Glossary :: S-Z
SATELLITE LINK – A radio link between a transmitting earth station and a receiving earth station through one satellite. A satellite link consists of one uplink and one downlink.
SATELLITE MASTER ANTENNA TELEVISION (SMATV) – A cable television system, sometimes serving a large area, but more commonly referring to service to an apartment building, housing complex, etc.
SATELLITE NETWORK – A satellite system or part of a satellite system, consisting of only one satellite and the cooperating earth stations.
SATELLITE SYSTEM – A space system that consists or more than one artificial earth satellites.
SCRAMBLING – Any system intended to render a received message unintelligible or unviewable without authorization. Also called encryption and encoding.
SECAM – Sequence Couleur Avec Memoire; the color television broadcasting standard of France and several other nations.
SELECTION – Accessing a particular terminal in a network.
SELECTIVE CALLING – A feature whereby a sending station can specify which of several receiving stations on a network is to actually receive the message.
SERIAL – A transmission technique in which the bits or a character are sent one after another.
SHANNON’S LAW – A “law” which relates the maximum theoretically possible datarate in a circuit to the signal-to-noise ratio of that circuit.
SHIP EARTH STATION – A mobile earth station in the maritime mobile satellite service located on board a ship.
SIDEBAND – The band of frequencies either side of a carrier frequency produced by the process of modulating it by other frequencies.
SIGNAL-TO-NOSIE RATIO (SNR) – The ratio of the strength of the signal to the strength of noise in a channel, usually expressed in decibels.
SIMPLEX – Transmission in one direction only.
SIMPLEX OPERATION – Operating method in which transmission is made possible alternately in each direction of a telecommunications channel, by means of manual control.
SLOW-SCAN TELEVISION – A television technique in which a still image is transmitted over a lowbandwidth channel. A new picture is usually transmitted periodically.
SPACE – A condition of a circuit indicated by a lock of current, usually indicating a digital 0.
SPACE OPERATION SERVICE – A radio communications service in which spacecraft, in particular space telemetry and space telecommand. These functions will normally be provided within the service in which the space station is operating.
SPACE RESEARCH SERVICE – A radio communications service in which spacecraft or other objects in space are used for scientific or technological research purposes.
SPACE STATION – A station located on a object which is beyond, the mayor portion of the earth’s atmosphere.
SPACE SYSTEM – Any group of cooperating earth stations and/or space stations employing space radio communications for specific purposes.
SPACE TELEMETRY – They use telemetry for the transmission from a space station of results of measurements made in a spacecraft, including those relating to the functioning of the spacecraft.
SPACE TRACKING – Determination of the orbit, velocity or instantaneous position of an object in space by means of radiodetermination, excluding primary radar, for the purpose of following the movement of the object.
SPACECRAFT – A manmade vehicle that is intended to go beyond the major portion of the earth’s atmosphere.
SPECIALIZED COMMON CARRIER (SCC) – Carrier that provides point-to-point common carrier services other than telephone services.
SPECTRUM – The entire range of frequencies of waves, such sound waves or electromagnetic waves, or the graphical depiction of such the strength of the waves as a function of frequency.
SPOT BEAM – A focused, highpower satellite signal that covers only a small region. Outside that area, the signal is undetectable, and will not interfere with other use of the same wavelength.
SPREAD SPECTRUM – A modulation technique in which the signal is spread over a wider than the minimum bandwidth in order to provide better signal-to-noise ratio and/or communications security.
SPREAD SPECTRUM MULTIPLE ACCESS – Also called CDMA, Code Division Multiple Access, a digital technique which allows multiple users access to a transmission path by assigning each a unique code which is combined with the data to produce the transmitted signal.
STANDARD FREQUENCY AND TIME SIGNAL SATELLITE SERVICE – A radio communications service using space stations on earth satellites for the same purposes as those of the standard frequency and times signal service. This service may also include feeder links necessary for its operation.
STANDARD FREQUENCY AND TIME SIGNAL SERVICE – A radio communications service for the scientific, technical and other purposes, providing the transmission of specified frequencies, time signal or both stated high precision, intended for general reception.
STAR NETWORK – A network configuration in which one major hub is connected to many nodes, which are not connected with one another. Also called point-to-multipoint.
STATISTICAL MULTIPLEXING – A technique of time-division multiplexing that allows the combining of many lowspeed signals onto fewer highspeed channels in order to use them more efficiently. Examples are TASI and DSI.
STOP BIT – A bit sent in asynchronous transmission indicating the end of the character.
STORE AND FORWARD – The technique of temporarily stopping the flow of a message from the sender to receiver some time later.
STORED PROGRAM CONTROL – The telephone switching system, either analog of digital, in which network operations are controlled by computers.
SUBVOICE GRADE CHANNEL – A communications channel with a bandwidth insufficient to carry a telephonequality voice signal.
SUPERGROUP – A frequency division multiplexing of five 12 channel groups, totaling 60 telephone channels.
SUPERVISORY SIGNAL – Signals used within a network to indicate its operating state.
SUPPRESED CARRIER – A transmission technique in which one or both sidebands of a modulated carrier are transmitted but the carrier is partially or totally removed.
SWITCHING CENTER – Any node in a network which has many incoming and outgoing lines and is able to switch traffic among them.
SWITCH OVER – The transfer of traffic from one part of the network to another, for example in case of failure of one link.
