ns-2 Distributed Clients Emulation: Accuracy and Scalability

ns-2 is a well known network simulator, recently extended with improvements to its emulation fa- cility. Real-time constraints and the boundary be- tween real-world and simulated entities impose scal- ability and accuracy limitations, and distort the sim- ulated network as perceived by the involved real- world applications. This paper presents results from a performance evaluation of the ns-2 emulation fa- cility. Conducting emulation experiments of differ- ing magnitudes, and under varying emulation envi- ronment set-ups, we unveil central types of scala- bility limitations and obtainable accuracy. We find throughput limits using high and low end comput- ers, and a significant throughput decrease when in- creasing the number of involved real-world applica- tions. We furthermore show how end-to-end delay increases both with traffic load and an increasing number of involved real-world applications. More- over, during these conditions, we find that the sys- tem treats these applications increasingly unfair by distributing total throughput unevenly between them, and by imposing different amounts of end-to-end de- lay.