Fiber Distributed Data Interface (FDDI) is a network protocol that connects two or more networks even over long distances. The access method used by FDDI is the token model.
FDDI uses two physical ring topologies. The transmission process usually uses one ring, but if a problem is found it will automatically use the second ring.
As explained above the FDDI network implements a recovery mechanism that allows the network to function properly even under a damaged ring. FDDI uses two rings to achieve recovery capability. As shown, tokens are passed simultaneously on the inner and outer rings of the network that back up each other.
As shown in the following figure if the connection is lost or a station malfunctions, the nearest station closes the network loop by sending a token it receives from outside.
An advantage of FDDI is the speed using fiber optic cable at speeds of 100 Mbps.