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.