2026年最新のCWNA-109問題集PDFでCWNA-109リアル試験問題解答
有効なCWNA-109テスト解答とCWNP CWNA-109試験PDF問題を試そう
CWNP CWNA-109 認定試験の出題範囲：
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質問 # 50
As an RF wave propagates through space, the wave front experiences natural expansion that reduces its signal strength in an area. What describes the rate at which this expansion happens?
- A. Fresnel zone thinning
- B. Ohm's law
- C. MU-MIMO
- D. Inverse square law
正解：D
解説：
The inverse square law states that the signal strength of an RF wave is inversely proportional to the square of the distance from the source. This means that as the distance from the transmitter increases, the signal strength decreases rapidly.
References: Wireless Network Administrator Official Study Guide, Chapter 3, page 64.
質問 # 51
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. DSSS-OFDM
- B. ERP-PBCC
- C. HR/DSSS
- D. OFDM
正解：D
解説：
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 aPHY 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 OFDMmode when the signal quality or SNR is too low for VHT mode. References: 1, Chapter 3, page 123; 2, Section 3.2
質問 # 52
You are reporting on the RF environment in your facility. The manager asks you to describe the noise floor noted in the report. Which of the following is the best explanation?
- A. The extra energy radiated by access points and client devices beyond that intended for the signal.
- B. The noise caused by elevators, microwave ovens, and video transmitters.
- C. The energy radiated by flooring materials that causes interference in the 2.4 GHz and 5 GHz bands.
- D. The RF energy that exists in the environment from intentional and unintentional RF radiators that forms the baseline above which the intentional signal of your WLAN must exist.
正解：D
解説：
The RF energy that exists in the environment from intentional and unintentional RF radiators that forms the baseline above which the intentional signal of your WLAN must exist is the best explanation of the noise floor noted in the report. The noise floor is a term that describes the level of background noise or interference in a wireless channel or band. The noise floor is measured in dBm (decibel-milliwatts) and it represents the minimum signal strength that can be detected or received by a wireless device. The noise floor is influenced by various factors, such as the sensitivity of the receiver, the antenna gain, the cable loss, and the ambient RF environment. The ambient RF environment consists of intentional and unintentional RF radiators that emit RF energy in the wireless spectrum. Intentional RF radiators are devices that are designed to transmit RF signals for communication purposes, such as Wi-Fi access points, Bluetooth devices, microwave ovens, or cordless phones. Unintentional RF radiators are devices that are not designed to transmit RF signals but generate electromagnetic radiation as a by-product of their operation, such as USB 3 devices, PC power supplies, or fluorescent lights. The noise floor affects WLAN performance and quality because it determines the minimum signal-to-noise ratio (SNR) that is required for a successful wireless transmission. SNR is the difference between the signal strength of the desired signal and the noise floor of the channel. SNR is also measured in dB and it indicates how much the signal stands out from the noise. A higher SNR means a better signal quality and a lower bit error rate. A lower SNR means a worse signal quality and a higher bit error rate. Therefore, to achieve a reliable WLAN connection, the intentional signal of your WLAN must exist above the noise floor by a certain margin that depends on the data rate and modulation scheme used. The other options are not accurate or complete explanations of the noise floor noted in the report. The noise caused by elevators, microwave ovens, and video transmitters is not the noise floor but rather examples of interference sources that contribute to the noise floor. The extra energy radiated by access points and client devices beyond that intended for the signal is not the noise floor but rather an example of spurious emissions that cause interference to other devices or channels. The energy radiated by flooring materials that causes interference in the 2.4 GHz and 5 GHz bands is not the noise floor but rather an example of attenuation or reflection that reduces or changes the direction of the signal. References: CWNA-109 Study Guide, Chapter 5: Radio Frequency Signal and Antenna Concepts, page 139
質問 # 53
You are a small business wireless network consultant and provide WLAN services for various companies. You receive a call from one of your customers stating that their laptop computers suddenly started experiencing much slower data transfers while connected to the WLAN. This company is located in a multi-tenant office building and the WLAN was designed to support laptops, tablets and mobile phones. What could cause a sudden change in performance for the laptop computers?
- A. The sky was not as cloudy that day as it typically is and the sun also radiates electromagnetic waves.
- B. A few of your customer's users have Bluetooth enabled wireless headsets.
- C. A new tenant in the building has set their AP to the same RF channel that your customer is using.
