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FDDI Network Architecture 61
6
This failure recovery mechanism is only supported by dual-attached stations
and concentrators; a single-attached station connected directly to the ring
cannot wrap around the fault because it is only connected to one ring at a time.
The effect of a cable or link failure on a basic FDDI network is very similar to a
station failure, as shown in Figure 6-9. The SMT entities on the stations on
either side of the failed connection reconfigure the network dynamically so
that the primary ring is wrapped onto the secondary ring.
Figure 6-9 Isolating a Single Cable Failure
Wrapping occurs within the MAC layer. Figure 6-10 on page 62 illustrates how
the dual-attached station is reconfigured to wrap the primary ring onto the
secondary ring. Dual-attached concentrators wrap in a similar way. In this
case, all of the single-attached stations connected to the concentrator are also
wrapped onto the secondary ring.
Secondary ring
Primary ring
FDDI DAS
FDDI DAS
FDDI DAS
FDDI DAS
Failed cable