With the rapidly increasing demands for access network bandwidth and service support

ring PON applications have become increasingly more important and still longer transmission range

supporting more ONU and seamless conversion with ring networks have become the prerequisites for the continued development of PON in MAN.This paper elaborates on the principle and key technologies of the ring-tree topology-based PON

discusses the typical applications of such an architecture and summarizes the advantages and disadvantages of different schemes

providing references for the study on the still deeper conversion of access networks with MAN.