E911 FAQs

E911 Frequently Asked Questions

What is E911?
E911 (Enhanced 911) is a service that automatically displays the telephone number and physical location of the 911 caller on the emergency operator’s screen. This is unlike Basic 911 service, where the distressed caller has to tell the operator where he or she is calling from. E911 is crucial in circumstances where the caller cannot communicate his or her whereabouts, as it ensures the operator is still able to send emergency response services to the correct location. E911 also involves Selective Routing, whereby the 911 call is routed to the appropriate PSAP (Public Safety Answering Point) based on the caller’s physical location.

What is an E911 location?
An E911 location is the dispatchable address where a 911 caller is located. It includes the caller’s civic address, but may also include details such as the floor, wing, room, or office of the caller to allow arriving first responders more quickly locate the source of the emergency.

What is a Public Safety Answering Point (PSAP)?
A Public Safety Answering Point (PSAP) is a dispatch center staffed by emergency operators, which receives 911 calls and dispatches fire, police, or medical services, depending on the nature of the emergency. PSAPs are generally controlled at the city or county level.

What is VoIP?
VoIP (Voice over Internet Protocol) is a communications technology for placing telephone calls over Internet Protocol (IP) networks, such as the Internet. Instead of sending phone calls over a physical phone line, VoIP works by converting voice calls into packets of data and sending them over an IP network. Because VoIP calls bypass a large part of the PSTN (Public Switched Telephone Network), VoIP phone service offers significant costs savings, especially for long distance calling. VoIP also offers a high level of mobility to its users: a VoIP phone number is not tied to a physical phone line, but rather can be plugged in anywhere there is an adequate IP connection.

What is an IP-PBX?
An IP-PBX (Private Branch Exchange) is a VoIP telephone system for private enterprises. The IP-PBX connects an enterprise’s many extensions to the PSTN, but it also connects phones within the enterprise network, even those found in different regional offices. This allows enterprises to save on long distance charges, as inter-branch calls use the company data network and bypass the PSTN entirely. As IP phones operate over the enterprise data network, they can also support various communication applications such as directories or email clients.

How does E911 service work for the PSTN?
With traditional phone service (PSTN), a telephone number is tied to the phone line’s physical location. For E911 purposes, this phone number is associated to the physical location in the local exchange carrier (LEC) regional Automatic Location Identification (ALI) database. Since the phone number is static, the phone number only needs to be associated to its physical location in the ALI database once. When 911 is dialed, the regional ALI database ensures the caller’s location information is displayed on the PSAP emergency operator’s screen, along with the caller’s telephone number.

Why do VoIP and IP-PBX systems pose problems for traditional 911 services?
Unlike phones using PSTN service, VoIP phones and soft phones are nomadic and can work from anywhere with connectivity to the Internet or the company network. Thus, the traditional association of a phone number to a single physical location in a regional ALI database may be problematic. For example, a VoIP phone could move from Florida to New York and still keep its Florida telephone number.

This poses a problem for call routing as, based on the caller’s telephone number, the 911 call will go to the Florida PSAP rather than to the PSAP closest to the caller’s actual location in New York. It also means that the location associated with the VoIP number in the ALI database may not reflect the phone’s current whereabouts.

Enterprises with centralized IP phone systems also experience problems with 911. When a branch office connects to an IP-PBX located at the main office, 911 calls will be transmitted to the PSAP serving the main office instead of going to the PSAP serving the branch office. In addition, because IP phones can move around easily on the company network while keeping the same phone number or extension, keeping track of each phone’s correct, up-to-date location information becomes extremely difficult. Advanced mobility features such as Shared Line Appearance and Extension Mobility only add to the difficulty in pinpointing a caller’s whereabouts.

What are ANI and ALI?
ANI (Automatic Number Identification) is the automatic display at the PSAP of the telephone number associated with the line which called 911. Each telephone number and the physical location to which it corresponds are stored in an ALI (Automatic Location Identification) database, managed by the local exchange carrier. In a 911 call, the PSAP uses the ANI to retrieve the caller’s physical address from the ALI database. Additionally, the ANI acts as a callback number should the PSAP lose its connection to the distressed caller. Both ANI and ALI are key capabilities of E911 service.

What is the difference between a regional ALI database and a national ALI database?
With traditional E911 service, ALI records are stored in regional ALI databases, and are usually administered by the local exchange carrier (LEC). When a phone’s location changes, the regional ALI database must be revised with new location information which can take up to 48 hours to update.

