Glossary of Important Terms for Distance Education

Telecommunications, technology, and education terms have been compiled by the Western Cooperative for Educational Telecommunications. In addition, we have appended a few useful terms that do not appear on the original list.

Glossary of Telecommunications Terms
Amplifier - electronic devices, spaced at intervals throughout a cable television system, used to boost the strength of the cable signal as it passes from the headend to the subscriber. In coaxial cable systems, amplifiers are needed approximately every 1,500 feet. Amplifiers are also used in twisted copper pair telephone lines.

Analog - a continuously varying electrical signal in a shape of a wave. It is represented by continuous wave forms that vary in size and number as the source of the information varies. The variations in voice, loudness or pitch that a user hears at the other end reflects differences or fluctuations in the electrical current. Analog is the form of information that comes out of an ordinary voice telephone or from a modem into a telephone line. "People talk" is analog; "computer talk" is digital.

ANSI - American National Standards Institute - ANSI disseminates basic standards like ASCII, and acts as the United States delegate to the ISO -- International Organization for Standardization. ISO is the coordinator of the main networking standards that are put into use today.

ARPA - Advanced Research Projects Agency - formerly named DARPA (Defense Advanced Research Projects Agency), it is the government agency that funded ARPAnet.

ARPAnet - the original ancestor of the Internet.

ASC - Accredited Standards Committee - a committee chartered by ANSI to work on standards in a particular area of commerce. ASC X 12 is the committee working on standards for the insurance industry, including health.

ASTM - American Society for Testing and Materials - one of the organizations that accredits standards committees.

Asynchronous communication - two-way communication in which there is a time delay between when a message is sent and when it's received (e.g., electronic mail and voice mail). The transmission is by individual bytes, not related to specific timing on the transmitting end.

ATM - Asynchronous Transfer Mode - a telecommunications technology, also known as cell switching, which is based on 553-byte cells. In contrast to frame relay which is based on packets of variable length, this fast networking protocol is based on small, uniform packets. Because all ATM cells are exactly alike, the routing equipment that shuttles them around the world can be designed to be extremely fast, and the transmission delays for a series of cells will be relatively constant. ATM communi- cations are suitable for continuous transfer of large amounts of data, including video streams.

Audiographic teleconferencing - refers to the transmission of graphic and text information over a narrowband telecommunications channel such as a telephone line or a sub-carrier.

Audio-teleconferencing - two way electronic voice communication between two or more people at two or more locations.

Backbone Network - a high speed transmission facility (e.g., optical fiber) designed to interconnect lower speed distribution channels.

Backhaul - a term used to describe the transmission of a signal (normally video) from the end of a microwave or broadcast system to a central point.

Bandwidth - a measure of the information carrying capacity of a communications channel; the higher the bandwidth, the greater the amount of information which can be carried.

Baud - a unit of digital transmission signaling speed of information transmission. It is used to describe the rate of information flow. Given in bits per second (bps) the rate is the highest number of single information elements (bits) transferred between two devices (such as modems or fax machines) in one second.

BBS (Bulletin Board Service) - a computer service that allows remote users to access a central "host" computer to read and post electronic messages.

Bit - stands for binary digit. It is the smallest possible unit of information making up a character or a word in digital code, and is represented as either "on" or "off" by the numbers "0" or "1." An electronic string of bits represents letters and symbols.

BITNET - The acronym for Because It's Time Network, an international electronic network. BITNET, privately owned by a consortium of U.S. colleges and universities, has about 2,500 host computers located primarily at universities.

Bridge - a device which is used to interconnect three or more telecommunications channels such as telephone lines, to permit simultaneous, two-way communication among all points which have been interconnected.

Broadband - communications which are capable of carrying a wide range of frequencies. Broadcast television, cable television, microwave, and satellite are examples of broadband technologies.

Browser - a system that provides access to distributed information located at network-based repositories on the Internet. It enables a user to locate, access, and display information composed of text and still images; to animate moving images; and to play associated sound tracks. Mosaic is an example of a public-domain browser.

