This Recommendation describes the general architecture of frequency distribution using packet-based methods. This version of the Recommendation focuses on the delivery of frequency using methods such as NTP or the precision time protocol (PTP) [IEEE 1588]. The requirements and architecture form a base for the specification of other functionality needed to achieve packetbased frequency distribution in a carrier environment. The architecture described covers the case where protocol interaction is at the end points of the network only, between a packet master clock and a packet slave clock. Details of requirements for other architectures involving devices that participate between the packet master and packet slave clocks are for further study.