Ntp Timing System: Reference Selection And Preference - Spectracom SecureSync User Reference Manual

3.4 Network Time Protocol (NTP)
3.4.4

NTP Timing System: Reference Selection and Preference

If desired, Time and PPS References for the NTP service can be configured as "Preferred". This
provides additional "weighting" to that particular NTP input reference during the selection process,
while NTP is deciding which reference it should select as its source (though "prefer" does not guar-
antee that reference will become the selected reference).
The Timing System Reference/Preferred (Enabled/Disabled) option configures NTP to
"weight" the Timing system input heavier than input from other NTP servers for its selection
(The Timing System inputs are normally more accurate than other NTP servers). However,
if the Timing System inputs are not normally available (such as with intermittent GNSS
reception or no other inputs are available), it may be desired not to prefer the Timing System
over an NTP reference, in which case this box should not be checked.
The Timing System 1PPS Reference (Enabled/Disabled) option determines whether or
not NTP uses the 1PPS input from the Timing System. The 1PPS input to NTP needs to
correlate with its "Time" input. If the Time and PPS inputs are originating from the same
source, they will be correlated. However, if the time is originating from another NTP server,
but the 1PPS is being derived by the Timing System, the two inputs may not always cor-
relate. Without this correlation, NTP performance will be degraded. In this scenario, it is
best not to use the System Time's 1PPS as a reference.
Normally, the NTP service will obtain its Time and PPS reference inputs from the Timing System
(the Timing System is the time as derived from the GNSS, IRIG, ASCII data inputs, etc.).
However, if desired, NTP can also obtain time from other NTP server(s). When the Timing System
references are normally available to SecureSync, the "Timing System 1PPS reference" should be
enabled and the "Timing System Reference" should be Preferred (both of the boxes at the top of
the page enabled). This provides NTP with the most accurate references.
In the case of Stratum synchronization (only syncing SecureSync to other NTP servers, instead of
the Timing System, so that is can operate as a Stratum 2 time server, for example), the Timing
System inputs are not going to be available, as the only available input will be other configured
NTP servers. In this scenario, it is best to uncheck both options at the top of the page so that the
Timing System is not preferred over a configured NTP server and to keep the Timing System's
1PPS from affecting the operation of NTP (as its 1PPS will not correlate with the NTP time input
being received from the other NTP servers).
102
NOTE – It is not normally recommended to enable the
ferred checkbox in addition to enabling any of the
ers table.
Normally, either select the
ferred boxes in the NTP servers table (if the Timing System inputs are normally avail-
able) or de-select the Prefer Timing System Reference
of the NTP servers in the NTP Servers table (if the Timing System inputs are not nor-
mally available).
Timing System Reference Pre-
Preferred
Prefer Timing System Reference
CHAPTER •
3 SecureSync User Reference Guide Rev. 18
boxes in the NTP Serv-
and none of the
Pre-
and enable Preferred on one