Introduction

Network emulation, in which real systems interact with a network simulation, is a common evaluation method in computer networking research. Until now, the simulation in charge of representing the network has been required to be real-time capable, as otherwise a time drift between the simulation and the real network devices may occur and corrupt the result.

Synchronized Network Emulation: The Concept behind SliceTime

The main goal of SliceTime is to enable investigations of arbitary communication software in a fully simulated network. This enables the communication software to be analyzed in a fully isolated environment and a very high degree of controllability.

For this purpose we have developed the concept of Synchronized Network Emulation, which comprises three types of components:

1. One or more network simulations model an arbitrary computer network, for instance a WAN scenario or a mobile network which also may involve node mobility. We do not put any restrictions on the network simulation and its run-time performance; it hence enables non-realtime network simulations.
2. Virtual Machines host a legacy operating system and the communication software to be investigated in the simulated network
3. The central synchronization component aligns the execution of all VMs and the network simulation. The synchronization is based on the provision of logical discrete time slices to all synchronized VMs and simulations. After one time slice, typically in the magnitude of a couple hundreds of microseconds, the components block their execution. The overall execution resumes when all clients have finished the time slice and after a new time slice has been assigned

Our paper SliceTime: A platform for scalable and accurate network emulation (NSDI 2011) provides an elaborate discussion of the used synchronization algorithm.