Sound quality

I have a problem with sound quality in the phones connected to Asterisk. The other end of the connection does not seem to be affected. The symptom is a sort of bubbling effect on the sound, quite rapid clipping. When the conversation starts the sound is fine, the effect starts after maybe a minute or so. Both softphones and hand sets show the same symptom.

We are connecting through a 2 Mbit/s SDSL line, not heavily used, to an IAX2 provider. The codec listed first is alaw, followed by ulaw. We’re using the ztdummy driver for timing. Asterisk version is 1.0.1.

We’re just starting out using Asterisk, so if there are any major omissions in the information I should have provided, please bear with me.

Any pointers to docs or other help to debug the problem is appreciated.

Ragnar Wisloff,
Oslo, Norway

Could be one of the following

+Problem on your server
Your server could be running low on resources. Post the output of ps aux

+Problem on your providers server
Call your provider or see if you have the same problem between FWD

+You are running into latency between the servers
Post the results of a “ping -c 20 yourIAXprovider”. Also post the results of a test from

  1. There is no problem with resources on the server, as seen from the perspective of a reasonably experienced sysadmin. Does Asterisk require anything special? From what I understand timing information is important and the ztdummy module provides that. It just loads, after that there are no noises from it.

  2. gives a score between 4 and 4.5 depending on the destination of the call.

  3. The servers of the provider or a firewall in front have ping disabled, so I cannot test that. It seems that we do not have the problem between the phones connected to Asterisk on our end. I don’t know what your term “FWD” means, so I cannot comment on that.