9-1-1 Terms and Definitions

DMS 100

A Class 5 End Office switch made by Nortel.

TRUNK1

A circuit is connecting switching equipment at two sites. TRUNK GROUP, one or more trunks terminated at the same two points.

TWO‐STAGE

A dispatch system in which the call‐taker and dispatcher functions are separated and are handled by separate 9-1-1 Officers.

END OFFICE

See CO (Central Office)

CUTOVER

The activation of a new telephone call processing or switching system.

PSDP

Public Safety Dispatch Point. A location that provides dispatch services for one or more public safety agencies.

PSTN

Public Switched Telephone Network. The totality of equipment, lines, and controls assembled to establish communication paths between calling and called parties.

TDD

Teletypewriter - A telecommunications device for the hearing and/or speech impaired.

CONVENTIONAL PSAP

A PSAP that has on‐site ANI controllers which interrogate the ALI and requires on‐site ALI multiplexers and other dedicated equipment and data circuits to receive, process, or transfer 9‐1‐1 calls.

REDUNDANT CALL

A call from a person reporting an incident that has already been received and who has no additional information to provide.

SWITCHHOOK

A switch on a telephone instrument that controls the on-hook/off‐hook status. A part of the handset cradle, the switch, operates when the handset is lifted or returned to the cradle.

ACD

Automatic Call Distributor. Equipment that distributes incoming calls to the available PSAP or PSDP personnel in the order the calls are received or holds the call until a call taker becomes available. The calls are routed to the least busy call taker.

CALL RELAY

Call handling procedure whereby pertinent information is copied by the PSAP call taker, who then forwards the information to the appropriate action agency.

CLEC

Certified Local Exchange Carrier. A telephone company is providing local telephone service.

DMC

Database Management Center. (Formerly known as ENAC, Emergency Number Administration Center.) The Verizon agency that is responsible for maintaining the ALI database.

MF

Multi‐Frequency. In‐band, analogy trunk signaling.

CALL VOLUME

This is the total number of calls for each Public Safety Answering Point.

CALL BACK NUMBER

(CBN) The caller's 10-digit telephone number used by the PSAP to reestablish the call if it was prematurely disconnected.

TOPS

(Traffic Operator Position System) A Workstation and the associated electronic switching system that permits the processing of operator‐handled calls (e.g., "0" plus, collect calls, etc.)

CALL TRANSFER

A call handling procedure in which a caller is transferred from a PSAP to another PSAP, PSDP, or other location, and in which the call taker has no need for additional information and therefore disconnects once the transfer has been completed.

ABANDONED CALL

A call placed to 9‐1‐1 in which the caller disconnects before the call can be answered by the PSAP.

EMERGENCY CALL

A call routed to a PSAP or PSDP reporting an incident that is either in progress or had just occurred, and which requires an immediate response from one or more Public Safety entities.

EXCHANGE

A defined telephone service area, identified by the three-number prefix (the first three numbers of a telephone number following the area code). Also referred to as NXX.

LOGGING RECORDER

A device that electronically records all voice communications and transactions on the 9‐1‐1 lines at PSAPs and PSDPs. A logging recorder operates on a continuous or controlled basis, documents time and date information for the transactions recorded, and is primarily for archival purposes.

MODEM

A device that modulates and demodulates a signal to make it compatible with another media, e.g., translating a digital signal into an analog signal to transmit computerized information across telephone lines.

SINGLE‐STAGE

A dispatch system where the call‐taker and DISPATCH SYSTEM responsibilities are handled by a single. Also referred to as a "one‐stage dispatch system" or "direct dispatch system."

FIXED TRANSFER

A feature that allows a PSAP to perform a single button transfer of an established 9‐1‐1 call to a predetermined location. These transfers do not change based on the ESN from which the call originated. The standard fixed transfers on 9‐1‐1 networks usually include Poison Control, Redundant Call message, and Non‐emergency Call message.

MANUAL TRANSFER

A feature that allows a PSAP to transfer an established 9‐1‐1 call by manually dialing a 3‐digit speed dial function, or a 7‐ digit or a 1+10‐digit public network number.

