Fiber Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) is a set of ANSI and ISO standards for high-speed data transmission in local area networks (LANs) using fiber optic cables. It was designed for large LANs that can extend up to 200 kilometers in diameter, providing reliable backbone connectivity for enterprise networks.

Key Features

• Dual Ring Architecture − Uses two counter-rotating token rings for redundancy and fault tolerance.

• High Data Rate − Provides 100 Mbps transmission speed, supporting thousands of users simultaneously.

• Fiber Optic Medium − Uses optical fiber as the physical transmission medium for immunity to electromagnetic interference.

• Token Passing Protocol − Implements ring-based token passing mechanism derived from IEEE 802.4 token bus standard.

• Extended Distance − Supports LANs up to 200 kilometers for long-distance voice and multimedia communication.

• OSI Layer Operation − Operates at the Physical and MAC sublayer of the Data Link layer.

FDDI Network Topology

Frame Format

FDDI uses a frame format similar to the IEEE 802.4 token bus standard. The frame structure provides efficient data transmission and error detection capabilities.

Frame Field Descriptions

• Preamble − 1 byte for frame synchronization between sender and receiver.

• Start Delimiter − 1 byte that marks the beginning of the frame.

• Frame Control − 1 byte specifying whether this is a data frame or control frame.

• Destination Address − 2-6 bytes specifying the address of the destination station.

• Source Address − 2-6 bytes specifying the address of the source station.

• Payload − Variable length field carrying data from the network layer.

• Checksum − 4 bytes frame check sequence for error detection and correction.

• End Delimiter − 1 byte that marks the end of the frame.

Advantages and Disadvantages

Conclusion

FDDI provided a robust, high-speed networking solution for large enterprise LANs with its dual ring architecture and 100 Mbps transmission rate. While largely replaced by modern Ethernet technologies, FDDI established important principles for fault-tolerant network design and fiber optic networking.