[asterisk-users] Phones lose contact

[Paul Douglas Franklin]

When off site, our IP phones lose contact after a few minutes of 
inactivity.  They no longer receive calls, though they can call out.  
Asterisk acts as if it is ringing the phone, but the phone does not ring.
The phones are behind a NAT/firewall.
What is the most reasonable solution?
--Paul

-- 
Paul Douglas Franklin
Computer Manager, Union Gospel Mission of Yakima, Washington
Husband of Danette
Father of Laurene, Miriam, Tycko, Timothy, Sarabeth, Marie, Dawnita, Anna Leah, Alexander, and Caleb