Configuring Synchronous Ethernet; About Synchronous Ethernet; Quality Levels Of Clocks; Clock Reference Selection - H3C CR16000-F Manual

Configuring synchronous Ethernet

About synchronous Ethernet

Synchronous Ethernet (SyncE) provides high-quality frequency synchronization on Ethernet at the
physical layer. It can provide the same level of clock precision as SONET/SDH.
Transferring frequency signals at the physical layer, SyncE functions regardless of the network
conditions such as congestion, packet loss, and delay.

Quality levels of clocks

SyncE devices use an Ethernet synchronization messaging channel (ESMC) to transmit the quality
level (QL) of their system clocks. A SyncE device uses QL information to select the optimal clock
reference from all available timing sources for its system clock.
The following are the QLs supported by the device, from the highest to the lowest:
•
PRC—G.811 primary reference clock.
•
SSU-A—G.812 primary-level SSU.
•
SSU-B—G.812 second-level SSU.
•
SEC—SDH equipment clock.
•
DNU—Do not use for synchronization.
•
UNK—Synchronization quality unknown.
DNU clock sources cannot participate in clock reference selection.

Clock reference selection

The system clock uses the clock reference selected with the highest QL from the following sources.
If these sources have the same QL, the system clock selects the clock reference by priority, from
the highest to the lowest:
•
External clock sources.
•
Line clock sources input from interfaces.
•
Internal clock sources.
The system clock uses the QL of the selected reference. Clock reference selection process starts
each time the QL of a source is updated.
NOTE:
If QLs are the same on two interfaces, the clock source input from the lower-numbered interface
has priority.
System clock QL distribution and SyncE port input QL
updating
Distribution of the system clock QL
When distributing the QL of the system clock, the system uses the following rules:
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