Lower Layer Protection A configurable holdoff timeout can suppress spurious responses
to expected span status glitches, by extending the time between detection and reporting
Name Acronym Description
Forced Switch FS A management directive that forces a span to be deactivated
Signal Fail SF A signal failure that deactivates a span
Signal Degrade SD A signal degradation that can deactivate a span
Manual Switch MS A management directive that can deactivate a scan
Wait to Restore WTR A timer that improves stability in the presence of transient failures
Idle IDLE None of the above
TABLE 12.2 Protection Hierarchy
344 Chapter 12
of a physical failure condition. The glitches could be due to protection switching of RPR
traffic by underlying SONET infrastructure, as shown in Figure 12.13.
As illustrated in Figure 12.13, if the hold off timeout is omitted, the RPR will protect
the services before SONET layer protection is completed. Soon after the SONET layer
completes its protection task, the RPR will detect that the failure has been removed,
and will restore the original path for the services. An unnecessary protection hit has
been performed.
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