hronization ITU-T G.8266 outlines the minimum requirements for the timing functions of the packet-based equipment clock-master (PEC-M), when timed from a physical frequency source traceable to a PRC/PRS or PRTC. It deals with the packet-based transport of frequency synchronization as op- posed to some physical method. From the scope of the recommendation: This Recommendation defines the minimum requirements for the timing functions of the telecom grandmaster clocks that operate in the network architecture as defined in [ITU-T G.8265] and the related profile defined in [ITU-T G.8265.1]. It supports frequency syn- chronization distribution when using packet-based methods. This recommendation includes the standard metrics of clock accuracy, noise tolerance, noise trans- fer, noise generation, and holdover specifications for T-GM clocks when used for frequency syn- chronization. Basically, it is a packet version of G.812 (G.8262 for Ethernet interfaces) with many of the same limits depending on whether the clock is Type I, II, or III. G.8266 defines the applicable limits at the PEC-M for frequency. This recommendation includes the following main topics, annex, and appendix: Frequency accuracy Pull-in, hold-in, and pull-out ranges Noise generation (wander and jitter) Noise tolerance and transfer Transient response and holdover performance Annex A, "Telecom grandmaster clock functional model" (includes a functional model for a T- GM/PEC-M) Appendix I, "Measurement method for wander transfer" Link to recommendation: https://handle.itu.int/11.1002/1000/13548 G.8272: Timing Characteristics of Primary Reference Time Clocks (PRTC) ITU-T G.8272 provides the requirements for PRTC clocks suitable as a source of time, phase, and frequency synchronization in packet networks. From the scope of the recommendation: This Recommendation defines the PRTC output requirements. The accuracy of the PRTC should be maintained as specified in this Recommendation. This Recommendation also covers the case where a PRTC is integrated with a T-GM