It's quite interesting - this isn't ethernet as we know it. Instead of each NIC using its own free-running clock, all the physical layers are sync'ed to each other at layer 1. (note that gigabit ethernet, which is what it uses, sends data at all times - when idle it sends the idle symbol)
Haven't looked into this in depth but sub-nanosecond sync for systems up to 10km apart is interesting since 10km is about 33 light microseconds. There is some trickery going on.
It's totally possible to achieve synchronization better than light transmission time. For the purposes of synchronization, the speed of light delay, and any other delay are indistinguishable, and need not be distinguished.
Two-way time transfer measures the round-trip propagation time. As a result, it's not directly relevant to the accuracy.
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?
The roundtrip time is measured and compensated. Even NTP does this. Knowing the distance is not necessary for time synchronization.
delay is easy
jitter kills
yes, it needs custom built hardware to work.
The gravity well time dilation is about 3.5 nanoseconds per meter per year near the surface of the earth. (time changes rate with altitude in a gravity well)
Sub-nanosecond synchronization is getting into the relativity is measurable realm.
That means you get a free clock cycle every 2-3 hours on top of a mountain compared to sea level!
Datacenters in spaaaace!
Yes, it uses phased locked loops and measures phase difference between the master clock and the local clock.
Haven't dug in on the technicals, but this is coming out of CERN, it looks like - and in that light, the links to "We're hiring" on that page almost feel like a flex...
Not on GitHub?
Its on gitlab but even there I failed to find sources, documentation/presentations are there though
If you run "make" in the papers/IBIC2013 directory you'll get this paper: https://cds.cern.ch/record/1743073/files/thbl2.pdf
It's quite interesting - this isn't ethernet as we know it. Instead of each NIC using its own free-running clock, all the physical layers are sync'ed to each other at layer 1. (note that gigabit ethernet, which is what it uses, sends data at all times - when idle it sends the idle symbol)
Haven't looked into this in depth but sub-nanosecond sync for systems up to 10km apart is interesting since 10km is about 33 light microseconds. There is some trickery going on.
It's totally possible to achieve synchronization better than light transmission time. For the purposes of synchronization, the speed of light delay, and any other delay are indistinguishable, and need not be distinguished.
Two-way time transfer measures the round-trip propagation time. As a result, it's not directly relevant to the accuracy.
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?
The roundtrip time is measured and compensated. Even NTP does this. Knowing the distance is not necessary for time synchronization.
delay is easy
jitter kills
yes, it needs custom built hardware to work.
The gravity well time dilation is about 3.5 nanoseconds per meter per year near the surface of the earth. (time changes rate with altitude in a gravity well)
Sub-nanosecond synchronization is getting into the relativity is measurable realm.
That means you get a free clock cycle every 2-3 hours on top of a mountain compared to sea level!
Datacenters in spaaaace!
Yes, it uses phased locked loops and measures phase difference between the master clock and the local clock.
Similar to the much smaller scale Wi-Wi setup that was on HN a few days ago (which came after WR): https://news.ycombinator.com/item?id=48209055
Some may find https://gitlab.com/ohwr/project/white-rabbit/-/wikis/home an easier starting point. Particularly the "Synchronization" page.
In short, it's about giving PTP and SyncE some extra smarts.
Probably even better to start at the collaboration website https://www.white-rabbit.tech/wr-technology/
Haven't dug in on the technicals, but this is coming out of CERN, it looks like - and in that light, the links to "We're hiring" on that page almost feel like a flex...
Not on GitHub?
Its on gitlab but even there I failed to find sources, documentation/presentations are there though
https://www.white-rabbit.tech/wr-technology/
Note that this is also for a large part a hardware-based technology