Cable television - a transmission system which distributes broadcast television signals and other services by means of coaxial cable. Residential cable subscribers are connected by means of cable to a central community antenna (CATV), which picks up signals from satellites for community distribution.

C-Band - a category of satellite transmission in the 6 GHz range.
C-Band transmission generally requires a large antenna, or "downlink dish" because of its use of longer wavelength frequencies when compared to other transmission systems such as Ku-Band.

CCD - Charge-Coupled Device - a photoelectric device that converts light information into electronic information. CCDs are commonly used in television cameras and image scanners. They consist of an array of sensors that collect and store light as a buildup of electrical charge. The resulting electrical signal can be converted into computer code and reconstructed to form an image.

CCD Scanner - a device that uses a CCD sensor to convert film images into electronic data.

CD-ROM Drive - Compact Disk Read-Only Memory - A CD-ROM drive is a read-only, information storage and retrieval device that is commonly used as a computer peripheral (i.e., it is like a computer harddrive, but is able to read information off computer Cds). It can store over 600 megabytes of data -- the equivalent of about 300,000 pages of typewritten text -- and is thus used to handle large databases, to store references such as encyclopedias and for large megabyte software applications. In 1988 the basic standard was extended to include specifications for storing audio, pictures and graphics (CD-ROMXA).

CDS - Clinical Decision Support - the use of information to help a clinician diagnose and/or treat a patient's health problem, including information about the patient and information about the kind of health problem affecting the patient and alternative test and treatments for it. A shared decision support system is a system designed to inform both patient and provider decisions regarding prevention, diagnosis, management and treatment.

Central Office (Switching Office) - a local telephone company facility that houses the switching system and related equipment needed to interconnect telephone calls for customers in the immediate geographic area. Every LATA must have at least one central office.

Channel - a radio frequency assignment made according to the frequency band being used and the geographic location of the send/receive sites.

Client - a computer that uses the services of another computer. If the user's computer is a PC or Macintosh and the user dials in to another system, the user's computer becomes a client of the system into which the user dialed.

Client/Server Model - a division of labor between computers. Computers that provide a service other computers can use are known as servers. Servers provide such services as FTP or the World Wide Web. If a user doesn't have these services on her own machine, she can connect to these machines and use these services; her computer thereby becomes a client.

Coaxial cable - a metal cable consisting of a conductor in the form of a tube which can carry broadband signals by guiding high frequency electromagnetic signals. It is used for voice, data, and video.

Codec - a term used for a "code/ decode" electrical device which converts an analog electrical signal into a digital form for transmission purposes. It is generally used to transform video signals into digital form for transmission over digital transmission systems. Generally speaking, this digital information must be reconverted into analog form at its point of reception.

Common carrier - A telecommunications company that is regulated by government agencies and offers communications relay services to the general public via shared circuits, charging published and non-discriminatory rates.

Compressed video - video images which have been processed to remove redundant information, reducing the amount of bandwidth needed to capture the necessary information so that the information can be sent over narrowband carriers such as a T1 telephone line.

Compression Ratio - the ratio of the number of bits in an original image to that in a compressed version of that image. E.g., a compression ratio of 2:1 would correspond to a com- pressed image with one-half the number of bits of the original. Compression technologies work by eliminating redundant information in images.

Computer conferencing - group communications through computers, or the use of shared computer files, remote terminal equipment and telecommuni- cations channels for two-way, real-time group communication.

Conference call - a telephone call which, by making use of a bridge, connects more than two individuals at geographically distinct locations for simultaneous conversation.

Customer Premises Equipment (CPE) - devices ranging from simple telephones to computers to TV monitors that are located at a customer's location and are used to send or receive information over a telephone network.

Dedicated line - a telephone line that is reserved for the exclusive use of one customer. It can be used 24 hours a day and usually offers better quality than a standard dial-up telephone line, but may not significantly increase the performance of data communications.

