Glossary of Terms

Automatic Location Identification - A display of the caller's address, type of service and if a business - the name of the business, if a residence - the listed name associated with the displayed telephone number. The PSAP will also get a display of the associated emergency service number (ESN) information (police, fire, and ambulance).
ALTERNATE ROUTING Alternate routing provides for a predetermined routing for 9-1-1 calls when the tandem office is unable to route the calls over the 9-1-1 trunks for a particular PSAP due to trouble, all trunks busy,or a power failure.
ANONYMOUS CALL If a caller misdials and dials the seven-digit number associated with the PSAP trunk group, the call will come in on a 9-1-1 trunk. The ANI display will display an anonymous call. The seven-digit numbers associated with the PSAP positions are not published, even to the PSAPs.


Automatic Number Identification - Corresponds to the caller’s ten-digit telephone number. The ANI displays at the PSAP on the digital E9-1-1 workstation monitor.
ANI FAILURE Failure of the end central office to identify the call and provide the automatic number identification to the tandem office; or, an ANI failure between the tandem office and the PSAP. Without ANI, the call cannot be properly routed or provide an ALI display.


The number of calls anticipated during each Public Safety Answering Point's busiest period.
CALL DETAIL RECORD When the 9-1-1 call is terminated by the PSAP operator, the ANI will automatically print out on the printer located at the PSAP. The printout will contain the caller's telephone number, the workstation number, the time the call came into the PSAP, the time it was answered by a telecommunicator, the time the call was transferred, if applicable, the time the call was terminated, and the trunk number associated with the call. Printouts of the ALI display will print out as soon as the call is answered.
CALL TRANSFER A call that is transmitted from a PSAP to another PSAP or to another emergency service (related) agency, and in which the telecommunicator has no need for additional information and therefore disconnects once the transfer has been completed.
CALL VOLUME This is the anticipated daily total number of calls for each PSAP.
Type of telephone from which a call is placed
(i.e. business, residential, coin, PBX, etc.)


Computer-Aided Dispatch - Public Safety dispatching with computers aiding in the process. This aid may be a simple display of pertinent information on a screen, up to the actual selection and notification of field unit(s) by the computer. 9-1-1 systems may be interfaced with CAD systems.
DMS Data Management System – A data base managed by the telephone company which includes ANI and ALI information.


Provides for routing of 9-1-1 calls when there is an ANI failure. The call will be routed to a predesignated PSAP or seven digit number. This occurs when a particular 9-1-1 call cannot be selectively routed for any reason.


Capability of the telephone company, when notified by the PSAP, to reroute 9-1-1 calls to some other predesignated location during a disaster situation.


Emergency Service Number - A three-digit number that is assigned to the caller's telephone number in the tandem office translations. The emergency service number routes the call to the proper PSAP. PSAPs also receive a display of the ESN information. The display shows which police, fire, and ambulance agency serve the telephone number calling 9-1-1.
END OFFICE Telephone central office which provides dial tone to the individual calling 9-1-1. The end office provides automatic number identification to the tandem office.


Enhanced 9-1-1 Emergency Telephone Number System consisting of telephone network features and PSAPs for users of the public telephone system to reach a PSAP by calling the digits "9-1-1". The system directs 9-1-1 calls to the appropriate PSAP by selective routing based on the geographical location from which the call originated and provides the capability for ANI and ALI display.
ESS Electronic Switching System - Computerized switching of telephone calls used by the telephone company.


The three number prefix (first three numbers of a telephone following the area code) which identifies the end office routing of the call.
FIXED TRANSFER Allows an established 9-1-1 call to be transferred by a PSAP telecommunicator to another specific location or another PSAP. Fixed transfer is accomplished by a predesignated transfer button and uses the speed calling feature of the 9-1-1 tandem office.


Foreign Exchange line. - The ANI telephone number is located in an area not within the geographical boundaries of the local 9-1-1 service area, but draws dial tone service from an end office within the 9-1-1 service area.
FORCED DISCONNECT The call is automatically disconnected when the Public Safety Answering Point telecommunicator hangs up.


Master Street Address Guide. - The MSAG contains all valid streets in the E9-1-1 service area. It includes low/high house numbers (address range), community name and ESN.


