This is a brief mini-howto on how to build a linux based wireless router out of what amounts to spare parts, using the linux router project's single disk router software. The total cost of each end of the router, including antennas and cabling, is less than 1300 US dollars, which is a considerable cost savings over the dedicated bridge units (typically about 3100 US each) available from the same manufacturer.
We live over 5 miles from the local telco central office. This meant that no ADSL or ISDN was available. A 56K line would have cost several hundred dollars per month, if they could pull it, and a T1 was going to cost in excess of 1250 per month with a 3,000 dollar install. Either option would require some sort of long term contract, too. Hybrid cable was available, but it's high latency and slow 28.8 modem based uplink was unacceptable for our purposes.
We could see bandwidth, only a few miles away, 384k ADSL for only $230/month, 6 times what we could get with a 56K frame relay. So we embarked on our wireless journey and eventually built what you are reading about here.
We figure the economics of high speed internet networking in parts of the world outside of California are even more biased in favor of the local telco monopoly. If you are willing to live with the occasional heavy weather based network outage, want to save money on an upfront and monthly basis, and are within LOS of somebody else with an internet connection who is less than 16 miles away, read on....
| Item | Name | Vendor | Price |
|---|---|---|---|
| Wireless Card | Aironet 655 (also known as the PC2300) | Network Access Solutions 7172 Regional Street Dublin, Ca, 94568 Attn Jim Bradfield at: (925)-803-2100 |
~800.00 ea |
| Antennas | Model | Also Network Access Solutions | ~200.00 ea |
| Cable | LMR-400 | Network Access Solutions | ~100 bux (cable+connector) |
| Connectors | Ham Radio Store | ~23.00 ea | |
| PC | P75 w 16MB ram, no hard disk | Junk store | ~200.00 ea |
| LRP Code | The Internet | FREE | |
| DOS Boot Disk | |||
| Arlan Setup Drivers | |||
| Current Arlan Driver |
What these tools are not good at is figuring out your height above ground
or if there is a building in the way. There is a tool that can figure out
LOS over and around obstructions, but I can't find the url for it.
Here's where a telescope
comes in handy. Even with a high quality telescope it's hard to see your
end points at extreme ranges (+10 miles). A good high powered colored light at
your downstream site helps a lot.
Ultimately we posted to the ba.internet newsgroup and the svlug mailing list and found a bunch of hackers willing to share their bandwidth, which was really heartwarming. However their grip on geography was generally quite weak and none of our 5+ volunteers was within LOS.
A few commercial ISPs did email us with offers to connect to us. Netcom, slip.net, and a few others all claimed to offer wireless service, but all of them got real nervous when we told them about our hardware. All of them wanted us to use their hardware and pay fees in the 250-450 month range for 384K access.
After another posting we finally ran into a very clueful ham radio dude smack dab in the middle of our LOS. We got a good connection on the the very first try. We were in business!
The trouble was, he didn't have an internet connection yet. But that's another story.
The point of this is that the community spirit of the internet is not dead, and it is certainly possible to find someone who can connect you to the internet who is within your line of sight, if you look in the right places.
So get a pair of P75 or better PCs, with 16MB of ram, a network card or two, and you're set.
Install the arlan cards (you might need to change their interrupts - these cards are not plug and play) and run their DOS based setup drivers. You'll need to pick a suitable network code, and spreadingCode. The networkcode is some random 6 digit number. We generated ours by dropping a cat on the numeric keypad, your methods may vary. It needs to be the same on both cards. The spreading Code is for 384Kbaud, 1Mbit, and 2Mbit operation. As a rule of thumb I'd suggest:
| Code | Speed | Distance |
|---|---|---|
| 4 | 2Mbit | up to 4 miles |
| 3 | 1Mbit | up to 16 miles |
| 1 | 384Kb | up to 25 miles |
Be conservative. Your goal in life at this point is to make the thing work, not make it fast. You can always go back and make it go fast later.
If you picked out a different network card than the NE2000, you're going to have to download the linux router project's code, an appropriate kernel, and install the proper modules on the lrp disk. This can be a complex procedure, so here's Greg's notes on the topic.
The last point is the registrationMode option. The wireless card supports both point to point and Accesspoint mode as a client only. If you want multiple points to connect to one antenna, you still need to get the Accesspoint router from Arlan. A registrationMode of 1 puts the card into Access Point mode. Point to point is 0.
When you insert the driver module into the linux kernel, you should have a command line of:
insmod arlan registrationMode=0 spreadingCode=3
Or whatever you've chosen as your spreadingCode earlier in this document.
Putting the router outside was not an option, so we built an 11' cable, mounted the wireless lan antenna on the TV arial, and drilled a hole in the side of the house to run the cable through. We ran power and a UPS up into the attic, and put the box up there.
We figure that it will stay warm enough through the winter, and we'll worry about the summer heat when the summer comes. Tenatively we're going to add a fan and switch to booting off a flashdisk in the springtime. We recognise that this is not a very scientific approach to the heat problem.
Although a 486-66 seems capable enough to handle the maximum number of packets we can transmit, it does behave badly under severe error conditions (driving rain, pea-soup fog, etc), so we recomend a minimum of a P75 or better for a long distance application. Your mileage may vary.
The only ongoing problem that remains is when 3 of us start playing quake (The game uses udp and sends enormous numbers of packets), the downstream router tends to stop transmitting for a minute or more at a time. Most of the evidence we've gathered to date suggests that the wireless card itself is not at fault but the ne2000 cards, so at some point we're going to upgrade to Netgear DecChip tulip based cards. (And incidentally, gain 100Mbit/sec capability).
The natural congestion management of the TCP protocol means that we NEVER see this problem when doing normal things (ftp,web,email,etc), and it also does not occur via NFS (also udp based), which is puzzling.
This project cost us lots of time, but we saved lots of money. The arrangement we worked out with our downstream ADSL guy was 2/3s of the cost of his ADSL - 154 bucks a month. The ADSL install charge from pac bell was 450.00. The total cost of all the hardware we bought was less than 3k.
The downstream router not only handles the wireless stuff, but has 2 network cards enabling it to do traffic shaping for the guest network. The upstream router has a modest amount of firewalling features turned on so we don't have to deal with people trying to hack or portscan us.
Ultimately we plan to build a SBC based solution using flashdisk technology and the PCMCIA version of this same card. Elmer says his current driver works now on the PCMCIA cards... we have the flashdisk stuff going... the single unit cost should be less than 2k, easily... now to get more funding....
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