Author(s): 1Rajat Sharma ,2Dr. Sartaj Singh Sodhi

Transmission Control Protocol (TCP) is the dominant transport protocol in the Internet and supports many of the most popular Internet applications, such as the World Wide Web (WWW), file transfer and e-mail. TCP is designed to perform well in traditional wired networks with the assumptions that packet losses are mainly due to network congestion and random bit error rate (BER) is eligible. However, networks with wireless links suffer from significant packet losses due to random bit errors and handoffs. TCP optimization in mobile ad hoc networks is a challenging issue because of some unique characteristics of MANETs. Some of the main reasons behind TCP's performance degradation in these networks are lossy channels, frequent route failures, network partitions because of high mobility of nodes. In this paper, a cross-layer approach to improving TCP performance in MANET is proposed. Medium access control (MAC) layer is responsible to decide the modulation scheme to be used at the physical layer depending on the signal strength and queue length of the receiver. This is a rate adaptive technique which changes the data rate according to available channel condition. An omnetpp-based simulation analysis of the proposed protocol which provides better TCP performance with minimum congestion than the existing wireless TCP protocols is described. The effects of mobility of nodes, number of connections on TCP parameters such as throughput, packet delivery ratio and round trip time are investigated.