Super Bowl Sunday 1999 was anything but super in New York City, and not only because the Broncos had knocked the Jets out of championship contention just 14 days earlier. For about an hour on Jan. 31, callers to 911 looking for help heard a busy signal instead of an emergency operator. One person...
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Super Bowl Sunday 1999 was anything but super in New York City, and not only because the Broncos had knocked the Jets out of championship contention just 14 days earlier. For about an hour on Jan. 31, callers to 911 looking for help heard a busy signal instead of an emergency operator. One person died of a heart attack, and inquiries are being made into what effect, if any, the outage had in this case.
In the wake of more recent incidents, concerns about the system continue to appear in the press. Both the public and public safety have come to rely on 911 for more than 30 years, a reliance that is well founded. Over one quarter of a million 911 calls are placed in the United States every day, and the overwhelming majority of them connect correctly. But what happens when they don’t? How frequently does 911 fail, and for what reasons? Can anything be done to make the system more reliable? How can emergencies be handled where 911 is out of service? In other words, what happens when the emergency number goes down?
what the caller needs
To answer these questions, it must first be noted that 911 is, in reality, just a telephone number. Although special care is given to improve its serviceability, 911 depends on many of the same resources as a standard telephone number. In order to dial 911 from a conventional telephone, a caller must have dial tone and a working telephone device. This means there are no interruptions in the cable that connects the caller with the telephone company central office, that the central office is functioning properly and that the caller has plugged an operating telephone into his or her end of the line.
The reverse is true for 911 to be able to answer – the central office must properly route the call, the circuits between the public safety answering point (PSAP) and the central office must be intact, and the PSAP equipment must be working. While this may sound complicated, it is only the beginning.
A caller who is located in another community or a different part of town from the 911 facility is likely to be served by a different central office, and perhaps even by a different telephone company. This means that in order for the call for help to be completed, both central offices must be operational, and the connection between the two facilities functioning properly.
Enhanced 911, which provides automatic number identification (ANI) and automatic location identification (ALI), adds further dependencies. Because the data used to populate the address and telephone number displays is usually stored in a remote database, every call in an enhanced 911 system generates a request to retrieve the appropriate information. The telephone company computers that maintain ANI and ALI serve large areas, and may not even be located in the same state as the caller. If the link to this master street address guide (MSAG) fails, the call will still be connected, but the telecommunicator will not know its origin.
when everything works
When all these things happen flawlessly, and most times they do, both voice and data are delivered to the PSAP. But in order to be completed, the call still must be routed through the premise equipment to be answered. This equipment can consist of a variety of devices such as an in-house telephone switch, ANI/ALI controller, automatic call distributor, or systems that integrate telephones and computers.
Despite the complexity inside the dispatch center, many 911 outages result from failures in the field that affect large segments of the public network. Perhaps the most notable of these incidents occurred in Hinsdale, IL, in May 1988. A fire in the central office of this suburban Chicago community cut off all telephone service to 500,000 customers. Recovery took the better part of a month.