Assuming consistent spacial interference, e.g.

  • The time for packet Z to get from point A to point B will always be constant.
  • The time for packet Z to get from point B to point A will always be constant.

Is there a way to know the time it takes for packet Z to get from A to B?

Obviously A to B to A could be determined and halved, but that would assume that the time it takes to get from A to B is the same as the time it takes to get from B to A.

Even with 3 points, it doesn't seem like there is a way to isolate the vector from A to B.

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  • 3
    Is this about NTP? – Zac67 Mar 31 '19 at 8:36

Practically, no.

If there's no common reference point with known latencies you can't measure path latency in an exact way.

However, in pretty much all practical situations simply halving the round-trip time (RTT) is "good enough" (this is what NTP does). Even if forward latency (Lf) is twice that of backward latency (Lb), (Lf+Lb)/2 would only cause an error of 25% or 50% respectively. Provided your RTT is within a reasonable range that error is usually acceptable (e.g. 20 ms RTT -> 10 ms error).

If you require better precision you need to provide a lower RTT path or determine a good value for the latency externally.

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