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CS601 - Data Communication - Lecture Handout 14

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Conversions

Introduction

  • Information must be transformed into signals before it can be transported across the communication media
  • How info is transformed depends on its original format and on the format used by the communication device
  • If you want to send a letter by a smoke signal, you need to know which smoke patterns make which words in your message before building the fire
  • Words are the Information and the puffs of smoke are representation of that information

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CS601 - Data Communication - Lecture Handout 15

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Conversions

Return to Zero (RZ)

  • Any time, data contains long strings of 1’s or 0’s, Rx can loose its timing
  • In unipolar, we have seen a good solution is to send a separate timing signal but this solution is both expensive and full of error
  • A better solution is to somehow include synch in encoded signal somewhat similar to what we did in NRZ-I but it should work for both strings of 0 & 1
  • One solution is RZ encoding which uses 3 values : Positive, Negative and Zero
  • Signal changes not b/w bits but during each bit
  • Like NRZ-L , +ve voltage means 1 and a –ve voltage means 0, but unlike NRZ- L, half way through each bit interval, the signal returns to zero
  • A 1 bit is represented by positive to zero and a 0 is represented by negative to zero transition
  • The only problem with RZ encoding is that it requires two signal changes to encode one bit and therefore occupies more BANDWIDTH
  • But of the 3 alternatives we have discussed, it is most effective value

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CS601 - Data Communication - Lecture Handout 16

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Conversions

Types of Digital-to-Digital Encoding

Types of Digital-to-Digital Encoding

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CS601 - Data Communication - Lecture Handout 17

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Conversion

Digital To Analog Conversion

  • Process of changing one of the characteristics of an analog signal based on the info in a digital signal
  • When you Tx data from one computer to the other using a public telephone line
  • Original data is digital but because telephone wires carry analog signal, original data must be converted
  • Digital data must be modulated on an analog signal that has been manipulated to look like two distinct values corresponding to binary 1 to binary 0

Digital To Analog Conversion

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