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Kyler Laird · Guest

[I posted this yesterday but I think the crosspost to
comp.std.wireless wedged it.]

Yesterday I demonstrated a project about which I'd asked some
questions here (comp.dcom.voice-over-ip). I haven't yet
written up the project but I appreciate the help I got so
here's a brief summary.

http://www.agry.purdue.edu/FieldDay/

I rigged a tractor and wagon with a Linksys WRT54GS running
OpenWRT and a Sipura SPA-2000 with two telephones on the
wagon. I used an inverter for power. (The WRT takes 12V
but the SPA takes 5V@2A. Ideally I'd use a DC-DC converter
to provide this but the inverter was available.)

At the site's office, I installed a panel computer connected
to a switch that's fed by a T1. The computer provided NAT
service to the wireless network and used a magnetic-mount
antenna stuck to the side of the building. (It did *not*
work well from inside. I finally realized that the glass
was not transparent to RF.)

In the main building I installed a similar panel computer
but this one fed another SPA-2000 with two telephones on
its wired network.

On a catwalk above some nearby grain bins, I placed another
WRT. It operated only as a repeater. Power was from 120VAC
although I had batteries ready to use.

All of the machines ran OLSR. Except for the T1 gateway,
they provided routing and DHCP to their wired networks and
advertised these networks through OLSR.

From the main building I could watch the routes as the wagon
moved around on the tour. My advisor and my wife arrived in
the afternoon and we finally tested using VoIP and it worked
surprisingly well. I'd only used it in my house before this
and it's hard to tell how good it is when the other person
is close enough to hear without the telephone.

Unfortunately the router got flakey as I tried to test it
while moving. I reset it once and it seemed to be o.k. but
then it went out again. I finally realized that being
wedged up against the window in a closed cab might be a
problem. It was *hot* to the touch so I pulled the power.

So...I didn't get to test voice continuity across routing
changes but I do have a log of pings to the device which
should give a decent idea of how it might perform.

I'd wanted to have another vehicle rigged in order to
exercise the mesh some more but instead I roamed the
grounds with my laptop and took notes.

Things learned...

Sipura devices are nice because they have a lot of built-in
intelligence. I wrote a script to query for all of the
connected devices and then set the autodialers on each to
contact all of the others directly without registration.
Being able to avoid having a full computer for each remote
is handy.

Consumer electronics shouldn't be expected to work well
when roasted.

OpenWRT is wonderful. I hope to exploit it much more. The
WRT boxes are incredibly handy. For events, attaching some
to deep-cycle 12V batteries would be a quick way to
establish a wireless network.

OLSR is usable out of the box. It allows tweaking though
and some thought should be given to using it in more taxing
situations. It definitely did some things that didn't seem
quite right and was not always solid but I expect that it
can be configured to behave in a more desirable way.

I deployed this network in an hour or two. Decent planning,
multiple people and plenty of zip ties could mean being able
to deploy a network like this in a few minutes. I think
about building a system that could be checked out from the
university for remote events. It could also be useful in
emergency situations.

--kyler

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