Research On Performance Optimization Technology For Satellite Network Transport Protocol

Satellite networks are playing a more and more important role in telecommunica-tion for their global coverage and 24-hour uninterrupted communication. Satellite net-works are characterized by long Round-Trip Time(RTT), high Bit Error Rate(BER), bigBandwidth-Delay Product(BDP). The original Transport Congestion Protocol(TCP) issuitable for wired networks, but its performance significantly degrades in satellite net-works. It is necessary to investigate the problems of improving the TCP performance insatellite networks.Based on carefully analysis on traditional TCP protocols and improved methods,the thesis mainly focuses on several key issues to improve TCP performance of satellitenetworks.First of all, the impact factors are theoretically studied for the average bandwidth ofTCP connection. Congestion control and error control are proved to be the two mainlyfactors that highly in?uence the performance. Second, several different strategies areadopted for these two types of control schemes to optimize performance, represented asfolows:(1) Research on TCP congestion control based on long RTT of satellite networks.TCP Peach is a novel congestion control scheme for satellite network. A new re-transmission scheme is designed based on Peach through accurately estimating RTT withtimestamp option in TCP Vegas. Lost packets can be detected by the new mechanismwithin the retransmission timeout, even without the second or third duplicate ACK. Thenumber of coarse-grain timeouts in Reno is also reduced by half.(2) Research on TCP error control based on high BER of satellite link.(a) Error detection mechanism.The wireless satellite channel will produce a lot of link errors. The communicationefficiency will certainly be affected if link errors are attributed to network congestion.Explicit Congestion Notification(ECN) are implemented to distinguish congestion packetloss from link error. With this method, unnecessary retransmission are reduced.(b) Error recovery mechanism.The wireless satellite channel will also causes multiple packet losses in a data win- dow. Detecting and retransmitting the lost packets will improve the TCP performance.Selective Acknowledgement(SACK) option is adopted to retransmit all the lost packetsin one RTT, and it has been observed that the proposed scheme can significantly improvethe performance.