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bdc6echapter16 - Chapter 16: Data Communication...

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Chapter 16: Data Communication Fundamentals Business Data Communications, 6e
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2 Data Communication Components 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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3 Analog DataSignal Options Analog data to analog signal Inexpensive, easy conversion (e.g., 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 (encoder/decoder) Allows use of digital telephony, voice mail
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4 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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Analog and Digital Signaling 5
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6 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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Analog and Digital Data and Signals Analog Signal Digital Signal Analog Data Two alternatives: (1) signal occupies the same spectrum as the analog data (2) Analog data are encoded to occupy a different spectrum. Analog data are encoded using a codec to produce a digital bit stream. Digital Data Digital data are encoded using a modem to produce analog signal. Two alternatives: (1) signal consists of two voltage levels to represent two binary values (2) digital data are encoded to produce a digital signal with desired properties. 7
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Analog and Digital Treatment of Signals Analog Transmission Digital Transmission Analog Signal Is propagated through amplifiers; same treatment whether signal is used to represent analog data or digital data. Assumes that the analog signal represents digital data. Signal is propagated through repeaters; at each repeater, digital data are recovered from inbound signal and used to generate a new analog outbound signal. Digital Signal Not used. Digital signal represents a stream of 1s and 0s which may represent digital data or may be an encoding of analog data. Signal is propagated though
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This note was uploaded on 11/06/2011 for the course EST 321 taught by Professor Matt during the Fall '11 term at SUNY Stony Brook.

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bdc6echapter16 - Chapter 16: Data Communication...

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