calls are routed based on the calling party number, not the called party
number. If an emergency call is disconnected for some reason (for example, the
caller hangs up), the PSAP needs to be able to call back the emergency caller
using the calling party number. The PSAP might also want to call back to obtain
updated information after ending an emergency call normally.
Responder converts a caller extension to an emergency location identification
number (ELIN), and this number is used to route the call and to enable PSAP
callbacks. Emergency Responder reuses the same set of numbers, and keeps track
of the internal extension of the phone from which the call was made for up to
three hours. When there is no active association of an ELIN to an internal
phone extension, Emergency Responder routes calls to that ELIN to on-site
To set up
the ELIN numbers, you must first obtain direct inward dial (DID) numbers from
your service provider. Because you must pay for each number, you might want to
limit the number of DIDs you obtain to two or three per ERL. The DIDs must be
unique for each ERL.
Responder reuses the ELIN numbers assigned to an ERL if necessary. For example,
if you configure two numbers for an ERL, and three emergency calls are made
within a three-hour period, the first emergency caller's ELIN mapping is
replaced by the third caller's extension. If the PSAP tries to call the first
caller, the PSAP reaches the third caller. This information will help as you
determine the number of DIDs you need for each ERL.
ERL Creation for information about how to
configure the ERLs with these numbers.