Memory consumption is a critical problem for large-scale network simulations. Particularly, the large memory footprint needed for maintaining routing tables can severely obturate scalability. We present an approach of composing large-scale network models using sharable model fragments to achieve significant reduction in the amount of memory required for storing forwarding tables in simulation. Our approach, called spherical routing, conducts static routing within spheres according to user-defined policies. Our routing scheme pre-calculates the forwarding table for each routing sphere, and allows spheres with identical sub-structures to share forwarding tables. Through extensive experiments we demonstrate that our approach can achieve several orders of magnitude in memory reduction for large-scale network models.

We present a software infrastructure that embeds physical hosts in a simulated network. Aiming to create a large-scale real-time virtual network testbed, our real-time interactive simulation approach combines the advantages of both simulation and emulation, by maintaining flexibility of the simulation models and increasing fidelity as real systems are included in the simulation. In our approach, real-world distributed applications and network services can run together with the real-time simulator; real packets are injected into the simulation and subject to the simulated network conditions computed as a result of both real and virtual traffic competing for network resources. A prototype of the proposed emulation infrastructure has been implemented based on virtual private network (VPN). One distinct advantage of our approach is that it does not require special hardware. Furthermore, it is flexible, secure, and scalable-attributes inherited directly from the VPN implementation. We conducted a set of preliminary experiments to assess the performance limitations of our emulation infrastructure. We also present an interesting case study to demonstrate the capability of our approach.