[2024年01月09日]CWNA-108認定ガイド問題と解答トレーニング
CWNA-108認定お試しセット最新CWNA-108のPDF問題集
質問 # 19
What factor does not influence the distance at which an RF signal can be effectively received?
- A. Free Space Path Loss
- B. Receiving station's radio sensitivity
- C. Transmitting station's output power
- D. Receiving station's output power
正解：B
質問 # 20
What frame type is used to reserve the wireless medium for the transmission of high data rate frames that may not be understood by all clients connected to the BSS?
- A. ACK
- B. PS-Poll
- C. Beacon
- D. RTS
正解：D
解説：
Explanation
The frame type that is used to reserve the wireless medium for the transmission of high data rate frames that may not be understood by all clients connected to the BSS is RTS. RTS stands for Request to Send and is a control frame that is sent by a station to request access to the medium for a specified duration. The RTS frame contains the source and destination MAC addresses, as well as a Network Allocation Vector (NAV) value that indicates how long the medium will be occupied. The destination station responds with a Clear to Send (CTS) frame that echoes the NAV value and grants permission to the source station. All other stations in the BSS hear either the RTS or CTS frame and update their NAV timers accordingly, deferring their transmissions until the medium is free. The RTS/CTS mechanism can be used to prevent hidden node problems, reduce collisions, and protect high data rate frames that use features such as 802.11n or 802.11ac that may not be compatible with legacy stations. ACK, Beacon, and PS-Poll are not used to reserve the medium for high data rate frames. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 112; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 102.
質問 # 21
The IEEE 802.11-2012 standard requires VHT capable devices to be backward compatible with devices using which other 802.11 physical layer specifications (PHYs)?
- A. ERP-PBCC
- B. OFDM
- C. DSSS-OFDM
- D. HR/DSSS
正解：B
解説：
Explanation
OFDM (Orthogonal Frequency Division Multiplexing) is the physical layer specification (PHY) that VHT capable devices must be backward compatible with according to the IEEE 802.11-2012 standard. VHT (Very High Throughput) is a PHY and MAC enhancement that is defined in the IEEE 802.11ac amendment and is also known as Wi-Fi 5. VHT operates only in the 5 GHz band and uses features such as wider channel bandwidths (up to 160 MHz), higher modulation schemes (up to 256-QAM), more spatial streams (up to eight), multi-user MIMO (MU-MIMO), beamforming, and VHT PHY and MAC enhancements. VHT can achieve data rates up to 6.9 Gbps.
According to the IEEE 802.11-2012 standard, VHT capable devices must be backward compatible with devices using OFDM PHY, which is defined in the IEEE 802.11a amendment and is also used by IEEE
802.11g, IEEE 802.11n, and IEEE 802.11h amendments. OFDM operates in both the 2.4 GHz and 5 GHz bands and uses features such as subcarriers, symbols, guard intervals, and OFDM PHY and MAC enhancements. OFDM can achieve data rates up to 54 Mbps.
Backward compatibility means that VHT capable devices can interoperate with OFDM devices on the same network by using common features and parameters that are supported by both PHYs. For example, VHT capable devices can use a channel bandwidth of 20 MHz, a modulation scheme of BPSK, QPSK, or 16-QAM, one spatial stream, no beamforming, and OFDM PHY and MAC headers when communicating with OFDM devices. Backward compatibility also means that VHT capable devices can fall back to OFDM mode when the signal quality or SNR is too low for VHT mode. References: 1, Chapter 3, page 123; 2, Section 3.2
質問 # 22
Which IEEE 802.11 physical layer (PHY) specification includes support for and compatibility with both ERP and HR/DSSS?
- A. OFDM (802.11a)
- B. DSSS (802.11-Prime)
- C. HT (802.11n)
- D. VHT (802.11ac)
正解：C
質問 # 23
What wireless networking term describe the increase of RF energy in an intentional direction with the use of an antenna?
- A. Directed Radiation
- B. Beam Digression
- C. Passive Gain
- D. Active Amplification
正解：C
質問 # 24
Prior to association, what parameter can 802.11 client devices measure and use to select the optimal access point for association?
- A. Proximity to potential access points
- B. Average round trip time to reach the Internet DNS server
- C. Average round trip time to reach the IP router
- D. Signal strength of access point beacons received
- E. Retry rate of probe request and response frames
正解：D
質問 # 25
ABC Company has thousands of Wi-Fi users accessing their network on a daily basis. Their WLAN consists of 700 access points, 6 WLAN controllers, and a wireless network management system.
What network functions are performed by the enterprise-class WNMS?
- A. Generating, encrypting, and decrypting 802.11 frames and collecting RF radio data.
- B. Centralized bridging of guest data traffic and application of firewall and QoS policies to data
- C. Management of WLAN controller configuration and provisioning of firmware updates
- D. Radio management, fast roaming, key caching, and other centralized control plane operations
正解：C
質問 # 26
When considering data rates available in HT and VHT PHY devices, in addition to the modulation, coding, channel width, and spatial streams, what impacts the data rate according to the MCS tables?
