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Layer 1 DoS attacks > Contraptions of mass disruption - Pg. 123

102 CHAPTER 4 Low tech wireless hacking As with the other antenna attacks, mitigation can be accomplished with good phys- ical security by way of smart mounting and appropriate locked or hidden enclosures. In addition, in an enterprise environment with wireless sensors, monitoring APs and RF management tools would catch sudden spikes in signal or power changes. NOTE To discuss these next low tech hacks, we have to have a little bit of background on some of the more fundamental nuances of the technology. Wireless, because of the physical properties of RF, is a half-duplex system. Wireless things are listening and then either sending or receiving, not both simultaneously. Without getting into too much of the boring stuff, 802.11 systems use a combination of detection methods to determine whether it's okay to transmit. When one station wants to talk to an AP or another station, CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) kicks in to see if the airwaves are clear. If they're not, the station (and any others in range) will hold off until the RF medium isn't busy. The severity and footprint of a collision avoidance attack depend on how it was initiated. We'll look at a couple of specific scenarios, each with different methodologies and effective reaches.