White Rabbit Project (2020) (opens in new tab)

(ohwr.org)

102 pointskimburgess3y ago20 comments

20 comments

12 comments · 6 top-level

orourke3y ago· 6 in thread

“sub-nanosecond synchronization”

“typical distances of 10 km between nodes”

Light travels 30cm in a nanosecond. How do they achieve sub-nanosecond accuracy over long distances?

Xarodon3y ago

Because they know the speed of light and the distance between nodes so they can account for the propagation delays of light due to distance.

They're not talking of sub millisecond latency in communications.

tgingold3y ago

No, we don't know the distance between nodes (although we could deduce it). But using timestamps, we can know the round-trip time.

See https://www.ohwr.org/project/white-rabbit/uploads/2b9d42b664... (page 9 and later for the principle).

If you want all the details, see https://ohwr.org/project/white-rabbit/uploads/6a357829064b9e...

2 more replies

dphidt3y ago

Even better, the actual in situ delays are measured and compensated for, and it works independent of the physical connection (and through fiber/copper, switch layers, etc.).

2 more replies

bestouff3y ago

Indeed. It's exactly the same (albeit on a different scale) as NTP synchronization, where you can frequently (ha!) reach a few ms accuracy over a hundred ms latency network.

faisalhackshah3y ago

It seems that you're implying that nodes cannot be synchronized within the time it takes for light to travel between the nodes.

Images both nodes having their own atomic clocks. Now allow them to timestamp transmitted and received messages with very high precision.

tgingold3y ago

In a white-rabbit network you don't need atomic clocks on each node. One atomic clock is enough, its frequency is distributed over the network.

willis9363y ago

Important and relevant piece of information: IEEE 1588-2019 HA (default profile) is interoperable with White Rabbit. Unfortunately I haven't seen any commercial support for this yet.

twic3y ago

Not mentioned in their list of users, but at least one stock exchange uses it internally, and exposes it to participants:

https://www.eurex.com/ex-en/support/initiatives/archive/high...

mitchbob3y ago

https://web.archive.org/web/20230623115746/https://ohwr.org/...

tracker13y ago

Not to be confused with: https://en.wikipedia.org/wiki/White_Rabbit_Project_(TV_serie...

throwoutway3y ago

Now getting a Gitlab 500 "Whoops, something went wrong on our end" error page on even the root domain

j / k navigate · click thread line to collapse

20 comments

12 comments · 6 top-level

orourke3y ago· 6 in thread

“sub-nanosecond synchronization”

“typical distances of 10 km between nodes”

Light travels 30cm in a nanosecond. How do they achieve sub-nanosecond accuracy over long distances?

Xarodon3y ago

Because they know the speed of light and the distance between nodes so they can account for the propagation delays of light due to distance.

They're not talking of sub millisecond latency in communications.

tgingold3y ago

No, we don't know the distance between nodes (although we could deduce it). But using timestamps, we can know the round-trip time.

See https://www.ohwr.org/project/white-rabbit/uploads/2b9d42b664... (page 9 and later for the principle).

If you want all the details, see https://ohwr.org/project/white-rabbit/uploads/6a357829064b9e...

2 more replies

dphidt3y ago

Even better, the actual in situ delays are measured and compensated for, and it works independent of the physical connection (and through fiber/copper, switch layers, etc.).

2 more replies

bestouff3y ago

Indeed. It's exactly the same (albeit on a different scale) as NTP synchronization, where you can frequently (ha!) reach a few ms accuracy over a hundred ms latency network.

faisalhackshah3y ago

It seems that you're implying that nodes cannot be synchronized within the time it takes for light to travel between the nodes.

Images both nodes having their own atomic clocks. Now allow them to timestamp transmitted and received messages with very high precision.

tgingold3y ago

In a white-rabbit network you don't need atomic clocks on each node. One atomic clock is enough, its frequency is distributed over the network.

willis9363y ago

Important and relevant piece of information: IEEE 1588-2019 HA (default profile) is interoperable with White Rabbit. Unfortunately I haven't seen any commercial support for this yet.

twic3y ago

Not mentioned in their list of users, but at least one stock exchange uses it internally, and exposes it to participants:

https://www.eurex.com/ex-en/support/initiatives/archive/high...

mitchbob3y ago

https://web.archive.org/web/20230623115746/https://ohwr.org/...

tracker13y ago

Not to be confused with: https://en.wikipedia.org/wiki/White_Rabbit_Project_(TV_serie...

throwoutway3y ago

Now getting a Gitlab 500 "Whoops, something went wrong on our end" error page on even the root domain

j / k navigate · click thread line to collapse