Recommendation ITU-T G.798 specifies both the components and the methodology that should be used in order to specify the optical transport network (OTN) functionality of network elements; it does not specify individual optical transport network equipment. Amendment 1 contains text modifications and additions for: -moving the ODUkP to Ethernet MAC layer and Ethernet Reconciliation sublayer adaptation functions from ITU-T G.8021 to ITU-T G.798. -supporting the adaptation of ODUkP to Ethernet Coding sublayer for 25 Gb/s, 200 Gb/s and 400 Gb/s Ethernet signals. - alignment with ITU-T G.8023. - replacing Appendix VIII to align with ITU-T G.872 and ITU-T G.873.1 Amendment 2 contains text modifications and additions for: -OTSi to OTU4 adaptation function with SC FEC. -OTSi to FlexO-1-SC adaptation function. -alignment with ITU-T G.709.1. Amendment 3 contains text modifications and additions for: -supporting 25 Gb/s and 50 Gb/s OTN interfaces. -supporting 200 Gb/s and 400 Gb/s FlexO interfaces. -supporting the adaptation of ODUkP to Ethernet Coding sublayer for 50 Gb/s Ethernet signals. -supporting the adaptation of ODUkP to SDI/1.5G SDI signals. -alignment with ITU-T G.709.1 and ITU-T G.709.3.