When the Optical Transport Manager performs root-cause analysis, it uses only a subset of the alarms that result from a given failure as symptoms. The Optical Transport Manager identifies the other alarms that occur as impacts of the root-cause problem. For instance, a line failure that occurs when a fiber is cut has the symptoms, LOS on the downstream PTP, and RDI-L on the upstream PTP. In addition, AIS-L, RDI-L, AIS-P and RDI-P alarms occur at various points along all paths that pass through the cut fiber. The Optical Transport Manager identifies all of these resulting alarms as impacts of the Down notification on the TopologicalLink that models the cut fiber.