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RTD[km] = Alpha" * min_RTT[msmsec] * 100200 [km/secmsec] |
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 give rise to errors of approximately 0.03%.
If we know the RTD and have measured the min_RTT then we can derive Alpha as:
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Alpha" = RTD[km] / (min_RTT[msec] * 200 [km/msec]) |
or since we normally think of the distance between the source and destination (D),
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Alpha = D(km) / (min_RTT[msmsec] * 100 [km/secmsec]) |
Thus assuming no queuing (which is why we use min_RTT) and negligible network device delays: large values of Alpha close to one indicate a very direct path (i.e. a great circle route); smaller values usually indicate a very indirect path.
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For a refractive index of 1.538 then the velocity of light in the fibre = 0.650138 * c = 194,906.469 km/sec or
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Alpha' = RTDD[km] / (min_RTT[ms] * 97.453235 [km/secmsec]) |
or Alpha' is roughly 2.6% > Alpha, and RTDD' = Alpha' + RTT * 100 is roughly 2.6% > RTDD.
Other causes for inaccuracies
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