7 ms·
So then you need to know distance / roundtrip-length within centimeter precision as well (below 29.98 cm for sub-nanosecond precision… to be precise). Since cm
by catoc 4mo ago
So then you need to know distance / roundtrip-length within centimeter precision as well (below 29.98 cm for sub-nanosecond precision… to be precise).
Since cm precision is often not possible, is roundtrip-length an estimated average from prior roundtrips?
- netjiro 4mo agodelay is easy jitter kills
- fsh 4mo agoThe roundtrip time is measured and compensated. Even NTP does this. Knowing the distance is not necessary for time synchronization.
- RossBencina 4mo agogPTP estimates the link delay and the peer clock ratio, see for example this random link I just found for you: https://blog.meinbergglobal.com/2024/03/27/what-is-gptp/ https://blog.meinbergglobal.com/2024/03/27/what-is-gptp/
- Gravityloss 4mo agoHmm one would expect heat expansion to change the length of fiber over tens of kilometers. Does it also affect light speed in the fiber? I think consumer fiber is not buried very deep on average, but maybe for these use cases you use something hefty anyway.
- tempay 4mo agoIt doesn't matter if the length changes provided: * you measure the round trip time often enough * the shift affects light in both directions equally
- numpad0 4mo ago... why would cm precision be often not possible?
- dudinax 4mo agoBecause you're using fibres laid years ago. Often pulse velocity isn't known to better than one part in 1000.