Reliability evaluation for distributed PONs with ring and tree topologies

This study describes resilient access network structures in time-division multiplexing passive optical networks (TDM-PONs) and wave-division multiplexing (WDM)/ TDM-PONs, and compares their network unavailability versus outage scale. In addition, this study discusses the unavailability for media networks with simple ladder and more realistic ring-to-tree topologies for cases with simplex and full/partial duplex configurations between drop points and central offices. In large-scale networks, the unavailability in duplex networks is drastically improved by 4-5 orders of magnitude compared with that in simplex networks for large outage scales. Cable failure significantly affects the unavailability, especially in feeder sections, whereas failures due to optical fiber or optical add-drop multiplexers are mostly masked by cable failure in WDM/TDM-PONs. Consequently, there is little difference in the unavailability of the two PON schemes, except for the difference due to PON splitters. A comparison of the unavailability for fully and partially duplicated networks shows that the latter with a ring-to-tree topology has the advantage of lower unavailability in large-scale regions. These results imply that a realistic duplication scheme successfully enhances the network reliability regardless of imperfect duplex structure.