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Ethernet/802.3 Frames

Data on an Ethernet is transmitted in frames. This term is used to describe, in general, any "link level" (ie, within-network) PDU which encapsulates higher-layer data for local delivery over a LAN. The Ethernet frame format is:
Ethernet/802.3 frame format
Preamble
7 bytes of 0101010101... This is used to synchronise the receiver's clock circuitry.
 
Start Of Frame
1 byte, thus: 01010111 -- notice the two "1" bits at the end.
 
CRC
A 4-byte checksum which allows the receiver to be absolutely certain that the frame does not contain any physical errors. If it does, then the frame is simply discarded at the receiver.

 


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