It's not like the old movies, where the cops had to keep you on the line for a minute or more to trace your call. The 911 system was designed to identify immediately who the caller is and where they are calling from so that the 911 call is automatically routed to the closest jurisdiction:
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First, the public telephone system already identifies the telephone number for every call placed on the network in order to properly bill the subscriber each month. When a 911 call is placed, this phone number is identified through what is known as Automatic Number Identification (ANI) and passed to the 911 network.
Second, telephone companies maintains a subscriber database for every assigned telephone number, the subscriber's name, physical address for a wired phone account, and billing information. The address is therefore identified through what is known as Automatic Location Identification (ALI).
Third, the telcom provider and the pubilc safety agencies collaborate to create an E911 Master Street Address Guide (MSAG), a database that cross-references every assigned telephone number, subscriber's address and the block number ranges for every street, in every jurisdiction served by the telephone company. This allows the phone company's computer to match the caller's location with its public safety jurisdiction, and then route the call to the appropriate communications center.
Note that "pubilc safety jurisdiction" may be different than the caller's political jurisdiction. That is, the caller may live in Oaktown, but their 911 calls are handled by Maple City, or Elm County. The MSAG is pre-programmed to take 911 calls and route them to the proper Public Safety Answering Point (PSAP) that will then dispatch emergency personnel in response to a 911 call.
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Need more to ponder...
ADG