Services enable 911 operators to:
Before this feature
was introduced, Cisco Unified CME supported only outbound calls to 911. With
basic 911 functionality, calls were simply routed to a public safety answering
point (PSAP). The 911 operator at the PSAP then had to verbally gather the
emergency information and location from the caller, before dispatching a
response team from the ambulance service, fire department, or police
department. Calls could not be routed to different PSAPs, based on the specific
geographic areas that they cover.
With Enhanced 911
Services, 911 calls are selectively routed to the closest PSAP based on the
caller’s location. In addition, the caller’s phone number and address
automatically display on a terminal at the PSAP. Therefore, the PSAP can
quickly dispatch emergency help, even if the caller is unable to communicate
the location. Also, if the caller disconnects prematurely, the PSAP has the
information it needs to contact the 911 caller.
To use Enhanced 911
Services, you must define an emergency response location (ERL) for each of the
geographic areas needed to cover all of the phones supported by
Cisco Unified CME. The geographic specifications for ERLs are determined by
local law. For example, you might have to define an ERL for each floor of a
building because an ERL must be less than 7000 square feet in area. Because the
ERL defines a known, specific location, this information is uploaded to the
PSAP’s database and is used by the 911 dispatcher to help the emergency
response team to quickly locate a caller.
To determine which
ERL is assigned to a 911 caller, the PSAP uses the caller’s unique phone
number, which is also known as the emergency location identification number
(ELIN). Before you can use Enhanced 911 Services you must supply the PSAP with
a list of your ELINs and street addresses for each ERL. This information is
saved in the PSAP’s automatic location identification (ALI) database.
Typically, you give this information to the PSAP when your phone system is
With the address
information in the ALI database, the PSAP can find the caller’s location and
can also use the ELIN to callback the 911 caller within a specified time limit.
This limit applies to the Last Caller table, which provides the PSAP with the
911 caller’s ELIN. If no time limit is specified for the Last Caller table, the
default expiry time is three hours.
In addition to
saving call formation in the temporary Last Caller table, you can configure
permanent call detail records. You can view the attributes in these records
from RADIUS accounting, the syslog service, or Cisco IOS
You have the option
of configuring zero, one, or two ELINs for each ERL. If you configure two
ELINs, the system uses a round-robin algorithm to select which ELIN is sent to
the PSAP. If you do not define an ELIN for an ERL, the PSAP sees the original
calling number. You may not want to define an ELIN if Cisco Unified CME is
using direct-inward-dial numbers or the call is from another Cisco voice
gateway that has already translated the extension to an ELIN.
Optionally define a
default ELIN that the PSAP can use if a 911 caller's IP phone's address does
not match the IP subnet of any location in any zone. This default ELIN can be
an existing ELIN that is already defined for one of the ERLs or it can be a
unique ELIN. If no default ELIN is defined and the 911 caller’s IP Address does
not match any of the ERLs’ IP subnets, a syslog message is issued stating that
no default ELIN is defined, and the original ANI remains intact.
You can also define
a designated callback number that is used when the callback information is lost
in the Last Caller table because of an expiry timeout or system restart. You
can use this designated callback number if the PSAP cannot reach the 911 caller
at the caller’s ELIN or the default ELIN for any other reason. You can further
customize your system by specifying the expiry time for data in the Last Caller
table and by enabling syslog messages that announce all emergency calls.
installations, you can optionally specify that calls from specific ERLs are
routed to specific PSAPs. This is done by configuring emergency response zones,
which lists the ERLs within each zone. This list of ERLs also includes a
ranking of the locations which controls the order of ERL searches when there
are multiple PSAPs. You do not need to configure emergency response zones if
all 911 calls on your system are routed to a single PSAP.
One or more ERLs can
be grouped into a zone which could be equivalent to the area serviced by a
PSAP. When an outbound emergency call is placed, configured emergency response
zones allow the searching of a subset of the ERLs in any order. The ERLs can be
ranked in the order of desired usage.
Zones are also used
to selectively route 911 calls to different PSAPs.You can configure selective
routing by creating a zone with a list of unique locations and assigning each
zone to a different outbound dial peer. In this case, zones route the call
based on the caller’s ERL. When an emergency call is made, each dial peer
matching the called number uses the zone’s list of locations to find a matching
IP subnet to the calling phone’s IP address. If an ERL and ELIN are found, the
dial peer’s interface is used to route the call. If no ERL or ELIN is found,
the next matched dial peer checks its zone.
If a caller’s
IP address does not match any location in its dial-peers zone, the last dial
peer that matched is used for routing and the default ELIN is used.
If you want
911 calls from any particular phone to always use the same dial peer when you
have multiple dial peers going to the same destination-pattern (911) and the
zones are different, you must configure the preferred dial peer to be the
highest priority by setting the preference field.
tags are not allowed in the same zone. However, the same location tag can be
defined in multiple zones. You are allowed to enter duplicate location
priorities in the same zone, however, the existing location’s priority is then
increased to the next number. For example, if you configure “location 36
priority 5” followed by “location 19 priority 5,” location 19 has priority 5
and location 36 becomes priority 6. Also, if two locations are assigned
priority 100, rather than bump the first location to priority 101, the first
location becomes the first nonprioritized location.
shows an example configuration for 911 services. In this example, the phone
system handles calls from multiple floors in multiple buildings. Five ERLs are
defined, with one ELIN defined for each ERL. At the PSAP, the ELIN is used to
find the caller’s physical address from the ALI database. Building 2 is closer
to the PSAP in San Francisco and Building 40 is closer to the PSAP in San Jose.
Therefore, in this case, we recommend that you configure two emergency response
zones to ensure that 911 calls are routed to the PSAP closest to the caller. In
this example, you can configure an emergency response zone that includes all of
the ERLS in building 2 and another zone that includes the ERLs in building 40.
If you choose to not configure emergency response zones, 911 calls are routed
based on matching the destination number configured for the outgoing dial
Figure 1. Implementation
of Enhanced 911 for Cisco Unified CME