Recently a customer who installed a new Asterisk based PBX had the following issue with their door phone.
They hooked up their existing analog door phone to the FXO port on the PBX and had it route to a ring group.
When someone rings the bell the system sees it as an incoming call and rings the phones in the ring group. The person that answers the phone can then “buzz” the person into the office using their keypad.
The problem was that it took about five seconds before the phones in the ring group would ring.
After some research I figured out that the issue was that the system was waiting for caller id which was not supplied by the door phone. After three to four seconds it timed out and continued.
The fix was very simple; in the zapta.conf set usecallerid=no and the delay is minimal.
VoIP4EA 