Performance analysis of VoIP codecs over multi-rate EDCA

Enhanced Distributed Channel Access (EDCA) is a mandatory part of the IEEE 802.11e standard which provides Medium Access Control (MAC) layer solution for Quality of Service (QoS) provisioning in Wireless Local Area Networks (WLANs). It is a contention based protocol which prioritizes channel access to QoS traffic using four Access Categories (ACs). In this paper, we introduce the performance evaluation of high priority Voice over Internet Protocol (VoIP) traffic over EDCA in multi-rate WLAN. In a multi-rate environment, the channel physical transmission rate is changed by the Access Point (AP) as the stations move towards or away from the AP. The AP performs rate adaptation on each frame according to the channel condition or signal quality that the frame is likely to experience when stations are considered mobile. We implement EDCA at the MAC layer over the physical layer of IEEE 802.11b radios using the network modeling and simulation tool QualNet. We simulate multiple VoIP nodes in a single QoS-enabled Basic Service Set (QBSS) with one QoS-enabled AP (QAP). The performance of each VoIP node is evaluated with three VoIP codecs. We first use codecs without jitter buffer and evaluate jitter with other performance parameters. The simulations are repeated for different codecs with jitter buffer. The effect of jitter buffer on Jitter, Delay and Mean Opinion Score (MOS) for each VoIP node is compared with other codecs in stationary and mobile environments. Simulation results show the effectiveness of using jitter buffer and its limitations in a multi-rate environment.