The utility of explicit rate-based flow control in mobile ad hoc networks

Flow control in a mobile ad hoc network (MANET) must face many new challenges such as frequent re-routing and bandwidth variation of the wireless links. TCP's implicit AIMD flow control performs poorly an this environment, because it often cannot keep up with the dynamics of the network. In this paper, we explore the potential utility of explicit flow control in the MANET domain. To this end, we propose an end-to-end rate-based flow control scheme (called EXACT), where a flow's allowed rate is explicitly conveyed from intermediate routers to the end-hosts in each data packet's special control header. As a result, EXACT reacts quickly and precisely to re-routing and bandwidth variation, which makes it especially suitable for a dynamic MANET network. We also discuss several supporting mechanisms required for such a scheme at the MAC and the transport layers. By ns-2 simulations, we show that EXACT outperforms TCP in terms of fairness and efficiency, especially in a highly dynamic MANET environment.