| Label | Definition | Layer | Description |
|---|---|---|---|
| LOSS OF SIGNAL | Loss of Signal (LOS)- nincs jel | ||
| LOSS OF FRAME | Loss of Frame (LOF) - nincs keretszinkron | ||
| OUT OF FRAME | Out of Frame (OOF) - | ||
| LOSS OF POINTER | Loss of Pointer - nincs keretszinkron | ((PATH), TU | STM-1 |
| AIS | Alarm Indication Signal | MS, PATH, TU PATH | STM-1 |
| PATTERN LOSS | |||
| CLOCK LOSS | |||
| A1A2 CHANGE | |||
| ERRORS | |||
| FERF | Far end Receive Failure (later RDI) | MS, PATH, TU PATH | STM-1 |
| POINTER ADJUST |