FDDI is a high-speed token-passing ring network that uses fiber-optic media and was developed for high-end computers.
FDDI uses a dual-ring topology. In this, there are two data streams flowing in opposite directions around two counter-rotating rings. One ring is called the primary ring and the other is called the secondary ring. The secondary ring acts as a backup. Computers may connect to one or both FDDI cables in a ring.