Copper Distributed Data Interface
A variant of the FDDI (Fibre Distributed Data Interface) networking scheme, which is based on dual loop token passing (and is thus self-mending) and runs at a nominal 100 megabits/second.
FDDI was used as one of the first fibre-based MAN (Metropolitan Area Network) deployments. MANs are more likely to be running ATM (Asynchronous Transfer Mode) in this late 20th century.
CDDI is a historical artifact of computer networking.