Within the United States and Canada, 911 is the official national emergency number; calls to 911 are directed to the most appropriate Public Safety Answering Point (PSAP) dispatcher for local emergency medical, fire, and law enforcement agencies via specialized infrastructure. Enhanced 911 (E911) systems automatically show the PSAP a calling number telephone number and location for wireline phones using the Automatic Location Identifier (ALI) database (maintained specifically for PSAP use, it translates a phone number from Automatic Number Identification (ANI) to a physical location). In 1996 the FCC established the wireless E911 program; which, when fully implemented, will provide a PSAP with a precise location for wireless 911 calls. Figure 15.2 is an example of an enhanced 911 system.

In this example, the ALI Location Database translates an ANI identifier into a physical location that can be used for emergency dispatch.

Given all the progress around E911 it may come as a surprise to you that 911 failures due to incomplete VoIP E911 design have led to several high-profile, preventable deaths (accompanied by lawsuits and demand for increased regulation). In fact, the rise of VoIP carriers that are interconnected with the PSTN has been accompanied by two massive breakdowns in E911 capability that eventually forced an urgent VoIP E911 order from the FCC in June, 2005. The first involves VoIP carriers not having adequate interconnection arrangements to pass E911 calls. But the second is the more interesting problem. What happens when you can register...