Recommendation ITU-T G.8272/Y.1367 specifies the requirements for primary reference time clocks (PRTCs) suitable for time, phase and frequency synchronization in packet networks. It defines the error allowed at the time output of the PRTC. These requirements apply under the normal environmental conditions specified for the equipment. Amendment 2 provides the following updates: Modification to scope. Updates to the reference Clause 2. Clause 6 text modified. Added reference to IEEE 1588-2019 in Clause 6.2. New text added under Clause 7. Holdover. [b-1588-2009] is removed from the bibliography section.