E911 (enhanced 911) is a technology that's designed to give ordinary landline telephones the ability to transmit critical location data quickly and transparently, as well as to provide accurate emergency-calling capabilities to nontraditional-telephony devices such as mobile and VoIP phones. The technology automatically connects callers to the closest PSAP (public-safety answering point), the emergency-service dispatch centers that respond to 911 calls. There are more than 6,000 primary and secondary PSAPs across the U.S.

The need for E911 technology spiked when devices that don't use a dedicated phone line began gaining popularity. A mobile-phone user, for example, can be located virtually anywhere, making it impossible for a service provider to determine the location of the nearest and most appropriate PSAP. VoIP subscribers, on the other hand, often use phone numbers assigned to locations many miles away from their actual physical presences — sometimes even in other countries — also making it often impossible for service providers to supply an appropriate PSAP connection.

Landline E911
E911 became a reality more than two decades ago when the technology debuted on landline phones. All landline phones send an ANI (automatic number identification) signal to the network. Originally used to help carriers create accurate long-distance billing records, the ANI consists of eight digits: seven are the caller's local number, while the eighth digit represents a regional area code.

Utilizing ANI data, a PSAP can conduct a reverse-directory search to request and receive the caller's physical address. As a result, the PSAP doesn't have to depend on the caller for location and callback information. The dispatcher can instead focus on helping the caller through the crisis, while quickly passing along relevant information to the appropriate public-safety authorities.

Wireless E911
Facing increasing pressure from mobile-phone customers for an effective, reliable 911 calling system, the Federal Communications Commission began taking steps in the late 1990s to force mobile carriers to adopt a wireless E911 strategy. The FCC deployed its E911 plan in two phases. In 1998, Phase I required carriers to deploy an E911 service that could identify the originating phone numbers of all 911 calls, as well as the location of the associated cell tower to within one mile. In 2001, Phase II mandated every mobile carrier offering service within the U.S. to provide either a handset- or network-based location-detection capability. The ALI (automatic location identification) service had to be able to determine an E911 caller's location by the geographic position of the mobile phone within 100 meters, and not simply by the location of the associated cell tower. This is usually accomplished by triangulating the signals of three or more nearby cell towers.

VoIP E911
Like mobile-phone users in the 1990s, VoIP subscribers in the early 21st century began requesting landline-equivalent 911 calling capabilities on their phones. Demands from the public, the media and lawmakers for VoIP E911 service quickly mounted after several highly publicized cases in which crime victims were unable to call for police help because their VoIP phones lacked 911 calling capabilities.

In 2005, the FCC began requiring VoIP service providers to offer localized E911 service to their customers. Under current FCC rules, all interconnected VoIP providers must automatically supply E911 service to all of their customers as a standard, mandatory feature without customers having to specifically request this service. VoIP providers may not allow their customers to "opt-out" of E911 service. VoIP providers must transmit each E911 call, as well as a callback number and the caller's registered physical location, to the PSAP.

Note that in this case the word 'interconnected' is very important. Virtual, soft-client-only VoIP services like Skype Ltd. specifically do not provide E911 services precisely because the services are meant to work from anywhere, and currently it is not possible to automatically deduce the actual location of the call. For example, a Skype user could be calling from a public Internet terminal at a cafe or a library rather than his or her home. In contrast, most residential-VoIP services use a specific VoIP router that is typically located at a single physical location.

VoIP E911 has proven to be problematic, however, since users may be either stationary or mobile, and they can often connect to the Internet in a variety of different ways. Although the FCC requires VoIP service providers to collect location information from their customers, this approach is imperfect. If a VoIP subscriber uses the service from a remote destination, for instance, the carrier will continue to route 911 calls to the registered location, even if the site is several thousand miles away from the place where the emergency is happening.

A power outage can also cause VoIP E911 to fail, since the technology requires Internet access, which depends on routers and other devices that use electrical service. As a result, many public-safety agencies recommend that VoIP customers keep a traditional phone line, in addition to their IP telephony service, in order to retain access to emergency-calling services during a power outage.

Nevertheless, residential-VoIP service providers now do offer E911 service, and it should work for calls made from the residence.

John Edwards