Due to the nomadic capabilities of IP phones, it can be difficult to ensure that the regional ALI is up-to-date. Whereas traditional telephone numbers are static, IP phones can be moved easily, forcing the user to notify a network administrator, who in turn must contact the LEC to update the phone’s location in the regional ALI database. Unfortunately, this process takes time to implement, and may be forgotten entirely by the user.

Additionally, IP phones can relocate to regions served by different ALI databases entirely. A VoIP service provider or enterprise would then need agreements with each LEC to update different regional ALI databases as phones move around the country.

Ultimately, it is difficult for regional ALI databases to stay current with nomadic VoIP users, and there is no guarantee that the VoIP caller’s accurate location information will be available in a crisis.

To ensure up-to-date ALI for all VoIP users, regardless of location, West’s Safety Services provide a single national ALI database (nALI) that maintains records from all 50 states and Canada. It includes real-time address validation and provisioning, ensuring that the location data associated to a VoIP phone is correct and can be properly interpreted by the local PSAPs. For enterprises with branch offices in different regions, the nALI eliminates the complexity of managing records in different regional ALI databases, simplifying administration and reducing costs.

What is an ERL?
An Emergency Response Location (ERL) is a specific geographic location to which a 911 emergency response team may be dispatched. For increased accuracy, to reduce response times, or to meet state E911 legislation, the PBX administrator may break down an organization’s campus or buildings into several different ERLs. This allows the organization to provide the PSAP with a 911 caller’s precise location, rather than simply the organization’s main billing address.

For example, each building within a campus or floor/wing of a building may be considered its own ERL; within a given ERL there may be several phones or extensions. In some states, regulations require that organizations maintain ERLs of a specific size or identifiable area (e.g. one ERL per 1000 square feet or per floor).

What is an ELIN?
An Emergency Location Identification Number (ELIN) is a ten digit DID number purchased from the local exchange carrier (LEC), and is one way for organizations to provide specific location information to the PSAP for a 911 call. First, enterprise administrators assign an ELIN to each ERL; one ELIN can be used for many phones within an ERL, but each ERL requires at least one unique ELIN. This mapping of ELINs to ERLs must then be loaded into the regional ALI database.

During a 911 call, the ELIN takes the place of the caller’s telephone number as the ANI and is used to route the call to the appropriate PSAP. The PSAP uses the ELIN to query the ALI database and retrieve the caller’s location (i.e. ERL). Should the caller be disconnected, the PSAP can also use the ELIN to call back the extension directly (which requires a temporary mapping of the 911 caller’s number to the ELIN), bypassing the PBX attendant or auto-attendant.

What is PS-ALI service?
PS-ALI (Private Switch Automatic Location Identification) is an E911 solution for PBX systems. Generally, when a 911 call is made through a PBX, only the enterprise’s main address is sent to the PSAP. For organizations spread across a large building or campus environment, it can be very difficult for emergency responders to find the distressed caller based on the main address. By purchasing a PS-ALI account from the local exchange carrier, enterprises can populate the regional ALI database with more specific location information, using ELINs and ERLs.

West’s Safety Services are PS-ALI compatible, allowing organizations to send automatic updates to the regional ALI database. We can also eliminate the need for PS-ALI accounts altogether with its national ALI database.

What is a VoIP Positioning Center?
A VoIP Positioning Center (VPC) is an IP-based service that acts as a replacement for PS-ALI. It allows organizations to upload all their phone records and ERLs to a single national ALI database, rather than to the local exchange carrier’s (LEC’s) regional ALI databases. Unlike PS-ALI, a VPC solution is not limited to the use of ELINs to identify the location of the caller. While a VPC supports the use of ten-digit numbers, the locations of 911 callers may also be associated to a variety of other unique identifiers (MAC, IP, extension) in the national ALI database. This eliminates the need to purchase ELINs from the LEC.

The VPC national ALI database also provides instantaneous ERL validation and provisioning, eliminating the lag time associated with updating PS-ALI records. This means that a VPC solution is better suited to the nomadic nature of VoIP telephony than PS-ALI solutions.

West’s VPC solution follows the recommended National Emergency Number Association (NENA) i2 architecture for the delivery of IP-based 911 calls to the PSAP.

What is Next Generation 911?
Next Generation 911 (NG911) refers to an all-IP E911 network that goes beyond voice calling. With NG911, callers will be able to send text, images, video, and data to the PSAP, which is IP-enabled to receive multimedia communications. NG911 is currently in its initial stages, with only a handful of PSAPs actively beginning to implement NG911 capabilities in their call centers.