FDDI
       Fiber Distributed Data Interface (ANSI, ISO 8314)

	

	Fiber Distributed Data Interface
FDDI

   (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.

   Usenet newsgroup: news:comp.dcom.lans.fddi.

   (1994-12-13)