hapter 6. In another sec- tion "Ethernet Synchronization Messaging Channel" in Chapter 6, the mechanism to carry QL in- formation using Ethernet frames is explained. This recommendation details that mechanism. This recommendation is slightly unusual (meaning that it is hard to classify) as it relates to the transport of physical clock quality levels across a packet network. This is the direct equivalent of the SSM from the SDH/SONET world as laid out in G.781. The main difference is that the informa- tion is carried in frames using a method native to Ethernet. And like G.781, G.8264 can be thought of as a recommendation that specifies control-plane functions for synchronization. G.8264: Distribution of Timing Information Through Packet Networks ITU-T G.8264 defines the mechanism that allows clock quality traceability in a packet network and initially focuses on Ethernet networks as opposed to other packet networks. This recommendation also details the required architecture in formal modelling language and uses timing flows to de- scribe where and how timing flows through the architecture. From the scope of the recommendation: It specifies the synchronization status message (SSM) transport channel namely the Ether- net synchronization messaging channel (ESMC), protocol behaviour and message format. The physical layer that is relevant to this Recommendation is the Ethernet media types defined in [IEEE 802.3]. Therefore, G.8264 defines ESMC and is designed to support SyncE. This recommendation includes the following main topics and appendixes: Packet network architectures, timing flows, and functional blocks Next-generation timing architectures Frequency transfer using SyncE SSM for SyncE Use of SyncE in a multi-operator context Appendix I, "Examples of timing flows" Appendix II, "Functional models based on ITU-T G.805 and ITU-T G.809" Amendment 1, released in 2018, makes changes to incorporate the ePRC into the tables of enhanced SSM codes for SyncE. Previous amendments added the enhanced QL values, which are carri