Free Mesh Networking with Metrix Pebble

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:

• A web-based configuration GUI, supporting SSL and PHP.
• olsrd from olsr.org, complete with real-time dot_draw route visualization and name service propagation.
• EVDO/1xRTT PCMCIA modem support.
• Automatic generation of network flows, wireless users, and radio link status graphs using rrdtool.
• Updated wireless drivers, tools, and just about everything else.

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:

• A router performing NAT from the DSL line to an 802.11a uplink in AP mode, performing bandwidth shaping along the way. The uplink was necessary because the Ethernet cable from the floor below wouldn't quite reach the conference space while keeping under 100 meters.
• Another router connecting that 802.11a link (through a wall, behind a locked door) to an 802.11g radio in ad-hoc mode. This router also had a self-powered USB hard drive attached to it, which contained a caching Squid proxy. With such a small pipe and so many power users, going without a transparent proxy server would be insanely inefficient. This box also provided DNS services for the network (via dnsmasq) and ran OLSR on the ad-hoc radio.
• Five more dual-radio boxes, with one radio on the 802.11g ad-hoc OLSR backbone, and the other providing traditional 802.11b AP services.

(photo by Ken Caruso)

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