CWNA-109 Online Practice Questions and Answers

Correct Answer: B

In addition to coverage analysis results, what should be included in a post- deployment site survey report to ensure WLAN users experience acceptable performance is Capacity analysis results. Capacity analysis is a method of testing the ability of the WLAN to support the expected number and type of users, devices, and applications. Capacity analysis can help to determine the optimal number and placement of access points, the appropriate channel and power settings, the required QoS policies, and the expected throughput and latency levels. Capacity analysis results can help to verify that the WLAN meets the performance requirements and service level agreements (SLAs) of the organization. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 548; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 518.

Correct Answer: C

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 802.3at, 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-109Study Guide, Chapter

7: Power over Ethernet (PoE), page 289.

Correct Answer: A

FT (Fast Transition) is an IEEE 802.11 standard method for fast roaming. FT is defined in the IEEE 802.11r amendment and is also known as Fast BSS Transition (FBT) or Fast Secure Roaming. 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 security of the connection. FT works by using pre-authentication and key caching mechanisms that allow the client station and the APs to exchange security information before the actual roaming occurs. This way, when the client station decides to roam to a new AP, it can use a fast reassociation request and response that contain only a few fields, instead of a full authentication and association exchange that require more time and data. References: 1, Chapter 9, page 367; 2, Section 6.3

Correct Answer: A

Weak signal strength is the likely cause of the low data rate issue for the client that has a signal strength of -84 dBm and a noise floor of -96 dBm. The client is an 802.11ac client and connects to an 802.11ac AP. Both the client and AP are 2x2:2 devices. Signal strength 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 traffic. The higher the signal strength, the better the signal quality and the higher the data rate. The lower the signal strength, the worse the signal quality and the lower the data rate. The data rate of an 802.11ac connection depends on several factors, such as channel bandwidth, modulation and coding scheme (MCS), spatial streams, guard interval, and beamforming. However, these factors are also influenced by the signal strength, as they require a certain signal-to-noise ratio (SNR) to operate properly. SNR is the ratio of the signal strength to the noise floor, which is the measure of the background noise or interference in the RF environment. The higher the SNR, the more robust and efficient the communication. The lower the SNR, the more prone and vulnerable to errors and retries. According to the CWNA Official Study Guide , Table 3.7, page 112, an 802.11ac connection with a channel bandwidth of 80 MHz, an MCS of 9, two spatial streams, a short guard interval, and no beamforming can achieve a maximum data rate of 867 Mbps. However, this data rate requires a minimum SNR of 30 dB to maintain a sufficient signal quality. If the signal strength is -84 dBm and the noise floor is -96 dBm, then the SNR is only 12 dB (-84 dBm - (-96 dBm) = 12 dB), which is far below the required SNR for this data rate. Therefore, the data rate will drop significantly to match the lower SNR and signal quality. To solve this problem, the signal strength should be increased to improve the SNR and data rate. This can be done by adjusting the output power or channel assignment of the AP or client, relocating or reorienting some APs or antennas to reduce attenuation or interference, updating or replacing some faulty oroutdated hardware or software components, etc. References: , Chapter 3, page 112; , Section 3.2

Correct Answer: D

Channel 144 is a new channel that was added to the 5 GHz band by the 802.11ac amendment, which defines the VHT (Very High Throughput) PHY for WLANs. Channel 144 has a center frequency of 5720 MHz and a bandwidth of 20 MHz. It can also be combined with adjacent channels to form wider channels of 40 MHz, 80 MHz, or 160 MHz. Channel 144 is available in some regions, such as North America and Europe, but not in others, such as Japan and China . References: [CWNA-109 Study Guide], Chapter

3: Antennas and Accessories, page 121; [CWNA-109Study Guide], Chapter 3: Antennas and Accessories, page 115; [Wikipedia], List of WLAN channels.

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

Correct Answer: A

USB 3 devices in the user's work area are the most likely cause of this interference when using a spectrum analyzer to look for non-Wi-Fi interference sources. A spectrum analyzer is a tool that measures and visualizes the radio frequency activity and interference in the wireless environment. A spectrum analyzer can show the spectrum usage and energy levels on each frequency band or channel and help identify and locate the sources of interference. Interference is any unwanted signal that disrupts or degrades the intended signal on a wireless channel. Interference can be caused by various sources, such as other Wi-Fi devices, non-Wi-Fi devices, or natural phenomena. Interference can affect WLAN performance and quality by causing signal loss, noise, distortion, or errors. USB 3 devices are non-Wi-Fi devices that use USB 3.0 technology to transfer data at high speeds between computers and peripherals, such as hard drives, flash drives, cameras, or printers. USB 3 devices can generate electromagnetic radiation that interferes with Wi-Fi signals in the 2.4 GHz band, especially when they are close to Wi-Fi devices or antennas. USB 3 devices can cause significant interference across the entire 2.4 GHz band (not on a few select frequencies) within the desktop area of a user's workspace, but the interference disappears quickly after just 2 meters. This is because USB 3 devices emit broadband interference that affects all channels in the 2.4 GHz band with a high intensity near the source but a low intensity at a distance due to attenuation. The other options are not likely to cause this interference pattern when using a spectrum analyzer to look for non-Wi-Fi interference sources. Bluetooth devices in the user's work area are non-Wi-Fi devices that use Bluetooth technology to communicate wirelessly between computers and peripherals, such as keyboards, mice, headphones, or speakers. Bluetooth devices can cause interference with Wi-Fi signals in the 2.4 GHz band, but they use frequency hopping spread spectrum (FHSS) technique that changes frequencies rapidly and randomly within a range of 79 channels. Therefore, Bluetooth devices do not cause significant interference across the entire 2.4 GHz band (not on a few select frequencies), but rather intermittent interference on some channels at different times. Excess RF energy from a nearby AP is not a non-Wi-Fi interference source but rather a Wi-Fi interference source that occurs when an AP transmits more power than necessary for its coverage area. Excess RF energy from a nearby AP can cause co-channel interference (CCI) with other APs or client devices that use the same channel within range of each other. CCI reduces performance and capacity because it causes contention and collisions on the wireless medium,

Correct Answer: C

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 oneach 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

Correct Answer: C

Authenticated and Unassociated. According to one of the web search results1, a STA can be authenticated to multiple APs, but it can only be associated to one AP at a time. Association is the process of establishing a logical link between the STA and the AP, which allows the STA to send and receive data frames through the AP2. Therefore, when a STA has authenticated to an AP-1, but still maintains a connection with another AP-2, it means that the STA is authenticated to both APs, but only associated to AP-2. The state of the STA on AP-1 is authenticated and unassociated, which means that the STA can switch to AP-1 without repeating the authentication process, but it cannot send or receive data frames through AP-1 until it becomes associated.

Correct Answer: A

PoE stands for Power over Ethernet, which is a technology that allows network devices to receive power and data over the same Ethernet cable. PoE eliminates the need for separate power adapters or outlets for devices such as IP phones, cameras, or APs. PoE requires two types of devices: PSE (Power Sourcing Equipment) and PD (Powered Device). A PSE is a device that provides power to the Ethernet cable, such as a switch, injector, or splitter. A PD is a device that receives power from the Ethernet cable, such as an IP phone, camera, or AP. When implementing PoE, a switch plays the role of a PSE910. References: CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 293; CWNA109Study Guide, Chapter 7: Power over Ethernet (PoE), page 287.