This recommendation includes the following main topics, annex, and appendixes: The need for time and phase synchronization, including the phase accuracy requirements for various types of mobile radio technologies Methods to distribute phase and time either using a distribution of GNSS receivers or packet- based approaches Network reference model and time and phase synchronization interfaces Annex A, "One pulse-per-second (1PPS) time and phase synchronization interface specifica- tion" (for 1PPS and ToD timing ports) Appendix I, "Time and phase noise sources in time distribution chains" (characteristics of tim- ing noise for PRTC, masters, and slaves) Appendix II, "Time and phase end application synchronization requirements" (gives more de- tails of the requirements for various types of mobile radio technologies, and includes references to source documents from other standards organizations) Appendixes III, IV, and V: Collectively cover asymmetry compensation in the network and transport links Appendix VI, "Time synchronization aspects in TDD based mobile communication systems (is- sues to note from mobile radio systems based on time division duplex techniques) Appendix VII, "Time scales" (information on various time scales) Appendix I is particularly interesting, even if you avoid some of the mathematics. It outlines all the various places where and the reasons why time error can creep in. A new complete reprint of G.8271 was consented in March 2020. Link to recommendation: https://handle.itu.int/11.1002/1000/14209 G.8271.1: Network Limits for Time Synchronization in Packet Networks with Full Timing Support from the Network ITU-T G.8271.1 specifies the network limits for time and phase synchronization in packet networks with full timing support from the network (or "with full on-path support"). This case with full on- path support is directly equivalent to the G.8271.2 recommendation that covers the case without the on-path support. Note that because the network defined here has full timing support, every node is