2 B+D ISDN	One of the two network-to-customer interface standards defined under ISDN, also called ISDN Basic Rate Interface. 2B+D ISDN comprises two B ("bearer") channels for voice, video, and data, and one D ("data") channel for control information. See ISDN in this section.
Algorithm	A step-by-step problem-solving procedure. Transmission of compressed video over a communications network requires sophisticated compression algorithms. Most videoconferencing systems offer both proprietary and standard compression algorithms.
Analog	Representation of coding of information in a continuous signal that varies in proportion to what's being represented, compared to digital, where information is coded into discrete numerical values. Voice and video sources (microphones, cameras) produce analog information; electronic equipment produces digital information. Conventional telephone networks and transmissions have been analog, with modems needed to convert digital computer data to analog form for sending over the network. Analog networks are subject to interference, relatively low in reproduction quality, and not able to handle large quantities of data. The analog network is rapidly being replaced by a digital network.
Analog signals	Audio/video signals currently used in broadcasting where the signal is represented by variable measurable physical quantities (such as voltage). Current TV and radio signals are analog, as are many telephone lines. (Contrast with digital)
Analog transmission	A method of sending signals whereby the transmitted signal is analogous to the original signal. The original sine wave is represented by sending a stream of continuously varying electrical waves.
Application	A software program that supports or enables an individual or group to accomplish a specific task using a computer. Examples include word processing, spreadsheets, distance learning, authoring systems, and telemedicine.
Application sharing	Application sharing is a feature that allows two people to work together when one of the individuals doesn't have the same application, or same version of the application. In application sharing, one user launches the application and it runs simultaneously. Both users can input information and otherwise control the application using the keyboard and mouse. Although it appears that the application is running on both PCs, it actually is running on only one, yet each user operates as though the application were running on both PCs. Files associated with the application can be easily transferred, so the results of the collaboration are available to both users immediately. The person who launched the application can lock out the other person from making changes, so the locked-out person sees the application running but cannot control it.
ASCII	A computer code to convert letters, numbers, and control code into a digital code that may be understood by most computers.
Aspect ratio	The ratio of the width to the height of an image or video displayed on a monitor. NTSC and PAL television uses an aspect ratio of 4 wide to 3 high, which is expressed 4:3.
Asymmetrical	Techniques where the decompression process is not the compression reverse of the compression process. Asymmetrical compression is more processing-intensive on the compression side so that video images can be easily decompressed at the desktop or in applications where sophisticated codecs are not cost effective.
Asynchronous	Information sent or exchanged independent of time. Lacking in synchronization. A method of transmitting data over a network using a start bit at the beginning of a character and a stop bit at the end. The time interval between characters may be of varying lengths. In video, a signal is asynchronous when its timing differs from that of the system reference signal.
ATM	Asynchronous Transfer Mode-high speed (up to 155 Mbps), high bandwidth, low-delay, transport technology, integrating multiple data types (voice, video, and data). ITU has selected ATM as the basis for the future broadband network because of its flexibility and suitability for both transmission and switching. May be used in the phone and computer networks of the future.
Audio	In video communications, electrical signals that carry sounds. The term is also used to describe systems concerned with sound recording and transmission; speech pickup systems, transmission links that carry sounds, amplifiers, and the like.
Audio bridge	Equipment that mixes multiple audio inputs and feeds back composite audio to each station after removing the individual station's input. This equipment may also be called a mix-minus audio system.
Audio conferencing	Voice only connection of two or more people using standard telephone or speaker phones. Audio bridges may link multiple sites.
Audio graphics	Telephone lines used to transmit audio and graphics. Ex., telefacsimile or electronic blackboard.
Auto focus	In a camera, a device for measuring the distance of the lens from a given object and automatically setting the lensfilm distance. This is important in videoconferences when there is almost no set-up time and subjects may be moving around from time-to-time.
Auto iris	A process that evaluates the light coming into a camera lens and controls the aperture size accordingly. A good feature in a videoconferencing camera.
B channel	The ISDN circuit-switched bearer channels, capable of transmitting 64 Kbps of digitized information.
Backbone network	A transmission facility used to interconnect distribution networks of typically lower speed. A backbone network often connects major sites (hubs) and from these sites spoke-like tail circuits or spurs, perhaps they themselves terminating in minor hubs, emanate.
Bandwidth	In casual use, the amount of information that can be transmitted in an information channel. High bandwidth Internet access means those web graphics load quickly on Netscape. High bandwidth videoconferencing means that the picture and sound will be clear. In computers, the speed at which data can be transmitted on a communications frequency. In telecommunications, the maximum frequency (spectrum) measured in Hertz or cycles per second, between the two limiting frequencies of a channel. The greater the bandwidth, the faster the rate of data transmission.
Bandwidth-on-demand	The ability to vary the transmission speed in support of various applications, videoconferencing being only one of several. In videoconferencing applications an inverse multiplexer or I-Mux takes a digital signal coming from a codec and divides it up into multiple 56- or 64 Kbps channels for transmission across a switched digital network. On the distant end, a compatible I-Mux recombines these channels for the receiving codec, ensuring that even if the data takes different transmission paths, it will be smoothly recombined at the receiving end.
Basic rate ISDN	See BRI and ISDN entries.
Baud rate	Bits of computer data that can be sent per second over the telephone lines.
BBS	Bulletin Board System-a computer hooked to a telephone so users may use a modem to call in, provides electronic messaging.
Bell Operating Company	Any of the 22 regulated telephone companies that were "spun off" from AT&T during divestiture. The BOCs are grouped into RBHCs (Regional Bell Holding Companies) such as NYNEX, BellSouth and others.
Bellcore	An abbreviation for Bell Communications Research. Bellcore is the research and coordinating entity that develops standards and ensures centralized services are offered by the BOCs and RBHCs. It was formed to take the place of Bell Labs which, after divestiture, severed all formal ties with the BOCs. It is owned by the seven RBHCs. This is a tricky position for Bellcore since the RBHCs view each other as competitors and periodically raid each other's service.
Bit	Binary Digit-the basic signaling unit in all digital transmission systems. The smallest unit of information with 2 possible states. 1 or 0, yes or no, on or off.
Bit map	The total of all bit planes used to represent a graphic. Its size is measured in horizontal, vertical, and depth of bits. In a one-bit (monochrome) system, there is only one bit plane. As additional planes are added color can be described. Two-bit planes yield four possible values per pixel, eight yield 256, and so on.
Bit rate	The number of bits of information transmitted over a channel in a given second. Typically expressed bps.
BNC	A twist-lock connector widely used for the connection of video cables.
bps	Bits per second-a unit of measurement of the speed of data transmission and thus of bandwidth. The higher the rate, the faster the transmission.
