I have the elastix server on real IP address I have remote extensions behind nat the remote extensions can call but can not be called I traced the problem in the asterisk log, I found the extension become unreachable after 64 to 65 seconds I reduced the sip expiration time in the sip phones to the minimum (I found the min. is 60 sec.), but I still have a problem in the last period of the 60 sec., after about 50 to 55 seconds the phone can not receive calls, and start to receive again after the 60 sec. I want to reduce the sip expiration to less than 50 sec., 30 if possible. Or expand the time of expiration in the network to be more than 70 sec. what is possible and how? Or are there any other solutions?