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Free Mesh Networking with Metrix Pebble

by Rob Flickenger, author of Wireless Hacks, Second Edition

Folks from the SeattleWireless group and I had an interesting time at MindCamp at the end of last year. I've already written a bit about the interesting logistics of the situation, including the initial fun (but aborted) attempt to run OLSR on everybody's laptop, but I haven't written much about what eventually made the whole thing work in the end.

Metrix Pebble is a variant of the popular Pebble Linux distribution supported by my wireless company, Metrix Communication. Although it is built on the framework laid down in the original Pebble, Metrix Pebble is very different from its aging progenitor in many important respects. In addition to Pebble's method of creating a simple read-only root filesystem, Metrix Pebble includes:

Metrix Pebble fits all of this in just under 64MB of flash memory. Combined with our Mark II dual-radio kits, that gave us a platform that could quickly adapt to just about any needed network topology. All told, we used seven nodes (a mix of Mark IIs and other Soekris-based APs) to build the network. This included:

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(photo by Ken Caruso)

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By using OLSR to connect the access points together, we were able to quickly roll out as many APs as needed to effectively cover the huge conference area. There was simply no wired infrastructure present at the event, and running CAT5 throughout the space was impractical. Using OLSR meant that we could simply plug in a node wherever power was present, and the network would "figure itself out." People connected to the network using the traditional AP services that were provided on the second radio, and their traffic was automatically forwarded over the mesh all the way back to the uplink.

We also used two Linksys WRT54Gs running the Freifunk firmware. These little guys only had one radio, but they served to fill in as repeaters where there were gaps in coverage. People couldn't connect to these directly (unless they were running OLSR) but they helped to forward traffic between the APs.

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This network design effectively allows for an arbitrarily large network to grow outward from the core as needed, simply by adding more APs. In Berlin, the Freifunk group has built a mesh of over 150 nodes on all sorts of hardware (including Linksys boxes, embedded computers, laptops, palmtops, and even refurbished PCs). OLSR will run on just about anything, including Windows, Mac OS X, Linux, BSD, and other platforms.

Without open source software (including Linux, open wireless drivers, network monitoring tools, and amazing new code like OLSR), the cost of such a self-forming, self-healing, next-to-zero-configuration network would be astronomical. By running it on an open hardware platform like the Mark II, you can build an arbitrarily large network without fear of vendor lock-in or mandatory downgrading (as just happened with the notorious Linksys WRT54G nightmare).

While it's likely that no amount of slick new technology could make a network of 150 power users, podcasters, and video bloggers all swamping the same 960Kbps DSL line seem zippy, Metrix Pebble made a quick and stable backbone network with minimal effort.

You can download Metrix Pebble here. It will run on just about any x86 platform with at least 64MB of storage (flash or hard drive) and 32MB of RAM. The distribution works best on embedded computers like the Soekris, and uses a serial port for the console. Of course, we ship it as the standard OS on all of our kits. Feedback and patches are always welcome!

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Once you've got it installed, you can enable OLSR through the web interface. This lets you build a functioning mesh network, complete with a graphical real-time route visualization and network-wide DNS service, in just minutes.

With free mesh software that runs on just about anything, one has to wonder just how far mesh networks will take us. How big of a mesh can you build?

Rob Flickenger is a long time supporter of FreeNetworks and DIY networking. Rob is the author of three O'Reilly books: Building Wireless Community Networks, Linux Server Hacks, and Wireless Hacks.

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