This reports which specific Threshold Crossing Alarm condition was declared on the SONET port, covering coding violation, severely errored second, errored second, and unavailable second alarms across the section, line, path, and VT layers, including far-end variants. It's accessible-for-notify, meaning it primarily exists to carry the alarm value inside the sonetPortTCAlarm trap. An admin receiving that trap reads this value to identify exactly which layer and metric crossed its configured threshold, for example sonet-line-farend-uas-tca-declared(11) pointing to far-end line unavailability.