Manchester Encoding


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Manchester Encoding

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Manchester Encoding

  1. 1. Manchester Encoding Theory and Use By Professor Tom Mavroidis January 31,2001
  2. 2. What is Manchester Encoding ? <ul><li>It is a process by which a Synchronous clock encoding technique is used by the OSI physical Layer to encode the clock and data of a synchronous bit stream. </li></ul>
  3. 3. What is the difference? <ul><li>In this technique the binary data to be transmitted over the cable are not sent as a sequence of logical 1 & 0’s known as non return to zero (NRZ), instead the bit are translated into a different format that has a number of advantages over using straight binary. </li></ul>
  4. 4. Where is it used? <ul><li>A popular technique used for encoding data on magnetic disks. </li></ul><ul><li>Also known as phase encoding </li></ul><ul><li>Problems include poor bit storage density </li></ul>
  5. 5. Resides in the Physical Layer <ul><li>Physical Layer serializes the frame (converts it to a series of bits) and send it across a circuit to the destination. </li></ul>
  6. 6. Three types of encoding discussed <ul><li>NRZ - Non Return to Zero </li></ul><ul><li>RZ - Return to zero </li></ul><ul><li>Manchester encoding </li></ul>
  7. 7. NRZ , Non Return to Zero transmission <ul><li>Each data bit is represented by a level. High = logic 1 low = logic 0 </li></ul>
  8. 8. Problem with NRZ <ul><li>Long runs of consecutive bits with the same value make it impossible to detect bit boundaries by the inability of the receiver to detect the clocking speed. </li></ul>
  9. 9. RZ - Return to zero <ul><li>Pulses used to represent bits </li></ul><ul><li>logic 1 = pulse logic 0 absence of pulse </li></ul>
  10. 10. RZ - Advantages <ul><li>Clock signals can be extracted from the logic 1 signals. </li></ul><ul><li>Halves the width of the pulse </li></ul><ul><li>Polar RZ sends pulses for both logic 0 and logic 1 </li></ul><ul><li>Requires an extra voltage level </li></ul>
  11. 11. Manchester Encoding <ul><li>Logic 1 is represented by a transition in a particular direction in the center of each bit. </li></ul><ul><li>Opposite direction used to represent logic 0 </li></ul>
  12. 12. Representation <ul><li>Logic 0 1 to 0 (downward transition at bit center) </li></ul><ul><li>Logic 1 0 to 1 (upward transition at bit center) </li></ul>
  13. 13. Manchester Encoding <ul><li>Was named after its birthplace in Manchester, England </li></ul><ul><li>Bit transitions do not always occur at the ‘bit boundaries. </li></ul><ul><li>There is always a transition at the center of the bit </li></ul>
  14. 14. Improved clocking <ul><li>Allows the receiver to extract the clock signal </li></ul><ul><li>Correctly decodes the value and timing of each bit </li></ul>
  15. 15. Receiver <ul><li>Reassembles the series of bits to form a frame and forwards the frame for processing by the link layer </li></ul><ul><li>Frame is then CRC checked and a retransmission is requested if the checksum is invalid. </li></ul>
  16. 16. Representation of phase shift
  17. 17. Uses <ul><li>Manchester encoding is used to : </li></ul><ul><li>Transmit data across systems </li></ul><ul><li>Store data on magnetic media, disks etc. </li></ul><ul><li>Communicate with Satellites </li></ul>
  18. 18. Conclusion <ul><li>Based on application different types of encoding can be used </li></ul><ul><li>Manchester encoding exhibits poor bit storage density but improved reliability. </li></ul>
  19. 19. Links <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>