© 1998, The Media Cottage, Inc.

ANALOG SIGNAL - An electrical signal whose voltage continuously and proportionately varies in amplitude over time to represent the information being carried or stored.

AMPLITUDE - The amount of voltage swing in a signal. Commonly thought of as the "height" of a wave at a given point in time.

AMERICAN STANDARD CODE FOR INFORMATION INTER EXCHANGE (ASCII) - A coding method used to convert letters, numbers, and control codes into a numeric code understood by most computers. For example, your keyboard's capital A is ASCII 65 (in decimal), or 01000001 (in binary). The ASCII standard defines that 7 bits of the 'byte' are allocated for data and the eighth bit for parity (error checking); this allows for 128 characters. Extended ASCII uses the eighth bit for the control key rather than parity and allows up to 256 characters.

APPLICATION SHARING - A feature of some computer conferencing software which allows individuals to share and simultaneously work and mark up a document across the conference link.

ASYNCHRONOUS - Communication in which interaction between parties does not take place simultaneously.

ASYNCHRONOUS TRANSFER MODE (ATM) - A transmission protocol which routes data in packets (or cells) of fixed 53 byte length. Each packet may take a different route over the network, arrive at irregular time intervals, but is ultimately reassembled, buffered, and output as the original data stream at the receiving end. (This sounds crude, but it is a really rich, and fast way to transmit data. Remember, only one stream of data can occupy a link at any given time - and everyone shares links. Each ATM packet, instead of waiting for its turn on a fixed link, takes any route it can find to get to its destination. There are always empty links somewhere - so why wait? While everyone else plays burst - wait - burst, ATM just keeps cooking!)

AUDIO BRIDGE - A device used to conference, or "patch", multiple audio telephone calls together to enable all parties to simultaneous participate in the audio conference.

AUDIOCONFERENCING - Voice only connection of more than two sites using standard telephone lines. Some or all of the sites may elect to use a 'speakerphone' type system to enable multiple participants at that site.

BACKBONE - A primary, high bandwidth, communication path connecting multiple service providers, institutions, or users. Usually DS3 (45Mbs), OC3 (150 Mbs), or multiples thereof.

BANDWIDTH - a designated amount of data capacity (frequency range for analog or bits per second for digital) carried by a circuit. In terms of frequency, the range between the lowest and highest frequencies used to transmit a signal from one site to another.

BINARY - A numbering scheme, (base 2), which only uses the digits 0 and 1 to represent any number. This is a most handy way for computers and other digital electronic circuits to deal with information: 1=ON=Yes, 0=OFF=No. The "byte" (8 bits) representation of the number 17 (base 10) in binary is "00010001". (digits read right to left: first digit either 0 or 1; second digit either 0 or 1 meaning 2; third either 0 or 1 meaning 4; forth either 0 or 1 meaning 8 - - get it? 1 ,2, 4, 8, 16, 32, 64, 128, 256,. . .)

or, perhaps,
10000001=yes, no, no, no, no, no, no, yes

BIT - Abbreviation for a single binary digit. A 'bit' can be either zero or one.

BROWSER - A graphical software interface that, utilizing "hyperlinking" techniques, allows you to find and see information and graphics on the world wide web.

BYTE - A single computer "statement" comprised of eight bits, reading right to left. The rightmost bit is the Least significant Digit, the leftmost the Most Significant Digit. One byte can represent 256 values - from zero to 255.

BRIDGE - In terms of digital signaling, a device used to split, route, and direct data among remote sites on a network. These devices go by many names such as router, bridge, or digital cross connect. In terms of analog signaling. See Audio Bridge.

CARRIER - (1) A telecommunications network provider ("phone company") which offers connectivity services between geographically separate networks. (2) A single frequency which can be 'modulated', either in amplitude or frequency deviation to carry information. [ Like AM and FM radio ]

CCITT (Consulting Committee for International Telegraphy and Telephony) Now known as ITU. The international body responsible for establishing interoperability standards for communications equipment.

CENTRAL OFFICE - The common term for the location of your telephone service providers switching equipment. All telephone and data circuits 'hub' to this location for switching and routing.

CENTRAL PROCESSING UNIT (CPU) - The "brain" component of a computer where data calculation and decision making takes place. The CPU is dependent on many ancillary sub-systems to function - including memory, input/output systems, and a set of detailed instructions - the program.

CHANNEL - A 'pipe' in which information is carried. Often, a subdivision of a circuit is referred to as a channel. A standard T1 digital circuit is comprised of 24 channels.

CIF - Common Intermediate Format - An international standard for video transmission and display between video codecs developed by the ITU. The CIF format defines video transmission at a resolution of 352 X 288, at either 15 or 30 frames per second.

CODEC - An electronic device which transcodes between analog and digital signals, often "compressing" the signal. Codec stands for COder/DECoder.

