TimeSync: enabling scalable, high-fidelity hybrid network emulation

In this paper, we discuss a time synchronization approach to the time divergence problem in hybrid network emulation. Such emulation comprises primarily a discrete-event simulated network and virtual machines that send and receive traffic through the simulated network. For slower than real-time network simulations, the rate of time advance on virtual machines (real time) is faster than that of the discrete-event time. Consequently, packet transmission latency and other metrics in such hybrid network emulations will be distorted. As a result, e.g., TCP sessions between virtual machines may unduly time out. To address this problem, we have developed TimeSync, which tracks discrete-event simulation time to control time advance on virtual machines for slower than real time simulations so that time perception in the hybrid network emulation system is synchronized. We describe how TimeSync works and present our experimental evaluation and analysis.