Digital - discrete signals such as those represented by means of bits (which are either "on" or "off") as opposed to continuously variable analog signals. Used in both electronic and light- based systems, digital signals transmit audio, video, and data as bits. Digital technology allows communications signals to be compressed for more efficient transmission and provides for faster communication with easier error prevention than analog communi- cations. Computers process the bits in the form of bytes. About a half million bytes make a single still picture on a TV screen.

Digital Signal - a form of informa- tion transmission in which the signal varies in discrete steps, not in a continuous manner.

Digital Switch - a type of switch in telephone company central offices; it is really a specialized type of computer that tells telephone calls where to go, based on the number "dialed-up" or "touch-toned" by the caller. Compared to previous kinds of switches, digital provides faster, higher quality service and more features for customers.

Digitize - the process by which analog information is converted into digital information. This process is a necessary function for computer imaging applications because visual information is inherently in analog format and most computers use only digital information.

Direct Broadcast Satellite (DBS) - a satellite designed with sufficient power so that inexpensive earth stations, or downlinks, can be used for direct residential reception.

Direct Digital Imaging - involves the direct capture of digital images (e.g., an MRI) so that they can be electronically transmitted. This is in contrast to an x-ray that is first made into a film and then photographed for digitization to send or store.

Dish - a parabolic antenna that is the primary element of a satellite earth station, or downlink.

Downlink - the path, or link, from the satellite to earth stations which receive its signals. The term is frequently applied to a parabolic antenna that receives signals from a satellite. It is often referred to as: a dish, a terminal, an earth station, or a TVRO (television receive only).

dpi - dots per inch - in conventional radiography, resolution is commonly expressed in pairs per millimeter (lp/mm). Film digitizer resolution is commonly expressed as dots (pixels) per inch.

DS1 - SEE T1

DS3 - SEE T3

Earth station - The ground equipment, including a dish and other electronics components needed to receive and/or transmit satellite telecommunications signals. An "uplink" is used for sending infor- mation to a satellite for distribution to various earth receiving stations, while a "downlink" is used to receive such information.

EDI (Electronic Data Interchange) - the sending and receiving of data directly between trading partners without paper or human intervention.

e-mail - electronic mail - electronic mail is a way to send and receive messages to and from computers. It works by transferring files from one address to another just like regular mail, except the envelope and letter is a computer file.

Equal Access - ability to choose between the different long distance carriers. In rural areas, some local exchange carriers are still serviced by only one long distance carrier.

Facsimile (Fax) - a device which electronically transmits and repro- duces documents over telephone lines.

Fiber Optics - hair-thin, flexible glass rods encased in cables that use light to transmit audio, video, and data signals.

Footprint - the geographic region on the earth underneath a satellite which is in the appropriate range to receive that satellite's information.

Frame Relay - a fast networking protocol in which data are packaged in variable-length frames or "envelopes", depending on the size of the packet inside, for shuttling between computer networks. Delays in receiving packets may lead to jumps in a video.

Freenet - a freenet is an open-access, free community computer system offering local community information and limited access to the Internet (e.g., the Cleveland Freenet). A local civic network is a public access network designed to broaden public access to governance, health care and education, and provide the means for citizens to conveniently discharge their public obligations.

Freeze frame - one method of transmitting still images over standard telephone lines. A single image is transmitted every 8-to-30 seconds. This is also referred to as slow scan.

Frequency - the rate at which an electromagnetic signal alternates. It is a term used with analog signals, and is reported in Hertz.

Full duplex - a communication channel over which both transmission and reception are possible in two directions at the same time. A standard telephone line is a full duplex system since people on either end of the connect can simultaneously speak while listening to sounds coming from the other end.

Full-motion video - a standard video signal that can be transmitted by a variety of means including television broadcast, microwave, fiber optics, and satellite. Full-motion video traditionally requires 6 MHz in analog format and 45 Mbps when encoded digitally.

