FDDI

Fiber Distributed Data Interface (FDDI) is a local-area network standard that uses fiber-optic cables to provide high-speed, reliable communication. It was designed as a high-bandwidth alternative for campus and backbone networks and is defined as part of the ISO/IEC 9314 family, with an ANSI origin in the late 1980s and early 1990s. The standard specifies a data rate of up to 100 megabits per second and supports full-duplex operation over optical fiber.

FDDI uses a dual-ring topology consisting of two counter-rotating rings: a primary ring for data and a secondary ring for fault tolerance. A token-passing MAC protocol governs access to the network, with a station allowed to transmit only when it possesses the token. Frames circulate around the rings, and the token is released after transmission. The secondary ring provides continued operation in the presence of failures, by reconfiguring traffic to the intact portions of the network. The architecture enables long-distance links and large network diameters, with theoretical spans up to about 200 kilometers when repeaters are used, though practical deployments are typically shorter.

Physical media for FDDI is fiber-optic cable, supporting both multimode and single-mode fibers. Connectors such as ST and SC are commonly used. Distances and performance depend on fiber type and transceivers, with FDDI designed to cover significant campus backbones and metropolitan-area networks.

By the late 1990s, FDDI was largely supplanted by switched Fast Ethernet and later Gigabit Ethernet solutions. It remains a notable example of early high-speed fiber LAN design and token-passing network methodology.