Experiences using Gateway-Enforced Rate-Limiting Techniques in Wireless Mesh Networks

Gateway nodes in a wireless mesh network (WMN) bridge traffic between the mesh nodes and the public Internet. This makes them a suitable aggregation point for policy enforcement or other traffic-shaping responsibilities that may be required to support a scalable, functional mesh network. In this paper we evaluate two gateway-enforced rate-limiting mechanisms so as to avoid congestion and support network-level fairness: automated queue management (AQM) techniques that have previously been widely studied in the context of wired networks, and our gateway rate control (GRC) mechanism. We evaluate the performance of these two techniques through simulations of an 802.11-based multihop mesh network. Our experiments show that the conventional use of AQM techniques fails to provide effective congestion control as these mesh networks exhibit different congestion characteristics than wired networks. Specifically, in a wired network, packet losses under congestion occur at the router queue feeding the bottleneck link. By contrast, in a WMN, many such geographically dispersed points of contention may exist due to asymmetric views of the channel state between different mesh routers. As such, gateway rate-limiting techniques like AQM are ineffective as the gateway queue is not the only bottleneck. Our GRC protocol takes a different approach by rate limiting each active flow to its fair share, thus preserving enough capacity to allow the disadvantaged flows to obtain their fair share of the network throughput. The GRC technique can be further extended to provide quality of service (QoS) guarantees or enforce different notions of fairness.