The maintenance of the ODN (optical distribution network) in PONs(Passive Optical Networks) to be used for the futuretelecommunication access networks is discussed. A review of thetechniques used to perform this function, aimed to guarantee theperformances of optical cables, splices, connectors, and otherpassive components of the network, is provided. Post-faultmaintenance (to detect, locate, and restore the faults) and preven-tive maintenance (to reduce the fault events) are both considered.The use of measuring and monitoring systems based on OTDRs (opticaltime domain reflectometers) is examined in detail, considering thedifferent proposed schemes. These are based on reference reflectorsset at the end of the branches, fiber selectors, wavelength divisionrouting, chained branches, and use of dedicated fibers. An overviewof the key components for the consid- ered measuring and monitoringsystems is given, considering the present status and the foreseeableevolution for the different devices f optical selec- tors, filters,reflectors, couplers, selective wavelength routers, and OTDRs.
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