RE: NS versus OPNET Modeler

[James Scott <jscott@GEYSERNETWORKS.COM>]

hi heather,

> I am negotiating a purchase of the OPNET Modeler software 
> and a friend reccommended NS.  Any old or current OPNET 
> users? Who could give me feedback?

i have used both opnet and ns.  the question of which is
the best tool would depend on the problem you're trying
to solve and the skills of the person who is doing the
work.

the process model OpNET provides is a powerful tool,
providing sort of a 4GL for building simulation models
of specific nodal processes.  additionally, the opnet i/o
is top notch.  and, if your work involves modelling ATM
nodes, opnet is clearly the way to go.  also, mil3 has 
recently provided a VHDL i/f for OpNET, which would be 
quite handy for cosimulation applications.

i've found NS to be superior in the area of source traffic
generation.  while OpNET does provide a flexible mechanism 
for generating various types of source traffic, NS has a 
larger number of source traffic generators, in addition to 
contributed models for higher layer protocols (HTTP, etc).
however, since OpNET provides an open API for source traffic
generation, there is nothing prohibiting you from using NS
generators to stimulate an OpNET model, depending on the
level of sophistication possessed by the developer doing
the work.  in the past, i've written pareto models to
stimulate OpNET process models.  had i known of NS at the
time, i could have saved some time by leveraging their
pareto model <shrug>.

in the area of routing, NS provides static and session-based 
routing using dijkstra, as well as dynamic routing using a 
distributed bellman-ford.  by comparison, the OpNET tools 
provides just static routing.

so, in summary, if you are modelling an IP network
and interesting in things like queueing behavior and
the interaction of higher-layer protocols on network
performance, go with NS.  you can use NS to model
specific behaviors of proprietary h/w, but its perhaps
not for the faint-of-heart.

there are probably other areas where NS would be preferred,
such as characterization of IP multicast and/or wireless IP,
but i haven't had experience with these areas so will reserve
comment.  the above is just one man's opinion.  both tools
are QUITE useful, depending on the task at hand (as well as
the size of your budget, and skills of your development crew).

good luck!

cheers,

james