From Simulation to Emulation: A System Design for Real-Time Replay of Simulated Network Path Characteristics

Emulation environments are widely used to evaluate the performance or behavior of real protocols, applications, or hardware under different network characteristics. However, such environments often treat these characteristics as static – an assumption untenable in dynamic networks like satellite constellations. Leveraging the benefits of discrete event simulators, this paper proposes a system design for replaying dynamic characteristics of end-to-end network paths in emulation environments. In contrast to other emulation methodologies, our approach introduces a split between the simulation and emulation to combine the advantages of both.ns-3 simulates the network topology, background traffic, and different network functions. In the simulated topology, additional Trace Packets are used to record the end-to-end path through the network and its characteristics; apart from that, the simulation remains unchanged. The path characteristics are exported to Trace Files and subsequently replayed in real time in an emulation environment, where the evaluation of higher-layer protocols, applications, or hardware takes place.In this paper, we describe the workflow of our approach with a proof-of-concept using a simple network topology. The resulting emulation environment is compared against a full simulation and a real testbed, demonstrating its ability to reproduce the behavior of a single TCP flow. Despite some limitations, such as the absence of feedback from the emulation environment back to the simulator, the approach offers potential for evaluating real systems with characteristics from different types of simulated networks.