The Research Of TCP Congestion Control Mechanism

TCP is the most popular end-to-end transmission protocol in the Internet now. Many new TCP congestion control algorithms, such as slow-start, congestion avoidance, fast retransmission and fast recovery, have appeared these years, which have improved the performance of network transmission much more.When more and more modern communication technologies such as DWDM have been used in the bottom of networks, the computer networks continuous develop to high speed. Along with the 1Gbps above high-speed networks going out of the lab and going into practice, the traditional TCPs running in such networks will come up against stable state and slow congestion window restoration issues.The characters of wireless networks are high bit error rates, low bandwidth, long time delay, frequency moving and so on, so there are high error rate in wireless network. In wireless networks, congestion is not the only reason for data losing. If we use the traditional congestion control technique in wireless networks, it can make the sender decrease the sending rate unnecessarily and results the decrease of the network performance.In this dissertation, the traditional TCP and the high-speed TCP congestion control algorithms have been investigated, the limitations of the TCP congestion control mechanisms in the high-speed network have been discussed, several TCPs commonly applied to the high-speed network have been analyzed and the TCP congestion control mechanism based on Vegas named TCP Logvegas in high-speed long-distance network has been proposed, which allows a logarithmic congestion window recovery after a packet loss event. Extensive simulations show that Logvegas can restore the TCP windows faster than Vegas after the packet loss event and improved the system throughput. In addition, the TCP congestion control mechanism amplied in wireless network has been described, the limitations of the TCP congestion control mechanisms in wireless network have been discussed, the mechanism of detecting packet corruption based on Vegas named TCP ED-Vegas in wireless networks has been proposed, which extends TCP Vegas header options and allows the receiver to return a special ACK generated in response to packet corruption. Extensive simulations show that the mechanism can make Vegas distinguish packet corruption from congestion, avoid lots of unwanted timeouts caused by retransmitted packet to be corrupted and hence, enhanced Vegas performance.