3.3.4 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 Hol-
dover mode, the time outputs are derived from the internal 10MHz 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derived even after all the primary references are no longer valid or present.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 hold-
over 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 asso-
ciated 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 Stratum1
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.
How long will the unit remain in Holdover mode?
VersaSync will remain in Holdover mode until either:
3.3 Managing References
CHAPTER 3 • VersaSync User Manual Rev. 12
219
To Next Page
Loading...
