Effective-capacity-based stochastic delay guarantees for systems with time-varying servers, with an application to IEEE 802.11 WLANs

Many network applications rely on stochastic QoS guarantees. With respect to loss-related performance, the effective bandwidth/capacity theory has proved useful for calculating loss probabilities in queues with complex input and server processes and for formulating simple admission control tests to ensure associated QoS guarantees. This success has motivated the application of the theory for delay-related QoS too. However, up until now this application has been justified only heuristically for queues with variable service rate. The paper fills this gap by establishing rigorously that the effective bandwidth/capacity theory may be used for the asymptotically correct calculation and enforcement of delay tail-probabilities in systems with variable rate servers too. Subsequently, the paper applies the general results to IEEE 802.11 WLANs, by representing each IEEE 802.11 station as an On/Off server and employing the effective capacity function for this model. Comparison of analytical results with simulation validates the effectiveness of the On/Off IEEE 802.11 model for delay-related QoS, complementing earlier results on loss-related performance.