[mgaunard]

In the ultra-low-latency space people just use PPS, either one pulse per second or 10Mhz.

WhiteRabbit and the like allow you to transmit such a signal with great accuracy.

There are timestamping layer 1 switches and NICs that support taking it as input.

[luma]

Same boat, major exchange backend and we just use 10MHz over 50ohm coax straight into the NIC which does the timestamping.

[willis936]

It's been folded into IEEE 1588-2019, but no one supports it.