- A. guard interval
- B. Frequency band in use
- C. client drivers
- D. Antenna Height
正解：A
解説：
Explanation
The guard interval is a short period of time inserted between the symbols of an OFDM signal to prevent inter-symbol interference and improve the robustness of the transmission1. The guard interval can have different values depending on the 802.11 standard and the configuration of the device. For example, 802.11n supports two guard intervals: 800 ns (normal) and 400 ns (short)2. 802.11ac supports the same guard intervals as 802.11n, plus an optional 200 ns guard interval for 80 MHz and 160 MHz channels3. 802.11ax supports three guard intervals: 800 ns, 1600 ns, and 3200 ns4.
The guard interval affects the data rate because it determines the duration of each symbol. A shorter guard interval means more symbols can be transmitted in a given time, resulting in a higher data rate. However, a shorter guard interval also means less protection against inter-symbol interference, which may degrade the signal quality and increase the error rate. Therefore, there is a trade-off between data rate and reliability when choosing the guard interval.
The MCS tables for HT and VHT PHY devices show the data rates for different combinations of modulation, coding, channel width, spatial streams, and guard intervals. For example, for a VHT device using MCS 9 with QAM-256 modulation, 5/6 coding rate, 80 MHz channel width, and one spatial stream, the data rate is 433.3 Mbps with a normal guard interval (800 ns) and 486.7 Mbps with a short guard interval (400 ns)2. Therefore, the guard interval impacts the data rate according to the MCS tables.
質問 # 27
802. 11ax (HE) introduces Resource Units that can be used to allow communications with multiple devices at the same time, on the same channel, in the same BSS. What feature of 802.1 lax provides this functionality?
- A. TWT
- B. OFDMA
- C. Wi-Fi-LTE
- D. 6 GHz support
正解：B
解説：
Explanation
The feature of 802.11ax (HE) that provides this functionality is OFDMA. OFDMA stands for Orthogonal Frequency Division Multiple Access and is a technology that allows multiple devices to communicate simultaneously on the same channel in the same BSS. OFDMA works by dividing a channel into smaller subchannels called Resource Units (RUs), which are composed of groups of subcarriers or tones. Each RU can be assigned to a different device based on its bandwidth requirement and signal quality. This way, OFDMA can increase the efficiency and capacity of the channel by reducing overhead, contention, and latency.
OFDMA can also support both uplink and downlink multi-user transmissions using trigger frames and buffer status reports. 6 GHz support, TWT, and Wi-Fi-LTE are not features of 802.11ax that provide this functionality. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 226; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 216.
質問 # 28
You are using a tool that allows you to see signal strength for all Aps in the area with a visual representation. It shows you SSIDs available and the security settings for each SSID. It allows you to filter by frequency band to see only 2.4 GHz networks or only 5 GHz networks. No additional features are available.
What kind of application is described?
- A. WLAN scanner tool
- B. Site survey utility
- C. Protocol analyzer
- D. Spectrum analyzer
正解：A
質問 # 29
In a long-distance RF link, what statement about Fade Margin is true?
- A. The Fade Margin of a long-distance radio link should be equivalent to the receiver's low noise filter gain.
- B. Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading.
- C. The Fade Margin is a measurement of signal loss through free space and is a function of frequency and distance.
- D. A Fade Margin is unnecessary on a long-distance RF link if more than 80% of the first Fresnel zone is clear of obstructions.
正解：B
解説：
Explanation
Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading. It is the difference between the receiver's sensitivity and the actual received signal level. A higher Fade Margin indicates a more robust link that can withstand interference, attenuation, or other factors that may reduce the signal strength. A lower Fade Margin means that the link is more susceptible to failure or performance degradation. Fade Margin is usually expressed in decibels (dB) and can be calculated by subtracting the receiver sensitivity from the received signal level. References: 1, Chapter 2, page 51; 2, Section 2.1
質問 # 30
You are attempting to explain RF shadow and how it can cause lack of coverage. What common building item frequently causes RF shadow and must be accounted for in coverage plans?
- A. Carpeted floors
- B. Wooden doors
- C. Elevators
- D. Cubicle partitions
正解：D
質問 # 31
You are implementing a VHT-capable AP. Which one of the following channels is available in the
802.11-2016 standard, which was not available before the ratification of 802.11ac?
- A. 0
- B. 1
- C. 2
- D. 3
正解：B
質問 # 32
An IEEE 802.11 amendment is in the daft state. What impact does this draft amendment have on the 802.11 standard?
- A. No impact: Draft amendments do not become part of the standard until a working group is formed.
- B. Devices will be released based on the draft amendment and the draft amendment features are part of the standard.
- C. The standard is changed to reflect the new capabilities as soon as an amendment enters the draft stage.
- D. No impact: Until an amendment is ratified, it does not become part of the standard.
