Glossary of Telecommunications Industry Terms: D to F
Bell Canada, 1998

See decibel.

See dynamically controlled routing.

See direct distance dialing.

See Digital Exchange Access.

death star satellite
French: étoile de la mort
A fixed-orbit communications satellite which, because of its ability to transmit hundreds of television channels, poses a threat to the established cable television industry.

decibel (dB)
French: décibel (dB)
A unit measuring the relative strength of sound or electrical power. The unit is useful to relate changes in loudness to changes in electrical power and vice versa. One decibel is the faintest audible sound. With respect to electrical power, it is generally used in measuring the loss or gain of power in a device or channel. One milliwatt is usually the electrical reference point for 0 decibels.

dedicated access
French: accès par liaison spécialisée
A direct connection between a terminal and a service, network, or computer dedicated to the specific use of a particular customer.

dedicated data channel
French: voie de données spécialisée
A data channel or circuit for the use of a particular customer.

French: dégradation
A deterioration in the characteristics of a signal or system.

French: démodulation
A process whereby a modulated signal is returned to its original form. A demodulator is a component of a data set or modem which converts analogue data to digital data by receiving tones sent over a communication line. (See modulation.)

French: 1) interdiction d'appel
2) refus; rejet

1) A call-blocking condition which occurs when the access to available circuits is restricted. For example, local calling may be allowed and long distance calling denied. (See blocking; Section 2: call blocking.) 2) A condition that occurs when no circuits are available and a busy tone is returned to the calling party.

dial access
French: accès par réseau commuté; accès par ligne commutée
The connection through the public switched telephone network from a terminal to a service, network or computer.

dial pulse (DP)
French: impulsion de cadran (IC): impulsion cadran; impulsion décimale (International French)
A short, direct current signal which is produced by, or simulated to look like, the opening and closing of contacts in a rotary-dial telephone when numbers are dialed. Dial pulses control the action of telephone switching equipment.

dial up
French: composition; numérotation
The use of a rotary-dial or Touch-Tone telephone to initiate a station-to-station telephone call.

digital compression
French: compression de signaux numériques; compression numérique
A collection of techniques used to compress a stream of computer-generated digital information, allowing information to be sent using less bandwidth. (See bandwidth.)

Digital Exchange Access (DEA)
French: accès local numérique (ALN)
Digital Exchange Access service provides digital access between a customer's premises or other service point and the public switched telephone network. (See public switched telephone network.)

Digital Multiplex System
See DMS.

digital signal
French: signal numérique
A discrete or discontinuous electrical signal made up of a series of on and off pulses.

digital switched network (DSN)
French: réseau commuté numérique (RCN)
A high-speed digital switched public network which allows business customers to access a huge range of calling capabilities (e.g., international telecommuting, videoconferencing, telemedicine, distance education and criminal identification) at prevailing long distance rates and discounts. DSN, which is available to customers who subscribe to Digital Exchange Access Service, Centrex Data or Integrated Services Digital Network (ISDN), is available in several countries around the world. (See Digital Exchange Access; Integrated Services Digital Network.)

digital transmission system
French: système de transmission numérique
A transmission system whereby sound waves and other information are transmitted in a series of on and off pulses, and in which the signals can be regenerated. This type of transmission is sharper, clearer and quieter than analogue transmission. (See analogue transmission; pulse modulation.)

French: numériser
The process of converting analogue signals to digital form.

direct distance dialing (DDD)
French: interurbain automatique (IA)
A telephone system which enables users to directly dial telephone numbers outside the user's local exchange area without the aid of an operator.

display unit
See visual display unit (VDU).

French: distorsion
The unwanted modification or change of signals from their true form by some characteristic of the channel or equipment being used for transmission or switching.

divestiture of AT&T
French: démantèlement d'AT&T
The settlement resulting from the U.S. Justice Department's anti-trust suit against AT&T in which that company was ordered to divest itself of its Bell operating companies (BOCs). The settlement also stipulated that the BOCs would be responsible for providing long distance service within their operating territories.

With the implementation of the settlement in 1984, ownership of the 22 BOCs (previously owned by AT&T), was consolidated into seven regional holding companies. AT&T was left with two main subsidiaries: AT&T Communications and AT&T Technologies. (See Regional Bell Operating Companies.)

