Going back to 0: What the GPS rollover means for your networks

On April 6, 2019, the Global Positioning System (GPS) will undergo a Week Number rollover event; the week number indicator digit that GPS uses for tracking dates is reaching its maximum value and has to rollover back to 0, just like the odometer in a car. The first time that this happened was 1999.

Who will be affected?

While most people are familiar with GPS for personal navigation needs on their mobile phones, GPS plays a crucial role in IT and OT operations, especially related to accurate timestamping of logging data, transactions and trades in capital markets, motion events in manufacturing, synchronization of clocking within utility telecom operations, and general time-of-date needs that are pervasive across all IT organizations.

In normal operation, a GPS clock can lose synchronization with the GPS constellation due to transient conditions, such as inclement weather or a failing antenna. When this happens, the clock enters a holdover period and relies on its internal oscillator to maintain frequency accuracy until a GPS signal can be reacquired. The length of time the clock can remain in holdover before the first “slip” (a synchronization error) occurs depends on the chemistry of the onboard oscillator; for example, ~48 hours with oven-controlled crystal oscillator (OCXO), ~14 days with rubidium oscillators.

Potential impacts of the Week Number rollover

It’s unclear how an unpatched clock will handle the rollover event; the clock may experience an error, go into holdover, but be unable to recover and lead to free-run condition. If this occurs, eventually the clock will experience slips, leading to inaccurate time and synchronization, which would negatively impact any system that relies on a clock.

Issues may include:

NTP (Network time Protocol) may provide incorrect time:

• Skewing system time of workstations, servers, and other equipment

• Incorrectly timestamped log data, especially used for security events or event correlation

• Authentication issues and other failures, especially those that use certificate-based or Kerberos-based authentication where correct timing is necessary for authentication to function

Networks synchronization timing may experience too many slips and break down:

• Causing channel banks, circuit emulation services on MPLS, and SONET networks to transport network traffic unreliably

• Negative impacts to synchrophasors, PMUs, and other substation-based equipment that require accurate PTP-based time

• Negative impacts to motion-based I/O sensors in manufacturing

Taking action

Modern clock hardware should already have support for the rollover event and may use a different internal rollover date sometime in the future (2022 and beyond), but it likely varies widely by clock vendor. It is strongly recommended for IT and engineering departments to examine each GPS-based clock and ensure that it is running the latest software to handle this event. If in doubt whether the current software is patched, reaching out to the equipment manufacturer may be appropriate as a confirmatory measure, but worth the time to mitigate the risk or ensure your clocks are already prepared for the event. Source: DOE Office of Electricity