正解：D
解説：
Explanation
An IEEE 802.11 amendment is a proposed change or addition to the existing 802.11 standard, which defines the specifications and protocols for wireless LANs. An amendment goes through several stages of development, such as draft, sponsor ballot, and final approval, before it is ratified by the IEEE Standards Association and becomes part of the standard. Until then, it has no official impact on the standard, although some vendors may release products based on draft amendments to gain a competitive edge or to influence the final outcome of the amendment . References: [CWNA-109 Study Guide], Chapter 1: Overview of Wireless Standards, Organizations, and Fundamentals, page 25; [CWNA-108 Study Guide], Chapter 1: Overview of Wireless Standards, Organizations, and Fundamentals, page 23; [IEEE website], IEEE-SA Standards Development Process.
質問 # 33
You are installing an AP to be used by 27 laptops. All laptops will connect on the 5 GHz frequency band. A neighbor network uses channels 1 and 6. What channel should be used for this AP and why?
- A. Channel 11, because channels 1 and 6 are in use nearby
- B. Channel 1, because it is best to use the channel with the lowest frequency
- C. A 5 GHz channel, because channels 1 and 6 are 2.4 GHz channels they have no impact on the decision
- D. Channel 6, because it is always best to use this channel
正解：C
解説：
Explanation
A 5 GHz channel should be used for this AP because channels 1 and 6 are 2.4 GHz channels and they have no impact on the decision. The 5 GHz frequency band offers more non-overlapping channels than the 2.4 GHz frequency band, which reduces interference and improves performance. The 5 GHz frequency band also supports higher data rates and wider channel bandwidths than the 2.4 GHz frequency band, which increases capacity and throughput. The 5 GHz frequency band also has less interference from other devices and sources than the 2.4 GHz frequency band, which enhances reliability and quality of service. Therefore, it is recommended to use the 5 GHz frequency band for WLANs whenever possible. Channels 1 and 6 are two of the three non-overlapping channels in the 2.4 GHz frequency band (the other one is channel 11). They are used by a neighbor network in this scenario, but they do not affect the channel selection for this AP because they operate in a different frequency band than the 5 GHz frequency band. Channel 6 is not always best to use; it depends on the interference and congestion level in the environment. Channel 1 is not best to use because it has a lower frequency than channel 6; frequency does not determine channel quality or performance. Channel
11 is not best to use because it is also a 2.4 GHz channel and it may interfere with channels 1 and
6. References: CWNA-109 Study Guide, Chapter 4: Antenna Systems and Radio Frequency (RF) Components, page 113
質問 # 34
As you prepare for a site survey in a multi-floor corporate office, you have learned about several wireless devices that support connection-oriented, real-time applications. These applications are sensitive to service interruptions and require excellent signal quality, low latency, and low loss.
For that reason, it is important to identify sources of RF interference as well as building characteristics that would cause RF blockage or dead spots.
What systems or environmental characteristics are most likely to cause interference or RF blockage and disrupt service for these applications? (Choose 2)
- A. Narrow hallways
- B. RFID chokepoints
- C. Elevator shafts
- D. Workspace dividers
- E. Microwave ovens
正解：C、E
質問 # 35
What statement about 802.3, Clause 33 Power over Ethernet is true?
- A. Only midspan PSEs are supported.
- B. The lowest voltage drop is achieved when using CAT6 cable instead of Cat5 or CAT5e.
- C. Only endpoint PSEs are supported.
- D. When using CAT5 cabling, you increase the maximum draw available to the PD over that available with CAT6.
正解：B
解説：
https://www.cablinginstall.com/articles/2012/08/cat-6a-vs-cat-5e-poe.html
質問 # 36
What statement about 802.11 WLAN performance is true?
- A. In most WLANs, no special skill or tuning is required to get peak performance
- B. WLANs perform better as more wireless clients connect with each AP
- C. To get the best performance out of an AP, you should disable data rates of 72 Mbps and lower
- D. In modern networks, both centralized and distributed data forwarding work well for most standard office deployments
正解：C
質問 # 37
You are troubleshooting a problem with interference from a non-802.11 device. Given that the device is not a WLAN device, you cannot use a protocol analyzer and have chosen to use a spectrum analyzer. You want to view the signal from the interfering device over time to see the activity that is generating.
What common spectrum analyzer view should you use for this analysis?
- A. APs
- B. Clients
- C. Waterfall/Spectrogram
- D. Real-time FFT
正解：C
解説：
Explanation
質問 # 38
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CWNA-108認定試験は、Certified Wireless Network Professional（CWNP）組織によって実施されます。この試験は、無線ネットワーク技術、無線周波数（RF）技術、無線LANハードウェアおよびソフトウェア、ネットワーク設計および計画、サイト調査および展開、トラブルシューティング、および無線セキュリティなどの候補者の知識と理解をテストするよう設計されています。CWNP組織は、候補者の実用的な知識と実世界の経験をテストするよう設計された厳格な認定プログラムで知られています。
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