Glossary :: D-L
D-CHANNEL – A 16 kbps channel within the ISDN system, usable for either packet data or network signaling.
DATE CIRCUIT – Termination Equipment. Device that is the interface between a data transmission facility and data terminal equipment.
DATA COMMUNICATION – The transfer of digital data by electronic or electrical means.
DATA SET – A device that provides the modem and control functions enabling data communications between terminals over some communications facilities.
DATA TERMINAL EQUIPMENT (DTE) – A device capable of transmitting digital data over a communications circuit.
DATAGRAM – A single packet of information transmitted over a packet network.
DATALINK – The circuit and equipment that allows data to be transmitted between terminals.
DATALINK PROTOCOL – A standard that governs how two terminals exchange data at the datalink level.
DATAPHONE DIGITAL SERVICE (DDS) – A digital privateline service offered by AT&T.
DECIBEL – One tenth of a bel, a unit of measure of signal strength. Bels and decibels are relative units using a logarithmic scale.
DECODER – A device that reconstructs an encrypted signal so that it can be clearly received.
DELAY DISTORTION – Distortion of a transmitted signal due to different frequencies traveling through a transmission path at different speeds.
DELAY EQUALIZER – A device to eliminate the effects of delay distortion in a transmission path.
DEMAND ASSIGNMENT MULTIPLE ACCESS (DAMA) – Any system whereby many users may access a network on demand, rather than be permanently connected.
DEMODULATION – The process of extracting the original signal from a modulated carrier.
DEMUX – Demultiplex.
DIAL PULSE – The pulse of DC current produced by a dial telephone.
DIAL-UP – The use of a telephone to place a call between two users.
DIGITAL SIGNAL – A signal that can take on only certain, discrete values.
DIGITAL SPEECH INTERPOLATION – A statistical multiplexing system which time-assigns channels to telephone calls only when a user is actually speaking.
DIGITAL TERMINATION SYSTEM – A highspeed microwave transmission service for local or intercity traffic.
DIRECT BROADCASTING SATELLITES (DBS) – Satellite operating in the 12GHz band range and beyond that provide direct-to-home transmissions.
DISSCONNECT SIGNAL – A signal within the telephone network indicating that the circuit should be disconnected.
DOMSAT – Domestic communications satellite.
DOWNCONVERTER – That portion of a satellite television receiver that translates signals in a certain frequency or block of frequencies to a lower portion of the electromagnetic spectrum, e.g., from microwave to UHF of VHF.
DOWNLINK – The signal sent from a communications satellite to the Earth station.
DUAL TONE MULTIFREQUENCY – A signaling system in which each digit dialed is indicated by two tones.
DUPLEX – A mode in which there exists two-way simulations transmission between the users.
DYNAMIC ALLOCATION – The location of transmission capacity depending upon demand.
EARTH EXPLORATION SATELLITE SERVICE – A radio communications service between an earth station and one or more space stations. The service may include links between space stations in which information relating to the characteristics of the earth and its natural phenomena is obtained from active or passive sensors on earth satellites. Similar information is collected from airborne or earth-based platforms and such information may be distributed to earth stations within the systems concerned. Platform interrogation may be included and the service may also include feeder links necessary for its operation.
EARTH STATION – The earth-based link in a communications satellites transmission system.
ECHO – The unwanted refection of a signal to its originator.
ECHO CANCELLER – A device which eliminates the echo in a channel.
ECHO CHECK – An error-checking technique in which data sent to a receiver is sent back to the sender for verification.
ECHO SUPPRESSOR – A device which reduces the signal coming back to a transmitter to reduce echo.
EFFECTIVE ISOTROPICALLY RADIATED POWER (EIRP) – A measure of the effective power emitted by a transmitter, or a measure of the signal strength received on Earth from a satellite.
EFFECTVIE MONOPOLERADIATED POWER (EMRP) (IN A GIVEN DIRECTION) – The product of the lower supplied to the antenna and its gain relative to a short vertical antenna in a given direction.
ELECTRONIC MAIL – The sending and receiving of written messages via electronic means.
ELEVATION – Angle between an antenna beam and horizontal plane.
E-MAIL – See Electronic Mail.
EMERGENCY POSITION INDICATION BEACONSTATION – A station in the mobile service the emission of which are intended to facilitate search and rescue operations.
ENCRYPTION – Scrambling (q.v.).
EQUALIZATION – The technique of compensating for difference in attenuation of a signal at different frequencies.
EQUALIZER – A device t perform equalization.
EQUIVALENT SATELLITE LINK NOISE TEMPERATURE – The noise station temperature of the receiving antenna of the earth station corresponding to the radio frequency noise power that produces the total observed noise at the ouput of the satellite link excluding noise due to interference coming from satellite links using other satellites and form terrestrial systems.
