The real-time scheduler (Scheduler/RealTime../ns-2/scheduler.cc) attempts to synchronize the execution of events with real-time. It is currently implemented as a subclass of the list scheduler. The real-time capability in ns is still under development, but is used to introduce an ns simulated network into a real-world topology to experiment with easily-configured network topologies, cross-traffic, etc. This only works for relatively slow network traffic data rates, as the simulator must be able to keep pace with the real-world packet arrival rate, and this synchronization is not presently enforced.