BRI	Basic Rate Interface (ISDN)-3 digital signals over a single pair of copper wires: 2 voice (B) channels and 1 signal (D) channel. (e.g., voice and fax on a single pair of wires). See also ISDN entry.
Bridge	In videoconferencing vernacular, a bridge connects three or more conference sites so they can simultaneously communicate. Bridges are often called MCUs - multipoint conferencing units. In IEEE 802 parlance, a bridge is a device that interconnects LAN's or LAN segments at the data-link layer of the OSI model to extend the LAN environment physically. They work with frames (as opposed to packets) of data, forwarding them between networks. They learn station addresses and they resolve problems with loops in the topology by participating in the spanning tree algorithm. Finally, the term bridge can be used in audio conferencing to refer to a device that connects multiple (more than two) voice calls so that all participants can hear and be heard.
Brightness	The luminance portion of a television or video signal.
Broadband	The term applied to networks having bandwidths significantly greater than that found in telephony networks. Broadband systems are capable of carrying a large number of moving images or a vast quantity of data simultaneously. It usually implies a speed greater than 1.544Mbps. (Contrast with wideband and narrowband) Broadband techniques usually depend on coaxial or optical cable for transmissions. They utilize multiplexing to permit the simultaneous operation of multiple channels or services on a single cable. Frequency division multiplexing or cell relay techniques can both be used in broadband transmission.
Browser	Easy to use software that allows you to find information on the Internet.
Burst	To send a group of bits in data communications, typically in a baseband transmission scheme. A color burst is used for synchronization in the NTSC standard for color television.
Bursty data	Information which flows in short intense data groupings (often packets) with relative long silent periods between each transmittion burst.
Business television	BTV-point-to-multipoint videoconferencing. Often refers to the corporate use of video for the transmission of company meetings, training and other one-to-many broadcasts. Typically uses satellite transmission methods and is migrating from analog to digital modulation techniques.
Byte	A group of eight bits; usually the smallest addressable unit of information in a data memory storage unit.
C-band	Frequencies used to transmit and receive satellite signals.
Cable	A number of insulated metallic conductors or optical fibers assembled in a group and covered by a flexible protective sheath. Sometimes used in a slang sense to refer to cable television.
Cable TV	Coaxial cable used to transmit broadcast TV signals or other data, has the potential for two-way communication.
Camcorder	Cameras and video recorder systems, packaged as a whole and permanently integrating camera, recorder and Microphone components. Camcorders are used for remote production work and consumer activities.
Camera	In video, an electronic (or in the past electromechanical) device used to convert visual images into electrical impulses. The camera scans an image and describes the light that is present using an optical system and a light-sensitive pick-up tube.
Camera presets	Allows pre-defined camera angles to be programmed into a video conferencing system.
Carrier	A term used to refer to various telephone companies that provide local, long distance, or value-added services; alternately, a system or systems whereby many channels of electrical information can be carried over a single transmission path. High frequency radio signal modulated to carry information long distances.
Carrier wave	A single frequency that can be modulated by another wave containing information. Thus, the information contained in the second wave form is superimposed on the carrier for the purpose of transmitting it.
Cathode ray tube	Developed by a German, Karl Ferdinand Braun, the CRT is a glass picture tube, narrow at one end and wide at the other. The narrow end contains a negative terminal called a cathode which emits a stream of electrons which are focused or beamed with a "gun" to "paint" an image on a luminescent screen at the wide end. The inside of the wide end is coated with phosphors that react to the electron beam by lighting up, thus creating a picture. CRTs are used in TV receivers, oscilloscopes, PC monitors, video displays, and cameras where they are part of the scanning mechanism, etc.
CATV	Community Antenna Television-developed in 1958, this technology was first used to carry television programming to areas where television service was not available. The term is now used to refer to cable television; which is a method of distributing multi-channel television signals to subscribers via a broadband cable or fiber-optics network. Early systems were generally branch-and-tree types, with all programs transmitted to all subscribers who used a channel selection switch to indicate which program they wanted.
CCD	Charge-coupled device used in cameras as an optical scanning mechanism. It consists of a shift register that stores samples of analog signals. An analog charge is sequentially passed along the device by the action of stepping voltages and stored in potential wells formed under electrodes. The charge is moved from one well to another by the stepping voltages.
CCITT	Consultative Committee for International Telegraphy and Telephoney, (now called the International Telecommunications Union's Telecommunications Standardization Sector or TSS) An international body responsible for establishing interoperability standards for communications systems. The world's leading telecommunications standards organization.
CCTV	Closed circuit television-typically used in security and surveillance applications and usually based on slow-scan technology.
CD-ROM	Compact Disc Read-Only Memory-a standard used to place any type of digital data onto a compact disc. Compact discs hold a huge amount of audio, text, or video data. On a single 4.7-inch disk, as much as 800Mbytes of information can be stored, the equivalent of 400,000 pages of text. They can now be used in multimedia applications; all CD-ROM drives available today support the Multimedia PC or MPC standard. Other standards including CD-I and DVI rely on CD-ROM. However, CD-ROMs are slow in the area of transferring the data they store, delivering it at transmission speeds between 1.2 to 1.8 Mbps.
Chair Person Control	In setting up a multipoint videoconference, one of the sites may request to have a chair person control what all of the other sites see and hear. Whoever builds the conference parameters of the MCU to allow chair control in that conference. The chair site determines what the others see and hear as well as what the chair sees on his monitor. The chair controls site can turn on/off: 1: the request the floor feature, 2. the voice activated switching feature.
Channel	Frequency asssignment.
Charge-coupled device	CCD (full name Interline Transfer Charge-Coupled Device or IT CCD)-CCDs are used as image sensors in an array of elements in which charges are produced by light focused on a surface. They are specialized semiconductors, based on MOS technology and consist of a rectangular array of hundreds of thousands of light-sensitive photo diodes (pixels). Light from a lens is focused on to the pixels, releasing electrons (charges) which accumulate in the photo diodes. The charges are periodically dumped into vertical shift registers and moved by charge-transfer so they can be amplified.
Chat	Internet Relay Chat - IRC-real-time conversation among as many as 50 people. May be restricted to a class or specific group.
Chip	An integrated circuit. The physical structure upon which circuits are fabricated as components of systems including memory systems, coding and decoding systems.
Chroma	The color information in a television or video signal, composed of hue and saturation.
Chromaticity	The quality of light, in terms of its color, as defined by its wavelength and purity. Chromaticity charts describe this combination of hue and saturation, independent of intensity. The color perceived is determined by the relative proportion of R, G, and B.
Chrominance	The combination of hue and saturation which, taken together with luminance (brightness), defines color.