DMS* (Digital Multiplex System)
French: DMS* (Digital Multiplex System)
A family of switching systems that provides digital circuit-switched service for voice and data transmission, and packet switched service for data transmission. DMS is characterized by the use of pulse code modulation (PCM) and time division multiplexing (TDM) throughout the switched network. The system allows the direct switching of PCM signals used in transmission systems without their conversion to analogue format. (See frame relay; pulse code modulation.)
*Trademark of Northern Telecom Limited

down time
French: temps d'arrêt
The period during which a computer system or device is malfunctioning.

See dial pulse.

drop; drop wire
French: branchement d'abonné; fil d'abonné
The portion of an outside telephone plant which extends from the telephone distribution cable to the customer's premises.

drop off
French: retrait
The number of customers who discontinue telephone service.

drop wire
See drop.

See digital switched network.

dynamically controlled routing (DCR)
French: acheminement adaptatif
A technique of changing transmission routing patterns dependent on network load. DCR provides significant cost efficiencies, increased flexibility and network survivability relative to the traditional hierarchical means of routing. (See high performance routing; local dynamic routing; regional dynamic routing.)

earth station
French: station terrienne
Ground facilities established for transmission and reception of telecommunications traffic to and from a satellite.

French: écho
An interference present on telephone circuits in which transmitted signals are reflected back to the source from the terminating end. This is particularly troublesome in voice communications and is overcome by the installation of echo suppressors in the transmission path which absorb the echo when each party is talking.

800 number portability
French: transférabilité des numéros 800
Enables business customers (i.e., those doing business in both Canada and the U.S.) to maintain the same 800 number, regardless of which carrier they choose, anywhere in North America.

electronic switching system (ESS)
French: système de commutation électronique
A type of analogue central office telephone switching system.

French: émulateur
Hardware or software built into a computer system which causes the system to appear as if it were another system.

French: chiffrement
The conversion of a clear text signal to a coded signal for security reasons.

equal access
French: accès égal
With equal access, customers can choose an alternative long distance company and dial 1 + the area code + the telephone number ("1 + dialing") to place all of their long distance calls on that network. (Prior to equal access, customers using alternative long distance companies had to dial up to 17 extra digits to place a long distance call.)

equivalent service
French: service de lignes groupées
Multiline telephone service in which calls are automatically completed at the next available line of a group when the dialed number is busy.

See electronic switching system.

French: circonscription; circ.
A basic unit for the administration and furnishing of telephone service which generally includes a city, town or village and adjacent areas. The territory served by an exchange, within which local rates apply, is known as the exchange area or local service area.

French: exclusion
A feature on some telephone systems permitting a user to exclude or prevent other users from gaining access to a line or channel. (See denial.)

French: installation de transmission; moyen de transmission
A transmission path between two or more locations without terminating or signaling equipment. The addition of terminating equipment would produce either a channel, a central office line or a trunk.

facsimile (fax)
French: télécopie
The transmission of pictures, maps, diagrams, etc., in which the image is scanned at a transmitter, reconstructed at a receiving station, and duplicated on some form of paper, film or computer memory.

See facsimile.

fiber optics transmission system (FOTS)
French: système de transmission par fibres optiques; système de transmission optique
A transmission system utilizing hair-thin glass fibers through which light is transmitted. Information is transferred by modulating the transmitted light. These modulated signals are detected by light-sensitive semiconductor devices. The signals are regenerated to relay the information and demodulated to retrieve the information. (See demodulation; modulation.)

flat rate service
French: service à tarif fixe
A service which is provided at a fixed monthly charge regardless of usage.

See frequency modulation.

French: zone de couverture
The geographical area throughout which signals may be transmitted to, and received from, a particular satellite.

French: droit de s'abstenir
A provision of the Telecommunications Act that allows the CRTC to refrain from regulating those sectors for which it believes regulation is not necessary. (See Telecommunications Act.)

foreign exchange service; FX service
French: service hors circonscription; service HC
A service that connects a customer's telephone to a remote exchange. This service provides the equivalent of local telephone service to and from the distant exchange.

See fiber optics transmission system.

frame relay
French: relais de trames
A high-speed packet switching data and transmission service.

French: FreeNet
A community-based, non-profit, electronic communications network, the primary purpose of which is to provide members of a regionally defined community with a single point of free access to public information.

frequency band
See band.

frequency modulation (FM)
French: modulation de fréquence (FM)
The process of modifying the frequency of a carrier wave in step with the amplitude variations of the signal to be transmitted.

fully competitive service
French: service entièrement concurrentiel
A service for which market forces are sufficiently strong to eliminate the need for service regulation (e.g., the sale and lease of terminal equipment). (See newly competitive service.)

FX service
See foreign exchange service.

A to B
G to N
O to S
T to Z