Recommendation ITU‑T G.8271/Y.1366 defines time and phase synchronization aspects in packet networks. It specifies the suitable methods to distribute the reference timing signals that can be used to recover the phase synchronization and/or time synchronization according to the required quality. The requirements for the synchronization characteristics that are specified in this Recommendation must be adhered to in order to ensure interoperability of equipment produced by different manufacturers and a satisfactory network performance. Amendment 1 to Recommendation G.8271 provides the following updates: Editorial changes replacing the term calibration with compensation that better reflect what is meant throughout this document. Moved appendix VII from this document to appendix II [ITU‑T G.8260] Change non-inclusive language in line with IEEE Std 1588g-2022 Added references to time services over 5GS Added reference to IEEE Std 1588-2019