csOc3LineCurrentUASs is a read-only PerfCurrentCount counter reporting the number of Unavailable Seconds — seconds counted once ten consecutive severely errored seconds occur at the Line layer — that the SONET/SDH Line layer of this OC3 port has recorded in the current 15-minute measurement interval, i.e. right now. A rising count here is the operational signal that an extended outage of the OC3 line is happening on that interface, which is exactly the kind of degradation a monitoring admin wants an early warning of before it causes an outage. For example, an admin polling csOc3LineCurrentUASs on the SONET/SDH Line layer of this OC3 port every few seconds and watching the count jump upward in real time would immediately suspect an extended outage of the OC3 line, and could start a bit-error-rate test before the fault gets worse.