Research On TCP Algorithm Over Satellite Network

The rapid development of Internet shows the enormous advantages and potential of TCP/IP protocols. At present, the demand for IP business is increasing, and the types of IP business become diversiform. It challenges the traditional network and the access methods. As satellite communication has several special advantages, such as remote communicating, broadcasting and spanning space; it has become an important method for Internet to expand new service and to widen the coverage.This paper studies the TCP algorithm over satellite network, and the main contents are listed as follows:(1) The congestion control is analyzed. The causes and the penalties of congestion are researched.(2) The indicators for evaluating TCP algorithm are given, which are effective throughput, fairness and friendliness. The effective throughput describes the ability to transmit data from the source to the destination, and the fairness and friendliness describe the ability of different TCP connections to share network bandwidth.(3) The problem confronted by the TCP algorithm is analyzed based on the specialty of the satellite network. In terrestrial network, because of the low BER, TCP assumes the source of all packet losses is network congestion. However, the satellite link is rarely as clean as those of the terrestrial networks. The network congestion is not the only reason of the packet loss. If we still use the traditional TCP algorithm in satellite network, TCP will invoke congestion control even that the loss is because of the link error. It will reduce its congestion window, and in turn, its transmission rate.(4) In order to solve the problem, we analyze the existent solution and propose an improved solution. In the literature[1], the Vegas algorithm extended SNACK option (Vegas-SNACK) is adopted. However, the Vegas-SNACK algorithm inherits the drawbacks of the Vegas algorithm. As indicated in simulation, the fairness and friendliness of the Vegas-SNACK is bad, so it is difficult to be applied to the practical network. We propose an improved algorithm Westwood-SNACK. We implemented the new algorithm in network simulation software NS-2 and analyze the performance of several algorithms by simulating in NS-2. The result shows: 1) compared to Vegas-SNACK, the effective throughput of Westwood-SNACK is greatly improved; 2) the fairness and friendliness of Westwood-SNACK is much better than those of Vegas-SNACK.