Effects of multipath routing on TCP performance in ad hoc networks

In mobile ad hoc networks, one might expect multipath routing to provide some robustness to link failures and facilitate the transmission of packets along paths that avoid regions of congestion. Consequently, one would expect an improvement in network performance in terms of the achieved throughput. We consider TCP goodput as the metric of performance. We find that, contrary to expectations, not all TCP connections enjoy the benefits of multipath routing. Specifically, we find that while long (in terms of hop-count) TCP connections seem to benefit, short connections in fact suffer a slight degradation in goodput as compared to TCP using the single shortest path. Furthermore, we find that alternate path routing, wherein packets are routed on a secondary alternate path only upon the failure of the primary path, helps achieve almost the same goodput as when the multiple paths are used simultaneously. The main benefits of currently proposed multipath routing schemes seem to be limited to improving the efficiency of route discoveries that are initiated either due to real route failures (due to mobility) or due to false failures (due to interference effects) for long TCP connections.