Analysis of TCP performance on ad hoc networks using preemptive maintenance routing

In mobile ad hoc networks, the topology of the network is constantly changing as nodes move in and out of each other´s range, breaking and establishing links. TCP performs poorly in such networks because packets that are lost due to path disconnections trigger TCP´s congestion avoidance mechanisms. We investigate the effect of preemptive routing protocols, where an alternative path is found before an actual disconnection occurs, on the performance of TCP. Preemptive routing should perform well for TCP traffic because it reduces the delays caused by TCP´s unnecessary use of congestion avoidance when paths break. We observe this behavior under some, but not all scenarios. Specifically, it appears that when the network is saturated, the additional traffic introduced by preemptive routing causes small degradation in performance. In the analysis process, we encountered an unfairness problem resulting from interaction between the routing protocol and the MAC layer under multiple continuous transmission cases. Similar unfairness problems were encountered by other studies-however the observations of those studies related those problems to the number of hops, and not the routing effects as we observed. This motivates the study of fairer wireless MAC protocols for multi-hop and ad hoc networks.