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Manchester Encoding

Manchester Encoding



Manchester Encoding

Manchester Encoding



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    Manchester Encoding Manchester Encoding Presentation Transcript

    • Manchester Encoding Theory and Use By Professor Tom Mavroidis January 31,2001
    • What is Manchester Encoding ?
      • 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.
    • What is the difference?
      • 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.
    • Where is it used?
      • A popular technique used for encoding data on magnetic disks.
      • Also known as phase encoding
      • Problems include poor bit storage density
    • Resides in the Physical Layer
      • Physical Layer serializes the frame (converts it to a series of bits) and send it across a circuit to the destination.
    • Three types of encoding discussed
      • NRZ - Non Return to Zero
      • RZ - Return to zero
      • Manchester encoding
    • NRZ , Non Return to Zero transmission
      • Each data bit is represented by a level. High = logic 1 low = logic 0
    • Problem with NRZ
      • 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.
    • RZ - Return to zero
      • Pulses used to represent bits
      • logic 1 = pulse logic 0 absence of pulse
    • RZ - Advantages
      • Clock signals can be extracted from the logic 1 signals.
      • Halves the width of the pulse
      • Polar RZ sends pulses for both logic 0 and logic 1
      • Requires an extra voltage level
    • Manchester Encoding
      • Logic 1 is represented by a transition in a particular direction in the center of each bit.
      • Opposite direction used to represent logic 0
    • Representation
      • Logic 0 1 to 0 (downward transition at bit center)
      • Logic 1 0 to 1 (upward transition at bit center)
    • Manchester Encoding
      • Was named after its birthplace in Manchester, England
      • Bit transitions do not always occur at the ‘bit boundaries.
      • There is always a transition at the center of the bit
    • Improved clocking
      • Allows the receiver to extract the clock signal
      • Correctly decodes the value and timing of each bit
    • Receiver
      • Reassembles the series of bits to form a frame and forwards the frame for processing by the link layer
      • Frame is then CRC checked and a retransmission is requested if the checksum is invalid.
    • Representation of phase shift
    • Uses
      • Manchester encoding is used to :
      • Transmit data across systems
      • Store data on magnetic media, disks etc.
      • Communicate with Satellites
    • Conclusion
      • Based on application different types of encoding can be used
      • Manchester encoding exhibits poor bit storage density but improved reliability.
    • Links
      • http://www.erg.abdn.ac.uk/users/gorry/course/phy-pages/man.html
      • http://home.europa.com/~celiac/manch_enc.html
      • http://csshaun.cs.ru/ac/za/netnotes/netnotes003.html
      • http://www.pdp8.net/tu56/tu56.shtml