Experimental Evaluation of 802.11e EDCA for Enhanced Voice over WLAN Performance

The 802.11e MAC protocol extends the 802.11 CSMA/CA contention mechanism by allowing the adjustment of MAC parameters that were previously fixed. While the 802.11e protocol has been extensively studied, this work is almost entirely confined to analytical and simulation studies. In this paper we demonstrate a technique for measuring one-way delay in an 802.11e hardware testbed and thereby study delay in the context of protecting a voice call competing against data traffic. We demonstrate that with the standard 802.11b MAC settings greedy data traffic is able to seize bandwidth from a low-rate voice call. Only 5 competing data stations are needed in order to induce a voice call loss rate exceeding 10%, which in practice would lead to an unacceptable level of voice quality and dropping of the call. We present experimental measurements which demonstrate that the use of 802.11e to provide a practical solution that can successfully deliver quality of service to voice traffic in a mixed voice/data environment. To our knowledge, this is the first experimental demonstration of accurate one way delay measurements being used to show the priorisation of voice in an 802.11e hardware test-bed.