An investigation of improving the traditional TCP over MANETs
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Transmission control protocol (TCP) is not originally design for use in the mobile ad hoc network (MANET) environments, and therefore it raises a serious performance issues. The transport layer issues such as link failure, network congestion and wireless channel error degrade TCP performance. A research on developing a method of improving TCP performance in MANETs is required to assist an efficient design and deployment of such systems. TCP-WELCOME (Wireless Environment, Link losses, and Congestion packet loss ModEls) is found be a better TCP variant suitable for MANETs. However, TCP-WELCOME has weaknesses especially it deployed the original congestion control mechanism of TCP New Reno to handle packet losses due to network congestion. The proposed TCP offers the most adequate recovery strategy corresponds to each identified packet loss by combining features of both TCP-WELCOME and TCP-AW (Adaptive Westwood), which improves the TCP performance especially when recovering from network congestion related packet losses. This research aims to improve the performance of TCP by redesigning TCP-WELCOME’s loss recovery algorithm and the resulting improvement is called ‘Enhanced TCP-WELCOME’. The performance of the proposed TCP is evaluated by extensive simulations using OPNET Modeler. This thesis investigates the effect of varying network sizes, node mobility, traffic loads and wireless channel conditions on the system performance. Empirical results obtained have shown that the proposed Enhanced TCP-WELCOME can offer higher throughputs and packet delivery ratio, and lower end-to-end delay and retransmission attempt than the existing TCP-WELCOME for medium to large size networks. An exhaustive comparative analysis of the proposed method and TCP-WELCOME is also presented in this thesis.