一种Ad Hoc网络端到端的TCP拥塞控制改进方案

An improved scheme of end-to-end TCP congestion control in Ad Hoc network

传统的TCP协议是为有线网络而设计的,它假定数据包的丢失是由网络拥塞引起的,然而在Ad Hoc网络中,除拥塞丢包外,其它非拥塞因素也会引起数据包的丢失。分析Ad Hoc网络影响TCP性能的主要因素,在原有拥塞控制方案MMJI的基础上,提出了一种端到端的TCP拥塞控制改进方案(ImpMMJI)。该方案能根据前向路径跳数自适应调整拥塞窗口的大小,防止拥塞窗口过快增长,当发生路由改变或链路中断时,重新计算拥塞窗口cwnd和ssthresh的值,以确保路由重建前后TCP连接负载率的一致性;并在ACK应答包的TCP首部增加了状态标志位,结合多个度量参数联合判断网络状态,提高网络状态识别的准确性,使发送端实时采取相应的措施。仿真结果表明,该方案能使网络吞吐量得到明显的提高,改善了TCP的性能。

The traditional TCP protocol is designed for wired networks,and it is assumed that the packet loss is caused by network congestion.However,in Ad Hoc network,in addition to the conges tion loss,other non congestion factors can also cause packet loss.The main factors affecting TCP per formance of Ad Hoc Network are analyzed,and an end-to-end TCP congestion control scheme （Imp MMJI） is proposed,which is based on the original congestion control scheme of MMJI.According to the forward path hops,the scheme adaptively adjusts the congestion window size and prevents the excessive growth of the congestion window.When the route changes or link interruption occurs,the scheme can calculate cwnd and ssthresh values of the congestion window in order to ensure the consistency of the TCP connection load rate when the routing is reconstructed.Besides,the scheme adds the state sign bit in TCP header of the ACK reply packet,which combines multiple measurement parameters to judge the network state so as to improve the network state recognition accuracy and make the sender respond in re al time.The simulation results show that the scheme can improve the network throughput and the TCP performance obviously.