Navigation note: Unless you have set different preferences in your browser, links that are red are links you haven’t visited; links that are blue are links you have already visited. Click on a letter of the alphabet to go to that part of the glossary. You can also return to TeleSpan’s home page or to the Buyer’s Guide Table of Contents by using the links in the menu bar.

If you don’t see a term defined here, you can also check the following links:
The Lycos Webopedia
The RIM/RATV 458 Glossary of Terms, a glossary from a Middle Tennessee State University course on Disk-based Audio Postproduction taught by Doug Mitchell.

For those interested in tutorials as well as an expanded view of terms which are linked to Packet or IP technology, and the standards they rely on, we strongly recommend visiting The Packetizer operated by Paul E. Jones.

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Acoustics: The science that studies sound waves and their propagation.

Algorithm: Specifications that define a specific method for transmitting video, audio, and/or data. [Source: Global Crossing]

Amplifier: An electrical device used to increase the level or strength of a signal. Used frequently for voice or audio signals but can be used for any signals transmitted over a communications channel. Satellite signals, for example, are amplified.

Analog: A communications channel or signal that uses a continuous electromagnetic waveform to convey information.

Audio: The voice portion of a communications link.

Audio conferencing: 1. A teleconferencing mode that allows individuals and groups to communicate through voice alone. 2. Telecommunication systems that allow participants to hear and be heard by one another [Source: Dr. Martin Elton, New York University]. 3. Two-way voice communication between two or more groups or three or more individuals, who are remote from one another and are using a telecommunications medium.

Audio conferencing services: Usually refers to independent telephone conferencing services that allow individuals and groups to hold audio teleconferences using bridges and services available through a supplier independent of the telephone company. However, most telephone companies offer this service as well.

Audio room design: The architectural and engineering factors to consider in converting a conference room into an audio teleconference room. Relies upon acoustical engineering.

Audiographic equipment: Equipment used in audiographic conferencing.

Audiographic conferencing: A teleconferencing mode that allows participants to share and interact through graphics, figures, and printed text.

Audiographics: Graphics, text and diagrams shared between sites in a teleconference and transmitted over narrowband or telephone channels. Includes such devices as facsimile, telewriters, and film-based projectors.

Audio-plus: An alternate term for audiographic conferencing.

Augmented audio: An alternate term for audiographic conferencing.

Automated bridging: See Fully automated.

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Bandwidth: In terms of signal frequency, the range between the lowest and the highest frequencies used to transmit a signal from one site to another. Bandwidth as a measure of an analog signal is measured in cycles per second. Contemporary units are Hertz (one cycle equals one Hertz). Bandwidth as a measure of a digital signal is measured in bits per second, and is usually referred to as data rate. For example, a regular Ethernet line has a bandwidth of 10 Mbps. High bandwidth allows fast transmission or the transmission of many signals at once. [Source: York Telecom]

Baseband: In analog terms, the original bandwidth of a signal from a device (e.g., 3 kHz for telephone, 4.5 mHz for television).

Baseband LAN: A local area network that has only one communications channel. See also Broadband LAN.

Bird: Slang for communication satellite.

Bit: A computer term denoting the smallest logical piece of information, a binary digit. Bit values are 1 and 0.

bps: bits per second, used to measure the speed of data transmission [Source: York Telecom]

BRI: Basic Rate Interface provides two 64 kbps B ("bearer") channels to carry information. A separate 16 kbps D ("data") channel is used for call setup and signaling. [Source: York Telecom]

Bridge: An electronic device that mixes the signals from three or more locations for audio or audiographic teleconferencing. The term bridge is as well used to describe a multipoint conference unit (MCU) that is used to bridge video locations.

Bridge and conferencing services: See Audio conferencing services.

Bridging: See Bridge.

Bridging equipment: See Bridge.

Bridging services: See Audio conferencing services..

Broadband (wideband) channel: A communications channel with a bandwidth larger than that required for baseband transmission. Very often any channel wider than voice grade is considered to be a broadband channel. In IP, tends to describe a connection that provides a minimum of 384 kbps in each direction or higher. Typically it describes an IP connection that can transmit 1.544 mbps in each direction of higher.

