Request System Time

Query the latest Iridium systemtime received from the network. The response is the form:

-MSSTM: <system_time>

<system_time> can take one of the following forms:

no network service

The ISU has not yet received systemtime from the network.

XXXXXXX

Where XXXXXXXX is the current Iridium system time available from the network. The system time as received through the Iridium Air Interface, is a 32 bit integer count of the number of 90 millisecond intervals that have elapsed since the epoch. The return value is formatted as an ASCII hexadecimal number without leading zeroes.
The counter will rollover approximately every 12 years or be changed to prevent a rollover and as a result should not be used as a time source for user applications.

At time of writing, the Iridium system time epoch is May 11, 2014, at 14:23:55.

Iridium system time source

The system time is available and valid only after the ISU has registered with the network and has received the Iridium system time from the network. Once the time is received, the ISU uses its internal clock to increment the counter. In addition, at least every 8 hours, or on location update or other event that requires re-registration, the ISU will obtain a new system time from the network.

Time localization

None. The system time value is always expressed in GMT time.

Resolution and accuracy

The resolution of the system time is one Iridium frame tick, or 90 ms. Accuracy as measured by the difference between the time reported and the actual time it is sent out the ISU’s serial port should not exceed 4 frame ticks (.36 seconds) and in most cases will be one frame tick (.09 seconds) or less.