Scott Pantall » PSAP

What happens when I call 9-1-1 from a cell phone?

Scott Pantall — Sat, 26 Dec 2009 10:45:37 +0000

You’ve found yourself in an emergency. You’re in a situation where you’re injured, someone else is injured, there is a good chance of someone getting injured or someone is trying to injure or kill someone else. So what do you do? You pull out your cell phone, you flip it open, slide it open or touch the screen and you call 9-1-1.

When The Dispatcher Answers The Phone…

Now depending on your cell phone carrier, the the area you’re calling from and other conditions, you’re 9-1-1 call will come across to the dispatcher as either phase 1 or phase 2.

Phase 1 – The dispatcher receives the cell-phone number of the 9-1-1 caller and the location of the cell-tower antenna the phone is using. The call is routed to the PSAP nearest to that tower. Here is an example of what the dispatcher sees on our map:

This map shows that the caller was somewhere south-west of the cell tower at 3455 S. Corona. This information may be helpful if you make a call in a rural area, but in an area like the densely populated area like the one pictured, it’s not much help at all. The dispatcher is still going to depend on you to tell them where you are. The only other information the dispatcher receives is the name of your cell phone carrier.

Phase 2 – The dispatcher receives the cell-phone number and the location of caller to an accuracy of 50 to 300 meters depending the type of location system being used by the wireless provider. The call is routed to the PSAP nearest to that location or nearest to the cell antenna in use. Here are 2 examples of what the dispatcher may see on a phase 2 call:

The first map shows a call from a phase 2 phone with a 182 meter confidence radius. While the caller was probably on Vassar between Lafayette and Humboldt, the caller could be anywhere within that red circle. This was probably caused because the caller was moving in a vehicle, but the dispatcher can not assume your location. The dispatcher is still going to depend on you to tell them where you are.

The second map shows a call from a phase 2 phone with a 9 meter confidence radius. This caller was almost definitely in the exact location shown on the map. Technology isn’t perfect though. The caller could’ve been in the building north of the phone icon, but the map was just a bit off. Once again, the dispatcher is going to depend on you to tell them where you are.

Just like with phase 1 calls, the only other info dispatchers receive is the carrier of the cell phone.

How Does The Call Get To The PSAP?

A phase 2 cell phone will attempt to figure out where it is when the 911 call is made. If the cell phone uses GPS, it’s considered handset-based and uses satellites to find out where it is. If the phone uses cell phone towers, it’s considered network-based. Both techniques uses a process called trilateration to come up with a location. If the process doesn’t work, the call will come in as phase 1.

Conclusion

As cool as technology gets, we will never fully depend on it to help people. An icon on a computer can help find a caller and we will depend on that information if we absolutely have to depend on it. There are also times when a caller doesn’t have a good idea on their location. A good mix of technology and people can help dispatchers get help to you as fast as possible.

Up Next: What happens when I call 9-1-1 from a VOIP phone?

Resources

http://people.howstuffworks.com/9-1-13.htm

What happens when I call 9-1-1 from a land-line?

Scott Pantall — Wed, 23 Dec 2009 10:43:58 +0000

Let’s say you’re in a situation where you’re injured, someone else is injured, there is a good chance of someone getting injured or someone is trying to injure or kill someone else. You’ve successfully found yourself in an emergency! So what do you do? You call 9-1-1.

If the phone you use to call 9-1-1 is plugged into a wall with a phone cord, you’re using a land-line. I’ll explain it a little more for those under 25 years old: If the phone your using doesn’t text, surf the internet, play music or play games, you’re probably using a land-line.

93% of the counties in the country operate E9-1-1 or Enhanced 9-1-1 service. So when you call 9-1-1 from a land-line phone, here’s what’s most likely going to happen:

Your call goes to a special 9-1-1 switch which then gets subscriber and location information for your phone number from the MSAG (Master Street Address Guide). Then your call, along with the data from the MSAG go to the PSAP (Public Safety Answering Point) that your address lists to.

When The Dispatcher Answers the Phone…

This is the information we receive:

Phone number that is placing the call
Class of phone (Residential, Business, Switchboard, Payphone, etc.)
Subscriber name
Address
Telephone Company

This is great! Before anyone says a word we know, with 99% accuracy, your phone number, your address, and the name of the household or business you’re calling from. We’re still going to ask you for your location, your name and your phone number though because 99% accuracy is not 100% accuracy.

This is what we see on our map:

That red phone shows us what address you’re calling from. Some of the information I mentioned above is shown in this program. The rest of the information goes to another program.

Conclusion

If you call 9-1-1 from a land-line telephone we will more than likely know where you’re calling from. We’re still going to ask you where you are because as someone who works at a desk with 5 computers attached to it, we have a healthy mistrust of technology.

Up Next: What happens when I call 9-1-1 from a cell phone?

Resources

http://people.howstuffworks.com/9-1-12.htm

How Does 9-1-1 Work? – Introduction

Scott Pantall — Tue, 22 Dec 2009 10:43:30 +0000

Since I have a month off between semesters at school, I’ve volunteered to help my co-workers understand the information we receive on our maps when a 9-1-1 call is made. But then I thought, why not help everyone understand what happens when you call 9-1-1?

What is 9-1-1 and how did it start?

I don’t really feel like I’m giving good educational value unless I throw some in some history. In 1957, the National Association of Fire Chiefs recommended use of a single number for reporting fires. Then in …..zzzzzzzzzzzzzzzzz… If you want to know the history of 9-1-1, go here¹. I’m not going bore you with a history lesson if you don’t want it.

What are the different ways dispatchers received 9-1-1 calls?

The information automatically received by the dispatcher depends on what kind of phone is used to call in…

Land Line: This is a phone that’s plugged into a wall that’s plugged into the phone system.
Phase 1 Cell Phone: A cell phone that provides the dispatcher with the telephone number and carrier of the originator of a wireless 911 call and the location of the cell site or base station transmitting the call².
Phase 2 Cell Phone: A cell phone that provides all the information that a Phase 1 cell phone provides plus a more precise location specifically, the latitude and longitude of the caller. This information is accurate to within 50 to 300 meters².
VOIP: Stands for Voice-Over-Internet-Protocol. This is a fancy way of saying “Using your computer as a phone and the internet as the phone system.”

If you’re still a little confused, don’t worry. We’re going to go over this stuff in much more detail in later posts.

Glossary

I’m including a glossary in the introduction post because becoming familiar with the terms now will help you read the following posts. I am going to try really hard to make this as non-technical as possible, but I’m willing to face the idea that I may fail spectacularly at that.

MSAG - Master Street Address Guide: Are you a conspiracy theorist who believes there’s a company based in Longmont, Colorado that has a giant database that links almost every land line telephone number to a subscriber, an address and a detailed description of the location of that address? If so, congratulations! You’re right! The MSAG database is how dispatchers know where you’re calling from when you call from a land line.
PSAP – Public Safety Answering Point: This is the catch-all term for the place where 911 dispatchers receive your call. A PSAP can either belong to a city, county or state-wide entity. There are also regional PSAPs that dispatch for multiple agencies. The important thing to remember is that these are where your 911 call goes.
Trilateration – Finding the distance between 3 different points to figure out your own location. GPS devices use satellites as their points. Network based phones use cell phone towers as their points. For a visual example, check out this site³.

Up Next: What happens when I call 9-1-1 from a land-line?