> I don't know if this is possible in Asterisk, but if it> is, I suggest that you include a checkbox when setting> up a route that says something like "this is an> emergency route" - it would normally be a route used> only for 911 (in North America) or similar> emergency-only numbers elsewhere. If a route is> designated as the emergency route, it should have the> ability to take over a trunk if none are free for the call.>> Ideally, I would suggest that, for example, when 911 is> dialed the system would first look for an available> trunk, but if none is found, it would first deliver a> quick recorded announcement to all parties on the> needed trunk (something like a couple of distinctive> alerting tones, followed by "This line is needed for an> emergency call - Goodbye" - it would then disconnect> the call, wait two seconds, seize the outgoing trunk> and dial the emergency number).>> This would primarily be useful for users that only have> one or two PSTN lines, but those are the only lines> that can send a 911 call to its proper location. The> only time an emergency call should fail is if all> useable trunks are already in use for emergency calls> (if an explosion happens, everybody in the building> might attempt to call 911 at the same time, and you> don't want the first person who gets through to be cut> off by a second, third, fourth, etc. caller just as> they are giving the details of the emergency).>> If there is more than one candidate trunk, I would> suggest that the trunk to seize would be selected by> this logic:>> First choice: Trunk with call not yet completed> (caller is listening to ringing or other call progress> tones).>> Second choice: Trunk with call in progress for 10> seconds or less (could make number of seconds> configurable) - if the call has JUST been established,> the caller is probably still listening to an IVR or> answering message or something like it. If more than> one trunk fits the criteria, then the one that's been> connected the shortest amount of time.>> Third choice: The call that's been in progress the> longest - chances are more likely they've got their> business completed and are just shooting the bull, so> to speak.>> My worry is that in cases where you only have one or> two PSTN trunks and they are in use, a caller trying to> call 911 will get congestion. It's better to have a> dedicated emergency trunk, of course, but most small> businesses and nearly all homes will NOT have a> dedicated emergency trunk.>
