Best Practices for Analyzing Voice over Wi-Fi (VoFi) with WildPackets

With 802.11n in full swing and 802.11ac rolling out next year, Voice over Wireless, or VoFi, is becoming more and more common in the workplace. Not only does this technology reduce cellular usage, but it also eliminates the issue of dropped calls at the office. Luckily for all of you, VoFi is also not a difficult technology to monitor and analyze with WildPackets.

Scan Your Environment
From a WildPackets perspective, VoFi data, like traditional VoIP, is just another data type on the network, so the first step in analyzing VoFi is no different than the first step in analyzing your overall Wi-Fi network – perform a scan of the 802.11 bands in use, 2.4GHz, 5GHz, or both. All that’s needed is a single, supported WLAN adapter for capturing traffic with OmniPeek, and you’re on your way. OmniPeek will scan through all of the channels you choose, dwelling on each channel for 500msec, or whatever dwell time you configure. A scan provides a great deal of information about not only your network, but the overall WLAN environment as well. The scan will identify all of your networks and APs (based on the location where the capture is performed), as well as all neighboring WLAN activity. Based on this information you may decide to do some channel reallocation to avoid conflicts with neighboring APs that are not under your control, or you may even decide to physically move some assets. The scan will also allow you to see the utilization of each of your APs, indicating potentially oversubscribed APs. Pay close attention to the wireless Expert events generated by OmniPeek, especially events like “Wireless RF Interference” and “Wireless Transmission Retries” which give you an overall indication of environmental issues that are affecting your WLAN performance, and which are likely to adversely affect VoFi performance.

Zoom In On Your Network
Now that you know exactly how your network fits in with your surroundings, it’s time to zoom in on your specific network. The best way to do this is to configure a supported WLAN adapter to capture traffic with OmniPeek on each channel in use by your WLAN, or at least each of the channels in use that can be seen from your current measurement point. This will give you complete, 100% coverage for all channels in use, making sure that you don’t miss any critical packets, and allowing for advanced inter-channel analysis like roaming. Identifying roaming events and measuring the overall roaming timing is critical for time-sensitive data like VoFi, as roaming latencies in excess of 150msec (not uncommon) will adversely affect VoFi call quality for any mobile VoFi user on your network.

Zoom In On Your VoFi Calls
As stated earlier, VoFi is just another data type on your network as far as OmniPeek is concerned, so if you’re capturing WLAN traffic you’re capturing VoFi traffic. There are several ways in OmniPeek to instantly isolate your VoFi traffic so you can get an immediate assessment. First, there’s the Voice and Video dashboard, which provides summary information regarding call quality, call volume (number of calls over time), and network utilization for VoFi versus all other data. A quick scan of the dashboard will let you know if you need more detailed analysis.  When you do, proceed to the Calls and Media views, which provide a detailed breakdown of each VoFi call. The Calls view provides detailed analysis regarding the signaling for each call, including a detailed, packet-by-packet bounce diagram so you can “see” the call setup in detail. The Media view breaks down each call into individual flows, since the packet path between the caller and the callee can differ from that between the callee and the caller. This view includes details of the quality of the actual voice transmission, including analysis of latency, packet loss, jitter, and MOS and R-Factor voice quality metrics. And if you’re really not sure how all of these metrics stack up regarding “real world” quality, you can play back either the entire call or just each leg of the call to hear what it really sounded like.

Remember that VoFi is just another data type or application on your network, so analysis is similar to any other running app. Start by testing out your overall environment, the end user experience, and gradually dive deeper into your network to find the problem.

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