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Glossary of Terms


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Abandoned Call, a call placed to 911 in which the caller disconnects before the call can be answered by the PSAP call taker.

ADA, Americans with Disabilities Act of 1990.

Agency, the municipality, county, state government, or private entity that operates a Public Safety Answering Point.

Alternate Routing, the capability of automatically rerouting 911 calls to a designated alternate location(s) (called an alternate PSAP) if all 911 trunks from a central office or to a PSAP are busy or out of service. May also be activated upon request, or automatically if detectable, when 911 equipment fails or the PSAP itself is disabled.

American Sign Language (ASL), a visual language based on hand shape, position, movement, and orientation of the hands in relation to each other and the body.

Answering Position, an appropriately equipped location within a PSAP that is used to receive incoming 911 calls.

Approved by the Board, a simple majority vote by members of the Statewide Enhanced 911 Board taken at a public meeting of the Board at which a quorum of the Board is present.

ASCII, an acronym for American Standard Code for Information Inter-exchange, which employs an eight-bit code for the purpose of transmitting data.

Audible Signal, a sound which indicates an incoming 911 call.

Auto-Dial, a PSAP function which allows an attendant to dial an outgoing programmable telephone number with a single button.

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

Automatic Location Identification (ALI), the system capability to identify automatically the geographical location of the telephone being used by the caller and to provide a display of that location information at any public safety answering point.

ALI Database, a derivative, verified set of records which contain, at a minimum, a telephone number and location identification for each unique building or publicly used facility within a defined geographic area in Vermont.

Automatic Number Identification (ANI), the system capability to identify automatically the calling telephone number and to provide a display of that number at any public safety answering point.

Average Busiest Hour, the one hour period during the week statistically shown over time to be the hour in which the most emergency telephone calls are received.

AnchorBarge-In Capability, the capability for multiple PSAP operators to establish simultaneous access to any emergency line or trunk in prior use for the purpose of assisting fellow personnel with difficult calls.

Baudot, a seven bit code, only five of which are information bits. Baudot is used by text telephones to communicate with each other.

Board, the Vermont Enhanced 911 Board.

CAD Interface, the means of automatically introducing the ALI data into a computer aided dispatch (CAD) system, rather than by manually entering the information.

Call Relay, disposition of a 911 call by the notation of pertinent information by the PSAP call-taker who forwards the information to the appropriate agency.

Call Referral, disposition of a 911 call by advice to the caller of the appropriate numbers to call other than 911.

Call Sequencer, equipment that distributes incoming calls to available PSAP positions in sequence.

Call Transfer, the extending of a 911 call by a PSAP call-taker to connect the caller with the appropriate agency.

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

Central Office Modification, hardware and/or software changes to a telephone company central office to specifically accommodate Enhanced 911 service.

Central Office Upgrade, scheduled hardware and/or software changes to a telephone company central office to improve the overall telephone service from that site.

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

Continuous Logging Recorder, a device which records date, time, voice and TTY communications, and other transactions involved in the processing of calls to the PSAP.

Dedicated Trunk, a telephone circuit used for one purpose only; i.e. transmission of 911 calls.

Dedicated Network, a point to point or multi point network where resources (switching or transmission facility) are reserved for a particular customer or type of traffic.

Default Routing, the capability to route a 911 call to a designated (default) answering point (called a default PSAP) when the incoming 911 call cannot be selectively routed due to an ANI failure, garbled digits, or other cause.

Department of Public Safety (DPS), the Vermont governmental entity responsible for all matters of public safety, including emergency management.

Director, the Executive Director of the Vermont Enhanced 911 Board.

Diverse routing, the practice of routing calls through different circuit paths in order to prevent total loss of the 911 system in the event an individual circuit is disabled.

DMS (Data Management System), a system of manual procedures and computer programs used to create, store and update the data required for selective routing and ALI information in support of enhanced 911.

Duplicate Street Name, a street name in which the name and any associated designator is exactly the same (example: Pine St. and Pine St.; NOT Pine St. and Pine RD.)

Emergency Service Providers, police (law enforcement), fire and ambulance services.

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

EMS (Emergency Medical Services), municipal based, private under municipal contract, private, or volunteer rescue squads or hospital based Advanced Life Support agency/providers whose sole purpose is to provide EMS to a municipality or group of municipalities.

(a) BLS (Basic Life Support), an EMS agency providing a level of basic life support service to a community.

(b) ALS (Advanced Life Support), advanced EMS provided by paramedics or EMTs with advanced training and who may not necessarily be part of a community’s BLS service.

Enhanced 911 System and Enhanced 911 Services, a system consisting of selective routing with the capability of delivering automatic number and location identification to a public safety answering point, network circuits, data bases and answering equipment, the combination of which enables a user to request emergency services by dialing the digits 911.

Enhanced 911 Equipment, equipment located at the PSAP or controller type equipment located at the Service Provider’s location that provides or supports enhanced 911 capability.

Fixed Transfer, the capability of a PSAP call-taker to transfer a 911 call using a single button.

Foreign Exchange (FX), a service connecting a telephone to a remote exchange providing the equivalent of local service from the distant exchange.

Host-Remote, the relationship between conventional central office switching equipment and a Remote Switching Unit (RSU) in another facility which usually has limited capability and may not be able to function independently if connecting links from the host office are interrupted.

