CWNP CWNP Certifications CWNA-109 Questions & Answers

• Question 51:

  Which one of the following is not a factor considered when calculating the Link Budget for an outdoor point-to- point WLAN bridge link?

  A. Operating frequency

  B. MU-MIMO capabilities of the bridges

  C. Receive antenna gain

  D. Transmit power

  Correct Answer: B

  MU-MIMO capabilities of the bridges are not a factor considered when calculating the Link Budget for an outdoor point-to-point WLAN bridge link. The Link Budget is acalculation of the expected signal strength at the receiver based on various factors that affect the RF transmission. Some of these factors are operating frequency, transmit power, receive antenna gain, free space path loss, cable loss, connector loss, and environmental loss. MU-MIMO stands for Multi-User Multiple Input Multiple Output, which is a technology that allows multiple devices to communicate simultaneously using multiple spatial streams. MU-MIMO is not relevant for a point-to-point link, where there are only two devices involved. References: 1, Chapter 2, page 59; 2, Section 2.2

• Question 52:

  You administer a WLAN that offers a guest SSID of GUESTNWORK. Users connect to the GUESTNWORK SSID, but report that they cannot browse the Internet. The devices simply report no Internet connection. What common problem causes this scenario?

  A. NTP issues

  B. Hardware issues

  C. IP routing issues

  D. Captive portal issues

  Correct Answer: D

  A common problem that causes this scenario is captive portal issues. A captive portal is a web page that requires users to authenticate or accept terms and conditions before accessing the Internet through a WLAN. A captive portal is often used for guest networks to provide security and control over the network access. A captive portal works by intercepting the user's web requests and redirecting them to the portal page until the user completes the required action. However, sometimes the captive portal may not work properly due to various reasons, such as browser settings, firewall rules, DNS configuration, or network errors. This can prevent the user from browsing the Internet or seeing the portal page. To troubleshoot captive portal issues, you can try to use a different browser, clear the browser cache andcookies, disable any VPN or proxy settings, manually enter the portal URL, or contact the network administrator. NTP issues, hardware issues, or IP routing issues are not common problems that cause this scenario. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 343; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 333.

• Question 53:

  You support a WLAN using dual-band 802.11ac three stream access points. All access points have both the 2.4 GHz and 5 GHz radios enabled and use 40 MHz channels in 5 GHz and 20 MHz channels in 2.4 GHz. A manager is concerned about the fact that each access point is connected using a 1 Gbps Ethernet link. He is concerned that the Ethernet link will not be able to handle the load from the wireless radios. What do you tell him?

  A. His concern is valid and the company should upgrade all Ethernet links to 10 Gbps immediately.

  B. His concern is valid and the company should immediately plan to run a second 1 Gbps Ethernet link to each AP.

  C. His concern is invalid because the AP will compress all data before transmitting it onto the Ethernet link.

  D. Due to 802.11 network operations and the dynamic rates used by devices on the network, the two radios will likely not exceed the 1 Gpbs Ethernet link.

  Correct Answer: D

  What you should tell him is that due to 802.11 network operations and the dynamic rates used by devices on the network, the two radios will likely not exceed the 1 Gbps Ethernet link. This is because the actual throughput of an 802.11 network is much lower than the theoretical data rates due to factors such as overhead, contention, interference, retransmissions, and environmental conditions. Moreover, the data rates used by devices on the network vary depending on their distance, signal quality, capabilities, and configuration. Therefore, it is unlikely that both radios of the AP will simultaneously use the maximum data rates and saturate the 1 Gbps Ethernet link. Upgrading to a 10 Gbps Ethernet link or running a second 1 Gbps Ethernet link may be unnecessary and costly. Compressing all data before transmitting it onto the Ethernet link may introduce additional overhead and latency. References: [CWNP CertifiedWireless Network Administrator Official Study Guide: ExamCWNA-109], page 227; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 217.

• Question 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. 2.427

  B. 2.422

  C. 2.413

  D. 2.417

  Correct Answer: A

  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

• Question 55:

  An RF signal sometimes bends as it passes through some material other than free space. What is the term that describes this behavior?

