asterisk users - Jun 2005 - Garbled one-way audio only with ulaw

For some reason a couple weeks ago users began experiencing garbled audio 
in one direction when dialing out via our VoIP provider. This happened at 
multiple sites simultaneously. The VoIP provider doesn't think it's
their
problem. If I switch to another codec so that Asterisk transcodes 
everything is fine. On conference calls (where Asterisk gets in the middle 
to relay ulaw to all channels) everything is fine. Calls between sites via 
ulaw are excellent.

We have plenty of bandwidth, and QoS in place. I've monitored and our QoS 
box never drops a VoIP packet (4569 UDP).

Phones are Polycom IP500s. We're running 1_0_7 stable. Plenty of CPU 
horsepower (P4 northwood, 2x256 dual channel DDR, 3ware RAID for 
mirroring) to handle maybe 6 calls simultaneously. This problem occurs 
even when there's only 1 call on the line. We're now running GSM with 
decent quality, but I would love to get them back to ulaw.

Any ideas?

TIA,
-Ron

rsenykoff@harrislogic.com wrote:
>For some reason a couple weeks ago users began experiencing garbled audio 
>in one direction when dialing out via our VoIP provider. 
>
Play with the jitter buffer, I'll bet this is your problem. I had 
exactly the same problem with a cable ISP. Also, watch for strange routing.

Chris