Apassiveopticalnetwork(PON)monitoringsystemcombinedlightpulseandfrequencysweeptechniquesisproposedandverifiedinafieldtest.Thelightpulsesurveysovertheallwholenetworkandthefrequencysweepareusedtoinvestigateanyfaultinthelink.Thefieldtestisperformedwith4PONs.EachPONismonitoredat4ports,oneisthesplitterportandtheotherthreearearbitrarychosenmultipleopticalunits(ONUs).AllthetestedPONsaremonitoredinturnsonceperhour.Faultsatthefeederandbranchfiberhavebeenobservedinthisfieldtestandhavebeenanalyzedwiththemonitoringsystem.