  A. Refraction

  B. Warping

  C. Scattering

  D. Reflection

  Correct Answer: A

  Refraction is the bending of an RF signal as it passes through a medium with a different density than free space. This can cause the signal to change its direction and speed, which can affect the accuracy and reliability of wireless communication. Refraction is influenced by factors such as temperature, humidity, and atmospheric pressure12. References: CWNA-109 Study Guide, Chapter 2: Radio Frequency Fundamentals, page 72; CWNA-109Study Guide, Chapter 2: Radio Frequency Fundamentals, page 67.

• Question 56:

  What can an impedance mismatch in the RF cables and connectors cause?

  A. Increased range of the RF signal

  B. Fewer MCS values in the MCS table

  C. Increased amplitude of the RF signal

  D. Excessive VSWR

  Correct Answer: D

  VSWR stands for Voltage Standing Wave Ratio, which is a measure of how well the impedance of the RF cable and connectors matches the impedance of the transmitter and the antenna. Impedance is the opposition to the flow of alternating current in an RF circuit, and it depends on the frequency, resistance, capacitance, and inductance of the components. A perfect impedance match would have a VSWR of 1:1, meaning that all the power is transferred from the transmitter to the antenna, and none is reflected back. However, in reality, there is always some degree of mismatch, which causes some power to be reflected back to the transmitter, creating standing waves along the cable. This reduces the efficiency and performance of the wireless system, and can also damage the transmitter. Excessive VSWR can be caused by using poor quality or damaged cables and connectors, or by using components that have different impedance ratings123. References: CWNA-109 Study Guide, Chapter 2: Radio Frequency Fundamentals, page 90; CWNA-109Study Guide, Chapter 2: Radio Frequency Fundamentals, page 86; CWNP website, CWNA Certification.

• Question 57:

  What statement about 802.11 WLAN performance is true?

  A. In modem networks, both centralized and distributed data forwarding work well for most standard office deployments

  B. In most WLANs, no special skill or tuning is required to get peak performance

  C. WLANs perform better as more wireless clients connect with each AP

  D. To get the best performance out of an AP, you should disable data rates of 72 Mbps and lower

  Correct Answer: A

  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

• Question 58:

  When compared with legacy Power Save mode, how does VHT TXOP power save improve battery life for devices on a WLAN?

  A. Legacy Power Save mode was removed in the 802.11ac amendment.

  B. VHT TXOP power save allows the WLAN transceiver to disable more components when in a low power state.

  C. VHT TXOP power save uses the partial AID in the preamble to allow clients to identify frames targeted for them.

  D. VHT TXOP power save allows stations to enter sleep mode and legacy Power Save does not.

  Correct Answer: B

  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.

• Question 59:

  What factor does not influence the distance at which an RF signal can be effectively received?

  A. Receiving station's radio sensitivity

  B. Receiving station's output power

  C. Transmitting station's output power

  D. Free Space Path Loss

  Correct Answer: B

  In wireless communication, several factors influence the effective reception of RF signals, including the receiving station's radio sensitivity, the transmitting station's output power, and free space path loss. However, the receiving station's

  output power does not influence the distance at which an RF signal can be effectively received. The key factors that impact signal reception distance are:

  Receiving Station's Radio Sensitivity: This refers to the lowest signal strength at which the receiver can process a signal with an acceptableerror rate. Higher sensitivity allows for better reception at greater distances. Transmitting Station's

  Output Power: This is the power with which a transmitter sends out a signal. Higher output power can extend the range of transmission, making it easier for distant receivers to detect the signal. Free Space Path Loss (FSPL): FSPL

  represents the attenuation of radio energy as it travels through free space. It increases with distance and frequency, reducing the signal strength as the distance from the transmitter increases. The output power of the receiving station is

  related to how strong a signal it sends out, not how well it can receive or process incoming signals. Therefore, it does not affect the reception distance of incoming RF signals.

  References:

  CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0- 105, by David D. Coleman and David A. Westcott.

  RF fundamentals and RF design considerations in wireless communication systems.

• Question 60:

  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. E-Mail

  C. FTP

  D. RTLS

  Correct Answer: A

  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