Performance analysis of VoIP codecs over multi-rate EDCA

Abstract

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.

Performance Analysis of Multi Traffic over Multi Rate EDCA of WLAN Network

“…In case of EDCF, as there was a separate queue for each priority traffic, a minor change in throughput, latency and drop ratio was observed for voice as compared to DCF [6].The EDCA QoS mechanism produced significant improvements in the transmission of voice, which was consequential in the case of highly loaded network. Measurement results had shown that the use of QoS mechanisms reduced values of the mean and maximum delay, jitter and lost packets as compared to the case without QoS mechanism [7].When G711 VoIP connections is reduction in the bandwidth available for data traffic by approximately 900 Kbps [8].The MOS (mean opinion score) value of different VOIP CODECs (G.711) found was 4.48322 without background traffic (data) over 802.11e and 802.11b [9] Dynamic jitter buffer schemes give the highest user satisfaction in VoIP codec (G.711) and WLAN environments where compared without dynamic jitter buffer schemes [10].…”