ONU user ports loopbacks will cause the discontinuation of all the services at the same PON user ports.This paper first analyzes the common causes for the loopbacks and the serious consequences arising from them.Then
it lists five methods that can be used to prevent the ONU’s UNI ports from loopbacks and
on this basis
presents a "special message detection" method
which can be used to automatically discover and block the user port loopbacks by sending