orks already built and in operation that serves as a testament to this approach. 8.4.1 Types of Standards for Packet-Based Synchronization The packet-based timing recommendations are broadly grouped, and within these categories, the following are key to packet-based timing: Definitions, architecture, and requirements: G.8260, G.8265, G.8273, G.8275 End-to-end solution and network performance: G.8271, G.8271.1, G.8271.2 Node and clock performance: G.8272, G.8272.1, G.8273.1, G.8273.2, G.8273.3, G.8273.4 PTP profiles: G.8265.1, G.8275.1, G.8275.2 Other documentation: G.8264, GSTR-GNSS, Supplement 68-Synchronization OAM Requirements The following sections summarize each of the recommendations within these categories. There is included an outline for each of the most important recommendations related to packet-based timing. The goal of this section for the reader is twofold: To point to where the recommendations define and describe the end-to-end solution To find where further information on implementation can be found, along with a summary of what is contained there As mentioned previously, each of these recommendations is available for download in PDF format from the https://www.itu.int website. 8.4.1 Definitions, Architecture, and Requirements These recommendations are the basis for all the other recommendations following. They contain the definitions and terminologies as well as the architecture and requirements for distributing fre- quency, time, and phase for packet-based synchronization. G.781.1: Synchronization Layer Functions for Packet-Based Networks G.781.1 specifies a functional architecture model and the corresponding atomic functions for the transport of time and frequency synchronization via packet-based methods (using PTP). From the scope of the recommendation: The functional architecture contains two synchronization layers, the network synchroniza- tion layer and the synchronization distribution layer. In addition, some of the synchroniza- tion-related atomic functions defined in this recommendation 