Understanding bandwidth-delay product in mobile ad hoc networks

Bandwidth-delay product (BDP) and its upper bound (BDP-UB) have been well-understood in wireline networks such as the Internet. However, they have not been carefully studied in the multi-hop wireless ad hoc network (MANET) domain. In this paper, we show that the most significant difference of computing BDP and BDP-UB in MANET is the coupling of bandwidth and delay over a wireless link, where only one packet is allowed to be transmitted over the channel at a time. Based on this observation, we prove that BDP-UB of a path in MANET is upper bounded by N, where N is the number of round-trip hops of the path. We then further obtain two tighter bounds of BDP-UB, and verify them through ns-2 simulations. The understanding of BDP and BDP-UB also contributes to the solution of how to properly set TCP's congestion window limit (CWL) in MANET, in order to mitigate TCP's congestion window overshooting problem. Past studies have shown that using a small CWL improves TCP performance in certain MANET scenarios, however, no quantitative guideline has been given. In this paper, we provide a systematic solution to this problem, by dynamically applying the path's BDP-UB as TCP's CWL. Simulation results show that our solution effectively improves TCP performance in a MANET environment.