nterface) Often pronounced "fiddy," it was a LAN and MAN access method that had its heyday in the mid-1990s. FDDI was an ANSI standard token passing network that transmitted 100 Mbps over optical fiber up to 10 kilometers. It included its own network management system and could optionally run over copper wire (CDDI) with distance limitations. FDDI II added circuit-switched service to this normally packet-switched technology in order to support isochronous traffic such as real-time voice and video.
Dual Rotating Rings
FDDI provided an optional dual counter-rotating ring topology that contained primary and secondary rings with data flowing in opposite directions. If a line broke, the ends of the primary and secondary rings were bridged together at the closest node to create a single ring again.
Single Attached and Dual Attached
Nodes could be configured as Single Attached Stations (SAS) connected to concentrators or as Dual Attached Stations (DAS) connected to both rings. Groups of stations were typically wired to concentrators connected in a hierarchical tree to the main ring. Large networks could be configured as a "dual ring of trees," in which the dual ring provided the backbone to which multiple hierarchies of concentrators were attached.