Measurement and Modeling of the Origins of Starvation of Congestion-Controlled Flows in Wireless Mesh Networks

Significant progress has been made in understanding the behavior of TCP and congestion-controlled traffic over CSMA-based multihop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which a one-hop flow contends with a two-hop flow for gateway access. In this paper, we demonstrate via real network measurements, testbed experiments, and an analytical model that starvation exists in such a scenario; i.e., the one-hop flow receives most of the bandwidth, while the two-hop flow starves. Our analytical model yields a solution consisting of a simple contention window policy that can be implemented via standard mechanisms defined in IEEE 802.11e. Despite its simplicity, we demonstrate through analysis, experiments, and simulations that the policy has a powerful effect on network-wide behavior, shifting the network's queuing points, mitigating problematic MAC and transport behavior, and ensuring that TCP flows obtain a fair share of the gateway bandwidth, irrespective of their spatial location.