Sunday, February 04, 2007

This is Radio Clash on pirate WLAN

OK, so this guy's designed a little program that is intended to provide access to pay-for-play wireless LANs. The idea is simple - one host actually pays up, and connects to the WLAN, and then acts as a proxy for other users, who treat the "WiFi Liberator" as a WLAN router. My initial thought was that "oh gawd, he says it's an art project....I hope he's not going to give the users of the Liberator RFC1918 addresses, seeing as practically all WLANs use private addresses and NAT."

In fact it's actually better engineered than that. Rather than multiple-natting, you have to set up a small web proxy server on a machine with a globally routable IP address, and the Liberator host tunnels into that machine, and the traffic is broken out onto the public Internet there. That, of course, also opens up some other useful possibilities - if the tunnel is encrypted, which it damn well should be, and the proxy is located in a civilised country, it's also censor-defeating. Actually, closer reading shows that the tunnel is implemented using TCP-over-ICMP, which despite being clever means that it's going to be slow. There's no mention of encryption, and the user is advised to leave the WLAN encryption off to preclude the need to give others a password - so this is certainly not for use anywhere dodgy.

One problem, though, and it's a traditional one. Why does nobody ever think of the children...sorry...the radio implications? WLAN can only be used as informally as it is because it has various features to deal with inter-network interference. Specifically, any device using it has to listen-before-transmitting, and renegotiate the channel with the other party if there is someone else there. This works, but the more interfering networks there are, the more time spent looking for a patch of the 2.4GHz ISM band quiet enough for a chat, and the lower the informational throughput - the first 11Mbits/s 802.11 cards sometimes used more than 50 per cent of the rated link speed for informational overheads like network control messages and resending dropped packets.

Now, the problem with this proposal is that it suggests that you plonk another WLAN router, transmitting merrily on the default channel, in somebody else's network where they will by definition interfere. This might be a feature, if you think making other people's Internet access shit will convince them of the rightness of your cause, but I reckon subjecting them to electronic warfare jamming is probably a loser.

No comments:

kostenloser Counter