TamoSoft: Network Analysis Tools & Security Software

Monitoring and Troubleshooting VoIP Networks with a Network Analyzer

Number of Clients per AP

Wi-Fi access points have limited bandwidth, effectively restricting the number of concurrent VoIP users. Depending on the choice of codecs by the endpoints and the 802.11 standard used in the hardware the number of simultaneous VoIP calls supported by a wireless access point may vary. Analyzing the average and peak numbers of connected clients is crucial for the deployment of a VoIP system, allowing making a weighed choice of hardware and codecs. The following screenshot illustrates a few clients connected to wireless access points, as well as a number of other parameters discussed in the next chapters.

With the advent of 802.11n technology that presently supports speeds up to 300 Mbps and will soon support 600 Mbps, the issue of the number of concurrent VoIP calls becomes less critical, but the older 802.11b (11 Mbps), 802.11g (54 Mbps), and 802.11a (54 Mbps) gear is still far more common than the newer 802.11n devices. Online bandwidth calculators are widely available; using one such calculator, the network administrator can get necessary metrics that depend on the 802.11 standard and codes being used. For example, for an 802.11g WLAN and G.729 as the VoIP codec, 27 simultaneous VoIP calls are recommended with an anticipated MOS of 3.8, with the maximum being 98 simultaneous VoIP calls with an anticipated MOS of 3.2. Using 802.11b instead of 802.11g decreases the number of simultaneous calls by approximately five times. Using a wideband G.711 codec with an 802.11g access point, 15 simultaneous VoIP calls are recommended with the anticipated MOS of 4.1, the maximum being 53 simultaneous VoIP calls with the anticipated MOS of 3.4.