Analysis And Improvement Strategy Of Tcp Performance For Ad Hoc Networks

As a particular network of wireless networks, Ad Hoc network has a good prospect of application because of its advantages of quick and easy networking, simple communication protocols, without any infrastructure, survivability capability, distributed topology and less energy consumption. The available study results show that TCP protocol, which was widely used in wired networks, can not be efficiently used in wireless networks. The reason is that packet loss is the only indication of congestion in TCP congestion control of wired networks, while in wireless network, besides the network congestion, the high error rate, interference, channel competition and the routing break due to mobility of the wireless environment can also cause packet loss. In Ad Hoc networks TCP can not distinguish these specific reason for packet loss and deals with it as congestion, resulting in the performance degrade dramatically.Now, how to solve the problem of TCP is one of the main problems facing to Ad Hoc networks. At present the researches mainly lies on the modification of MAC, Network and Transport layer.This paper generalizes the proposed improved TCP schemes and evaluates them.This paper simulates Ad Hoc networks scenes on the OPNET simulation platform, and varieties of stability and fairness of TCP,and analyzes intensively in this thesis.The main reasons that affect the performance of Ad Hoc networks is that inequality of channel competiton caused by IEEE802.11DCF used in MAC layer,hidden terminal and exposed terminal problems.Therefore this paper makes improvement on the MAC layer, and verifies it by simulation results. The simulation results demonstrate that it can improve the stability of TCP, and the fairness of at least two TCP connections over Ad Hoc networks, enhancing the performance. This paper explains and analyzes the Internet congestion phenomenon. Next, this paper discusses several kinds of TCP congestion control algorithms. On the basis of this, it analyzes a new improved congestion control algorithm which is named TCP Veno, and varieties of the performance by simulation results. At last in the scene of few confestion, high error rate and node mobility, this paper makes an improvement of TCP Veno which can freeze the timeout timer and slow RTT increasing, and verifies it by simulation results. The simulation results demonstrate that it can improve throughput of TCP Veno, and enhance the performance.