scope:

This Recommendation specifies minimum requirements for time and phase synchronization equipment used in synchronization networks that operates in the assisted partial timing support (APTS) and partial timing support (PTS) architectures.

The APTS and PTS architectures are specified in [ITU-T G.8271], [ITU-T G.8271.2] and [ITU-T G.8275]. The applicable profile is established in [ITU-T G.8275.2], which specifies unicast PTS/APTS time or phase synchronization distribution for packet-based networks.

This Recommendation allows for proper network operation for phase/time synchronization distribution when a network equipment embedding an APTS or a PTS clock is timed from another telecom boundary clock (T-BC) or a telecom grandmaster (T-GM). This Recommendation specifies the minimum requirements for APTS and PTS clocks in network elements (NEs). These requirements apply under the normal environmental conditions specified for the equipment.

This Recommendation includes noise generation, noise tolerance, noise transfer, and transient response for APTS and PTS clocks.

Synchronous equipment clocks (per [ITU-T G.8262]) are optional in this Recommendation, and they are not used for APTS. For PTS, if a piece of equipment implements a synchronous equipment clock, as described in Appendix III and in Appendix IV, then the requirements in clause 8 still apply.

NOTE - For APTS, double failure (coincident failure of both global navigation satellite system (GNSS) and precision time protocol (PTP) input references) is not addressed in this Recommendation, except for short-term holdover scenarios (see clause 7.6.1) when the primary GNSS source is lost and a backup PTP source is temporarily unavailable. APTS double failure is for further study.