GLOSSARY OF TERMS

Videoconferencing Terms

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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.

ADSL
Asymmetrical Digital Subscriber Line. High band-width network technology that transmits at a higher rate in one direction than the other. Uses standard POTS wiring for band-width up to several Mbps.

AGC
Automatic Gain Control. Algorithm to normalize voulume regardless of speaker's position relative to the microphone.

ANS
Automatic Noise Suppression. Reduces back-ground noise from audio signal.

ATM
Asynchronous Transfer Mode. High bandwidth packet-based network technology.

bps
Bits per second, a unit of measurement of the speed of data transmission and thus of bandwidth.

B-channel
The ISDN circuit-switched bearer channels, capable of transmitting 64 Kbps of digitized information.

Bandwidth
The relative range of frequencies that can be passed without distortion by a transmission medium. The greater the bandwidth, the greater the information-carrying capacity of the medium.

Baud
The rate of data transmission based on the number of signal elements or symbols transmitted per second. Today most digital signals are characterized in bits per second.

BRI
Basic-Rate Interface for ISDN lines consisting of 2B + D channels.

Bit
A single digital unit of information

Bit Error Rate
The fraction of a sequence of message bits that are in error. A bit error rate of 10-6 means that there is an average of one error per million bits.

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 speed of a digital transmission, measured in bits per second.

Bonding
Method for making several BRI lines look like one high-rate line by use of an IMUX.

Bridge
An abbreviation for a multipoint bridge which enables the linking together of three or more conference sites so they can communicate simultaneously.

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. 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.

Broadcast
A packet delivery system where a copy of given packet is given to all hosts attached to the network. Example: Ethernet.

B-Router
Concatenation of "bridge" and "router". Used to refer to devices which perform both bridging and routing functions.

Burtsy data
Information which flows in short intense data groupings (often packets) with relative long silent periods between each transmission burst.

Byte
A group of eight bits; usually the smallest addressable unit of information in a data memory storage unit.

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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.

CCITT
Consultative Committee for international Telegraphy and Telephoney, (now called the ITU-T) An international body responsible for establishing interoperability standards for communications systems.

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 verticle 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.

Codec
An acronym for coder-decoder. A device that encodes analog signals for transmission and decodes digital signals to analog for receiving.

Compression
The process of reducing the information content of a signal so that it occupies less space on a transmission channel or storage device and a fundamental concept of video communications.

Continuous Presence
A technique allowing each participant in a multipoint conference to simultaneously view several end-points.

Channel
A pathway through which data is transmitted between two or more points.

Compression
The method for processing raw data so that it can be transmitted using less bandwidth.

Data compression
Reducing the size of a data file by reducing unnecessary information, such as blanks and repeating or redundant characters or patterns.

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.

DBS
Direct broadcast videoconference. Refers to service that uses videoconferences to broadcast multiple channels of television programming directly to home mounted small-dish antennas.

Decoder
A television set-top device which enables the home subscriber to convert an electronically scrambled television picture into a viewable signal. This should not be confused with a digital coder/decoder known as a CODEC which is used in conjunction with digital transmissions.

Delay
The time it takes for a signal to go from the sending station through the videoconference to the receiving station. This transmission delay for a single hop videoconference connection is very close on one-quarter of a second.

Demodulator
A videoconference receiver circuit which extracts or "demodulates" the "wanted "signals from the received carrier.

Digital
Conversion of information into bits of data for transmission through wire, fiber optic cable, videoconference, or over air techniques. Method allows simultaneous transmission of voice, data or video.

Digital Speech Interpolation
DSI - A means of transmitting telephony. Two and One half to three times more efficiently based on the principle that people are talking only about 40% of the time.

Distance learning
The incorporation of video and audio technologies into the educational process so that students can attend classes and training sessions in a location distant from that 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.

Document sharing - See Whiteboarding.

Domain
In the Internet, a part of a naming hierarchy consisting of a sequence of names (labels) seperated by periods (dots). e.g., videoconference.com.

DVB
Digital Video Broadcast, the standard for direct broadcast television in Europe and the U.S. Based on MPEG2 Compression.

Echo Canceller
An electronic circuit which attenuates or eliminates the echo effect on videoconference telephony links. Echo cancellers are largely replacing obsolete echo suppressors.

Encoder
A device used to electronically alter a signal so that it can only be viewed on a receiver equipped with a special decoder.

Ethernet
A LAN running on coaxial or twisted pair wiring, at 1 or 10 Mbps.

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Fast ethernet
A way to run ethernet at 100Mbps on one or two pairs of standard, unshielded telephone copper wire.

Forward Error Correction (FEC)
Adds unique codes to the digital signal at the source so errors can be detected and corrected at the receiver.

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 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.

