²The  6.2.1 experiment differed from this one in that the former generated traffic on PlanetLab from two simultaneous BT’s, while this experiment ran only one BT at a time. This unfortunate methodological difference could explain much of the difference between ACIM and the simple cloud model, but only if the simultaneous BT’s in  6.2.1 significantly affected each other. That seemed unlikely due to the high degree of stat muxing we expect on I2 (and probably GÉANT) paths, both apriori and from the results in Sec. 4.3. However, that assumption needs study.