[e2e] Simulator for wireless network
keshav at uwaterloo.ca
Sun Apr 15 07:18:13 PDT 2007
The discussions on this topic should convince you, I hope, that
before using simulations, their role has to be clearly understood.
For physical systems, such as planes, cars, and sailboats, the
primary operational parameters are the laws of physics, which can be
modeled to as great a degree of accuracy as desired. In other words,
I can overlay a 2D or 3D grid on the underlying system and apply the
laws of physics at each grid point. This is why it's possible to
accurately design physical systems from computer simulations.
For computer systems, where a single line of code can completely
change the behavior of the system, one has to confront the fact that
no simulation is ever going to be accurate. As has been pointed out
already, the issue is not just of radio propagation modeling, which
is hard enough, but the problem is that there are many layers of
software that intervene from the receipt of a radio signal and a user-
perceptible effect. A slight change in any of these can materially
affect the result. For instance, a slight change in the card firmware
can change the way in which packets are handed to the driver, which
can change the timing at which packets are received by an
application, which may result in user-perceptible audio effects for
VOIP over WLAN. It is practically impossible to model these with any
accuracy, and even if you do, a patch to the firmware, driver, OS, or
application will invalidate your results.
This is the reason why 'proof by simulation', for computer systems,
at least, is farcical. Not only are simulators known to be buggy, but
they are also simulating a system that is too loosely coupled to be
So, does this mean that simulation is useless? Not really.
Simulations are useful in helping to form intuitions about the
underlying system. They can also help explore the parameter space
systematically. But, one has to realize that it is a coarse tool, and
necessarily so. As long as you go in with your eyes open, simulations
are a reasonable first step (but only the first step).
More information about the end2end-interest