Broadband LAN: A local area network that has multiple communications channels. See also Baseband LAN.

Broadcast fax: A call announcement process that sends a fax to all participants prior to a conference call. [Source: Global Crossing]

Broadcast system: A system that allows public access to electronically transmitted information. Typically a commercial television or radio station regulated by the Federal Communications Commission (FCC).

Broadcasting: The transmission of electronic information over radio frequencies (through the air) by a broadcast system.

Built-in system: An audio or videoconferencing system that is permanently built into a room. Often built-in systems can be found in board of directors’ conference rooms or in distance-education rooms. Often the systems have custom cabinets made to house the electronics.

Byte: A computer term denoting the number of bits of information representing a character.

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Channel: A band of frequencies allocated for communications.

Circuit: An electrical connection between electric or electronic components.

Clearance line: A connection between an operator and a representative from the host company that is used to obtain authorization for participants to join the conference. [Source: Global Crossing]

Codec: acronym for Coder/Decoder or Compression/Decompression systems. An electronic circuit that converts analog audio and/or video signals to digital form and vice versa. [Source: York Telecom]

Codec, video: A codec that converts an analog video signal to digital form and vice versa. In addition, video codecs generally compress or reduce the data rate to multiples of 56 kbps or 64 kbps, typically 112/128 kbps, 384 kbps, and 768 kbps. Coding is typically in multiples of "B" or bearer channels of 64 kbps. (See ISDN.)

Codec, voice: A codec that converts an analog voice signal to digital form and vice versa. Typically the voice signals are converted to data rates ranging from 64 kbps down to 9.6 kbps.

Communication line: A connection between an operator and a representative from the host company that is used to manipulate the Q&A session, give status updates, and troubleshoot. [Source: Global Crossing]

Compression: The action taken by a video codec in reducing the data rate required for the transmission of television signals between sites.

Conditional replenishment: A coding scheme used by video codecs in reducing the data rate required for the transmission of full motion, full color video images in teleconferencing. It is an interframe coding scheme that relies upon conveying only the differences between two successive frames in a sequence. Arun Netravali of Bell Telephone Laboratories suggests that this is one of the two major types of interframe coding schemes, the other being motion compensation.

Conference bridges: See Bridge.

Conference calls: Telephone conversations connecting three or more individuals.

Continuous presence: A videoconference in which each participant is seen in one quadrant of the screen for the entire length of the meeting. [Source: Global Crossing]

Convergence: A term synonymous with multimedia describing the coming together of various media, such as voice, video, and data, in a single teleconference. The term was used frequently in the 1990s to suggest that teleconferences and even phone calls in the decade of 2000 would use more than one media at the same time.

Cosine transform coding: An algorithm or method used by some video codecs to compress digitized motion video images to very low data rates. Relies upon the mathematical transform referred to as the cosine transform. Generally used in intraframe coding.

COST 211: Co-Operation in Scientific and Technical research; a project involving seven countries, which developed a European T1 (2.048 Mbps) codec.

Customer premises: A physical location under the control of a company or organization. Generally a location containing a room where individuals or groups congregate for participation in a teleconference.

Customer premises equipment: Equipment owned by a customer and used at a location controlled by the customer’s organization.

Customized room system: These systems require an experienced systems integrator to install. Considered "smart rooms," they are built with base model codecs integrated into a room system with projection, lighting, VCR, DVD, Electronic Whiteboards and other technological meeting tools. These rooms also utilize a control system like AMX or Crestron. [Source: York Telecom]

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Data conferencing: A teleconference where non-voice information, such as PC data, text, images, PowerPoint presentations, and graphics, are shared in a teleconference. The term is synonymous with Web conferencing, and even audiographics. The term was first used in the 1990s when the ITU recommended the T.120 standard for sharing data during a teleconference. The term is now widely used to include other earlier audiographic forms of conferencing including what used to be called “screen/tablet” and “electronic blackboards.” In its simplest form, it allows one person to present information to an unlimited number of others through a PowerPoint presentation or through streaming software.

