Acoustical design:
The art of designing rooms and other building structures to reduce or eliminate undesired sound; the control of noise and reverberation (reflected sound) in a room.

Ad hoc teleconferencing:
Special event or "as needed" teleconferencing that uses facilities that are rented or specially arranged for that specific occasion. Usually refers to a satellite-carried video conference sent from one location to many locations in hotels, television studios or other sites networked together for that program.

Add-on Conference:
A telephone or PBX feature that allows a user to add a third party to a two-party conversation. Also referred to as three-way calling or three-way conferencing.

Alphanumeric:
An expression derived from the words "alphabetic" and "numeric" which means including both numbers and letters.

Amplified telephone:
A general term for a hands-free telephone (e.g., a speakerphone) which contains a sound amplifier to broadcast incoming voice signals into the room.

Analog:
A form of information which is represented by continuous wave forms that vary as the source varies. Contrast to digital.

ASCII:
American Standard Code for Information Interchange; usually pronounced ask-ee. An eight-level code for data transfer adopted by the American Standards Association to achieve compatibility between data services.

Asynchronous:
Characteristic of any operation that is independent of a master clock or time signals; also refers to information that is sent or exchanged independent of any specific time.

Attenuation:
The decrease in signal power over distance.

Audio speaker-microphone system:
Equipment that includes at least one loudspeaker, one or more microphones and a telecommunications interface to accommodate a group of people in a teleconference.

Audio teleconferencing:
(1) Two-way voice communication between two or more groups, or three or more individuals, who are in separate locations linked by a telecommunications medium; (2) Two-way group communication by voice-only using a telecommunications medium.

Audiographic teleconferencing.
(I) Two-way voice and graphics communication between two or more groups, or three or more individuals, who are in separate locations linked by a telecommunications medium; (2) Two-way group communication by voice and graphics using a telecommunications medium; (3) The transmission of graphic and alphanumeric information (diagrams, charts, text, freehand drawings, etc.) as an adjunct to audio teleconferencing.

Bandwidth:
The maximum frequency (spectrum) measured in Hertz or cycles per second, between the two limiting frequencies of a transmission channel; the range of frequencies that can be carried by a transmission medium without undue distortion.

Baud:
A rate of information flow. Given in bits per second (bps or b/s) the rate is the highest number of single elements (bits) that can be transferred between two devices in one second.

Binary:
The basis for calculations in computers; a numbering system having only two possible states, On or Off as designated by O and 1.

Bit:
An abbreviation of "binary digit" which represents a single character in a group; either a O or 1.

Bit rate:
The speed at which bit positions are transmitted, normally expressed in bits per second.

Bit stream:
A continuous string of bit positions occurring serially in time.

BOCs:
Bell Operating Companies; telephone companies owned by AT&T before divestiture in 1984 and now organized under seven Regional Holding Companies (RHCs).

Bridge:
A device that is designed to interconnect three or more telephone lines; used to link multiple locations for audio or audiographic teleconferencing.

Bridging services:
Companies that sell bridge time and related services to customers who want to link multiple locations for teleconferencing purposes.

Broadband (wideband):
A telecommunications medium that carries high frequency signals; includes television frequencies of 3 to 6 million Hertz.

Broadcast:
The one-way transmission of information.

Buffer:
A temporary storage facility used as an interface between system elements whose data rates are different.

Byte:
The number of bits needed to represent one alphanumeric character.

Cable television.
A transmission system that distributes broadcast television signals and other services by means of a coaxial cable. Most cable systems have the potential for two-way communication in addition to broadcast television.

C-band:
Satellite transmissions in the 4 to 6 gigahertz (gHz) portion of the microwave spectrum.

CCITT:
Consultive Committee International Telegraph and Telephone; an international group that establishes transmission standards for telecommunications.

Central Office:
Telephone company facility housing switching equipment for interconnecting lines.

