amplitude (KQ 7.1, p. 7.3) In analog transmission, the height of a wave within a given period of time.

asynchronous transmission (KQ 7.3, p. 7.19) Also called start-stop transmission; data is sent one byte (character) at a time. Each string of bits making up the byte is bracketed with special control bits; a “start” bit represents the beginning of a character, and a “stop” bit represents its end.

bandwidth (KQ 7.3, p. 7.16) Difference between the lowest and highest frequencies transmitted in a particular channel or system.

bits per second (bps) (KQ 7.1, p. 7.5) Measurement of data transmission speeds. Most modems today transmit at 28, 800, 33,600, and 56,000 bps (28.8 Kbps, 33.6 Kbps, and 56 Kbps, respectively).

bridge (KQ 7.5, p. 7.30) Interface that enables similar networks to communicate.

bus network (KQ 7.5, p. 7.32) Type of network in which all communications devices are connected to a common channel, with no central server. Each communications device transmits electronic messages to other devices. If some of those messages collide, the device waits and tries to retransmit.

cable modem (KQ 7.1, P. 7.7) Modem connecting a PC to a cable-TV system that offers online services, as well as TV.

client-server LAN (KQ 7.5, p. 7.27) Type of local area network (LAN); it consists of requesting microcomputers, called clients, and supplying devices that provide a service, called servers. The server is a computer that manages shared information or devices, such as laser printers.

coaxial cable (KQ 7.2, p. 7.9) Type of communications channel; commonly called co-ax, it consists of insulated copper wire wrapped in a solid or braided metal shield, then in an external cover.

communications (KQ 7.1, p. 7.2) Also called telecommunications; the electronic transfer of information from one location to another. Also refers to electromagnetic devices and systems for communicating data.

communications channel (KQ 7.2, p. 7.8) The path—the physical medium—over which data travels in a telecommunications system from its source to its destination.

communications satellites (KQ 7.2, p. 7.11) Microwave relay stations that orbit the earth, most at an altitude of 22,300 miles above the equator. Because their speed matches the earth’s rate of rotation, they appear stationary in space, and thus microwave earth stations can beam signals to a fixed location above. The satellite has solar-powered receivers and transmitters (transponders) that receive the signals, amplify them, and retransmit them to another earth station.

download (KQ 7.4, p. 7.26) To retrieve files online from another computer and store them in the user’s own microcomputer. Compare with upload.

electronic data interchange (EDI) (KQ 7.6, p. 7.37) Direct electronic exchange of standard business documents—such as purchase orders, invoices, and shipping documents between organizations’ computer systems.

e-mail (electronic mail) (KQ 7.6, p. 7.34) System in which computer users, linked by wired or wireless communications lines, use their keyboards to post messages and to read responses on their display screens.

extranet (KQ 7.6, p. 7.37) Extended intranet that uses Internet and Web technology to connect not only internal personnel in a company but also select customers, suppliers, and other strategic offices.

fax (KQ 7.6, p. 7.33) Stands for facsimile transmission or reproduction; a message sent by dedicated fax machine or by fax modem.

FDDI network (KQ 7.5, p. 7.32) Short for Fiber Distributed Data Interface; a type of local area network that uses fiber-optic cable with a duplex token ring topology.

fiber-optic cable (KQ 7.2, p. 7.10) Type of communications channel consisting of hundreds or thousands of thin strands of glass that transmit pulsating beams of light. These strands, each as thin as a human hair, can transmit billions of pulses per second, each “on” pulse representing 1 bit.

file server (KQ 7.5, p. 7.28) Type of computer used on a local area network (LAN) that acts like a disk drive and stores the programs and data files shared buy users of the LAN.

firewall (KQ 7.6, p. 7.37) Software used in corporate networks (intranets and extranets) to prevent unauthorized people from accessing the network.

frequency (KQ 7.1, p. 7.3) Number of times a radio wave repeats during a specific time interval—that is, how many times it completes a cycle in a second; 1 Hertz = 1 cycle per second.

full-duplex transmission (KQ 7.3, p. 7.18) Type of data transmission in which data is transmitted back and forth at the same time, unlike simplex and half-duplex transmission.

gateway (KQ 7.5, p. 7.30) Interface that enables dissimilar networks to communicate with one another.

GPS (Global Positioning System) (KQ 7.2, p. 7.12) System of a series of earth-orbiting satellites that continuously transmit timed radio signals used to identify locations on earth.

half-duplex transmission (KQ 7.3, p. 7.18) Type of data transmission in which data travels in both directions but only in one direction at a time, as with CB or marine radios; both parties must take turns talking.

host computer (KQ 7.4, p. 7.25) The central computer that controls a network. On a local area network, the host’s functions may be performed by a computer called a server.

hybrid network (KQ 7.5, p. 7.32) Type of local area network (LAN) that combines star, ring, and bus networks.

intranet (KQ 7.6, p. 7.37) Internal corporate network that uses the infrastructure and standards of the Internet and the World Wide Web.