SELECTIVE TRANSFER

A feature that allows an established 9‐1‐1 call to be selectively transferred by the 9‐1‐1 tandem office from the PSAP to the correct PSDP associated with the caller's associated ANI without the PSAP personnel having to determine and manually dial the digits for the correct destination. The 9‐1‐1 tandem office uses the ANI/ESN data from the initial routing of the call to reroute the call to the correct secondary agency.

PUBLIC SAFETY AGENCY

A functional division of a public agency that provides firefighting, police, EMS, emergency management, or another emergency service.

P.01 GRADE OF SERVICE

A grade of emergency telephone service in which no more than one call in 100 attempts will be blocked during the average busiest hour.

POISSON TABLES

A mathematical table used in calculating telephone trunk capacity based on the desired grade of service and the hundred‐call‐seconds (CCS) anticipated.

CALL DETAIL LOGGING

A means of establishing chronological and operational accountability for each 9‐1‐1 call processed. The log minimally consists of the caller's telephone number, the date and 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 call-taker position that processed the call.

CIRCUIT ROUTES

A means of two-way communication between two terminal installations

IN‐BAND SIGNALING

A method of controlling information in a telecommunications network by using tones or other signals carried within the same band, or channel, as the information being carried.

CALL CONFERENCING

A procedure by which the caller is transferred from a PSAP to another PSAP, PSDP, or other location, and in which the call taker remains on the line to obtain or relay additional information.

BLIND TRANSFER

A procedure in which the call taker fails to advise the caller of the transfer and/or fails to remain on the line to ensure an appropriate transfer has been completed. This procedure is statutorily prohibited on 9‐1‐1 calls in many states.

CLASS OF SERVICE

A service order code designation of the telephones service features to which business and residential customers subscribe (i.e., business, residential, coin, PBX). This information appears online nine on the ALI screen information.

CRANK

A single button used to transfer a non‐emergency call to a recorded message, such as advising the caller they have dialed 9‐1‐1 for a non‐emergency event and recommending they call back on the appropriate seven‐digit number.

TANDEM

A switching system in a telephone network that establishes 9‐ 1‐1 call routing.

PILOT NUMBER

A telephone customer's main account number, lead number, listed number, or billing number.

SPEED CALL NUMBER

A two‐digit number prefixed with an asterisk (*), used to transfer a call to a location not on a preset routing button. Also called "Speed dial number."

ALS

Advanced Life Support. Service provided by special teams, which may be composed of Paramedics, Nurses, Doctors, and EMTs. These teams respond to the most serious, life-threatening medical emergencies and can administer medication, defibrillation, and airway management.

NETWORK CORE COMPONENTS

All facilities and equipment required to perform functions necessary to complete a 9‐1‐1 call successfully. PSAP Circuits are not included in this category.

CONFERENCING

Allowing multiple parties to talk to each other simultaneously on the same line.

INTERLOCAL SERVICES

An agreement among government jurisdictions or privately-owned systems within a specified area to share 9‐1‐1 system costs, maintenance responsibilities, and other considerations.

ANSWERING POSITION

An appropriately equipped location within a PSAP that is used to receive incoming 9‐1‐1 calls.

NETWORK

An arrangement of main stations interconnected by means of communications channels organized to perform or serve a common function.

IDLE CIRCUIT TONE

An audible tone generated when the caller hangs up before the PSAP answers. This feature enables the PSAP personnel to distinguish between calls that have been abandoned before being answered and calls where the calling party is connected but unable to speak.

BASIC 9‐1‐1

An emergency telephone number system using the digits "9‐1‐1" for access and routing all such calls from a central office to a single 9‐1‐1 answering point. No ANI or ALI features are available with this service.

ENHANCED 9‐1‐1

An emergency telephone number system using the digits 9‐1‐1 for access to a PSAP. Among the enhancements included are the provision of ANI, ALI, and selective routing of calls to the appropriate PSAP. Also referred to as "E 9‐1‐1" or "9‐1‐1 E."

DIRECT DISPATCH

An operational method in which the 9‐1‐1 call answering and Public Safety dispatching are done by the personnel at the PSAP.

