Capacity and Quality of Service (QoS) are two of the most important issues that need to be resolved before the commercial deployment of VoIP over wireless LAN (WLAN). The capacity is highly dependent on the chosen speech codec. Thus, several codecs are studied (namely, G.711 and G.723.1 and G.729) to determine their effects on the available capacity supported. On top of that, factors affecting QoS such as packet loss, jitter, throughput, and delay for various capacity networks are studied in this paper. This was done by simulating VoIP traffics over the WLAN using Network Simulator 2 (ns2) and predicting voice quality based on E-model. The simulation measurements were verified by the theoretical analysis. In conclusion, G.711 codec allows up to 5 simultaneous VoIP nodes, G.723.1 codec allows up to 15 nodes and G.729 codec allows up to 5 nodes for a voice quality greater than R=70 and distance 10 meter from VoIP nodes to access point (AP)
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