I have a similar issue where the call goes one way audio after 12 minutes
If you put the call on hold and back again the audio is restored
so far i have figured out the the time is from the session timer in the peer (1440sec =24min)
I have the session refresh timer set at 50% = 12 miinutes
We have increased the timer to 1800 sec (30 minutes) and the issue happens at 15 minutes
So the quick fix is to max out the timer at 9999 and set the refresh percentage to 99%
or set timer to 0
You will risk having stale sip session build up if you set the timer to 0
Could work around this with a weekly/monthly reboot schedule
Let me know how you get on
Here is the current timer page in the peer. It does not appear to me that this is where the problem lies unless I'm looking in the wrong place.
Keep-Alive (OPTIONS) Period   120    
Registration Period   3600    
Registration Period Refresh (%)   50    
Registration Maximum Timeout   90    
Session Timer   0    
Subscription Period   3600    
Subscription Period Minimum   300    
Subscription Period Refresh (%)   80    
Invite Ringing Response Timer   0    
Dale