Spectracom - Essential Ingenuity

NTP's "Local (0)" Clock reference

Question

After we upgraded the time server from software version 4.8.9 to version 5.0.2, why doesn't the Status -> NTP page show a "LOCAL" clock reference but a time server with an older version still does?

Answer


User-added image

The Local (0) clock reference ("127.127.1.0") is a method Spectracom used in the past to force NTP to go to Stratum 16 when NTP has no references to sync with.  NTP has its own internal reference that it can use for its sync (known as the Local clock reference), and in earlier software versions, Spectacom used this Local reference to have NTP go to Stratum 16, when NTP selected its own internal reference. This value is displayed in the NTP Reference Status table on the Status -> NTP page of the browser.

In most scenarios, this approach works very well.  However, if the input reference happens to be jittery (such as an IRIG input from an unsynchronized IRIG generator, for example), NTP may keep “changing its mind" on which one is the better reference. The jittery IRIG input is a higher stratum (NTP prefers this), but its internal reference is more stable than the higher Stratum reference. So sometimes, it is Stratum 1, and other times it goes to Stratum 16.
If you were to disable the Local reference and the IRIG input is then lost, NTP still remains Stratum 1 and useable by the clients. It can no longer go to Stratum 16.

Prior to Archive software version 4.8.6, 127.127.1.0 is always listed in the NTP Reference Status table.  Starting in Archive version 4.8.6 (until version 4.8.9) a field in the Network > NTP setup page of the browser, NTP Servers tab, allows this Local Clock reference to be either enabled or disabled (enabled by factory default). When enabled, 127.127.1.0 will be listed in the table NTP Reference Status.  When disabled, it is not displayed and NTP will not be able to go to Stratum 16.  It will always be a useable time source, whether or not it is synced by an external reference or if its synced to itself.

Because Spectracom has seen a few instances of NTP switching back and forth between Stratum 1 and 16, even though the primary input is always present, the Spectracom Engineering team devised anotherr method to allow NTP to still go to Stratum 16 when there are no references present (which prevents NTP clients from syncing to the time server). This was implemented in version 5.0.0.

Starting in Archive version 5.0.0, the Local Clock reference 127.127.1.0 is no longer continuously listed in the NTP Reference Status table.  It is now a dynamic reference that is only momentarily entered into this table when SecureSync goes from in sync state to out of sync state.  Normally, the 127.127.1.0 reference will not be displayed in this table. However, if the web browser just happens to refresh when the SecureSync exits the Sync state (goes out of time sync) the reference is momentarily added to the table and this value may be briefly displayed in the table. But very shortly thereafter, it will no longer be displayed in the table again (it will not be added back into the table unless SecureSync goes back into Sync and then sometime thereafter, loses sync once again).


Was this information helpful?

 Yes  No