ISDN (Integrated Services Digital Network) (KQ 7.1, p. 7.7) Hardware and software system standard for transmitting voice, video, and data simultaneously as digital signals over traditional telephone lines.

kilobits per second (Kbps) (KQ 7.1, p. 7.5) Thousand bits per second, a measure of data transmission speed.

local area network (LAN) (KQ 7.5, 7.27) Network that serves users within a confined geographical area; consists of a communications link, network operating system, microcomputers or workstations, servers, and other shared hardware such as printers or storage devices. LANs are of two principal types: client-server and peer-to-peer.

local network (KQ 7.4, p. 7.25) Privately owned communications network that serves users within a confined geographical area. The maximum range is usually a mile.

metropolitan area network (MAN) (KQ 7.4, p. 7.25) Communications network that covers a geographic area the size of a city or a suburb.

microwave systems (KQ 7.2, p. 7.10) Communications systems that transmit voice and data through the atmosphere as super-high-frequency radio waves. Microwaves are electromagnetic waves that vibrate at 1 billion hertz per second or higher.

modem (KQ 7.1, p. 7.3) Short for modulator/demodulator; device that converts digital signals into a representation of analog form (modulation) to send over phone lines; a receiving modem then converts the analog signal back to a digital signal (demodulation).

multiplexing (KQ 7.3, p. 7.22) The transmission of multiple signals over a single communications channel.

network (KQ 7.4, p. 7.23) Also called communications network; a system of interconnected computers, telephones, or other communications devices that can communicate with one another and share applications and data.

network interface card (KQ 7.5, p. 7.29) Circuit board inserted into an expansion slot in a microcomputer that enables it to send and receive messages on a local area network.

node (KQ 7.4, p. 7.25) Any device that is attached to a network.

OSI (Open Systems Interconnection) (KQ 7.3, p. 7.23) International standard that defines seven layers of protocols, or software responsibilities, for worldwide computer communications.

packet (KQ 7.3, p. 7.20) Fixed-maximum-length block of data for transmission. The packet also contains instructions about its destination.

packet switching (KQ 7.3, p. 7.20) Technique for dividing electronic messages into packets—fixed-length blocks of data—for transmission to their destination over a network, through the most expedient route. A sending computer breaks an electronic message apart into packets, which are sent through a communications network via different routes and speeds. At their destination, a receiving computer reassembles them into proper sequence to complete the message.

parallel data transmission (KQ 7.3, p. 7.17) Method of transmitting data in which bits are sent through separate lines simultaneously.

peer-to-peer LAN (KQ 7.5, p. 7.29) Type of local area network (LAN); all microcomputers on the network communicate directly with one another without relying on a server.

private branch exchange (PBX) (KQ 7.5, p. 7.27) Private or leased telephone switching system that connects telephone extensions in-house and link them to the outside telephone system.

protocol (KQ 7.3, p. 7.23) Set of conventions governing the exchange of data between hardware and/or software components in a communications network.

ring network (KQ 7.5, p. 7.31) Type of local area network (LAN) in which all communications devices are connected in a continuous loop and messages are passed around the ring until they reach the right destination. There is no central server.

router (KQ 7.5, p. 7.30) Highly intelligent device that supports connectivity between both like and unlike LANs and between LANs and WANs/MANs. Routers operate at the bottom three layers of the OSI model.

serial data transmission (KQ 7.3, p. 7.17) Method of data transmission in which bits are sent sequentially, one after the other, through a single line.

server (KQ 7.4, p. 7.25) Computer shared by several users in a network.

simplex transmission (KQ 7.3, p. 7.18) Type of transmission in which data travels in only one direction; there is no return signal.

star network (KQ 7.5, p. 7.31) Type of local area network in which all microcomputers and other communications devices are connected to a central hub, such as a file server. Electronic messages are routed through the central hub to their destinations. The central hub monitors the flow of traffic.

synchronous transmission (KQ 7.3, p. 7.19) Type of transmission in which data is sent in blocks. Start and stop bit patterns, called sync bytes, are transmitted at the beginning and end of the blocks. These start and end bit patterns synchronize internal clocks in the sending and receiving devices.

telecommuting (KQ 7.6, p. 7.38) Way of working at home and communicating with (“commuting” to) the office by phone, fax, and computer.

twisted-pair wire (KQ 7.2, p. 7.9) Type of communications channel consisting of two strands of insulated copper wire, twisted around each other.

upload (KQ 7.4, p. 7.26) To send files from a user’s microcomputer to another computer. Compare with download.

videoconferencing (KQ 7.6, p. 7.35) Also called teleconferencing; form of conferencing using video cameras and monitors that allow people at different locations to see, hear, and talk with one another.

virtual office (KQ 7.6, p. 7.38) A nonpermanent and mobile office run with computer and communications technology.

voice mail (KQ 7.6, p. 7.34) System in which incoming voice messages are stored in a recipient’s “voice mailbox” in digitized form. The system converts the digitized versions back to voice messages when they are retrieved. With voice mail, callers can direct calls within an office using buttons on their Touch-Tone phone.

wide area network (WAN) (KQ 7.4, p. 7.25) Communications network that covers a wide geographical area, such as a state or a county.