Manchester encoding is a technique used in the physical layer of the OSI model to encode data for transmission. It works by assigning transitions from 0 to 1 or 1 to 0 in the center of each bit to represent the bit value. This allows the receiver to easily extract the clock signal and correctly decode each bit. While it provides improved clocking and reliability over other encoding schemes, Manchester encoding exhibits poorer bit storage density for storing data on magnetic media.

1. Manchester Encoding Theory and Use By Professor Tom Mavroidis January 31,2001

2. 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.

3. 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.

4. 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

5. 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.

6. Three types of encoding discussed NRZ - Non Return to Zero RZ - Return to zero Manchester encoding

7. NRZ , Non Return to Zero transmission Each data bit is represented by a level. High = logic 1 low = logic 0

8. 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.

9. RZ - Return to zero Pulses used to represent bits logic 1 = pulse logic 0 absence of pulse

10. 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

11. 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

12. Representation Logic 0 1 to 0 (downward transition at bit center) Logic 1 0 to 1 (upward transition at bit center)

13. 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

14. Improved clocking Allows the receiver to extract the clock signal Correctly decodes the value and timing of each bit

15. 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.

16. Representation of phase shift

17. Uses Manchester encoding is used to : Transmit data across systems Store data on magnetic media, disks etc. Communicate with Satellites

18. Conclusion Based on application different types of encoding can be used Manchester encoding exhibits poor bit storage density but improved reliability.

19. 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