Configuration and Confusion

Exciting things happened today.

To start, I ate some really good bread at J's house. The label said "Sunday garlic and cheddar artisan bread," but the most notable thing about it was the large quantity of poppy seeds scattered throughout; it tasted like a poppy seed bagel, but was soft and fluffy like whole wheat bread! Miraculous.

There are more changes to the system. I'm still hoping to try the thing where we cut out the first Bullet, but for now we're going to keep it just to make things simple. According to the Internet, not all WDS-enabled devices from different manufacturers can work together. So now we have four Bullets and four antennas.

Configuration setup for two-hop link. I will write in the antenna specs, cable lengths, and types as soon as those are finalized.

The testing will go differently than I thought. Now we can only test a link of about 0.7 km tomorrow, because we can't actually configure just three Ubiquiti Bullet modems to repeat a signal over many miles from the first to the third link. So says a tech support person from Ubiquiti Networks.

I don't entirely understand the reason yet, but this is what I gathered from what the tech support person told me: In the case that I only had the omnidirectional antenna at the midpoint, Bullets #1 and 3 would have to be configured as WDS Stations (receivers) and Bullet #2 would have to be the WDS Access Point. (See picture above for what these terms mean.) Since the access point would only be able to send out signals to within a certain radius (of no more than a few thousand feet), they would not be able to "hear" the access point even if the access point could "hear" them.


What confuses me about this reasoning is that if the directional antennas at the receivers are powerful enough to send out signals that will reach the midpoint Bullet, why wouldn't they be able to pick up signals equally far away? I had read that increasing the gain of the antenna at one end of a link strengthened the connection as a whole, not just one end. So even if the antenna on one side of the connection had a lower gain because it was omnidirectional, the very high gain of the directional antenna on the other side could make up for it. But does that only apply when both antennas are directional? I'll have to look that up. I might still be right.

But for now, I've bought another Bullet and POE injector to set up the network as the tech support person recommended, because I can! We happened to have two extra 19 dBi antennas that we had been planning to replace with the 24 dBi ones; now we can use all four, which is a much more powerful combination than the two 24 dBi's with the 12 dBi omni in the middle. This way we will have a much narrower Fresnell zone (the football-shaped area in which the signal travels between antennas), and our antennas' limited height above the ground (limited because we're putting them on roofs, not towers) may not matter so much.

Then again, adding an extra hop will cut the bandwidth in half. So unless we get to Tanzania and see that there are definitely large trees or buildings blocking our line of sight, the main plan is to create a single-hop point to point link using only our most powerful antennas. The two extra Bullets are backup.

More things I learned from Ubiquiti tech support (way to go, them!):

It's easiest to troubleshoot a multi-hop link when each machine on the link has a distinct static IP address. So the two main broadcasting and receiving Bullets are 192.168.1.2 and 192.168.1.3, respectively. The two backups will be 192.168.1.4 and 192.168.1.5, and whatever 3G router is acting as their Internet gateway will be 192.168.1.1 (as is default and proper for a consumer router). Since the AirOS interface for Bullet 2 wouldn't let me change their IP addresses without specifying DNS server IPs, I was instructed to put bogus IPs (1.1.1.1 and 1.1.1.2) as the primary and secondary DNS servers for all of them; apparently it doesn't matter, because the 3G router would be handling the DNS stuff. Very interesting. I wonder how the different devices tell each other these things.

What I have left to do today is figure out all the cable lengths and draw a picture for my UROP adviser so he can hopefully approve some cable purchases. Then maybe a run? And sleep.

Random note: Dyed my hair bright red in honor of the Maasai colors (red and black). I hope they approve! (Second best option: I hope they don't notice!)

-E