diagnose and locate routing faults. With explicit telemetry, label reading is a local
process implemented within each node, while the implicit type involves correla-
tion of information from many nodes. Implicit path trace can be implemented with
technology that is already present in the network, but it may be unable to detect
certain hardware or software flaws that cause a ROADM to report its status
incorrectly. In addition, amplified spontaneous emission (A SE) noise can be
spectrally shaped by the ROADM nodes such that over long distances the accu-
mulated ASE may acquire the spectral signature of a low power channel. Both
types of telemetry are susceptible to some of the same challenges that complicate
channel monitoring (see above), due to signal ...