Rate-based transport control for mobile ad hoc networks

The traditional congestion control mechanism, i.e., TCP, when applied in mobile ad hoc networks (MANET), encounters a number of new challenges, such as wireless link error, medium contention and frequent route failures. Very poor performance of TCP in MANET has been reported in many recent studies. We focus on the problems resulting from medium contention and propose a novel rate based end-to-end congestion control scheme (RBCC). We first illustrate that, under the impact of medium contention, a window based congestion control algorithm is unstable and hence may not be appropriate for MANET because the optimum congestion window size is very small and may even be less than one, i.e., the source should send less than one packet in one round trip time (RTT). Based on the novel use of channel busyness ratio, which, we show, is an accurate sign of the network utilization and congestion status, a new rate control scheme has been proposed to support the transport service in MANET efficiently and reliably. In RBCC, a sublayer consisting of a leaky bucket is added under TCP to control the sending rate based on the network layer feedback at the bottleneck node. Extensive simulations show that our scheme significantly outperforms traditional TCP in terms of channel utilization, delay and fairness.