Users Guide

Synchronous Ethernet (SyncE)
Frequency and time synchronization over a network is a key requirement for network service providers. Frequency
synchronization over Ethernet interfaces can be achieved in two ways:
● Synchronous Ethernet (SyncE)—SyncE achieves frequency synchronization by recovering clock frequency from the physical
layer of Ethernet. SyncE supports the frequency transfer from hop-to-hop.
● Precision Time Protocol (PTP)—PTP achieves frequency synchronization based on the timing event messages.
The advantage of using SyncE for network synchronization as compared to PTP is that it provides high-quality frequency
synchronization irrespective of the network load. When SyncE is enabled on the physical Ethernet interface and switch,
frequency recovery from the received signal on the physical line and frequency synchronization is done in the hardware. It
uses Synchronization Status Message (SSM) and Ethernet Synchronization Message Channel (ESMC) for clock selection,
traceability, and failover. For the SyncE functionality to work correctly, ensure that each network element along the network
supports SyncE.
Use hybrid clocking (PTP and SyncE) to frequency synchronize the clock using SyncE, and Time of Day (ToD) and phase
synchronization using PTP. For more information, see Hybrid clocking.
NOTE: See Appendix III of ITU G.8262 standard for the list of SyncE compatible interfaces.
Synchronization Status Message (SSM)
Synchronization status message indicates the quality level (QL) of the transmitting clock to the neighboring nodes. Clock quality
helps a synchronous Ethernet node derive timing from the most reliable source and prevent timing loops by selecting the clock
source with best QL. Benefits of SSM are as follows:
● Provides fast recovery when a part of the network fails by switching to the next best available clock source.
● Ensures that a node derives timing from the most reliable clock source.
Ethernet Synchronization Message Channel (ESMC)
ESMC is the logical channel that uses Ethernet PDU to exchange SSM information over the SyncE link. ESMC packets are
received and processed on the SyncE-enabled ports that are configured as clock sources. The clock selection algorithm uses the
QL values to select the best clock source.
Supported platforms
OS10 supports SyncE only on the following platforms:
● S5224F-ON
● S5232F-ON
● S5248F-ON
●
S5296F-ON
Clock source selection
The clock selection algorithm selects the best available synchronization source from the Candidate sources. OS10 supports the
following clock selection modes:
● QL-enabled
● QL-disabled
Each mode uses different criteria to select the best available clock source. Use the sync-e mode command to configure the
QL mode to select the clock source for synchronization.
Use the sync-e esmc command to enable ESMC capability in the QL-enabled mode.
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System management