Recommendation ITU-T G.8272 specifies the requirements for primary reference time clocks (PRTCs) 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. New note added to Appendix II. New Appendix V Considerations on the use of GNSS for the PRTC.