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176 Chapter 4 • Communication Security: Wireless

large amount of frequently repeating and well-known patterns,WEP may be vul-
nerable to known plaintext attacks, although it does include safeguards against this
kind of attack.

EXAM WARNING
Make sure you completely understand WEP and its vulnerabilities. WEP
is discussed in more detail later in this chapter.

Wireless Local Area Networks

Wireless local area networks (WLANs) are covered by the IEEE 802.11 standards.
The purpose of these standards is to provide a wireless equivalent to IEEE 802.3
Ethernet-based networks.The IEEE 802.3 standard defines a method for dealing
with collisions (CSMA/CD), speeds of operation (10 Mbps, 100 Mbps, and faster),
and cabling types (Category 5 twisted pair and fiber).The standard ensures the
interoperability of various devices despite different speeds and cabling types.
As with the 802.3 standard, the 802.11 standard defines methods for dealing
with collision and speeds of operation. However, because of the differences in the
media (air as opposed to wires), the devices being used, the potential mobility of
users connected to the network, and the possible wireless network topologies, the
802.11 standard differs significantly from the 802.3 standard.As mentioned earlier,
802.11 networks use CSMA/CA as the method to deal with potential collisions,
instead of the CSMA/CD used by Ethernet networks, because not all stations on a
wireless network can hear collisions that occur on a network.
In addition to providing a solution to the problems created by collisions that
occur on a wireless network, the 802.11 standard must deal with other issues spe-
cific to the nature of wireless devices and wireless communications in general. For
example, wireless devices need to be able to locate other wireless devices, such as
APs, and communicate with them.Wireless users are mobile and therefore should
be able to move seamlessly from one wireless zone to another. Many wireless-
enabled devices such as laptops and hand-held computers, use battery power and
should be able to conserve power when not actively communicating with the net-
work.Wireless communication over the air needs to be secure to mitigate both pas-
sive and active attacks.

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