On the impact of alternate path routing for load balancing in mobile ad hoc networks

Alternate path routing (APR) can provide load balancing and route failure protection by distributing traffic among a set of diverse paths. These benefits make APR appear to be an ideal candidate for the bandwidth limited and mobile ad-hoc networks. However, we find that APR's potential is not fully realized in ad-hoc networks because of route coupling resulting from the geographic proximity of candidate paths between common endpoints. In multiple channel networks, coupling occurs when paths share common intermediate nodes. The coupling problem is much more serious in single channel networks, where coupling also occurs where one path crosses the radio coverage area of another path. The network's inherent route coupling is further aggravated by the routing protocol, which may provide an incomplete view of current network connectivity. Through analysis and simulation, we demonstrate the impact of route coupling on APR's delay performance in ad-hoc networks. In multiple channel environments, APR is able to provide a 20% reduction in end-to-end delay for bursty data streams. Though these gains are appreciable, they are about half what we would expect from APR with independently operating routes. Route coupling is so severe in single channel networks that APR provides only negligible improvements in quality of service.