Optical network simulator

Does anyone happen to know of an optical network simulator?

I'm trying to examine the behaviour of a 3-8 node sonet ADM ring using 2-fiber UPSR when one interface has intermittent severely errored seconds.

Free or costly? There is Opnet on the costly side, unless the old free academic version will do this.

Free is preferred

Free is always preferred... :wink:

Free is too costly. Unless you have zero-cost labor...