Online mobile VoIP (or VoFi) is coming. In-Stat anticipates 171.3 million users by 2013, with annual revenues projected at $10.8 billion ("Mobile VoIP - Transforming the Future of Wireless Voice; In-Stat In-Depth Analysis," Frank Dickson, Sept. 2009). Previously on our blog we've talked about why VoFi and why now, specifically the benefits of VoFi. Now we'll focus on VoFi monitoring, analysis, and troubleshooting.
Before you panic, take a deep breath. Analyzing VoFi traffic is basically the same as analyzing VoIP traffic. Remember though that wireless exacerbates factors such as jitter, latency, and packet loss that affect VoIP. Watch Using VoIP Metrics to Identify Network Problems for the specifics.
Begin at the Beginning: Your End User's Call
When problems arise with VoIP or VoFi applications, you start in the same place. Your first step - before you begin to worry about statistics or packets - is to take the time to listen to representative calls. You want to hear what your end users are experiencing. Your ear will reveal telltale signs of latency, jitter, and packet loss. Be sure your VoIP analysis application supports playback of call audio, specifically the playback of individual RTP streams as well as the playback of the complete call. Without the audio, you can spend hours tracking down problems that aren't due to either the application or the network - for example, clicking due to a damaged handset.
Take Your Network's Pulse
Once you have listened to the call, you'll want to take a look at what's going on in your network.
Figure 1: Overview of Network Health
Immediately you see what you heard - the call quality was poor. The Mean Opinion Score graph gives an average over all calls occurring on your network. In this example there's just one call, so you see the average for the duration of that call.
With Expert Events you're able to verify what your ear told you.
Figure 2: Event Summary
With this call, you can see that there are a lot of physical errors: late packet arrival, retries, out of sequence packets, packet loss, excessive jitter, and more. With the cause identified, you can quickly begin to fix the problem. Looking at the call in its entirety, you'll notice the call is closed, it had a successful ending - meaning the call wasn't truncated - what CODEC was used, how long it was, and what the Mean Opinion Score was.
Figure 3: Call Statistics
In this example, the mean opinion score of 2.5 lets you know that the quality of the call was pretty poor. In the media view, you can drill down into each segment leg to determine why the quality was poor.
Figure 4: Call Details - R Factor, Mean Opinion Score, Packet Loss Percentage, One Way Delay, Etc.
Understand the Differences between Wired VoIP and VoFi Calls
The next two figures show both a Wired VoIP call and a VoFi call packet-by-packet. (For an in-depth discussion of these calls, watch Anatomy of a VoFi Call: Packet-by-Packet.) You'll notice that they're pretty similar. The protocols used are different and with VoFi there's the additional step of authentication.
Figure 5: The Anatomy of a Wired VoIP Call
The differences involve: wireless segments instead of wired segments; signal interference; and wireless roaming.
Figure 6: The Anatomy of a Mobile VoIP (VoFi) Call
Last week in Toronto, Joe Habib, Director of Global Services, presented "QoS of IP Telephony: Slaying the Three-Headed Beast of Jitter, Latency, and Packet Loss" at IT360. His presentation (PDF) is now available online. If you're interested in ensuring QoS for your current (or future) VoFi deployment, you should definitely check it out.
In the presentation, you will learn:
- What six factors contribute to poor voice quality
- How to establish metrics for evaluating VoIP call quality
- How to balance high-speed, bursty data requirements with requirements of high quality voice calls
- How to capture data for VoFi Analysis and use VoIP metrics to identify developing problems
- How to analyze a VoFi call packet-by-packet and verify voice quality with call playback