9-1-1 Public Safety Terminology
and Acronym Definitions

9-1-1: a three- (3) digit telephone number to facilitate the reporting of an incident or situation requiring response by a public safety agency.

Abandoned Call: a call placed to 9-1 -1 in which the caller disconnects before the PSAP attendant can answer the call.

Alternate Routing: the capability of automatically rerouting 9-1 -1 calls to a designated alternate location if all 9-1-1 trunks to the primary PSAP are busy. May also be activated upon request when 9-1-1 equipment fails or the PSAP itself is disabled.

Association of Public-Safety Communications Officers International (APCO)

Answering Position: an appropriately equipped location within a PSAP that is used to receive incoming 9-1-1 calls.

Audible Signal: a sound that indicates an incoming 9-1-1 call.

Automatic Call Distributor (ACD): equipment that distributes incoming calls to available PSAP call attendants in the order the calls are received, or holds calls until a call attendant becomes available.

Automatic Location Identifier (ALI): automatic display at the PSAP of the calling party's telephone number, the address for the telephone and supplementary information.

Automatic Number Identification (ANI): automatic display at the PSAP of the calling party's telephone number.

Basic 9-1-1: allows the calling party to dial 9-1-1 however, no ANI or ALI is displayed. Basic 9-1-1 usually provides a ring back feature for the dispatcher.

Call Detail Recording: a means of establishing chronological and operational accountability for each 9-1-1 call processed, consisting minimally of the caller's telephone number, the time the 9-1-1 telephone equipment established initial connection (trunk seizure), the time the call was answered, the time the call was transferred (if applicable), the time the call was disconnected, the trunk line used, and the identity of the SAP call attendant's position.

Call Party Hold: the capability that enables a PSAP call attendant to maintain control of an incoming 9-1-1 call for tracing or conformation of an emergency even if the caller disconnects.

Call Progress Signals: audible cues to advise 9-1 -1 users of the status of their calls.

Call Relay: disposition of a service request by the notation of pertinent information by the initial PSAP call attendant who forwards the information to the action agency.

Call Transfer: the extending of a 9-1 -1 call by a PSAP attendant to the action agency, connecting the calling party with the action agency.

Central Office: a telephone company facility that houses the switching and trunking equipment serving telephones in a defined area.

Computer Aided Dispatch (CAD): a computer based system intended to increase the efficiency and accuracy of public safety call handling and dispatching.

CAD Interface: the means of automatically introducing the ALI data into a CAD system, as opposed to manually entering the information.

Conference Transfer: the capability of allowing a PSAP call attendant to monitor an incoming call after it has been transferred to the action agency. Also known as Three-Way Calling.

Cross Tandem Transfer: the capability of transferring a call from a PSAP served by one tandem office to another PSAP served by a different tandem office.

Customer Premises Equipment (CPE)

Data Management System (DMS): the combination of manual procedures and computer programs used to create, store, manipulate, and update required to provide selective routing and ALI.

Default Routing: the capability to route a 9-1-1 call to a designated (default) PSAP when the incoming 9-1-1 call cannot be selectively routed due to an ANI failure, garbled digits or other cause.

Dial Tone First: the provision of dial tone to originate 9-1 -1 calls from coin telephones without charge.

Direct Dispatch: the functions of 9-1-1 call answering and dispatching are both performed by personnel at the primary PSAP.

Emergency Service Number (ESN): a number used to designate the public safety agencies responsible for service to the location of each telephone in a 9-1-1 service area, for the purpose of determining call routing.

Emergency Service Zone (ESZ): a defined geographical territory consisting of a specific combination of law enforcement, fire, and EMS coverage areas.

Enhanced 9-1-1 (E9-1-1): a telephone system that includes selective routing, ANI and ALI to facilitate appropriate public safety response.

Enhanced 9-1-1 Service Surcharge: a charge set by the 9-1 -1 service area operating authority and assessed on each access line which physically terminates within the 91-1 service area.

Forced Disconnect: the capability of a PSAP call attendant to disconnect a 9-1-1 call to prevent jamming or overloading of the incoming lines.

Geographic Information System (GIS)

Logging Recorder: a device that records date/time/voice communications and other transactions involved in the processing of calls to a PSAP.

Master Street Address Guide (MSAG): a database of street names containing address ranges with their associated communities that defines emergency service zones for 9-1-1 purposes.

National Computer Information Center (NCIC)

National Incident Based Reporting System (NIBRS)

National Emergency Number Association (NENA)

National Telecommunications and Information Administration, United States Department of Commerce (NTIA)

Non Recurring Costs: one-time charges.

NXX: the first three digits of a local telephone number that identifies the central office switching location within its area code. Also referred to as NNX.

Pilot Number: a telephone customer's main account number, lead number, listed number or billing number.

Private Branch Exchange (PBX): a private, internally switched telephone system of significance to 9-1-1 systems because internal stations may not be individually contained in the DMS and, as a result, will not be displayed by ANI or ALI equipment.

Public Safety Agency: an entity, which provides fire, fighting law enforcement, emergency medical service or other emergency response.

Public Safety Answering Point (PSAP): the location where a 9-1 -1 call is received for action by a public safety agency.

Public Switched Telephone Network (PSTN): the totality of equipment, lines, and controls assembled to establish communications paths between calling and called parties.

Ring Back: the capability that permits the PSAP call attendant to cause the telephone on a held circuit to ring. Also known as re-ring.

Recurring Costs: monthly or annual charges associated with the 9-1-1 system.

State Computer Information Center (SCIC)

Selective Routing (SR): the capability of routing a 9-1-1 call from a central office to a designated PSAP based upon the telephone number and/or the location of the calling party.

Selective Transfer: the capability of automatically transferring a 9-1-1 call to the action agency by operation of a single button switch, based on the origin of the incoming call.

Tandem: a switching system in the public switched telephone network that establishes trunk to trunk routing.

TDD/TTY: a telecommunication device for the hearing and speech impaired.

Thousands Number Group: the entire last four-digit group of numbers in an exchange sometimes used to determine default routing locations.

Trunk: a circuit connecting switching equipment at two sites.

Trunk Seizure: the point at which a call is assigned to a trunk and acknowledgement is provided by the 9-1-1 call.

Unbundling: different parts of E9-1-1 can be charged for separately rather than charged as one system.