ERLANG – A measure of intensity of traffic on a circuit, equal to the average number of circuits in use.
ERROR-DETECTING CODE – A technique by which a message is sent along with additional information derived from the message by which means the receiver can determine if any errors occurred during transmission.
ESCAPE MECHANISM – A technique in which a control character signifies to the receiver that one or more following codes are to be given some alternative meaning.
EUTELSAT – European Telecommunications Satellite Organization.
EXCHANGE – A local hub in a telecommunications network connected to end users.
EXPANDER – A device which expands the dynamic range of the strength of an input signal.
EXTENDED BINARY-CODED DECIMAL INTERCHANGE CODE (EBCDIC) – An IBM originated 8-bit code used to represent characters internally in IBM equipment and sometime for external communications.
FACSIMILE (FAX) – Any system intended for the scanning, transmission, and reproduction of images of documents.
FAS-CONNECT CIRCUIT SWITCH – A circuit switch which establishes its connection typically in milliseconds.
FEDERAL COMMUNICATIONS COMMISSION – An U.S. Executive Branch administrative body, headed by a panel of seven Commissioners appointed by the President, which has authority over all interstate and foreign electromagnetic communications originating in the U.S.
FEED – For a transmitter, the part of the antenna from which the signal originates; for a receiver, the place where the reflector brings the received signal to a focus.
FEEDER LINK – A radio link from an earth station at a specified fixed point to a space station, or vice versa, that conveys information for a space radio communications service other than for the fixed satellite service.
FIBER OPTICS – The technology in which a modulated beam of light carries information through a thin glass or plastic fiber.
FILTER – A device designed to allow only a predetermined range of frequencies t pass through it.
FIXED SATELLITE SERVICE (FSS) – The telecommunications service between nonmoving Earth stations (but the antennas may be moveable, just not in motion at the time of use).
FLOW CONTROL – Any technique for governing the flow of information through a network.
FOOTPRINT – The geological range of reception of a satellite signal, usually given with signal strength.
FORWARD ERROR CORRECTION – A technique for transmitting with an item of information enough additional information to enable the receiver to reconstruct the original information if it is received with errors.
FOUR-WIRE CIRCUIT – A circuit in which a pair of wires or coax is used to copy a signal in each direction between two terminals.
FOUR-WIRE EQUIVALENT CIRCUIT – A two-wire circuit which allows simultaneous two-way communications by utilizing different carrier frequencies in the opposite directions.
FRAME – A unit block of data.
FREQUENCY DERIVED CHANNEL – A channel within a frequency divided multiplexed group of channels.
FREQUENCY DIVISION MULTIPLE ACCESS – A technique for allowing many users to share a transmission bandwidth such that the sum of all such user bandwidths is equal to the allowed bandwidth.
FREQUENCY DIVISION MULTIPLEX – A system in which each baseband signal occupies a small part of a wideband channel, each at a different frequency.
FREQUENCY MODULATION (FM) – A technique whereby a carrier wave is made to carry information by changing its frequency in portion to variations in strength of a lower frequency signal.
FREQUENCY SHIFT KEYING (FSK) – A FM technique in which different states of the original signal are transmitted as different frequencies of the carrier wave.
FULL DUPLEX – A circuit which carriers information in both directions at the same time.
GAIN OF AN ANTENNA – The ratio, usually expressed in decibels, of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given direction, the same field strength or the same power fluxdensity at the same distance. When not specified otherwise, the gain refers to the direction of maximum radiation. The gain may be considered for a specified poloarization.
GATEWAY – Any device which is an interface between difference networks.
GEOSTATIONARY ORBIT (GEO) – A special geosynchronous orbit which is circular and lying over the equator such that the satellite seems to remain stationary in the sky as seem from a location on the surface of Earth.
GEOSYNCHRONOUS ORBIT (GSO) – An orbit around the Earth with an average distance from the center of Earth of about 26,000 miles, in which a satellite would have a period equal to the rotation period of the Earth.
GIGAHERTZ (GHZ) – Unit of frequency equal to one billion cycles per second.
GRADE OF SERVICE – A measure of the probability of a user being unable to use a network because it is busy.
G/T – Gain-to-noise temperature. Express in decibels the relationship between the gain of a TVRO antenna system and the surrounding ambient noise.
GUARD BAND – A narrow band of frequencies separating frequency channel in an FDM system, used to avoid crosstalk between them.
HALF-DUPLEX (HDX) – A circuit which can carry information in both directions, but on in one direction at a time.
HANDSHAKING – Those predetermined signals which allow the establishment of a connection between two devices or networks.
