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Chapter 5: Encoding

Chapter 5: Encoding. Information must be encoded into signals before it can be transported across communication media Information can be either Digital, or Analog Signals can be also of two types: Digital Analog. Types of Encoding. Digital-to-Digital Encoding. Unipolar.

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Chapter 5: Encoding

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  1. Chapter 5: Encoding • Information must be encoded into signals before it can be transported across communication media • Information can be either • Digital, or • Analog • Signals can be also of two types: • Digital • Analog CS433 - Data Communication and Computer Networks

  2. Types of Encoding CS433 - Data Communication and Computer Networks

  3. Digital-to-Digital Encoding CS433 - Data Communication and Computer Networks

  4. Unipolar • Uses only one level of value (polarity) • Pros: simple and inexpensive • Cons: DC component direct current component with zero frequency) and synchronization (occur whenever the data stream includes a long uninterrupted series of 1’s and 0’s the solution is another line carrying a clock pulse allow the receiver to resynchronize its timer but cost is high) • Digital Transmission systems work by sending voltage pulses along a medium • Polarity: weather the pulse is negative or positive 1’s are positive values 0’s are 0 values 0 1 0 0 1 1 1 CS433 - Data Communication and Computer Networks

  5. Polar • Uses two levels of amplitude • Each bit consists of both positive and negative voltage • Dc component is totally eliminated CS433 - Data Communication and Computer Networks

  6. Non-Return to Zero (NZR) • The level of the signal is always either positive or negative • NRZ-Level : the level of the signal is dependent on the state of the bit (ex. +  1 and –  0) a problem arises when long stream of 0’s and 1’s in the data so the receiver receives a continuous voltage and cannot determine number of bits its clock cannot synchronize with sender clock. • NRZ-Inverted: The signal is inverted if a 1 is encountered supirur to • Less DC-component and more synchronization than Unipolar CS433 - Data Communication and Computer Networks

  7. 0 1 0 0 1 1 1 0 NRZ NRZ-L NRZ-I CS433 - Data Communication and Computer Networks

  8. Return to Zero (RZ) • Uses three signal values: positive, zero, and negative • There is a signal change for each bit (negative-to-zero for 0 and positive-to-zero for 1 • Excellent synchronization • Disadvantage: It needs more bandwidth since two signal changes per bit CS433 - Data Communication and Computer Networks

  9. 0 1 0 0 1 1 1 0 RZ CS433 - Data Communication and Computer Networks

  10. Biphase • Manchester: negative-to-positive transition represents 1 and a positive-to-negative transition represents 0. • Transition at the middle of the bit is used for both synchronization and bit representation. • Differential Manchester: a transition means 0 and no transition means 1. • Transition at the middle of the bit is used only for synchronization. Bit representation is shown by the inversion or noninversion at the beginning of the bit. CS433 - Data Communication and Computer Networks

  11. 0 1 0 0 1 1 1 0 Biphase Manchester Differential Manchester CS433 - Data Communication and Computer Networks

  12. Bipolar • Uses three signal levels: positive, zero, and negative • Zero level represents binary 0 • Positive and negative levels represent alternating 1s CS433 - Data Communication and Computer Networks

  13. Bipolar Encoding Bipolar AMI B8ZS HDB3 CS433 - Data Communication and Computer Networks

  14. 0 1 0 0 1 1 1 0 Alternate Mark Inversion (AMI) • Zero voltage represents binary 0. • Binary 1s are represented by alternating positive and negative signals. CS433 - Data Communication and Computer Networks

  15. Digital signal encoding formats 0 1 0 0 1 1 0 0 0 1 Unipolar NRZL NRZI RZ Manchester Differential Manchester Bipolar-AMI Pseudoternary CS433 - Data Communication and Computer Networks

  16. Bipolar 8-Zero Substitution (8BZS) • A convention adopted in North America to provide synchronization of long string of 0s • If eight or more consecutive 0s are encountered, enforce violations to the bipolar coding as follows: • if the previous polarity is positive: 000+-0-+ • if the previous polarity is negative: 000-+0+- CS433 - Data Communication and Computer Networks

  17. + 0 0 0 0 + 0 0 0 0 - 0 0 0 0 - 0 0 0 0 + 0 0 0 + + - 0 0 - - 0 0 0 - - + 0 0 + High-Density Bipolar 3 (HDB3) • Adopted in Europe and Japan. Number of 1s since last substitution is odd Number of 1s since last substitution is even CS433 - Data Communication and Computer Networks

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