Recommendation ITU-T G.8131/Y.1382 provides architecture and mechanisms for subnetwork connection (SNC) protection switching for MPLS transport profile (MPLS-TP) networks. It describes the SNC protection architectures type, the uni- and bidirectional switching types and the revertive/non-revertive operation types. It defines an automatic protection coordination protocol used to coordinate both ends of the protected domain. Amendment 1 provided the format of APC specific information, and descriptions about management (MI) signals and trail protection architecture. Amendment 2 to Recommendation ITU-T G.8131/Y.1382 (2014) provided: - Support for pseudowire (PW) protection. - Modifications to the references of terms related to new Recommendation ITU-T G.808 Amendment 3 provides updates on the following: - Initialization behaviour, - State transition modification, and - Operation related to state transition table lookup.