CIF	Common Intermediate Format-an international standard for video display formats developed by TSS. The QCIF format, which employs half the CIF spatial resolution in both horizontal and vertical directions, is the mandatory H.261 format. QCIF is used for most desktop videoconferencing applications where head and shoulder pictures are sent from desk to desk. QCIF displays 176 pixels grouped in 144 non-interlaced luminance lines. Conversely, full CIF (FCIF) format is used for videoconferencing where several people must be viewed or details need to be magnified over a full screen. FCIF displays video frames containing 352 pixels grouped in 288 non-interlaced luminance lines.
Circuit	In telecommunications, pair of channels which together provide bi-directional communications. A circuit includes the associated terminal equipment at the carrier's switching center.
Circuit switching	The process of establishing a connection for the purpose of communication in which the full use of the circuit is guaranteed to the parties or devices exchanging information. After the communication has ended, the connection is released for use by others.
Classroom facilitator	Principle communication link between the instructor and distance learning coordinator. He or she guides the instructor in using the facilities and should have the expertise in program planning, technologies, and troubleshooting.
Clear channel	The characteristic of a digital transmission path where the circuit's entire bandwidth is available for information exchange. This differs from channels where part of the channel is reserved for signaling, control, or framing bits.
Client	In a LAN environment, an intelligent workstation (for example, a PC) that can ask for services, such as file storage and retrieval, printing, and use of applications, from the server. By extension, a client application is a subprogram that shares information with, and requests series from, a larger program. The larger program lets the client applications work together.
CO	Central Office. A CO can be one of many types of switching systems, either analog or digital, that connect subscriber lines to other lines and network trunks on a circuit-switched basis. The two most common in the U.S. are AT&T's 5ESS and Northern Telecom's DMS-100, both of which are digital.
Coaxial cable	Metal cable which can carry broadband signals. A popular and inexpensive networking cable with large capacity and low error rates. Typically used by cable television services and in LANs (as an alternative to twisted-pair wiring). The cable itself is composed of insulated central conducting wire wrapped in another cylindrical conducting wire. The whole thing is usually wrapped in another insulating layer and an outer protective layer.
CODEC	Coder-Decoder-videoconferencing hardware that codes the outgoing video and audio signals and decodes the incoming signals. Prior to transmission, the codec converts analog signals to digital signals and compresses the digital signals. Incoming audio and video must be decompressed and converted from digital back to analog. The compression method may be proprietary or standards-based.
Codec conversion	The back-to-back transfer of an analog signal from one codec into another codec in order to convert from one proprietary coding scheme to another. The analog signal, instead of being displayed to a monitor, is delivered to the dissimilar codec where it is redigitized, compressed, and passed to the receiving end. This is obviously a bi-directional process. Conversion service is offered by carriers such as AT&T, MCI, and Sprint.
Color burst	A few cycles (8 to 12) of sub-carrier frequency which serves as a color synch signal and communicates the proper hues to a video monitor or television. The absence of color burst indicates black and white video or television.
Color depth	The number of bits that are used to describe a color determine the color depth. With 8-bit color, there can be 256 different color values (28) while with 16-bit color, there can be 65,536 colors (216). The more bits used the greater the picture's resolution.
Common carrier	A private or public corporation that provides telecommunications service in a given area.
Community link	A two-way, full-motion, multi-site, multi-channel network. Fiber optic cable to link any or all sites with video and audio.
Composite video	A television signal where the chrominance signal is a sine wave that is modulated onto the luminance signal which acts as a subcarrier. This is used in NTSC and PAL systems.
Compressed video	When the vast amount of information in a normal TV transmission is squeezed into a fraction of its former bandwidth by a codec, the resulting compressed video can be transmitted more economically over a smaller carrier. Some information is sacrificed in the process, which may result in diminished picture and sound quality.
Compression	The process of reducing the information content of a signal so it occupies less space on a transmission channel or storage device and a fundamental concept of video communications. An uncompressed NTSC signal requires about 90Mbps of throughput, greatly exceeding the speed of all but the fastest and shortest of today's networks. Squeezing the video information can be accomplished by reducing the quality (sending fewer frames in a second or displaying the information in a smaller window) or by eliminating redundancy.
Computer conferencing	A process that allows individuals at different locations to communicate directly with each other through computers. Usually in real time. New applications are generically termed whiteboarding (allows two-way annotation on a white screen), and application sharing (both users can make changes to each others' document or spreadsheet).
Conferencing	The ability to meet over distance where meetings can include both visual and audible information. Typically, videoconferencing systems incorporate screens that can show the faces of distant-end participants, graphics, close-ups of documents or diagrams, and other objects.
Continuous Presence	Certain MCUs have the ability to display up to four sites on a monitor at each of the sites. For example, in a 5 point conference, each of the sites would have the video of all the other sites displayed on their monitor. The MCU electronically splits the outgoing signals into 4 quadrants. Each site's monitor would display this signal from the MCU as a quad split with the video from each site in each of the quadrants.
Contrast	The range of light-to-dark values of an image which are proportional to the voltage differences between the black and white levels of the signal.
D-channel	In an ISDN network, the D-channel is a signaling channel over which packet-switched information is passed by the carrier. The D-channel can also support the transmission of low-speed data or telemetry sent by the subscriber.
Data compression	Reducing the size of a data file by reducing unnecessary information, such as blanks and repeating, or redundant, characters or patterns.
Desktop video	Communications that rely either on video-phones or personal computers offering a video window.
Desktop videoconferencing	Videoconferencing on a personal computer. Most appropriate for small groups or individuals (compare with room-based videoconferencing). Many desktop videoconferencing systems support document sharing.
Dial-up	The ability to arrange a switched connection, whether it be analog or digital, by entering a terminating address such as a telephone number, in order that the call can be routed by the network. Differs from point-to-point services that can be used only to communicate between two locations.
Dial-up teleconference	Using public phone lines for communication between groups in various locations.
Digital	Representation or coding of information in discrete numeric values. Compare to analog, where information is coded into continuously variable form. Digital phone networks are rapidly replacing analog networks.
Digital signals	Audio/video signals represented by discrete variations (in voltage, fequency, amplitude, location, etc.) A digital clock, for example, displays the time as discrete numeric values rather than angular displacement of analog hands. In general, digital signals can be transmitted faster and more accurately than analog signals. As an example, music from digital CD's is usually more clear than music from analog records. (Contrast with analog signals.)
Digital switch	A means of supporting multiway conferencing in a fully digital network. Digital switches permit multiple users with similar codecs to conference, generally with voice-activated switching.
Digital transmission	While an analog signal is a continuous wave, digital transmission is a code of discrete binary signals (on and off, zero and one, high and low, etc.). Digital transmission is expressed by number of bits per second, or data rate.
