network simulator tool NS2. Simulation results have shown that the protocol transition gateway scheme is able to greatly enhance the TCP performance over satellite networks and ensures that the available bandwidth resources of the satellite link are fully utilized.In order to test the performance of the proposed method in a real satellite environment, this thesis designs and implements the protocol transition gateway on a hardware platform based on DSP. |
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