Author Topic: HOWTO: Filesharing via Wifi  (Read 34560 times)

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Offline Nemo

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Re: HOWTO: Filesharing via Wifi
« Reply #15 on: August 27, 2008, 06:19:41 AM »
The FCC rules for Wifi won't allow universities or other organizations to stop P2P over Wifi.

Universities have no authority or control over the airwaves owned by the People.

They have no cause or jurisdiction to spy on or regulate speed on Wifi networks since stations are mandated to accept any interference from other stations. No excuse that students are interfering with "campus wireless" since the university doesn't own the airwaves, we the people do.
If the wireless campus network works on WLAN channel 1, 6 and 11 (for better throughput and less interference), then every other WLAN device creates interference and collisions (quote from Wikipedia article about Wi-Fi: "A very confusing aspect is the fact that a Wi-Fi signal actually occupies five channels in the 2.4 GHz band resulting in only three non-overlapped channels in the U.S.: 1, 6, 11"; see in German Wikipedia a list with used frequencies, every channel occupies 20MHz while channels are 5MHz wide...  :()

It's possible that the campus has a policy against usage of own access points. Technically it's possible to build an campus-wide adhoc Wi-Fi network but perhaps it means the end of the studies...

During the lasts Chaos Communication Congresses they had an external firm which provided the Wi-Fi coverage of the building. They had a policy against own access points and with this high tech equipment they were able to locate interference sources in real time for enforcing this policy!


Offline Nightwalker_z

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Re: HOWTO: Filesharing via Wifi
« Reply #16 on: August 27, 2008, 08:01:56 AM »
This even goes further. Today bigger campuses or companies make use of WLAN Controllers. Each big vendor (Cisco, Enterasys, Extreme ...) has these controllers in their inventory.
So what does such a device?
The idea is, that the APs itself are dumb devices. It's just an Ethernet to wireless bridge. All the other stuff like encryption, associations, RADIUS .... is managed by the controller. The AP's are connected to the controller (normally a tunnel is formed) and the user traffic is emerging at the central controller.
But the important point is, that the controller has knowledge over the complete valid wireless infrastructure. All other APs that are not connected to the controller are rogue AP's. These rpgue APs are discovered by the valid APs and can even be localized. It's possible to attack these rogue APs with deassociation floods, that no client will be able to associate to them.
The controller may also detect rogue clients (clients that are connected to a rogue AP). I made several of these installations and this stuff is quite effective. You can even detect, if the rogue AP is connected to the wired network and isolate the switchport.
Yeah - great new world  :)

So, there are (simple) ways to detect and influence not wanted WLANs in the campus. Wi-Fi is not a bad idea, but like other technologies it is not bullet proof.

Offline scripter

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Re: HOWTO: Filesharing via Wifi
« Reply #17 on: August 27, 2008, 09:33:59 AM »
Hi Nemo,

In the USA and possibly other countries it would be a freedom of speech issue trying to prevent someone from using the airwaves they own (we all own them together and we let the FCC regulate them within limits). Or restricting the use of devices because the university wants to own the airwaves exclusively.

"(1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation." meaning that the parties operating such a device can not seek redress from other parties operating radio communication services.

See the FCC ruling in "MassPort" - "The genius of this unlicensed technology is that no central authority controls or manages how and where these networks spring up. Instead, any private or commercial operator who sees a need for a local Wi-Fi network may build and operate one." .... "When it comes to providing broadband over the unlicensed bands, the airwaves are truly the people's airwaves." Theres a weapon to use if you are having troubles at your university.

The principal that a unlicensed frequency can't be owned and controlled by anyone is clear.

The FCC recently opened up more frequencies in the 5 gigahertz range for unlicensed wireless networking services. Companies already make stuff for 5Ghz so students could move off the more popular frequencies at a reasonable cost (and get higher speeds as a bonus).

There are other frequencies that a group of smart students can use that allow communications of 1W or less without license. HAMs (amateur radio operators) have been known to use frequency multipliers or up/down converters to move existing equipment to different frequencies so it's possible to change the frequency of existing Wifi equipment (although quite technical, probably a good project for students). Most stuff under 100mW is unlicensed anyway.

Wifi Direct Sequence Spread Spectrum (DSSS) including special modulations with the chipping codes etc.. can allow more than one station to use the channel at the same time, although some will argue with this, you must consider that stations are not always at full strength or in direct contact with each other and that newer software attempts to prevent jamming. Also, stations may drop to a different speed, which can change the modulation.

802.11a (5GHz) and 802.11g (2.4Ghz) both at 54mb/s, use Orthogonal Frequency Division Multiplexing (OFDM) and should support more than one station at a time on the channel better than DSSS does and there are many more channels available (at 5Ghz).

With these technologies it's not always as simple as someone is transmitting on my channel so I can't talk.

There's articles on the net about "cantennas", where people use tin cans to make highly directional antennas. Students could use these to direct signals more narrowly and prevent interference possibly going from building to building through windows and at lower power. Make it a art project.

Now you've gotten rid of the too many stations on one channel problem and the "rogue AP" detection problem Nightwalker mentioned. It would also make spying and monitoring harder.

Students can add or cluster stations that repeat traffic at different frequencies, combining routers together including adding cabling to provide "service" to an entire dorm complex and adding Wifi stations that cover the dorm area from building to building. Then it's possible to have full LAN speeds some of the time.

It's probably better for overall security if the students mix it up since it would make it harder and more expensive for someone to try to block or spy on all the different modes.

There's also the option of going optical, for those situations where Wifi just won't do :)

FCC MassPort article (or use google)