Centrex (CTX):
Central office switching equipment located either in the local telephone company's facilities or on the customer's premises; an alternative to PBX switching equipment.

Channel:
A band of frequencies allocated for communications.

Chip:
A thin silicon wafer on which electronic components are deposited in the form of integrated circuits; the basis of digital systems.

Circuit:
A means of both-way communication between two or more points; a complete two-way telecommunications loop.

Closed circuit television:
A private system for transmitting television signals, such as a university TV network.

Coaxial cable:
A metal cable consisting of a conductor surrounded by another conductor in the form of a tube which can carry broadband signals by guiding high-frequency electromagnetic radiation.

Codec:
A coder-decoder that is used to convert analog signals, such as voice or video, into digital form for transmission over a digital medium and, upon reception, reconverts the signals to the original analog form; may also perform other signal processing functions.

Common carrier:
An organization (such as a telephone operating company) that provides communication services to the general public at nondiscriminatory rates, without control of message content.

Communications satellite:
A "relay system" in orbit above the earth's surface for telecommunications signals such as voice, video and data; requires earth stations to transmit and receive the signals at the ground locations.

Compressed video:
Video images that have been processed to remove redundant information, thereby reducing the amount of bandwidth required to send them over a telecommunications channel. See video compression.

Compressed video codec:
A signal coding and processing device that decreases (compresses) the amount of information in a video image; may also perform other signal processing functions.

Computer conferencing:
(I) Group communication through computers. (2) The use of shared computer files, remote terminal equipment and telecommunications channels for two-way group communications in real or non-real (asynchronous) time.

Computer graphics:
The alphanumeric and graphic information generated by a computer.

Conference call:
A dial-up, operator-assisted telephone call that connects more than two individuals.

Continuous presence video:
Refers to a type of video teleconference that provides simultaneous and continuous pictures of all participants. The images are usually close- range shots of the group and may be viewed on a large screen or on one or more monitors. Contrast to voice-switched video.

Control unit (controller):
(1) A device that links pieces of equipment and controls the signal processing functions; (2) A unit that allows the user to operate a piece of equipment.

Crosstalk:
The unwanted transfer of energy from one telecommunications circuit to another.

CRT:
Cathode ray tube; a common computer display terminal.

Decibel(db):
A tenth of a bel; a unit on a logarithmic scale for measuring the relative strength of a signal, such as its power or voltage; a unit expressing the relative intensity of sounds.

Dedicated lines:
Leased telecommunications circuits that are devoted to a specific application; e.g., leased telephone lines used for a teleconference network connecting fixed locations.

Dedicated system:
A facility that is devoted to a specific purpose, such as teleconferencing.

Dial-In bridge:
A device that interconnects multiple telephone lines. Participants dial the bridge number to join the teleconference. Also called meet-me bridge.

Dial-out bridge:
A device that interconnects multiple telephone lines. Participants join the teleconference by having a bridge operator dial out to them to bring them on-line.

Dial-up lines:
Voice-grade telephone circuits on the public telephone network.

Dial-up teleconferencing
Using the public switched telephone network to interconnect lines for a teleconference either with or without operator assistance.

Digital:
A form of information that is represented by signals at discrete intervals or steps, as contrasted to continuous or analog signals.

Direct broadcast satellite (DBS):
A satellite designed with sufficient power that smaller earth stations can be used for direct on-site reception of signals.

Directional microphone:
A microphone that detects and transmits sound from only a certain direction.

Dish:
A parabolic antenna that is the primary element of a satellite earth station.

Disk (disc):
A record-like, magnetic-coated piece of material that can store digital information; may be a hard disc or pliable (floppy) disc.

Display terminal:
A device that is used to view information; usually a CRT (cathode ray tube) monitor or plasma panel.

Domestic satellite:
A satellite that provides communication services primarily to one nation.

Downlink:
An earth station that receives satellite signals.

