ITU-T G.8272.2 PDF

This Recommendation specifies requirements for coherent network primary reference time clocks (cnPRTCs) suitable for time, phase and frequency synchronization in networks. These requirements apply under normal environmental conditions specified for the equipment.

A cnPRTC provides a reference time signal traceable to a recognized time standard and a frequency reference. The cnPRTC is subject to stringent output performance requirements utilizing sources referenced to a coordinated universal time (UTC) realization such as the global navigation satellite system (GNSS), frequency inputs from autonomous primary reference clocks, and connections to other cnPRTC clocks for further resilience and enhanced performance.

A cnPRTC provides the reference signal for time, phase and frequency synchronization for clocks within an entire or section of a network. In particular, the cnPRTC can also provide the reference signal to the telecom grandmaster (T-GM) within the network node where the cnPRTC is located.

This Recommendation specifies cnPRTC output requirements, including those for a cnPRTC integrated with a T-GM clock.

In addition to an individual, is a group of cnPRTC clocks deployed in a network, a cnPRTC ensemble, is also important. There are performance requirements associated with a cnPRTC ensemble, one of which is that for coherency. This is the relative time accuracy required between deployed cnPRTC clocks. This coherency requirement is in addition to the accuracy to a recognized time standard referred to in the second paragraph. This is for further study.