Speed and Accuracy of Network Simulation in the SimGrid Framework

The experimental study of distributed systems and algorithms for large-scale internet platforms typically requires simulation of compute and network resources. This paper focuses on network simulation issues. While many packet-level network simulators are available and enable high-accuracy simulation, they can lead to prohibitively long simulation times. Consequently, a number of simulation frameworks have been developed that simulate networks at higher levels, thus enabling fast simulation but losing accuracy. One such framework, SimGrid, uses a flow-level approach that approximates the behavior of TCP networks, including TCP's bandwidth sharing properties. In this paper we perform a quantitative evaluation of SimGrid and compare it to popular packet-level simulators. We identify the regimes in which SimGrid's accuracy is comparable to that of these packet-level simulators, and the regimes in which SimGrid's accuracy may not be acceptable. We then describe an integration of the GTNetS packet-level simulator and SimGrid, which allows SimGrid users to easily opt either for fast but potentially inaccurate flow-level simulation or for accurate but potentially prohibitively slow packet-level simulation.