LAN FDDI (Fiber Distributed Data Interface) technology is network access technology over fibre optic type lines. It is in fact a pair of rings (one is called “primary“, the other which makes it possible to capture errors from the first, is called “secondary“) FDDI is a token ring network with detection and correction of errors (it is here where the secondary ring becomes important).
The token circulates between the machines at a very high speed. If it does not arrive after a certain time frame, the machine considers that there has been an error on the network.
FDDI topology closely resembles that of a token ring with the small difference that a computer making up part of an FDDI network can also be connected to a MAU hub from a second network. We then talk about a biconnected system.