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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.

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To avoid the network congestion and let the end hosts share the link resources fairly, F. P. Kelly proposed Classic Kelly Model based on an optimal theory. This model can deduce algorithm which has proportional fairness equilibrium point and has asymptotically stability. However, the primal algorithm of Kelly model leads to the packet accumulation in the queue of the bottle link. By using heuristic fuzzy rules, this paper designs a fuzzy controller to adjust the additive increase parameter of the primal algorithm. The primal algorithm with the fuzzy controller can let the aggregate data flow send by hosts equal the bandwidth of the bottle link, so it can avoid the packet accumulation in queue. The fuzzy control mechanism also keeps the fairness and asymptotically stability. The simulation validates the feasibility and adaptability of our fuzzy controller.

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