Sluggish WiFi Connections Hurt Everyone

MindNumbingOblivion writes "Wireless technology has revolutionized access to local area networks when one can't always be close to an ethernet jack. But a recent research paper from the French Centre Nationale de la Recherche Scientifique tells how one slow user accessing a hot point can hurt the whole group. Apparently the very nature of CSMA/CD guarantees such anomalies. Here's the story, and here's the release from CNRS (in French)."

Comments

Taking bets on

[groove10]

How long before this becomes an exploit in order to perform a DOS attack on wifi points?

I say about 1 month, maybe less. Any takers?

Re:Taking bets on

[child_of_mercy]

so, for example, i could buy a cheap(ish) handheld with wifi, get this program running on it, tape it under a table at a starbucks and deny their access point as long as the batteries held out?

interesting,

I really, really hate Starbucks...

There are solutions

[That_Dan_Guy]

If you have an 11b AP with a bunch of PCs with 11 meg cards and some kind of 2 meg hand held device then the 2 meg device is going to hog the connection until its done.

A solution would be to leave the 802.11b AP inplace and servicing the older 2 meg devices and put an 11a or 11g AP in next to it to service the faster devices. Alternitively you might be able to put the slower devices on channel 1 and put the faster one on 6 and 11 (they have to be 5 apart to avoid overlap, and in the US you only have a total of 11 unregulated channels)

Wireless is different than wired communication. People are just going to ahve to get used to it. More stuff to learn, more rules to follow, more work for people like me.

Its a good thing- especially in this economy.

Re:There are solutions

[Anonymous Coward]

Those with 802.11b cards that handle 11Mbps should not complain too loudly about those that connect at only 1Mbps. The 11Mbps connections slow faster wireless networks down to their speed.

802.11g is supposed to be both 54Mbps and backwards compatible to 802.11b. From my own experience with 802.11g, if there is even one person using an 11Mbps connection, the rest of the wireless nodes also slow down.

Just like driving on a one lane country highway behind a slow car doing only 11 mph in a 54 mph zone.

Not likely

[ezraekman]

This isn't something that's likely to become a serious exploit, for the simple reason that the attacker would need to bring a compatible device within range of the access point. Unless someone has a serious grudge against the owner of the network, who'd want to spend the time? You'd either have to be present with a laptop/pda, or leave it behind. Remember, we are talking about radio waves here. Plenty of technology exists to track 802.11x signals, and all it takes is a well equipped sysadmin and a properly filed lawsuit to discourage the attacker.

It's the nature of the system, but...

[jeffmeden]

Its good to see this sort of stuff put to paper anyway. As a Free/Open software implementer working on developing cheap-as-possible wireless access points for rural area internet distribution, I can say this IS useful. Problems like this, and many others, creep out of nowhere and are very hard to track down without expensive equipment. This specific problem happened and was remedied after much head-scratching by dividing one site into multiple cells so slow users had more 'time' to get their data. just my 0.02

jeff

Re:WiFi doesn't use CSMA/CD

[aXis100]

Unfortunately, RTS/CTS is almost worthless in a situation that requires it - when you've got hidden nodes, the RTS mechanism can just as easily cause collisions.

The users of WAFreeNet (Perth, Australia) have just released some open source software (frottle) to combat this. Essentially it provides a polled/token operation at the IP layer, virtually eliminating collisions. This is a similar application to WiCCP, and we've been helping/competeing with the WiCCP developers. The other alternative is Karlnet Turbocell - expensive proprietarty software, firmware and hardware, with poor linux support.

I cant post any url's now - the websites wouldnt appreciate the slashdotting. For those of you than can find the sites for yourself, it may be well worth your time.

Jamming

[gnarled]

Who needs sophisticated DOS attacks when simple jamming would do the trick quite well.

Milwaukee has this issue

[citking]

The Milwaukee Journal/Sentinel ran a story about becoming the 2nd US city to offer public WI-FI in two downtown parks last week. According to the article, "Randy Gschwind, the city's chief information officer... said the network serves 20 to 40 users before it becomes clogged."

Taking into consideration that Milwaukee is a city of ~600,000 people, that not many are going to have wireless laptops and even fewer are gonna spend time in a park surfing the web, it still seems like 20-40 users clogging a public WI-FI is a bit odd.

I suppose they can't complain, though, since the city paid less than a couple of hundred dollars for the setup. Still, it just seems somewhat pointless if it's gonna be clogged all the time.