Advances in Network Simulation

ion Abstraction is a common approach to improving simulator performance. All simulators adopt some level of abstraction when choosing what to simulate. FlowSim was the first network simulator to make this trade-off explicit.7 Ns supports several levels of abstraction. Numerous simulation interfaces are possible, including programming in a high-level scripting language, a more traditional systems language, and sometimes both. Some systems, such as x-Sim8 and Maisie,4 focus on allowing the same code to run in simulation and on a live network. Most systems have augmented programming with a GUI shell of some kind. Ns provides a split-level programming model in which packet processing is done in a systems language while simulation setup is done in a scripting language. Nam,9 currently being enhanced to support simple scenario editing, provides visualization output. Network emulators Early work in network emulation included the use of “flakeways” (gateways that could alter or drop packets) for early TCP/IP tests. More recent work includes special-purpose stand-alone network emulators supporting packet delays and drops.10 Developers usually implement these systems as kernel drop-in modules that intercept the IP layer packet-forwarding path, and thus look like routers to end stations. Their capabilities are generally limited to simple packet manipulation and do not provide for interference from simulated cross traffic. Moreover, these systems do not include the general simulation capability that ns provides. References 1. S. Keshav, REAL: A Network Simulator, tech. report 88/472, Univ. California,