Why would a person or organization be interested in deploying
wireless communication in their home or business? The most common
reason for both groups is flexibility. This being said, there are
some things to think about before jumping into the wireless world.
As is usually the case with networking, whenever one thing becomes
simpler, it usually complicates other things. In this case, it's
security and connectivity. This white paper presents a
straightforward description of basic wireless networking concepts
and wireless communication terminology.
Introduction
For home users, this means they have the ability to download
files, check e-mails, or watch streaming videos from anywhere
within their home without the burden of running CAT 5e UTP
(unshielded, twisted pair) cable to every room with jacks six feet
apart. Many people had one wired connection in their house, usually
in an office, and now they want to be able to open their laptop and
connect to the Internet from anywhere within their homes. With
wireless connections, they can surf the Internet, check e-mails,
and watch streaming videos, all while working in the kitchen
preparing dinner or in the living room while watching TV.
As far as businesses are concerned, flexibility means the
ability of employees to take their "desktop" with them and connect
to the network resources they need to get their job done. They can
work in the lunch room, a meeting room, or pick up their laptop
(which may have a specific application or confidential data stored
on it) and bring it to the conference room while maintaining
physical security. Being able to haul your laptop around with you
and connect wherever you are simplifies things in a way that we
could only dream of "back in the day."
This being said, there are some things to think about before
jumping into the wireless world. As is usually the case in the
wonderful world of networking, whenever one thing becomes simpler,
it almost always complicates something else. In this case, security
and connectivity are going to be our main concerns.
Basic Connectivity
Wireless communication refers to the transmission of
electromagnetic waves (radio frequencies) and the electronic data
carried on those waves. The upside of wireless communication is
that we can transmit signals to and from locations that would be
impractical using wires or cables.
The downside is that these waves can be interfered with in
numerous ways. You have probably experienced this while driving
down the road listening to your FM radio. Signals tend to be weaker
or stronger depending on the distance between the receiver (your
car's antenna) and transmitter (the radio stations transmitting
antenna). In addition, simply driving through a small valley or
under high voltage wires can disrupt transmission. The price for
flexibility is that we have to expect and deal with these sorts of
challenges in a wireless environment.
The FCC has provided several frequency ranges that wireless
transmissions, such as the wireless access points that we are
familiar with, we are permitted to use. Much in the way that FM
radio stations must use frequencies between 88.1 MHz and 108.1 MHz,
we are given the ranges of 2.4 GHz through 2.4835 GHz (let's just
call it 2.4 GHz shall we?) In addition, we're allowed to use the
5.725 GHz through 5.850 GHz range. These frequency ranges are
broken into smaller "channels" that can be used to transmit
data.
However, since these channels overlap, not all of the channels
are made available for us to transmit on. For example, the 2.4 GHz
range is broken into 11 22MHz-wide channels but because of the
tendency for transmissions to overlap from one channel into the
next, only 3 channels, (1, 6 and 11) are typically used. The 5 GHz
range is broken into 23 non-overlapping 20MHz channels.
One nice thing is that these ranges provide no "exclusive use,"
which means, unlike FM radio stations, we don't have to purchase
the right to transmit exclusively in that range. We can all use
them without paying a fee. These ranges are called the ISM
(industry, scientific, and medical) frequency band. Of course, when
anything is free people will basically step on each other to get
access to it. That means that there are a number of devices that
transmit in these ranges; mostly in the 2.4 GHz range: cordless
phones, baby monitors, wireless game controllers, microwave ovens,
etc. A wireless network must compete, potentially, with many of
these devices.
How Do We Put Data on the Radio Waves?
This is a great question to ask, but a detailed answer is beyond
the scope of this white paper. However, to put it simply, we use a
process called "modulation." Modulation refers to the changing of a
tone or signal (think of the sine wave and making it longer or
shorter, narrower or wider) and adding "data" to that wave using
something called "encoding." Now, there are several modulation
techniques and several encoding techniques used on each of them,
but let's just touch on one or two.