synchronize their clock at the bit-level with the transmitter. The preamble is followed by the SFD, which ends with a 1 instead of 0, to break the bit pattern of the preamble and signal the start of the actual frame.

Physical layer transceiver circuitry (PHY for short) is required to connect the Ethernet MAC to the physical medium. The connection between a PHY and MAC is independent of the physical medium and uses a bus from the media-independent interface (MII)