COMPRESSION - The action taken by some video codecs to reduce the data rate (bandwidth) required for the transmission of videoconferencing signals between sites. Although a very complex task, the nature of the process is the elimination of all information which repeats (does not change) from one frame of video to the next. Consequently, slow fluid movements can be transmitted nicely via a compressed video system, while rapid motion will cause the received picture to break up or "tile" into squares on the screen.

COMPUTER ASSISTED INSTRUCTION (CAI) - Teaching process in which a computer and interactive software are utilized to enhance the learning process by assisting students in gaining mastery over a specific skill.

CPE (Customer Premises Equipment) - all terminal gear, network interfaces and customer equipment which connect to the carrier or phone company data transmission lines.

CSU -Customer Service Unit. A network interface which is placed between the incoming data service line and the customers equipment. This device electrically isolates the customers equipment from the Network, and allows the phone company to perform remote diagnostics and loop-backs for testing purposes.

CYBERSPACE - The nebulous "place" where humans meet and interact over computer networks while browsing the Internet. Coined by William Gibson in Neuromancer.

DEDICATED NETWORK - Network lines or circuits which are leased full time providing direct, continuous connection between sites; a circuit that is used exclusively by one customer for a discreet purpose. Dedicated service lessens problems such as interference and bottle-necking data caused by other users' demands on the bandwidth. This type of service is usually billed at one fixed monthly rate.

DEMARC - The "line of demarcation" between your equipment and the phone companies circuits. Usually a RJ-45 jack provided by the phone company for the customer to connect his/her equipment to the network. Here's the deal: If you call the phone company, and it turns out the problem is on "your" side of the demarc then expect a bill.

DESKTOP VIDEOCONFERENCING - Videoconferencing via a personal computer that has had special hardware and software installed. Desktop videoconferencing can be via the H.323 standard (over the Internet or other TCP/IP network), or the H.320 standard over dedicated or dial up digital circuits. Some systems offer the ability to use either standard.

DIAL-UP TELECONFERENCE - Using the public switched network channels for communications links among various locations.

DIGITAL SIGNAL - An electrical signal that is comprised of a stream of digits utilizing only two voltage levels representing either "ON (1)" or "OFF (0)". Whereas analog signals are dependant on the amount of voltage at any given time, digital signals are defined by only the presence or absence of voltage.

DISTANCE EDUCATION - The process of providing instruction when students and instructors are separated by physical distance. Technology, often in tandem with face-to-face communication, is used to bridge the geographical gap.

DISTANCE LEARNING - The desired outcome of distance education.

DOWNLOAD - The transfer of a file from a remote computer to your computer.

DS3 - A bandwidth allocation of 45 Mbs. One DS3 roughly equals twenty-eight T1 lines. Optical Fiber is almost always required for DS3 transmission. (Also referred to as T3)

ECHO CANCELLER - A device that blocks audio echo reflections during a conference while maintaining full duplex audio.

ELECTRONIC MAIL (E-mail) - Sending messages from one computer to another via a data network.

ENCRYPTION / DECRYPTION - A technique for securing information transmitted over a communication channel with the intent of excluding all other than authorized receivers from interpreting the message. Encryption utilizes a "key" to scramble the data which must also be used to reconstruct the data on the receiving end. Can be used for voice, video, and other communications signals.

FIBER OPTIC CABLE - Transmission lines composed of thin, high purity glass strands (fibers) used for laser-light transmission of video, audio, and/or data.

FILE TRANSFER PROTOCOL (FTP) - A protocol that allows you to move files between a distant computer and a local computer via a network such as the Internet.

FREQUENTLY ASKED QUESTIONS (FAQ) - A collection of information on the basics of any given subject; often used on the WWW.

FULL DUPLEX AUDIO - Bidirectional transmission of audio which allows all sites to simultaneously talk and listen.

FULL DUPLEX CONFERENCE - Two-way communication as opposed to simplex or half duplex, one-way communication. In a two-site duplex videoconference, both parties can send and receive video, audio and data simultaneously.

FULL MOTION VIDEO - Transmission of a complete, full resolution, non-compressed video signal at 30 fps (frames per second).

FULLY INTERACTIVE VIDEO - (Two way interactive video) Two or more sites simultaneously interacting with audio and video as if they were co-located.

GATEWAY - (1) A device which can translate between protocols and provide connectivity between otherwise non-connectable networks or devices.

H.320 - A standardized compression method and protocol for the transmission of audio, video, and data between videoconferencing codecs. It is this standardization which now allows codecs from different manufacturers to communicate with each other. Although many codec manufacturers offer their own proprietary compression algorithm, it is essential that they also offer H.320 if you desire to be able to communicate with ALL manufacturers codecs.

