Today's networking community is becoming increasingly skeptical of the significance of research results founded wholly upon experimental results conducted in simulation. Now, with the availability of wide-area distributed testbeds such as PlanetLab, it is feasible to move beyond evaluation by simulation, and to perform wide-area experiments across the Internet as an alternative. However, while use of a distributed testbed affords much greater realism than a network simulation, there is a significant downside, as tight control over one's experiments is relinquished. We argue that providing services for distributed testbeds that capture aspects of the specifiable, repeatable behavior implicit in simulation and emulation will be an integral component of next-generation testbeds. As a case study, we consider the following problem: given a desired end-system topology consisting of a set of pairwise constraints (such as upper and lower bounds on bandwidth and delay), locate a repre...
Jeffrey Considine, John W. Byers, Ketan Meyer-Pate