CH 03 -Data Transmission.pptx - Data and Computer...

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Data and Computer Communications Tenth Edition by William Stallings
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Data Transmission CHAPTER 3
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Contents 3.1 Concepts and Terminology 3.2 Analogue and Digital Data Transmission 3.3 Transmission Impairments 3.4 Channel Capacity
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“I have been trying to prove the following theorem: for any operators T,R the length of an arbitrary message f1 multiplied by its essential spectrum and divided by the distortion of the system is less than a certain constant times the time of transmission of F multiplied by its essential spectrum width or—roughly speaking—it is impossible to reduce bandwidth times transmission time for a given distortion. This seems to be true although I do not have a general proof as yet.” —Letter to Vannevar Bush, February 16, 1939, from Claude Shannon
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Transmission Terminology Data transmission occurs between transmitter and receiver over some transmission medium Communication is in the form of electromagnetic waves Guided media Twisted pair, coaxial cable, optical fiber Unguided media (wireless) Propagation through air, vacuum, and seawater
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Transmission Terminology No intermediate devices other than amplifiers or repeaters used to increase signal strength Direct link Direct link Direct link between two devices Are the only 2 devices sharing medium Point-to-point Point-to-point More than two devices share the same medium Multi-point Multi-point
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Transmission Terminology Simplex Signals are transmitted in only one direction One station is transmitter and the other is receiver Half Duplex Both stations transmit, but only one at a time Full Duplex Both stations may transmit simultaneously The medium is carrying signals in both directions at the same time
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Amplitude (volts) Time (a) Analog Amplitude (volts) Time (b) Digital Figure 3.1 Analog and Digital Waveforms
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Amplitude (volts) A Time 0 –A Amplitude (volts) A Time 0 –A ( a ) S i n e w a v e ( b ) S q u a r e w a v e F i g u r e 3 . 2 E x a m p l e s o f P e r i o d i c S i g n a l s period = T = 1/ f period = T = 1/ f
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Sine Wave Is the fundamental periodic signal Can be represented by three parameters Peak amplitude ( A ) Maximum value or strength of the signal over time Typically measured in volts Frequency ( f ) Rate at which the signal repeats Hertz (Hz) or cycles per second Period ( T ) is the amount of time for one repetition T = 1/ f Phase ( ) Relative position in time within a single period of signal
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Wavelength ( ) The wavelength of a signal is the distance occupied by a single cycle The wavelength of a signal is the distance occupied by a single cycle Can also be stated as the distance between two points of corresponding phase of two consecutive cycles Can also be stated as the distance between two points of corresponding phase of two consecutive cycles Assuming signal velocity v , then the wavelength is related to the period as = vT Assuming signal velocity v , then the wavelength is related to the period as = vT Or equivalently f = v
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