Gateway - a system that interconnects networks (or applications) that communicate using different proto- cols, and bridges their differences by transforming one protocol into another (i.e., it reformats the data so that it is acceptable for the new network before passing it on).

Gb (Gigabit) - one billion bits of information - usually used to express a data transfer rate (e.g., 1 gigabit/ /second = 1Gbps). The bandwidth of optical fiber is often in the gigabit or billion-bits-per-second range.

Geostationary orbit - describes the orbit of a satellite whose position relative to the earth's surface is constant so it appears to hover over one spot on the earth's equator.

GHz (Gigahertz) - one billion cycles per second. It is a measurement of analog signal transmission.

Gopher - A system or navigational tool that enables the user to find information on the Internet by using menus. To use Gopher, the user telnets to a Gopher server and begins browsing the menus. The Gopher software was developed by the University of Minnesota for "tunneling" through the Internet.

GUI - Graphical User Interface - a GUI is a display format that uses icons, windows and other graphic elements to execute commands. The Macintosh, Microsoft Windows and OS/2 are GUIs.

Gray Scale - the number of different shades of levels of gray that can be stored and displayed by a computer system. The number of gray levels is directly related to the number of bits used in each pixel: e.g., 6 bits = 64 gray levels; 7 bits = 128 gray levels; 8 bits = 256 gray levels; 10 bits = 1024 gray levels; and 12 bits = 4096 gray levels.

Half duplex - a communication channel over which both transmission and reception are possible but only in one direction at a time.

HDTV (High Definition Television) - an advanced television system that produces video images as clear as high-quality photography.

Hertz - a unit of frequency equal to one cycle per second.

HPCC (High Performance Computing and Communications Program) - the HPCC initiative is a federal coordinated, interagency research and development effort designed to accelerate the availability and utilization of the next generation of high performance computers and networks.

Hypertext - a system of writing and displaying text that enables the text to contain links to related documents. Hypertext is able to handle graphics and sounds as well as text, and hypermedia documents can thus contain links to other forms of media - sounds, images and movies, as well as to other pieces of text. (In hypertext, selected words in the document are "expanded" -- i.e., linked to other text, file or picture documents.) Hypertext is used in the WWW.

					hypertext markup language (html) - the text composition language that allows a user to compose a document/ /file which may contain text, audio, and still and moving images, and have embedded links to files located on other computing systems.
					hypertext transport protocol (http) - the communications protocol used by WWW servers and client systems to identify sources of information and transfer the files containing html-based multimedia objects.

IEEE - Institute of Electrical and Electronics Engineers

Image Compression - a method to reduce the amount of data needed to reproduce an image. Lossless image compression means there is no loss of original digital image information upon reconstruction. Lossey compression means that there is some permanent loss of digital image data.

Independent Telephone Company - a local exchange carrier that is not part of the Bell system of operating companies (BOCs). In rural areas, many of the independent telephone companies are cooperatives.

Informatics - the application of computer science and information science to the management and processing of data, information, and knowledge.

Information Infrastructure - the telecommunication networks, computers, and other end-user devices, software, standards, and skills that collectively enable people to connect to each other and to a vast array of services and information resources.

INTERNET - the largest international computer network. It is a network of computer networks linking computers from colleges and universities, government agencies, institutions, and commercial organizations worldwide. These networks are able to communi- cate with each other because they all use the same protocol for sending data (i.e., TCP/IP). Some computers act as gateways connecting the various networks together. Owned by the U.S. government, until recently it was used primarily for research and educational purposes.

ISDN (Integrated Services Digital Network) - a digital telecommuni- cations channel that allows for the integrated transmission of voice, video, and data; a protocol for high-speed digital transmission. (see Table 2) It uses out-of-band switching (i.e., separate connections carry the switching information). For example, the basic ISDN rate has 2 DS-O channels and a lower capacity channel for the switching signals.

ITFS (Instructional Television Fixed Service) - a non-broadcast television service that is typically used for closed-circuit instructional applications. It requires special antennas and converters to translate signals for viewing.

