This chapter covers the following subjects:The 802.11 Protocol Family Overview: A brief overview of the 802.11 family of WLAN protocols... What is the maximum data rate that the original
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dipole, radiation pattern, isotropic radiator, directional antenna, rubber duck, Yagi-Uda, parabolic dish, dual-patch “omnidirectional,” Reverse-Polarity Threaded Neill-Concelman (RP-TNC), N connector, attenuator, amplifier, lightning arrestor, splitter
References in This Chapter
Cisco Systems, “Cisco Aironet Antennas and Accessories Reference Guide,” http://tinyurl com/2v2dp2
Trang 3This chapter covers the following subjects:
The 802.11 Protocol Family Overview: A brief overview of the 802.11 family of WLAN protocols
The Original 802.11 Protocol: A look at the original 802.11 protocol
The 802.11b Protocol: A look at the 802.11b protocol
The 802.11g Protocol: A look at the 802.11g pro-tocol and how it operates with 802.11b clients
The 802.11a Protocol: A look at the 802.11a pro-tocol
The 802.11n Protocol: A look at the 802.11n draft standard
Trang 4CHAPTER 6
Overview of the 802.11 WLAN Protocols
The wireless space consists of numerous protocols Specifically in the WLAN area, the In-stitute of Engineers Electrical and Electronic Engineers (IEEE) has created several proto-cols within the 802.11 category to facilitate the networking process These protoproto-cols define the data rates, the modulation techniques, and more An understanding of these protocols is essential for any administrator of wireless networks
In this chapter, you will learn about the 802.11 family of protocols, including 802.11, 802.11a, b, and g In addition, you will gain an introduction to the 802.11n draft standard
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 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 6-1 details the major topics discussed in this chap-ter and their corresponding quiz questions
Table 6-1 “Do I Know This Already?” Section-to-Question Mapping
Foundation Topics Section Questions
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1. What organization standardizes the 802.11 set of protocols?
a. IANA
b. IEEE
c. FCC
d. ETSI
2. What is the maximum data rate that the original 802.11 protocol supports?
a. 1 Mbps
b. 5 Mbps
c. 2 Mbps
d. 3 Mbps
3. The original 802.11 protocol supported which two RF technologies? (Choose two.)
a. FHSS
b. CDMA
c. IETF
d. DSSS
4. The original 802.11 protocol operates in which frequency range?
a. 2.0 GHz
b. 900 MHz
c. 5.0 GHz
d. 2.4 GHz
5. The original 802.11 protocol operates in the ISM bands True or false?
a. True
b. False
6. 802.11b operates on which frequency range?
a. 2.0 GHz
b. 900 MHz
c. 5.0 GHz
d. 2.4 GHz
7. 802.11b has how many nonoverlapping channels?
a. 2
b. 3
c. 4
d. 8
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8. Which of the following modulation techniques are used by 802.11b? (Choose all that apply.)
a. DBPSK
b. 16-QAM
c. DQPSK
d. 64-QAM
9. What coding method is used by 802.11b? (Choose all that apply.)
a. Barker 11
b. CCK
c. Barker 8
d. QAM-CCK
10. Which 802.11b channels do not overlap? (Choose all that apply.)
a. 1
b. 3
c. 6
d. 11
11. What modulation technique is used by the 802.11g protocol? (Choose all that apply.)
a. DBPSK
b. DQPSK
c. QAM
d. Barker
12. What is the maximum data rate that the 802.11g protocol supports?
a. 22 Mbps
b. 48 Mbps
c. 54 Mbps
d. 90 Mbps
13. When no 802.11b clients are in an 802.11b/g cell, what information will be in the
AP beacon?
a. NON_ERP present: yes; Use Protection: no
b. NON_ERP present: no; Use Protection: yes
c. NON_ERP present: yes; Use Protection: yes
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14. What are two protection methods used by 802.11g clients when an 802.11b client is
in the cell? (Choose two.)
a. RTS/CTS
b. LMI
c. CTS to self
d. RTS to self
15. The 802.11a protocol is backward compatible only with 802.11g because they sup-port the same maximum data rates True or false?
a. True
b. False
16. An 802.11a client must support which data rates?
a. 6, 12, 24 Mbps
b. 11, 24, 54 Mbps
c. 6, 9, 12, 18, 24, 36, 48, 54 Mbps
d. 6, 11, 24, 48 Mbps
17. The 802.11a protocol operates in which frequency spectrum?
a. 2.0 GHz
b. 900 MHz
c. 5.0 GHz
d. 2.4 GHz
18. Which is not a valid modulation technique for 802.11a?
a. BPSK
b. QPSK
c. Barker 11
d. QAM
19. 802.11a uses the UNII-1, UNII-2, and UNII-3 bands Which bands are usable without
a license in Europe? (Choose all that apply.)
a. UNII-1
b. UNII-2
c. UNII-3
d. UNII-4.1
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20. The FCC and ETSI have imposed what requirements for use in the 2 and
UNII-3 bands? (Choose all that apply.)
a. DFC
b. TPC
c. CSMA/CA
d. MIMO
21. 802.11n supports multiple antennas using what technology?
