Configuration > TimeKeeper configuration: Timing Sources
Out of the box, VelaSync comes with only one timing source pre-configured: TimeKeeper GPS. While this configuration will suffice for basic operation, it is advisable to add other timing sources for improved failover performance. Below are some general recommendations:
Note: When filling out the menu forms for a newly added source, many if not most of the fields can be left blank. There are very few fields that must be populated e.g., NTP server.
- Add timing sources: In order to allow VelaSync to failover to another timing source in the event the GPS signal will be lost temporarily, it is advisable to create at least one additional timing source e.g., a PTP or NTP server. While TimeKeeper will continue to provide time to VelaSync's network clients after loss of a GPS signal and expiration of the holdover period, it will do so without its internal clock being steered by an external reference. As a consequence, the time served will be:
- less stable (+/- variation)
- likely drift over time
- not be traceable.
It is noteworthy to mention that, while there is no valid GPS signal present, TimeKeeper's internal clock will NOT be steered by VelaSync's high-precision oscillator, once the holdover time has expired.
To add a PTP or NTP timing source:
- Utilize VelaSync's oscillator for failover handling: Applications that are using PTP/NTP as primary source can be configured to use the oscillator as a failover source, i.e. TimeKeeper will accept the time and PPS signal generated by the oscillator, even if the oscillator is temporarily not steered ("disciplined") by the PTP/NTP timing source. (Note that this configuration is not supported with GPS as a primary source.)
In fact, the oscillator's accuracy tends to be significantly better than the timing signal obtained from a typical NTP server. Which raises the question why not use it in the first place, i.e. instead of an NTP server? The answer is: Because without external references such as NTP or PTP servers VelaSync operates in "freerun" mode, and while the time served by VelaSync may be very accurate, it is not traceable.
Hence, allowing the un-disciplined oscillator to steer TimeKeeper's internal clock as a primary failover source is only advisable if there is no need for an auditing trail, and it is permissible to serve a time that has no direct reference to UTC. However, for most applications it is generally advisable to add the oscillator as the lowest priority timing source.
- Navigate to Configuration > TimeKeeper configuration > Sources: Add a new source: Internal GPS/Oscillator.
- Uncheck TimeKeeper GPS device, and check Disable GPS steering.
- Add the newly created source, and leave it at its default lowest-priority position. (Or, drag&drop it to position (1) right below TimeKeeper GPS, in order to use the un-disciplined oscillator as the primary failover source.
- Click Save TimeKeeper changes.
Note: Another option to allow the un-disciplined oscillator to steer TimeKeeper's internal clock for an extended period of time, before failing over to e.g., a PTP or NTP server, is to increase the Holdover Time under Application Settings from 7200 seconds to a longer period.
- Utilize Sourcecheck: Even if no NTP or PTP servers are available, it may be advisable to add two public time servers (such as NIST and pool.ntp). While these normally will be not accurate enough to act as as a quality failover timing source, they can be used by TimeKeeper's Sourcecheck feature.
Sourcecheck utilizes standby timing sources to verify the validity of an incoming GPS signal, thus enabling the detection of accidental or intentional spoofing of the satellite timing signal.
To use Sourcecheck:
- Designate the newly added public time servers as a low quality source so as to limit their permission to discipline the oscillator.
- Under Application Settings, enable Source Check.
- Special use case: No GPS available at all: Even in the case of complete absence of a GPS source e.g.,
- during initial installation of VelaSync while the GPS antenna has yet to be installed,
- or if for other reasons the time to be distributed by VelaSync does not need to be linked to UTC,
… it is also possible to use the internal oscillator as the primary timing source, i.e. instead of the TimeKeeper GPS source.
Please note, however, that while the time distributed by TimeKeeper will be very stable, it most likely will differ from UTC, because of the lack of any external steering.
To configure VelaSync's oscillator to become TimeKeeper's primary timing source:
- Open the PRIMARY (0) TimeKeeper GPS source, uncheck TimeKeeper GPS device, and check Disable GPS steering. Click Save TimeKeeper changes and wait for TimeKeeper to restart.
Note: Should you accidentally delete the TimeKeeper GPS timing source, create a new one by navigating to Add a new source > Internal GPS/Oscillator. Leave the default settings for TimeKeeper GPS device (checked) and Disable GPS steering (unchecked), and drag&drop the newly added source to list position (0).