- D. The antennas in the laptops have been repositioned.
正解：C
解説：
A possible cause of a sudden change in performance for the laptop computers is that a new tenant in the building has set their AP to the same RF channel that your customer is using. This can create co-channel interference (CCI), which is a situation where two or more APs or devices use the same or overlapping channels in the same area. CCI can degrade the performance of WLANs by increasing contention, collisions, retransmissions, and latency. CCI can also reduce the effective range and throughput of WLANs by lowering the signal-to-noise ratio (SNR). To avoid or mitigate CCI, it is recommended to use non-overlapping channels, adjust transmit power levels, or implement channel management techniques such as dynamic frequency selection (DFS) or load balancing. The sky condition, antenna position, or Bluetooth headset are not likely to cause a sudden change in performance for the laptop computers. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 81; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 71.
質問 # 54
The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz). What is the center frequency of channel 4?
- A. 2.422
- B. 2.427
- C. 2.417
- D. 2.413
正解：B
解説：
The center frequency of channel 4 in the 2.4 GHz band is 2.427 GHz (2427 MHz). The center frequency of a channel is the midpoint of its frequency range, where the signal strength is highest and most concentrated.
The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz), as given in the question.
The center frequency of each subsequent channel is obtained by adding 5 MHz to the previous channel's center frequency, since the channels are spaced 5 MHz apart from each other in this band. Therefore, to find the center frequency of channel 4, we need to add 15 MHz (5 MHz x 3) to the center frequency of channel 1:
2.412 GHz + 0.015 GHz = 2.427 GHz
Alternatively, we can use a formula to calculate the center frequency of any channel in the 2.4 GHz band:
Center frequency (GHz) = 2.407 + (0.005 x Channel number)
Using this formula for channel 4, we get:
Center frequency (GHz) = 2.407 + (0.005 x 4)
Center frequency (GHz) = 2.407 + 0.02
Center frequency (GHz) = 2.427 References: 1, Chapter 3, page 85; 2, Section 3.2
質問 # 55
You recently purchased four laptops containing dual-band 802.11ac adapters. The laptops can connect to your
2.4 GHz network, but they cannot connect to the 5 GHz network. The laptops do not show the 5 GHz SSIds, which are different than the 2.4 GHz SSIDs. Existing devices can connect to the 5 GHz SSIDs with no difficulty. What is the likely problem?
- A. DoS attack
- B. Interference from non-Wi-Fi sources
- C. Interference from other WLANs
- D. Faulty drivers
正解：D
解説：
The likely problem that causes this scenario is faulty drivers. Drivers are software components that enable the communication between the operating system and the hardware devices, such as the wireless adapters. Faulty drivers can cause various issues with the wireless connectivity, such as not detecting or connecting to certain networks, dropping connections, or reducing performance. Faulty drivers can be caused by corrupted files, outdated versions, incompatible settings, or hardware defects. To fix faulty drivers, you can try to update, reinstall, or roll back the drivers, or contact the manufacturer for support. Interference from non-Wi-Fi sources, DoS attack, or interference from other WLANs are not likely to cause this scenario, as they would affect all devices in the same area, not just the new laptops. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 562; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 532.
質問 # 56
You are troubleshooting a WLAN problem and you suspect hidden node as the cause. What should you look for in a protocol analyzer?
- A. Frames with the retry bit set to 0
- B. Frames transmitted from the AP without acknowledgement
- C. Retransmitted frames from multiple STAs with higher retry counts than other STAs Frames with the HN bit set to 1
正解：C
解説：
The CWNA Official Study Guide (CWNA-109), Chapter 8: Troubleshooting and Spectrum Analysis, explains that hidden node problems occur when two or more client stations cannot hear each other but can both communicate with the same access point. This leads to collisions at the AP because the clients transmit simultaneously without sensing each other's signals.
"Hidden node problems can often be identified in a protocol analyzer by observing excessive retransmissions from specific client stations. These retransmissions occur because the station's frames are not acknowledged due to collisions caused by other stations that the transmitter cannot hear."
- CWNA-108 Study Guide, Chapter 8, Hidden Node Problem Analysis, p. 393-395 Therefore, when analyzing for a hidden node issue, you will typically observe:
* Retransmitted frames from multiple STAs.
* Higher retry counts for affected stations compared to others.
Hence, the correct answer is C. Retransmitted frames from multiple STAs with higher retry counts than other STAs.
