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A constraint satisfaction approach to testbed embedding services

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 alternate. 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 textbeds. 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 representative subtopology within a wide-area testbed that satisfies those constraints. Previous work on Netbed addresses wide-area embedding problems of this form using an optimization framework, whereas we employ constraint satisfaction. We discuss the relative merits of these approaches, outline the theoretical foundations of a distributed service that provides a synergy between adaptive network measurements and the embedding process, and report on preliminary experimental results conducted on PlanetLab.