ANSI Fiber Distributed Data Interface (FDDI)

ANSI Fiber Distributed Data Interface (FDDI)
The Fiber Distributed Data Interface (FDDI) standard was produced by the ANSI X3T9.5 standards
committee in the mid-1980s, and it specifies a 100Mbps dual token ring campus network.
FDDI specifies the use of optical-fiber medium and will support simultaneous
transmission of both synchronous and prioritized asynchronous traffic. The Copper Data
Distributed Interface (CDDI) version of FDDI operates over category 5 twisted-pair wiring.
FDDI is an effective solution as a reliable high-speed interface within a LAN or corporate network.  FDDI is an expensive solution, but it is effective for supporting high-speed deterministic access
to network resources. Some organizations find it necessary to use FDDI for connecting servers
in a server pool. It’s also beneficial to use FDDI as the backbone for a campus or enterprise
network. The synchronous mode of FDDI is used for applications whose bandwidth and
response time limits are predictable in advance, permitting them to be preallocated by the
FDDI Station Management Protocol. The asynchronous mode is used for applications whose
bandwidth requirements are less predictable or whose response time requirements are less critical.
Asynchronous bandwidth is instantaneously allocated from a pool of remaining ring bandwidth
that is unallocated, unused, or both.
ANSI is currently developing FDDI II, which is an extension of FDDI. It is unclear when
ANSI will release this standard. FDDI II has two modes: Basic mode, which is the existing
FDDI, and hybrid mode, which will incorporate the functionality of basic mode plus circuit
switching. The addition of circuit switching enables the support of isochronous traffic.
Isochronous transmission is similar to synchronous transmission, but, with isochronous, a node
is capable of sending data at specific times. This simplifies the transmission of real-time information
because of decreased source buffering and signal processing.