CSMA / CD Frame Structure (IEEE 802.3)

• Pre = preamble, 7 bytes = 56 bits

• sd = start delimiter

• dest, src = dest & src addresses, = 2 or 6 bytes

• lngth = length of data in bytes

• pad set so that data + pad is > some minimum, eg, 64 bytes, or 512 bits

• fcs = frame (error) check sequence, CRC-32

pre sd dest src lngth data pad fcs

7 1 2/ 6 2/ 6 2 var var 4

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