When a failure occurs in a WDM network, alarms can propagate from the failure points both upstream and downstream and also through the OTS, OMS, OCH, and OCN layers. The impact correlation feature of the Optical Transport Manager identifies these alarms as impacts of the underlying root cause. In large networks, hundreds or even thousands of such impacts may be identified, leaving the few root-cause problems to be more easily tracked and managed through their resolution.

Impact correlation on page 86 provides more information.