FDDI (Fiber Distributed Data Interface) is a high-speed network standard that uses fiber optic cables to transmit data at 100 Mbps over long distances with fault-tolerant dual-ring topology.

Overview

FDDI is a network protocol developed in the 1980s for high-speed local area networks (LANs) and wide-area networks (WANs) that require reliable, long-distance data transmission . It primarily uses fiber optic cables as the physical medium, though a copper variant called CDDI (Copper Distributed Data Interface) also exists . FDDI supports data rates of 100 Mbps and can connect up to 1000 devices, making it suitable for large-scale networks .

Topology and Operation

FDDI employs a dual-ring topology:

• Primary ring: Handles normal data traffic.
• Secondary ring: Serves as a backup in case of failure, providing fault tolerance and high network availability . Data is transmitted using a token-passing mechanism, where a token circulates around the ring, granting permission to send data. This ensures orderly access and reduces collisions. FDDI also supports synchronous and asynchronous traffic classes, allowing prioritization of critical data streams .

Fiber Optic Cable Advantages

Using fiber optic cables in FDDI provides several benefits:

• Long-distance transmission: Signals can travel up to 200 kilometers without significant degradation .
• Immunity to electromagnetic interference (EMI): Fiber optics are not affected by electrical noise, ensuring signal integrity .
• High security: Fiber is difficult to tap, enhancing network security .
• Durability and lightweight: Fiber cables are less prone to breakage and lighter than copper cables .

Applications

FDDI was widely used as a backbone network in universities, research institutes, and large corporations to interconnect multiple buildings or departments . It supported high-bandwidth applications like video, voice, and real-time data transfer in industries such as banking, manufacturing, and telecommunications . Its ability to maintain network operation even if one ring fails made it ideal for mission-critical environments.

Advantages and Disadvantages

Advantages:

• High bandwidth and speed (100 Mbps)
• Fault-tolerant dual-ring design
• Long-distance coverage
• Immunity to EMI and high security
• Supports large numbers of devices Disadvantages:
• Complex installation and maintenance
• Higher cost due to fiber optic cables and specialized hardware FDDI has largely been superseded by Fast Ethernet and Gigabit Ethernet, which offer similar or higher speeds at lower costs, but it remains a significant milestone in the evolution of high-speed fiber optic networking .