Background on the event

The Russian GLONASS system is designed in a way that it represents the date as days since the start of the last leap year. This means that every four years, at midnight moscow time, the date resets and there is no way for receivers to tell which four year period it is, absent outside information.

Modern GNSS receivers are designed to handle this rollover gracefully. When they see the date reset to zero, they know that it's the start of a new 4 year period and will continue on like nothing happened. Or at least they're supposed to.

Last time the rollover occurred (at the end of 2019 and the start of 2020), certain GNSS receivers shipped by PacketFlux and others didn't handle the rollover gracefully. Receivers with this issue started failing in unique and bizarre ways such as reporting a date four years earlier, or refusing to lock onto perfectly good GNSS satellites. Of interest to our customers, these failures would cause the 1PPS signal we provide to Cambium Radios to become unreliable. This resulted in various customer impacts.

Back in 2019 our phone started ringing shortly after the rollover. We quickly discovered that a restart of an affected GNSS receiver would resolve the issue for those receivers that did not recover on their own. Due to the widespread availability of remote management, most of our customers recovered from the event quickly and without a lot of effort. We know there were a few though that had receivers in hard to reach places without remote access. We hope that the information we provide here will help those customers have a quicker recovery this go around.

After the event, we some time getting to the root cause. After some research we discovered that GLONASS had just experienced a rollover event and through simulation verified that it was the cause. Additional research determined that it was a longstanding bug in the multi-GNSS receivers we had been using. Shortly thereafter we switched to a different vendor who had updated firmware that fixed the rollover bug.

So... Fast forward nearly four years, and we're back on the eve of another rollover event. We believe that all receivers that shipped since mid-2020 should be good to go this time, along with some much older receivers. In theory, only those receivers that experienced the issue in 2019/2020, along with a few that shipped shortly after the event should be affected.

The rest of the pages on this website are designed to hopefully help our customers be a bit better prepared for this rollover than the last one. If failures do occur, we hope that this will also be able to quickly recover in a more graceful manner. As you review this website, if you find something which seems wrong or unclear (or simply missing), please email us at custsvc@packetflux.com. There is every chance we missed something and any feedback will help us improve this documentation for you and for our other customers.