WIFI by Marshall Brain
WiFi is the wireless way to handle networking. It is also known as 802.11 networking and
wireless networking. The big advantage of WiFi is its simplicity. You can connect computers
anywhere in your home or office without the need for wires. The computers connect to the
network using radio signals, and computers can be up to 100 feet or so
The Walkie-Talkie Network
If you want to understand wireless networking at its simplest level, think
about a pair of $5 walkie-talkies that you might purchase at Wal-Mart.
These are small radios that can transmit and receive radio signals. When
you talk into a Walkie-Talkie, your 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 your
voice from the radio signal and drive a speaker.
Let's imagine that you want to connect two computers together in a network
using walkie-talkie technology:
You would equip each computer with a walkie-talkie.
You would give each computer a way to set whether it wants to transmit or
You 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. The only problem would be that the data rate
would be very slow. A $5 walkie-talkie is designed to handle the human
voice (and it's a pretty scratchy rendition at that), so you would not be
able to send very much data this way. Maybe 1,000 bits per second.
WiFi's Radio Technology
The radios used in WiFi are not so different from the radios used in $5
walkie-talkies. They have the ability to transmit and receive. They have
the ability to convert 1s and 0s into radio waves and then back into 1s
and 0s. There are three big differences between WiFi radios and
WiFi 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.
WiFi radios use much more efficient coding techniques that also
contribute to the much higher data rates. For 802.11a and 802.11g, the technique is
known as orthogonal frequency-division multiplexing (OFDM). For 802.11b,
it is called Complementary Code Keying (CCK). See this page for details.
The radios used for WiFi have the ability to change frequencies.
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 WiFi cards to
talk simultaneously without interfering with each other.
Because they are transmitting at much higher frequencies than a
Walkie-Talkie, and because of the encoding techniques, WiFi radios can
handle a lot more data per second. 802.11b can handle up to 11 megabits
per second (although 7 megabits per second is more typical, and 802.11b
may fall back as low as 1 or 2 megabits per second if there is a lot of
interference). 802.11a and 802.11g can handle up to 54 megabits per second
(although 30 megabits per second is more typical).