The speed of light in fibre is roughly 0.66*c where c is the velocity of light in vacuum. The speed of light in a vacuum is 299,792,.458km/sec exactly or roughly 300km/sec (to
about 0.06% accuracy). Thus:
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RTD[km] = Alpha * min_RTT[ms] * 100 [km/sec] |
where RTD = Round Trip Distance. If we know the coordinates (latitude and longitude) of the source (monitoring host) and target (remote node) then we can obtain the RTD using the Haversine formula to calculate the great circle distance and double this to get the RTD. Note that the Haversine formula assumes the earth is a spheroid whereas it is an ellipsoid (6356.78 km at pole and 6378.14 km at equator) and this can rise to errors of a few tens of kilometersapproximately 0.03%.
If we know the RTD and have measured the min_RTT then we can derive Alpha as:
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