Studies On TCP Congestion Control Of GEO Relay Network

In the recent years, with the fast development of network，the amount and type ofdata traffic are increasing. Geostationary satellite(GEO) relay network has graduallybecome an important part of Internet with the advantages of large coverage, remotecommunication distance and low cost of transmitting data. At present, GEO relaynetwork mainly supports the service of TCP/IP, so End-to-end transmission control is animportant guarantee for the efficiency and reliability of transmitting data in GEO relaynetwork. Transmission Control Protocol(TCP) was originally proposed for the groundwired communication network and its congestion control strategy has guaranteed thereliability of data communication. However, GEO relay network has the characteristicsof long round-trip time(RTT) and high bit error ratio. Directly applying the traditionalTCP congestion control algorithm to GEO relay network will result in some problemssuch as too long time of Slow Start and frequently halving congestion window, so thenetwork resources can’t be reasonably and fully utilized.After the analysis and comparison of existing and typical TCP congestion controlalgorithm, lbss_asca algorithm is proposed as an improvement mainly for Slow Startand Congestion Avoidance. In the phase of Slow Start, lbss_asca combines thebandwidth estimation and the idea of pacing together, dramatically reduces the timespent by Slow Start and effectively avoids network congestion caused by the large burstof traffic. For Congestion Avoidance, lbss_asca divides it into three phases includingRecovery Phase, Transition Phase and Probing Phase, and takes the appropriate windowadjustment strategies at each phase. Moreover, lbss_asca gives up halving thecongestion window of traditional TCP when discovers a packet loss. So lbss_ascaalgorithm has a good adaption in GEO relay network, greatly improves the utilization ofnetwork bandwidth and enhances the performance of the TCP.The simulation results show that lbss_asca can shorten the Slow Start time andimprove the bandwidth utilization when transmitting a small amount of data in differentscenarios; effectively improve the steady-state throughput; also obtain betterperformance in the case of different bit error ratios especially in the case of high biterror ratio. Its competitiveness is between Reno and CUBIC, and has a better share ofnetwork resources with data flows of other TCP protocols. Obviously, compared withother TCP congestion control algorithms, Lbss_asca has good performance in terms of throughput and can make full use of bandwidth resources in GEO relay network.Moreover, Lbss_asca can not only improve TCP’s performance, but also have a goodTCP fairness and friendliness.