質問 # 57
You are deploying a WLAN monitoring solution that utilizes distributed sensor devices. Where should sensors be deployed for best results? Choose the single best answer.
- A. Above the plenum on each floor
- B. Every 5 meters and alongside each AP
- C. In switching closets
- D. In critical areas where WLAN performance must be high
正解：D
解説：
Sensors should be deployed in critical areas where WLAN performance must be high for best results when using a WLAN monitoring solution that utilizes distributed sensor devices. A WLAN monitoring solution is a system that collects, analyzes, and reports on the status and performance of a WLAN. A WLAN monitoring solution can use different methods to gather data from the WLAN, such as embedded software agents, external hardware probes, or distributed sensor devices. Distributed sensor devices are dedicated devices that are deployed throughout the WLAN coverage area to monitor the wireless traffic and environment.
Distributed sensor devices can perform various functions, such as scanning the spectrum, capturing wireless frames, measuring signal quality, detecting rogue access points, testing connectivity, and generating alerts.
Distributed sensor devices can provide more accurate and comprehensive data than other methods, but they also require more planning and deployment costs. Therefore, it is important to deploy sensors strategically in critical areas where WLAN performance must be high, such as high-density zones, high-priority applications, or high-security locations. By deploying sensors in critical areas, the WLAN monitoring solution can ensure optimal WLAN performance and reliability in those areas and identify and resolve any issues or problems that may arise. The other options are not the best places to deploy sensors for best results. Deploying sensors in switching closets is not effective because sensors need to be close to the wireless medium to monitor it properly. Deploying sensors every 5 meters and alongside each AP is not efficient because sensors may overlap or interfere with each other and cause unnecessary redundancy or complexity. Deploying sensors above the plenum on each floor is not practical because sensors may not capture the wireless traffic and environment accurately due to attenuation or reflection from the ceiling materials or objects. References: CWNA-109 Study Guide, Chapter 14: Troubleshooting Wireless LANs, page 4831
質問 # 58
What feature of 802.1 lax (HE) may impact design decisions related to AP placement and the spacing between same-channel BSS cells (3SAs) because it is designed to reduce overlapping BSS contention?
- A. TWT
- B. uplink MU-MIMO
- C. BSS Color
- D. 6 GHz band support
正解：C
解説：
In the 802.11ax (High Efficiency, HE) amendment, one of the key features introduced is BSS (Basic Service Set) Coloring. This feature is designed to mitigate issues arising from overlapping BSSs (OBSS), which can lead to contention and interference in dense wireless environments. BSS Coloring works by:
* Assigning a "color" (a small number) to each BSS: This helps devices differentiate between frames from their own BSS and those from neighboring BSSs.
* Reducing Inter-BSS Interference: Devices can ignore frames from different BSSs (with a different
"color") under certain conditions, reducing the impact of OBSS interference.
* Improving Spatial Reuse: By distinguishing between transmissions from different BSSs, devices can make more informed decisions about when to transmit, improving the efficiency of spatial reuse and reducing unnecessary contention.
This feature directly impacts design decisions related to AP placement and the spacing between same-channel BSS cells, as it allows for closer placement of APs on the same channel without significantly increasing interference, thus improving overall network capacity and efficiency.
The other options, while features of 802.11ax, do not directly pertain to reducing overlapping BSS contention in the same manner:
* TWT (Target Wake Time)optimizes device sleep schedules to conserve power.
* Uplink MU-MIMOenhances uplink data transmission capabilities but doesn't specifically address
* OBSS contention.
* 6 GHz Band Supportintroduces new spectrum for Wi-Fi use but is not a feature aimed at reducing OBSS contention within the 802.11ax framework.
Therefore, the correct answer is B, BSS Color.
References:
* IEEE 802.11ax-2021: Enhancements for High Efficiency WLAN.
* CWNA Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109, by David D: Coleman and David A. Westcott.
質問 # 59
What factor is likely to cause the least impact on the application layer throughput of an 802.11n client station in a 2.4 GHz HT BSS?
