> It seems to me, that for a given host pair, there is some RTT
> theorectical minimum, which represents a completely empty network, and
> perhaps one can observe something close to it in the samples, and maybe
> a periodic ICMP ping would have been in order, particularly when the
> host pair was not observed to have any traffic flowing.  
> 
> The question of queuing delay then can be answered by how much higher
> the RTT is over some minimum. 

The solid lines in the plots in figure 1 are the minimums.  The lines on
figure 2 represent the difference between the samples and the
corresponding minimum.

allman