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Benchmark now, rejoice later

Some thoughts on establishing benchmarks for your VoIP network.

So you've implemented your IP Telephony system. You've rolled it out, tested it, migrated your users onto it and everybody's happy. Now what do you do? Well, while you're sitting around surveying your handiwork and patting yourself on the back, it's a good time to survey your handiwork and take some notes.

Benchmarking can be extremely helpful later on for two reasons. First, when things break, and you know they will... if you have a good benchmark, you'll have something for comparison and that usually points you to the problem pretty fast. Second, you can watch your trends over time and know when to upgrade.

Here are some good aspects of your VoIP network to make a note of while things are good:

  • Latency – this is a no-brainer. Make a note of how long it takes packets to get from point A to point B in your network. Take measurements at various times of the day.
  • Call setup times – how long does it take for each call leg; from IP phone to gateway, from gateway to gateway, etc.
  • Network paths – copy some traceroutes. Often, when service degrades for some reason, it's because a component in the network failed, and your network rerouted to a backup path that is likely constrained in some manner. This is hard to tell though, if you don't know what path users normally take.
  • Noise-levels – find the commands for your hardware that show what your db gain is set to for your gateways. While you're in there, make a note of your echo-canceller's settings too.
  • Finally, capture some traces of calls. For a good benchmark, set up a voicemail box with a lengthy message, call it and let it play the message to you, and capture the whole thing. When users complain of poor voice quality, call this mailbox and capture a trace again. Then you can use one of the tools that estimate an MOS to see if they're different. This way, you can be relatively sure you're comparing apples to apples.

Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.


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