Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

FDDI is a 100-Mbit/sec networking technology developed by the ANSI (American National Standards Institute) X3T9.5 committee. It was originally designed for fiber-optic cable, but was later modified to support copper cable over shorter distances. Before Fast Ethernet and Gigabit Ethernet came along, FDDI was commonly used in the LAN and campus environment, as well as a backbone to tie together devices on service provider networks and at exchange points on the Internet. FDDI uses a redundant dual-ring topology that supports 500 nodes over a maximum distance of 100 kilometers (60 miles). Such distances also qualify FDDI for use as a MAN (metropolitan area network). The dual counter-rotating rings offer redundancy (fault tolerance). If a link fails or the cable is cut, the network continues operating as shown on the right in Figure F-3 (see book). Each station contains relays that join the rings in case of a break or bypass the station in case it is having problems.