Khamis, 16 Disember 2010

How a Wi-Fi Network Works

In order to understand wireless networking at its simplest level, imagine about a pair of $5 walkie-talkies that you might purchase at mall. The walkie-talkies are small radios that can transmit and receive radio signals. When somebody talks into a walkie-talkie, his voice is picked up by a microphone, encoded onto a radio frequency and transmitted with the antenna.

Another walkie-talkie can receive the transmission with its antenna, decode the voice from the radio signal and drive a speaker. Simple walkie-talkies like this transmit at signal strength of about 0.25 watts, and they can transmit about 500 to 1,000 feet. In order to consider how these walkie-talkies can be used to communicate between the two computers, we have to require that each computer is equipped with a walkie-talkie. Then, we would give each computer a way to set whether it wants to transmit or receive. After that, we would give the computer a way to turn its binary 1s and 0s into two different beeps that the walkie-talkie could transmit and receive and convert back and forth between beeps and 1s/0s. This would actually work.

However, there are some problems with that. The problem would be that the data rate would be very slow. A $5 walkie-talkie is designed to handle the human voice. So, it would not be able to send very much data this way. Another problem is the walkie-talkies could not be used to connect to the internet. The radios used in Wi-Fi are not so different from the radios used in the walkie-talkies. They have the ability to transmit and receive. They also have the ability to convert 1s and 0s into radio waves and then back into 1s and 0s. However, there are major differences between them. Wi-Fi radios that work with the 802.11b and 802.11g standards transmit at 2.4 GHz, while those that comply with the 802.11a standard transmit at 5 GHz. Normal walkie-talkies normally operate at 49 MHz The higher frequency allows higher data rates. Wi-Fi radios use much more efficient coding techniques (process of converting 0’s and 1’s into efficient radio signals) that also contribute to the much higher data rates. The radios used for Wi-Fi also have the ability to change frequencies. For example, 802.11b cards can transmit directly on any of three bands, or they can split the available radio bandwidth into dozens of channels and frequency hop rapidly between them. The advantage of frequency hopping is that it is much more immune to interference and can allow dozens of Wi-Fi cards to talk simultaneously without interfering with each other.

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