by Administrator
29. June 2009 22:35
FDDI is a LAN protocol standardised by ANSI and ITU-T. It supports data rates of
100 Mbps and provides a high-speed alternative to Ethernet and token ring. When FDDI
was designed, the data rate of 100 Mbps required fibre-optic cable.
The access method in FDDI is also called token passing. In a token ring network,
a station can send only one frame each time it captures the token. In FDDI, the token
passing mechanism is slightly different in that access is limited by time. Each station
keeps a timer which shows when the token should leave the station. If a station receives
the token earlier than the designated time, it can keep the token and send data until the
scheduled leaving time. On the other hand, if a station receives the token at the designated
time or later than this time, it should let the token pass to the next station and wait for
its next turn.
FDDI is implemented as a dual ring. In most cases, data transmission is confined to the
primary ring. The secondary ring is provided in case of the primary ring’s failure. When
a problem occurs on the primary ring, the secondary ring can be activated to complete
data circuits and maintain service.
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Tags: fiber