This means that you could reduce your packet size by stripping off the most signficant bits of the timestamp, and then extrapolating them on the remote side. This must be done immediately, though, because a slow packet could actually spends 30 seconds on the wire or in a queue waiting for acknowledgement. Once the clock on every machine is accurate within about 6 milliseconds of each other, it becomes easy to compare timestamps and perform detection or prediction in real time. B. There are problems, of course. One fix is to widen the tolerance from 3 to 7 milliseconds over time, so that clocks are well synchronized at start and touched later only if they drift heavily.
Assymmetric links are another problem.
This and other network time issues are still under active research.