We looked at plots of RTT vs Distance for pairs of Landmarks within 25ms and 1000km radii for Europe and N. America. Typically a formula of the form distance = alpha * RTT is used to derive the distance from the measured RTT. Typical values of alpha are 40 km/ms. However the value of alpha can vary dramatically based on the route the cable takes versus teh great circle distance. Fior example from the US to Japan the route is pretty direct leading to high values of alpha. However from Europe to Japan the route today goes West around the bay of Biscay, through the Mediterranean and the Red Sea, South of India, then passes via Singapore and North up the East coast of Asia to Japan. This result in smaller values of alpha. There are plans afoot to provide more direct routes via the Arctic Ocean.
When we measured the RTTs between landmarks of known location and derived the values of alpha, Europe seemed better behaved. We looked at the network topology for the major Academic and Research (A&R) networks in N. America, i.e. Internet2, ESnet and Canarie. They are shown below.
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