IXC (Interexchange Carrier) - a telephone company such as AT&T, Sprint, or MCI that carries long distance calls. The IXCs are authorized by the FCC to carry interLATA, interstate traffic and can be authorized by state PUCs to carry interLATA, intrastate traffic. Also known as Long Distance Carriers.

JPEG (Joint Photographic Experts Group) - a standard for compression of static images; it also denotes a graphic file.

Kbs - stands for kilobits (1000 bits) per second. It is a way of reporting the rate of transmission of digital information per second.

Ku-Band - frequencies in the 11-to-14 GHz band used to send and receive signals to and from satellites. Being somewhat more narrow than C-Band transmissions, the dish needed to receive these signals is smaller; Ku-Band tends to be somewhat less expensive than C-Band for this reason.

LANs (Local Area Networks) - data communication networks that are fairly limited in their reach - e.g., the premises of a building or a campus. They are private networks that facilitate the sharing of information and computer resources by the members of a group.

Laser Film Scanner - a device that uses a laser beam to convert an image on X-ray film into digital image data.

Laser Optical Card - a plastic device the size of a credit card that can hold large amounts of digital data. Typically, the data cannot be altered once they are written to the card. O

LATA - Local Access Transport Area - the 161 local telephone service areas created by the divestiture of the regional Bell operating companies (RBOCs), formerly associated with AT&T, in 1984.

LDC (Long Distance Carrier) - see IXC (Interexchange Carrier)

Leased lines - a line rented from a telephone company for the exclusive use of a customer. May also be called a dedicated line.

LEC (Local Exchange Carrier) - a telephone company that carries local calls.

LISTSERV - a family of programs that automatically manage mailing lists, distributing messages posted to the list, adding and deleting members, without the tedium of someone doing it manually.

Low-Altitude Satellites - satellites that orbit the Earth at lower altitudes than the geosynchronous satellites and cannot maintain a constant position above the Earth. Thus, they are only accessible when they come into view of the receiving dish, two or three times a day for a few minutes at a time.

Magnetic Stripe Card - a plastic card with a magnetic strip on the back that can store about 250 characters, mainly for identification and verifi- cation of eligibility for insurance benefits.

Mbps - Megabits per second, or one million bits per second.

Medical informatics - the combination of computer science, information science, and the health sciences (medicine) designed to assist in the management and processing of data to support the delivery of health care.

Microwave - high frequency radio waves used for point-to-point communication of audio, video, and data signals. They can be simplex (omnidirectional) or duplex. The microwave spectrum is generally above 2 GHz. Microwave transmission requires line of sight transmission between sending and receiving antennas.

Modem - a modulator/demodulator. This device converts digital informa- tion into analog form for transmission over a telecommunications channel, and reconverts it to digital form at the point of reception.

Mosaic - software that lets you browse the WWW with "point and click" ease. It is one of many WWW browsers.

MPEG - (Motion Picture Experts Group) - a video compression standard; it also denotes a movie file.

Multiplexer - equipment which transmits two or more lines of voice, data, or video information over a single channel. For example, a multiplexer enables a single T1 telephone line to be split into a number of different "channels" to allow for multiple applications to be carried along the same T1 line.

Multiplexing - the combining of many low-capacity communications channels into one high-capacity communications channel by interleaving the various channels in discrete time or frequency slices.

Narrowband - a telecommunications medium, such as copper wire or part of a coaxial cable channel, that uses (relatively) low frequency signals. Generally speaking, narrowband transmissions go up to 1.544 Mbps.

Network - a set of nodes, points, or locations which are connected by means of data, voice, and video communications for the purpose of exchanging information.

NII - National Information Infrastructure initiative - a federal policy initiative to facilitate and accelerate the development and utilization of the nation's information infrastructure. The Administration's vision of the NII is a seamless web of communications networks, computers, databases and consumer electronics that will put vast amounts of informa- tion at users' fingertips.

