As you know, there existe a plenty of Network Simulators for research (e.g. NS-2, NS-3, Opnet, omnet++, ... name them) . I would like to open a small discussion about the real (or the major) reasons behind the choice of a particular network simulator among many others. Is it the simulator performance? the availability of a particular simulation model? the programming language? the researcher previous experience? .... or just the fact that you like that simulator, and then you try to find a justification for that choice later!