Recommendation ITU-T G.8265.1/Y.1365.1 describes the architecture and requirements for packet-based frequency distribution in telecom networks. Examples of packet-based frequency distribution include the network time protocol (NTP), IEEE-1588-2008 and IEEE 1588-2019 and are briefly described here. Details necessary to utilize IEEE-1588-2008 and IEEE 588-2019 in a manner consistent with the architecture are defined in other Recommendations.