What's the cheapest way to provide satellite or roaming uplink (33.6k-1Mb/sec)/GPS/direction to a Linux box housed in a vending machine or a moving vehicle or boat? Any howtos?

-- Li-fan Chen (obiwantcp@hotmail.com), December 08, 2000

Answers

[Communication]

It depends on what you want to do with that resource. If you need reliability you will need to try several different source of uplink. There are 4 major existing and upcoming systems in North America I am aware of: 1. Satellite phones (GlobalStar?); 2. Cellular digital data networks (Minstrel?); 3. Bi-directional satellite dish-based surfing (being implemented); 4. Private infrastructure over unregulated radio frequency bands (Lucent WaveLAN with directional antennas?)

1 & 2 is alright for fast moving vehicle. 3 & 4 is better with non- moving terminals. None of them are perfect. They all have consumer versions but often that version cost too much (unless you buy these networking cards and antennas in bulk/OEM--but then you have no one to go to for support)

*2* If you are made of gold, you could try the fairly ubiquitous digital cell data networks--which normally supports wireless ip. If you're not made of gold, it's still worth using--just keep the traffic use down. The monthly fee per remote ip node is still hefty regardless of the traffic usage.

*2.1* It's not great for internet cafes due to high bandwidth charges- -but the modem is inexpensive. *2.2* The transportation automation industry (package delivery, shipping, dispatching) have made a collective transition to it. *2.3* You don't have to go overboard and create your own custom thrifty protocol to save money over the long run--but don't let people surf on the end-nodes. *2.4* Things you can do to save bandwidth for digital cell data networks: *2.4.1* Bundle the transactions (think CGI forms) and compress it (use the web's ability to do gzip as a compression encoding--see Accept-Encoding/Content-Encoding). *2.4.2* Use smart clients who renders all static "skins" or user interfaces from a periodically updated client-side cache directory. This prevents repetitive downloads of large images and information. This means you will have to classify your data into things that are dynamic and things that stay static. *2.4.3* Personalize when possible. Prevent repetition of form filling. Keep the end-nodes (clients) smart. Use a client-side webserver that supports scripting. Use a periodically updatable RDBMS like PostgreSQL on the client so the client-side webserver can be kept busy. *2.4.4* Have a smooth system where people can update the remote end- nodes easily and uniformly.

*3* If price is not a problem: Bi-directional satellite dish-based surfing abilities will be offered to North America soon.

*3.1* You probably can't buy one of these buggers for each of your vending machine. Vehicle office maybe. *3.2* It's a great way to provide redundancies. If you use both satellites and land-line. One could fail and the uplink would still be up (assuming that both providers aren't on the same back-bone). *3.3* If you need high-speed bandwidth in your vehicle (because you want to be productive and kept up to date), you have to figure out how to keep the dish from constantly pointing in the wrong direction. The direction and adjustment should be a mere irritant if the vehicle is usually parked.

*4* WaveLANs cards are cheap. But modifying them to send out directional signals is not a piece of cake. *4.1* First, they really do need line of sight (you can only amplify the general radius so far with an amplifier--but you can go farther with a directional antenna--10km max?). *4.2* Second, it uses a busy and dirty airwave. There's no guarantee of bandwidth. *4.3* Forth, not all of your vending machines could be within the narrow line of sight or degree of reception. There's talk that if you set up a hub with 6 or 8 WaveLAN directional antennas pointing in all directions this problem could be solved. But you can't expect to pull an antenna to the top of a commercial building just to feed a vending machine.

[Navigation] Electronic compass and GPS receivers both come in various types of packages--all the way from a little more than a circuit board with online specs in PDFs to a complete computer with an interactive map database. I don't know much about them. You can probably get compasses to talk over serial or USB using a reasonable protocol and write a Linux driver. It's probably the same with GPS. If you need a map you'll need to build one yourself and stuff it into an RDBMS (like PostgreSQL).

-- Li-fan Chen (obiwantcp@hotmail.com), December 08, 2000.