Important Technical Bulletin From MetOcean – Iridium Re-Epoch
Dear Customer,
Please note, this notice is intended for review by person(s) with technical knowledge of Iridium Products.
Iridium has once again decided to move forward with a “re-epoch” of their system time count. The last time Iridium implemented a “re-epoch” of their system time was in the 2014-2015 period.
What is a “Re-Epoch”?
As part of standard satellite network operations, Iridium periodically resets the Iridium L-Band system time count. This event is known as a “Re-Epoch”.
Important Items to Note:
- Iridium Time is a 32-bit unsigned integer that corresponds to the number of 90ms intervals since the last epoch, May 11, 2014,14:23:55.
- The ERA3 EPOCH will correspond to February 14, 2025, at 18:14:17.000Z
- This count is known as the Iridium L-Band Frame Number (LBFN).
- As detailed in the Iridium developer documentation, Iridium may set a new epoch from time to time, which means that the LBFN will not increase indefinitely, and at some point, may roll over to zero, or be reduced to a defined number based on any number of requirements from Iridium themselves.
- Iridium has announced that a new epoch will be rolled out, targeting January 14, 2026. However, official dates/times and further details to be announced shortly.
Potential Risks & Issues:
- In the past, Iridium has made it very clear that development of product should never programmatically rely on, or depend on in any way, Iridium Time to function correctly.
- Iridium recommends retrieving any required form of time from other sources, such as GNSS, or a separate RTC, etc.
AT Commands Relevant to Iridium Time:
- AT-MSGEO, AT-MSGEOS, AT-MSSTM, AT+CRISX – These commands provide the Iridium time value in hexadecimal format. After the epoch change, this value will match the valid Iridium time with the new, later epoch. The ISU AT Command Reference section for command AT-MSSTM warns about possible future epoch change and warns NOT to rely on this value for the current time. Any algorithm in the field application that converts this value using the old Iridium time epoch will generate an invalid result after the epoch change. Any algorithm in the field application that compares the value of subsequent calls to this AT command in order to determine time difference will generate a one-time invalid result immediately after the epoch change.
- AT+CCLK – This command provides the current UTC time derived from the ISU’s local time and hard-coded Iridium time epoch corresponding to the Epoch. After the epoch change, this command will provide an invalid response and should NOT be used.
Conclusion & Next Steps:
While Iridium anticipates that nearly all devices on the network will be unaffected, it is imperative that partners and developers take the time to verify their own applications to be certain. Failure to do so may result in devices that become unresponsive in the field. Iridium themselves are continuing to review their own products, with the potential of Firmware and Software updates to ensure a smooth transition with the new epoch.
As important dates and times become publicly available, Iridium, and MetOcean, will be able to provide this information to our customers and partners.
We appreciate your patience during this time, if you have any questions or concerns regarding the re-epoch, please do not hesitate to contact the MetOcean Technical Support Team at support@metocean.com.
FAQ’S
Q. What is the significance of February 14th, 2025?
A. February 14, 2025 at 18:14:17.000Z is when the Era 3 Epoch begins. Partners will not experience any changes but this is the new date the 0x0 LBFN will correspond to.
Q. What is the significance of January 14th, 2026?
A. January 14, 2026 is when the Iridium satellite vehicles will start transmitting time in the new epoch.
Q. If we are using the Iridium 9602 / 9603 or Iridium Core 9523 and none of the AT commands you mentioned, do we need to do anything?
A. If you are not using the specified AT commands, then it is unlikely any further actions are required.
Q. Based on experience with the last Iridium Time Epoch, most of us have not relied on LBFN, so if there is no reliance on LBFN it is just a matter of direction in terms of firmware and software updates, correct?
A. If there is no reliance on Iridium Time/LBFN, then no further actions are required.
Q. If we want to send and test our field applications and solutions for testing, how can we inform you?
A. If you have concerns that you may possibly be affected by the RE-EPOCH, and are interested in simulated Re-Epoch testing and verification, please reach out to your MetOcean sales account manager for further discussion.