a. MIMO
b. MAO
c. Multi-scan antenna output
d. Spatial coding
22. What type of multiplexing does 802.11n use?
a. Spatial
b. OFDM
c. DSSS
d. FHSS
23. What task does TxBF accomplish in 802.11n networks?
a. The signal is sent over multiple transmit antennas, improving performance at the receiver
b. The signal increases in gain to accomplish greater distances
c. The signal is spread across multiple channels and then re-created at the receiver
to negate interference issues on sidebands
d. The signal is bonded on a 40-MHz channel, giving you more bandwidth
24. How does 802.11n improve the throughput with acknowledgments?
a. It uses a 1-for-1 acknowledgment option; 1 sent = 1 acknowledged
b. It does not use acknowledgments
c. It uses block acknowledgments
d. It uses a 2-to-1 ratio of sent frames to acknowledgments
25. A device that has two transmit antennas and two receive antennas is referred to as which of the following?
a. Dual TxRx
b. 2X2
c. 2x
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Foundation Topics
The 802.11 Protocol Family Overview
The IEEE helps to standardize wireless protocols Those that you must be familiar with for the CCNA Wireless Exam are the 802.11 a/b/g and n protocols These four IEEE standards define the wireless family that is used in almost all wireless LANS today The standardiza-tion of wireless networking started with the original 802.11 protocol in 1997, and each protocol thereafter has simply added to the benefit of wireless technologies This chapter looks at the 802.11 protocol families, their history, and how they operate The 802.11 pro-tocols encompass the 2.4-GHz and 5-GHz range
The Original 802.11 Protocol
The original 802.11 protocol was where wireless LANs find there beginnings It is rare to find this original protocol in new hardware today, probably because it only operates at 1 and 2 Mbps The 802.11 standard describes frequency-hopping spread spectrum (FHSS), which operates only at 1 and 2 Mbps The standard also describes direct sequence spread spectrum (DSSS), which operates only at 1 and 2 Mbps If a client operates at any other data rate, it is considered non-802.11 compliant, even if it can use the 1- and 2-Mbps rates Table 6-2 highlights the characteristics of the original 802.11 protocol
The original 802.11 protocol falls within the industry, scientific, and medical (ISM) bands and operates only in the 2.4-GHz range The 2.4-GHz range has up to 14 channels depend-ing on the country you are in In the United States, the FCC allows channels 1 through 11
to be used This gives you 3 nonoverlapping channels: 1, 6, and 11 This is important be-cause you do not want to have APs and clients operating on the same channel placed near each other for interference reasons
The 802.11b Protocol
802.11b is a supplement to the 802.11 protocol To get an better feel for how the 802.11 protocols progressed, understand that technology moves faster than the standards do 802.11 was quickly outgrown because wired networks offered 10 Mbps versus the 1 and 2 Mbps of 802.11 Vendors developed methods of achieving higher data rates The danger in vendor-designed protocols, of course, is interoperability The job of the IEEE was simply
Table 6-2 The 802.11 Protocol
RF Technology FHSS and DSSS
Frequency Spectrum 2.4-GHz
Key
Topic
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to define a standard that all vendors could follow based on the proprietary implementa-tions that they were using
802.11b offers higher data rates—up to 11 Mbps—with backward compatibility at 1 and
2 Mbps At 1 and 2 Mbps, the same coding and modulation as 802.11 is used When oper-ating at the new speeds—5.5 Mbps and 11 Mbps—a different modulation and coding is used 802.11 uses Barker 11 coding, as covered in Chapter 1, “Introduction to Wireless Networking Concepts,” and 802.11b uses complementary code keying (CCK) for coding
For modulation, 802.11 uses differential binary phase-shift keying (DBPSK), whereas 802.11b uses differential quadrature phase-shift keying (DQPSK) The result is more data sent in the same period
802.11b was ratified in September 1999 The United States has 11 channels, the same as 802.11 In Europe, the ETSI defines 13 channels, and Japan has 14 802.11b allows dynamic rate shifting (DRS) to enable clients to shift rates to lower rates as they travel far-ther away from an AP and higher rates as they get closer to an AP Today, 802.11b is the most popular and most widely deployed wireless standard Table 6-3 gives some basic in-formation on the 802.11b standard
The 802.11g Protocol
The IEEE ratified 802.11g in June 2003 In addition to the four data rates of 802.11b, it added eight more The maximum data rate of 54 Mbps places 802.11g in the same speed range as 802.11a; however, it remains in the 2.4-Ghz frequency range On the lower end, 802.11g is still compatible with 802.11b, using the same modulation and coding as 802.11b for the 1-, 2-, 5.5-, and 11-Mbps rates To achieve the higher data rates, 802.11g uses or-thogonal frequency division multiplexing (OFDM) for modulation OFDM is the same modulation that 802.11a uses
There are still only three nonoverlapping channels With OFDM, you must be careful about power outputs; the power needs to be reduced to handle the peaks in the modula-tion technique and still fall within governmental regulamodula-tions Table 6-4 shows some details about 802.11g
Table 6-3 The 802.11b Protocol
Frequency Spectrum 2.4-GHz
Modulation DBPSK and DQPSK
Data Rates 1, 2, 5.5, 11 Mbps
Nonoverlapping Channels 1, 6, 11
Key Topic
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