A user interface to a network simulator facilitates the use of application layer parameters and application layer logic. The user interface is configured to allow the user to define the input in a graphic form, or a text/programming form, or a combination of both. Preferably, the user interface provides common graphic forms for both inputting the data to the simulator as well as for displaying the resultant data from the simulator, thereby easing the progression from the analysis of output from one simulation to the generation of new input for a subsequent simulation.