Experiences parallelizing a commercial network simulator

Most current approaches of parallel simulation focus on building new parallel simulation engines that require the development of new models and software. An alternate, emerging approach is to extend sequential simulators to execute on parallel computers. We describe a methodology for realizing parallel simulations in this manner. This work is specifically concerned with parallelization of commercial simulators where source code for some or all of the sequential simulator is not available. We describe our experiences in applying this methodology to realize a parallel version of the OPNET simulator for modeling computer networks. We show significant speedup can be readily obtained for some OPNET models if proper partitioning strategies are applied and the simulation attributes are tuned appropriately. However, we observe that substantial modifications to other OPNET models are needed to achieve efficient parallel execution because of their extensive use of global variables and "zero lookahead events"