Detection and localization of link quality degradation in WDM networks

We consider the problem of detection and localization of link quality degradation in transparent WDM networks. In particular, we consider the degradation of the optical signal to-noise ratio (OSNR), which is a key parameter for link quality monitoring in WDM networks. With transparency in WDM networks, transmission lightpaths can bypass electronic processing at intermediate nodes. Accordingly, links cannot always be monitored by receivers at their end nodes. This paper proposes the use of optical multicast probes to monitor OSNR degradations on optical links. We relate this problem to network tomography for Internet and packet based networks. The estimation of OSNR degradations is based on a maximum likelihood estimator whose implementation is obtained from the expectation maximization algorithm.