lec15 - ENGR 111 Lecture 15 Digital...

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ENGR 111 Lecture 15 Digital Information/Transmission Reading: Class notes, Chapter 33 Notes derived from Leon-Garcia’s book
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Summary of last lecture z Easy to represent information digitally z Text, images, audio, video –all in digital z Makes it feasible to store and transmit multiple types of data over one infrastructure z More reasons …to learn in the future lectures
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A Transmission System Transmitter z Converts information into signal suitable for transmission z Injects energy into communications medium or channel { Telephone converts voice into electric current { Modem converts bits into tones Receiver z Receives energy from medium z Converts received signal into form suitable for delivery to user { Telephone converts current into voice { Modem converts tones into bits Receiver Communication channel Transmitter
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Transmission Delay Use data compression to reduce L Use higher speed modem to increase R Place server closer to reduce d z L number of bits in message z R bps speed of digital transmission system z L/R time to transmit the information z t prop time for signal to propagate across medium z d distance in meters z c speed of light (3x10 8 m/s in vacuum) Delay = t prop + L/R = d/c + L/R seconds
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Transmission Delay z More information to transmit => more time z Transmit over longer distances =>more time z Information is compressed to save time { More redundancy –easier to compress { In this lecture, “information” is repeated often – compress by saying “info” or “I” z Technology allows higher transmission rates over time { 1200bits/s over phone modem lines –56kbps { ADSL –in Mbps on the same wires now
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lec15 - ENGR 111 Lecture 15 Digital...

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