Question 88 - CWNA-109 discussion

Elevators are a common building item that frequently causes RF shadow and must be accounted for in coverage plans. RF shadow is a term that describes an area where wireless signals are blocked or significantly weakened by an obstacle or an object that absorbs or reflects RF energy. RF shadow can cause lack of coverage or poor performance in a WLAN because wireless devices in those areas may not be able to communicate with access points or other devices. RF shadow can be mitigated by adjusting access point placement, antenna orientation, transmit power level, or channel selection to avoid or overcome the obstacle or object that causes it. Elevators are a common building item that frequently causes RF shadow because they are made of metal and they move up and down within a shaft. Metal is a material that has high attenuation and reflection values, which means it can block or bounce off wireless signals very effectively. A moving elevator can create dynamic RF shadow that changes depending on its position and direction. Therefore, elevators must be accounted for in coverage plans to ensure adequate WLAN coverage and performance throughout the facility. The other options are not common building items that frequently cause RF shadow or must be accounted for in coverage plans. Wooden doors are not likely to cause RF shadow because they are made of wood, which is a material that has low attenuation and reflection values, which means it can pass through or slightly weaken wireless signals. Carpeted floors are not likely to cause RF shadow because they are made of fabric, which is a material that has low attenuation and reflection values, which means it can pass through or slightly weaken wireless signals. Cubicle partitions are not likely to cause RF shadow because they are made of thin plastic or cardboard, which are materials that have low attenuation and reflection values, which means they can pass through or slightly weaken wireless signals.Reference:CWNA-109 Study Guide, Chapter 13: Wireless LAN Site Surveys - Types & Processes , page 433