This is a little belated, but better late than never...
When FabFi goes linking, FabFi goes big. After verifying that there was a good link from the FabLab on our last outing, Andreas, Smari and I went into networking high-gear. Smari set up a linux box with a proxy server to run DNS, dhcp, and a proxy server to cache web pages and locally mirror MIT Open CourseWare (we did a local dump of wikipedia too, just for kicks). Meanwhile Andreas and I worked out a network topology for the rest of the system that would allow us to daisy chain links easily. In retrospect, it could have been a lot cleaner, but here's the breakdown, starting with a 10.0.0.0/8 network.
FabFi router subnet (serves all FabFi links) = 10.1.0.0/16- AP wan = dhcp (netmask /8)
- AP lan = 10.2.1xx.0/16
- STA wan = 10.2.1xx.0/16, statically assigned
- STA lan = 10.3.1xx.0/16
- Each STA/AP pair shares the same class B address
This works well for allowing us to daisy chain links, but the open netmasks allow some strange things to happen with dhcp addresses. I believe, in retrospect, these could be restricted to /24 without restricting the daisy chain feature.
The firewall is currently forwarding everything which seems to be working fine, and computers on the FabFi network can't see any of the computers locally at the FabLab or the Taj except for the OCW server, so I'm not worried about security (yet). At the same time, the SSIDs for the wireless links are still visible, and somehow people at one of the downlinks have jumped onto the AP directly with their laptops. This is puzzling since there's not supposed to be dhcp available from the AP.
Anyway, on to the numbers. After doing some peaking with a pair of big antennas using window screen as the reflective surface, we achieved -67dB over 2.41 miles. It turns our we almost have line of sight, though we're shooting through one very large foliated tree. Data throughput is 4.43Mbps to the FabLab with virtually no packet loss and very reliable ping times (Amy got 1.8Mbps to the web from one of the downlinks) As you can see below, we moved the whole setup down to the catwalk level of the tower and tied it down. Plastic bags and tape served as weatherproofing, and a line from the hospital is providing the juice.

After over a week of intermittenet rain and wind, everything is still functioning well to the tower, and both downlinks are connected, though there have been some user complaints of patchy service, most likely do to our fiddling with the network here at the Lab.
Thanks to a confluence of circumstances, I'm in the field for another two weeks, during which time I hope ot be able to tie up a lot of the loose ends and make a couple more links, the coolest of which will be Bagrami School (more about that soon). Stay tuned.