Passive optical networks (PONs) can generally be considered point-to-multipoint networks, much like wireless networks such as wireless fidelity (Wi-Fi), 2G-4G or the hybrid fibre coax (HFC) networks used by multiple system operators. Redundancy is generally not fundamental in these networks as contrasted with ring-based topologies.
Nonetheless, there are services such as business services, mobile backhaul and high-density residential services, which may justify the addition of PON redundancy and protection switching.
Recommendation ITU-T G.984.1 outlines several topologies for achieving redundancy; these have been named Type A, Type B, Type C and Type D. Since the publication of ITU-T G.984.1, many other studies of various aspects of PON availability, redundancy and switching have been made available.
The ITU-T G.987 series, ITU-T G.989 series and ITU-T G.9807.1 describe the 10-Gigabit-capable passive optical network (XG-PON), the 40-Gigabit-capable passive optical network (NG PON2) and the 10-Gigabit-capable symmetric passive optical network (XGS-PON) systems. Each of these further describe protection aspects of those systems. In particular, the details of automatic protection switching in Type B has been more fully worked out.
This Supplement collects this information, and guided by input from operators, distils it into use cases and methods that are recommended for adding redundancy and increasing the reliability of PON networks.