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ITU-T G.8262

Timing characteristics of synchronous equipment slave clock

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Organization: ITU-T
Publication Date: 1 November 2018
Status: active
Page Count: 44
scope:

This Recommendation outlines minimum requirements for timing devices used in synchronizing network equipment that support synchronous clocks. It supports clock distribution based on the network-synchronous line-code methods (e.g., synchronous Ethernet, synchronous OTN to deliver frequency synchronization).

This Recommendation focuses on the requirements for the synchronous Ethernet equipment clock (EEC) and the synchronous OTN equipment clock (OEC).

The Recommendation allows for proper network operation when a synchronous equipment clock (Option 1 or 2) 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 two options for synchronous equipment clocks. The first option, referred to as "Option 1", applies to synchronous equipment designed to interwork with networks optimized for the 2048 kbit/s hierarchy. These networks allow the worst-case synchronization reference chain as specified in Figure 8-5 of [ITU-T G.803]. The second option, referred to as "Option 2", applies to synchronous equipment designed to interwork with networks optimized for the 1544 kbit/s hierarchy. The synchronization reference chain for these networks is defined in clause II.3 of [ITU-T G.813].

A synchronous equipment slave clock should comply with all the requirements specific to one option and should not mix requirements between Options 1 and 2. In the clauses where one requirement is specified, the requirements are common to both options.

The intent of the synchronous Ethernet and synchronous OTN is to interoperate with each other and with existing synchronization networks based on [ITU-T G.813].

Careful consideration should be taken when interworking between networks with synchronous equipment clocks based on Option 1 and networks with synchronous equipment clocks based on Option 2.

Some synchronous network elements (NEs) may have a higher-quality clock. This Recommendation allows for proper network operation when synchronous equipment (Option 1 or 2) is timed from either another synchronous equipment (like option) clock, or a higher-quality clock. Hierarchical timing distribution is recommended for synchronous networks. Timing should not be passed from a synchronous clock in free-run/holdover mode to a higher-quality clock since the higher-quality clock should not follow the free-run/holdover signal during fault conditions.

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].

Document History

March 1, 2020
Internet protocol aspects – Transport Timing characteristics of synchronous equipment slave clock Amendment 1
A description is not available for this item.
ITU-T G.8262
November 1, 2018
Timing characteristics of synchronous equipment slave clock
This Recommendation outlines minimum requirements for timing devices used in synchronizing network equipment that support synchronous clocks. It supports clock distribution based on the...
November 1, 2016
Timing characteristics of synchronous Ethernet equipment slave clock Corrigendum 1
A description is not available for this item.
January 1, 2015
Timing characteristics of synchronous Ethernet equipment slave clock
This Recommendation outlines minimum requirements for timing devices used in synchronizing network equipments that support synchronous Ethernet. It supports clock distribution based on the...
October 1, 2012
Timing characteristics of a synchronous Ethernet equipment slave clock Amendment 2
A description is not available for this item.
February 1, 2012
Timing characteristics of a synchronous Ethernet equipment slave clock Amendment 1
A description is not available for this item.
July 1, 2010
Timing characteristics of a synchronous Ethernet equipment slave clock
This Recommendation outlines minimum requirements for timing devices used in synchronizing network equipment that supports Synchronous Ethernet. It supports clock distribution based on...
January 1, 2010
Timing characteristics of a synchronous Ethernet equipment slave clock (EEC) Amendment 2
A description is not available for this item.
October 6, 2009
Timing characteristics of synchronous Ethernet equipment slave clock (EEC)
A description is not available for this item.
April 1, 2008
Timing characteristics of synchronous Ethernet equipment slave clock (EEC) Amendment 1
A description is not available for this item.
August 1, 2007
Timing characteristics of synchronous Ethernet equipment slave clock (EEC)
A description is not available for this item.

References

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