Impending GPS Week Number rollover


If you are synchronizing time from national NTP servers or servers that derive their time from national NTP servers, this is most likely a non-event for you. National NTP servers typically use local (terrestrial) accurate clocks to serve time and don't rely on GPS for time distribution. I should mention that I can't speak for any of these public deployments. I am optimistic that they all will fare just fine tomorrow.

If you are using GPS time source(s), this information is relevant to you.

Disclaimer: Microsoft neither endorses, manufactures nor sells any GPS-enabled time sources or servers. This post is just an FYI, based on information published by GPS/USNO.

GPS time sources are widely used in accurate, reliable NTP and PTP time servers and it is my understanding that they are often used to supply time to Microsoft Windows deployments as well. Other operating systems in your environment are likely be affected by time issues arising from this event. Hence this last minute blog post to give a heads up about an impending GPS event that can potentially affect the time in your systems.

The "Week Number" field in the GPS messaging is scheduled to rollover in about 22 hours time from when this post is made, just before April 7th, 2019 UTC rolls in.

You can read about this event on the dedicated USNO website or on gps.gov homepage. The latter website has a countdown clock to the event for easy visualization.

Whether or not the Microsoft Windows machines in your deployment are affected depends on many factors. The most important factor is the GPS time source you are using and whether it handles the week rollover correctly. Subsequent factors include your time distribution topology and W32time service configuration on the individual Windows machines.

Please refer to documentation from your GPS time source supplier about how the equipment will fare during this rollover.

The default W32time service settings should prevent it from accepting very large time corrections from upstream sources. How your Windows machine(s) is/are affected depends on your specific settings.

In any case, I would suggest to keep an eye out for unusual time issues when the rollover occurs tomorrow. (And be cautious using your GPS for navigation tomorrow, may be?)


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