How does the Ethernet handles start of frame collision? The Ethernet preamble, 56 bits of alternating 1 and 0 bits, allowing the receiver to synchronize its clock to the transmitter, followed by a one-octet **start frame delimiter byte** (10101011) and then the header. What happens when the header or the payload collides with the SoF? (10101011) Or how is it avoided? Also, if the mechanism considers the whole pack (preamble + start frame), the question remains, what happens when the header or data contains this sequence? 10101010 10101010 10101010 10101010 10101010 10101010 10101010 |Preamble |Sof | Other way to see this question is, how can I send data equals too `10101010 10101010 10101010 10101010 10101010 10101010 10101010` in the ethernet payload?

_Any_ kind of signal that is transmitted concurrently to another signal causes a collision (in half-duplex mode).

You need to understand that the signal on the medium is analog, not binary. So, on shared wire (coax), the signals _add_ to one another, causing illegal voltage levels. On duplex media (twisted pair, fiber), collision detection is simpler: any carrier detection on the receiver side while transmitting is a collision.

A preamble-like sequence somewhere in the middle of a frame doesn't matter. The preamble is used to synchronize the receiver's bit and byte shifters to the carrier. After that, the sequence has no meaning (it's just data) until the current frame has ended (loss of carrier or end-of-frame symbol, depending on the physical layer variant), and the receiver returns to carrier sense mode.