Distance learning	The incorporation of video and audio technologies into the educational process so students can attend classes and training sessions in a location distant from where the course is being presented. Distance learning systems are usually interactive and are becoming a highly-valuable tool in the delivery of training and education to widely-dispersed students in remote locations or in instances where the instructor cannot travel to the student's site. The use of video and audio technologies in the educational process to connect students to the real world outside of their classroom. These technologies provide students the opportunity to interact with the workplace and learn from genuine workplace applications and to enrich their education through interactions with the arts community and all levels of government.
Document camera	A camera used during a videoconference for taking pictures of still images, pictures, graphics, pages of text, and 3-D objects. All images can be sent stand alone to a TV monitor or as part of a videoconference.
Document sharing	A feature supported by many desktop videoconferencing systems that allows participants at both ends of a videoconfeference to view and edit the same computer document. See also Whiteboarding.
Downlink	Receiver of electronic communication from a satellite.
Download	Using the network to transfer files from one computer to another.
Drop	Distribution to a subscriber's premises.
DSP	Digital signal processor-a specialized computer chip designed to perform speedy and complex operations on digitized waveforms. Useful in processing sound and video signals.
DSU	Data service unit-a device used to transmit digital data on digital transmission facilities. It typically interfaces to data terminal equipment via an RS-232-C or other terminal interface, connecting this device to a DSX-1 (digital system cross connect) interface.
Duplex	Communications where data can be sent and received simultaneously.
E-mail	Electronic mail, messages, and files sent over a network from one user to another.
Echo	The reflection of sound waves that results when they bounce off an object such as a window or wall. Reflected signals sound like a distorted and attenuated version of the talker's speech. Echoes in telephone and videoconferencing applications are caused by impedance mismatches: points where energy levels are not equal. In a four-wire to two-wire connection, the voice signal moving along the four-wire section has more energy than the two-wire section can absorb, thus the excess energy bounces back and is returned along the four-wire path. When the return-delay approaches 500 ms, speakers will hear their own words echoed back to them.
Echo cancellation	A process that uses a mathematical process to "guess" at an echo and remove that portion of the signal from an audio waveform so as to eliminate acoustical echo.
Echo modeling	A mathematical process where an echo is created from an audio waveform and subtracted from that form. The process involves sampling the acoustical properties of a room and guessing about what form an echo might take, then removing that information from the signal.
Echo suppression	Used to reduce annoying echoes in the audio portion of a videoconference. An echo suppressor is a voice-activated "on/off" switch that is connected to the four-wire side of a circuit. It silences all sound, when it is on, by temporarily deadening the communication link in one direction. Unfortunately, not only the echo is stopped but also the remote end's new speech, which results in clipping.
Electronic whiteboard	A computer application that allows graphics to be shared among two computers over the telephone network simultaneously. Each user can see and annotate the graphics as needed. Standards are currently being developed to allow multipoint whiteboarding.
Encryption	Scrambling of communication to provide security.
Ethernet	A Local Area Network (LAN) running on coaxial or twisted pair wiring, at 1 or 10 Mbps.
Ethernet switch	A device that connects local area networks. Ethernet switching is viewed as one solution to deliver 10 Base T networks that are bandwidth-constrained because of a new requirement to carry multimedia messages and interactive videoconferencing communications. To qualify as an Ethernet Switch, a device must be capable of switching packets from one Ethernet segment to another "on the fly" and exhibit very low port-to-port latency.
Exchange	A telephone company's switching center or wire center where subscriber lines terminate at a central location and are switched to other lines and to trunks.
Facilitator	Person responsible for the local component of a videoconference site.
Fast ethernet	A way to run Ethernet at 100 Mbps on one or two pairs of standard, unshielded telephone copper wire.
FCIF/QCIF	Standards-based formats for communicating between videoconferencing systems from different vendors. QCIF is one quarter of the resolution of FCIF. See also CIF.
Fiber optic cable	Glass (plastic) fiber and laser transmission of video, audio, or data.
Field of view	The focal length, combined with the size of the image area, light is focused on. Field of view is measured in degrees and is not dependent on the distance from a subject.
File transfer protocol	FTP-A protocol that allows you to move files from a distant computer to a local computer using a network like Internet.
Footprint	Geographic region that can easily receive and interpret a satellite signal.
Fps	Frames per second.
Fractional T-1	FT-1 or fractional T-1 refers to any data transmission rate between 56 Kbps and 1.544 Mbps. It is typically provided by a carrier in lieu of a full T-1 connection and is a point-to-point arrangement. A specialized multiplexer is used by the customer to channelize the carrier's signals.
Frame	In video, a single, complete picture displayed on a TV screen. A video frame consists of two interlaced fields of 525 lines (the NTSC standard), being transmitted at the rate of 30 frames per second. In videoconferencing, a variable number of frames, usually between 8 and 30, are sent, depending upon the amount of bandwidth available. Motion in video up to around 12 frames per second looks jerky.
Frame rate	Frequency in which video frames are displayed on a monitor, typically described in frames-per-second (fps). Higher frame rate improves the appearance of video motion. Broadcast TV (full-motion video) is 30 frames-per-second. See Full-motion video.
Frame store	A system capable of storing complete frames of video information in digital form. This system is used for television standards conversion, computer applications incorporating graphics, video walls, and various video production and editing systems.
Freeze frame	A method of transmitting video images where fewer than one or two are sent in any given second. Also known as slow-scan, still video, or captured frame video. In the system, a series of still pictures are provided, each with a successive image refreshing the scene but lacking a sense of continuous motion. This technology is often used in security and graphics conferencing systems.
Full-CIF (FCIF)-	See CIF.
Full duplex	Communication channel that allows transmission and reception in two directions at the same time.
Full-duplex audio	Two-way audio simultaneously transmitted and received without any interference or "clipping." A common feature of room-based videoconferencing systems. Contrast with half duplex audio.
Full-duplex (FDX)	Two-way, simultaneous transmission of data; a communication protocol in which the communications channel can send and recieve data at the same time. Compare to half-duplex, where information can only be sent in one direction at a time.
Full-motion video	Video reproduction at 30 frames per second (fps) for NTSC signals or 25 fps for PAL signals. Also known as continuous-motion video. Full motion video is equivalent to broadcast television video with a frame rate of 30 fps. Images are sent in real time and motion is continuous. In the videoconferencing world, the term "full-motion video" is often used and often misunderstood. Videoconferencing systems cannot provide 30 fps for all resolutions at all times nor is that rate always needed for a high-quality, satisfying video image. Picture quality must sometimes be sacrificed to achieve interactive visual communication across the telephone network economically. Videoconferencing vendors often use "full-motion video" to refer to any system that isn't still-frame. Most videoconferencing systems today run 10 to 15 frames per second at 112 Kbps.
