The Improved ECN Congestion Control in Ad Hoc Network and Simulation Test

The traditional TCP Reno, TCP Vegas and many other TCP variants used in wire network can not perform well in ad hoc environment. Because ad hoc network usually uses wireless channel and it has not the base station. And more, the ad hoc node can be mobile. The mechanism of detecting congestion by packet losses can not be valid. In ad hoc network, temporary link outages or fading-induced bit errors will result in packet losses, so TCP will decrease cwnd improperly. Some new mechanisms have been developed to improve the transport protocol performance for wireless network. These approaches progress along two directions: one direction is to hide any losses not related to congestion from the sender, so that the sender can only detect the packet losses due to congestion, such as I-TCP or snoopy protocol. However these protocols are not fit for ad hoc network in which there are not middle base stations between wire link and wireless link. Thus, the other direction, explicit congestion notification (ECN), is a promising direction in wireless network. In the paper, we propose a new stable congestion based on expanded ECN mechanism to respond packet losses in wireless environment more properly. The paper gives the idea to construct the new mechanism, and analyses the stability of the new mechanism. By using NS-2 simulator, the paper compares the new mechanism on throughput, drop ratio and delay time with TCP Reno and TCP Vegas. The simulation result indicates the renovation mechanism can get better tradeoff of throughput and delay time, so it can work well in ad hoc network.