I would assume it’s similar to dab etc, and it’s ptp that carried that data on IP. In the broadcast tv world we use ptp, or more traditionally black and burst, or word clocks in audio.

The source is still the same - your grandmaster (ptp) or sync generator (b+b) is fed from a good timing source - often GPS, with one or two inputs, but sometimes local atomic clocks.

I’ve seen issues before with 40ms audio gaps when a GPS antenna has died and the coders can’t cope with frame drift so they incentive a 40ms silence in the audio every 40 minutes or so as the source and destination clocks are different speeds by about 1 part in 60,000.

In DAB the tolerances are far lower, there was a problem about 10 years ago due to a GPs satellite being a few microseconds off

https://www.radioworld.com/trends-1/gps-anomalies-caused-pro...

No, it absolutely is not.

That timing requires a very tight time, frequency and phase reference. It’s derived from local high stability GNSS-disciplined time references.

No. The official report seems to suggest that software in IMS core (the subsystem that controls VOIP signalling in the mobile network) bugged out after the time was shifted back 20 years. That doesn't narrow down the specific failure that stopped calls from going through very much. IMS core is full of timers, but it could also have been a license server issue for all the report said about it.