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BDC4e Chapter 8 - Chapter 8 Data Communication Fundamentals...

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Chapter 8: Data Communication Fundamentals Business Data Communications, 4e
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Three Components of Data Communication Data Analog: Continuous value data (sound, light, temperature) Digital: Discrete value (text, integers, symbols) Signal Analog: Continuously varying electromagnetic wave Digital: Series of voltage pulses (square wave) Transmission Analog: Works the same for analog or digital signals Digital: Used only with digital signals
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Analog Data-->Signal Options Analog data to analog signal Inexpensive, easy conversion (eg telephone) Data may be shifted to a different part of the available spectrum (multiplexing) Used in traditional analog telephony Analog data to digital signal Requires a codec (en co der/ dec oder) Allows use of digital telephony, voice mail
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Digital Data-->Signal Options Digital data to analog signal Requires modem ( mo dulator/ dem odulator) Allows use of PSTN to send data Necessary when analog transmission is used Digital data to digital signal Requires CSU/DSU (channel service unit/data service unit) Less expensive when large amounts of data are involved More reliable because no conversion is involved
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Transmission Choices Analog transmission only transmits analog signals, without regard for data content attenuation overcome with amplifiers signal is not evaluated or regenerated Digital transmission transmits analog or digital signals uses repeaters rather than amplifiers switching equipment evaluates and regenerates signal
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Data Signal Transmission System A D D D A A Data, Signal, and Transmission Matrix
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Advantages of Digital Transmission The signal is exact Signals can be checked for errors Noise/interference are easily filtered out A variety of services can be offered over one line Higher bandwidth is possible with data compression
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Why Use Analog Transmission? Already in place Significantly less expensive Lower attentuation rates Fully sufficient for transmission of voice signals
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Analog Encoding of Digital Data Data encoding and decoding technique to represent data using the properties of analog waves Modulation: the conversion of digital signals to analog form Demodulation: the conversion of analog data signals back to digital form
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