PRIVATE SAFETY AGENCY

Any entity, except a municipality or Public Safety agency, that provides emergency medical, firefighting, or other emergency services.

ALI

Automatic Location Identification. The automatic display at the PSAP or PSDP of the caller's telephone number, address for the telephone, and supplementary information.

ANI

Automatic Number Identification. The automatic display at the PSAP or PSDP of the caller's telephone number.

BLS

Basic Life Support. Service provided by EMTs that includes such care as CPR, Extrication, and wound care.

CALL REFERRAL

Call handling procedure in which a call is disposed of by providing the caller the appropriate number to call other than 9‐1‐1.

CO

Central Office. Telephone company facility that houses the switching and trunking equipment serving telephones in a defined area. A central office may handle one or more telephone exchanges. Also referred to as an End Office.

ESS

Electronic Switching System. A modern central office with programmable phone switching logic.

EMSS

Emergency Medical Services System. That personnel involved in any aspect of the provision of emergency medical care. This includes, but is not limited to, Emergency Medical Dispatchers (EMD), First Responders, Basic Life Support (BLS), Advanced Life Support (ALS), and Aeromedical Response teams

ESN

Emergency Service Number. A four-digit number assigned to an Emergency Service Zone (ESZ). The 9‐1‐1 computer associates the ESN with the address a call is received from and routes the call to the appropriate PSAP. This information appears online 11 on the ALI display. For cellular calls, this number indicates the specific cell site where the call was first received.

ESZ

Emergency Service Zone. A geographical area is having a unique combination of police, fire, and medical emergency response agencies. Also, see ESN.

EMSE

Emergency Services Message Entity. An entity in the emergency services network, which serves as the point of interface to an MSC for common channel emergency, services messaging. ESME is another term for an ALI database.

ETNS

Emergency Telephone Number System. Any system designed to give area citizens access to emergency response agencies via the telephone.

FX

Foreign Exchange (line). The ANI telephone number is in an area not within the boundaries of the local 9‐1‐1 service area, but it draws service from a CO within the 9‐1‐1 area.

REDUNDANCY

Having backup systems available to provide uninterrupted continuous service in the case of a failure in the main system.

DATABASE

Information that describes a collection of items. In the 9‐1‐1 environment, these items are the telephone numbers, address information and routing information for the telephone subscribers

LEC

Local Exchange Carrier. A telephone company that provides local telephone service.

MPC

Mobile Position Center. The interface between the wireless network and the ALI database. Serves as the wireless network entity that retrieves, forwards, stores, and controls position data within the wireless location network.

MSC

Mobile Switching Center is the wireless equivalent of a Central Office. It provides switching functions for wireless calls. Is the interface between the radio system and the public switched telephone network?

MTSO

Mobile Telephone Switching Office. See MSC

PSAP PERSONNEL

Persons responsible for answering incoming 9‐1‐1 calls at a PSAP, determining the action to be taken, and executing the PSAP's procedures in the disposition of such calls. Also referred to as Call‐takers, 9‐1‐1 Officers, 9‐1‐1 Operators, Dispatchers, Public Safety, or PSAP Attendants.

POTS

Plain Old Telephone Service. The traditional telephone service for the transmission of speech across the telephone network.

PDE

Position Determining Equipment. Determines the geographic location of a wireless handset when the user places a 9‐1‐1 call or in‐progress call.

PBX

Private Branch Exchange. (Also known as Private Switch, PS) A private telephone system with a switch and many stations that are not individually identifiable to the telephone company's switching network and as a result, the individual station number and location information will not be displayed by the PSAP ANI or ALI equipment.

PANI

Pseudo Automatic Number Identification. These numbers have several applications. They are assigned to a cell site sector to be used for routing a cellular 9‐1‐1 call to a PSAP. They are also used for 9‐1‐1 network access from outside the states by out‐of‐state telephone operators and remote motorist aid centers.

PSAP

Public Safety Answering Point. A facility equipped and staffed to receive 9‐1‐1 calls.

SS7

Signaling System 7. A digital network that allows call control and transaction messages from integrated voice and data networks to be transferred on communications paths that are separate from the voice and data connections.

