Since 1968, the U.S. has had a nationwide 911 emergency system. The system stayed the same for decades, but the emergence of mobile phones and voice-over-IP (VoIP) has required a retooling of the emergency system. Enter E911.
All wireless and VoIP providers that connect to the PSTN network—substitutes for a traditional telephone, basically—are required by the Federal Communications Commission to provide E911 access to emergency services.
E911 differs from traditional 911 service in that it must deal with the mobile nature of callers; unlike a landline, cell phones and VoIP calls cannot be tied to a single geographic location.
In the case of VoIP, E911 works by having VoIP service providers use a database of addresses that its subscribers provide. That information, in turn, is used to decide which 911 call center the call is sent to.
Helping pin down VoIP callers to their actual geographic location are two services: a voice-positioning center and an emergency services gateway. The voice-positioning center maintains the database of subscribers' self-reported addresses and determines where to route the emergency call. An emergency services gateway converts Session Initiation Protocol (News - Alert) (SIP)-based VoIP calls to the time division multiplexing signaling used by the existing 911 system.
For wireless phones, a workaround was developed where a call is sent to the public safety answering point, passes through a mobile positioning center that gets the cell and sector ID from the wireless carrier. It then decides where to send the call.
With analog phones being phased out entirely for an all-IP-based phone network, a new version of E911 will avoid the workaround by baking location services right into the system.
The new system will consist of emergency services IP networks, IP-based software services and applications, as well as databases and data management processes that are interconnected to the public safety answering point premise equipment. This system provides location-based routing to the appropriate emergency entity and has advanced features such as the ability to route calls to call centers in other geographic locations in case of natural disaster.
It can also incorporate other available data elements and business policies to augment public safety answering point routing and delivers geodetic and civic location information and the call-back number.
One of the biggest challenges with this system is that self-reported location information is unreliable, and voice-positioning centers and emergency service gateways are expensive. So service providers sometimes develop workarounds that are imperfect at best.
A second big challenge is funding the upgrade to the 911 system.
Congress historically puts up a grant that states match, but Congress is in no mood right now to hand out grants.
Edited by Rory J. Thompson