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(314)432-0756
Proudly Presents
The MCI Telecommunications Glossary
Part I Volume I (A - D)
taken directly from
The MCI School of Telecommunications Management Reference Guide
and typed by Knight Lightning
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- A -
A & B LEADS Designation of leads derived from the
midpoints of the two 2-wire pairs
comprising a 4-wire circuit.
ABBREVIATED DIALING The ability of a telephone user to
reach frequently called numbers by
using less than seven digits.
Synonym: Speed Dialing
ACCESS CHARGE A fee paid for the use of local lines.
ACCESS CODE A digit or number of digits required
to be connected to a privat line
arranged for dial access.
ACCESS LINE A telephone circuit which connects a
customer location to a network switching
center.
AIRLINE MILEAGE Calculated point-to-point mileage
between terminal facilities.
ALL TRUNKS BUSY (ATB) A single tone interrupted at a 120 ipm
(impulsess per minute) rate to indicate
all lines or trunks in a routing group
are busy.
ALTERNATE ROUTE A secondary communications path used to
reach a destination if the primary path
is unavailable.
ALTERNATE USE The ability to switch communications
facilities from one type of service to
another, i.e., voice to data, etc.
ALTERNATE VOICE DATA (AVD) A single transmission facility which
can be used for either voice or data.
AMERICAN STANDARD CODE FOR An 8 level code developed for the
INFORMATION INTERCHANGE (ASCII) interchange of information between data
processing and communications systems.
ANALOG SIGNAL A signal in the form of a continuous
varying physical quantity, e.g., voltage
which reflects variations in some
quantity, e.g., loudness in the human
voice.
ANNUNICATOR An audible intercept device that states
the condition or restrictions
associated with circuits or procedures.
ANSWER BACK An electrical and/or visual indication
to the calling or sending end that the
called or received station is on the
line.
ANSWER SUPERVISION An off-hook signal transmitted toward
the calling end of a switched
connection when the called party
answers.
AREA CODE Synonym: Numbering Plan Area (NPA).
A three digit number identifying more
than 150 geographic areas of the United
States and Canada which permits direct
distance dialing on the telephone
system. A similar global numbering
plan has been established for
international subscriber dialing.
ATTENDANT POSITION A telephone switchboard operator's
position. It provides either
automatic (cordless) or manual (plug
and jack) operator controls for
incoming and/or outgoing telephone
calls.
ATTENTUATION A general term used to denote the
decrease in power between that
transmitted and that received due to
loss through equipment, lines, or
other transmission devices. It is
usually expressed as a ration in db
(decibel).
AUDIBLE RINGING TONE An audible signal heard by the calling
party during the ringing-interval.
AUTHORIZATION CODE An identification number that the
caller enters when placing a call
which is used for billing purposes.
AUTHORIZED USER A person, firm, organization,
corporation or any other entity
authorized by the customer to send or
receive communications over a specific
communications network.
AUTO ANSWER A machine feature that allows a
transmission control unit or station to
automatically respond to a call that it
receives.
AUTOMATIC CALL DISTRIBUTOR (ACD) A switching system designed to queue
and/or distribute a large volume of
incoming calls to a group of attendents
to the next available "answering"
position.
AUTOMATIC DIALING UNIT A device which automatically generates
a predetermined set of dialing digits.
AUTOMATIC IDENTIFICATION OF A computer generated report showing all
OUTWARD DIALING (AIOD) long distance calls placed over AT&T's
toll network.
AUTOMATIC NUMBER IDENTIFICATION (ANI) Automatic equipment at a local dial
office used on customer dialed calls to
identify the calling-station.
AUTOMATIC ROUTE SELECTION (ARS) Least cost routing via AT&T CENTREX
system.
- B -
BAND (1) The range of frequencies between
two defined limits. (2) In reference
to WATS, one of the five specific
geographic areas as defined by AT&T.
Synonym: BANDWIDTH.
BANDWIDTH See BAND.
BASEBAND The total frequency band occupied by
the aggregate of all the voice and
data signals used to modulate a radio
carrier.
BAUD A unit of signaling speed. The speed in
baud is the number of discrete conditions
conditions or signal elements per
second. If each signal event represents
only one bit condition, then Baud is the
same as bits per second. When each
signal event represents other than one
bit, Baud does not equal bits per
second.
