Recommendation ITU-T G.9961 belongs to the family of ITU-T G.996x Recommendations. Recommendation ITU-T G.9961 specifies the data link layer (DLL) for wireline-based home networking transceivers capable of operating over premises wiring including inside telephone wiring, coaxial cable, and power-line wiring. It complements the system architecture and physical (PHY) layer specification in Recommendation ITU-T G.9960, and the power spectral density (PSD) specification in Recommendation ITU-T G.9964. This revision comprises ITU-T G.9961 (2018) plus its Amendments 1, 2 and 3, and Corrigenda 1 and 2, along with a new Annex B on authentication to a domain using external authentication for smart grid applications.