Signal loss on a fiber port on CISCO switch

How much signal loss on a fiber port on a CISCO switch is required to constitute the link state as down?
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A SONET link must see a certain number of digital bit transitions (from 1 to 0 and 0 to 1) in order to ensure proper synchronization. LOS is declared when no bit transitions are detected on the incoming signal (before descrambling) for 2.3 to 100 microseconds. The LOS defect is cleared after a 125 microsecond interval (one frame) during which no LOS defect is detected.

Note: LOS typically occurs in back-to-back lab setups because the receiver is saturated with too much light, particularly when long-reach single mode interfaces are used. Try to attenuate the signal.

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