Choppy voice when simultaneous talk

Unanswered Question
May 10th, 2007


I have a VoIP network made of a gateway-CME with an E1 30 channels to the PSTN and dial peer voip sending out an E1 data towards another CME and IP phones


I have no voice issue except when both talker of a call speak at the same time.

When they do speak at the same time each talker gets choppy voice from the other.

Any Idea ?

Thanks in advance

I have this problem too.
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Hieu Cao Thu, 05/10/2007 - 10:22

Do you have QoS running in your routers? If you do, check to see if packets are dropped for the Voice class and increase allocated bw for this class. If you don't have QoS running, I recommmend that you implement it to prioritize voice packets.

Take a look at these documents..



earrigault Fri, 05/11/2007 - 01:38

Hi Hieu,

Thanks for responding.

I implemented LLQ out the EI data (toward the other CME) on each side of that E1 128Kb/s by the way. Working VOIP calls with G729r8 in between CMEs, I have made a Priority class in a policy reserving a strict priority of 96 Kb/s (the maximum available Bandwith by default).

Having the link bandwith below 768 Kb/s, I also configured PPP Multilink on each side for fragmentation with fragment size of 10s (to have minimum delay garanty in case of unwanted FTP transfert on the E1)

I have'nt check yet if I had drops during simultaneous talk..

I'll do it shortly and give you my feedback

The wierd thing is that the choppy voice symptom appears only when simultaneously talking and only in this case. It's pretty strange to me.

I was thinking maybe VAD coul be involve in this issue. Could VAD (when misconfigured)impact a voice conversation the way I described it ?

Hieu Cao Fri, 05/11/2007 - 08:36

I suppose that VAD can be an issue if not configured properly. The link from my previous post has a section talking about VAD, so you might want to take a look at it. As a test, you can try disabling VAD in your router to see if the problem goes away.

I don't have VAD in use in our enviroment, and everythign is working fine.

If you can, please post your QoS config.




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