Configuring Emergency Services 131
The processor on which the phone extension is configured is referred to
as the home call processor. The processor to which the phone is
connected is referred to as the foreign call processor.
Although the phone has been assigned an extension configured on the
remote home processor (a branch office, for example), the phone retains
the IP address that was assigned when the phone booted at the foreign
call processor (a regional office, for example). An ELIN (see the previous
section) is associated with a range of phone IP addresses.
Note the following implications for emergency calls made by a roaming
user:
■If a roaming user makes an emergency call using a dialing pattern that
matches an emergency number configured for the foreign site, the
foreign call processor intercepts the call and routes it locally.
■If a roaming user makes an emergency call using the dialing pattern
for his or her home site, and that pattern does not match the pattern
configured on the foreign call processor, the emergency call is routed
using the home site configuration. As a result, the user may be sent to
an emergency response center that cannot support the location that
originated the call.
■For enhanced emergency services to work for all roaming situations,
the home site (for example, a branch office) and its backup site (for
example, the regional office to which the branch is connected) must
have IP address range-based ERLs defined for the phones at each site.
In this case, VCX software will use the a phone’s assigned IP address to
determine if an ERL from the home location or the ERL from the
backup location should be used. This covers both of the following
cases:
■A branch phone makes an emergency call when the phone has
roamed to its regional call processor. This enables the emergency
call to go to regional emergency center.
■A branch phone makes an emergency call when the phone has
failed over to its regional (backup) call processor. This enables the
emergency call to go to branch emergency center.
Adding ERLs When ERLs are configured, you can configure Emergency Location
Identification Numbers (ELIN), which are assigned through an emergency
services administrator.