Study of Intra and Inter Flow Contentions In Manet |
Since the mobile ad hoc network (MANET) is suitablefor providing communication in the environment where network infrastructure isnot available, it has become a hot research topic in recent years. Despiteconsiderable research efforts expended, the interaction between the congestionof traffic flows and the MAC layer contentions have not been well understood. We study this problem for reliable service, say TCPtraffic, in this paper. We first characterize the interaction as intra-flowcontention and inter-flow contention and illustrate their severe impact on theperformance of MANET. Then we propose a novel distributed scheme combining bothflow control and media access control to alleviate these two kinds ofcontentions. The key idea is to differentiate packet transmissions. Morespecifically, better transmission opportunities are assigned to urgent orbacklogged packets, which may be those just received by the downstream nodes orthose accumulated at the congested nodes. By doing so, our scheme can promptlyand smoothly forward each packet to the destination without incurring explosiveincrease in the number of control packets at the MAC layer or excessivequeueing delay. Extensive simulations in ns-2 demonstrate that our scheme cangreatly reduce the MAC layer contention and collision and improve theend-to-end throughput of TCP traffic.