Distributed data interface networks

A Fiber Distributed Data Interface (FDDI) is an optical fiber-based local area network (LAN) that uses the American National Standards Institute (ANSI) 3T9.5 standard for a media access control (MAC) protocol of token ring.

In FDDI networks, devices such as stations, concentrators, and bridges are physically connected to one or both of the counter-rotating rings. Typically, only the primary ring in an FDDI network is active. The secondary ring is used to maintain the network when a dual-access station or a concentrator becomes inactive. The rings operate at 100 Mbps.