Recommendation ITU-T G.8271.1/Y.1366.1 specifies the maximum network limits of phase and time error that shall not be exceeded. It specifies the minimum equipment tolerance to phase and time error that shall be provided at the boundary of packet networks at phase and time synchronization interfaces. It also outlines the minimum requirements for the synchronization function of network elements. This Recommendation addresses the case of time and phase distribution across a network by a packet-based method with full timing support to the protocol level from the network. Amendment 1 to Recommendation ITU-T G.8271.1 (03/2020) provides the following update: -Addition of new clause 7.5 -New version of Figure II.6, and addition of text to Appendix II -Clarifications to Appendix V -Addition of clause XII.5 and XII.6