Abstract
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 link-layer 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 a node using imperfect local knowledge. We find that common router-assisted flow control schemes used in wired networks fail in WMNs because they assume that (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.
Highlights
Wireless mesh networks (WMNs) based on the commodity IEEE 802.11 radios are a low-cost alternative for last mile broadband access
We describe these below: 1. carrier sense multiple access with collision avoidance (CSMA/CA) transmitters located outside mutual carrier sense range may produce misaligned transmissions that result in excessive collisions at a receiver or deprive some nodes of transmission opportunities
We explore the feasibility of using centralized rate control that can be enforced at traffic aggregation points such as gateway routers
Summary
Wireless mesh networks (WMNs) based on the commodity IEEE 802.11 radios are a low-cost alternative for last mile broadband access. Given a desired rate-allocation policy objective (e.g., max-min allocation [7]), we evaluate the effectiveness of gateway rate control in enforcing this objective in a 802.11-based WMN This evaluation is necessary because multihop wireless network characteristics are distinct from wired networks or even one-hop wireless local area networks (WLANs): competing flows in a WMN traverse different number of hops, each flow experiencing varying levels of link contention along its path; further, transmissions along individual links are scheduled based only on the localized view of the CSMA/CA transmitters.
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