E-MAC: Self-Organizing 802.11-Compatible MAC with Elastic Real-time Scheduling

To overcome the lack of strict QoS guarantees in existing hotspots, in this paper we present a system for realtime traffic support in 802.11 networks that works in either infrastructure or ad-hoc mode. The proposed mechanism, called elastic MAC (E-MAC) protocol, helps stations with real-time traffic to organize and establish a transmission schedule in a distributed manner, while coexisting with standard 802.11 stations. This distributed scheduling guarantees very short delays and a minimum reserved data rate for real-time stations, while protecting best-effort 802.11 traffic from starvation. Another feature of our mechanism is time-slot reuse, which improves the network efficiency by allowing other real-time stations to take over unused slots (e.g., in case of using voice codecs with silence suppression). We evaluate the performance of our system using a testbed implementation, ns-2 simulations and a mathematical model, and show how it outperforms other QoS schemes (e.g., 802.11e) in terms of throughput, delay, and jitter.