图13.4802.3的MAC帧 Preamble:56 bits of alternating 1s and Os. SFD:Start frame delimiter,flag(10101011) Preamble SFD Destination Source Length CRC address address Data and padding or type 7 bytes 1 byte 6 bytes 6 bytes 2 bytes 4 bytes Physical layer header 13.7 13.7 图13.4 802.3的MAC帧