CCNA Wireless Official Exam Certification Guide part 4 ppt

Cisco Published 640-721 IUWNE Exam Topics
Covered in This Part
Describe WLAN fundamentals
■ Describe basics of spread spectrum technology (modulation, DSS, OFDM, MIMO,
Channels reuse and overlap, Rate-shifting, CSMA/CA)
■ Describe the impact of various wireless technologies (Bluetooth, WiMAX, ZigBee,
cordless phone)
■ Describe wireless regulatory bodies, standards and certifications (FCC, ETSI,
802.11a/b/g/n, WiFi Alliance)
■ Describe WLAN RF principles (antenna types, RF gain/loss, EIRP, refraction, reflec-
tion, ETC)
■ Describe networking technologies used in wireless (SSID —> WLAN_ID —>
Interface — >VLAN, 802.1q trunking)
■ Describe wireless topologies (IBSS, BSS, ESS, Point-to-Point, Point-to-Multipoint,
basic Mesh, bridging)
■ Describe frame types (associated/unassociated, management, control, data)
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Chapter 1 Introduction to Wireless Networking Concepts
Chapter 2 Standards Bodies
Chapter 3 WLAN RF Principles
Chapter 4 WLAN Technologies and Topologies
Chapter 5 Antenna Communications
Chapter 6 Overview of the 802.11 WLAN Protocols
Chapter 7 Wireless Traffic Flow and AP Discovery
Chapter 8 Additional Wireless Technologies
Chapter 9 Delivering Packets from the Wireless to Wired Network
Part I: Wireless LAN
Fundamentals
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This chapter covers the following subjects:
Wireless Local-Area Networks: A brief history

of wireless networking and some of the basic con-
cepts.
How Bandwidth Is Achieved from RF
Signals: The frequency spectrum used in RF
transmissions.
Modulation Techniques and How They
Work: How binary data is represented and trans-
mitted using RF technology.
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CHAPTER 1
Introduction to Wireless
Networking Concepts
Table 1-1 “Do I Know This Already?” Section-to-Question Mapping
Foundation Topics Section Questions
Wireless Local-Area Networks 1–2
How Bandwidth Is Achieved from RF Signals 3–6
Modulation Techniques and How They Work 7–10
Perhaps this is the first time you have ever delved into the world of wireless networking.
Or maybe you have been in networking for some time and are now beginning to see the
vast possibilities that come with wireless networking. Either way, this chapter can help
you understand topics that are not only tested on the CCNA Wireless exam but provide a
good foundation for the chapters to come. If you are comfortable with the available fre-
quency bands, the modulation techniques used in wireless LANs, and some of the stan-
dards and regulatory bodies that exist for wireless networking, you may want to skip to
Chapter 2, “Standards Bodies.”
This chapter provides a brief history of wireless networks and explores the basics of radio
technology, the modulation techniques used, and some of the issues seen in wireless LANs.
You should do the “Do I Know This Already?” quiz first. If you score 80 percent or higher,
you might want to skip to the section “Exam Preparation Tasks.” If you score below 80
percent, you should spend the time reviewing the entire chapter. Refer to Appendix A,

“Answers to the ‘Do I Know This Already?’ Quizzes” to confirm your answers.
“Do I Know This Already?” Quiz
The “Do I Know This Already?” quiz helps you determine your level of knowledge of this
chapter’s topics before you begin. Table 1-1 details the major topics discussed in this chap-
ter and their corresponding quiz questions.
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1. Which of the following accurately describes the goal of RF technology?
a. To send as much data as far as possible and as fast as possible
b. To send secure data to remote terminals
c. To send small amounts of data periodically
d. To send data and voice short distances using encryption
2. Which of the following is a significant problem experienced with wireless networks?
a. Infection
b. Policing
c. Transmission
d. Interference
3. Which two of the following are unlicensed frequency bands used in the United
Stated? (Choose two.)
a. 2.0 MHz
b. 2.4 GHz
c. 5.0 GHz
d. 6.8 GHz
4. Each 2.4-GHz channel is how many megahertz wide?
a. 22 MHz
b. 26 MHz
c. 24 MHz
d. 28 MHz
5. How many nonoverlapping channels exist in the 2.4-GHz ISM range?
a. 9
b. 3

c. 17
d. 13
6. The 5.0-GHz range is used by which two of the following 802.11 standards?
(Choose two.)
a. 802.11
b. 802.11b/g
c. 802.11n
d. 802.11a
6 CCNA Wireless Official Exam Certification Guide
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Chapter 1: Introduction to Wireless Networking Concepts 7
7. Which three of the following modulation techniques do WLANs today use?
(Choose three.)
a. OFDM
b. AM
c. FM
d. DSSS
e. MIMO
8. DSSS uses a chipping code to encode redundant data into the modulated signal.
Which two of the following are examples of chipping codes that DSSS uses?
(Choose two.)
a. Barker code
b. Baker code
c. Complementary code keying (CCK)
d. Cypher block chaining (CBC)
9. DSSS binary phase-shift keying uses what method of encoding at the 1-Mbps data rate?
a. 11-chip Barker code
b. 8-chip CCK
c. 11-chip CCK
d. 8-chip Barker code

