FDDI MAC standard (FDDI-MAC)
The FDDI- MAC standard is located as a substandard of the Data Link Layer on layer 2A. The FDDI MAC defines access to the physical layer, addressing, the format of the FDDI data packets, token management and token timing.
For active stations on the FDDI ring, the entire data stream of the FDDI ring passes through the MAC layer, i.e. all FDDI data is transferred from the network input to the network output. The MAC protocol works as an intermediary between the physical layer( PHY) and the LLC. During active data transmission, the MAC layer must wait until a token is received. This token is removed from the ring and instead the FDDI controller sends the data packet onto the ring. After successful data transmission, a token is generated again and the data is transferred from the network input to the network output.
A frame consists of an 8-bytepreamble as a synchronization bit sequence, the one- byte Starting Delimiter( SD) for marking the start of the frame, and the Frame Control( FC).