Earth station (earth terminal):
The ground equipment including a dish and its associated electronics used to transmit and/or receive satellite communications signals.

Echo:
In telecommunications transmission, the reflections of signal energy that cause a signal to return to the transmitter or to the receiver.

Echo canceler, echo suppressor:
A device used to eliminate or block echo on a transmission channel

Electromechanical pen:
A pen that has a mechanical arm attaching it to an electronic tablet; used to create or reproduce first-hand information that is sent or received over a telecommunications channel, usually a telephone line.

Electronic whiteboard or blackboard:
A device that looks like an ordinary whiteboard or blackboard but which has a special conductive surface for creating freehand information that can be sent over a telecommunications channel, usually a telephone line.

Electronic communication:
A general term referring to the transmission and reception of information in analog or digital form over a telecommunications channel.

Electronic mail:
A system of electronic communication whereby an individual sends a message to another individual or group of people; includes computer mail and facsimile.

Electronic tablet:
(1) A device that has a conductive surface and electronic pen for producing a freehand drawing or writing that can be sent over a telecommunications channel, usually a telephone line; (2) A device that is used to enter, edit and position graphics elements to construct computer graphics displays. Often called a digitizing tablet when used with a computer system.

Encryption:
The special coding, or scrambling, of a signal for secure communications; the signal must be decoded, or unscrambled, before it can be deciphered.

End loop (local loop):
A communications circuit that extends from the customer to the local switching center; sometimes called the last mile.

End user:
The ultimate consumer of a service.

Ergonomics:
The design of the human-machine interface for a particular piece of equipment; implies that human factors are incorporated into the design.

Facsimile:
A device that electronically transmits and reproduces page copies and documents via a telecommunications channel, usually a telephone line; sometimes called a telecopier.

Fiber optics:
A communications medium based on a laser transmission that uses a fiber, or threadlike material, which carries light.

Footprint:
The geographic region of the earth that can receive signals transmitted from a communications satellite.

Four-wire circuit:
A circuit that has two pairs of conductors (four wires), one pair for the send channel and one pair for the receive channel; allows two parties to talk and be heard simultaneously.

Frame:
(1) One complete video image consisting of two fields. A standard NTSC frame has 525 scan lines, with half the lines allocated to each field. (2) One complete cycle of events in time-division multiplexing.

Freeze-frame video:
(1) A device that transmits and/or receives still video pictures over a telecommunications channel, usually a voice-grade telephone line of lower-speed data channel. (2) May refer specifically to a still frame video unit that "grabs" the image from the camera or other video source and freezes it in a fraction of a second. See slow-scan video.

Frequency:
The rate at which a current alternates, measured in Hertz (cycles per second), on a telecommunications medium.

Full-duplex:
(1) A communication channel over which both transmission and reception are possible in two directions at the same time (e.g., a four-wire circuit). (2) A communication system or equipment capable of simultaneous transmission in two directions.

Gain:
An increase in signal power in transmission from one point to another; usually expressed in decibels.

Gigahertz:
One billion Hertz (cycles per second).

Geosynchronous orbit:
A circular satellite orbit 22,300 miles above the equator that matches the earth's rotation so that the satellite remains in the same position in relation to a fixed point on the earth's surface.

Graphics and image workstation:
A device that has the capability to generate both computer or freehand graphics as well as video images captured by a TV camera; usually refers to a system that integrates freeze-frame video with computer graphics or telewriting/annotation capability. Also called integrated graphics system, integrated graphics workstation or videographics system.

Graphic tablet:
See electronic tablet.

Gray scale:
The number of shades of gray that represent a monochrome picture.

Half-duplex:
A communications channel over which both transmission and reception are possible but only in one direction at one time; e.g., a two-wire circuit.

Hard copy:
Information printed in some permanent form; information printed on paper.

Hardware:
Physical equipment components; equipment as opposed to software.

Hertz (Hz):
Unit of signal frequency. One Hertz is equal to one cycle per second. Named in honor of Heinrich Hertz, first to detect sound waves in 1883.

