MANUAL P/N 900000165 REV H
AUTO-OFF / Holdover
This provides a mechanism for non-standard NTP or SNTP clients that do not properly adhere to
NTP protocols such as RFC1305. In particular where the leap indicator flags are not used or the
monitoring of reference time is not taken into account. For these situations the auto-off
mechanism will stop the NTP80 servicing NTP requests after a period specified, in seconds,
from the time that synchronisation is lost. Initially when this is enabled the holdover time will
be set to 86400s, i.e. 24 hours. This will mean that any NTP client will not be able to use this
server after this time regardless of how that client is implemented. Note that the Holdover time
specified should take into account the oscillator that is fitted to the NTP80. The reliability of
time will be greater for longer for a Rubidium unit than one with a TCXO. All can be within the
NTP Stratum 1 specification of 1ms after 1 day of holdover assuming good GPS reception for a
significant period of time prior to loss of synchronisation.
Signal Mask
A signal level value below which satellites ignored for timing, 0 – 55. The default value is 35,
reduce this if there are problems with GNSS synchronisation.
Elevation Mask
Elevation below which satellites will not be used for timing. The default value is 10°.
Peer Servers 1-4
If the NTP server is a peer-to-peer model, with no GPS fitted, then the GPS checkbox must not
be ticked. The configuration then allows for up to four NTP servers to synchronise with. These
are specified in Peer server 1 to 4. They can either be a DNS name or an IP address. The min and
max poll indicate the minimum and maximum rate of NTP requests. This number is a power of 2
and can be from 6 to 9, so the standard minimum poll interval is 2
6
= 64s and the maximum is
2
9
= 512s. If these fields are left blank then the NTP service will decide on the appropriate
polling interval.
The NTP server follows the standard NTP protocol to determine the best of the specified clocks
to synchronise to. One may be selected as preferential by setting the prefer option radio button
for that server.
The peer NTP servers can also be set up with a GNSS unit. These can then take over following
the loss of GPS synchronisation. Note that depending on the oscillator fitted and the period for
which GPS is lost, the performance when synchronising to another NTP server will not be as
good as running in holdover. If peer NTP servers are available in this configuration the AUTO-
OFF will not function until all possible synchronisation sources have failed.
Mulitcast (or Broadcast) Address
The NTP80 can be used as a broadcast NTP server. A broadcast address or multicast address can
be specified in the multicast address box along with the poll interval. The unit will then transmit
NTP messages at this interval to the multicast or broadcast address.
To Next Page
Loading...