H.323 - A standardized compression method and protocol for the transmission of audio, video, and data between videoconferencing codecs over IP networks, the Internet or other TCP/IP based network. This standard was implemented for and was initially used for desktop - computer to computer - videoconferencing. Recently, as bandwidth has become more available, H.323 conferencing is being implemented by many educational and other institutional organizations.

HOME PAGE - A document with an address (URL) on the world wide web maintained by a person or organization which is the usual entry point into a web site. The home page contains pointers, or "hyperlinks" to other pages of information.

HOST COMPUTER - A network computer located at the central "hub" of an interactive network which can serve data and receive information from other computers. Often, it is the job of the host computer to authenticate users and allow access to the network.

HYPER TEXT MARKUP LANGUAGE (HTML) - A software "language" used to create interactive, linked documents. Extensively used to create web pages. A sub-set of the SGML language used for years by the electronic publishing industry and some desktop publishing software (Ventura Publisher).

HYPERTEXT TRANSFER PROTOCOL (HTTP) - The multimedia rich protocol used for sending and receiving world wide web information. Emphasis is on performance rather than absolute accuracy.

HYPERTEXT - A document which has been created, usually with HTML, to allow a user to select "hot" (linked) words or pictures within the document, click on them, and connect to further, related information.

INTEGRATED SERVICES DIGITAL NETWORK (ISDN) - A digital protocol developed to bring standardization to the transmission of "dial-up" data services. ISDN is a media-rich protocol which allows the simultaneous transmission of voice, data and video through the same channel. It is available in two basic configurations: BRI (Basic Rate Interface)(2B+D) comprised of two 64 Kbs data channels and a 16 Kbs signaling channel, and PRI (Primary Rate Interface)(23B+D) comprised of 23 64 Kbs data channels and a 64 Kbs signaling channel. A PRI is the rough equivalent of a T1 circuit. However, a T1 offers 24 56 Kbs channels (8 Kb of EACH channel is used for signaling overhead).

INTERNET - An international "network of networks" originally implemented by the United States government and used to connect military and research facilities. The Internet is now a ubiquitous network available to educational, corporate, and private individuals that spans the entire globe.

IMUX Inverse Multiplexer - a device which allows the "bonding" of individual communications channels into a channel with bandwidth equaling the SUM of all the channels bonded. For example, if you had three ISDN BRI circuits (each offering dual 64 Kbs service) you could use an IMUX to bond all six channels into a 384 Kbs communications channel. [ 384 Kbs is the almost universal transmission rate being used between schools and corporations for compressed video distant learning and videoconferencing applications in the United States.]

Kbs - 1000 bits of data per second (actually 1024 bits per second; in the binary system, everything is based on the power of 2, thus the products are: 0, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, etc.)

LINK - (1) A communications channel which ties together two sites. A network is made up of many links. (2) A target destination of a hyperlinked tag in an HTML or WEB document.

LOCAL AREA NETWORK (LAN) - Two or more local computers, printers, or other computing devices that are physically connected in a manner which allows the sharing of data and resources.

Mbs - megabits per second, or one million bits per second. (Actually 1,048,576 bits per second; see Kbs)

MICROWAVE - Electromagnetic waves, just adjacent to the frequency of light. Microwaves behave much like light; they travel in a straight "beam" and can be reflected. They are used to transmit to and from satellites, and for short terrestrial distances (i.e., up to 30 miles).

MODEM - (MOdulator / DEModulator) - A device to allow for a dial up connection to a remote computer over standard telephone lines. A modem modulates the digital data from your computer to an analog "audible" signal suitable for transmission over the voice telephone network.

MPEG (Moving Pictures Experts Group) - A compression scheme(s) which allow a superior mechanism for the compression and transmission of audio and video data over limited bandwidths. When bandwidths of 512 Kbs (1/2 T1) or above are available, MPEG is vastly superior to H.320 for the coding and transmission of videoconferencing or distant learning applications. MPEG 1 offers approximately the same resolution of H.320 systems with better motion handling abilities, while MPEG 2 offers resolution exceeding standard television broadcasts. DSS satellite broadcasts utilize MPEG 2 encoding.

MULTIMEDIA - Any medium which uses multiple forms of communication, such as text, audio, and/or video to convey information or entertainment.

MULTIPOINT CONTROL UNIT (MCU) - A " video bridge" which allows multiple videoconferencing sites to interconnect in a "multipoint conference". Usually, the site which is "talking" causes the MCU to transmit that sites picture to all the other sites in the conference. When another site begins talking, the MCU automatically switches and transmits that site to all other parties.

MULTIPLEX - To combine several different signals (video, audio, data) onto a single communication channel for transmission. Demultiplexing separates each signal on receipt.


NETWORK - An interconnected cluster of various equipment or services which communicate with each other via LAN or WAN communications channels.

