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Holdover Mode

When input references have been supplying input to VersaSync and input from all the references has been lost, VersaSync will not immediately declare loss of time synchronization, but first will go into Holdover mode. While the unit is in Holdover mode, the time outputs are derived from the internal 10 MHz oscillator incrementing the System Time, but the oscillator is not disciplined/steered by the external reference e.g., GNSS.

Because of the stability of the internal oscillator, accurate time can still be derived even after all the primary references are no longer valid or present. The more stable the oscillator is without an external reference, the longer this holdover period can be and have it still maintain very accurate outputs. The benefit of Holdover is that time synchronization and the availability of the time outputs is not immediately lost when input references are no longer available.

While VersaSync is in Holdover, the only difference is the Holdover and associated Minor alarm are asserted. There are no changes to NTP or any of the other outputs, i.e. while in Holdover mode, NTP inside VersaSync continues to be at the same Stratum level it was at before going into Holdover mode (such as Stratum 1 when synced to GPS). Should the Holdover period expire, however, or the unit is rebooted, the NTP Stratum will go to 16, preventing any clients from being able to sync with VersaSync until GPS or another reference has been restored.