ns-2 distributed clients emulation: accuracy and scalability

ns-2 is a well known network simulator, recently extended with improvements to its emulation facility. Real-time constraints and the boundary between real-world and simulated entities impose scalability and accuracy limitations, and distort the simulated network as perceived by the involved real-world applications. This paper presents results from a performance evaluation of the ns-2 emulation facility. Conducting emulation experiments of differing magnitudes, and under varying emulation environment set-ups, we unveil central types of scalability limitations and obtainable accuracy. We find throughput limits using high and low end computers, and a significant throughput decrease when increasing the number of involved real-world applications. We furthermore show how end-to-end delay increases both with traffic load and an increasing number of involved real-world applications. Moreover, during these conditions, we find that the system treats these applications increasingly unfair by distributing total throughput unevenly between them, and by imposing different amounts of end-to-end delay.