Fiber Distributed Data Interface

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FDDI Specifications

FDDI is not just one, but four specification pertaining to the Physical and Media Access layers of the OSI model.  FDDI is similar to IEEE 802.3 Ethernet and IEEE 802.5 Token Ring in its relationship with the OSI model.  The four specifications, as shown below are, MAC layer spec, Physical layer spec, Physical medium dependent spec, and the Station Management spec. 



The MAC and LLC packets used in FDDI are shown below, followed by a description of the fields within each packet.  The MTU of FDDI is 4352 octets is needed to provide means to transmit IP or ARP over FDDI

A description of the fields in each of the packets:


FDDI Physical Parameters

  • Data Rate: 100Mbps.
  • Topology: physical ring of trees, logical ring.
  • Maximum distance between adjacent stations: 2 km.
  • Total max. ring length: 100 km.
  • Max. number of attached stations: 1000.



FDDI Definitions





On the physical layer, FDDI uses Non Return to Zero Invert (NRZI) data encoding scheme to generate the signal representing 4B/5B encoding bits onto the ring.  This prevents continuous 0's from being passed around the ring