NREN (National Research and Education Network) - the international, interconnected gigabit computer system network proposed under the HPCC initiative. The term "Interagency Interim NREN (IINREN) is now being used to describe the network.

NSFNET (National Science Foundation Network) - NSFNET is the high-speed network that connects mid-level regional computer (Internet) networks to support scientific research facilities throughout the country.

Packet - a bundle of data. On the Internet, data is broken up into small chunks, called packets; each packet traverses the network independently. Packet sizes can vary from roughly 40 to 32,000 bytes, depending on network hardware and media, but packets are normally less than 1500 bytes long.

Packet Switching - the process of transmitting digital information by means of addressed packets - which include data, call control signals, and error control information - so that a channel is occupied only during the transmission of the packet. In contrast, data sent using modems occupies a circuit for the entire duration of the transmission, even when no data is actually traveling over the lines. Using packet switching, the various packets of information can travel along different routes on the network, allowing the carrier to optimize its network capacity.

PACS - Picture Archiving and Communication System - a computer-based system of storing and retrieving radiographic and other images in digital form.

PBX - stands for Private Branch Exchange, a computerized version of the telephone switchboard but with an expanded range of voice and data services. It operates as a private telephone exchange that serves a particular organization and has connections to the public telephone network.

Pixel - Picture Element - the smallest piece of information that can be displayed on a CRT (cathode ray tube) - the monitor or display device. It is represented by a numerical code within the computer and displayed on the monitor as a dot of a specific color or intensity. An image is composed of a large array of pixels of differing intensities or colors. A voxel (volume element) is a three-dimensional version of a pixel. Voxels are generated by computer-based imaging systems, such as CT or MRI. Using voxels, three dimensional simulations of objects can be reconstructed by imaging systems.

POP (Point of Presence) - The point at which an interexchange carrier's circuits connect with local circuits for transmission and reception of long distance phone calls.

Port - a circuit in an electronic device for the input or output of signals.

Proprietary Standard - a technological standard developed by a single vendor or vendor group. The standard's specifications may be publicized or held confidential.

Protocols - a formal description of message formats and the rules two computers must follow to exchange those messages. Protocols can describe low-level details of machine-to-machine interfaces (e.g., the order in which bits and bytes are sent across a wire) or high-level exchanges between allocation programs (e.g., the way in which two programs transfer a file across the Internet). Standard protocols allow computers from different manufacturers to communicate.

file transfer protocol - a method of transferring one or more files from one computer to another on a network or phone line (e.g., the most commonly used dial-up protocols are xmodem, ymodem, zmodem and Kermit). The Internet has its own file-transfer protocol, called FTP, to transfer both binary and ASCII files, among computers on the Internet. Anonymous FTP, also known as 'anon FTP' is a service provided to make files available to the general Internet community. I.e., software and information files are stored on "anonymous" FTP servers to which there is public access and the login is anonymous.  http - hypertext transport protocol - the communications protocol used by WWW servers and client systems to identify sources of information and transfer the files containing html-based multimedia objects.  IP - Internet Protocol - the most important of the protocols on which the Internet is based; it provides for the routing of packets of data over multiple networks on their way to their final destination.  TCP/IP - Transfer or Transmission Control Protocol/Internet Protocol - one of the protocols on which the Internet is based, it allows networks to communicate with each other on the Internet. It supports such services as remote login (telnet), file transfer (FTP) and mail (SMTP)  Telnet - a terminal emulation protocol that allows the user to log in to one computer on the Internet by accessing it from another. Once logged in, it is as if the user's keyboard is connected directly to that remote computer, allowing the user to access the services (e.g., online library services or data- bases) of the remote computer. This command line is rapidly being replaced by graphical user interfaces (GUIs) such as Mosaic and Netscape.

PSTN (Public Switched Telephone Network) - the public telephone network.

Radio technology - used for telecommunications and broadcast services. Used for radio waves in frequencies that are distinct from those assigned to microwave services.

