Recommendation ITU-T G.8272.1 specifies the requirements for enhanced primary reference time clocks (ePRTCs) suitable for time, phase and frequency synchronization in packet networks. These requirements apply under the normal environmental conditions specified for the equipment. This amendment provides the following updates: Adds the synchronous Ethernet interface along with associated performance requirements. Edits to clause 6.1 including reference to [ITU-T G.8272] Appendix V Considerations on the use of GNSS for the PRTC. New note added to clause 8.2. Note added to Appendix I.