Unlike the hacker perspective previously mentioned, a defender would like his or her wireless network signal to be attenuated as much as possible beyond the network's Sphere of Influence Limit (SOIL). However, defenders face a much tougher task because they have to balance the requirements of sufficient area coverage with the need to stop RF leakage. When combined with the fact that RF is not constrained by a wire like Ethernet is and flows freely through three-dimensional space, defenders have to resort to physical measures to attenuate the signal.
As a defender, you can use attenuation to your advantage by placing multiple obstacles in three-dimensional space to cause reflective, refractive, and absorptive effects to a given wireless signal and to use high-density materials such as sandwiched-metal office partitions and appropriately spaced wire-meshing to limit the ability of an hacker to receive your wireless signals. Aluminum-laced paint is another defensive option, with an early entrant being DefendAir Radio Shield paint, from a company called Force Field Wireless. Anti-RF wallpaper is in the cards as well, with British Aerospace reportedly having already developed a frequency selective surface (FSS) wallpaper that can be set to block particular frequencies while letting others through.
To combat diffraction, you may opt to use RF equipment with short wavelengths (i.e., high frequencies). An example is eschewing 802.11b/g-based equipment in favor of 802.11a-based equipment. This is because, as distance from a signal grows, a given signal may be unable to propagate around obstacles encountered, such as walls or buildings. This results in a "shadow zone" on the leeward side of an obstacle between the transmitter and the receiver. The shadow zone is an area void of the RF signal that is unable to bend around the obstruction. An attacker in this area would be unlikely to effect any RF-based communications with the signal source. Of course, the use of 802.11a in place of 802.11b/g requires a cost-benefit-analysis for corporate deployments because most equipment on the market is designed to be b/g compatible.
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