[dphidt]

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.).

[tgingold]

Only over fiber. Copper SFPs are not deterministic enough to precisely synchronize networks.

[willis936]

And even better: they suggest the use of a single medium for both transmission and receiving (1000BASE-BX10) to minimize asymmetry.

https://ohwr.org/project/white-rabbit/wikis/SFP