Research On TCP-friendly Protocol Of Wired And Wireless Hybrid Network

With the rapid development of network communication technology, the services and applications based on wireless data transmission become more and more popular; TCP was first designed for wired networks and provided end-to-end reliable flow control for application layer. The performance of formal TCP in wireless network or hybrid network such as throughout degrade drastically due to the effects of high link error rate, long delay, the asymmetry of links, the intermittent link, narrow and fluctuant bandwidth. Therefore, how to improve the performance of TCP in wireless network and hybrid network is a significant question for discussion, especially when the wireless resources are limited.Along with the increasing number of applications of multimedia businesses based on UDP on the Internet, TCP applications suffer from "starve to death" when competing for the limited bandwidth. Multimedia businesses most use UDP with a lack of congestion control, however, TCP flows could not compete with UDP flows because of its schemes including slow start, congestion avoidance, fast retransmission and fast recovery, based on which the network may collapse of congestion at the end. Therefore, in order to make the development of the Internet more healthy, it is important to do some research in the TCP-friendly protocols, which have congestion control and can compete with TCP fairly. Nevertheless, the standardized TFRC (TCP-friendly Rate Control) still cannot be applied in the hybrid network appropriately, because TFRC has no loss differentiate mechanism to split the wireless error losses with wired congestion losses; by which wireless losses are mistaken for signals of network congestion and causes unnecessary throughput control, which gives rise to performance degradation of TFRC.The thesis takes the research of the transmission efficiency of wired/wireless hybrid network. On the one hand, considering reducing wireless losses, we analyze the relationship of loss rate with packet length and Bit Error Rate (BER) in wireless network, and establish the equation of Effective Utilization of Bandwidth (BEU). We found an optimal packet length to maximize BEU for a given BER. On the other hand, considering improving end-to-end transmission rate, we analyze the throughput model and propose an Expected Transmission Count (ETX), and introduce ETX to throughput model to establish Effective Transmission Rate (ETR) model. Furthermore, combining BEU and ETR, the equation of optimal packet length and loss rate, which can be used for processing mechanism of wireless loss in transport control protocol, could be derived from numerical solution for objective function of throughput optimization problem by curve fitting.Based on the thorough study of TFRC mechanism and transmission efficiency of hybrid network, this thesis designs a transport control protocol named WM-TFRC, which is suitable to wired/wireless hybrid network. WM-TFRC uses modified Biaz loss differentiate algorithm to compensate the shortage of TFRC which cannot differentiate loss and excessively reduce sending rate. WM-TFRC introduces Veno TCP throughput model to TFRC to adjust the sending rate when network is congested, and keeps TCP friendly and bandwidth stable. For the losses due to wireless error, according to the result of transmission efficiency of hybrid network, WM-TFRC adjusts adaptively based on the equation of optimal packet length and loss rate to enhance the end-to-end transmission efficiency. Consequently, WM-TFRC could work well in both wireless network and wired network. Through NS-2, we simulate the performance of WM-TFRC under the situation of wired network, wireless network, wired/wireless hybrid network and hybrid network with mobile node, and compare WM-TFRC with TFRC RFC3448 and TCP-Reno.