How does 911 call routing work?

Emergency calls placed from mobile phones used to be harder to track, but tech improvements plus new federal regulations are making 911 routing more consistent.
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Francis Scialabba

· 4 min read

Cell phones have simplified so many parts of our lives. Need to schedule a ride? There’s an app for that. Need to deposit a check? Just snap a pic. Need to check in with your doctor? Book a video appointment.

But there’s one major thing they’ve complicated: emergency call response times. Now that people in distress can dial 911 from anywhere, mobile carriers and public safety officials have had to work out different systems for quickly identifying the precise locations of callers. As numerous stories show, in an emergency, every second matters.

Here’s how a 911 call makes it from the scene of an emergency to first responders.

Modern methods

Let’s start with a scenario: You’re at the scene of a car accident. You reach into your pocket for your cell phone and dial 911.

“At the time that the call is placed, your phone will use location services, sort of a special flavor of location services that’s for emergency calls,” Brandon Abley, CTO of the National Emergency Number Association (NENA), told Tech Brew. “It’s built into Apple and Google devices and will send the best available location it has for the purposes of routing.”

This “special flavor” can include aggregating data points like nearby wi-fi networks and third-party data from the caller’s phone to help pinpoint their location, he said.

The initial location that’s transmitted to the 911 system has to be somewhat precise under federal regulatory rules that went into effect in January: within roughly one-and-a-half football fields of the caller with 90% certainty. The phone will later send an updated location that’s within about half a football field of the caller, and that location is typically used to dispatch first responders to the site, Abley said.

Industry improvements

Using cell phone location data to pinpoint a caller’s whereabouts is a relatively recent development, according to April Heinze, NENA’s chief of 911 operations.

Under the status quo, a mobile 911 call pings the nearest cell tower, which then transmits the call to the public safety answering point (PSAP) associated with that tower. However, that dispatch center might not actually be the one closest to the caller, which can lead to confusion and lost time.

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“You get a lot of transfer calls because of that,” she told us. “Location-based routing is going to be…more accurate and go to the more appropriate 911 center.”

As Tech Brew previously reported, mobile carriers are starting to roll out location-based routing, signaling that the technology is advanced enough to implement industrywide. The Federal Communications Commission voted to require the implementation of this advanced method in January.

Other 911 sources

“Realistically, close to 90% of 911 calls originate from mobile devices,” NENA CEO Brian Fontes said, but a small percentage still come from landline phones, multiline phone systems commonly found in offices, and voice over internet protocol (VoIP) sources—such as calls placed over WhatsApp or Microsoft Teams.

While dynamic location tracking is becoming more common for VoIP systems, static addresses associated with these systems can contain typos or be entered in ways that the 911 system doesn’t recognize. The lines can also be tied to “a static location of the home base of that phone system, as opposed to this precise location of where that phone is,” Heinze said.

However, she noted that instances in which first responders struggle to locate callers from various devices are becoming less common due to regulatory improvements. For example, the FCC implemented rules requiring more precision in not just horizontal locations, but vertical locations as well. This can help pinpoint where a caller is in a multi-story office building.

Another encouraging aspect? As phones get smarter, so will the data that’s passed onto first responders.

“It’s not just the 911 center or just the carrier’s network, per se, but it’s also intelligence that’s being built in the handset,” Fontes said. “Additional data-mapping capabilities associated with that call as it moves through the process and into the center allows for greater location accuracy.”

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