- A. Implementation of several other clients in the same BSS using 802.11g radios
- B. Increasing or decreasing the number of spatial streams in use by the client station and AP
- C. RF interference from more than 10 nearby Bluetooth transmitters
- D. Implementing Fast BSS Transition (FT) for roaming
正解：D
解説：
Implementing Fast BSS Transition (FT) for roaming is likely to cause the least impact on the application layer throughput of an 802.11n client station in a 2.4 GHz HT BSS. FT is a feature that allows a client station to quickly switch from one AP to another within the same ESS (Extended Service Set) without having to re-authenticate and re-associate with each AP. This reduces the latency and packet loss that may occur during roaming, thus improving the user experience and maintaining the application layer throughput. FT is defined in the IEEE 802.11r amendment and is also known as Fast Roaming or Fast Secure Roaming. References: , Chapter 9, page 367; , Section 6.3
質問 # 60
What is an advantage of using WPA3-Personal instead of WPA2-Personal as a security solution for 802.11 networks?
- A. WPA3-Personal, also called WPA3-SAE, uses a stronger authentication exchange to better secure the network
- B. WPA3-Personal, also called WPA3-SAE, uses a better encryption algorithm than WPA2-Personal
- C. WPA3-Personal, also called WPA3-SAE, uses an authentication exchange and WPA2-Personal does not
- D. WPA3-Personal, also called WPA3-SAE, uses AES for encryption and WPA2-Personal does not
正解：A
解説：
An advantage of using WPA3-Personal instead of WPA2-Personal as a security solution for 802.11 networks is that WPA3-Personal, also called WPA3-SAE, uses a stronger authentication exchange to better secure the network. WPA3-Personal uses Simultaneous Authentication of Equals (SAE) as the key exchange protocol, which provides stronger protection against offline dictionary attacks and password guessing than WPA2-Personal. SAE uses a Diffie-Hellman key exchange with elliptic curve cryptography (ECC) to establish a pairwise master key (PMK) between the AP and the client without revealing it to any eavesdropper. SAE also provides forward secrecy, which means that if one PMK is compromised, it does not affect the security of other PMKs. WPA2-Personal uses Pre-Shared Key (PSK) as the key exchangeprotocol, which is vulnerable to offline brute-force attacks if the passphrase is weak or leaked. Both WPA3-Personal and WPA2-Personal use AES for encryption, so there is no difference in that aspect. WPA3-Personal does not use a different encryption algorithm than WPA2-Personal, but rather a different key exchange protocol. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 307; [CWNA:
Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 297.
質問 # 61
When a client station sends a broadcast probe request frame with a wildcard SSID, how do APs respond?
- A. For each probe request frame, only one AP may reply with a probe response.
- B. After waiting a SIFS, all APs reply at the same time with a probe response.
- C. Each AP responds in turn after preparing a probe response and winning contention.
- D. Each AP checks with the DHCP server to see if it can respond and then acts accordingly.
正解：C
解説：
In the 802.11 wireless networking protocols, when a client station sends a broadcast probe request frame with a wildcard SSID (Service Set Identifier), it is essentially asking for any nearby access points (APs) to identify themselves. The way APs respond to such a probe request is governed by standard 802.11 behavior, which includes:
* Probe Request Handling: Upon receiving a broadcast probe request, each AP that can serve the client prepares a probe response. The response includes information about the AP, such as its SSID, supported data rates, and other capabilities.
* Contention-Based Mechanism: Wireless networks use a contention-based mechanism (CSMA/CA - Carrier Sense Multiple Access with Collision Avoidance) for medium access. Each AP must wait for a clear channel and win the contention process before it can send its probe response.
* Independent Responses: Each AP operates independently in responding to the probe request. There is no coordination between APs to decide which one responds first or at all, leading to multiple APs sending probe responses, each after winning the contention for the medium.
Option A accurately reflects this process, indicating that each AP prepares and sends a probe response in turn, contingent upon winning the medium contention. The other options suggest mechanisms (such as coordination with a DHCP server or simultaneous responses after a Short Interframe Space (SIFS)) that do not align with standard 802.11 procedures for handling broadcast probe requests.
References:
* IEEE 802.11 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.
* CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, by David D.
Coleman and David A. Westcott.
質問 # 62
ABC Company is planning to install a new 802.11ac WLAN, but wants to upgrade its wired infrastructure first to provide the best user experience possible. ABC Company has hired you to perform the RF site survey.
During the interview with the network manager, you are told that the new Ethernet edge switches will support VoIP phones and 802.11 access points, both using 802.3 PoE.
After hearing this information, what immediate concerns do you note?
