Call Admission Control for IEEE 802.11 Contention Access Mechanism.pdf

Call Admission Control for IEEE 802.11 Contention Access Mechanism Dennis Pong and Tim Moors School of Electrical Engineering and Telecommunications, The University of New South Wales, Australia Email: dennisp@.au and t.moors@.au Abstract— This paper proposes an admission control algorithm that enables the upcoming IEEE 802.11e contention based En- hanced Distributed Channel Access (EDCA) to provide quanti- tative bandwidth guarantees for Wireless Local Area Networks (WLANs), rather than a relative prioritized service. The algo- rithm estimates the throughput that flows would achieve if a new flow with certain parameters was admitted, and so indicates whether such a new flow can be admitted while preserving the Quality of Service (QoS) of existing flows. The algorithm deals with the EDCA parameters of minimum contention window size and transmission opportunity duration, and indicates what values should be used for different flows. Simulation results confirm the accuracy of the throughput estimates and the effectiveness of the admission control algorithm. I. INTRODUCTION The IEEE 802.11 MAC uses the contention based Dis- tributed Coordination Function (DCF) as the basic access mechanism and a polling based Point Coordination Function (PCF) to provide contention free channel access. IEEE 802.11 task group E is defining mechanisms to enhance the QoS of the original MAC standard, including a new contention access scheme called Enhanced Distributed Channel Access (EDCA) [1] and an improved polling scheme based on PCF. Contention based access mechanisms are simple and ro- bust, but they cannot guarantee delay and throughput be- cause of their probabilistic nature. With small modification to the DCF access mechanism, which virtually all wireless LAN cards implement, relative priority service is provided. This paper focuses on the contention based EDCA access scheme, which provides a prioritized QoS service using an independent transmit queue and channel access function for