High-resolution system:
A system that provides a greater resolution than the standard 525-line video image, allowing more detailed images to be seen dearly; often refers to a system with a resolution of 1,000 lines.

Hollywood syndrome:
The tendency to base one's video teleconferencing behavior on a model that includes a highly polished presentation rather than interaction and the use of fast-paced visuals for effect rather than substance.

Hybrid system:
A system that combines two or more communication technologies.

Image storage unit:
A device that stores frames of visual information, usually on magnetic discs. Also called frame storage unit or frame store.

Instructional Television Fixed Service (ITFS):
A television service that is typically used for closed circuit educational applications and requires special antennas and converters to translate the signals for viewing on ordinary television sets.

Integrated Services Digital Network (ISDN):
A digital telecommunications channel that allows for the integrated transmission of voice, video and data.

Interactive media:
Refers to telecommunications channels that allow the two-way exchange of information.

Interface:
The place at which two systems or pieces of equipment meet and interact with each other.

Ka-band:
A satellite transmission in the 20 and 30 gigahertz frequency of the microwave spectrum.

Kb/s, Kbps:
Kilobits per second; one thousand bits per second; a measure of rate of digital information flow; bit rate.

Key telephone System:
A multi-linetelephone terminal; lines are usually accessed by push-button and may be central office lines, foreign exchange lines, private lines, and so forth.

KiloHertz:
One thousand Hertz (cycles per second).

Ku-band:
A satellite transmission in the 12 and 14 gigahertz frequency of the microwave spectrum.

Light pen:
A pen-like device that contains a photosensitive cell and small aperture lens that produces or detects electronic signals; can be used to write freehand directly on a TV screen or to enter, edit and position computer text or graphics.

Local Area Network (LAN):
A private digital telecommunications network carrying voice, video, data and other communications among desks or work stations in a discrete area.

Mb/s, Mbps:
Megabits per second; one million bits per second; a measure of rate of digital information flow; bit rate.

Meet-me bridge:
A type of telephone bridge that can be accessed directly by calling a certain telephone number; provides dial-in teleconferencing. The term meet-me bridging refers to the use of this type of bridge.

Meet-me teleconferencing:
A teleconference that uses a meet- me (dial-in) bridge to interconnect telephone lines.

Megahertz:
One million Hertz (cycles per second).

Memory:
A computer's information storage capability.

Menu:
A list of symbols and functions that can be selected on a computer system.

Microwave:
High-frequency radio waves used for the transmission of audio, video or data. Requires a clear line of sight between transmitter and receiver.

Modem:
Modulator-demodulator; a device that modulates and demodulates a signal (varies its amplitude, frequency or phase) for transmission over a telecommunications channel.

Multiplexing:
A technique used to transmit signals from different sources over a single channel at the same time.

Narrowband:
A telecommunications medium that carries lower frequency signals; includes telephone frequencies of about 3,000 Hertz and radio subcarrier signals of about 15,000 Hertz.

Off-premises system:
Refers to a teleconferencing room or equipment located outside of a user organization's facility; e.g., a video teleconferencing room operated by a vendor and available to the public for free.

Omnidirectional microphone:
A microphone that detects and transmits sound from all directions.

On-premises system:
Refers to a teleconferencing room or equipment that is located within the user organization's own facility.

Open microphone:
A microphone that is active, detecting and transmitting sound on a continuous basis.

PBX:
An automatic PBX, private branch exchange.

Packet switching:
A technique of switching digital signals whereby the signal stream is broken into small packets and reassembled in correct sequence at its destination; allows high-capacity and high-speed transmission for data networks, satellite communications and secure voice communications.

Peripheral device:
A piece of equipment that is attached to, but not a direct part of a central unit; e.g., an input or output device attached to the central processing unit of a computer.

