Bad sound quality with IAX2 (remote connection)

Hello all !

I did setup an IAX2 extension in Freepbx. The Astersik (Elastix distribution) is on a box that is inside a private network, connected to the internet through an ADSL router. I did put the asterisk server in the DMZ.

Now, when somebody connects to this extension from the internet, everything works fine, there is little delay, and for him (using the extension from the internet), the audio quality is good (using alaw or gsm). BUT : for the other side (for example another extension calling or being called) there are a lot of little “cuts” in the communication. I do not find the correct word in Enghlish, it’s like micro cuttings. Hope you see what I mean.

Is there anybody who knows a solution to this ?

Thanks a lot for any help !



Take a look at your upload bandwidth on your ADSL connection. I suspect that you are maxing out your upload bandwidth, which is why your folks on the other end are hearing jitter and little breaks in the audio. Remember, the audio stream is a file that is being uploaded.

Dear John,

Thanks for your help.
In fact I am sure that the bandwidth is rather ok (I use gsm codec and have 64 kb free for upload).

What do you think ?


If 64 kbits/sec is your max upload speed, I think that is the problem. If I am not mistaken, GSM is a compressed codec and while compressed codecs are more efficient users of bandwidth, all of the packets have to make it to the destination or the computer on the other cannot decode the stream.

I think if you had more upload bandwidth available, this would work better. A way to test would be to turn off everything else on the network and make a call and see if that helps. If it does, upload bandwidth is probably the issue. An uncompressed codec would take about 80 kbits/sec to run.

Hi John,

thanks for your additional infos !
It seems that you’re right. I will do some more testing and come back to you.