10. With DRS, when a laptop operating at 11 Mbps moves farther away from an access
point, what happens?
a. The laptop roams to another AP.
b. The laptop loses its connection.
c. The rate shifts dynamically to 5.5 Mbps.
d. The rate increases, providing more throughput.
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8 CCNA Wireless Official Exam Certification Guide
Foundation Topics
Wireless Local-Area Networks
Although wireless networking began to penetrate the market in the 1990s, the technology
has actually been around since the 1800s. A musician and astronomer, Sir William Her-
schel (1738 to 1822) made a discovery that infrared light existed and was beyond the visi-
bility of the human eye. The discovery of infrared light led the way to the electromagnetic
wave theory, which was explored in-depth by a man named James Maxwell (1831 to
1879). Much of his discoveries related to electromagnetism were based on research done
by Michael Faraday (1791 to 1867) and Andre-Marie Ampere (1775 to 1836), who were
researchers that came before him. Heinrich Hertz (1857 to 1894) built on the discoveries
of Maxwell by proving that electromagnetic waves travel at the speed of light and that
electricity can be carried on these waves.
Although these discoveries are interesting, you might be asking yourself how they relate
to wireless local-area networks (WLANs). Here is the tie-in: In standard LANs, data is
propagated over wires such as an Ethernet cable, in the form of electrical signals. The dis-
covery that Hertz made opens the airways to transfer the same data, as electrical signals,
without wires. Therefore, the simple answer to the relationship between WLANs and the
other discoveries previously mentioned is that a WLAN is a LAN that does not need ca-
bles to transfer data between devices, and this technology exists because of the research
and discoveries that Herschel, Maxwell, Ampere, and Hertz made. This is accomplished
by way of Radio Frequencies (RF).
With RF, the goal is to send as much data as far as possible and as fast as possible. The

problem is the numerous influences on radio frequencies that need to be either overcome
or dealt with. One of these problems is interference, which is discussed at length in
Chapter 5, “Antennae Communications.” For now, just understand that the concept of
wireless LANs is doable, but it is not always going to be easy. To begin to understand how
to overcome the issues, and for that matter what the issues are, you need to understand
how RF is used.
How Bandwidth Is Achieved from RF Signals
To send data over the airwaves, the IEEE has developed the 802.11 specification, which de-
fines half-duplex operations using the same frequency for send and receive operations on a
WLAN. No licensing is required to use the 802.11 standards; however, you must follow the
rules that the FCC has set forth. The IEEE defines standards that help to operate within
the FCC rules. The FCC governs not only the frequencies that can be used without li-
censes but the power levels at which WLAN devices can operate, the transmission tech-
nologies that can be used, and the locations where certain WLAN devices can be
deployed.
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Chapter 1: Introduction to Wireless Networking Concepts 9
Note: The FCC is the regulatory body that exists in the United States. The European
Telecommunications Standards Institute (ETSI) is the European equivalent to the FCC.
Other countries have different regulatory bodies.
To achieve bandwidth from RF signals, you need to send data as electrical signals using
some type of emission method. One such emission method is known as Spread Spectrum.
In 1986, the FCC agreed to allow the use of spread spectrum in the commercial market
using what is known as the industry, scientific, and medical (ISM) frequency bands. To
place data on the RF signals, you use a modulation technique. Modulation is the addition
of data to a carrier signal. You are probably familiar with this already. To send music,
news, or speech over the airwaves, you use frequency modulation (FM) or amplitude
modulation (AM). The last time you were sitting in traffic listening to the radio, you were
using this technology.
Unlicensed Frequency Bands Used in WLANs

As you place more information on a signal, you use more frequency spectrum, or band-
width. You may be familiar with using terms like bits, kilobits, megabits, and gigabits
when you refer to bandwidth. In wireless networking, the word bandwidth can mean two
different things. In one sense of the word, it can refer to data rates. In another sense of the
word, it can refer to the width of an RF channel.
Note: This book uses the term bandwidth to refer to the width of the RF channel and not
to data rates.
When referring to bandwidth in a wireless network, the standard unit of measure is the
Hertz (Hz). A Hertz measures the number of cycles per second. One Hertz is one cycle
per second. In radio technology, a Citizens’ Band (CB) radio is pretty low quality. It uses
about 3 kHz of bandwidth. FM radio is generally a higher quality, using about 175 kHz of
bandwidth. Compare that to a television signal, which sends both voice and video over the
air. The TV signal you receive uses almost 4500 kHz of bandwidth.
Figure 1-1 shows the entire electromagnetic spectrum. Notice that the frequency ranges
used in CB radio, FM radio, and TV broadcasts are only a fraction of the entire spectrum.
Most of the spectrum is governed by folks like the FCC. This means that you cannot use
the same frequencies that FM radio uses in your wireless networks.
As Figure 1-1 illustrates, the electromagnetic spectrum spans from Extremely Low Fre-
quency (ELF) at 3 to 30 Hz to Extremely High Frequency (EHF) at 30 GHz to 300 GHz.
The data you send is not done so in either of these ranges. In fact, the data you send using
WLANs is either in the 900-MHz, 2.4-GHz, or 5-GHz frequency ranges. This places you in
the Ultra High Frequency (UHF) or Super High Frequency (SHF) ranges. Again, this is just
a fraction of the available spectrum, but remember that the FCC controls it. You are
locked into the frequency ranges you can use. Table 1-2 lists the ranges that can be used in
the United States, along with the frequency ranges allowed in Japan and Europe.
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10 CCNA Wireless Official Exam Certification Guide
Table 1-2 Usable Frequency Bands in Europe, the United States, and Japan
Europe USA Japan Frequency
2.4 GHz 900 MHz

