CCNA Wireless Official Exam Certification Guide part 10 pps

62 CCNA Wireless Official Exam Certification GuideOutdoor Mesh Networks As you can see, bridges are a good way to connect remote sites.. The solution is to deploy a mesh network such as

62 CCNA Wireless Official Exam Certification Guide

Outdoor Mesh Networks

As you can see, bridges are a good way to connect remote sites However, suppose that you are operating in a point-to-multipoint topology, and the central site experiences con-gestion Who suffers? Just the central site? Just the remote site? No; the answer is every-one When two remote sites communicate through a central site, the central site makes all the difference

Assume that the central site goes down, as shown in Figure 4-10

Now the remote sites can’t communicate with each other or the central site This can be

a major issue to contend with The solution is to deploy a mesh network such as the one illustrated in Figure 4-11

Site A

Point-to-Multipoint

Figure 4-10 Wireless Bridge Issues

LWAPP

LWAPP

LWAPP

LWAPP

LWAPP

LWAPP

LWAPP

LWAPP

LWAPP

Wireless Mesh Controller

Wireless Mesh Controller

Figure 4-11 Wireless Mesh Solution

Key

Topic

Chapter 4: WLAN Technologies and Topologies 63

The mesh solution is appropriate when connectivity is important, because multiple paths can be used The IEEE is currently working on a mesh standard (802.11s) However, the solution discussed here is a Cisco solution in which a wireless controller, also shown in Figure 4-11, is involved

When you have a mesh network, some nodes (another term for APs in a mesh network)

are connected to a wired network Some nodes simply act as repeaters A mesh node re-peats data to nearby nodes More than one path is available, so a special algorithm is used

to determine the best path The alternative paths can be used when there is congestion or when a wireless mesh node goes down

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Exam Preparation Tasks

Review All the Key Topics

Review the most important topics from this chapter, denoted with the Key Topic icon Table 4-2 lists these key topics and the page number where you can find each one

Definition of Key Terms

Define the following key terms from this chapter, and check your answers in the glossary: WPAN, SIG, WLAN, IEEE, WMAN, WiMax, WWAN, GSM, CDMA, ad hoc, infrastruc-ture, distribution system, BSS, IBSS, STA, infrastructure device, BSA, ESA, roaming, SSID, BSSID, MBSSID, co-channel interference, WGB, aWGB, uWGB, repeater, node

Table 4-2 Key Topics for Chapter 4

Figure 4-8 Point-to-point wireless bridge topology 61 Figure 4-9 Point-to-multipoint wireless bridge topology 61

This chapter covers the following subjects:

Principles of Antennas: Covers antenna concepts

Common Antenna Types: Describes omnidirectional and directional antennas

Antenna Connectors and Hardware: Looks at some of the connectors used in wireless deploy-ments as well as other common hardware

CHAPTER 5

Antenna Communications

Table 5-1 “Do I Know This Already?” Section-to-Question Mapping

In any wireless network, the capability to propagate the signal is key Without that capa-bility, the whole concept of a wireless network falls apart In this chapter, you will learn about antenna principles, along with some common antenna and connector types

You should take the “Do I Know This Already Quiz?” first If you score 80 percent or higher, you may want to skip to the section “Exam Preparation Tasks.” If you score below

80 percent, you should review the entire chapter

“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 5-1 details the major topics discussed in this chap-ter and their corresponding quiz questions

1. Which of the following are types of polarization? (Choose all that apply.)

a. Vertical

b. Horizontal

c. Nautical

d. Circular

2. All Cisco antennas use what type of polarization?

a. Linear

b. Circular

c. Magnetic

d. Perpendicular

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3. In an electromagnetic wave, where is the magnetic wave found in relation to the elec-tric wave?

