This Recommendation specifies minimum requirements for time and phase synchronization devices used in synchronizing network equipment, which operates in the network architecture as defined in [ITU-T G.8271] and [ITU-T G.8275]. It supports time and/or phase synchronization distribution for packet-based networks. The telecom transparent clock (T-TC) must be operating in end-to-end transparent clock (TC) mode.

This Recommendation assumes operation within the framework specified in [ITU-T G.8273], and that the physical layer reference chain behaviors given in [ITU-T G.803] and [ITU-T G.8261] are followed. It is also assumed that the network limits given in [ITU-T G.8271.1] are met and that the profile given in [ITU-T G.8275.1] is applied.

This Recommendation allows for proper network operation when a network equipment clock is timed from another network equipment clock or a higher quality clock.

This Recommendation defines the minimum requirements for transparent clocks. These requirements apply under normal environmental conditions specified for the equipment.

Guidelines for testing are described in Appendix I.

For T-TC classes A and B, this version of the Recommendation focuses on syntonized T-TCs with frequency reference provided by the physical layer based on [ITU-T G.8262] Option 1 (and [ITU-T G.813] Option 1 as the requirements are identical). [ITU-T G.8262] Option 2 and [ITU-T G.813] Option 2 are for further study. A T-TC without a frequency reference provided by the physical layer is for further study. [ITU-T G.8262.1] is a higher accuracy clock compared to [ITU-T G.8262], therefore it can also be used for T-TC classes A and B.

For T-TC class C, this version of the Recommendation focuses on syntonized T-TCs with frequency reference provided by the physical layer based on [ITU-T G.8262.1].

NOTE 1 – This Recommendation does not modify the physical layer reference chain behaviour, according to [ITU-T G.803] and [ITU-T G.8261]. This Recommendation does not exclude the use of other physical layer clocks (e.g., [ITU-T G.812] Type I) within the frequency transport network. The equipment specification of a T-TC assisted by a physical layer equipment clock, other than [ITU-T G.8262] Option 1 and [ITU-T G.8262.1], such as [ITU-T G.812] Type I, is for further study.

NOTE 2 – This version of the Recommendation was developed based on the hypothetical reference model (HRM) defined in clause II.2 of [ITU-T G.8271.1]. The use of T-TCs for more stringent network limits than that of accuracy level 4 in Table 1 of [ITU-T G.8271] is for further study.