What is Enhanced 911 (E911)?

A 911 call picks up two pieces of data on its way to the 911 center. One is a number to call back. Automatic Number Identification, or ANI, identifies the calling party, and the FCC's definitions say it may be used as the callback number. The other is the location. Automatic Location Information, or ALI, tells emergency services where the caller is. For internet-based phone service, 47 CFR 9.11 requires that location to be available to the 911 center from or through the ALI database.

The location also steers the call. The same rule sends a VoIP 911 call to the 911 center that serves the caller's dispatchable location, so a stale address can put the call in front of dispatchers in the wrong jurisdiction.

That location comes from one of two places: a record stored for the phone or number, or the network the device is connected to when it dials. A stored record shows whatever was last typed into it. A desk phone with a manually entered record that moved from the second floor to the fifth in March keeps reporting the second floor until someone updates the entry.

Some devices can't be located automatically, such as a softphone on a home network. For that kind of non-fixed service, the rule lets the provider use a Registered Location the user supplied, use alternative location information, or route the call to a national emergency call center.

47 CFR 9.16, the rule that carries out Kari's Law, covers multi-line phone systems manufactured, imported, first sold or leased, or installed after February 16, 2020. People using a covered system must be able to reach 911 "without dialing any additional digit, code, prefix, or post-fix." That means no 9 for an outside line. Where the system can be configured for it without hardware or software changes, it also has to alert a central location, on site or elsewhere, where someone is likely to see or hear the alert. The notice says a 911 call was made, and it includes a callback number and the caller's location where those are technically feasible to provide.

A cloud PBX service counts as a multi-line telephone system just as a PBX in a wiring closet does, because the FCC's definition names network-based and premises-based systems such as Centrex and VoIP. The February 16, 2020 cutoff applies to hosted and on-site systems alike.

Section 9.16 then sets a location duty for each kind of device, and the duty depends on whether the device can move. The FCC describes a fixed device as one the user cannot readily move. An automated location is one generated without any action by the caller.

The same section bars anyone from managing or operating a covered system unless it is configured to convey the required location. The FCC's definitions describe the manager as the entity that distributes lines and assigns telephone numbers after installation. In an office that is usually the IT team or an office manager, so the location records need an owner inside the business after the provider finishes the install. The table below shows what each kind of device owes.

Atlantech sells E911 two ways, and its explanation of the two shows the choice any business has to make. With static E911, one address is assigned to each phone number. It fits a small number of phones in one fixed location where the street address alone finds the caller. The record holds the street address without a floor, suite or room, and someone updates it by hand when a phone moves.

With dynamic E911, which Atlantech also calls nomadic, the location is configured on each LAN switch and Wi-Fi access point. When a phone connected to that equipment dials 911, the location travels with the call in PIDF-LO headers, a standard format for location data. The record can carry a floor, suite or room, and it follows the phone to whichever switch or access point it joins.

Dynamic E911 asks more of the network. The equipment has to support PIDF-LO and be configured correctly, the network gateway needs a valid address, and the firewall or NAT device has to pass the headers unaltered. A multi-floor office, or one where softphones and Wi-Fi handsets roam, takes on that work because responders need the floor.

Suppose a 60-person firm leases floors two through four of an office building. Staff use Microsoft Teams softphones on laptops, and about a third of them work from home on any given day. The firm buys its calling service from Atlantech and sets up dynamic E911.

IT starts by assigning a floor and an area to every LAN switch and Wi-Fi access point. For Teams, those locations live in Microsoft's Location Information Server, where subnets, switch ports and access points are tied to civic addresses in the Teams Admin Center or PowerShell. Atlantech provisions the addresses from the customer's data and can add places such as a floor, suite or room. At the same stage, the firm confirms with Atlantech that 911 goes out from every extension with no prefix. It also asks which number the 911 center receives when an extension without its own direct number dials 911. A dispatcher uses that number if the call drops, so it should ring somewhere a person will answer.

A laptop at home is off the mapped office network, and Atlantech advises against adding home networks as trusted addresses because an internet provider can change them. What a remote user experiences depends on the Teams calling product. With Direct Routing, a 911 call from outside the corporate network goes to a 24/7 national emergency call center, which transfers it to the right 911 center. With Operator Connect, off-premises users are prompted to confirm their current address, and that address is validated and used for routing. Tell remote staff which of the two they'll meet, so it doesn't surprise them in an emergency.

Then the firm turns on notification. Atlantech's E911 notification comes with its voice service at no extra charge. The firm emails support@atlantech.net, asks to enable it and names the address that should receive alerts. It accepts a single address, and that address can be a distribution list.

Testing is done by dialing 933. Atlantech describes a 933 call as a test that the correct physical address reaches the 911 center. Place one from a phone on each floor and one from a softphone on Wi-Fi, and compare the address the test returns with where the caller is sitting. Each 933 call also triggers the notification email, so the same test shows whether the alert reaches a person and what it contains. Atlantech's Operator Connect onboarding includes guided E911 validation and test access to a 911 center.

After launch, the work is keeping the records current. A softphone that changes floors reports the new floor as long as the access point it joins is mapped. A new or relocated switch or access point needs its location entered before anyone uses it, followed by another 933 test. Atlantech recommends testing 933 at least once a year, and a network change is a reason to test sooner.

The firm names one person to update location records and run the 933 test after each move.