ELI5, How does calling the emergency line connect you to the nearest PD?


ELI5, How does calling the emergency line connect you to the nearest PD?

In: 3

You don’t actually speak to your local PD.

When you diall 911 you are connected to a regional dispatch centre. The dispatcher assesses the circumstances based on what you tell them (location, nature of the emergency) and *dispatches* resources from the appropriate local agency.

The cellular provider has to do it, generally as a part of the contract to allow them to operate. When you place an emergency call, it’s not the same as a regular call, so the cell towers know to process it differently. The network knows where the local emergency providers are and what their phone numbers are, so your emergency call is automatically routed to the provider/dispatcher.

This is also why you can place emergency calls even if you are in a poor service area. Any cell tower must service an emergency call, even if they are a competitor to your specific cellular service provider.

This is done differently in different places of the world.

Here, the call center that takes all the emergency calls has A LOT of incoming phone numbers. Really, really long ones.

Whenever you make an emergency call, the phone operator is responsible for rerouting the emergency call number *to the long number that best describes the geographical location of the caller*.

After that, the emergency number routes the call to the nearest call centre (because there are quite a few of them, nation wide) where there is currently an operator available.

Depends on what kind of phone. For traditional landlines, your phone number was inextricably linked to your physical location, so it was easy to work with local departments and route calls to the appropriate department.

I used to work in 911 provisioning for a VOIP provider, since those phones are not permanently linked to your location but was likely linked to your house (and might be a number corresponding to a different area), we had to have the customer self-report their address, then we would work with local 911 centers to confirm their calls were going to the correct place. This was often challenging in rural areas, where people had Rural Route addresses for mail delivery and didn’t have house numbers or even live on named roads. Once I had to figure out what to do with a guy whose house was in one town, but the street his house was on was actually in the next town over and neither town wanted to take responsibility for his 911 calls.

Landlines are listed in ALI and ANI databases; automatic location information and automatic name information. The locations are mapped to a certain PSAP, public safety access point. That’s the dispatch that answers the call.

Cellular is different as there is no location DB to reference. The call tower is assigned its nearest PSAP and will manage the connection, create the voice path, and hand it off to the assigned PSAP.