Fundamental limits of optical transparency

Summary form only given. Network management is complicated by transparency in that there is no simple way to assure that signals entering or leaving a node are valid. One can envisage monitoring optical power or signal-to-noise ratio, but these analog measurements will not detect pulse distortion arising from nonlinearity and dispersion, for example. When performance is found to be degraded at an endpoint of a connection, there is no simple way to determine in what part of the network the degradation occurred.