Wireless Communications

Wireless LANs enable users to communicate without any cabling. However, devices on these wireless LANs need to communicate with the devices on the "wired LANs," so this seemed like an appropriate place to cover the basics of wireless LANs.

Wireless communication happens all around us—literally. Cordless phones are relatively common, with commmunications between the phone and the base unit happening using radio waves. Similarly, mobile phones use radio waves to communicate to a transmitter and receiver on a cell tower nearby. Your TV remote control even performs some basic wireless communication using infrared waves.

Wireless communication uses some form of electromagnetic energy that passes through space. The energy propagates through the air at varying wavelengths. Depending on the wavelength of the energy, the energy might be visible or not. Given the large number of applications for wireless in the world, different wavelengths of energy are given different names, such as infrared for one range, radio frequency for another, and so on.

Electromagnetic energy actually can pass through matter, but often the matter reflects the energy to some degree and absorbs part of the energy as well. Some wavelengths require a line-of-sight for communication to happen because the wavelengths do not pass through matter well. For instance, a TV remote control using infrared typically requires a line-of-sight. Others, such as the wavelengths used for your cell phone, do not require line-of-sight but are affected to some degree by the number, thickness, and materials in the obstructions the phone and the cell tower. Many of you have probably walked around a building trying to find a place with good reception for your mobile phone—the problems are caused in part to the building absorbing and reflecting some of the energy.

Wireless LANs have become hugely popular in companies as well as in the home. The beauty of all wireless communication, including wireless LANs, is the lack of wires. No cables are required, and there's no need to open up walls, get a ladder to get up in the ceiling, or pay $100 plus per cable to get new cables run. The downsides relate to the speeds (generally less than those of wired LANs today), security risks (anyone nearby can attempt to eavesdrop), and the extra engineering effort to make sure you have enough coverage in the area in which you allow people to roam with their wireless devices.

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