1. A method for fault isolation within a network element (NE) in an optical network, the method comprising the steps of: identifying root cause alarms within the optical network by using a directed acyclic graph (DAG); masking of all remaining correlated alarms within the NE; and displaying said root cause alarms; wherein the DAG represents the NE each vertex in which represents a physical port direction in the NE and edges are directed between the vertices based on the NE topology.