Research On Congestion Control Algorithm Over Satellite Communication Networks

Nowadays, many communication technologies of terrestrial networks are quite mature,however, the congestion control algorithms, which are originally designed for terrestrialnetworks, work pool when they are used in satellite networks with the characteristics of highdelay, high bit error and asymmetric bandwidth. The new congestion control algorithms withhigher requirement are needed for efficient and reliable transmission of information insatellite networks as the important infrastructure of global mobile communication system.In order to improve the performance of the existing congestion control algorithms, firstly,the characteristics of spatial information networks are described and the research status in thecountry and abroad of the subject of congestion control algorithms are introduced. Secondly,there’s an introduction to the working principle of TCP and TCP westwood algorithm widelyused in terrestrial wireless networks, meanwhile, disadvantages, which are resulted in whenTCP westwood algorithm is used in satellite networks, have been analyzed. Finally, newalgorithms are proposed for adapting to the satellite networks with the characteristics of highdynamic delay and asymmetric bandwidth.The main innovation and research achievements are summarized as follows,(1) Over satellite networks, round-trip time changes suddenly due to communication pathchanges have an adverse impact on retransmission timeout estimation and congestion windowcalculation in TCP westwood algorithm. A new congestion control algorithm namedTCPW-BLC is proposed, which implements bandwidth estimation based on length ofcommunication path. TCPW-BLC provides a method for properly setting congestion window,slow start threshold and the gain factors of related parameters to retransmission timeout timerby calculating the length of communication path, in order to keep the algorithm highthroughput and performance in satellite network environment when round-trip time changessuddenly.(2) Over asymmetric satellite networks, acknowledgment packets delay or loss due toreverse link congestion, restrain the sending rate of forward link and result in the degradationof TCP performance. A new congestion control algorithm named TCP-ASN is proposed,which properly sets the congestion window in source node through reverse link congestiondetection and congestion warning mechanism. The algorithm monitors the network status bycomparing the relative velocity of sending data packets in forward link and receiving acknowledgment packets in reverse link, and activates the corresponding congestion controlstrategy to different network status to achieve the effect of improving the TCP performanceover asymmetric satellite network.According to the simulation results using NS-2network simulator, TCPW-BLCoutperforms the rest of TCP versions, improving the throughput compared with that of TCPwestwood and alleviating effectively the effect of abrupt delay changes to congestion controlmechanism in satellite networks. Also the results show that the throughput performance ofTCP-ASN algorithm is significantly better than other algorithms when the reverse linkcongestion occurs, and the algorithm avoids the bandwidth waste of satellite link effectively.