I have setup elastix 1.6-12. I have two types of phones Cisco 7940 and 7970. Th problem is when we are calling from a 7970 to a 7970 or 7940 the call drops in exactly 20 secs. If we call from 7940 to 7970 the problem is not there. Also for call to / from external the problem is not there. Need help as I am quite new to this and have been at it for many days and been reading on the sites but with no success.