Improving TCP Performance In Ad Hoc Network

Ad Hoc network is a kind of self-organized, peer to peer and multi-hop wireless mobile communication system and will be the one of ideal transfer means in wireless network in the future. Traditional TCP is a mechanism of transmission and control designed for wireless network , which it misinterprets the package ' loss over the wireless links as congestion in network. But in Ad Hoc network, other factors such as channel error ,network partition and route changes also can invoke package loss, at the moment slow-start and fast recovery property of traditional TCP will decrease the transmission performance. So it is necessary to optimizing TCP to adapt the Ad Hoc networks.This thesis gives a brief review of the present research situation and main problem of optimizing transmission in the Ad Hoc networks first. After the introduction of the congestion and control mechanism of traditional TCP, several major solutions for optimizing TCP were summarized and compared. author discussed in detail the influence of channel contention in the MAC layer upon TCP performance. utilizing the interaction between TCP and MAC layer, a method for optimizing TCP based on contention window feedback ( BCWFTCP ) was presented,which adaptively adjusted the TCP maximum window size according to the MAC channel contention index ,it was computed based on the MAC contention window feedback.By way of controling the number of TCP packets in the network and decreasing the channel contention, the improving of throughput and stability of TCP were realized.Secondly, a new type scheme based on Header Compression and ACK decrease (HCADTCP) for improving the transmission performance was particularly proposed ,which aimed at a lots of short packages transmission in Ad Hoc networks. By means of compressing the same contents and related transmissing the different contents in the header ,the size was compressed to one eighth of the original,meanwhile we modified the old way of sending ACK packets from confirming one by one to batches confirming,it greatly reduced the number of ACK packets in the network.Finally,we do simulation experiments on NS-2 simulator to testify the performance of BCWFTCP and HCADTCP, the results show that the BCWFTCP can effectively improve the throughput and stability of TCP and the HCADTCP can remarkably cut down the network cost and promote the network throughput in short packages transmission in Ad Hoc networks.