[Asterisk-Users] need help troubleshooting clipping and garbled VOIP calls

[T. Shaw]

Hello all,
I have a problem with call quality with my Asterisk setup. I'm doing VOIP 
only so far, but have a zaptel TDM400P in the box not being used. The 
problem i'm having is that when calls are placed, connected, and the far-end 
is reporting that they are experiencing clipping, choppy, and garbled voice 
conversations. So bad that we have to resort to using our cell phones. This 
entire setup is still being built, but any phone attached is experiencing 
this. Call volume is almost nil (under 20 total incoming calls a day). This 
is a small business setup. The server is used exclusively for Asterisk, so 
it isn't a fileserver, or anything else.

The setup is as such:

ipphone  <--->cisco 2900XL switch <----> Cisco 2621 router <---> dsl modem 
<-->DSL <---> VOIPprovider

I've configured the switch and the router to set priority and qos to 
prioritize voice traffic above data.
Funny thing is, there is not data REALLY hitting the network. I have setup 2 
vlans, data vlan, and voice vlan. There are two work stations on the 
network, and neither is being used to hit the internet heavily (office is 
still being setup).

Any pointers or suggestions anyone have for me as to were to look for this 
poor quality?
It seems only the Far-end (called party), is hearing this and not the 
calling party.

I haven't tried switching out the phones because we only have 1 type, and 
any of the phones i used exhibit these problems. I will try softphones to 
see if it is truly a "networking" issue or Phone issue.

Is anyone using a cisco 2900 switch or router and care to provide config 
samples of their COS/QOS setup?

Thanks!

Terrelle Shaw