Air-Stream Kilkenny

For the past week I have been sitting on my roof with a towel over my head:

Well actually I have been setting up an Air-Stream Access Point (AP) at my house. The towel blocks out enough sunlight so I can see my laptop screen.

Air-stream is a community wireless network that covers much of Adelaide, the city of 1 million people where I live. The map below shows the Air-Stream nodes covering the city. For scale, the map is around 50km from north to south. The geography is favorable for wireless as the Adelaide Hills (which run along the eastern edge of the city) overlook the suburbs which are located on a flat plain. So a wireless radio in the hills often has direct line of sight to the rest of the city. The low population density of Adelaide means the Air-stream network is quite spaced out – there are many long (10km ) links between nodes compared to community networks in European cities.

After some initial stumbling of Air-Stream signals I decided to invest in some router hardware from Wifi Extreme:

  1. Mikrotik Routerboard RB333
  2. Ubiquiti XR2 600mW mini-PCI wireless card
  3. Atheros AR5212A 100mW mini-PCI wireless card
  4. 8dBi Omni Antenna
  5. 15dB directional antenna
  6. UP85 Box, cables, POE injector, power supply

The 600mW radio drives the Omni antenna, so people can access my AP. The 100mW radio connects to the directional antenna for the back haul link to the rest of the network. Both radios are configured for 2.4GHz 801.11b. Air-stream uses BGP for routing.

Here is a picture of the router hardware, and some pictures of the installation on my roof:

Setting up Mikrotik Routers for WEP

Wifi configuration is a new area to me so I relied heavily on the Air-stream community (especially Daniel) to help me set up the AP. Thanks guys!

Configuring the Mikrotik router for WEP took a while to work out. It comes with a nice Windows GUI (that you download from the router) called Winbox. The same features can also be accessed via a command line Terminal interface.

Here is a short How-To on setting up WEP on the Mikrotik RB333 using Winbox. From the Wireless menu click on the Security Profile Tab and click on the profile your wish to use (profile1 in my case). In the mode box select “static keys required”:

Then click on the “static keys” tab and from the Key 0 menu select “40bit wep” and enter your WEP key in the adjacent 0x box:

Note that the Miktotik router software can only accept hex keys. I converted my ASCII WEP key by copying what my Linux box did with the ASCII key:
root# iwconfig eth1 essid Air-Stream-Kilkenny key s:mykey
root# iwconfig
eth1
IEEE 802.11b ESSID:"Air-Stream-Kilkenny"
Mode:Managed Frequency:2.417 GHz
Access Point: 00:15:6D:63:A0:45
Bit Rate:11 Mb/s Tx-Power:13 dBm
Retry limit:15 RTS thr:off Fragment thr:off
Encryption key:6D79-6B65-79 Security mode:open

So 6D79-6B65-79 is the equivalent of the ASCII WEP key “mykey”.

Network Diagram and IP Alias

Here a netwiork diagram of the Access Point (AP) showing the various subnets and devices attached:

Clients to connect to the AP via wlan1 and their traffic is routed traffic over the Air-Stream network. My AP connects to the rest of the Air-Stream network via wlan1. In this case the 15dB directional antenna connects to the Omni antenna of another AP located about 10km away. In some cases dedicated and/or redundant links exists for the back haul.

The ether1 interface is connected to my LAN, which runs a 192.168.1.0/24 subnet. Daniel showed me a neat trick – IP Aliasing. This allows devices configured for the 192.168.1.0/24 subnet to simultaneously communicate on the 10.104.0.0 subnet using the same Ethernet card and physical LAN:
# ifconfig eth0:1 10.104.0.3 netmask 255.255.255.224
# route add -net 10.96.0.0/11 gw 10.104.0.1

Tweaks, Site Survey and Further Work

Once we had the AP connected to the Air-stream network, Daniel could login and tweak the configuration a little. We started at a throughput of 125 kB/sec, and brought it up to 250 kB/sec after tweaking the channel and power levels of either end of wlan2 back haul link. About 700 KB/sec should be possible with a better antenna. But it’s a good start, and useful for my experiments.

I performed a basic site survey by associating an OLPC laptop to my AP and driving around the neighborhood. Roughly 500m range with the laptop sitting on the dashboard of my car (non line of sight). I have also had a report of stumbling my AP from 12km away with a good antenna mounted on a mast.

Things to do:

  1. Connect a couple of IP04s over the Air-Stream network and test voice quality.
  2. Experiment with ad-hoc connections all over the city to simulate the Village Telco network. It took me about a week of messing around (and lots of help) to set up a basic long distance wireless connection. For the Village Telco concept it would be great if a semi-literate, non geeky person can set up a VOIP over Wifi node. How easy can we make this connecting to a Wifi network? Can we reduce the time and expertise required so that anyone can do it? I have a few ideas in this area that I will explore over the next few weeks.

4 thoughts on “Air-Stream Kilkenny”

  1. Take a look at what the B.A.T.M.A.N and R.OB.IN projects are doing with self-configuring wifi mesh networks. BATMAN advanced is (to me) especially cool — essentially a self-configuring mesh layer 2 ethernet network, routed at the MAC layer (not spanning-tree).

  2. Hello there, I’ll be connecting to Airstream wireless WAN and I live in the Kilkenny area. Could you please give me a few pointers on connecting to your AP (coordinates, adress etc). Thanks.

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