Picture element, pixel:
One of many monochrome or color "dots" that comprise a television picture (also called pixel).

Plasma panel:
A device that is used to display information; it has two glass plates separated by neon gas that light up in response to electronic signals.

Plotter:
A computer output device that draws information, such as curves and lines, on paper.

Port:
A circuit in an electronic device for the input or output of signals. In a teleconference bridge, one port is needed for each telephone line

Press-to-talk microphone:
A microphone that is activated by depressing a bar or button.

Pulse code modulation (PCM):
The most frequently used method of convening analog signals into digital bits.

Quasi-duplex:
Implies that transmission and reception are possible in both directions at the same time on a half-duplex channel; also called simulated full-duplex.

Rainbarrel effect:
The condition produced by the transmission of reflected sound (room echo) along with the talker's voice, causing the received voice quality to seem hollow or as if coming from the bottom of a barrel.

Random access:
The ability to select any one of several items in any order; e.g., random access microfiche projector.

Resolution:
The amount of picture information in a video display as measured by the number of lines and picture elements.

Rollabout:
A console or cabinet that is movable (on rollers); refers to a transportable console or cabinet that houses video cameras, monitors and accessories that are ready to use for video teleconferencing.

Room Integration:
Refers to the design and/or construction of a total teleconferencing room, including the equipment, associated electronics and environment.

RS-232-C:
A standard interface between a piece of equipment and a telephone circuit.

SCA-FM:
Subsidiary Communications Authorization; an electronic technique that places the radio signal on the FM spectrum; these signals can only be picked up with special tuners that distinguish the SCA from the FWl signals.

Scan converter:
A device that converts video frequency signals to audio frequencies and vice versa; used in freeze-frame video to transmit video signals over telephone lines.

Screen density:
The maximum number of accessible screen elements in a video display.

Screen format:
The number of rows and columns in an alphanumeric display.

Shared visual space:
Refers to a system's capacity to allow participants to interact with a common graphics display area; e.g., any person can change a display element and that change is seen by all participants at all locations.

Simplex:
A communications channel or device which carries information in one direction.

Slow-scan video:
(1) A device that transmits and/or receives still video pictures over a narrow band telecommunications channel; (2) May refer specifically to a still frame video unit that accepts an image from a camera or other video source one line at a time, necessitating that the subject in front of the camera remain stationary for a number of seconds. See freeze-frame video.

Software:
A set of programs, procedures or related documentation associated with a system; materials for use with audiovisual equipment; programs in contrast to equipment.

Special event teleconferencing:
See ad hoc teleconferencing.

Switched network:
A telecommunications network in which each network site can link to any other site also on that network; examples are the public telephone network or the low-speed telex network.

Switching system:
Telecommunications equipment that interconnects and routes information carried by a network.

Synchronous:
Any operation where a series of events takes place under the control of a clocking device; also refers to information that is sent or exchanged at a certain time.

T channel:
A high-speed digital data channel. A T1 channel has a data rate of 1.544 Mb/s and is often used for compressed video teleconferencing networks. The European data rate is 2.048 Mb/s.

Tandem bridging:
A group of two or more telephone bridges that are interconnected; provides the capacity to link a greater number of telephone lines.

Telecommunications:
The use of wire, radio, optical or other electromagnetic channel to transmit or receive signals for voice, video and data communications; communications over distance using electrical means.

Teleconferencing:
Two-way electronic communication between two or more groups, or three or more individuals, who are in separate locations; includes group communication via audio, audiographic, video and computer systems.

Telecopier:
See facsimile.

Telepatcher: A device that interconnects (patches together) two or more telephone lines.

Telephone conference bridge:
A device that is designed to link three or more telephone channels for a teleconference; usually refers to a bridge that provides only dial-up teleconferencing where an operator calls each participant Contrast to meet-me bridge.

Telephony:
Design and manufacture of telephone equipment; transmission of sound by electrical means between distant stations.

