Recommendation ITU-T G.8121.1/Y.1381.1 specifies both the functional components and the methodology that should be used in order to specify multi-protocol label switching – transport profile (MPLS-TP) layer network functionality of network elements based on the protocol neutral constructs defined in Recommendation ITU-T G.8121 and on the tools defined in Recommendation ITU‑T G.8113.1/Y.1372.1. Corrigendum 1 replaces "Maintenance Communication Channel (MCC)" with "Management Communication Channel (MCC)" in alignment with ITU‑T G.8113.1/Y.1372.1. Corrigendum 2 corrects MI_1TH_Start arguments at sink function in Figure 8-57, Table 9-4, and Figure 9-13 and adds missing MI_1TH_OAM_Tool at sink function in Figure 8-57.