scope:

This Recommendation outlines new requirements for timing devices used in synchronizing network equipment that supports synchronous clocks, involved in time and phase transport. It supports clock distribution based on network-synchronous line-code methods (e.g., synchronous Ethernet, synchronous optical transport network (OTN) to deliver frequency synchronization).

This Recommendation focuses on the requirements for the enhanced synchronous Ethernet equipment clock (eEEC) and the enhanced synchronous OTN equipment clock (eOEC).

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

Included in this Recommendation are requirements for clock accuracy, noise transfer, holdover performance, noise tolerance and noise generation. These requirements apply under the normal environmental conditions specified for the equipment.

This Recommendation contains a single option for enhanced synchronous equipment clock. The networks containing enhanced synchronous equipment clock allow the worst-case synchronization reference chain as specified in Figure 8-5 of [ITU-T G.803].

Careful consideration should be taken when using both ITU-T G.8262.1 and ITU-T G.8262 clocks in the same chain as this may lead to not meeting the performance required by the relevant time and phase synchronization application. The highest performance can be achieved in networks where only enhanced EEC or better clocks are implemented, see [ITU-T G.8261] for the applicable network limits.

OTN 3R regenerators, as specified in [ITU-T G.8251], provide through-timing capability and can transmit timing via synchronous OTN.

More information on synchronous Ethernet can be found in [ITU-T G.781], [ITU-T G.8261] and [ITU-T G.8264], and for synchronous OTN can be found in [ITU-T G.709] and [ITU-T G.7041].

NOTE - The clock specified in this Recommendation is compatible with the Option 1 clock specified in [ITU-T G.8262].