What for ?

With the pervasive deployment of hotspots all around the globe, and since wireless network cards are becoming a "natural" companion of our laptops (or even built-in), wireless networks - mainly based on IEEE 802.11 - are becoming an essential medium to be always online.

Users need more and more bandwidth. Video streaming, large file downloads / uploads and delay sensitive applications such as voice over IP (VoIP) are commonly used nowadays.

The spectrum of pricing for wireless access goes from free access (in open community networks) to almost 1 euro or dollar per minute!

From a greedy user's point of view, "cheating" increases the quality of service and reduces the expense.

From a WISP (Wireless ISP) point of view, fairness and customer satisfaction must be guaranteed. DOMINO is on the WISPs side, to help them detect misbehaving users.

Is it easy to cheat ?

Unfortunately, Yes!

The new generation of wireless cards is easily programmable. Most of the MAC layer parameters can be configured at the driver's level (in contrast with the firmware of the older generation of cards). Open source drivers are available for download from the Internet. No need for sophisticated programming skills, just a few hints, and the user can change the driver to increase his share of -or even monopolize- the bandwidth.

For example, with a single line of code, unsophisticated hackers can reduce the contention window size, realizing a considerable redistribution of throughput shares among stations competing for the wireless bandwidth.

Other cheating techniques include the modification of the protocol timers (e.g., DIFS), the misuse of collision-avoidance mechanisms such as the Net Allocation Vector, and selective scrambling of other users' frames [3]. We have simulated and prototyped most of these techniques, to show how easily they can be performed. (See [1] for more technical details.)

What does a cheater get ?

Higher data rates and lower packet delivery delays/jitters, at the cost of lower data rates and higher delays/jitters for well-behaved users.

Figure 1 shows experimental results of a well-behaved node and a greedy user sharing a hotspot's bandwidth.
We can see the dramatic impact of the cheater's behavior on the distribution of the bandwidth.

Figure 1: Throughputs of a cheater and a well-behaved node's vs. the misbehaving coefficient of the cheater.

To prevent this from happening, we have designed DOMINO (system for the Detection Of greedy behavior in the MAC layer of IEEE 802.11 public NetwOrks) [1], a piece of software to be installed in the Access Point in order to detect and identify greedy stations (Figure 2). DOMINO induces a negligible computation and storage overhead.

How does DOMINO work ?

Access points (AP) equipped with DOMINO (Fig. 2) enable the wireless Internet service provider (WISP) to detect greedy misbehaviors and therefore to guarantee fair customer services.

Figure 2:

DOMINO is totally compatible with existing user equipment and wireless infrastructures. It runs at the AP and has negligible processing overhead. It captures all packets sent on the radio channel and analyzes them to check their compliance with the IEEE 802.11 standard. It takes DOMINO fractions of a second to few seconds to detect a cheater, depending on the density of the traffic he sends and the cheating technique he uses.

False detections are reduced with proper selection of DOMINO parameters. DOMINO detects all misbehaving techniques currently known, and we are pursuing our research efforts to foresee other potential threats to public hotspots.

We are currently seeking companies interested to license our technology and its related patent [2] and to collaborate with us in this research field.

Bibliography

[1] M. Raya, J.-P. Hubaux, and I. Aad,
``DOMINO: A System to Detect Greedy Behavior in IEEE 802.11 Hotspots''
in Proceedings of ACM MobiSys, Boston - MA, 2004,

[2] M. Raya, I. Aad, and J.-P. Hubaux,
``Misbehaving detection method for contention-based wireless communications (domino),'' US patent filed, SERIAL NUMBER 10/782,802,
FILING DATE 23 February 2004, REFERENCE P-26-487-US.

[3] M. Cagalj, S. Ganeriwal, I. Aad and J.-P. Hubaux,
"On Selfish Behavior in CSMA/CA Networks"
in Proceedings of IEEE INFOCOM Miami - FL, 2005,

[4] M. Raya, I. Aad, J.-P. Hubaux and A. Elfawal,
``DOMINO: Detecting MAC layer greedy behavior in IEEE 802.11 hotspots''
To appear in TMC, 2006

More information

Click to see video (16MB)

Click to see video in wmp

Scientific paper (pdf)

Executive summary (pdf)

From the press

Attack of the bandwidth-hogging hackers
The Register Newsletter
02/06/2004

Domino tool could knock down wi-fi cheats
Computer  Weekly
10/06/2004

The DOMINO Theory: How to Thwart Wi-Fi Cheats
LinuxWorld.com
09/06/2004

L’EPFL pousse Domino pour sécuriser le wi-fi
Tribune de Genève
21/06/2004

Gare aux vampires du haut débit!
24 Heures
27/06/2004

Contact persons

For scientific and technical inquiry :

Prof. Jean-Pierre Hubaux
School of Computer and
Communication Sciences
EPFL, Switzerland

jean-pierre.hubaux@epfl.ch
Phone: +4121 6932627
Fax:     +4121 6936610

For licensing inquiry :

Mehdi Aminian
Licensing officer
EPFL, Switzerland

mehdi.aminian@epfl.ch
Phone: +4121 6935461
Fax:     +4121 6937040