HARMONIC DISTORTION – Overtones (harmonics) produced when a simple signal wave is sent through a circuit with nonlinear electrical characteristics.
HERTZ – One cycle per second of a wave.
HIERARCHICAL NETWORK – A telecommunications network in which a message is passed through nodes or different classes.
HIGH DEFINITION TELEVISION (HTDV) — The process of dividing television pictures into twice as many horizontal lines per frame as the typical television picture. HDTV increases the picture’s horizontal and vertical definition to the level of 35mm film.
HIGH LEVEL DATALINK CONTROL (HDLC) – A bit-oriented datalink protocol standardized by the ISO.
HUB POLLING – A polling technique in which a polling signals is sent sequentially form on terminal to the next.
INCLINATION OF AN ORBIT (OF AN EARTH SATELLITE) – The angle determined by the plane containing the orbit and the plane of the Earth’s equator.
INMARSAT – The international Maritime Satellite Organization, a body which international maritime satellite telephone traffic via satellites.
INTEGRATED DIGITAL NETWORK (IDN) – A telecommunications network employing both digital switching and digital transmission of information.
INTEGRATED RECEIVER DECODER (IRD) – A satellite receiver which contains a decoding circuit for scrambled signals.
INTEGRATED SERVICES DIGITAL NETWORK (ISDN) – A telecommunications network capable of carrying any form of traffic (voice, data, etc.) in a digital form.
INTELSAT – The International Telecommunications Satellite Organization, a body which international telecommunications traffic, especially from the public telephone networks, via satellites placed over regions.
INTERCHANGE CARRIER – A common carrier which carries traffic between LATA’s.
INTERCHANGE CHANNEL – A link between two changes.
INTERNATIONAL ALPHABET NO. 2 (IA2) – A CCITT standard 5-bit character code.
INTERNATIONAL ALPHABET NO.5 (IA5) – A CCITT standard 7-bit character code widely used for data transmission. ASCII is a dialect of IA5.
INTERNATIONAL TELECOMMUNICATIONS UNION (ITU) – The world’s oldest telecommunications standards organization, now a part of the United Nations. Its working bodies include the CCITT, CCIR, and IFRB.
INTER-OFFICE TRUNK – A trunk line between telephone exchanges.
INTER-SATELLITE SERVICE – A radio communications service that provides links between artificial earth satellites.
INPLANT – Those components of a telecommunication system which are located in a user’s facilities and do not utilize a common carrier.
JUMBOGROUP – A frequency division multiplexing of six mastergroups, totaling of 3,600 telephone channels.
JUMBOGROUP MULTIPLEX – A frequency division mulitplexing of three jumbo groups, totaling only, 10,800 telephone channels.
K- (OR KU-) BAND – Frequencies in roughly the 10 to 20 GHz range.
Ka- BAND – Frequencies in roughly the 18 GHz to 31 GHz range.
KEYBOARD SEND/RECEIVE (KSR) – A teletypewriter capable of sending from a keyboard only, as well as receiving.
L-BAND – Used loosley for maritime satellite systems downlinking in the 1.6 GHz region.
LAND MOBILE SATELLITE SERVICE – A mobile satellite service in which mobile earth stations are located on land.
LATA – See Local Acess and Transport Area.
LEASED FACILITY – A telecommunications facility leased for the sole use of on e customer. Also called a private line.
LINE CONDITIONING – See Conditioning.
LINE SWITCHING – Circuit switching.
LINE TERMINATION DEVICE – Any device, such as a modern, which connects a data machine to a transmission facility.
LINK – See Channel.
LINK ACESS PROTOCOL (LAP) – A CCITT standard bit-oriented protocol. Link Access Protocol Balanced (LAPB) is a variant. Both are subsets of HDLC.
LNA (LOW NOISE CONVETER) – A preamplifier used to strengthen a weak satellite signal. The LNA is used at the feedhorn of the TVRO satellite antenna and typically features a nosie figure to 120 degrees Kelvin.
LOADING – The adding of loading, or inductance, coils to a transmission circuit to minimize distortion.
LOCAL ACCESS AND TRANSPORT AREA (LATA) – A geological area within which a local telephone company provides service. Service between LATA’s os carried by IEC’s.
LOCAL AREA NETWORK (LAN) – A private data communication network connecting terminals usually within a limited geological range, and operating at high speed.
LOCAL EXCHANGE – Also called an end office, the exchange in a telephone network where the user’s line terminate.
LOCAL LOOP – A (usually 2-wire) connection between a telephone exchange office and a subscriber.
LONGITUDINAL REDUNDANCY CHECK – A technique for detecting errors in transmitted blocks of information.