The soon to be ratified IEEE 802.11e MAC layer QoS enhancements to the 802.11 protocol are making their way into production wireless networking equipment. As greater numbers of local area networks utilize the QoS features of 802.11e, we can expect to see aggregation of these networks into larger systems capable of addressing the needs for high bandwidth, real time services. We present a practical and accurate analytical model for the saturation transmission delay of EDCA. Our model is distinguished by its ability to provide a cumulative distribution function for transmission delay and by its treatment of the post-collision period, heretofore ignored by all other 802.11 models. We prove that our model accurately predicts the cumulative distribution of transmission delay with results from the ns-2 simulator.

The IEEE 802.11 Task Group E will soon approve the 802.11e standard for medium access control (MAC) layer quality-of-service (QoS) enhancements to the 802.11 protocol, and it is widely believed that these enhancements will allow 802.11 technology to form the foundation of high-bandwidth vertically integrated networks. At the heart of 802.11e is a modified contention-based access mechanism, named the enhanced distributed coordination function (EDCF). In this paper, we propose and validate an analytical model for the saturation throughput of EDCF. Key to the accuracy of our model is a treatment of the postcollision period, which has been ignored by all previous 802.11 models. With results from the ns-2 simulator, we show that our model can accurately predict throughput over a wide range of scenarios, and thereby demonstrate its usefulness as a predictive tool for use in QoS provision. With context provided by our analytical model, we discuss the primary throughput differentiation mechanisms of EDCF.