Frequency
The number of times that an alternating current goes through its complete cycle in one second of time. One cycle per second is also referred to as one hertz; 1000 cycles per second, one kilohertz; 1,000,000 cycles per second, one megahertz: and 1,000,000,000 cycles per second, one gigahertz.

FTP
File Transfer Protocol. The Internet protocol (and program) used to transfer files between hosts.

Full-CIF (FCIF) - See CIF

Full-duplex (FDX)
Two-way, simultaneous transmission of data; a communication protocol in which the communications channel can send and receive 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. 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.

Gatekeeper
An H.323 device that sits on an IP network and manages the flow of traffic across a network or between networks. It can be programmed to allocate bandwidth and services on an individual subscriber basis, allowing particular services and user to be prioritized.

Gateway
The software/hardware combination through which two different networks meet. An H.323 - H.320 gateway can link endpoints on a LAN to an ISDN line. A gateway can manage network traffic and provide address and protocol transmission.

Gigahertz (GHz)
One billion cycles per second. Signals operating above 3 Gigahertz are known as microwaves. above 30 GHz they are know as millimeter waves. As one moves above the millimeter waves signals begin to take on the characteristics of Iightwaves.

H.320
Suite of standards for multimedia conferencing on narrow band switched digital networks. Can be used from 56Kbps to 2 Mbps. 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.323
Suite of standards for multimedia conferencing over packet-switched LANs. H.323 is a development of the H.320 family of standards and therefore utilizes some of the sub-standards defined in H.320.

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.

Hertz (Hz)
The name given to the basic measure of radio frequency characteristics. An electromagnetic wave completes a full oscillation from its positive to its negative pole and back again in what is known as a cycle. A single Hertz is thus equal to one cycle per second.

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 is an arrangement whereby a LAN segment might support only one workstation. This relieves congestion through a process called micro-segmenting.

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IBS
INTELSAT Business Services.

INTELSAT
The International Telecommunications Satellite Organization operates a network of Satellites for international transmissions.

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.

IMUX
Inverse Multiplexer. A Device that bonds two or more BRI lines to form a higher rate channel.

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.

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 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 64Kbps B ("bearer") channels to carry information content, the voice, video, and data substance of a transmission. A separate 16Kbps 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 2.048Mps, respectively. Each channel (time slot) is 64Kbps. One channel is reserved as the D channel; the other 23, as bearer channels (23+D).

ISO
International Standards Organization.

ITU
International Telecommunications Union (formerly called the CCITT) is one of the specialized agencies of the United Nations and defines standards for worldwide telecommunications.

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 provides may be interstate or intrastate, as long as it's between local areas.

IP
Internet Protocol. Packet-based communication standard for transmitting information over a LAN or the Internet.

ISP
Internet service provider.

IXC
Interexchange carrier, long distance service providers in the U.S. that provide inter-LATA service

JPEG
ISO Joint Picture Expert Group standard for the compression of still pictures.

Kbps
Kilobits per second. Refers to transmission speed of 1,000 bits per second.

Kilohertz (kHz)
Refers to a unit of frequency equal to 1,000 Hertz.

Ku Band
The satellite frequency range from 10.9 to 17 GHz.

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.

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.

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.

Leased Line
A dedicated circuit typically supplied by the telephone company.

Margin
The amount of signal in dB by which a satellite videoconference system exceeds the minimum levels required for operation.

MBONE
Multicast Backbone. A collection of Internet routers that support IP multi-casting. The MBONE is used as a "broadcast (actually multi-cast) channel" on which various public and private audio and video programs are sent.

Mbps
Megabits per second.

Megahertz (MHz)
Refers to a frequency equal to one million Hertz, or cycles per second.

Microwave
Line-of sight, point-to-point transmission of signals at high frequency. Many CATV systems receive some television signals from a distant antenna location with the antenna and the system connected by microwave relay. Microwaves are also used for data, voice, and indeed all types of information transmission. The growth of fiber optic networks have tended to curtail the growth and use of microwave relays.

Modulation
The process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.

Modulator
A device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in videoconference transponders. Modulators are also used by CATV companies to place a baseband video television signal onto a desired VHF or UHF channel. Home video tape recorders also have built-in modulators which enable the recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4.

MPEG
Moving Picture Experts Group. MPEG has established standards for compression and storage of motion video.

Multiplexing
Techniques that allow a number of simultaneous transmissions over a single circuit.

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 that more than three parties can participate in a video conference. The MCU uses fast switching techniques to patch the presenters or speaker's input to the output ports representing the other participants.

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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.

Noise
Any unwanted and unmodulated energy that is always present to some extent within any signal.

