ITU-T G.8032 PDF

This Recommendation defines the automatic protection switching (APS) protocol and protection switching mechanisms for ETH layer Ethernet ring topologies. The protection protocol defined in this Recommendation enables protected point-to-point, point-to-multipoint and multipoint-tomultipoint connectivity within a ring or interconnected rings, called "multi-ring/ladder network" topology.

The ETH layer ring maps to the physical layer ring structure. Protection schemes for the other layers, including the ETY layer, are out of the scope of this Recommendation.