Experiences in building a scalable distributed network emulation system

Network emulation systems are widely used to explore the behavior of network protocols and to test and evaluate protocol implementations and applications. The major problem of a network emulation system is its scalability in terms of emulation capacity and emulation capability of specific network parameters such as maximum emulated bandwidth and emulated packet delay of the system. In particular, an emulator with a large number of workstations is generally too costly for researchers to afford. We present our experience in building a scalable distributed network emulation system named "EMPOWER". EMPOWER provides the unique feature of precisely emulating multiple nodes with a single workstation, making it possible to support large network emulation with a limited number of commodity computers. We describe some critical design issues such as the system resource competition within an emulator node and its impact on the emulation of network throughput and packet delay. We present our methods to determine the maximum number of virtual routers an emulator node can generate and some techniques to improve maximum throughput and packet delay accuracy of an emulator node. We believe such experiences are valuable for the study, design and implementation, performance tuning of a variety of systems such as network emulators and high performance host-based routers.