Introduction
different ways that a radio circuit and an antenna can cause an
electromagnetic wave to wiggle, and different bit representations offer
different advantages along with different disadvantages. The
consideration of the representation of bits based on some particular way
of jiggling the electromagnetic wave is the physical (PHY) layer of
communication. You'll be introduced to the various 802.11 PHY
standards and you'll see how they've evolved and how they differ.
There are a number of behavioral rules that an 802.11 WLAN
communicator must follow, and these rules, along with various PHY
standards, are stipulated by working groups within the IEEE. The
802.11 group is subdivided with letters of the alphabet to form the
802.11a, b, c, d, e, f, etc., all the way up to 802.11k and beyond! To be
an expert in the analysis of WLAN communication, it's necessary to
understand the expected rules of protocol behavior, and you will be
introduced to those rules, and the associated 802.11 standards, as you
read through this book.
Of course, a WLAN doesn't operate apart from some type of wired
network infrastructure. 802.11 radios ("access points") are typically
connected together through Ethernet cables, switches, and routers.
There can be wireless "backhaul" connections between access points,
but you're going to encounter a cable somewhere along the line. As
you read, you'll be introduced to these infrastructure components, and
you'll see how the whole system fits together.
The very thing that makes a wireless network attractive also creates a
security exposure. Since users don't need to physically "plug in" (an
attractive feature), it's possible for an unauthorized person to gain
access to the wireless network (a security exposure). Prior to 2004 the
only security options that were part of the 802.11 standard ("Wired
Equivalent Privacy, WEP") were determined to be flawed. Today, new
recommendations and standards ("Wi-Fi Protected Access, WPA" and
the 802.11i standards) have provided the capability to effectively
secure a wireless network. Security is a crucial part of wireless
network design and administration and awareness of security issues is a
key part of any WLAN engineer's education.
Today there are two groups of engineers in the communications arena
who are converging into the WLAN space. Neither group brings with