a. Parallel to the electric wave

b. At a 45-degree angle to the electric wave

c. Perpendicular (at a 90-degree angle)

d. There is no magnetic wave

4. How many antennas are used with diversity?

a. Three

b. Four

c. One

d. Two

5. What does diversity listen to when choosing a better antenna to use?

a. The destination MAC address

b. The preamble

c. The data

d. The source MAC address

6 How far apart should antennas be placed when using diversity?

a. 2 meters

b. Two wavelengths

c. One wavelength

d. 1 meter

7 True or false: Two antennas using diversity can cover two areas.

a. True

b. False

8. What are the main families of antennas? (Choose all that apply.)

a. Omnidirectional

b. Unidirectional

c. Directional

d. Yagi

9. In relation to sending a linear waveform, the horizontal plane (H-plane) is also called what?

a. Vertical plane

b. Azimuth

c. Axis

d. Linear plane

Chapter 5: Antenna Communications 69

10. To display the coverage from top to bottom, what plane is represented?

a. A-plane

b. E-plane

c. C-plane

d. Airplane

11. The 2.2 dipole antenna is designed for what type of deployment?

a. Indoor omnidirectional

b. Indoor directional

c. Outdoor point-to-point

d. Outdoor omnidirectional

12. Which antenna is considered a “special” omnidirectional antenna?

a. AIR-ANT1728

b. AIR-ANT3338

c. AIR-ANT2485P-R

d. AIR-ANT3213

13. A yagi antenna is best used in what setting or settings? (Choose all that apply.)

a. Warehouse where multiple antennas are lined up

b. Conference room

c. Point-to-point over long distances

d. Long hallways

14. True or false: A parabolic dish antenna uses a wide RF path

a. True

b. False

15. For mounting reasons, what can be changed on a parabolic antenna?

a. Polarity

b. Diversity

c. Shape

d. Radiation pattern

16. The AIR-ANT3213 uses how many antennas?

a. Two

b. Four

c. Six

d. One

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17. Cisco uses which types of connectors? (Choose all that apply.)

a. SMA

b. N-connector

c. RP-TNC

d. TNC

18. To lower the amount of energy being sent to the antenna, which of the following devices could be used?

a. Amplifier

b. Attenuator

c. Lightning arrestor

d. Fiber-patch

19. To increase the amount of energy, which of the following devices could be used?

a. Amplifier

b. Attenuator

c. Lightning arrestor

d. Fiber-patch

20. True or false: Lightning arrestors are designed to withstand a full lightning strike

a. True

b. False

Chapter 5: Antenna Communications 71

Foundation Topics

Principles of Antennas

If someone asked you what the most important part of a wireless network is, what would you say? I’d have to say the antenna Why? Without it, you have a nice little AP that can offer network services for anyone within about 3 feet But that’s not what you want You want to make sure that your space is properly covered You need antennas to do this In fact, you need the right antennas to do this In this section you will learn about the factors

involved in dealing with antennas, which include polarity and diversity.

Polarization The goal of an antenna is to emit electromagnetic waves The electro portion of the term electromagnetic describes the wave and that it can move in different ways The way that it moves is its polarization There are three types of polarization:

■ Vertical

■ Horizontal

■ Circular

As shown in Figure 5-1, vertical polarization means that the wave moves up and down in

a linear way Horizontal polarization means that the wave moves left and right in a linear

way

The third type of polarization,circular polarization, indicates that the wave circles as

it moves forward, as illustrated in Figure 5-2

The electric field is generated by stationary charges, or current There is also a magnetic field—hence the term electromagnetic The magnetic field is found perpendicular (at a 90-degree angle) to the electric field This magnetic field is generated at the same time as the electric field; however, the magnetic field is generated by moving charges Cisco antennas are always vertically polarized in wireless networks This makes the electric field vertical

Why is this important? The importance is that the antenna is designed to propagate sig-nals in a certain direction Here is where installation errors can hurt you For example, if you have a long tube-like antenna, it would face up/down If you placed it flat instead, the signal would propagate in a different direction and would end up degraded

Although this is not a huge factor in indoor deployments, it can be in outdoor ments Usually other factors degrade your wireless signal propagation on indoor deploy-ments

Diversity

By now you should understand what the multipath issue is Traffic takes different paths because of the obstacles in the wireless path One way to deal with multipath issues is to use two antennas on one AP Diversity is the use of two antennas for each radio to

in-crease the odds that you receive a better signal on either of the antennas