This OID counts, in seconds, how much time this WAN 10G SONET (WAN-PHY) interface has spent in a loss-of-signal condition since its statistics were last cleared. A rising count here means the receiver has lost the expected incoming signal for real, measurable stretches of time, one of the most severe faults a transport link can report since no traffic at all can cross during those seconds. For example, on a 10G WAN-PHY interface carrying SONET-framed Ethernet across a long-haul span, a fiber that gets physically disconnected for two minutes during a patch-panel move would add roughly 120 seconds to this counter.