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174 Chapter 4 • Communication Security: Wireless

physical connections between devices, such as how the medium and low bits (0s
and 1s) are encoded and decoded. Both FHSS and DSSS are implemented at the
PHY layer.The data link layer is divided into two sublayers, the Media Access
Control (MAC) and Logical Link Control (LLC) layers.
The MAC layer is responsible for such things as:
■ Framing data

■ Error control
■ Synchronization
■ Collision detection and avoidance

The Ethernet 802.3 standard, which defines the Carrier Sense Multiple Access
with Collision Detection (CSMA/CD) method for protecting against data loss as
result of data collisions on the cable, is defined at this layer.

Nitty Gritty Details
Head of the Class… exam wireless content will continue to grow as the networking world
Wireless networks and wireless networking in general are tested on the
Security+ exam, and as the test is revised in the future, the Security+

and corporate enterprises embrace more of the technology.
Unfortunately, we (the authors of this book) have to balance our goal of
providing a broad education with providing the specific knowledge
needed to pass the Security+ exam. The explanation of wireless, how it
works, and what you can do with it, is strictly background information to
further your understanding of the technology. Security+ exam questions
are not based on FHSS and DSSS technologies, so if this information
seems overly technical, do not panic! It is important, however, to know
this information as a security analyst. It is our mission to teach you every-
thing you need to know to transition from the Security+ exam to the real
world of security analysts.

CSMA/CD and CSMA/CA

In contrast to Ethernet 802.3 networks, wireless networks defined by the 802.11
standard do not use CSMA/CD as a method to protect against data loss resulting
from collisions. Instead, 802.11 networks use a method known as Carrier Sense
Multiple Access with Collision Avoidance (CSMA/CA). CSMA/CD works by
detecting whether a collision has occurred on the network and then retransmitting
the data in the event of such an occurrence. However, this method is not practical

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