NT-1 - A network termination device which is used between an ISDN BRI line and the customers equipment. The NT-1 converts the telephone companies two wire ISDN circuit into a 4 wire interface to the equipment. See CSU

ON-LINE - Network communication is established and prepared for operation. Also suggests access to a computer network such as the Internet.

ORIGINATION SITE - The location from which a teleconference originates.

POINT OF PRESENCE (POP) - Point of connection provided by a digital service provider or interexchange carrier to the local user. The digital access point into the network. Pops are usually located in a phone company Central Office.

POINT-TO-POINT - A conference or transmission between two sites. Often one way with an origination and receive site.

POINT-TO-MULTIPOINT - A conference configuration which allows information to be communicated from one point to many points. In some point-to-multipoint teleconferencing systems, the receive sites can transmit back to the point of origination, but not to the other receive sites. Standard broadcast television is a point to multipoint scenario.

POTS - Plain Old Telephone Service; the acronym often used for ordinary analog telephone connections as used in a residence. POTS lines have an analog bandwidth limitation of about 3Khz. Has nothing to do with line features such as call waiting or caller ID. If it's analogue, two wire, and on the public switched network it's POTS.

PROTOCOL - A formal set of standards, rules, or formats for exchanging data that assures uniformity and accuracy of data exchange between computers and applications.

PSN - PUBLIC SWITCHED NETWORK - The "dial-up" network which allows a user to 'dial' a number and establish connection with another user. Usually refers to the analog telephone network, but digital service is now available via dial-up access (switched 56, ISDN, etc.) Placing your data or videoconferencing system on the PSN allows connectivity, at will, with any other user of the PSN.

RJ-11 - The standard 6 pin jack utilized to connect an ordinary telephone. Most residences have RJ-11 jacks for telephone service. (Some digital telephones on PBX's in offices also use RJ-11 jacks)

RJ-45 - A slightly larger (8 pin) version of the RJ-11. Used to connect computers to local area networks (Ethernet, 10 base T or 100 base T) and also used for the connection (demarc) point of an ISDN or T1 line. Note: The pin-out is DIFFERENT for BRI, PRI, and T1; beware.

ROUTER - A device, usually located between your local area network and the transmission link to a wide area network, which segments your local area network into divisions or departments, and "firewalls" your network from entry by unauthorized users.

SATELLITE TV - A point to multipoint scenario with video and audio signals relayed via a communication satellite to multiple receive sites.

SIMPLEX (half duplex) - One-way "at a time" communication, as opposed to full duplex transmission. Think in terms of "push to talk" two way radio.

STILL FRAME - A single image transmitted over a communications link. Usually, a very high resolution image can be transferred in this manner as no motion is involved.


SYNCHRONOUS - Communication in which all packets of information are sent in a continuous bit stream over a dedicated path. A synchronous network requires a single "clock" reference to time all elements of the network. Most videoconference networks are synchronous with the clock derived from the "phone company" via the communications link.

T1 - A communications link operating at 1.54 Mbs. Channelized T1's offer 24 channels of 56 Kbs each. ( If you multiplied and are wondering, each 64 Kbs channel loses 8 Kbs for signaling and handshake information; An ISDN PRI T1 has 23 full 64 Kbs channels and utilizes the remaining channel for signaling / handshaking for all the other 23 channels)

TELECOMMUNICATION - The science of electronic information transport using wire, radio, optical, or electromagnetic channels to transmit and receive signals for voice, video or data communications.

TELECONFERENCING - The use of electronic communications to allow two or more people at two or more locations to interact with each other in real time. Includes videoconferencing, audioconferencing, audiographic conferencing, and computer conferencing.

TRANSMISSION CONTROL PROTOCOL (TCP) - A protocol which makes sure that packets of data are transmitted and received over the network in the intended order.

TRANSPONDER - Satellite transmitter and receiver that receives a signal from earth on one frequency and amplifies the signal prior to retransmission back to earth on another frequency. A typical C-band satellite has 12 transponders which receive and transmit 24 channels (12 polarized vertical, 12 polarized horizontal)

UNIFORM RESOURCE LOCATOR (URL) - The addressing scheme utilized by the Internet. Each network and subnetwork, or domain, has a unique URL address.

UPLINK - The communication link (the dish and associated electronics) used for transmitting from the earth station to the satellite.

VIDEOCONFERENCING - Communication between two or more individuals or groups who are remote from one another using telecommunications channels for fully interactive video and audio exchange. This includes full-motion video, compressed video, and, in some definitions, freeze-frame video images.

WAN - Wide Area Network - The incorporation of two or more LAN's into a larger, interconnected network via data transmission lines connecting the geographically separated networks.

WORD - A single computer "statement" comprised of 16 bits (two bytes).

WORLD WIDE WEB (WWW) - A graphical based, hypertext linked, URL indexed network that provides access to custom information (web sites) created by individuals, businesses, and other organizations.