"This Recommendation specifies the requirements for primary reference time clocks (PRTCs) suitable for time and phase synchronization in packet networks. These requirements apply under the normal environmental conditions specified for the equipment. A typical PRTC provides the reference signal for time synchronization and/or phase 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""1 within the network nodes where the PRTC is located. The PRTC provides a reference time signal traceable to a recognized time standard (e.g.@ UTC). This Recommendation defines the PRTC output requirements. The accuracy of the PRTC should be maintained as specified in this Recommendation. 1 ""Telecom Grand Master"" is currently under study within ITU-T."