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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FDDI

(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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* Hardware: Four Data General MV processors, upgraded to eight AViiON RISC servers in an FDDI ring. The LAN connects to more than 1,000 PC workstations -- located at each bedside and throughout the nurse stations, ancillary care departments and administrative areas -- running terminal emulation software under Microsoft Windows.
They are attached to the enterprise network via a dual FDDI ring, which provides network redundancy.
An FDDI ring for including server systems is also available.
A third FDDI ring, at the manufacturing site, is connected to the main building via InteLAN using the Multi Protocol Router (MPN) and a Hewlett-Packard remote bridge over one T1 link.
By designing the network with two FDDI rings in the main building, our network analysts and telecomm management teams have designed a system that provides equal yet separate connectivity for both corporate and engineering users.
There are two reasons for different FDDI rings. This network configuration localizes data traffic and protects corporate users from network surges or interruptions during engineering's developmental testing.
For a 10 Mb/s Ethernet LAN with 12 users, that means 120Mbs/s of virtual bandwidth--more than an FDDI ring.
In the pilot testing, we routed IP traffic over Ethernet from its laboratory onto the FDDI ring and were able to bridge and route network traffic at full line speeds.
Lillemoen figures he has enough fiber capacity between buildings to handle network growth for the next five years, even with upgrading to an FDDI ring or Sonet.
For their switches and hubs, officials say they selected 3Com Corp., of Santa Clara, Calif., over competing firms for several reasons: the LANplex Product family's Intelligent Switching Engines (ISE) application specific integrated circuits (ASICs) provide reliable high-speed Ethernet-to-FDDI switching; their virtual LAN capability offers secure desktop and server connections to LANs regardless of the port to which these devices physically connect; their ability to separate PC and Macintosh traffic on distinct FDDI rings; and their Transcend network management software's intelligent monitoring capabilities.
We looked at a number of options to expand our network: First, we considered laying fiber cable and building additional FDDI rings. Unformtunately, because of the river separating our Egan and Chippewa Falls locations, we estimated it would cost over $1 million to lay fiber.