RANs (Rural Area Networks) - as conceptualized by the U.S. Congress, Office of Technology Assessment, RANs would be shared-usage networks, configured to include a wide range of users in rural communities - such as educational, health, and business entities.

RBOC (Regional Bell Operating Company) or Regional Holding Company - one of the seven regional companies formed by the AT&T divestiture (Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Telesis, Southwestern Bell and U.S. West. The BOCs (Bell Operating Companies) are grouped under the seven regional holding companies.

Repeater - a bi-directional device used in channels to amplify or regenerate signals.

Resolution - When discussing computer images, resolution refers to the number of pixels (or dots of light) a monitor and video card display to create an image. The higher the resolution, the smaller the dots and therefore the sharper the image. More text and graphics can be displayed on a screen with higher resolutions. The most common video resolution is video graphic array (VGA), which displays 640 by 480 pixels. (Super VGA is a term that refers to video resolution greater than 640 by 480 pixels (e.g., 1280 by 1024).)

RF - stands for radio frequency. Radio frequencies are electromagnetic signals which range from microwave to radio in length.

Routing - The assignment of a communication path by which a telephone call will reach its destination.

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

Rural Radio Service - the use of certain frequencies, distinct from those in microwave toll service, used to provide wireless telephony in rural areas. It can support the transmission of both analog and digital signals. It provides short-haul telecommuni- cations, and requires different power, transmission, and reception capabilities and devices.

Satellite - an electronics retrans- mission device serving as a repeater, normally placed in orbit around the earth in geostationary orbit for the purpose of receiving and retrans- mitting electromagnetic signals. It normally receives signals from a single source and retransmits them over a wide geographic area, known as the satellite's "footprint."

Scanner - A device that acts like a photocopier for a PC. When an article or picture is scanned, the scanner copies it into the computer as an image file.

Slow scan video - a device that transmits and receives still video pictures over a narrow telecommuni- cations channel, such as standard telephone lines.

Smart Card - a plastic device the size of a credit card with an embedded computer processor and memory.

SMDS - (Switched Multimegabit Data Service) - SMDS is a high-speed, fast packet-switched service provided in a campus, or ring, type arrangement situated within a 50-mile radius.

SS7 (Signaling System 7) - a recent development in control systems for the public telephone network. It allows telephone company computers to communicate with each other, making telephone call processing faster and more efficient and enabling more services to be made available to consumers.

Standards - standards are agreements on how to implement technologies. Standards for interchanging health data and assigning codes to medical concepts underlie all efforts to make patient records electronically accessible.

Switch - a mechanical or solid state device that opens or closes circuits, changes operating parameters, or selects paths or circuits on a space or time division basis.

Switched 56 - a data communications service that lets digital information flow at 56,000 bits per second using ordinary copper cable. Quite decent slow-motion video can be transmitted over switched 56. Business customers often dial-up this bandwidth when needed, e.g., for a video phone call.

Switched Network - a type of system where each user has a unique address (e.g., a phone number) which allows the network to connect any two points directly.

Synchronous - data communications in which transmissions are sent at a fixed rate, with the sending and receiving devices synchronized.

T1 (also known as DS1) - refers to a digital carrier capable of transmitting 1.544 Mbps of electronic information. It is the general term for a digital carrier available for high volume voice, data, or compressed video traffic. T1 is a standard for trans- mission that is accepted in North America. A T1 line is comprised of twenty-four 56 (or 64) kbps digital channels. Fractional T1 or sub T1 tariffs are rates for bandwidths between 56 Kbps and 1.544 Mbps, such as 384 Kbps = 1/2 a T1.

T3 (also known as DS3) - a carrier of 45 Mbps bandwidth. One T3 channel can carry 28 T1 channels.

T-carrier - a series of transmission systems using pulse code modulation technology at various channel capacities and bit rates to send digital information over telephone lines, including optical fiber lines, or another transmission medium.

Telecommunications - the use of wire, radio, optical, or other electromagnetic channels to transmit or receive signals for voice, data, and video communications.

