What is FDDI in the Computer Network?

FDDI stands for Fiber Distributed Data Interface. It is a collection of ANSI and ISO standards for data transmission on fiber-optic lines in a local area network (LAN) that can extend up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol and provides high-speed data transmission at 100 Mbps.

FDDI is generally implemented as a dual token-passing ring topology, suitable for campus networks and building backbones. This dual-ring architecture provides fault tolerance, making it ideal for mission-critical network infrastructure.

FDDI Architecture

FDDI cabling consists of two fiber rings operating in opposite directions:

• Primary Ring − Transmits data clockwise and handles normal data traffic

• Secondary Ring − Transmits counterclockwise and serves as a backup in case the primary ring fails

Station Types

FDDI allows nodes to connect to the network through different attachment methods:

• Single Attachment Station (SAS) − Connects to the network via a single cable to the primary ring only

• Dual Attachment Station (DAS) − Connects to both primary and secondary rings, providing better fault tolerance

Traffic Types

FDDI supports two types of traffic based on timing requirements:

Token Management

FDDI uses three essential timers for token management:

• Token Holding Timer − Determines how long a station may continue transmitting after acquiring a token

• Token Rotation Timer − Monitors token circulation and detects if the token is lost

• Transmission Timer − Handles timeout and recovery from transient ring errors

Conclusion

FDDI provides a robust, high-speed fiber-optic network solution with dual-ring fault tolerance. Its 100 Mbps speed and 200 km range make it suitable for backbone networks requiring high reliability and performance.