Data rate: The measurement for bandwidth in bits per second. In general, the higher the data rate, the higher the quality of video. [Source: Global Crossing]

Dedicated-Private Network: Typically available via T1/E1 access lines. This service is also provided in fractions of T1. [Source: York Telecom]

Definition: Commonly used in place of the term "resolution" for television systems.

Desktop system: Also known as a Personal System, these are designed for geographically dispersed individuals who need to share, create and modify information. They are usually based on a PC hardware platform. [Source: York Telecom]

Desktop video: A videoconference held using a codec that is embedded in a personal computer system. [Source: Global Crossing]

Dial-in: Generally an audio teleconferencing system or bridge that requires participants to dial in through normal telephone circuits to participate in the teleconference. Also referred to as "meet-me."

Dial-out: A teleconferencing system that uses a bridging device requiring a conference operator to dial out to bring participants into the conference.

Differential Pulse Code Modulation (DPCM): A “predictive” coding scheme used in picture processors. Examines the difference between adjacent picture elements (pixels) on a television line in an attempt to reduce the amount of data transmitted. Used in intraframe coding.

Digital: A method of representing information using a sequence of ones and zeros for storage and interpretation by a computer. In digital transmission, analog signals that are originally in a continuous form are converted to discrete signals of zeros or ones to be transmitted to a receive site, interpreted, and used to reconstruct the original analog signal.

Digital compression: The process by which a codec reduces the amount of data needed to be transmitted to represent the original analog signal. Used in audio and in video.

Digital phone equipment: Telephones in today’s offices are connected to devices called private branch exchanges (PBXs) using a proprietary method of communications that often relies on digital technology. Manufacturers of quality speakerphones ship their units so that they can be connected to these PBXs and digital phone equipment.

Digitizing camera: A camera that outputs a digital representation of the image, rather than an analog signal.

Dish: Slang for antenna or earth station.

Distance learning: (Sometimes distant learning.) The use of video and audio technologies in the educational process, which allows students at one location to attend classes or seminars at another. [Source: York Telecom]

Document camera: A specialized camera used for taking pictures of still images—pictures, graphics, text pages—which can be sent as a part of a videoconference. [Source: Global Crossing]

DOMSAT: Domestic satellite.

Downlink: Site that receives the signal from the satellite in a videoconference. May also refer to the equipment used to receive the signal. See also Earth station.

DPCM: See Differential Pulse Code Modulation.

DTMF: See Dual tone multifrequency pulsing (below).

Dual tone multifrequency pulsing (DTMF): A means of sending signals through the telephone network. The signal consists of two tones, a high frequency tone and a low frequency tone, which together uniquely identify it. Usually accomplished using a Touch-Tone™ telephone keypad.

Duplex audio: An audio conferencing system that allows all sites to be heard simultaneously. These systems generally do not use voice switches and operate like normal telephone handsets used between two sites. Sometimes referred to as open audio.

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Earnings calls: See Investor Relations calls.

Earth station: Ground terminals used for the reception and/or transmission of information to/from a communications satellite. Generally used in teleconferencing for the transmission and reception of video teleconferencing signals.

Echo: In telephony, because of impedance irregularities in the terminating networks, a small amount of energy transmitted in one direction over the switched network is often reflected at the receiving end back toward the originating end. This reflection is commonly referred to as “talker echo.” A second echo at the receiving end is called a “listener echo,” or singing.

Echo cancel: An echo control technique that eliminates the echo by synthesizing a replica of the echo and subtracting it from the actual echo.

Echo suppressor: An echo control device that blocks the echo reflections by switching off the transmission path from the listening party to the talking party. Usually used on trunks longer than 3,000 km.

Electronic blackboard: A generic name used for large tablet audiographic devices. Used by AT&T Technologies in the late 1970s when it introduced its Gemini® 100 product.

Electronic slate/tablet: A device commonly used in audiographic teleconferencing that uses a special surface and stylus or electronic pen for producing graphic images at the origination site; distributed to participating sites for interaction through audiographic teleconferencing.

Encryption/decryption: A digital technique for securing information transmitted over a communications channel with the intent of excluding all other than authorized receivers from interpreting the message. Can be used for voice, video, and other communications signals.

Entry and Exit tones: Tones that sound when a participant joins or leaves a conference. [Source: Global Crossing]

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