An opportunistic cross layer multi path routing protocol to improve TCP performance over Mobile Ad Hoc Networks

Multi path routing protocol such as AOMDV establishes multiple link disjoint paths between source and destination to improve the reliability, fault tolerance and thereby TCP performance over multi hop MANETs. But, TCP misinterprets the frequent link failure and wireless channel errors as congestion and slow starts the window size, even during the presence of alternate paths in the routing table. In this paper, we analyze the TCP misbehavior and propose cross layer mechanisms that effectively utilizes AOMDV. Our protocol finds out multiple link disjoint paths using AOMDV but next hop selection is done based on current wireless channel condition to reduce wireless channel errors. During primary route failure, we make the TCP source to select a new window size for alternate path. This opportunistic selection of window size is based on the distance between the origin of alternate path and destination. We study the performance of our mechanisms using NS2 and evaluate them individually against AOMDV in terms of TCP throughput, window size, packet delivery ratio and BER and shows significant improvement.