Wednesday, September 30, 2009

Dispatches from the front - Link Photos

I just received photos from two new fabfi users in JBad. The placements and attachment strategies for new reflectors are 0ften very creative:

Monday, September 28, 2009

LQ, NLQ & Sharing Reflectors

For those of you out there building big networks (and I know there are at least two of you!), I just posted a section on the fabfi wiki explaining LQ, NLQ, ETX and how to figure out if you can use a single reflector to point at multiple endpoints


Sunday, September 27, 2009

Mesh Channel Selection

There's been a lot of discussion about how to select wireless channels in JBad. As anyone reading along will notice, it's getting really crowded up on the water tower (nine downlinks) to the point where it's important to worry about airtime on the radios:

A standard wireless router has 11 available wireless channels. Of these 11, only three are completely non-overlapping (ie: can talk at the same time without interfering with each other).

In our implementation, no two nodes can communicate unless they're on the same channel. In short, this is because if they could, eventually everything would end up on the same channel, which we don't want. In terms of OLSR this is important, because if two nodes are on separate overlapping channels, they will interfere on each other's transmissions if they try to talk at the same time, but will ignore each other's RTS CTS messages, so they won't ever coordinate. As a result, you get crappy throughput if you have two busy nodes on, channels 5 and 6 right next to each other.

In our implementation most of the downlinks on the water tower were channel 6. We then deployed a pair on channel 5, and despite good signal were seeing an ETX of 4.5 instead of the < 1.1 that we would expect for a link of this quality. Switching the channel to 6 brought the ETX down to 1.05.

Take Home:

Wireless channels must be either the same or non-overalpping for any nodes in your network that can hear each other.

FabFi 2.0-AF wrap-up.

Oi, it's been a long time since the last post. Hard to write when you're gettin' 'er done...

I'm gonna make this short since Amy beat me to just about everything important (I tend to avoid it until I have time to compose something neatly organized and complete, whereas she tends to work on the newsflash model). Anyway, here's the skinny:

Fabfi 2.0 was a gigantic success. In two weeks we moved the FabLab, got the shop bot running, turned out a pile of fabfis, upgraded all the hardware and software and made two new links.

After we left, there was a hardware failure on the 4km link, and one of the little reflectors on the tower pointed in the same direction transparently picked up the slack! (then I broke it from afar before Amy replaced the bad box)

More importantly, we've had another pair come up in our absence, bringing the total number of downlinks off the tower to nine. Live stats and network diagrams are are now available at (though they will be slightly broken for the next week while we make some changes) and you can download all the latest files to make everything yourself at