Research And Improvement On TCP Performance In Heterogeneous Wireless Networks

With the rapid development of wireless communication technology, a variety of wireless access networks coexist. Heterogeneous wireless network is a logical network that is constituted by different kinds of wireless access network with different bandwidth, time delay and coverage. Compared with the rapid development of the access technology, upper-layer protocols develops slowly . In heterogeneous wireless network, end to end congestion control is very important to the robust and stability thus becomes the research focus.In heterogeneous wireless network, changes of transmission performance after vertical handoff may wrongly arouse the TCP congestion control mechanism. This paper proposes an improved algorithm B-EVegas based on TCP Vegas to enhance the transmission performance of TCP when vertical handoff happen. An threshold-based mechanism of Vegas is also proposed to improve competitiveness to the bandwidth.In this paper, at the very beginning,introduces the wireless access technology be widely used now, studies the technology of vertical handoff and Mobile IP. We introduce the main content of TCP, analysis the influence of wireless environment to its performance, summarize and compare the schemes which are used to improve TCP performance in wireless environment. This paper proposes an algorithm B-Evegas based on TCP Vegas. B-Evegas contaions four mechanisms which are used to solve the problem of performance degradation of transport layer during vertical handoff. This paper also proposes an algorithm T-EVegas based on Vegas which use variable threshold mechanism to solve the issue of fairness when compete with other TCP flavors.The simulations results show that the B-EVegas can effectively enhance the throughput or reduce the end-to-end delay of TCP link after vertical handoff in heterogeneous wireless network and the T-EVegas can achieves a higher fairness than Vegas when conexist with TCP Reno.