Glossary of Telecom Terms

ACD - Automatic Call Distributor A special facility of a PABX or Central Office switch that automatically routes incoming calls to the next available or longest idle agent or attendant in a line hunt group.

AGC - Automatic Gain Control Electronic circuit which automatically increases the volume when someone is speaking quietly and drops the volume when someone is speaking loudly, to keep the transmitted signal constant.

Analog Single Line Station - An extension port on a PABX/KSU that will allow a standard household type phone to  interface with the system. (POTS)

BOM - Beginning of Message A short electrical pulse provided by a digital announcer when used in certain 4 wire E & M modes. The pulse alerts the PABX that the Beginning of a Message is coming.

Butt Set: a sophisticated one piece telephone used by technicians to diagnose telephone lines or equipment.

Carbon Transmitter (Handset) - The microphone of a telephone handset which uses carbon granules and a diaphragm. The diaphragm responds to voice and varies the pressure on the granules and hence, their resistance.

C.O./CO - Central Office A main telephone office where switching equipment is housed and customer lines originate. Also contains trunk line connections to other Central Offices. A C.O. line is a phone line coming from the Central Office and terminating at the userís premise.

Centrex - A name for an umbrella service offering of the local telephone company. Customers lease a portion of the Central Office switch to create a centralized point of control and routing. In concept, Centrex is providing similar features to a PABX.

CNG - CalliNG - 1100 Hz .5 second tone generated every 3.5 seconds by fax machines

Contact Closure - Contacts that when "closed" connect a pair of wires together and disconnects the wires when "open". A doorbell button is a simple example of a momentary contact closure.

CPC - Calling Party Control (Disconnect Supervision) A short break in the line current in the called partyís phone line when the calling party hangs up. Not available on PABXís.

DID - Direct Inward Dialing is a feature allowing callers to directly reach a PABX extension without an operators assistance.

Distinctive Ringing (also known as ringmate, custom ring, identifying ring master) - Different patterns of ringing that allow a user to identify the source of the call, outside, or inside (intercom) or who the call is for. Usually two burst or three burst with different durations.

DSL - Digital Subscriber Line

DTMF - Dual Tone Multi-Frequency (Touch Tone) Audible tones which conform to North American Telephone Standards. These are generated by push-button telephones to dial telephone numbers, as well as to provide control or data input to voice processing systems. Especially significant in the operation of Viking automated attendants and fax/data line sharing devices.

E2 Memory (See Non-Volatile)

E & M - Control (4 wire E & M), (the receive and transmit leads of the signaling system) An equipment signaling system usually used in PABX applications with a digital announcer. This interface control scheme is standard equipment on most Viking announcers.

Earth Ground - A wire conductor that terminates in the earth for electrical purposes.

FCC - Federal Communications Commission

Ground Start Line - A type of call signaling. In this scheme, when a call is routed to a subscriber, the phone company will apply a ground signal on the TIP side of the line even before a ring signal is sent. By detecting this signal, phone systems can immediately determine that the line is about to be in use, and avoid call crashing.

Hook Switch Flash or Switch Hook Flash - A signal originated by momentarily depressing the switch hook on a single line phone. Typically used for accessing C.O. or PABX features.

Hz - Hertz Indicates the frequency (number of cycles per second) of alternating current such as ringing voltage or Touch Tone signals.

Intercept - To stop a telephone call directed to an improper telephone number, and redirect that call to an operator or recording.

Industry Canada - (Formally DOC) is the equivalent of U.S. FCC.

ISDN - Integrated Services Digital Network An emerging international standard that defines interfaces for simultaneous voice and data transmission through a single channel over the public network.

ISDN Terminal Adapter - An interface between an ISDN line and a computer. Often these provide 1 or 2 analog POTS output ports.

KSU - Key Service Unit A central control cabinet serving many multi-button key telephones. Contains equipment which enables the user to pick up and hold PABX or Central Office lines and provide flashing line, steady, busy and wink hold signals. Dial intercom service is also an option.

LED - Light emitting diode

Loop Current - (typically 20 to 50 Ma) Current that flows from the C.O. when a telecom device goes off hook.

Loop Start Line - A type of calling signal that relies on a telecom device to allow DC current to flow when it goes into an off hook condition. The C.O. or PABX senses this current and intercepts it as a request for service. Also known as "POTS".

MOH - Music On Hold

N.O. /N.C. - Normally Open/Normally Closed Contact

"No KSU" - A phone containing all control functions normally associated with a KSU, thus not requiring a KSU.

Non-Volatile E 2 Memory - Memory that will not be lost from a power failure: Does not need battery backup.

OPX - Off Premise Extension A telephone line from the phone system terminated in a different building than the phone system.

PABX - Private Automatic Branch Exchange Phone system used to switch telephones between extensions and to outside lines. For incoming and outgoing (dial 9) calls.


PCB - Printed Circuit Board

POTS - Plain Old Telephone Service (See C.O., Analog Single Line Station, Loop Start Line)

Rack Mount - Equipment which is designed to mount in a standard steel framework consisting of parallel pairs of steel channel verticals spaced 19" and drilled for mounting screws.

RAD/RAN Device - A Record/ANnounce device such as a Digital Announcer.

RAN Trunk/RAN Circuit - A Record/ANnounce trunk or circuit that connects the telephone system to a record/announce device.

REN - Ringer Equivalency Number 1 REN = The energy to ring 1 Plain Old Telephone. The REN number can be found on the FCC label on the device. The total ringer load on a line is equal to the sum of all the REN numbers of all the telephone devices connected to the line.

Ring Back Tone - The sound you hear when the phone you call is ringing.

Ringdown Circuit - A circuit connecting 2 devices so that when one device goes off hook it automatically rings the other device.

Ring Generator - A circuit producing AC voltage that is higher that 50 VRMS and has a frequency of 20 Hz.

Ring Signal - Same as ringback

Ring Trip - The process of stopping the AC ring signal and connecting the voice path at the C.O. when the ringing telephone is answered.

Ring Voltage - A 20 Hz AC voltage higher than 50V superimposed on the phone line to ring bells, activate ring detectors in phone systems, faxes, modems, etc.

RJ-11, RJ-14, RJ-21X, RJ-25 - Request Fax back Document No. 839

RMS - Root Mean Square. This is simply a fancy way of describing the average voltage level of an audio signal.

RS232 - An Electronic Industry Association (EIA) standard that defines a computer interface for connecting serial communication devices such as printers and modems.

66 Block - A terminal block where up to 4 sets of up to 25 pairs of wire can be interconnected. The installer uses a special "punch down" tool to connect the wires.

SLT - Single Line Telephone

SOHO - Small Office/Home Office An acronym for a new class of employment where the employee may be performing part or all of their work at home in a small office set up.

Subscriber Line - The telephone line connecting the local Telco Central Office to the customerís telephone instrument or telephone system.

Talk Battery - DC voltage supplied by the C.O. to the subscriberís loop to operate the telephone equipment.

Telco - Local Telephone Company

Terminal Device - Telephone, phone system, fax, modem, etc. capable of terminating an analog phone line.

Trunk - A telephone communication path or channel between two points, one usually being a Central Office.

Trunk Port - An input on a PABX or KSU that is used to interface the system with C.O. lines.

UCD - Uniform Call Distributor An ACD programmed to distribute calls to agents or representatives on a basis other than the next available. (See ACD). Each person in the group receives the same number of calls.

UPS - Uninterruptible Power Supply Provides power to your phone equipment, computers, etc., in the event of a commercial power failure.

VOX - Voice Operated eXchange Your voice starts it. When you stop speaking its stops.

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