I have a use case where I want to get somewhere between 1-30 ms accuracy. While NTP might work, it sounds like worst case it can give ~100 ms error, which is not ideal. So I am looking at PTP (precision time control) as a better option. However PTP seems more complex and has more hardware requirements.
Is PTP suitable when the two machines I want to synchronize are on an arbitrary public network (can be on LAN, cellular network, etc.) If so, do I need special hardware on these devices?
For the machine that is the master, what are the minimum hardware requirements for this? Is there any good 3rd party providers of (cloud) servers for this purpose?