Recommendation ITU‑T G.8275 describes the architecture and requirements for packet-based time and phase distribution in telecom networks. The architecture described is mainly applicable to the use of IEEE 1588. Details necessary to utilize IEEE 1588 in a manner consistent with the architecture are defined in other Recommendations. Amendment 1 incorporates the following updates: Updated clause 8, created Appendix XIII for security. Update Annex E (add sub-titles) Update Annex F (general enhancement) Update Appendix VII (stepped deployment for cnPRTCs) Update Appendix VIII (updated holdover terminology and tables) Update Table III.2 Remove all occurrences in “shall” and “must” in informative text (Appendices, notes).