SYNCHRONOUS TRANSMISSION – System for data transmission in which all stations operate at the same frequency determined by a master clock.
SYSTEM NETWORK ARCHITECTURE (SNA) – A network architecture from IBM comprising protocols and standards intended for data communications.
T1 – A carrier system in which a 24 digitized telephone channels (12 2-way calls) are combined and transmitted at 1.544 Mbps.
TANDEM OFFICE – An office in the telephone network which interconnects end offices which are particularly heavily used.
TARIFF – The established rate for and specifications of a telecommunication service.
TELECOMMUNICATIONS – The conveying of information by electrical or electronic means.
TELEMETRY – The use of telecommunications for automatically indicating or recording measurements at a distance from the measuring instrument.
TELEPROCESSING – A data processing facility which uses telecommunications.
TETEXT – An information distribution system that transmits text and graphical information over the used vertical blanking interval in a standard television picture.
TELETYPEWRITER EXCHANGE SERVICE (TWX) – A public switched teletypewriter service of AT&T.
TELEX – A worldwide dialup telegraph service.
TERMINAL – Any device which can send and/or receive information.
TIE LINE – A private line.
TIME ASSIGNED SPEECH INTERPOLATION – A technique of dynamic channel assignment in which a channel is actually assigned only when someone is actually speaking at any given instant.
TIME-DERIVED CHANNEL – A communications channel obtained by time division multiplexing.
TIME DIVISION MULTIPOINT ACCESS – A technique in which many users are assigned time slots during which they may make use of a transmission facility.
TIME DIVISION MULTIPLEXING – A technique of combining many slower speed signals into one higher speed signal to maximize efficient use of a transmission facility.
TOKEN PASSING NETWORK – A network, common in LANs, in which an electronic signal, the token, is passed from station to station. When received by a station, it may either pas the token to the next station, or transmits a message followed by the token.
TOLL CENTER – A telephone central office at which many channels terminate.
TOLL CIRCUIT – The American term for a circuit connecting two exchanges. In the U.K. called a “trunk circuit” if over 15 miles in length, a “junction circuit” if shorter.
TRACKING, TELEMETRY, AND CONTROL – The “housekeeping functions” for a satellite, intended to keep it on station and to monitor and control its operation.
TRNSCEIVER – A device that can both transmit and receive.
TRANSLATOR – A device which converts information expressed in one system to the proper expression in another system.
TRANSPARENT – A property of a device or system whereby it appears not exists, so that the end users need not be aware of its operation.
TRANSPARENT TEXT – A mode of operation of a datalink in which the message may contain any sequence of bits.
TRANSPONDER – The circuit aboard a communications satellite that receives the uplink signal sent from the ground, shifts its frequency to the downlink frequency, amplifies it, and transmits it to the ground.
TREE NETWORK – A hierarchical network configuration in which primary nodes are connected to secondary nodes, which are in turn connected to tertiary nodes, and so on.
TRUNK CIRCUIT – See Toll Circuit.
TRUNK EXCHANGE – An exchange connecting trunk lines rather than end users.
TSAT – A VSAT station capable of handling T1 rate traffic.
TURNKEY – A term indicating that the manufacturer or dealer performs all aspects of an installation, e.g., a turnkey satellite earth station.
TVRO – Television receive-only; the “backyarddish” satellite reception market.
TWO-WIRE CIRCUIT – A circuit in which a pair of wires or coax is used as the transmission link.
UNPROTECTED-USE TRANSPONDER – A transponder whose protection is not offered by the common carrier. Should the transponder fail, the programmer is not guaranteed replacement or service restoration.
UPLINK – The signal sent by an Earth station up to communications satellite.
VALUE-ADDED CARRIER – A carrier which provides special features in addition to carriage of telecommunications traffic. Also called value-added network.
VERY SMALL APERTURE TERMINAL (VSAT) – A satellite dish between 1.2 an 1.8 meters in diameter, typically located at a retail or other remote locations as an endpoint of a VAST network.
VIDEOCRYPT – Most commonly used European encryption system for subscription television broadcasting via satellite.
VIDEOCIPHER II – A widely used encryption technique, and the equipment which performs the encryption and decryption, invented by M/A Com and now sold by General Instrument.
VIRTUAL – A property of a circuit or device whereby it appears to exits even though it does not.
VIRTUAL TELECOMMUNICATIONS ACCESS METHOD – A system of standards for interfacing with mainframe computers.
VOICE FREQUENCY (VF) – The range of frequencies carrier in the public telephone network without special line conditioning, from about 300 Hz. Sometimes called Audio Frequencies (AF), but actually smaller bandwidth.
VOICE GRADE CHANNEL – A channel capable of carrying a telephone quality voice signal.
WORLD ADMINISTRATIVE RADIO INTERFERNCE (WARC) – The policymaking meetings of the ITU which considers global issues.
WIDE AREA TELEPHONE SERVICE (WATS) – A telephone company service which provides a user with charges based not on number or length of calls.
WIDEBAND – See Broadband.
WORKSTATION – A terminal which includes the features of both a computer terminal and a telephone.
X-BAND – Used loosely to refer to satellites operating in the 8/7 GHz range.
ZERO BIT INSERTION – A technique used in bit-oriented protocols to ensure than six 1’s never appear consecutively in the data stream.