Teleconferencing - interactive electronic communication between two or more people at two or more sites which make use of voice, video, and/or data transmission systems: audio, audiographics, computer, and video systems.

TeleHealth - the use of modern information and telecommunication technologies to provide health care services and access to health information, including health databases, for health professionals and consumers; to train and educate health professionals; to increase awareness and educate the public about health-related issues; and to facilitate research about health care issues, across a distance.

Telematics - a term used in Europe to refer to the merger of telecommunication and computer (informatics) technologies

Teletext - a broadcasting service using several otherwise unused scanning lines (vertical blanking intervals) between frames of TV pictures to transmit information from a central database to receiving television sets.

Terrestrial Carrier - a telecommunications transmission system using land-based facilities (microwave towers, telephone lines, coaxial cable, fiber optic cable) as distinguished from satellite transmission.

Translator - a broadband network operation. A translator is a device which is located in a central retrans- mission facility to filter incoming microwave signals and retransmit them in a higher frequency band.

Transmission Speed - the speed at which information passes over the line; defined in either bits per second (bps) or baud.

Transponder - a microwave repeater (receiver and transmitter) in a satellite that receives signals being sent from earth, amplifies them, and sends them back down to earth for reception purposes. Domestic communication satellites use either 12 or 24 trans- ponders, equivalent to a single channel, which usually have a 36 MHz bandwidth.

Trunk - a large capacity, long distance channel used by common carriers to transfer information between its customers.

Turn-key system - a telecommunications system in which all components and installation services needed for operational teleconferencing have been provided by a single vendor or contractor.

TVRO (Television Receive Only) - an earth station capable of receiving satellite TV signals but not of transmitting them; a "downlink."

Twisted Pair - cable made of a pair of insulated copper wires wrapped around each other to cancel the effects of electrical noise. It can transmit voice and data and, in some cases, low-grade video. It is the most prevalent type of medium in PSTN's local loops. The wire-pair sizes typically range from 19-to-26 gauge. Cables with as many as 2,700 pairs of 26-gauge wire are used in urban areas.

Uplink - the path, or link, from a transmitting earth station to the satellite. The term is frequently applied to a transmitting earth station.

URL - Universal Resource Locators - the WWW electronic addressing protocol. It is a way of naming network resources and was originally developed for linking pages together in the World Wide Web.

Voice grade channel - a telephone circuit of sufficient bandwidth to carry signals in the voice frequency range of 300-to-3400 Hertz.

Voice Switching - an electrical technique for opening and closing a circuit, such as changing from one microphone to another microphone or from one video camera to another video camera, in response to the presence or absence of sound.

VSAT (Very Small Aperture Terminal) - a type of satellite dish (1.8-2.4 meters in diameter). Used primarily for data transmissions (low speed to high speed). Can send and receive voice, data and video signals if enhanced. VSATs can transmit over wide areas by relaying to satellites in geosynchronous orbit.

WAIS - Wide Area Information Servers - a powerful system/software for looking up information in WAIS- indexed databases across the Internet.

WANs (Wide Area Networks) - data communication networks that provide long-haul connectivity among separate networks located in different geographic areas.

WATS (Wide Area Telephone Service) - a flat rate or measured bulk rate long distance service provided on an incoming or outgoing basis. WATS permits a customer, by use of an access line, to make telephone calls to any dial-able telephone number in a specific zone for a flat or bulk monthly rate using an 800 number.

WEDI - Workgroup for Electronic Data Interchange

Wireless technologies - communications technologies that utilize radio, microwave or satellite communication channels versus wire, coaxial or optical fiber.

WWW - World Wide Web - an Internet navigation tool (i.e., a hypermedia system for finding and accessing Internet resources). Rather than using menus, the Web uses hypertext links to jump from document to document. The link can be on any computer anywhere in the world. Well-known WWW browsers are Mosaic and Netscape.

Updated 7/10/97

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