Effects of MAC retransmission on TCP performance in IEEE 802.11-based ad-hoc networks

In this paper, TCP performance in multi-hop ad-hoc networks under a static chain topology is simulated firstly and results show that TCP segments may experience disorder and spurious timeout, and many spurious retransmissions are induced by the failure of ACK transmission in the reverse path due to the MAC channel access unfairness. Spurious retransmissions can result in retransmission competition between link-layer and transport layer. Then the effects of MAC retransmission limits on end-to-end TCP performance are evaluated with different background loads, which indicates that when the network load is light, a larger retransmission limit makes the TCP throughput more appreciable; and when the load is heavy, too large a retransmission limit results in drastic performance degradation. In addition, simulation results under a dynamic ad-hoc topology indicate that topology changes of the ad-hoc network itself are not sensitive to MAC retransmission limits. The paper ends with proposals for improving TCP performance in IEEE 802.11-based ad-hoc networks.