StrikeAwe

Asterisk PBX

Posted March 11, 2009 by Gabriel Hurley

My company runs an Asterisk PBX server to handle several VOIP phone numbers for us. Its versatility and featureset is pretty staggering; among the various things it lets us do:

• Ring all of our cell phones simultaneously when a call comes in so any of us can answer our "main line" wherever we may be.
• Email voicemail messages to specific groups of people so that messages are logged and distributed automatically.
• Decentralize our operations and allow us to be untethered from a "place of business"

However, it's also a nightmare to set the thing up. It's practically got its own language and the configuration is all done in flat text files. The GUI interfaces for it are generally lacking numerous features and hamper things as much as they make them easier.

But the biggest problem we've been having is that our connection has been experiencing strange problems with the audio cutting out for seconds at a time or generally becoming garbled. I spent quite a bit of time trying to diagnose this and although it's not solved, it's now substantially better.

Some useful information:

• Make sure your cli.conf file contains the following lines uncommented so you'll get useful information when someone calls into your system:

  sip set debug on = yes
  core set verbose 3 = yes
  core set debug 1 = yes

• Use the iax2 show netstats commands liberally. Since it doesn't update, you have to check it periodically to get the latest info. It will tell you useful information on where the problems lie during a call, though.
• If you're experiencing a lot of dropped packets (like we were) or a lot of jitter/delay then switching to an uncompressed audio format makes the audio A LOT more intelligible. The tradeoff is it takes a lot more bandwidth, but packet loss will make compressed audio all but unusable. The easiest way to change this setting is to add the bandwidth = high variable to your iax.conf file.

Doing those things allowed us to make our system very usable for now, though we're still filing a trouble ticket with our VOIP provider since the iax2 show netstats command is indicating massive packet loss on their end.