BELL OPERATING COMPANY (BOC) /BELL Any of the 24 AT&T affiliated
SYSTEMS OPERATING COMPANY (BSOC) companies providing local service.
BELL SYSTEM The aggregate of AT&T's 24 associated
telephone companies, Long Lines,
Western Electric, and Bell Labs.
BILLING NUMBER The MCI term for the number which
identifies a customer on a billing
location level, assigned to Network
Service Customer (by COMS). Assigned for
each unique customer name and billing
location. For internal use only.
BINARY A number system that uses only two
characters ("0" and "1").
BIT A binary digit. The smallest unit of
coded information.
BITS PER SECOND (BPS) The rate at which data transmission
is measured.
BLOCKED CALLS Attempted calls that are not connected
because (1) all lines to the central
offices are in use; or (2) all connecting
connecting paths through the PBX/switch
are in use.
BLOCKED ANI ANI prohibited from completing a call
over the MCI network.
BREAK A means of interrupting transmission,
a momentary interruption of a circuit.
BROADBAND A transmission facility having a
bandwidth of greater then 20 kHz.
BUS A heavy conductor, or group of
conductors, to which several units of
the same type of equipment may be
connected.
BUSY The condition in which facilities over
which a call is to be connected are
already in use.
BUSY HOUR The time of day when phone lines are
most in demand.
BUSY TONE A single that is interrupted at
60 ipm (impulses per minute) rate to
indicate that the terminal point of a
call is already in use.
BYTE A group of binary digits that are
processed by a computer as a unit.
- C -
CARRIER High frequency current that can be
modulated with voice or digital signals
for bulk transmission via cable or radio
circuits.
CARRIER SYSTEM A system for providing several
communications channels over a single
path.
CATHODE RAY TUBE (CRT) The "television-like" screen used to
display the output from a computer.
CELLULAR MOBILE RADIO A system providing exchange telephone
service to a station located in an auto
or other mobile vehicle, using radio
circuits to a base radio station which
covers a specific geographical area and
as the vehicle moves from one area to
another, different base radio stations
handle the call.
CENTRAL OFFICE (CO) A telephone switching center that
provides local access to the public
network. Sometimes referred to as:
Class 5 office, end office, or Local
Dial Office.
CENTREX, CO PBX Service provided by a switch located
at the telephone company central office.
CENTREX, CU A variation on Centrex CO provided by
a telephone company maintained "Central
Office" type switch located at the
customer's premises.
CENTRAL PRCESSING UNIT (CPU) The control unit within a computer which
handles all the intelligent functions of
the systems. In a telephone switch,
directs all potions of the system to
carry out their appropiate functions.
Synonym: Common Control.
CHANNEL A communication path via a carrier or
microwave radio.
CHARACTER Any letter, digit, or special symbol.
In data transmission would be
represented by a specific code made up
of a group of binary digits.
CIRCUIT A path for the transmission of
electromagnetic signals to include all
conditioning and signaling equipment.
Synonym: Facility
CIRCUIT SWITCHING A switching system that completes a
dedicated transmission path from sender
to receiver at the time of transmission.
CLASS OF SERVICE/CLASS MARK (COS) A subgrouping of telephone customers or
users for the sake of rate distinction
or limitation of service.
COAXIAL CABLE A cable having several coaxial lines
under a single protective sheath.
Usually used as a high capicity carrier
in urban areas between interexchange and
toll offices.
CODEC Coder-Decoder. Used to convert analog
signals to digital form for transmission
over a digital median and back again to
the original analog form.
COMMON CARRIER A government regulated private company
that provides the general public with
telecommunications services and
facilities.
COMMON CHANNEL INTEROFFICE A digital technology used by AT&T to
SIGNALING (CCIS) enhance their Integrated Services
Digital Network. It uses a seperate
data line to route interoffice signals
to provide faster call set-up and more
efficient use of trunks.
COMMON CONTROL SWITCHING ARRANGEMENT An arrangement for telecommunications
(CCSA) networks in which common controlled
switching machines are used to route
traffic over network routes and access
lines. The switching machine may be
shared with other users and is
maintained by the telephone company.
COMPUTER PORT/TKI PORT The interface through which the computer
connects to the communications circuit.
