When one call 911, how is the call automatically local?


Hypothetically speaking, if someone is living in New York and they call 911, how does the call not go through a hospital in Los Angeles or other city from another state? How does the call automatically transfer to a local hospital in the area one lives in?

In: Technology


It doesn’t transfer to a local hospital. It gets routed to a local 9-1-1 dispatch centre which then forwards the call to EMS, Fire or Police as needed.

The other answer, while not wrong, doesn’t really answer this question, so:

When you call 911, your service provider looks up the “Emergency Service Number”, which is a regular 10 digit phone number, that connects to the 911 call center physically closest to you. Every area has one of these, and they look up which one is closest to your area based on your billing address or cell tower.

They redirect your call to this 10 digit number, and from there it’ll ring at your local 911 call center.

I feel very old having to explain this.

In the 1950s-1970s, there was no 911. If you didn’t know the phone numbers to your local ambulance service, police department, and fire department, you were SOL. (Well, you could probably call the operator and hope that got you somewhere.) If you bought a (landline) phone in the 1970s to mid-1990s it usually had a little card with a clear plastic cover, with a blue police car or shield symbol, red fire or fire truck symbol, and red cross symbol, for writing down phone numbers for police/fire/ambulance. When you bought a new phone you were supposed to fill these things out.

In the 1960s-1990s, 911 service was rolled out throughout North America. The idea was that when you dialed 911, your call would be automatically routed to whatever local authority (often a police station) agreed to service the block of phone numbers that includes yours. No need to memorize numbers – no matter where you lived, you dialed 911 and got someone who could either help or direct you to help. The rollout was very slow. Emergency phone number cards and stickers were still a big thing for decades.

By the late 1980s, 911 service was almost everywhere, and it was no longer necessary to call your local FD/PD/EMS directly. The 911 system was great – you made a call, and you got a 911 center assigned to your phone number. The ubiquitous emergency stickers with police/fire/ambulance next to every phone slowly disappeared.

Then cellphones became a thing. They operated in the same system – you called 911 and got a 911 center assigned to your phone number. That might be on the other side of the continent if you were traveling.

Enter Enhanced 911, or E911. Under this system, the 911 system was improved, so that 911 calls weren’t blindly sent to whatever police department claimed that block of numbers, but instead went to Public Safety Access Points (PSAP) with equipment and operators that could make sure the caller was physically in the region, determine what sort of emergency response was required, and redirect the caller if necessary. For cellphone users, the tower used to make the call was encoded as metadata, and used to redirect the 911 call to the PSAP associated with the tower, *not* the PSAP associated with the phone number.

E911 has some additional features, such as the ability to poll your phone for location data, if your phone has GPS/AGPS enabled. This of course only works if your phone has an active and accurate location fix at the time of the call, and the PSAP has the equipment to poll that information.

To make the reasoning short and non-technical,

Your phone operator is at all times aware of where you are. When your phone is on, it talks to the cellphone towers.

To make it possible to call you, it’s required that the cellphone tower that you are currently communicating with knows that you are supposed to be there. For any of it to work, the tower ALSO needs to share that information with a centralised control system.

The first thing the phone system does when it tries to forward a call to you, is that it asks the centralised system “alright, who is it that talks to that phone right now?” so that the actual phonecall can be forwarded specifically to that cell tower that is tasked with maintaining the phonecall.

There are some more fiddling that occurs when a phone moves out of convenient reach of a cell-tower, and hooks up to another instead in a fashion that appears seamless. But those are not relevant for this explanation, besides that you need to know that when the phone moves, the centralised system gets an updated summary of where you are instead.

When you make a 911 call, the phone operator is forced by law to look at this information and make a sensible assumption on which emergency call centre to forward the call to. Generally speaking, this is a manually assigned decision on each and every cell tower, when it’s erected.

To top it off, many cell towers are “divided” into several cells. One antenna in each direction, so to speak. And that also offers an ability for the cell-tower to distinguish your rough direction relative to the cell-tower. And that information is also passed along to the call centre, together with the cell towers physical location. (It still gives a lot of guesswork since the information is something like “I am at 2200 Main Street, and my westward pointing antenna can hear this phone. It ought to be somewhere within a mile or so in that general direction.” But at least it’s something.)

In some places, regulations are pushing for cell towers to be able to force phones to activate their GPS and track themselves. In some places, cell towers already force phones to activate their GPS occasionally. But there are still phones on the market that has absolutely no GPS in them, and the technical information from the cell tower always works, which makes it a convenient start.

imagine you are in one of a large number of adjacent rooms (phone network) . each room also has a manager (call router) , that knows the managers of the other rooms. usually when you want to make a call the manager would transfer you to the other rooms until you me the person you want to speak with. but in an emergency you need that help locally. so the manager also knows where the first-aid kits are located in his room an can send you there directly

When you make a phone call, it has to be routed through the phone system – so your mobile will connect to a specific cell tower, and your landline will be physically wired through a specific phone exchange.

When you phone 911 the phone system recognises you are calling an emergency number, and it notes which tower or exchange your call is coming from – this lets it route your phone to the appropriate dispatcher for your area who will then organise the response.