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. Check to see if your ISDN equipment requires an external NT-1 to operate.
NTSC - National Television Standards Committee A video standard established by the United States (RCA/NBC} and adopted by numerous other countries. This is a 525-line video with 3.58-MHz chroma subcarrier and 60 cycles per second. Frames are displayed at 30 frames per second.

Packet Switching
Data transmission method that divides messages into standard-sized packets for greater efficiency of routing and transport through a network.

PAL - Phase Alternative Line System
The European TV standard based upon 50 cycles.per second electrical system and 625 lines per frame and 25 Frames per Second. (NTSC, the North American standard is based on 30 frames per second) (French use SECAM)

Pan
To pivot a camera in a horizontal direction, tilt is to pivot in the vertical direction.

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.

Pixel
The smallest element of the computer or television display on the raster scale.

POTS
Plain Old Telephone Service. Conventional analog telephone lines using twisted-pair copper wire. This is used to provide residential service.

PRI - See ISDN.

Pulse Code Modulation
A time division modulation technique in which analog signals are sampled and quantized at periodic intervals into digital signals. The values observed are typically represented by a coded arrangement of 8 bits of which one may be for parity.

Rain Outage
Loss of signal at Ku or Ka Band satellite frequencies due to absorption and increased sky-noise temperature caused by heavy rainfall.

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, BellAtlantic, 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.

Receiver (Rx)
An electronic device which enables a particular videoconference signal to be separated from all others being received by an earth station, and converts the signal format into a format for video, voice or data.

RJ-11
The standard plug for phone lines.

RJ-45
The standard plug for ISDN (BRI).

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.

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Scrambler
A device used to electronically alter a signal so that it can only be viewed or heard on a receiver equipped with a special decoder.

Secam
A color television. system developed by the French and used in the USSR. Secam operates with 625 lines per picture frame and 50 cycles per second, but is incompatible in operation with the European PAL system or the U.S. NTSC system.

Signal to Noise Ratio (S/N)
The ratio of the signal power and noise power. A video S/N of 54 to 56 dB is considered to be an excellent S/N, that is, of broadcast quality. A video S/N of 48 to 52 dB is considered to be a good S/N at the headend for Cable TV.

Single-Channel-Per-Carrier (SCPC)
A method used to transmit a large number of digital signals over a single satellite transponder. Digital Business Television typically uses an SCPC transmission format.

Spectrum
The range of electromagnetic radio frequencies used in transmission of voice, data and television.

Splitter
A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously.

Spread Spectrum
The transmission of a signal using a much wider bandwidth and power than would normally be required. Spread spectrum also involves the use of narrower signals that are frequency hopped through various parts of the transponder. Both techniques produce low levels of interference Between the users. They also provide security in that the signals appear as though they were random noise to unauthorized earth stations. Both military and civil videoconference applications have developed for spread spectrum transmissions.

Synchronization (Sync)
The process of orienting the transmitter and receiver circuits in the proper manner in order that they can be synchronized . Home television sets are synchronized by an incoming sync signal with the television cameras in the studios 60 times per second. The horizontal and vertical hold controls on the television set are used to set the receiver circuits to the approximate sync frequencies of incoming television picture and the sync pulses in the signal then fine tune the circuits to the exact frequency and phase.

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 that 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.

10Base-T
Standard ethernet. A variant of IEEE 802.3 which allows stations to be attached via twisted pair cable.

T1
The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.

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.

T3 Channel (DS-3)
In North America, a digital channel which communicates at 45.304 Mbps.

TDMA
Time division multiple access. Refers to a form of multiple access where a single carrier is the shared by many users. Signals from earth stations reaching the videoconference consecutively are processed in time segments without overlapping.

TELCO
Generic term for telephone company. Can refer to an Interexchange Carrier or to the Local Exchange Carrier.

TA
Terminal Adapter. Used to connect to ISDN.
TCP/IP Transmission Control Protocol / Internet Protocol. Protocol layer that guarantees delivery of information across IP.

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.

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.

Transmitter
An electronic device consisting of oscillator, modulator and other circuits which produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.

Transponder
A combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to ten watts, operate over a frequency band with a 36 to 72 megahertz bandwidth in the L, C, Ku bands. Communications satellites typically have between 12 and 24 onboard transponders although the INTELSAT VI at the extreme end has 50.

Uplink
The earth station used to transmit signals for a satellite videoconference.

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VCS
Video Conferencing System.

VSAT
Very small aperture terminal. Refers to small earth stations, usually in the 1.2 to 2.4 meter range. Small aperture terminals under 0.5 meters are sometimes referred to Ultra Small Aperture Terminals (USAT's)

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.

Wireless
Transmission via radio waves or satellite. Wireless transmission is likely to be used in many computer networks of the future.

X.25
A set of packet switching standards published by the CCITT.

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.

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