A FDDI data frame is comprised of nine different fields, including a preamble that marks the beginning of a frame. FDDI actually makes use of an encoding scheme that translates groups of 4 bits into 5-bit symbols, referred to as 4B/5B. These symbols are used to represent control, error, and data information. FDDI frames include the following fields:
Start Delimiter. Indicates the beginning of a frame.
Frame Control. Used to determine whether the frame is a token or data frame.
Destination Address. The destination MAC address for the frame.
Source Address. The source MAC address for the frame.
Data. The data encapsulated by upper-layer protocols.
Frame Check Sequence. Contains the CRC value for the frame.
End Delimiter. Used to indicate the end of a frame.
Frame Status. Field used by the source station to ensure that the data was received at the destination.