Teletext: A broadcasting service using several otherwise unused scanning lines (vertical blanking intervals) between frames of TV pictures to transmit information form a central data base to receiving television sets.

Teletraining:
An integrated system for the planning, delivery and management of training or instructional programs using teleconferencing; a way for organizations to connect students atone or more remote sites with their instructor at a central classroom. Also called teleteaching, tele-education or distance education.

Telewriter:
A general term that refers to a type of system that produces freehand information that can be sent over a telecommunications channel, usually a telephone line. Includes electronic tablets, boards and similar systems used to transmit and display freehand writing and drawing.

Three-way conferencing:
See add-on conference.

Tie-line:
A telecommunications circuit or trunk between two PBXs Private Branch Exchanges).

Transceiver:
A terminal that can both transmit and receive information.

Transmission channel:
The medium by which a signal is sent and received between separate locations.

Transmission loss:
The decrease in signal energy in transmission along a circuit due to resistance or impedance.

Transponder:
The equipment on a satellite that accepts the signal sent from earth and, after amplifying and changing the frequency, sends it back to earth for reception; may be referred to as a repeater.

Transportable console:
See rollabout.

Transportable earth station:
An earth station that is mounted on a trailer and can be moved from site-to-site.

Turnkey supplier:
A vendor or contractor that supplies all components and installation services required for an operational teleconferencing system.

TVRO:
Television receive-only; an earth station that receives satellite signals; downlink.

Two-wire circuit:
A typical telephone circuit on he public switched network; a circuit on the public switched network; a circuit formed by two conductors insulated from each other to provide a send and receive channel in the same frequency.

Uplink:
An earth station that transmits a signal to a communications satellite.

Video compression:
A coding technique used to reduce he bandwidth required for the transmission of video images by reducing redundant information within or between video frames; also called bandwidth compression, data compression or bit rate reduction.

Video hard copy unit:
A device that electronically reproduces video images on paper.

Video Pointer:
An electronic device that produces an arrow or symbol that can be positioned anywhere on a displayed image to point out or highlight information.

Video teleconferencing (video conferencing):
(l) Two-way voice and video comer between two or more groups, or three or more individuals, who are in separate locations linked by a telecommunications medium; (2) Two-way group communication by voice and a telecommunications medium. Includes full-motion and compressed video systems that are fully interactive or provide two-way voice and one-way video.

Videodisc:
A hard disc that stores information in microscopic "pits" indented into the surface; provides a high-capacity storage medium of over 50,000 frames of information; used to store and retrieve video, audio and other information.

Videotex:
A service similar to teletext except that information is delivered by telephone channels and a user can interact with the data base to select information for viewing

Virtual space:
Refers to a type of video conference in which each participant is assigned a separate camera and is seen on a separate monitor, large screen or assigned spatial area.

Voice actuated:
The ability of a piece of equipment to become activated in response to the sound of a voice.

Voice/data terminal:
A desktop device that has combined capability for voice and data communications.

Voice Grade channel:
A telephone circuit that carries signals in the voice frequency range of 300 to 3,000 Hertz

Voice-switched microphone:
A microphone that is activated by a sound of sufficient amplitude; generally allows only one person to speak at a time.

Voice-switched video:
Refers to a type of video conference in which the cameras are activated by voice signals to send a picture of a particular person in the group. Not all participants can be seen at any one time in contrast to continuous presence video.

Voice-switching:
An electrical technique for opening and closing a circuit in response to the presence or absence of sound.

WATS line:
Wide Area Telecommunications Service; a type of telephone service in which subscribers pay a base rate rather than a charge per call. An in-WATS line allows anyone in a designated area to phone an 800 number and pay nothing for the call. An out-WATS line allows users to place outgoing long-distance calls.

Wideband audio:
The transmission of voice signals at a frequency of either 7,000 or 15,000 Hertz. Provides better voice quality than the normal transmission frequency of about 3,000 Hertz.