Subject: Simulating Wireless Nets

From: Chip Elliott <[email-masked]>
Date: Fri, 25 Jul 1997 08:20:19 -0400

Howdy,

Bevan, thanks very much for that bibliography. You guys
seem to be doing good work with your ad hoc routing.

We at BBN are doing a fair amount of simulation and modeling
for the NTDR ad hoc network. Here are the things that
we have found useful thus far:

a) Pathloss model for a given terrain
   (eg rolling hills with foliage, desert mountains, etc;
    we try to use real places rather than dreamed up models)

b) Initial laydown of nodes on terrain

c) Mobility scenario, which includes:
   1. trajectories of nodes
   2. nodes powering on/off over time
   3. various types of jamming

d) Traffic scenario

e) Exact modeling of the protocols and algorithms
   (in our case, same code in OPNET model, simulator, and radios)

In my opinion, models must have reasonable fidelity in
the following areas or they will give very misleading results:

   - Pathloss  (free space gives VERY unrealistic results)
   - Traffic   (most traffic is highly correlated, rather than
                uniform distribution, and this affects interference)
   - Trajectories  (the usual 'brownian' gives very optimistic results,
                    as no one really goes anywhere)

Naturally the desire for realism conflicts horribly
with the desire to run simulations of large (400 node) nets.

We have a reasonably elaborate system of "scenarios" which
feed into both our OPNET model and our 50-node testbed, so
we can run experiments repeatedly and measure the results
as we tune things. A scenario consists of a selection of
values for items a-d above.

Another interesting set of questions is... what do you
want to MEASURE...?

Hope that a reasonable group will show up at the IETF
as it would be very interesting to talk.

Cheers,

- Chip Elliott