THE CUSTOMIZATION TOOLS: E911 & PS-ALI
When it has been determined that the ANI/ALI delivered using the in-place trunks will not provide an ideal or acceptable level of accuracy for 911 calling, it is time to look at customizing the ALI environment. This is where enterprise E911 capability comes into play.
In its simplest form, E911 capability is the application within the telephone system that allows the administrator to ignore the default trunk ANI/ALI information and assign telephone users "custom" ANI information that will be correlated with "custom" ALI information. As an example, if a user's DID number is "212 555-2222," the E911 application can allow the administrator to assign a different DID number to be passed when the user calls 911, say "212 555-4444." Why would this be of value? Because it is the ANI that drives the entire 911 call process. When someone dials 911, their receiving central office forwards the call to their regional 911 selective router, which performs a lookup against the ANI to determine which PSAP should get the call--it then delivers the call to the serving PSAP. As the call rings into the PSAP, a data connection between the PSAP and the regional ALI database processes a query using the caller’s ANI to "spill" the caller's ALI information to the dispatcher’s console screen a split second after the call is received.
It is important to understand that when it comes to customizing what the PSAP sees, the E911 application in the telephone system is just half of the equation. A 911 caller can only pass their ANI (whether it is their "real" ANI or a pseudo-ANI spoofed by the E911 application)--the ALI (location information) associated with an ANI resides in the carrier's ALI database. Getting access to the carrier's ALI database in order to show "customized" location information is the second half of the equation. It is done by purchasing a Private Switch ALI (PS-ALI) service from the ILEC/CLEC or a PS-ALI service provider. This service allows for "custom" location records to be related to specific ANIs and then uploaded to the carrier's regional "live" ALI database. Once this is done, a 911 call made with one of the ANIs built in the PS-ALI service will match up with the custom ALI record in the regional database and "spill" the appropriate location information to the PSAP. It should be noted that PS-ALI service is typically priced in direct proportion to the number of unique ANI/ALI records required to be built and carried in the database, so the more records, the more costly.
UNDERSTANDING THE E911 APPLICATIONS
Without the use of an E911 application in the telephone system, the method of delivering customized, accurate ANI/ALI to PSAPs requires the 100% use of a PS-ALI service. In this scenario, since every telephone/DID user would by default pass their unique ANI and the default trunk billing address, there is a need to build a "custom" ALI record for every DID instance in the enterprise. Therefore, if an enterprise has 1,000 telephone (DID) users, the PS-ALI service would require 1,000 unique ANI/ALI records to avoid passing the default billing address for any of the 1,000 phone users. This is both expensive and burdensome to manage. In this environment, anytime a DID user moves within the organization, the administrator needs to update the PS-ALI database to show the new location information, and then the carrier needs to upload this information to their "live" regional ALI database (or databases); this database refresh can take from minutes to hours to accomplish.
Manufacturers and third party providers have developed E911 applications to economize and simplify the process of customizing and managing 911 information for enterprise users. The E911 capability found either standard or optionally within most systems can be used to reduce the number of PS-ALI records required and simplify the administration of MAC activity and associated integrity of 911 call processing.
The major function of the E911 application is to allow for the capability to out-pulse a pseudo-ANI rather than the user’s actual ANI when making a 911 call. This allows DID users to be grouped together in "zones" and assigned a common pseudo-ANI that will be out pulsed when anyone assigned to the group dials "911;" this ANI will reference an ALI record in the PS-ALI database that will identify the building’s address plus a granular location within the building that multiple telephone users can reference (e.g., 3rd floor, West end). This geographic "zone" is referred to as an Emergency Response Location (ERL). The DID number that is out pulsed and used to reference a custom address/ERL in the PS-ALI service is known as an Emergency Location Identification Number (ELIN) or a Customer Emergency Service Identification (CESID). Using ELINs/CESIDs to serve a proximate group of users reduces the number of records needed in the PS-ALI database, thereby reducing cost, simplifying setup of the E911 database, and simplifying 911 Move/Add/Change administration.
Interestingly, E911 application functionality is not without potential drawbacks. For instance, with the use of ELINs/CESIDs, instead of a 911 caller passing their true ANI, the E911 application will in many cases pass the caller's ELIN to the PSAP (the "spoofed" or pseudo-ANI used when out-pulsing a 911 call). If this is the case, enterprises must make sure that every ELIN rings into a station(s) that would normally be tended in case the PSAP were to call back on a disconnected 911 call. In some cases the manufacturers are able to overcome this shortcoming (e.g., some systems are capable of recognizing a 911 call back and ringing it to the actual DID of the most recent 911 caller).
Another potential shortcoming with some E911 applications is that where a separate application server is used, a failure of this server may result in enterprise 911 calls passing default trunk information to the PSAP (in most cases, a redundant server is an available option to mitigate this vulnerability).
Besides the core function of enabling 911 calls to pass customized DID assignments, most E911 applications provide other important benefits. One is the ability to provide real-time notification to one or several users that a 911 call was just placed (and identify who placed it) with the option of allowing authorized phones to join in and listen to the call. This capability is important to environments where false 911 calls are a problem (e.g., K-12 Education) or security departments want to be apprised of internal emergencies (e.g., Manufacturing, Higher Ed). Another capability typically found is the automatic administration of Move/Add/Change re-assignments so that as IP phones are moved within the organization they are automatically and accurately updated with the proper ELIN assignments. Although manufacturers vary somewhat in their approach to mapping the data network and tracking phones that move on the network, IP phones can typically be moved anywhere in the enterprise and the E911 application will know enough about the data network to know what ELIN should be assigned. This is typically accomplished by using subnet assignments or a Layer 2 approach to assign users based on the switch or switch port being used by the IP phone so that 911 calls can be processed with the correct location information without any administrative intervention.
