From: Przemyslaw Karwasiecki (karwas@xxxxxxxxxxxxx)
Date: Fri Aug 23 2002 - 17:47:27 GMT-3
On Fri, 2002-08-23 at 15:52, Wade Edwards wrote:
(snip)
>
> This is what I found about Manchester encoding: A method of transmitting
> bits which enables the receiver to easily synchronize with the sender.
> To me this means that Ethernet starts sending the preamble of a frame
> and the receivers synchronize with the Manchester encoded data stream.
> This gives them time to synchronize before actual data (i.e. network
> traffic) is sent.
>
In manchester encoding, receiver clock is _continuously_ synchronizing,
while receiving data. Otherwise, in 1500 octets == 12000 bits
Ethernet frame, receiver clock would have to be nearly perfectly
accurate to avoid slips at the end of the frame.
Manchester waste bandwidth of communication channel,
but provides clock all the time, during transmission.
Each one is transmitted as 10 and each zero as 01,
so regardless of pattern of bits in frame (can be all zeros,
can be all ones, can be whatever) there will be ALWAYS transition
of a signal in each and every bit. Those transitions are used to
synchronize receiver clock.
Przemek
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