An optical fiber-based LAN using the ANSI X3T9.5 standard for a token-passing ring MAC protocol and its physical attachments. Stations, concentrators, and bridges in a DDI network are physically connected to one or both of a pair of counter-rotating rings operating at 100Mbps. The term DDI is used to represent all LAN types based on the fiber distributed data interface (FDDI) specifications, regardless of the media used (optical fiber, copper, or shielded twisted pair).