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Unformatted text preview: ltiplexing is cost effective. One serious disadvantage with multiplexing relates
to a transmission line failure. If the line goes out, everything is dead. With
individual lines only one terminal is likely to be lost.
A concentrator performs the same function as a multiplexer, but concentrators
have the ability to actually reduce the number of signals. For example, 100 signals
from different devices coming into the concentrator could leave as only 70 or 80
signals. The signals are concentrated to form a fewer number of signals. This
requires intelligence. This intelligence normally takes the form of microprocessors
or even minicomputers. Thus, a concentrator is basically an intelligent
The advantage of using a concentrator is that devices of varying speeds and types
are connected to the concentrator, which in turn is connected to the host computer
by high-speed lines. Concentrators are especially useful where data
communication cost is high, such as long-distance international communications.
In general, concentrators are more expensive than multiplexers. For some longdistance and international data communication applications, however, the use of
concentrators is cost justified.
Front-End Processors (FEP) If information is to be moved from point-to-point in a computer network, then
some type of control is necessary. Network processing (also known as
communications processing) is the control of information movement between the
various locations of the network. This is a substantial task.
In the early network days, the communications processing job was handled by the
main computer. This began to place heavy additional loads on the CPU. Thus, the
ability of the computer to do information processing, i.e., the job for which it was
intended, was seriously degraded. As a result, manufactures introduced the frontend processor. This is a separate processor designed specifically to handle the
network processing task (see Figure 17.14).
A front-end processor is usually installed...
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- Spring '14