Fully interactive audio/video	(2-way interactive video) Two sites interact with audio and video as if they were in the same place.
Genlock	Video devices require a synchronization source in order to determine the exact moment at which a video frame begins. Genlock allows multiple devices (video records, cameras, etc.) to be used together with precise timing so that they capture a scene in unison.
Graphics	Transmission of still images, usually from a video source (a camera or presentation stand), but in some cases PC-generated. Graphics may also include on-screen annotation involving drawing or text.
Graphics Camera	A camera located within a teaching room having the primary purpose of photographinc written or pictorial representation. It can be ceiling located to focus on a desktop, or directed toward a whiteboard or wall.
H.221	The ITU-T standard relating to the communications protocol for videoconferencing.
H.242	Part of the ITU-T's H.320 family of video interoperability recommendations. This recommendation specifies the protocol for establishing an audio session and taking it down after the communication has terminated.
H.243	ITU-T recommendation setting the procedures for establishing communication between three or more videoconferencing sites.
H.261	The ITU-T's recommendation that allows dissimilar video codecs to interpret how a signal has been encoded and compressed and to decode and decompress that signal. The standard also identifies two picture formats: the Common Intermediate Format (CIF) and the Quarter Common Intermediate Format (QCIF). These two formats are compatible with all three television standards: NTSC, PAL, and SECAM.
H.320	A recommendation of the ITU-T based on Discrete Cosine Transform, CCM, and motion compensation techniques. It can be a video system's sole compression method or supplementary algorithm, used instead of a proprietary algorithm when two dissimilar codecs have need to interoperate. H.320 includes a number of individual recommendations for coding, framing, signaling, and establishing connections. It also includes three audio algorithms: G.721, G.722, and G.728.
H.320 standard	A widely-used video compression standard that allows a wide variety of videoconferencing systems to communicate.
Half duplex	Transmission and reception are possible in one direction at a time.
Half-duplex audio	Two-way audio transmitted and received in turn (rather than simultaneously) so only one site can speak at a time. Contrast with full duplex audio.
Handshake	The electrical exchange of predetermined signals by devices wishing to set up a connection. Once completed, the transmission begins. Used in video communications by codecs wishing to interoperate whereby they seek out a common algorithm.
HDTV	High Definition Television-TV display systems with about four times the resolution of standard television systems. Systems labeled as HDTV typically offer at least 1,000 lines of resolution and an aspect ratio of 16:9.
Hertz-Hz	Basic measure of frequency with which an electromagnetic wave completes a full cycle from its positive to its negative pole and back again. Herz is a unit of frequency equal to one cycle per second.
Hollywood syndrome	Behavior based on a highly polished presentation using fast-paced visuals for effect. Often lacks interaction and substance.
Home page	A document with an address (URL) on WWW, maintained by a person or organization, contains pointers to other pieces of information.
HTML	Hyper Text Markup Language-the code or protocol used to create a home page.
Hub	A network's or system's signal distribution point where multiple circuits convene and are connected. Some type of switching or information transfer can then take place. Switching hubs can also be used in Ethernet LAN environments in an arrangement whereby a LAN segment might support only one workstation. This relieves congestion through a process called micro-segmenting.
IEC	Interexchange Carrier-long-distance carrier providing service between local area exchanges (LECs). AT&T, MCI, and GTE-Sprint are IECs. The services an IEC provide may be interstate or intrastate, as long as it is between local areas.
Indeo	Intel's compression/decompressional algorithm for video playback and CD-ROM applications. Indeo is similar to Motion JPEG. This algorithm has been harnessed by Microsoft in their Video for Windows, IBM in their OS/2, and Apple in their Quick Time. It supports playback at rates of 15 frames per second. These can be viewed full-screen while maintaining the same playback rate.
Interactive	Communication in which all participating sites have equal capability. Interactive videoconferencing permits all sites to see and hear one another.
Interactive media	Channel that allows for a two-way interaction or exchange of information.
Interexchange carrier	IXC or IEC-the long distance companies in the U.S. that provide interLATA telephony and communications services.
Interface	A place where equipment meets and interacts.
Internet	A computer network that joins numerous governmental and educational institutions and agencies and, thanks to various for-profit Internet providers, many commercial enterprises as well. Set up by the Department of Defense in 1969, its growth has been exponential. In 1992, there were 727,000 computers connected to the Internet; in January of 1993, there were 1,313,000, an 80 percent increase. There are presently more than ten master hub sites around the country.
Interoperability	The ability of electronic components produced by different manufacturers to communicate across product lines. The trend toward embracing standards has greatly furthered the interoperability process.
Intra-LATA	A connection that does not cross over a LATA boundary and one that regulated LECs are allowed to carry on an end-to-end basis.
ISA	Industry Standard Architecture-a bus specification for 16-bit PC adapter cards, the standard bus used in IBM-compatible PCs with AT (80286, 80386, and 80486) CPUs. AT-bus ISA or EISA specifications are used in 98% of installed PCs.
ISDN	Integrated Services Digital Network. A set of protocol and interface standards that effectively constitute an integrated (voice, video, and data) telephone "network." These standards promote global availability and compatibility of ISDN products and services. The two types of ISDN discussed in this Guide are Basic Rate Interface (BRI) and Primary Rate Interface (PRI). ISDN BRI (ISDN Basic Rate Interface) is the interface to connect the desktop to the digital long distance network. ISDN BRI provides two 64 bps B ("bearer") channels to carry information content, the voice, video, and data substance of a transmission. A separate 16 Kbps D ("data") channel is used for call setup and signaling. ISDN BRI is often called "2B+D" ISDN, for its combination of two B and one D channel. This service is marketed and supported by the LECs. ISDN PRI (Primary Rate Interface) is the ISDN equivalent of a T-1 circuit. It provides 23B+D (in North America) or 30B+D (in Europe) running at 1.544 Mbps and 2.048 Mps, respectively. Each channel (time slot) is 64 Kbps. One channel is reserved as the D channel; the other 23, as bearer channels (23+D).
ISO	International Standardization Organization. An international standards body establishing and coordinating global standards for communications and information exchange. A branch of the United Nations, ISO is headquartered in Geneva, Switzerland. ISO members are the leading standards organizations in their own countries; the United States ISO member is ANSI.
Isochronous	Pronounced "I-sockronous"-Data transmission where timing is derived from the signal carrying the data. No timing or clock lead is provided at the customer interface. In isochronous data transmission, data has no embedded timing-send it slower and it is still valid, only late. Voice and video are intimately tied to timing. With TMD (Time Division Multiplexing) services, there is a direct relationship between the signal rate used to digitize the voice and samples and the bearer channel rate, allowing accurate reconstruction of the voice (or other signals) at the far end. In packet technologies, no such relationship exists. Services like ATM must use care in transfering such signals so timing can be recovered since it cannot be derived from the ATM bearer channel.
