Microsemi SyncServer S350i, Руководство пользователя

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TIMING - Holdover
TIMING - Holdover
Overview
The SyncServer uses holdover to continue operating as a stratum 1 NTP server/peer for a
period of time if the Input References become unavailable.
For example: A SyncServer in a downtown office building gets time from GPS
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. Surrounding
skyscrapers occasionally block signals from the GPS satellites as they move across the sky,
causing "gaps" that last several hours. The SyncServer uses holdover to continue operating
as a stratum 1 NTP server during these gaps.
The factory default settings are appropriate for most situations. However, the user should
consider extending holdover to cover the longest anticipated "gap" if more than one of the fol-
lowing conditions is true:
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The SyncServer is the only NTP server available to the NTP clients.
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The SyncServer only has one Hardware Clock Input Reference (e.g., GPS, Timecode).
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The Hardware Clock is the only NTP association listed on the NTP - Assoc page.
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Restoring an Input Reference would take longer than the holdover period in days.
Please note the Holdover settings on this page also affect NTP if Override Behavior is selec-
ted on the NTP - Prefs page.
Also see Stratum (on page 202).
The Settings
The user can simply set the number of days Holdover lasts, or specify a Time Error Limit . Set-
ting either field generates an equivalent value in the other field.
About Time Error : When no Input References are available, the oscillator drifts away from
the correct time, accumulating time error . The type of oscillator affects how quickly time error
grows. The SyncServer keeps an ongoing estimate of the time error. Holdover ends when
the estimated time error is equal to or greater than the user-configured Time Error Limit.
The Oscillator Type affects the rate at which the oscillator accumulates time error when no
Input References are available.
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TCXO – The standard temperature-compensated oscillator.
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OCXO – The optional oven-compensated oscillator is more stable and offers better hol-
dover performance than the TCXO.
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Rubidium – The optional rubidium oscillator has the best stability and holdover per-
formance.
Several methods are available for the user to adjust Holdover or Time Error Limit:
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Entering a value for Holdover Limit or Time Error Limit and click the SET button.
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Sliding the green vertical bar on the Holdover graph left or right.
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Sliding the one of the black spheres under Holdover Limit or Time Error Limit left or right.
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The SyncServer S350i does not include a GPS receiver.
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