Английский для пользователей компьютеров. Ч.2. Белобородова М.Л - 32 стр.

transmission is used by large computers to transmit huge volumes of data at
high speeds.
Data communications technology must also consider the direction of data
traffic:
simplex (one way only), half-duplex (two-way traffic but only one direction at
a time), or full-duplex (two-way traffic passing at the same time).
    The media most commonly used for communication are telephone wires
(open and twisted-wire), coaxial cables, atmosphere (microwave and satellite
systems), and fiber optic cables. Each of these media differs in terms of the
form of the transmitted data (electrical pulses, electromagnetic waves, or light
pulses), the rate at which data moves through it, and its susceptibility to noise
and "eavesdropping."
    The hardware typically used to communicate between computers includes
modems, multiplexers, concentrators, controllers, front-end processors, and
microcomputer protocol converters. Multiplexers, concentrators, controllers,
and front-end processors all allow multiplexing—the sharing of one high-speed
communications line by multiple users or devices. A concentrator, which is
like a multiplexer, is more "intelligent" because it can store and forward
transmissions. A controller performs more functions than a multiplexer or a
concentrator. A front-end processor, a smaller computer connected to the main
computer, not only allows multiplexing but also relieves the main computer of
many routine data traffic management and communications functions.
    To communicate, the sending and receiving computers must follow the
same rules, or protocols. In the case of microcomputer communications, the
software parameters can be set on both ends to agree. In other cases, protocol
converters must be used. For example, a protocol converter could be used to
allow a microcomputer in asynchronous mode to communicate with a
mainframe operating in synchronous mode.
Companies often set up communications networks, which are collections of
data communications hardware, computers, communications software, and
communications media connected in a meaningful group to allow users to
share data and information. Three basic types of networks are private, public,
and international. Private networks support the communications needs of
particular business organizations. Public networks provide paying subscribers
with voice or data communications over a large geographical area.
International networks provide users with intercontinental voice and data
communications facilities.
Networks can be set up in different "shapes": star (and hierarchical)
network, bus network, and ring (and token ring) network. The normal
business user may encounter one of these network shapes in the context of
a local area network (LAN), which is a private network that serves a
company or a part of a company that is located on one floor, in a single
building, or in offices within approximately two miles of one another.
    The star network uses a host computer or a file server connected to a