Distributed Simulation with MPI in ns-3

While small topology simulations are important for valida- tion and educational purposes, large-scale network simula- tions are a fundamental part of active networking research. Therefore, it is important for a network simulator to pro- vide scalable and efficient solutions to execute these types of scenarios. Using standard sequential simulation techniques, large-scale topologies with substantial network traffic will require lengthy simulation execution times and a consider- able amount of computer memory. Often, these execution times are too long for a networking researcher to run mul- tiple simulations and collect significant data. Parallel and distributed simulation is one method that allows researchers to efficiently simulate these large topologies by distributing a single simulation program over multiple interconnected processors. To enable this scalable simulation methodol- ogy in ns-3, we formally present our distributed simulator, introduced in ns-3.8. This simulator uses the Message Pass- ing Interface (MPI) standard and a conservative lookahead mechanism. Using the distributed simulator, we conducted a performance study using a large-scale point-to-point cam- pus network scenario with a variable number of nodes dis- tributed across several interconnected processors within a computer cluster. We show near-optimal improvements in simulation execution time are possible using the distributed simulator in ns-3.