Configuring Synchronous Ethernet; Overview; Quality Levels Of Clocks; Clock Reference Selection And Timing Distribution - H3C SR6600-X Configuration Manual

Configuring synchronous Ethernet

Overview

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.81 1 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 and timing distribution

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.
When distributing the QL of the system clock, the system uses the following rules:
If the clock reference is not from a SyncE port, the system distributes the QL out of all SyncE ports.
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