Alleviating intra-flow and inter-flow contentions for reliable service in mobile ad hoc networks

In this paper, we focus on the problems from interaction between the congestion of traffic flows and the MAC layer contentions for reliable service, say TCP traffic. We first characterize the interaction as infra-flow contention and inter-flow contention and illustrate their severe impact on the performance of MANET. Then we propose a novel distributed scheme combining both flow control and media access control to alleviate these two kinds of contentions. The key idea is to differentiate packet transmissions. More specifically, better transmission opportunities are assigned to urgent or backlogged packets, which may be those just received by the downstream nodes or those accumulated at the congested nodes. By doing so, our scheme can promptly and smoothly forward each packet to the destination without incurring explosive increase in the number of control packets at the MAC layer or excessive queueing delay. Extensive simulations in ns-2 demonstrate that our scheme can greatly reduce the MAC layer contention and collision and improve the end-to-end throughput of TCP traffic.