Research On Congestion Control Mechanism Of TCP In Wireless Network

Recently, with the development of mobile communication technology and Internet, wireless technology is more and more important in the wireless Internet of all over the world. Mobile nodes and its wireless communication links are going to be an important part in the future Internet.TCP Protocol used widely now is an end to end transmission protocol, which is designed for reliable communication between network nodes. The arithmetic of congestion control embedded in TCP can effectively improve efficiency of network transmission and prevent network collapse. The arithmetic assumes that the links are quite credible, the loss and delay of packets are made by network congestion. But TCP used well in wired network does not work well in the wireless network, because the precondition of credibility in links of the wired network does not occur in wireless network, that is to say, the loss and delay of packets are made not surely by network congestion but the characteristics of the wireless links: high bit error, long delay of transmission, frequent move of the terminals, long latent period of switch and so on. So it must improve transmission control protocols used before or put forward the new protocols in order to keep high efficiency of communication and good throughput of network in the wireless network.Now, many schemes are designed to improve the performance of TCP in wireless networks. They can be classified into four broad categories: end-to-end protocols; split-connection protocols; link-layer protocols and integrated protocols. The end-to-end protocols are research keystone now, they only modify tow ends of protocols and do not need help of middle nodes, ensuring the integrality of link from sender to receiver. For instance, New Reno, SACK, FACK, Freeze TCP, TCP Westwood are end-to-end protocols, TCP Westwood is extremely effective in wireless networks, it is a sender-side modification of the TCP congestion window algorithm that improves the performance of TCP Reno in wired as well as wireless networks. Its key innovative idea is to continuously measure the bandwidth used by the connection via monitoring the rate of returning ACKs at the TCP sender side. The estimation is then used to compute congestion window and slow start threshold after a congestion episode. Experimental studies reveal improvements in throughput performance, as well as in fairness.The main work in the thesis are listed as follows:(1) In wireless networks, as the outburst of packets loss, multiple packets can be lost from the...