The Implementation Of TCP Performance In Mulit-hop Ad Hoc Networks

Mobile Ad Hoc network (Mobile Ad Hoc network, MANET) as a new kind of network is developing rapidly in the wireless communication field. Ad Hoc network is a multi-hop and temporary autonomous system which is determined by a group of mobile devices with a wireless transceiver without fixed network facilities. The wireless network nodes can move ,which form the dynamic topology and they are no center, multi-hop routing, however it is these properties make it impossible that the traditional TCP protocol were directly used in Ad Hoc network. Traditional TCP protocol attributes packet losses to the network congestion, while in Ad Hoc networkst package losses is not only caused by the network congestion.if we directly use the traditional TCP protocol in Ad Hoc network, this will results in network throughput fall.So how to improve the performance of the TCP in Ad Hoc network is a very important research subject.This paper first introduces the Ad Hoc network knowledge and the traditional TCP protocol and congestion control mechanism, combined with the Ad Hoc network peculiar attribute, based on the protocol layer it analyze the effect on TCP performance caused by each layer,then on the basis of understanding present improvement proposals, many present typical improvement proposals that improve TCP performance are analyzed and compared . By examining the interactions between TCP and the IEEE802.11 MAC protocol, we have identified that the false link failure has significant negative impacts on TCP performance in terms of throughput stability. We have proposed a scheme of BTAS algorithm to reduceing false link failure .This scheme use a narrow-bandwidth busy tone channel to make reservation for broadcast and link error detection frames. The sender transmit two short messages in the busy tone channel before sending broadcast or link error detection frames in the data channel. The proposed scheme can dramatically reduce the collision probability of broadcast and link error detection frames.We have simulated the algorithm's effectiveness using NS simulation tools. The simulation results indicate that the modified algorithm is able to maintain high throughput over the wired/wireless link, improve the performance of TCP.