IsoEthernet	An extension to the Ethernet LAN standard. IsoEthernet adds 6Mbps of capacity to regular Ethernet, specifically to carry low delay, constant bit rate, isochronous data. This isochronous capacity appear as up to 96 telephony channels of 64Kbps each. Like FDDI-II, IsoEthernet has the potential to carry both live voice and video calls together with LAN packet data on the same channel.
ITCA	International Teleconferencing Association, a professional association organized to promote the use of teleconferencing (audio and videoconferencing). Located in Washington, D.C.
ITU-T	International Telecommunication Union-Telecommunication sector. An organization established by the United Nations with membership from almost every government in the world. Its objective is to set telecommunications standards. Replaces the CCITT.
IXC	Interexchange carrier, long distance service providers in the U.S. that provide inter-LATA service.
JPEG	Joint Photographic Experts Group, a joint effort of ISO and TSS. JPEG has established an international standard for still image compression.
Kbps	Kilobits per second-the transporting of digitized information over a network at a rate of 1,000 bits in any given second.
Khz	Kilohertz-one thousand Hertz or cycles.
Kilobyte	1,024 bytes of data.
Kiosk	A small structure, open at one or more sides located in a public place. Kiosks today can be equipped with motion video-enabled and multimedia displays designed to educate people, untrained in the use of such a system, on a particular topic or product. Typically, they use point-and-click or single-press methods for video-enabled information retrieval.
LAN	Local Area Network, a computer network linking workstations, file servers, printers, and other devices within a local area, such as an office. LANs allow the sharing of resources and the exchange of both video and data.
LAN segmentation	Splitting one large LAN into two or more smaller LANs. This technique is used to keep LANs from getting clogged up with multimedia and desktop video applications.
LATA	Local Access and Transport Areas-the areas within which the Bell Operating and independent telephone companies can provide transport services. Inter-LATA connections must be provided by Interexchange carriers.
Lavalier	A small clip-on microphone, popular because it is unobtrusive and maintains a fixed distance to the speaker's mouth.
LEC	Local exchange company-the local telephone office that provides service between the long-distance carrier and the customer premises. Depending on the location, the LEC may be part of an RBOC (Regional Bell Operating Company) or an independent telephone company, such as GTE or United Telephone. RBOC refers to the seven Bell companies that were part of AT&T before divestiture. Each RBOC is broken down into a number of LECs. For example, the Ameritech RBOC includes Illinois Bell, Ohio Bell, Wisconsin Bell, etc.
Lens	An optical device of one or more elements in an illuminating or image forming system such as the objective of a camera or projector.
Loop	The connection between the customer's location and the local switching office.
MAN	Metropolitan Area Network.
Mbps	Megabits per second. Million bytes per second or 8 million bits per second.
MCU	Multipoint Control Unit-a bridging device that enables multiparty, multichannel (voice, video, and data) calls.
Microwave	Signals travel in straight ominidirectional lines, used to and from satellite, short distances (30 mi.)
Modem	The modulator/demodulator that converts digital signals from a computer to analog form, for sending over an analog telephone network. The modem also converts the analog signal to digital so the computer can receive data over an analog line.
Monitor	A precision display for viewing a picture. The word is now often applied to any TV set with a video (as opposed to RF) input. A reciever-monitor is a set that is both a conventional TV used for viewing broadcast television but which also accepts video input from a computer. Also refers to computer displays.
Motion JPEG	A compression technique which applies JPEG compression to each frame of a video clip. See also JPEG.
MPEG	Motion Picture Experts Group-MPEG has established standards for compression and storage of motion video that are used for storage and playback of multimedia images from CD-ROM. This standard and will expand into use in broadcasting and videoconferencing.
MPEG-1	A DCT-based compression technique used to squeeze motion video sequences when the desired image resolution is approximately 240 lines with 360 pixels per line and providing a digital image transfer rate up to about 1.5 Mbps and compression rates of about 100:1.
Multimedia	Applications depending on more than one medium for the transmittal of information: text, motion video, still image, audio, and graphics can all be combined in multimedia applications. Generally, multimedia refers to these media in a digital format for it is the digitization of voice and video information that is lending much of the power to multimedia communications in the 1900s.
Multiplexer	Hardware that brings several low-speed communication lines together and transforms them into a high-speed channel and then reverses the operation at the other end.
Multipoint	Communication configuration in which several terminals or stations are connected. Compare to point-to-point, where communication is between two stations only.
Multipoint control unit	MCU-a device that bridges together multiple inputs so more than three parties can participate in a video conference. The MCU uses fast switching techniques to patch the presenters to speaker's input to the output ports representing the other participants. See also Bridge.
Multipoint videoconference	Videoconference with more than two sites. The sites must connect via a video bridge. Compare with point-to-point videoconference.
Narrowband	A low-capacity communications circuit/path. It usually implies a speed of 56Kbps or less. Contrast with wideband and broadband.
Netscape	A software package that allows you to design a home page and to browse what is on the WWW. It is user friendly.
Network	A group of stations (computers, telephones, or other devices) connected by communications facilities for exchanging information. Connection can be permanent, via cable, or temporary, through telephone or other communications links.The transmission medium can be physical (copper, wire, fiber optic cable, etc.) or wireless, for example via satellite.
Node	A concentration point in a network where numerous trunks come together at the same switch.
NT-1	Network Termination type 1- the NT- 1 is a device which converts the two-wire line (or "U" interface) coming from your telephone company into a 4-wire line (or "S/T" interface). The NT-1 is physically connected between the ISDN board of your videoconferencing system and your ISDN phone line. The NT-1 supports network maintenance functions such as loop testing.
NTSC	National Television Standards Committee, an organization that establishes standards for TV broadcasting in the United States, Canada, and Japan. NTSC TV scans at 525 lines per frame and displays frames at the rate of 30 per second, the standard for full-motion video. Consumer video products with NTSC video connections use RCA-type phono plugs and jacks. The counterpart of NTSC in Western Europe (except France) is PAL. France follows the SECAM standard.
OLE	Object linking and embedding. This is a function where all objects you copy and paste to the notebook using the Paste Special command are automatically linked with their origination applications. You or your colleague can double-click on an object and the application associated with that object launches automatically in that person's PC (provided it is installed). Using the application, that person can edit the object. The snapshot in the notebook is updated in both the local and the remote PC's. In addition, you can update the original file from which you copied the object, if you choose.
Packet	A sequence of digitized information that is sent and switched as a unit. Computer data is sent via packets.
