NS-3 PyViz is a live simulation visualizer, meaning that it uses no
trace files. It can be most useful for debugging purposes, i.e. to
figure out if mobility models are what you expect, where packets are
being dropped, etc. There's also a builtin interactive python console
that can be used to debug the state of the running objects. Although
it is mostly written in Python, it works both with Python and pure C++
simulations.

For more information, see http://www.nsnam.org/wiki/PyViz
