Voice issues with Asterisk


I’ve been running Asterisk in our office for a couple of years but haven’t been able to resolve a certain voice issue. The configuration looks like:

10 Cisco 7940 phones
SIP firmware: App Load ID P0S3-08-7-00, Boot Load ID PC030301, DSP Load ID 4.0(2.0)[A0]


Netgear switch FS726TP

Voip provider is Teliax (SIP)

The issue is sporadic choppiness in voice, and it sounds like a robot talking (very slowly). It lasts for a few seconds and then goes away. I thought first that the issue was only with outbound calls over Teliax, but it seems to be happening on internal calls as well (one extension to another).

I’ve read some posts related to RTCP with Asterisk/Cisco 7940 being the root cause of this, but I’m not sure if that is indeed the case. I have noticed that a Polycom conference room phone (IP4000) doesn’t seem to have this issue (or maybe I haven’t noticed it yet since I don’t use it much).

Any ideas would be much appreciated.


Which machine is running your Asterisk ? What is the load on the server ? Are you using virtualization ?

Thanks for replying.

The server (physical, not virtual) running Asterisk is a dual Opteron Tyan S3892 board with 8GB RAM and hardware RAID 5 (3WARE RAID controller). OS is Centos 5. Kernel is 2.6.9-55.0.2.ELsmp I haven’t seen any resource constraints (CPU, memory, network). Load average in top is usually 0.00 most of the time. The server is not used for anything else.

Are you using a dedicated network for VoIP ? If not do you have some QoS in place ?

Yes, the Netgear switch is only used for voice, so it’s a dedicated network.

Please try some QoS monitoring tool to analyze the behavior. Make sure it gives you indication on jitter & packet loss.
You can find more information in http://www.voip-info.org/wiki/view/QoS