Are two interfaces better than one?

Many of the community-area networks use commodity 802.11 hardware to form small wireless networks. Generally organized as a mesh, employing a single channel, and having a few gateways for wider-area access, they tend to offer poor bandwidth to end users. To increase bandwidth, the idea of leveraging multiple interfaces operating on different, non-overlapping, channels has been put forward recently. In this paper, we examine the performance of community wireless networks based on such multi-interface nodes. Our experiments demonstrate that the mere use of more dual-interface nodes does not necessarily create higher capacity. Indeed, in a number of cases we show that the throughput is lower than cases where fewer interfaces are used. We identify three causes for this throughput limitation: channel load, RTS/CTS and exposed nodes, and unfairness due to local traffic. Furthermore, we show that in random topologies, it is very often hard to achieve adequate throughput gain.