- A. If the switches are in optimal locations for VoIP phones, they are likely to be suboptimal locations for
802.11 APs - B. VoIP phones and 802.11 access points should not be powered by the same edge switch due to distortion.
- C. The edge Ethernet switches should support Ether-channel to get the best results out of the network.
- D. The power budget in the edge switches must be carefully planned and monitored based on the number of supported PoE devices.
正解：D
解説：
An immediate concern that you note after hearing this information is that the power budget in the edge switches must be carefully planned and monitored based on the number of supported PoE devices. PoE stands for Power over Ethernet and is a technology that allows Ethernet switches to deliver power along with data to devices such as VoIP phones and 802.11 access points. PoE devices are classified into different classes based on their power consumption and output. The edge switches have a limited power budget that determines how many PoE devices they can support simultaneously. If the power budget is exceeded, some PoE devices may not receive enough power or may shut down unexpectedly. Therefore, it is important to plan and monitor the power budget in the edge switches based on the number and class of PoE devices connected to them. Using Ether-channel, placing switches in optimal locations, or avoiding distortion are not immediate concerns related to PoE devices. References: [CWNP Certified Wireless Network Administrator Official Study Guide:
Exam CWNA-109], page 234; [CWNA: Certified Wireless Network Administrator Official Study Guide:
Exam CWNA-109], page 224.
質問 # 63
When compared with legacy Power Save mode, how does VHT TXOP power save improve battery life for devices on a WLAN?
- A. VHT TXOP power save uses the partial AID in the preamble to allow clients to identify frames targeted for them.
- B. Legacy Power Save mode was removed in the 802.11ac amendment.
- C. VHT TXOP power save allows the WLAN transceiver to disable more components when in a low power state.
- D. VHT TXOP power save allows stations to enter sleep mode and legacy Power Save does not.
正解：C
解説：
VHT TXOP (Very High Throughput Transmit Opportunity) power save is a feature introduced with the
802.11ac amendment, which is designed to improve the power efficiency of devices connected to a WLAN.
This feature enhances battery life in several ways, compared to the legacy Power Save mode:
* Enhanced Power Saving: VHT TXOP power save allows devices to disable more components of the WLAN transceiver when they are in a low power state. This reduces the power consumption during periods when the device is not actively transmitting or receiving data.
* Intelligent Wake-Up Mechanisms: It employs more sophisticated mechanisms for devices to determine when they need to wake up and listen to the channel, further reducing unnecessary power usage.
* Optimized Operation: This power save mode is optimized for the high-throughput environment of
802.11ac networks, allowing devices to efficiently manage power while maintaining high performance.
Legacy Power Save mode, introduced in earlier versions of the 802.11 standards, does not provide the same level of component disablement or the intelligent wake-up mechanisms found in VHT TXOP power save, making option B the correct answer.
References:
* IEEE 802.11ac-2013 Amendment: Enhancements for Very High Throughput for Operation in Bands below 6 GHz.
* CWNA Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109, by David D: Coleman and David A. Westcott.
質問 # 64
XYZ Company has decided to install an 802.11 WLAN system that will support 1083 wireless users, but they are concerned about network security. XYZ is interested in deploying standardized security features. In addition to WPA2-Enterprise with PEAP and role-based access control, XYZ would like to support management frame protection as well as a fast secure roaming protocol for future mobile handsets.
As XYZ Company selects a product to deploy, what two IEEE amendments, which are included in
802.11-2016, and 802.11-2020 should be supported to provide the management frame protection and fast secure roaming security features?
- A. 802.11r and 802.11w
- B. 802.11j and 802.11z
- C. 802.11j and 802.11k
- D. 802.11k and 802.11v
正解：A
解説：
The two IEEE amendments that should be supported to provide the management frame protection and fast secure roaming security features are 802.11r and 802.11w12.
* 802.11r (Fast BSS Transition): This amendment to the IEEE 802.11 standard permits continuous connectivity aboard wireless devices in motion, with fast and secure client transitions from one Basic Service Set to another1.
* 802.11w (Management Frame Protection): This amendment increases the security of its management frames2.
質問 # 65
An 802.11-based network uses an AP and has several connecting clients. The clients include iPhones, iPads, laptops and one desktop. What WLAN use case is represented?
