Fiber Distributed Data Interface

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Fiber Distributed Data Interface

(FDDI) A 100 Mbit/s ANSI standard local area network architecture, defined in X3T9.5. The underlying medium is optical fibre (though it can be copper cable, in which case it may be called CDDI) and the topology is a dual-attached, counter-rotating token ring.

FDDI rings are normally constructed in the form of a "dual ring of trees". A small number of devices, typically infrastructure devices such as routers and concentrators rather than host computers, are connected to both rings - these are referred to as "dual-attached". Host computers are then connected as single-attached devices to the routers or concentrators. The dual ring in its most degenerate form is simply collapsed into a single device. In any case, the whole dual ring is typically contained within a computer room.

This network topology is required because the dual ring actually passes through each connected device and requires each such device to remain continuously operational (the standard actually allows for optical bypasses but these are considered to be unreliable and error-prone). Devices such as workstations and minicomputers that may not be under the control of the network managers are not suitable for connection to the dual ring.

As an alternative to a dual-attached connection, the same degree of resilience is available to a workstation through a dual-homed connection which is made simultaneously to two separate devices in the same FDDI ring. One of the connections becomes active while the other one is automatically blocked. If the first connection fails, the backup link takes over with no perceptible delay.

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(Fiber Distributed Data Interface) 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.

MIC Connector
FDDI used a dual-fiber MIC plug and socket for connection to devices. See fiber-optic connectors.

MIC Connector
FDDI used a dual-fiber MIC plug and socket for connection to devices. See fiber-optic connectors.
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Fibre Distributed Data Interface (FDDI) is capable of data rates of up to 100 Mbit/sec.

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