What Is Wi-Fi?
The very short version is that Wi-Fi is a way for wireless
devices to communicate.
Wi-Fi, short for wireless
fidelity, is the Wi-Fi Alliance's name for a wireless standard, or
protocol, used for wireless communication. I'll tell you a bit more about this
wireless standard and its variations, known collectively as IEEE 802.11, in Chapter 2, "Understanding Wi-Fi." (IEEE
stands for the Institute of Electrical and Electronics Engineers, which defines
the standard.)
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The Wi-Fi Alliance is a not-for-profit organization that
certifies the interoperability of wireless devices built around the 802.11
standard. The goals of the Wi-Fi Alliance are to promote interoperability of
devices based on 802.11, and, presumably, to promote and enhance the standard.
For better or worse, this is no neutral organization. The
members of the Wi-Fi Alliance are manufacturers that build 802.11 devices. As of
this writing, there are 205 companies that belong to the Wi-Fi Alliance and more
than 900 products that have been certified as Wi-Fi interoperable.
The promise that the Wi-Fi Alliance makes is that if you buy an
802.11 device with the Wi-Fi seal of certification, the device will work
seamlessly with any other Wi-Fi certified device.
You can find more information about the Wi-Fi Alliance at the
Alliance's Web site, www.wi-fi.org. |
Standards and protocols are mostly of interest to engineers
(however, see the sidebar "What Is a
Standard?" for more information if you are curious).
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The words standard and protocol are
essentially synonymous (protocol is a slightly more technical term). When used
in its engineering context, a standard means the technical form of something
such as a message or a communication. In other words, a standard might specify
how the communication is made.
If you know the standard, you know how to decode the message.
In order to work with a standard (called complying with a standard), a device needs to know both
how to encode into the standard and decode from the standard.
A standard for working with communications, such as the Wi-Fi
standard, will generally involve specifications both at the hardware and the
software level (in geek-speak, these levels are called layers).
You can think of the standard as a kind of secret handshake
that gets you into a club. If you (or your wireless device) know how the secret
handshake works, you can find out what the other people in the club (the other
wireless devices) are actually saying. |
But Wi-Fi has garnered a huge amount of attention from people
who would normally be unconcerned about engineering details: in other words,
normal human beings like you and me. Students, professionals, homemakers,
English Lit majors, and office workers are all talking about Wi-Fi.
The really big question is: Why is Wi-Fi getting all this
attention? I'll get to that soon. I'll also show you how Wi-Fi can change your
life (for real!). But first I'd like to tell you a little bit more about what
Wi-Fi is.
For now, you need to know that Wi-Fi devices are certified
interoperable and run on some flavor of 802.11, a medium-range wireless
networking standard. 802.11 runs at speeds roughly comparable to those of wired
networks. (I'll be telling you in more detail about transmission speeds in Chapter 2.)
Wireless Spectrums
Unlike many other wireless standards, 802.11 runs on "free"
portions of the radio spectrum. This means that (unlike cell telephone
communications) no license is required to broadcast or communicate using 802.11
(or Wi-Fi).
The free portions of the radio spectrum used by 802.11 (and
Wi-Fi) are the 2.4GHz band, and, more recently, the 5GHz band. As you may know,
many household appliances such as microwave ovens and (most significantly)
wireless telephone handsets also use these free spectrums.
With a wireless telephone handset, a base station is connected
to the telephone line, and the handset communicates with the base station over
the "free" radio frequency, so that you can roam about your home or office while
talking on the phone. Clearly, these wireless telephone handsets are not the
same thing as cell phones, which do not connect to a telephone wire at all and
use licensed portions of the spectrum.
 |
In this increasingly complex world of ours, there are more and
more appliances and devices that broadcast and receive wireless signals, many of
them on the same "free" radio spectrums used by
Wi-Fi. |
The 802.11 (and Wi-Fi) standard includes what is called a physical layer. This physical layer uses something
known as Direct Sequence Spread Spectrum technology (DSSS) to prevent collisions
and avoid interference between devices operating on the same spectrum. You'll
find much the same kind of technology in your wireless telephone handset. The
idea here is that you don't want the signal coming out of your microwave unit to
interfere with your email (or vice versa).
In addition to its physical layer, each 802.11 Wi-Fi device has
an access control layer. The access control layer
specifies how a Wi-Fi device, such as a mobile computer, communicates with
another Wi-Fi device, such as a wireless access point.
tip
 |
If you find that your Wi-Fi device is getting interference from
some other appliance such as a microwave or wireless telephone, one of the first
things to try is moving either your Wi-Fi device, or the other device, to a new
physical location. |
A recent addition to the Wi-Fi standard is the Wi-Fi Protected
Access solution (WPA). WPA will be explained in greater detail in Chapter 19, "Securing Your Wi-Fi
Network."
Together, the physical and access control layers, along with
extensions intended to implement extra features (such as WAP for security) make
up the 802.11 Wi-Fi standard.
Using Wi-Fi
If you've picked up this book, you probably have a use in mind
for Wi-Fi. More precisely, you have a use in mind for a device that uses the
Wi-Fi standard to broadcast and receive information.
The two most common uses for these devices both involve
freedom:
-
You can work almost anywhere by using a mobile Wi-Fi device to
connect to the Internet without wires when away from your home or office.
-
You can free yourself from the need to drill holes and snake
wires by creating a network at the home or office using Wi-Fi
devices.
In this chapter, I'll give you a picture of the hundred-mile
view of each of these important uses for Wi-Fi devices. Your perspective is
going to be pretty different if you've bought this book to learn how best to
take your laptop on the road (or what kind of mobile device to buy) than if
you've bought this book to learn how to create a wireless network.
Some preliminary footwork is necessary to both topics. These
preliminaries are explained in this first part of the book, "Why Wi-Fi?"
But if you're reading this book to learn to travel with Wi-Fi,
I've got lots of information and goodies for you (see Chapter 3, "Hitting the Road with Wi-Fi," and Part III, "Going Mobile with
Wi-Fi"). On the other hand, if your primary interest is in setting up a wireless
network, you may just want to turn straight away to Part IV, "Creating a Wi-Fi Network."
You'll find everything you always wanted to know about buying
and configuring a Wi-Fi device in Part II, "Setting Up Your Computer for Wi-Fi."
Part V,
"Securing Your Wi-Fi Computer and Network," provides plentiful information about
that perennially pesky topic, security and wireless computing.
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