Adaptive Setting of TCP´s Maximum Window in Ad Hoc Multihop Networks with a Single Flow

An emerging approach for improving the performance of TCP in ad hoc multihop networks is to limit the maximum congestion window (CWNDmax) that a TCP connection is allowed to reach, in order to eliminate the number of outstanding segments and increase the TCP stability. In the present work, we propose an adaptive scheme to bound the CWNDmax value in an IEEE 802.11 ad hoc network. Our contributions are the following. First, we conduct simulation experiments to establish the argument that the optimum CWNDmax value depends on the buffer availability, when the network is not saturated, and is irrelevant to it, otherwise. Then, we introduce a time based expression for the network´s bandwidth-delay product (BDP), in order to set CWNDmax dynamically. This expression accounts both for spatial reuse and for the packets´ queue waiting time. The latter is necessary, since the TCP timer is set according to the round-trip delay, which includes the buffering latency in all hops. The proposed model can be implemented in a real environment, whereas the simulation experiments show that it improves the TCP window stability. The idea of limiting CWNDmax proves interesting, mainly because it aims to leave TCP unchanged.