- A. BSS
- B. IBSS
- C. Ad-hoc
- D. WPAN
正解：A
解説：
A BSS (Basic Service Set) is a WLAN use case that represents an 802.11-based network that uses an AP (Access Point) and has several connecting clients. The AP acts as a central point of coordination and communication for the clients, which can include iPhones, iPads, laptops, desktops, or any other devices that have Wi-Fi capabilities. A BSS can be identified by a unique BSSID (Basic Service Set Identifier), which is usually the MAC address of the AP's radio interface. A BSS can also be associated with an SSID (Service Set Identifier), which is a human-readable name that identifies the network. References: , Chapter 1, page 23; , Section 1.1
質問 # 66
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. To get the best performance out of an AP, you should disable data rates of 72 Mbps and lower
- C. WLANs perform better as more wireless clients connect with each AP
- D. In modem networks, both centralized and distributed data forwarding work well for most standard office deployments
正解：D
解説：
The statement that in modern networks, both centralized and distributed data forwarding work well for most standard office deployments is true about WLAN performance. Data forwarding refers to how wireless frames are transmitted from wireless clients to wired networks or vice versa through wireless access points (APs).
Centralized data forwarding means that all wireless frames are sent to a central controller or gateway before being forwarded to their destinations. Distributed data forwarding means that wireless frames are forwarded directly by the APs to their destinations without going through a central controller or gateway. Both methods have their advantages and disadvantages, depending on the network size, topology, traffic pattern, security, and management requirements. However, in modern networks, both methods can achieve high performance and scalability for most standard office deployments, as they can leverage advanced features such as fast roaming, load balancing, quality of service, and encryption. The other statements about WLAN performance are false. In most WLANs, special skill or tuning is required to get peak performance, such as selecting the appropriate channel, power, data rate, and antenna settings. WLANs perform worse as more wireless clients connect with each AP, as they cause more contention and interference on the wireless medium. To get the best performance out of an AP, you should not disable data rates of 72 Mbps and lower, as they are needed for backward compatibility and range extension. References: CWNA-109 Study Guide, Chapter 9: Wireless LAN Architecture, page 2811
質問 # 67
A dual-band 802.11ac AP must be powered by PoE. As a class 4 device, what power level should be received at the AP?
- A. 25.5 W
- B. 15.4 W
- C. 30 W
- D. 12.95 W
正解：A
解説：
PoE has different standards that define different power levels for PSEs and PDs. The original standard, IEEE
802.3af, defines two classes of PSEs: Class 3 (15.4 W) and Class 4 (30 W). The newer standard, IEEE 802.3 at, also known as PoE+, defines four classes of PSEs: Class 0 (15.4 W), Class 1 (4 W), Class 2 (7 W), and Class 3 (12.95 W). The power level received at the PD is always lower than the power level provided by the PSE, due to cable resistance and power dissipation. The IEEE standards specify the minimum power level that must be received at the PD for each class of PSE. For a Class 4 PSE, the minimum power level received at the PD is 25.5 W910. References: CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page
295; CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 289.
質問 # 68
The requirements for a WLAN you are installing state that it must support unidirectional delays of less than
150 ms and the signal strength at all receivers can be no lower than -67 dBm. What application is likely used that demands these requirements?
- A. VoIP
- B. FTP
- C. E-Mail
- D. RTLS
正解：A
解説：
VoIP (Voice over Internet Protocol) is an application that is likely used that demands the requirements of unidirectional delays of less than 150 ms and the signal strength at all receivers can be no lower than -67 dBm.
VoIP is an application that allows users to make and receive voice calls over a network, such as the Internet or a WLAN. VoIP is a real-time and interactive application that requires high quality of service (QoS) to ensure good user experience and satisfaction. One of the QoS metrics for VoIP is delay, which is the time it takes for a voice packet to travel from the sender to the receiver. Delay can affect the quality and intelligibility of the voice conversation, as well as the synchronization and naturalness of the dialogue. The ITU-T G.114 recommendation suggests that the maximum acceptable one-way delay for VoIP should be less than 150 ms, as anything higher than that can cause noticeable degradation and annoyance to the users. Another QoS metric for VoIP is signal strength, which is the measure of how strong the RF signal is at the receiver. Signal strength can affect the reliability and performance of the wireless connection, as well as the data rate and throughput of the VoIP traffic. The CWNA Official Study Guide recommends that the minimum signal strength for VoIP should be -67 dBm, as anything lower than that can cause packet loss, retries, jitter, and other issues that can impair the voice quality. References: 1, Chapter 10, page 398; 2, Section 6.1
質問 # 69
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