ADN-MIB::adnsonetSectionLOS tracks how long (in counter units) loss-of-signal (complete absence of optical light at the receiver) has persisted on the line. Network engineers use this to diagnose whether a fiber cut, laser failure, or receiver failure has occurred and how long the outage lasted. A counter jump from 0 to 100 indicates a 100-unit duration of LOS, which likely correlates with the service outage your customers reported.