Spectracom SecureSync User Reference Manual page 430

5.5 Network Interface Option Cards
The proper TAI or UTC time (including the current year)
The current TAI to UTC offset (required even if the reference's time is in TAI)
Pending leap second information at least a day in advance.
If the reference does not transmit this information, it must be provided by the user in order for the
Master Clock to function properly.
The built-in GNSS reference provides all information needed with no user intervention.
PTP-specific configuration steps:
Confirm that:
From the PTP Status window under the Advanced tab, check that PTP Port Activity is
enabled (if not, enable it from the PTP Edit window, under the Ethernet tab).
From the PTP Edit window under the Main tab, check that the clock is set to be a Master .
From the PTP Status window under the Main tab, check that a valid IP address is currently
being used.
When the PTP Module is set to be a Master Clock, the module will immediately attempt to become
the active Master Clock on the network ( Port State = Master ). If it does, it will start to transmit
PTP packets (even if the SecureSync is not yet synchronized).
There are several reasons why the PTP Module may not become the active Master Clock, or may
not be broadcasting the correct time, even if it is set to be a Master Clock:
a.
If using any reference other than self for 1PPS, the SecureSync will not become an active
Master Clock until the Time Figure of Merit ( TFOM ) value of the system is less than 15.
After first going into sync after power-up, it may take a minute or two for the Time Figure of
Merit (TFOM) value to fall to an acceptable level. The current Time Figure of Merit (TFOM)
value is available in the Time Properties panel under the Advanced tab on the PTP Status
window page.
b.
PTP uses the TAI timescale to transfer time. Many timing references communicate time in
the UTC timescale. UTC is offset from TAI by a small amount which changes every time a
leap second occurs. The TAI to UTC Offset is part of the PTP Specification and must be
provided to a Master Clock. If no active reference can provide that information, the offset
must be provided by the Host. The TAI to UTC Offset can be set from the
MANAGEMENT/OTHER/Time Management page (while setting the GPS to UTC Off-
set).
c.
The PTP Protocol also provides for the transfer of Leap Second information. If the active
time reference does not provide Leap Second information, it must be added by the user
through the MANAGEMENT/OTHER/Time Management page. If this is not done, the
PTP network will have the incorrect UTC time after a leap second event.
d.
If there are multiple multicast Master Clocks on the network, the PTP Module uses the Best
Master Clock (BMC) algorithm specified in the PTP Specification to decide whether or not
to become the active Master Clock. The BMC algorithm selects the Best Master Clock on
the network from the following criteria:
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5 SecureSync User Reference Guide Rev. 18