Fault localization at the WDM layer

A single failure in a communication network may trigger many alarms. When t he communication network uses optical fibers as transmission medium and inc reases its capacity by using Wavelength Division Multiplexing (WDM), the nu mber of alarms and the difficulty to locate the failure are considerably hi gher. In this case, a single failure may interrupt several channels which c auses a large information loss. We propose an Alarm Filtering Algorithm (AFA) for the fault management of a n optical network that supports multiple failures and works in the presence of non-alarming elements, that is, network components which may fail but n ever generate an alarm (e.g. optical fibers). The algorithm provides a list of components whose failure explain the observed alarms. It avoids the use of failure probabilities, which are difficult to estimate, and does not ne ed a global knowledge of the network topology. Moreover it also tolerates a larm losses and false alarms. The algorithm is tailored to the specific behavior of the hardware componen ts of an optical network when a failure occurs. The classification of the n etwork components according to the alarm signals they generate enables a fo rmalization of the alarm-filtering problem and results in an efficient algo rithm for localizing the failure(s). This algorithm is applied to the WDM r ings of the COBNET network [1] (COBNET is a European ACTS project) and to a meshed optical network with the ARPA2 topology.