PAL	Phase-Alternative Line system, the TV transmission standard for Western Europe (except France, which uses SECAM). PAL TV scans at 625 lines per frame and displays frames at the rate of 25 per second.
PAN	To pivot a camera in a horizontal direction.
Pan/Tilt camera	A camera equipped with gears and braking to allow a full circular range of motion, usually controlled remotely.
PBX	Private Branch Exchange. A telephone switch, usually located on a customer's premises, connected to the telephone network but operated by the customer. A PBX provides pooled access to a given number of inside (extension) lines in a smaller number of outside lines (trunks). Often, outgoing calls are dialed directly, incoming calls are handled by an operator or switched automatically by the PBX software.
PC	A self-contained desktop or notebook computer that can be operated as a stand alone machine or connected to other PCs or mainframes via telephone lines or a LAN.
Peripherals	Document cameras, scanners, disks, optical storage devices, and the like that work with a system but are not integral to it.
Personal conferencing stand (PCS)	Developed by a group led by Intel, the Personal Conferencing Standard (PCS) addresses the needs of the individual PC users. It defines an interconnected set of data types, protocols and interfaces especially matched for the PC environment. The Personal Conferencing Standard emphasizes sharing information as it is being instantaneously created by software applications like spreadsheets, word processing, graphic draw, and so forth. It also extends this to sharing actual application packages among multiple conferencing users. In April 1995, Intel voted to make this standard fully compatible with the international H.320 video standard.
Picturephone	AT&T's video-telephone which was introduced at the 1964 World's Fair in Flushing Meadow, New York. The device had a camera mounted on the top and a 5.25" x 4.75" screen. Audio signals were transmitted separately from video signals and the system could not use the PSTN, having a transmission bandwidth requirement of 6.3 Mbps.
Pixel	The smallest element of a raster display. A picture cell with specific color and/or brightness.
Point-to-multipoint (videoconference)	Videoconfernce between multiple locations using a bridge.
Point-to-point videoconference	Videoconference between two sites. (Compare with multipoint videoconference.)
POP	Point of presence. Typically, the closest location of a carrier to a subscriber and the point at which that subscriber will be supplied with service from that carrier.
POTS	Plain Old Telephone Service. Conventional analog telephone lines using twisted-pair copper wire. This is used to provide residential service.
PRI	See ISDN.
PRI ISDN	See ISDN.
Proprietary compression algorithm	A vendor-specific algorithm for compression of a video signal. A videoconferencing system using a proprietary algorithm can only communicate with a remote site using the same algorithm. Many vendors also adhere to standard compression algorithms to facilitate communication across platforms.
Protocol	Standards, rules, formats for exchanging data that assures uniformity between computers and applications.
Public room	Videoconferencing service offered to the public on a fee-for-usage basis.
Px64	Pronounced "P times 64". (Synonymous with the ITU H.261 standard and often used to refer to the entire set of ITU videoconferencing standards; sometimes shown as P*64) An evolving multi-dimensional video telephone conferencing standard defining compression of audio and motion video images at either of two resolutions, CIF or QCIF. Px64 supports JPEG intra-frame compression, compressing by leaving out redundant information within a frame.
QCIF	See CIF.
Rate-adapted videoconferencing	Currently done in an analog gateway. In the near future will be done in a modified MCU called a digital switch called a Multiway Conferencing Systems (MCS). Ability for multiple sites to conference with each other at different transmission speeds simultaneously.
RBOC	Pronounced "R-BOCK." Regional Bell Operating Company, one of the seven Bell companies that resulted from the AT&T divestiture. Each RBOC is broken down into a number of LECs. The RBOCs are NYNEX, Bell Atlantic, Bell South, Southwestern Bell, Ameritech, US West, and Pacific Telesis.
Real-time	The processing of information that returns a result so rapidly that the interaction appears to be instantaneous. Telephone calls and videoconferencing are examples of real-time applications. These kinds of real-time information not only need to be processed almost instantaneously, but it needs to arrive in the exact order it's sent. A delay between parts of a word, or the transmission of video frames out of sequence, makes the communication unintelligible. The telephone network is designed for real-time communication.
Resolution	A measure of sharpness of clarity on a video monitor.
RGB	Red, green, blue. The additive used in color video systems. Color television signals are oriented as three separate pictures: red, green and blue. Typically, they are merged together as a composite signal; but for maximum quality and in computer applications, the signals are segregated.
Roll-about	A totally self-contained videoconferencing system consisting of codec, monitor(s), audio system, network interfaces, etc. These systems can, in theory, be moved from room-to-room. In fact, they are not really portable because they include electronic equipment that does not profit from a great deal of jostling about and, moreover, is quite heavy.
Room-based videoconferencing	Videoconferencing using a sophisticated system. Appropriate for large groups (compare to desktop videoconferencing).
Routing	Quickest path a message takes to reach destination, may be switched to different paths.
RS-232-C	A set of standards specifying various electrical and mechanical signals for interfaces between computers, terminals, and modems. In personal computer world, the original PC and PC/XT used the 25-pin RS-232 connector. With the introduction of the AT-class personal computers, the serial connector was reduced to the 9-pin version.
RS-449	Transmission interface between the codec and the transmission link that typically connects to a T-1 multiplexer.
Satellite TV	Video and audio signals are relayed via a communication device that orbits around the earth.
Scan converter	Changes a video signal to an audio signal and back again, allows freeze frame transmission of video.
SECAM	Sequential Couleur Avec Memoire. The color television system offering 625 scan lines and 25 interlaced frames per second. It was developed after NTSC and PAL and is used in France, the former Soviet Union, the Former Eastern bloc countries, and parts of the Middle east. Two versions of SECAM exist: horizontal SECAM and vertical SECAM. In this system, frequency modulation is used to encode the chrominance signal.
Server	In a LAN environment, a computer that provides services, such as file storage and retrieval, printing and application programs, for client workstations. The client/server concept has been extended to other contexts, as in Windows applications that are OLE (Object Linking and Embedding) clients capable of receiving information from servers, or servers capable of providing information to clients.
Slow scan video	Transmitter/receiver of still video over narrow band channels. In real time transmission, camera subjects must remain still.
Standard compression algorithm	An algorithm convention for compression of a video signal. Adherence to standards allows communication among a wide variety of videoconferencing systems, though not with the same clarity as two similar systems using a proprietary algorithm. H.320 is the most widely accepted standard in use today.
Still image video	Still images transmitted over standard telephone lines allowing for real-time interaction.
Switched 56	Switched 56 service allows customers to dial up and transmit digital information up to 56,000 bits per second in much the same way they dial up an analog telephone call. The service is billed like a voice line-a monthly charge plus a cost for each minute of usage. Nearly all LECs and IXCs offer switched 56 service and any switched 56 offering can connect with any other offering, regardless of which carrier offers the service.
