The efficacy of centralized flow rate control in 802.11-based wireless mesh networks

Commodity WiFi-based Wireless Mesh Networks (WMNs) can be used to provide last mile Internet access. These networks exhibit extreme unfairness with backlogged traffic sources. Current solutions propose distributed source rate control algorithms requiring MAC or transport-layer changes on all mesh nodes. This is often infeasible in large practical deployments. In wireline networks, router-assisted rate control techniques have been proposed for use alongside end-to-end mechanisms. We wish to evaluate the feasibility of establishing similar centralized control via gateways in WMNs. In this paper we focus on the efficacy of this control, rather than the specifics of the controller design mechanism. We answer the question: Given sources that react predictably to congestion notification, can we enforce a desired rate allocation through a single centralized controller? The answer is not obvious because flows experience varying contention levels, and transmissions are scheduled by CSMA/CAMAC using imperfect local knowledge. We find that common router-assisted flow control schemes used in wired networks fail in WMNs because they assume: (1) links are independent, and (2) router queue buildups are sufficient for detecting congestion. We show that non-work-conserving rate-based centralized scheduling can effectively enforce rate allocation. It can achieve results comparable to source rate limiting, without requiring any modifications to mesh routers or client devices.