The success of advancing technologies critical to designing future-generation high-performance global networks and reliable distributed applications hinges on the available tools that can effectively prototype test, and analyze new ideas. The project will enable advances in the area of high-performance modeling and simulation of large-scale networks. The research includes an investigation of the fundamental technologies that enable real-time large-scale network simulationsand the development of a real-time immersive network simulation environment. Real-time network simulation combines the advantages of both simulation and emulation by running simulation models that interact with the physical world. Immersive large-scale network simulation requires that the simulation not only capture important characteristics of the target global network, but also support seamless interactions with distributed applications in real time. The project is divided into three research thrusts: imprecise simulation, GPU co-simulation, and the development of the immersive network simulation environment. Imprecise simulation, extended from the imprecise computation technique originally designed for real-time systems, aims to achieve real-time performance of large-scale network simulations, by allowing the simulation to choose among models with different modeling representations and with variable computing requirements during run-time. GPU co-simulation exploits the computing resource of graphics processors, which are almost omnipresent on todays desktop computers and become more powerful than CPUs; certain numerical computations, such as the network background traffic calculation, can be offloaded to the graphics hardware, so that the CPUs can concentrate on more critical tasks for real-time simulation. An immersive network simulation environment will be developed based on the imprecise simulation and GPU co-simulation techniques, and will also include models of network protocols of alternative designs of the layered network structures.