Intermitten dropped calls and static

Asterisk Version
Asterisk SVN-branch-1.4-r89618

Currently experiencing static on random calls where the call is choppy. The voice on the other end can barely be heard and noise is in the background. Also experiencing dropped calls after briefly connecting, there are 10 calls being made concurrently.

If anyone has any solutions to this problem, I would really appreciate any feedback. This problem has persisted for a few weeks.

So here are the details:

CentOS 5.x running Asterisk 1.4-SVN.

For most of the time, Asterisk seems just fine. But frequently enough there are quality issues. I’m quick to blame our VoIP providers (Vitelity, ViaTalk, etc), but it can’t be that simple.

I thought I’d blame myself for using SVN, but I’ve tried updates (haven’t downgraded though) and hasn’t helped.

While I haven’t done a SIP packet dump, I’ve never questioned a bandwidth issue because we’re colocated and multi-homed. I’ve never had an issue running 150 concurrent ULAW phone calls (all servers together) and the box in question is doing a max of maybe 30 concurrent outbound trunks.

No issue with processor overload. It’s quad core and not even a single core gets close to maxing out. Yey for multi-threaded.

I really want to blame the phone provider, but as I’ve said, I’m smart enough to decide this one is not them (though I’ve had issues in the past that were their faults and it took me a week to convince them of that before they acted on the problem… silly Vitelity). Multiple phone providers really helps in deciding who’s at fault.

My next move is to try another operating system with a much more robust (and well tested) version of Asterisk. This will help me tell about issues with Zaptel or SVN Asterisk.

Can anyone else suggest anything to try in addition? Rather have some things to try than be scratching my head if the new OS doesn’t solve the issue (though somehow I expect it might).