Lecture_02

Lecture_02 - 1 Lecture slides prepared by Dr Lawrie Brown...

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Unformatted text preview: 1 Lecture slides prepared by Dr Lawrie Brown ([email protected]) for “Data and Computer Communications”, 8/e, by William Stallings, Chapter 3 “Data Transmission”. Modified by Dr. Mohan Das, July 2008. 2 The frst section presents some concepts and terms From the feld oF electrical engineering. This should provide suFfcient background to deal with the remainder oF the chapter. Data transmission occurs between transmitter and receiver over some transmission medium. Transmission media may be classifed as guided or unguided. In both cases, communication is in the Form oF electromagnetic waves. With guided media , the waves are guided along a physical path; examples oF guided media are twisted pair, coaxial cable, and optical fber. Unguided media , also called wireless , provide a means For transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum, and seawater. 3 The term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitter to receiver with no intermediate devices, other than ampliFers or repeaters used to increase signal strength. A guided transmission medium is point to point if it provides a direct link between two devices and those are the only two devices sharing the medium. In a multipoint guided conFguration, more than two devices share the same medium. 4 A transmission may be simplex, half duplex, or full duplex. In simplex transmission, signals are transmitted in only one direction; one station is transmitter and the other is receiver. In half-duplex operation, both stations may transmit, but only one at a time. In full-duplex operation, both stations may transmit simultaneously, and the medium is carrying signals in both directions at the same time. We should note that the deFnitions just given are the ones in common use in the United States (ANSI deFnitions). Elsewhere (ITU-T deFnitions), the term simplex is used to correspond to half duplex and duplex is used to correspond to full duplex. 5 In this book, we are concerned with electromagnetic signals used as a means to transmit data. The signal is a function of time, but it can also be expressed as a function of frequency; that is, the signal consists of components of different frequencies. It turns out that the frequency domain view of a signal is more important to an understanding of data transmission than a time domain view. Viewed as a function of time, an electromagnetic signal can be either analog or digital. An analog signal is one in which the signal intensity varies in a smooth fashion over time. A digital signal is one in which the signal intensity maintains a constant level for some period of time and then abruptly changes to another constant level. This is an idealized definition. In fact, the transition from one voltage level to another will not be instantaneous, but there will be a small transition period....
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This note was uploaded on 08/15/2010 for the course FIT 1005 taught by Professor Lyn during the One '10 term at Monash.

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Lecture_02 - 1 Lecture slides prepared by Dr Lawrie Brown...

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