Asterisk ring-all + conferencing

Dear all,

I have this requirement from aviation customer, where they would like to modernize their “Emergency Voice Communication” system. They would like the person at Control Tower, when emergency event happen, just by lift a handset or dial certain number, it will ring all extension in other dept (police, fire, ambulance etc) and other dept will pick-up the phone and have a audio conf with all parties. I know the features involved will be ‘ring-all’ and also ‘conferencing’. But from what i know, ‘ring-all’ will cause all extension to ring, and the the first person to pickup will stop the ringing at other places, whereas they want the ring to continuous at other places until somebody pickup, during that time, anybody who already pick-up the phone can straight way have conferencing with Control Tower.

Do you have any idea on how to implement this? Any help is appreciated. Diagram is as attached. Thanks.

Check out this previous post of mine… You dial a number, it causes the system to initiate calls to the other parties, meanwhile putting you into the conference room. The other parties phones ring as a call is being originated to them, when they answer they will be placed in the conference room. You could easily add that when they answer a playback message could tell them this is an emergency notification prior to being conferenced in.