This PerfCounter64 counts Far End Unavailable Seconds for a SONET/SDH Line in the history bin, tracking how many seconds the far end considered its receive path on this line unavailable. An admin uses far-end UAS to confirm whether an outage reported by the remote site actually correlates with what this line was carrying, which is useful when troubleshooting a customer-reported outage that the near end's own counters don't show. If a customer at the far-end site reports an outage window and ocnStmHistoryLineFarEndUASs for that history bin shows a matching block of unavailable seconds, the admin has confirmation the line itself was the cause rather than far-end customer equipment.