DEDICATED TRUNKS

Telephone circuits used for one purpose only; i.e., the transmission of 9‐1‐1 calls. Other trunks are shared by multiple telephone numbers.

Master Street Address Guide (MSAG)

The MSAG contains all valid streets in the enhanced 9‐1‐1 service area. It includes low/high house numbers (address ranges), community name, and ESN assignments.

CONTROL CENTER

The Verizon Agency that serves as a central point for all PSAP trouble reports via the toll-free number 800‐773‐79‐1‐1.

LOCAL NUMBER PORTABILITY (LNP)

The ability of telephone subscribers to maintain their phone numbers when they change local telephone companies.

ONE BUTTON TRANSFER

The ability to conference another public safety agency onto a 9‐1‐1 call by pressing one button. Designed for Enhanced 9‐1‐1 systems, it requires Automatic Number Identification service.

ALTERNATE ROUTING

The capability of automatically rerouting 9‐1‐1 calls to designated alternate locations if all 9‐1‐1 trunks are busy or out of service. This capability may be activated upon request when 9‐1‐1 equipment fails, or the PSAP itself is disabled.

RINGBACK

The capability of permitting a PSAP to cause the telephone on a holding circuit to ring. This feature is not available on some 9‐1‐1 networks. Also referred to as "re‐ring."

CALLED PARTY HOLD

The capability to maintain control of an incoming 9‐1‐1 call by a PSAP for tracing or confirmation of an emergency even if the caller hangs up.

SPLASH RING

The capability to provide an audible signal simultaneously with the trunk seizure on an incoming 9‐1‐1 call.

DEFAULT ROUTING

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

INTERCONNECT

The connection of the operating telephone company's equipment with the equipment of another vendor. Also, a generic term used to refer to another vendor.

NXX

The first three digits of a local telephone number that uniquely identifies the central office switching location within its area code. Also referred to as "NNX" or Exchange.

THOUSANDS NUMBER GROUP

The last four digits of a telephone number. Also known as "line number."

TRANSFER LOCATION

The location to which a 9‐1‐1 caller is transferred when the service needed is not supplied at the PSAP.

CAD INTERFACE

The means of automatically inserting the ALI data into a Computer Aided Dispatch (CAD) system, as opposed to manually entering the information.

BUSY HOUR CALLS

The number of calls anticipated during each Public Safety Answering Point's busiest period.

AVERAGE BUSIEST HOUR

The one hour during the week statistically shown over time to be the hour in which the most emergency telephone calls are received.

TRUNK SEIZURE

The point at which a call is assigned to a trunk and acknowledgment is provided by the 9‐1‐1 call processing equipment.

DIVERSE ROUTING

The practice of routing calls through different circuit paths to prevent the total loss of the 9‐1‐1 system in the event an individual circuit is disabled.

DIAL TONE FIRST

The provision of dial tone to enable a caller to originate and complete 9‐1‐1 calls from public telephones without inserting a coin or any other device, such as a credit card. Also referred to as "coin free dialing."

ACTION AGENCY

The public safety agency has a legal or consensual obligation to respond to a call for help.

MAIN STATION

The working telephone number at a residence or business. It is directly connected to a central office and is not an extension.

FORCED DISCONNECT

This feature allows the PSAP personnel to disconnect a 9‐1‐1 call to prevent jamming of incoming lines.

UPS

Uninterruptible Power Supply. Equipment with the capability of providing a continuous source of power without regard to interruption or loss of commercial power.

CAD

Computer Aided Dispatch. A computer-based system designed to increase the efficiency and accuracy of Public Safety call handling and dispatching. This aid may range from a simple display of pertinent information on a screen, up to the actual selection, and notification of field units by the computer. 9‐1‐1 systems may be interfaced with CAD systems.

CDC

Cooperative Dispatch Center. Two or more public safety agencies combined to share communications resources. Also referred to as a Regional Dispatch Center.

CPE

Customer Premise Equipment. Equipment located at the customer's (PSAP or PSDP) location.

PS

Private Switch. See PBX