Emergency Call Routing - E911 and Cisco Emergency Responder

Emergency call routing is commonly referred to as 911 in the United States because of our use of the 911 pattern to route emergency calls to the local emergency services call center. The emergency services call center is commonly referred to as the Public Safety Answering Point (PSAP). Agents at the PSAP take emergency phone calls and dispatch an Emergency Response Team (ERT). First responders (ERT) include members of the fire department, police department, and/or ambulance depending on the emergency situation.

Local exchange carriers (LEC) use selective routing devices (selective router) to properly route 911 calls to the closest available 911 call center agent. Call center agents are able to identify the location of the caller based on the Automatic Number Identification (ANI) of the calling party. Automatic Location Identification (ALI) is performed by looking up the calling party’s phone number (ANI) against a PS-ALI database which has access to a Master Street Address Guide (MSAG). The MSAG includes the address of the caller who placed the call to the 911 center.

Traditional fixed line residential lookups are performed in the manner explained thus far in this article. Multiple Line Telephone Systems (MLTS) identification requirements offer more of a challenge because the traditional key system of private branch exchange (PBX) platform must identify the calling party within a certain square footage range as mandated by local municipality law standards. PBX administrators can meet this challenge by mapping different ANI numbers to ranges of phones that are in a similar geographical proximity. A company that occupies multiple floors in a high rise building may be required to locate a caller to a floor of the building. A company occupying ten floors of the building at One State Street in New York City would register ten different ANI numbers with the PSAP. Each of the ten ANI numbers would be registered as Emergency Line Identification Numbers (ELIN) with the PSAP.

One of the greatest benefits of Voice over IP and unified communications systems is the mobile nature of the technology. A Cisco IP phone can be moved between locations on the same floor, different floors, or even different buildings with zero administrator interaction. As long as the Cisco IP phone receives a DHCP lease from the new location and there is IP connectivity to the Cisco Unified Communications Manager (CUCM), the Cisco IP phone will register. Cisco IP Communicator (CIPC), Cisco Unified Personal Communicator (CUPC), and Cisco Unified Mobile Communicator (CUMC) are software based Cisco phone offerings that are loaded on devices that frequently move between locations. Cisco also offers a variety of wireless LAN (WLAN) based phones (7920, 7921, 7925) and software based phones that access CUCM via a wireless access point (WAP) cannot be identified to a particular floor because wireless signals can cross floors in a building.

The ability to quickly and easily move devices with no administrative interaction can be viewed as one of the system’s greatest weaknesses from an emergency call routing perspective. The device mobility feature added in Call Manager 4.2 and CUCM 6.0, has partially addressed this mobility issue by mapping IP subnets to dynamic locations changing the call routing to a local PSTN gateway that will locally route emergency calls. The device mobility feature is useful, but does not have the ability to map a caller’s ANI to an ELIN registered with the PSAP.

Cisco Emergency Responder (CER) is a server that has the ability to dynamically map a caller to a particular ELIN. The next blog will continue our conversation on emergency call routing and Cisco Emergency Responder.

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• CER ANI ALI ELIN PSTN PSAP e911 CUPC CIPC CUCM CUMC WAP MLTS LEC 911 ERT MSAG PS-ALI