To start, note that the notion of time in a simulation is not directly related to the actual time that it takes to run a simulation (as measured by a wall-clock or the computer's own clock), but simply a variable maintained by the simulation program. This variable is more precisely referred to as simulation time to clearly distinguish it from real (wall-clock) time. NetSim is a discrete event simulator (DES), and in any DES, the progression of the model over simulation time is decomposed into individual events where change can take place. The flow is time is only between events and is not continuous. Therefore, simulation time is not allowed to progress during an event, but only between events. In fact, the simulation time is always equal to the time at which the current event occurs. Therefore, simulation time can be viewed as a variable that "jumps" to track the time specified for each new event.

Users have the question "will NetSim run for 10 seconds if Simulation time is set to 10 sec?" and the answer is that the simulation may take more than 10 seconds (Wall clock) if the network scenario is very large and heavy traffic load. It may take a much shorter time (wall clock) for small networks with low traffic loads.

Please note that when running in "Emulation mode" simulation time and wall clock will be exactly equal since it involves the transfer of real packets.

In NetSim, the current simulation time can be got using -pstruEventDetails->dEventTime