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Dell SmartFabric OS10 User Guide Release 10.5.3

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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.

QL-enabled mode

In the QL-enabled mode, the switch considers the following factors when selecting a clock source on the SyncE-enabled interfaces:

  • Clock quality level (QL)
  • Clock availability or signal fail through QL-FAILED
  • Priority
  • External commands (SyncE force switch or manual switch)

In this mode, the switch always selects the clock source with the best QL value. SSM codes indicate the QL values, which are defined for the different regions such as Europe and America (see sync-e ssm-network-option). When multiple clock sources are available on the network, a clock source is selected according to the following rules:

  • If no external switch commands are active, the switch selects the clock source with the highest QL that does not experience a signal fail condition.
  • If multiple clock sources have the same highest QL, the clock source with the highest priority is selected.
  • If multiple clock sources have the same highest priority and QL, the switch remains synchronized to the current clock source or an arbitrary clock source from the group is selected.

QL-disabled mode

In the QL-disabled mode, the switch considers the following factors when selecting a clock source on the SyncE-enabled interfaces:

  • Clock availability or signal fail through QL-FAILED
  • Priority
  • External commands (SyncE force switch or manual switch)

When multiple clock sources are available on the network, a clock source is selected according to the following rules:

  • If no external switch commands are active, the switch selects the clock source with the highest priority that does not experience a signal fail condition.
  • If multiple clock sources have the same highest priority, the switch remains synchronized to the current clock source or an arbitrary clock source from the group is selected.

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