I'm reading book about networking now and can't understand one thing. As I've read Manchester encoding uses transition of voltage to interpret incoming signal. Question: When I'm sending data via Ethernet using Manchester encoding how receiver understands whether first byte is 0 or 1.

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I think you are speaking of bits, not bytes.

Before sending a frame, the sender put a preamble of 64 bits (8 bytes):

Byte 1   Byte 2   Byte 3   Byte 4   Byte 5   Byte 6   Byte 7   Byte 8  
10101010 10101010 10101010 10101010 10101010 10101010 10101010 10101011

The first 7 bytes are the same: 10101010. The last byte called the Start of Frame byte is slightly different: 10101011.

The preamble is not officially counted as part of the Ethernet frame. The frame begins immediately after the Start of Frame, without a gap.

As the preamble is a fixed and known pattern, it is used by the receiver to "lock-in" the clock and from then it can easily understand the incoming frame.


The encoding is fixed in the standard,see this desciption

The frame's preamble is known, so that helps to determine what bit this is, or a collision is taking place.

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