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

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)

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

CHAPTER 1

Introduction to Wireless Networking Concepts

Table 1-1 “Do I Know This Already?” Section-to-Question Mapping

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

Chapter 1: Introduction to Wireless Networking Concepts 7

7. Which three of the following modulation techniques do WLANs today use?

(Choose three.)

d. DSSS

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

Chapter 1: Introduction to Wireless Networking Concepts 9

Note: The FCC is the regulatory body that exists in the United States TheEuropean 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 likebits, kilobits, megabits, and gigabits

when you refer to bandwidth In wireless networking, the wordbandwidth 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 FreFre-quency (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

2.4 GHz 900 MHz

2.4 GHz 2.0–2.495 GHz CEPT A UNII-1 5.15–5.25 GHz 5.15–5.25 GHz

CEPT B UNII-2 Extended 5.47–5.7253 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

2.4

000 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

Topic

Key

Topic

Chapter 1: Introduction to Wireless Networking Concepts 11

22 MHz Wide

22 MHz Wide

22 MHz Wide

Channel:

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 usesdirect 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 Topic

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