A Joint Traffic Shaping and Routing Approach to Improve the Performance of 802.11 Mesh Networks

Wireless Local Area Networks (WLANs) based on IEEE 802.11 standards are becoming widespread and are now being considered as potential solutions for providing "last-mile" wireless IP-based services. One of the challenges to this end however comes from the grave inefficiencies in the CSMA-based 802.11 medium access control (MAC) when used with application payloads that are relatively small. This is the case seen in the important application of Voice over IP (VoIP). The inefficiencies becomes even more severe in multi-hop wireless mesh systems that use 802.11 radio interfaces. In this paper we present novel strategies that are in conformance with the 802.11 mechanism while at the same time providing significant performance improvements for such applications. Our main approach will be one of jointly combining routing and traffic shaping decisions together to improve the efficiency of DCF functions. Specifically we try to change the traffic characteristics at different hops in the network by combining multiple flows to produce new traffic and flow statistics. Correct routing enables one to do such changes and, therefore, by performing routing and traffic shaping decisions jointly we can improve the efficiency of 802.11 mesh networks. To demonstrate the effectiveness of the proposed scheme, we focus on the two-hop mesh architectures and consider the VoIP traffic as the application of interest. We specifically investigate the achievable throughput region with and without the traffic shaping mechanisms. Our experiments show that more than a 3-fold call-capacity improvements can be gained over the conventional transport methods.