This Recommendation specifies the requirements for primary reference time clocks (PRTCs) suitablefor time, phase and frequency synchronization in packet networks. These requirements apply underthe normal environmental conditions specified for the equipment.

A typical PRTC provides the reference signal for time, phase and frequency synchronization for other clocks within a network or section of a network. In particular, the PRTC can also provide the reference signal to the telecom grand master (T-GM) within the network nodes where the PRTC is located.

The PRTC provides a reference time signal traceable to a recognized time standard.

This Recommendation defines the PRTC output requirements. The accuracy of the PRTC should be maintained as specified in this Recommendation.

This Recommendation also covers the case where a PRTC is integrated with a T-GM clock. In this case it defines the performance at the output of the combined PRTC and T-GM function, i.e., the precision time protocol (PTP) messages.

This Recommendation defines two types of PRTCs, PRTC-A and PRTC-B. The time output of a PRTC-B is more accurate than that of a PRTC-A, and is therefore appropriate for applications where more accurate absolute time is required. In order to facilitate conformance to the relevant requirements, the PRTC-B is suitable for locations where it is possible to guarantee optimized environmental conditions (e.g., controlled temperature variation in indoor deployments). Typical examples are central location and large aggregation sites. However, this does not preclude other applications.