[CS-FSLUG] wireless network in a disaster?

Marco Tedaldi marco.tedaldi at gmx.ch
Wed May 6 00:33:46 CDT 2009

Ron Thompson wrote

> >
> > Although I've not done it; a router should be able to present it's own
> > page whenever a client computer tries to connect to *any* webpage.  Just
> > think about what happens in many hotels.  You open your browser and you
> > see the hotel's page asking for credentials to use the system.  You
> > could put your page in that place.  Your page could have multiple links
> > because you might have redundant "command centres".
>     This is the information I wanted to know.  Its do-able and may be
> easier 
> and better than I'd thought.

There is almost nothing that has not been done before. It's about messing around with iptables and some java-script in the case of freifunk firmware and it works quite well.

> >
> > When Marco and I mentioned "limited range"; we are talking about not
> > being able to reach the other end of your own block.  You need a *large*
> > number of routers in a mesh network (like one on every block) for many
> > computers to communicate in this manner.  If the mesh is dense enough,
> > there should be alternate routes available for access to the "command
> > centre".
>     What if a high gain external antenna and a higher powered router were 
> used?  I found this product, and while I don't understand all the lingo,
> it 
> looked interesting.
> http://www.ubnt.com/products/ps2.php

This is a quite cool product. One thing to remember is, that the figures about range are only true if here are about similar devices on each end of the link. So a notebook might be able to receive the signal from the router over a vast distance. But will it be able to answer? I'd say: no.

Another point is that there are quite strict regulations about tx-power in most industrial countries. In case of a desaster I think this is not an issue, but if you want to run the network the whole time (which should be done to make sure it works) it could be.

You can extend the range of many routers (also the linksys ones) by using better antennaes. But when mounting a better antenna don't forget to reduce the output power of the sender. More output power on only one side of the link only increases noise levels for all the others without improving the performance.

My own observation is that two routers can connect over distances of up to 600m in free air. In urban areas with houses this goes down to 30m sometimes. It's best to put the routers in water proof cases (I'm using tupperware boxes, the are still useable even after over a year in direct sunlight while other plastic boxes break apart after some months outside) outside. At walls of buildings or on roofs (unused chimneys are really good, since you can get the power cable trough there).


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