SyncE

SyncE is a standard for transmitting clock signals over the Ethernet physical layer to synchronize clocks across the network by propagating frequency using the transmission rate of symbols in the network. A dedicated Ethernet channel, (ESMC), manages this synchronization.

The Cumulus Linux switch includes a SyncE controller and a SyncE daemon.

• The SyncE controller reads performance counters to calculate the differences between TX and RX ethernet symbols on the physical layer to fine tune the clock frequency.
• The SyncE daemon (syncd) manages:
  • Transmitting and receiving SSMs on all SyncE enabled ports using the Ethernet Synchronization Messaging Channel (ESMC).
  • The synchronization hierarchy and runs the master selection algorithm to choose the best reference clock from the QL in the SSM.
  • Using to the next best clock when the master clock fails. The selection algorithm only selects the best source, which is the Primary Clock source.
  • The switchover time if the algorithm also selects a secondary reference clock in case of primary failure.

Basic Configuration

Basic SyncE configuration requires you:

• Enable SyncE on the switch.
• Configure SyncE on at least one interface or bond so that the interface is a timing source that passes to the selection algorithm.

The basic configuration shown below uses the default settings:

• The QL for the switch is set to option 1, which includes PRC, SSU-A, SSU-B, SEC and DNU.
• The frequency source priority on the interface is set to 100.
• The amount of time SyncE waits after the interface comes up before using it for synchronization is set to 5 minutes.

cumulus@switch:~$ nv set synce enable on
cumulus@switch:~$ nv set interface swp2 synce enable on
cumulus@switch:~$ nv config apply

Optional Global Configuration

QL for the Switch

You can specify the ITU-T QL for the switch. You can specify one of the following values. The default is option 1.

• option 1 includes PRC, SSU-A, SSU-B, SEC and DNU.
• option 2 includes PRS, STU, ST2, ST3, SMC, ST4, RES and DUS.
• option 3 includes PRS, STU, ST2, ST3, TNC, ST3E, SMC, ST4, PROV and DUS.

The following command example sets the QL for the switch to option 2:

cumulus@switch:~$ nv set synce network-type option 2
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

Logging

By default, SyncE logging is off on the switch. You can enable logging to write a log message:

• Every time there is a change to the selected source in addition to errors
• Only when there are no available frequency sources or when the only available frequency source is the internal oscillator

The following command example sets logging to write a log message every time there is a change to the selected source in addition to errors:

cumulus@switch:~$ nv set synce changes
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

The following command example sets logging to write a log message only when there are no available frequency sources or when the only available frequency source is the internal oscillator:

cumulus@switch:~$ nv set synce errors
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

Optional Interface Configuration

Frequency Source Priority

The clock selection algorithm uses the frequency source priority on an interface to choose between two sources that have the same QL. You can specify a value between 1 (the highest priority) and 256 (the lowest priority). The default value is 100.

The following command example sets the priority on swp2 to 254:

cumulus@switch:~$ nv set interface swp2 synce priority 254
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

Wait to Restore Time

The wait to restore time is the amount of time SyncE waits after the interface comes up before using it for synchronization. You can set a value betwen 0 and 12 minutes. The default value is 5 minutes.

The following command example sets the wait to restore time to 3 minutes:

cumulus@switch:~$ nv set interface swp2 synce wait-to-restore 3
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

Disable Synchronization Status Messages

You can disable SSMs on an interface to prevent sending ESMC packets and ignore any received ESMC packets.

The following command example disables SSMs on swp2:

cumulus@switch:~$ nv set interface swp2 synce ssm disable
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

QL to Transmit in Status Messages

To override the QL (option 1, option 2 generation 1, or option 2 generation 2) transmitted in SSM messages, you can set the following options:

• exact <ql> specifies the exact QL regardless of the value received.
• highest <ql> specifies an upper limit on the QL. If the selected source has a higher QL than the QL specified here, the switch transmits this QL instead.
• lowest <ql> specifies a lower limit on the QL. If the selected source has a lower QL than the QL specified here, the switch transmits DNU instead.

The following command example specifies an upper limit of option 1:

cumulus@switch:~$ nv set interface swp2 synce highest option 1
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

QL to Receive in Status Messages

To override the QL (option 1, option 2 generation 1, or option 2 generation 2) received in SSM messages before using it in the selection algorithm, you can set one of the following options:

• exact <quality-level> specifies the exact QL regardless of the value received unless the received value is DNU.
• highest <quality-level> specifies an upper limit on the received QL. If the received value is higher than this specified QL, the switch transmits this QL instead.
• lowest <quality-level> specifies a lower limit on the received QL. If the received value is lower than this specified QL, the switch transmits DNU instead.

The following command example specifies a lower limit of option 2 generation 1:

cumulus@switch:~$ nv set interface swp2 synce lowest option 2 generation 1
cumulus@switch:~$ nv config apply

EXAMPLE FILE HERE

cumulus@switch:~$ sudo systemctl restart syncd

Troubleshooting

To show SyncE configuration, run the nv show synce command:

cumulus@switch:~$ nv show synce
ADD OUTPUT

To show SyncE statistics for all the enabled interfaces, run the nv show synce interface statistics command:

cumulus@switch:~$ nv show synce interface statistics
ADD OUTPUT

To show SyncE statistics for a specific interfaces, run the nv show synce interface statistics <interface> command:

cumulus@switch:~$ nv show synce interface statistics swp2
ADD OUTPUT

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