e911

e911, commonly written as E911, stands for enhanced 911. It refers to a set of systems and procedures that automatically convey to emergency responders the caller's telephone number and location when a 911 call is placed. E911 is widely deployed in North America for traditional landlines, mobile networks, and increasingly for Voice over Internet Protocol (VoIP) services, with the aim of reducing response times and improving dispatch accuracy.

On landlines, the network uses Automatic Number Identification (ANI) and Automatic Location Identification (ALI) to link the call to the subscriber's registered address, which is displayed to the answering public safety answering point (PSAP). For wireless and VoIP, E911 involves additional location data delivery. Wireless E911 has two phases: Phase I provides the calling party's cell site (the tower) to the PSAP, while Phase II delivers a more precise geographic location, typically derived from GPS, device sensors, or network-based positioning, with typical accuracy in tens to hundreds of meters.

VoIP-based E911 requires the service provider to associate the user's service address with the account and, where possible, provide device location to PSAPs. If the user is mobile, or if the registered address does not reflect the caller's actual location, location data may be less accurate or not available, potentially leading to misrouting.

Regulatory framework: In the United States, the Federal Communications Commission (FCC) imposes E911 requirements on wireless carriers and sets standards for location data delivery. Canada and other jurisdictions have implemented similar requirements. Privacy and security considerations apply to location data, and access is restricted to emergency responders and authorized personnel.