However at microwave frequencies the electromagnetic

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Unformatted text preview: with speed. Hence a thorough analysis of the business needs and associated costs is necessary in making a proper choice. DATA TRANSMISSION MEDIA The sender-medium-receiver concept has actually been with us for a very long time. For example, shouting to another person does in fact involve voice transmission over a distance via the medium air, which carries the sound wave. Needless to say, the use of telephone lines as a transmission medium considerably enhances the possible distance. Like telephone lines, there are several types of physical channels (communication media) through which data can be transmitted from one point to another. Some of the most common data transmission medium are briefly described below. Twisted-Pair Wire A twisted-pair wire consists of two bunches of thin copper wires, each bunch enclosed separately in a plastic insulation, then twisted around each other to reduce interference by adjacent wires (see Figure 17.3). It is also called unshielded twisted-pair (UTP) cable because other than the plastic coating around the two individual bunches of copper wires, nothing shields it from outside interference. UTP cables are commonly used in local telephone communication and short distance (up to about 1 km) digital data transmission. They are normally used to connect terminals to the main computer if they are placed at a short distance from the main computer! Data transmission speed of up to 9600 bits per second (or 9600 baud) can be achieved if the distance is not more than 100 meters. However, for longer distance data transmission, local telephone lines are used. In this case, typical speed of digital signal transmission is 1200 bits per second. UTP cables are an inexpensive medium of data transmission. They are easy to install and use. However, their use is limited because they easily pick up noise signals, which results in high error rates when the line length extends beyond 100 meters. Coaxial Cable Coaxial cables are groups of specially wrapped and insulated wire lines that are able to transmit data at high rates. As shown in Figure 17.4, they consist of a central copper wire sur...
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This document was uploaded on 04/07/2014.

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