There's a lot of areas in modeling with OPNET that I capable to but it seems vanish with zero demand. To appreciate it, I believe we should develop our own simulation software but not to leave behind the OPNET itself. Once you master the simulation process, you can model any system.
Just like
Prof. Khalid Al-Begain said to me: "The difference is just an Admission Control" and to
Prof Richard Harris : "You must know what actually you are dealing with and have know-how to explain especially on the modeling and analysis parts."
That's how I learned the area of network modeling and simulation eversince 1997. And thing keeps on going...