|  | 7.2 | Basics of Fiber Distributed Data Interface (FDDI)
| 7.2.2 | FDDI format
The fields of an FDDI frame are as follows: preamble - prepares each station for the upcoming frame start delimiter - indicates the beginning of the frame, and consists of signaling patterns that differentiate it from the rest of the frame frame control - indicates the size of the address fields, whether the frame contains asynchronous or synchronous data, and other control information destination address - contains a unicast (singular), multicast (group), or broadcast (every station) address, destination addresses are 6 bytes (like Ethernet and Token Ring) source address - identifies the single station that sent the frame, source addresses are 6 bytes (like Ethernet and Token Ring) data - control information, or information destined for an upper-layer protocol frame check sequence (FCS) - filled by the source station with a calculated cyclic redundancy check (CRC), value dependent on the frame contents (as with Token Ring and Ethernet). The destination station recalculates the value to determine whether the frame may have been damaged in transit. If it has been, the frame is discarded. end delimiter - contains non-data symbols that indicate the end of the frame frame status - allows the source station to determine if an error occurred and if the frame was recognized and copied by a receiving station