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number of bits depends upon the communication system used, commonly
encountered systems use a total of either 10 or 11 bits per character. Hence a
terminal having a speed of 30 characters per second would probably be used with
a communication system, which transmits at the rate of 300 bits per second.
The communication data transfer rate is measured in a unit called baud. In general
usage, baud is identical to bits per second. For instance, a rate of 300 baud is 300
bits per second. Therefore the 30 characters per second terminal would be said to
operate at 300 baud. However, technically baud refers to the number of signal (state) changes per second. Thus, using more sophisticated coding techniques, 1
baud can represent 2 or even 3 bits per second. But, with most communication
systems, 1 baud represents only one signal change per second and thus is
equivalent to 1 bit per second.
Depending on their transmission speeds, communication channels (paths) are
grouped into three basic categories -narrowband, voiceband, and broadband.
Narrowband or subvoice grade channels range in speed from 45 to 300 baud. They
are used for handling low data volumes and are adequate for low-speed devices.
They are used mainly for telegraph lines and low speed terminals.
Voiceband channels handle moderate data volumes and can transmit data at speeds
up to 9600 baud. They are so called because their major application is for ordinary
telephone voice communication. They are also used for data transmission from
slow I/O devices to CPU or from CPU to slow I/O devices. Moreover, most
remote terminals are connected to computers through voiceband channels.
Broadband or wideband-channels are used when large volumes of data are to be
transmitted at high speed. These systems provide data transmission rates of 1
million baud or more. A company might use a broadband facility for high-speed
computer-to-computer communication or for simultaneous transmission of data to
several different devices.
As might be expected, the cost of the service increases...
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This document was uploaded on 04/07/2014.
- Spring '14