I have read a few papers recently which relied on network simulations to evaluate some new approach to solving a problem. At first I had a bit of a negative attitude about that practice, simply because a simulation isn't the real thing.
On second thought, I am starting to warm up to the idea. One nice thing about simulations is of course that they tend to be more practical. But I don't believe that is the only reason to use them. I believe that simulations can be used to test extreme conditions which might rarely occur naturally. Simulations can be used to test a much broader set of conditions than those which most commonly occur.
It seems to me that few people actually complain that some new protocol was evaluated using simulations. I'm used to people addressing what they perceive are the weaknesses in some new proposal. But those weaknesses seem to be revealed through simulations just as well as by observing real traffic.
I don't remember ever reading that some proposal evaluated in simulation, turned out not to hold in the wild. In fact, I am wondering now if the simulation environment isn't potentially a better place to validate a proposal.