[asterisk-users] audio drop out half channel

[Jerry Geis]

I am having half channel audio after about 6 minutes. asterisk 1.2.11 
and 1.2.8 zaptel.
My call is originating on a a SIP extension going out to nufone to my cell.
After about 6 minutes the SIP extension can still hear me on my cell
but I cannot hear the SIP extension.

If the SIP extension hits a key I hear it on my cell.
If the SIP extension is talking and hits hold the cell hears about 2 
seconds of audio then
nothing again.

What might this be or what should I do to find out what is going on.

Jerry