Log Message:
Import gt-itm.

GT-ITM contains code to generate graphs that model the topological
structure of internetworks.  In addition, some sample graphs are
provided.  More detail on most of the methods can be found in the
paper:

"How to Model an Internetwork," Ellen Zegura, Ken Calvert,
and Samrat Bhattacharjee, Proceedings of IEEE Infocom '96.