asterisk users - Jan 2005 - IAX2 dropped calls: need debug suggestions

Hi,

I'm trying to determine why IAX2 calls are getting dropped after a 4-24
hours of continuous connect time. My project requires that calls stay up for
days at a time. When I turn on IAX2 debugging, I see "max retries
exceeded" for control frames just before the connection is dropped.

My test setup is:

Zap Phone => Local Asterisk Server/IAX2/GSM => NAT => Internet =>
NAT(port mapped) => Remote Asterisk server/IAX2/GSM => Echo App

I also tried it without NAT on another pair of systems and it made no
difference:

Zap Phone => Local Asterisk Server/IAX2/GSM => Internet =>  =>
Remote Asterisk server/IAX2/GSM => Echo App

Note: An SSH connection stays up indefinitely to the from the calling server to
the called server.

I wrote a small UDP echo client and server, and installed it on both ends, and
noticed that a few packets are dropped every hour, but the connection seems
solid with this simple client and server combo.

How resilient is the IAX2 protocol to receiving out-of-order packets, and how
well does it deal with short term packet loss?

Has anyone else experienced problems with long duration calls over IAX2?

Thanks

Steve.