Not always “local” I saw a car getting broken into and called the police an officer showed up and told me that after crossing the intersection he was no longer within his jurisdiction and that he would pursue the perp but he couldn’t legally do anything and he’d call it into the local PD.

I’m a 911 dispatcher and can answer this. The way 911 works, it routes your call to whatever center is in charge of the first cell tower your phone hits. Once that happens the 911 system keeps refreshing and working on pinging the next 2 closest towers to get a very accurate location (I’ve seen as close as on the physical building to about 50 meters away). Now it’s very common for that first tower that your phone hits to not be in the actual jurisdiction that you’re in, that’s where the triangulation comes in, you’ll then be transferred to the correct agency/center. Now with landlines this is different. Landlines are programmed to ring to the proper agency when they are set up. I hope this answer helps.

Is this a system (localization) that is available in every country?

Phone systems use numbers as codes and for routing. For example, the US uses the North American Numbering Plan. 1+ a number indicates long distance. Then there are area codes (NPA). 212 is in New York, 404 is Georgia etc. Lastly you have NXX which routes you to a specific central office. The final 4 digits would indicate which piece of equipment was tied into the subscriber.

Now a lot has changed and that is over simplified but that’s the point of the sub. All that being said, they just program 911 to be picked up to route for emergencies using these same routing technologies. So whenever it picks up a call to 911 instead of sending it around the US it just routes it to a local 911 call center which from my experience is maintained by a local government authority.

Here in Australia we have to tell emergency services our state and town plus the closest crossroad, we’ll from all my ambulance calling experience, ive had to anyway

On top of the great answers, you would actually be amazed at the number of people who seem to think 911 is a nationally based thing. Like their call might be handled by someone in Wyoming or something if they live in Florida.

Get people who call all of the time and want to make sure I am familiar with the one major road that runs through the entire county. (I’m in a very rural place)

So. My friends mom is a 911 operator.

Here’s how it works according to her.

Your house phone is attached to an area code. When you call that, it connects to the service that does call routing. It takes your area code and patches you to the nearest call center. 99% of the time it’s local. But, like during the riots last year, it was so busy, a small county had been answering calls and reporting it to our Police.

Now cell phones use two methods. The E911 service which bases it on cellular triangulation and GPS when available, followed by the attached area code.

The same method works except the having tracking tools to locate an active call.

Some 911 is a call center for all services, other times its for Police who then route the call to Fire or EMS.

I’ll tell you a quick story: while living in Bryan, TX I had to call 911 multiple times and each time it went to the 911 center of college station, TX. Which was the city that was connected to Bryan, and each time they had to transfer me to the correct center. Which added almost a minute to the call because the “wires kept getting crossed”.

there are settings associated with your phone number in your service providers switch that control where the call goes to when you dial 911

They can systematically do this based on the PBX for landline or based on cell tower if its cellular.

911 on a cell phone now hits to the closest cell phone tower. Depending on where you are, it will hit with local police, your sheriff or your highway patrol.

But then it depends on how busy your area is. For example, if you’re calling 911 for a sideshow in a bigger city, most likely so will another 50 people. The first x amount of calls will go to the local police, cuz they’ll hit off those cell towers. But if all those lines are busy, cuz of too many callers, it’ll bounce till it finds an open line, and sometimes that’s with a different agency. When that happens we can usually transfer you over easy.

Thats why we say, if you already know someone’s calling, don’t call too thinking more calls means faster response. Just means your call is in the same line as another different emergency, and could be holding that person up.

Going back to the old days of simple telephone systems, when you dial a number, your phone is connected to a local exchange. The exchange receives the numbers in the order they are dialled, and routes the call accordingly. In the NANP (North American Numbering Plan), a “normal” number is 7 digits, with the first group of three digits identifying the exchange and the second group of 4 identifying the individual line from that exchange. When the plan was created, it was felt that no local area would need 1000 local exchanges, so it was possible to reserve certain numbers that would never be allocated to normal exchanges for specific purposes.

555, for example, is generally dedicated for dramatic use. It is never allocated as a real number, so film and TV can use numbers starting 555 for fiction, and there will never be a real phone with that number. 0 was reserved for the operator and 1 was reserved for accessing long distance trunk dialling, so no exchange starts with a 0 or a 1. The numbers x11 were all reserved for specific purposes in the local area. For example 611 was used for reporting faults with the phone system. If a number in this range is dialled, the local exchange will route it, locally, to the relevant service. When it was decided to adopt a universal emergency number, 911 had not been allocated for any other purpose, so it was free for this use.

Back in the day, if you dialled 911, it would route you from your local phone exchange to the local emergency services operator, based on the exchange to which the phone you are calling from is connected. Obviously with cellular phones things are a little more complicated, but basically the same principal applies: if you dial 911 from a cell phone, it routes you to the emergency operator that is local to whichever cell phone tower your phone is connecting to.

I’ll add on here, so typical cell phone triangulation is done using the 3 closest towers to get a “general” location. Phones now have a more information they can provide which 911 systems can take advantage of, pedometer, wifi hotspots, gps, things like that. Which make services like Rapid S.O.S work

For home numbers the carriers provide 911 with that information via ani,ali information. Where as with cell phones a clearing house is involved. I would give the name but it changes often.

With voip providers it’s whatever information you put in with the company (think vonage,skype) so keep that up to date.