Identical Street Name, (see Duplicate Street Name)

Instant Playback Recorder, a device that allows for the instant playback of the audio portion of the last 911 call.

Integrated Services Digital Network (ISDN) Basic Service, provides an integrated digital access to voice, switched data and packet switched data transport services using ISDN network technology. ISDN Basic Service provides two bearer (B) channels which are capable of transmitting voice, circuit switched data and packet switched data at speeds of up to 64 kilobits per second (Kbps) and on signaling (D) channel used for call control and transmission of packet switched data at rates up to 9.6 Kbps.

Local Enhanced 911 System, an independent local system that is not funded by the State Enhanced 911 Fund, and which consists of selective routing with the capability of delivering automatic number and location identification to a public safety answering point, network circuits, data bases and answering equipment, the combination of which enables a user to request emergency services by dialing the digits 911.

Local Exchange Company (LEC), includes all persons, firms, corporations, associations and joint stock associations or companies, as defined in 30 V.S.A §201, furnishing or rendering local telephone exchange service.

May, indicates the possibility of taking action. (See shall, should)

MCO, Maintenance Control Office

Municipality, any city, town, incorporated village, other governmental unit, unorganized town, gore, grant or other political subdivision of the State of Vermont.

MSAG, Master Street Address Guide

Network Provider, any communications company providing a network and access to it.

PBX (Private Branch Exchange), a private telephone system allowing communications within a business, and between a business and the outside world.

Private Telephone System, privately owned and operated telephone systems that include PBX, Centrex and key systems.

Public Service Board (PSB), the quasi-judicial governmental entity that regulates utilities.

Public Service Department(PSD), the Vermont governmental entity responsible for representing the interests of the public in regulated utility matters.

Public Safety Answering Point (PSAP), a facility assigned the responsibility of receiving 911 calls and, as appropriate, directly dispatching emergency response services or transferring or relaying 911 calls to other public or private safety agencies.

(a) A Primary PSAP is equipped with automatic number identification and automatic location identification displays, and is the first point of reception of a 911 call. It may serve a municipality or a region, and other cities and towns as may be determined by the Board.
A Primary PSAP may be located in a centralized, consolidated radio dispatch facility that serves all public safety agencies in a region or municipality. A Primary PSAP may also be engaged in, pursuant to inter-municipal agreements in force, the dispatching, or control pf public safety resources serving several jurisdictions. A Primary PSAP shall be a facility that serves at least two of the emergency services and that operates on a 24 hour, 7 days a week, 365 days a year basis.

(b) A Secondary PSAP is equipped with automatic number identification, automatic location identification displays and all other features common to Primary PSAPs. It receives 911 calls only when they are transferred from the Primary PSAP or on an alternate routing basis when calls cannot be completed to the Primary PSAP.

(c) A Limited Secondary Public Safety Answering Point is a facility equipped, at a minimum, with ALI/ANI display/printout capability. It receives 911 calls only when they are transferred from the Primary PSAP. Data sent to a Limited Secondary PSAP cannot be re-routed to another location and may not necessarily be transmitted simultaneously with the voice call.

(d) A Ringing Public Safety Answering Point is a facility equipped for the receipt of voice communications only, which may not necessarily operate 24 hours each day. It receives 911 calls that are transferred from the Primary PSAP.
Public Switched Network, a multi point network which provides the capability to establish connections to essentially all customers regardless of location.

Redundancy, having one or more "backup" systems available in case of failure of the main system.

Selective Routing, a telecommunications switching system that enables all 911 calls originating from within a defined geographical region to be answered at a pre-designated PSAP.

Service Provider, any entity that provides a portion of the statewide enhanced 911 system to the system provider.

Shall, indicates a mandatory obligation to act. (See may, should)

Should, indicates a recommendation or that which is advised but not required. (See may, shall)

Silent call, a 911 call received at a PSAP and no audible voice or tone is received.

Supervisory Call Monitoring, the capability for supervisory personnel to listen to calls in progress for purposes of quality assurance and training.

System Provider, any entity that provides the entire statewide Enhanced 911 system (general contractor) and is the single point of contact on an ongoing basis for any matters relating to the system.

Tandem, a switching system in the Enhanced 911 telephone network that establishes 911 call routing.

TTY, a telecommunications device consisting of modems that permit typed telephone conversations with or between deaf, hard of hearing or speech impaired people.

TTY Call Diverter, a device that monitors and detects Baudot tones and ASCII and then automatically routes the TTY call to a specified position.

TTY Detector, a device that monitors a trunk for Baudot tones and ASCII and upon recognition, indicates the receipt of that type of call with a response sequence.

Text Telephone (TT), a machine that employs graphic communication in the transmission of coded signals through a wire or radio communication system. It is interchangeable with the term "TTY" or "telecommunications device for the deaf."

Trunk, incoming 911 circuit.

Trunk Seizure, the point at which a call is assigned to a trunk and acknowledgment is provided by the 911 call processing equipment.

TT, Text Telephone

Uninterruptible Power Supply (UPS), a system designed to provide power indefinitely, without delay or transients, during a period when the normal power supply is incapable of performing acceptably.


For a more extensive listing visit the NENA (National Emergency Numbers Association) Master Glossary Of 911 Terminology.