2.4 GHz ISM 2.0–2.4835 GHz
2.4 GHz 2.0–2.495 GHz
CEPT A UNII-1 5.15–5.25 GHz 5.15–5.25 GHz
CEPT A UNII-2 5.25–5.35 GHz
CEPT B UNII-2 Extended 5.47–5.7253 GHz
ISM 5.725–5.850 GHz
5.0 GHz 5.038–5.091 GHz
4.9 GHz 4.9–5.0 GHz
3 Hz
30 Hz
ELF
30 Hz
300 Hz
SLF
300 Hz
3 kHz
ULF
3 kHz
30 kHz
VLF
30 kHz
300 kHz
LF
300 kHz
3 MHz
MF
3 MHz
30 MHz
HF
30 MHz

300 MHz
VHF
300 MHz
3 GHz
UHF
3 GHz
30 GHz
SHF
30 GHz
300 GHz
EHF
The Entire Electromagnetic Radio Spectrum
CB Radio
26.965 MHz – 27.405 MHz
FM Radio
88.1 MHz – 108.1 MHz
802.11b/g
2.4000 MHz – 2.3835 MHz
802.11a
5.47 GHz – 5.725 GHz
Figure 1-1 Electromagnetic Spectrum
Table 1-2 clearly shows that not all things are equal, depending on which country you are in.
In Europe, the 2.4-GHz range and the 5.0-GHz range are used. The 5.0-GHz frequency
ranges that are used in Europe are called the Conference of European Post and Telecommu-
nication (CEPT) A, CEPT B, CEPT C, and CEPT C bands. In the United States, the 900-
MHz, 2.4-GHz ISM, and 5.0-GHz Unlicensed National Information Infrastructure (UNII)
bands are used. Japan has its own ranges in the 2.4- and 5.0-GHz range. The following sec-
tions explain the U.S. frequency bands in more detail.
Key
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Key
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Chapter 1: Introduction to Wireless Networking Concepts 11
22 MHz
Wide
22 MHz
Wide
22 MHz
Wide
1
111098765432Channel:
Figure 1-2 2.4-GHz Channels
900 MHz
The 900-MHz band starts at 902 MHz and goes to 928 MHz. This frequency range is
likely the most familiar to you because you probably had a cordless phone that operated
in this range. This is a good way to understand what wireless channels are. You might have
picked up your cordless phone only to hear a lot of static or even a neighbor on his cord-
less phone. If this happened, you could press the Channel button to switch to a channel
that did not have as much interference. When you found a clear channel, you could make
your call. The channel you were changing to was simply a different range of frequencies.
This way, even though both your phone and your neighbor’s were operating in the 900-
MHz range, you could select a channel in that range and have more than one device oper-
ating at the same time.
2.4 GHz
The 2.4-GHz range is probably the most widely used frequency range in WLANs. It is used
by the 802.11, 802.11b, 802.11g, and 802.11n IEEE standards. The 2.4-GHz frequency
range that can be used by WLANs is subdivided into channels that range from 2.4000 to

2.4835 GHz. The United States has 11 channels, and each channel is 22-MHz wide. Some
channels overlap with others and cause interference. For this reason, channels 1, 6, and 11
are most commonly used because they do not overlap. In fact, many consumer-grade wire-
less devices are hard set so you can choose only one of the three channels. Figure 1-2
shows the 11 channels, including overlap. Again, notice that channels 1, 6, and 11 do not
overlap.
With 802.11b and 802.11g, the energy is spread out over a wide area of the band. With
802.11b or 802.11g products, the channels have a bandwidth of 22 MHz. This allows three
nonoverlapping, noninterfering channels to be used in the same area.
The 2.4-GHz range uses direct sequence spread spectrum (DSSS) modulation. DSSS is dis-
cussed later in this chapter in the section “DSSS.” Data rates of 1 Mbps, 2 Mbps, 5.5 Mbps,
and 11 Mbps are defined for this range.
Key
Topi
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