Maybe they don’t. Not every GPS device have the ability to output PPS signals.
You wouldn’t need sub-second accuracy for anything in the car besides navigation. More to the point, if they are querying NTP via cellular, why are they not simply querying the cell system for the time?!?!?!
The standard command to get (and set) time for mobile devices is:
You don’t need a subscription for that command (or a bunch of others either).
Sometimes people just like to do things the complicated way for no good reason. sigh
Mobile carriers can disable the option to provide time for its clients, at the cellular level. In Taiwan, Taiwan Mobile does practice this; I believe there are other carriers in the world also disabled providing time. So we know the developers from Cisco:
- Want to cut cost by not including PPS and other GPS timing measure in their product
- And they are fully aware that cellular time is not provided everywhere
- So they just decide to query ntppool through the car owner’s data plan, without building their own time service
AFAIK, most GPS device can provide time via NMEA-0183 command. Maybe just because GPS signal is not so stable. (i.e. drive into a tunnel, parking in a building)