Switched network	A network where communication is established by closing switches (for example, by dialing). In a switched network, a connection is made, used, and ended. Compare this to a leased line, where the connection is continuously open.
Synchronous	Timing is clock dependent like a TV show.
T-1 (DS-1)	High-speed digital transmission system characterized by a bit rate of 1.544 Mbps and subdivided, via time division multiplexing, into 24 channels, each with a bit rate of 64 Kbps. Frames of data are created 8,000 times a second by combining each channel's 8-bit time slot into a group of 192 bits; a synchronization bit is added to the frame making it 193 bits wide. These 193-bit frames are sent 8,000 times a second and received by a channel bank of T-1 multiplexer.
T-3 (DS-3)	A carrier of 45 Mbps bandwidth. One T-3 channel can carry 28 T-1 channels. Used for digital video transmissions or for major PBX-PBX interconnection.
T.120	A standard for audiographics exchange. While H.320 does provide a basic means of graphics transfer, T.120 will support higher resolutions, pointing, and annotation. Users can share and manipulate information much as they would employ if they were in the same room though they are working over distance and using a PC platform. T.120 will allow audio bridge manufacturers to add graphics to their products in support of a wide range of applications.
Talking head	The portion of a person that can be seen in the typical business-meeting style videoconference; the head and shoulders. This type of image is fairly easy to capture with compressed video because there is very little motion in a talking head image and most occurs in facial expression and torso movement.
TELCO	Generic term for telephone company. Can refer to an Interexchange Carrier or to the Local Exchange Carrier. In this guide, we use IEC and LEC to make it clear which is being discussed. TELCO is used in the generic sense, as for the TELCO cable that runs between a phone outlet in the wall and the jack in the telephone unit.
Telecommunication	The combination of computer and communication technology that expands the capacities of both.
Telecommunicat-ions network	A group of interconnected telephones, switches, computers, and other equipment used for transmitting and receiving voice, data, and video traffic.
Telecommuting	The process of commuting to work electronically rather than physically. Telecommuting will find much greater acceptance as the public switched telephone network becomes more robust and digital and as videoconferencing and multimedia technologies arrive at the desktop.
Teleconference	An audio, audiographic, or video conference where participants are in geographically separate locations.
Teleconferencing	Two-way electronic communication between two or more groups in separate locations via audio, audiographic, video, and computer systems.
Telecourse	A course that is sent/received electronically.
Telemedicine	The practice of using videoconferencing technologies to diagnose illness and provide medical treatment over a distance. Used in rural areas where health care is not readily available and to provide medical services to prisoners, among other applications.
Telephony	Telephone technology, including the conversion of sound into electrical signals, their transmission to another location, and their reconversion to sound. Can be with wires or wireless.
Token ring	A LAN running on coaxial or twisted-pair wiring at 4 or 16 Mbps.
Transponder	Microwave receiver and transmitter.
TSS	Telecommunications Standardization Sector. The TSS develops technically-oriented international communications standards. All member countries of the International Telecommunications Union (ITU), one of the specialized agencies of the United Nations, can participate in the work of the TSS. A plenary assembly is usually held at four-year intervals, at which time all the recommendations that have been developed since the last formal meeting are voted on, adopted, and published. These standards have an important influence on the design and manufacture of telecommunications equipment worldwide. In addition to approving new standards, the ITU-T's plenary assembly compiles new lists of technical questions, the study of which leads to improvements in international telephony. These questions are entrusted to Study Groups composed of experts from different countries.
Twisted pair	A pair of copper wires twisted to minimize noise pickup; the conventional medium linking subscribers to their telephone office.
Uplink	Able to transmit to a satellite.
Upload	Send a file from your computer to another computer
URL	Uniform Resource Locator-Address on the WWW.
UTP	Unshielded Twisted Pair Wiring. A cable medium with one or more pairs of twisted insulated copper conductors bound in a single sheath. Now the most common method of bringing telephone and data to the desktop.
Video bridge	Computerized switching system which allows multipoint videoconferencing.
Video capture board	A PC circuit board that can capture the two fields that comprise a single video frame. Most 386SX PCs can support such boards. The best source of single-frame video images is a laser disk player which can pause and display a perfect frame of video without noise or jitter. Video cameras or camcorders aimed at a static image also work well. VCRs, which produces a jittery image when the tape is paused, are the poorest source.
Video for Windows	An extension of Microsoft's Windows operating evnironment and an architecture for incorporating different media types into Windows applications. The "shrink wrapped" product includes a set of low-end software tools for the playback, capture, and editing of video. It includes three different codecs; Intel's Indeo, Microsoft's Video 1, and a run length encoding codec. It also includes a CD-ROM with hundreds of sample video clips. The product offers "scalable performance", it automatically adapts the size and frame rate of a video image to the computer hardware available.
Video mail	Electronic mail that includes moving or still images that are embedded into the message.
Video teleconferencing	A teleconference including two-way video.
Videoconferencing	Communication across long distances with video and audio contact that may also include graphics and data exchange.
Virtual space	A videoconference where each person is the focus of a separate camera and has its own space on the monitor. Enables instructor to see each person at multiple sites at the same time.
Voice actuated	Equipment becomes active at the sound of a voice.
Voice-activated mulipoint videoconferencing	The MCU is set to switch between sites depending on who is speaking.
WAN	Wide Area Network. A communications network that services a geographic area larger than that served by a local area network or metropolitan area network. WANs include commercial or educational dial-up networks such as CompuServe, InterNet, and BITNET.
Whiteboarding	A term used to describe the placement of shared documents on an on-screen "shared notebook" or "whiteboard." Desktop videoconferencing software includes "snapshot" tools that enable you to capture entire windows or portions of windows and place them on the whiteboard. You can also use familiar Windows operations (cut and paste) to put snapshots on the whiteboard. You work with familiar tools to mark up the electronic whiteboard much like you do with a traditional wall mounted board.
Wideband	A medium-capacity communications circuit/path. It usually implies a speed from 64 Kbps to 1.544 Mbps. (Contrast with broadband and narrowband)
Wire	Sometimes used synonymously with copper wire, sometimes used for any physical transmission medium.
Wireless	Transmission via radio waves or satellite. Wireless transmission is likely to be used in many computer networks of the future.
WWW	World Wide Web-Software that provides easy access to almost all Internet based information including images and sound.
Y/C	In component video, the "Y" or luminance signal is kept separate from the "C" (hue and color saturation signal) to allow greater control and to enable enhanced quality images. The luminance is recorded at a higher frequency and, therefore, more resolution lines are available. Super-VHS and Hi8 systems use V/C video.