Subject: OPNET simulations of Mobile Ad-hoc Networks

From: John Zavgren <[email-masked]>
Date: Thu, 03 Dec 1998 16:27:11 -0500

All:

 I couldn't resist forwarding this note that I sent to our friends at MIL3
when they asked me what we do with OPNET at BBN. When I get caught up a bit
more on my work, I plan to publish some results from our MANET work....
maybe early next year, after a big demo that we have to do for the
government in March.

-------

We are using OPNET to model a mobile ad-hoc packet radio network that we
are designing for the NTDR (Near Term Digital Radio) program. We have
developed a way to allow this OPNET model use almost all of the software
that we have written for the actual Hardware/OS (PC/Venix) platform that
our router uses. We call this "code sharing". Code Sharing eliminates the
error-prone process of transliterating software between the two platforms:
OPNET model, and actual hardware. It also guarantees that our model is
always synchronized with the router code. The model has proven to be an
effective way for us to debug the actual code that we run in our router, as
well as for verifying the correctness and performance of its protocols.

We do not use any of the OPNET utilities for statistics gathering, mobility
modeling, or animation. 

Instead, we have tools that create a "mobility script" that defines the
nodes' positions and pathloss at discrete time steps. This mobility script
can be used  by the OPNET model as well as a facility that we call the
"50-node" testbed. The testbed consists of the same PC hardware that the
real routers use. However, their radio interface has been replaced with an
Ethernet card and a driver that appears to be the actual radio driver to
the OS, but in fact is an Ethernet driver that can be programmed to define
radio neighborhoods.

Each process in each node collects time stamped statistics that can be
harvested after an experiment is completed. These statistics are merged and
sorted by time and then displayed as a function of time by a Java Applet
that can be run from any WWW browser. VCR-style control buttons are used to
fast forward, backup, stop, etc. The same statistics collection and display
procedure applies to the simulation, the 50-node testbed, and real, live
field trials. We call this technique viztools.

The end result is an animated playback of the network's topological
evolution. One can trace the protocol message flowing between routers, see
links going up and down, nodes moving, etc. Viztools has just been
developed recently, but it is proving to be extremely valuable for
debugging protocols, and explaining them to non experts.

------------------------------------

Dr. John Zavgren
617-873-2280
978-635-0771 (home)