CONDITIONING EQUIPMENT Equipment modifications or adjustments
necessary to match transmission levels
and impedances and which equalizes
transmission and delay to bring circuit
losses, levels, and distortion within
established standards.
CONFIGURATION The combination of long-distance
services and/or equipment that make up a
communications system.
CONTROL UNIT (CU) The central processor of a telephone
switching device.
CORPORATE ID NUMBER The MCI term for the number which
identifies a customer on a corporate
level. (Not all MCI customers have
this).
COST COMPONENT The price of each type of long distance
service and/or equipment that
constitutes a configuration.
COST PER HOUR (CPH) Total cost of different services divided
by total holding time (in minutes).
CROSS CONNECTION The wire connections running between
terminals on the two sides of a
distribution frame, or between binding
posts in a terminal.
CROSS TALK The unwanted energy (speech or tone)
transferred from one circuit to another
circuit.
CUSTOMER OWNED AND MAINTAINED (COAM) Customer provided communications
apparatus, and their associated wiring.
CUSTOMER PREMISE EQUIPMENT (CPE) Telephone equipment, usually including
wiring located within the customer's
part of a building.
CUT To transfer a sevice from one facility
to another.
CUT THROUGH The establishment of a complete path for
signaling and/or audio communications.
- D -
DATA Any representation, such as characters
to which a meaning is assigned.
DATA COMMUNICATIONS The movement of coded information by
means of electronic transmission
systems.
DATA SET A device which converts data into
signals suitable for transmission over
communications lines.
DATA TERMINAL A station in a system capable of sending
and/or receiving data signals.
DECIBEL (db) A unit measurment represented as a ratio
of two voltages, currents or powers and
is used to measure transmission loss or
gain.
DELAY DIAL A dialing configuration whereby local
dial equipment will wait until it
receives the entire telephone number
before seizing a circuit to transmit
the call.
DELTA MODULATION (DM) A variant of pulse code modulation
whereby a code representing the
difference between the amplitude of a
sample and t~he amplitude of a previous
one is sent. Operates well in the
presence of noise, but requires a wide
frequency band.
DEMODULATION The process of retrieving data from a
modulated signal.
DIAL LEVEL The selection of stations or services
associated with a PBX using a one to
four digit code (e.g., dialing 9 for
access to outside dial tone).
DIAL PULSING The transmitting of telephone address
signals by momentarily opening a DC
circuit a number of times corresponding
to the decimal digit which is dialed.
DIAL REPEATING TIE LINE/ A tie line which permits direct station
DIAL REPEATING TIE TRUNK to station calling without use of the
attendant.
DIAL SELECTIVE SIGNALING A multipoint network in which the called
party is selected by a prearranged
dialing code.
DIAL TONE A tone indicating that automatic
switching equipment is ready to receive
dial signals.
DIALING PLAN A description of the dialing
arrangements for customer use on a
networks.
DIGITAL Referring to the use of digits to
formulate and solve problems, or to
encode information.
DIMENSION CUSTOM TELEPHONE SERVICE AT&T's electronically programmable
(DCTS) telephone station sets which use special
buttons to access PBX features.
DIRECT DISTANCE DIALING (DDD) A toll service that permits customers to
dial their own long distance call
without the aid of an operator.
DIRECT INWARD DIALING (DID) A PBX or CENTREX feature that allows a
customer outside the system to directly
dial a station within the system.
DIRECT OUTWARD DIALING A PBX or CENTREX feature that allows a
station user to gain direct access to
an exchange network.
DROP That direction of a circuit which looks
towards the local operator.
DRY CIRCUIT A circuit which transmits voice signals
and carries no direct current.
DUAL TONE MULTI-FREQUENCY (DTMF) Also know as Touch Tone. A type of
signaling which emits two distinct
frequencies for each indicaated digit.
DUPLEX Simultaneous two-way independent
transmission.
DX SIGNALING A long-range bidirectional signaling
method using paths derived from
transmission cable pairs. It is based
on a balanced and symetrical circuit
that is identical at both ends. This
circuit presents an E&M lead interface
to connecting circuits.
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This concludes Part 1 Volume I of the MCI Telecommunications Glossary. Look for
more G-philes from The MCI School of Telecommunications Management Reference
Guide coming soon.
This has been a 2600 Club production
Thanx to Taran King