A condition that results in the 9-1-1 call going to the wrong PSAP. A call can be misrouted if the emergency service number and associated routing information are incorrect in the E9-1-1 database and/or tandem database. A call can also be misrouted if the call is an ANI failure, which automatically default routes.
NO ANI This condition means the PSAP received a call but no telephone number displayed on the workstation monitor. The PSAP should report this condition immediately to Repair Service.
NO DISPLAYS The PSAP ALI display portion of the workstation monitor is blank. Try the Repeat ALI button for another look-up at the database. If screen is still blank, report this type of trouble immediately to Repair Service. If all monitors at the PSAP are blank, it is an indication that the problem is in the circuits from the PSAP to the E9-1-1 network computer.
ONE BUTTON TRANSFER The ability to transfer a 9-1-1 call to another public safety agency by pressing one button; can be fixed or selective transfer.
PARTIAL DISPLAYS The PSAP receives an ANI display, but the display is incomplete (missing alpha or numeric characters). Try the Repeat ALI button for another lookup at the database. If the screen is still garbled, report this to Repair Service.
The entire seven-digit telephone number will be displayed on the ALI screen. The pilot telephone number is the main number of the telephone service. This information would be important if someone dials 9-1-1 from an outward-only line and then hangs up. The PSAP would be unable to reach them at that number, but would be able to reach someone at the main number. In most cases, the pilot telephone number and the actual telephone number are the same.
PSAP Public Safety Answering Point. - A facility operated on a twenty-four hour basis, assigned the responsibility of receiving 9-1-1 calls and, as appropriate, directly dispatching emergency response services, or transferring or relaying 9-1-1 calls to other public safety agencies. The PSAP is the first point of reception of a 9-1-1 call.


If the host computer is unable to do a look-up on a given ANI request from the PSAP, it will forward a Record Not Found message to the PSAP ALI screen. This could be the result of service order activity for a given individual not being processed into the E9-1-1 database, or problems with the host computer system whereby the records cannot be accessed.
SELECTIVE ROUTING The capability to route a call to the particular PSAP based on the geographical location from which the call originated. Selective routing is achieved by building telephone number/emergency service number translations in the tandem central office. These translations cause the E9-1-1 database to assign the emergency service number to each telephone number based on the customer's address. Service order activity keeps the E9-1-1 database updated. The E9-1-1 database, in turn, generates recent changes to the tandem office to update the telephone number/ESN translations in the tandem database.
SELECTIVE TRANSFER  Provides the PSAP with the ability to transfer the incoming 9-1-1 call to a fire, police, or ambulance for the particular number calling 9-1-1 by pushing one button. For example, if an incoming 9-1-1 caller was reporting a fire, the PSAP operator would push the fire button on the workstation. The call would go back to the tandem office. In the tandem office, the computer would do a "look-up" for the ESN and automatically route the call to the correct fire department. This differs from fixed transfer, which routes every call to the same fire or rescue number whenever the fire or rescue button is pushed.

9-1-1 CALL

Occasionally, the PSAP will get a call that is not associated with a caller dialing 9-1-1 for an emergency. The PSAP may get a call that rings and there is a caller on the line who has not dialed 9-1-1, but is dialing another number, or has just picked up the phone and was connected with the PSAP. The PSAP may get a call and no one is on the line. If the number is called back, it may be disconnected or no one answers. Cordless telephones can also generate "spurious" calls into the PSAPs. Generally, the PSAP will hear conversation, but the parties are not calling 9-1-1 and cannot hear the PSAP operator. The PSAP may hear static, music, or other noise, which are also indications of a call prompted by a cordless phone. All of the above problems need to be reported using the E9-1-1 Inquiry Form.
TANDEM OFFICE Telephone central office which serves a tandem area for all 9-1-1 calls. It must be a 1AESS type of central office. The tandem office translations contain the telephone number/ESN which route the 9-1-1 call to the proper PSAP. The tandem office looks up the ANI that it receives from the end office and finds the emergency service number (routing information) which corresponds to a PSAP.
TRUNK LINE Telephone company circuit from the end office to the phone user's location.