asterisk users - Jan 2010 - Asterisk 1.4.28 intermittent one way audio?

Hi All,

I made the decision recently to update some old call servers from
1.2.x to the latest 1.4.28.

I spent 2 weeks in the lab testing every production requirement for
these voice servers.  Nothing too special, SIP in, database lookup,
SIP out, a couple of special applications, write CDR to billing
server, nothing intensive at all.  I also performed stress testing for
call capacity, database performance and media handling.  So after all
the testing was finished, I was very confident this was the right
thing to do.  This was a plain jane asterisk install from stable
release on debian etch, SIP only, no zaptel or dahdi.

I shut down one of my 1.2 voice servers and turned up the new 1.4.28
server in it's place.  Within a couple of hours I started getting
calls from a couple of customers complaining about intermittent
one-way audio issues, they could her the caller, but the caller could
not hear them.  This was only happening on inbound calls.  I collected
call examples for the next few days.

I was able to trace almost all the calls back to the new 1.4.28
server.  No other changes in the infrastructure other than putting in
the 1.4.28 server.  And the new server is built on the same hardware
as the 1.2 servers are on.  I could not find any relevant errors on
any associated network element or upstream/downstream voice server, I
could not find any errors on the 1.4.28 server either.  No errors
anywhere, nothing, nada, no retransmits, critical packets, rtp
warnings, zilch.  I pulled the 1.4.28 server out of call rotation, no
more customer complaints.

The call volume passing through the server is not a lot, 40 to 80
active calls at any time, and maybe 1 to 2 calls per second max,
usually a call every 3 or 4 seconds.  The one way audio issue occurred
at both high and low call volume and was truly random.  I captured 14
calls out of several thousand.  I'm sure there was a lot more that
that, but these were the only ones reported to me for investigation.

So my question is, has anyone else experienced intermittent one way
audio specific to Asterisk 1.4 that can be identified and resolved.
Or maybe suggest another version of 1.4 that does not have an issue
like this at these volumes?

Thanks.

JR
-- 
JR Richardson
Engineering for the Masses