
About Line Protocols
114078 Rev. A 2-7
FDDI Dual Counter-Rotating Ring Architecture
FDDI LANs comprise two independent, counter-rotating rings: a primary ring
and a secondary ring. Data flows in opposite directions on the rings. Both rings
can carry data; however, in high-bandwidth applications, Bay Networks specifies
that the primary ring transmits data and the secondary ring is a backup device.
The counter-rotating ring architecture prevents data loss in the event of a link
failure, a node failure, or the failure of both the primary and secondary links
between any two nodes, as follows:
• If a link on the primary ring fails, the secondary ring transmits the data.
• If a node or corresponding links on both the primary and secondary rings fail,
one ring wraps to the other around the faulty components, forming a single
ring (Figures
2-5 and 2-6).
When the component can function again, the architecture reverts to dual-ring.
Figure 2-5. Failure of Corresponding Links on Both Rings
x
x
Primary ring wraps
to secondary ring,
isolating faulty links.
x
x
LS0007A
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