A Stable Congestion Control Mechanism in Ad Hoc Network

Ad hoc network is network in which there is no base station and any node can be connected to network temporarily. To support mobility, Node in ad hoc network generally communicates by wireless channel. In Ad hoc network, TCP Reno or TCP Vegas do not work well as they do in wire network, because they take packet losses or timeout as the signal of congestion. However, in ad hoc network, temporary link outages or fading-induced bit errors will result in packet losses, so TCP will decrease cwnd improperly. Some variations of TCP have been developed to improve the transport protocol performance for wire 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.