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Experimental analysis of VoIP call quality support in IEEE 802.11 DCF

In recent years the interest in supporting voice over IP (VoIP) services over wireless local area networks (WLANs) based on IEEE 802.11 standard is growing. A key issue on this topic is to understand how well the 802.11 can support quality of service (QoS) for VoIP services. Recently ITU-T has released the E-model recommendation to evaluate voice quality perceived by users. In this paper we present via experimental trials with commercial equipments, the relationship between the E-model and network metrics like packet, delay, jitter and packet loss in order to find the optimal working point for a WLAN supporting VoIP applications. Result analysis shows how packet loss is the metric with major influence on quality degradation for the considered scenarios. Following these results, we select packet loss ratio (PLR) as the fundamental parameter to determine the voice call quality. Finally, we introduce a procedure to compute PLR in the wireless stations based on parsing the sequence number field in the RTP header.