CWNA-109 Sample Questions Answers

A pre-design site visit in preparation for a predictive wireless LAN design is essential for gathering physical and environmental data about the site. The key tasks to be performed during such a visit include:

Evaluating Building Materials: Different materials (concrete, glass, wood, etc.) have varying effects on RF signal propagation. Understanding the materials present helps in accurately predicting how signals will behave within the environment.

Floor Plan Verification: Ensuring that the floor plan documents are an accurate representation of the actual building layout is crucial. Discrepancies between the floor plans and the physical layout can lead to inaccuracies in the predictive design.

The other options, while potentially valuable in other contexts, are not directly related to preparing for a predictive design:

Installing APs(option A) for testing co-channel interference is more aligned with an active site survey rather than a pre-design visit for a predictive design.

Collecting information about security requirements(option B) is important but is not directly related to the physical aspects of the site that would impact a predictive design.

Testing antenna types(option C) would typically be part of an active site survey or the actual deployment phase, not a pre-design visit for predictive modeling.

Therefore, option D is the correct answer, focusing on evaluating physical aspects crucial for accurate predictive modeling.

References:

CWNA Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109, by David D. Coleman and David A. Westcott.

Best practices for conducting pre-design site visits in wireless network planning.

Calibrating the floor plan is what you must do before gathering survey data after the floor plan is imported when using a site survey tool for post-implementation validation. A site survey tool is a software application that can run on a laptop, tablet, smartphone, or other device that has a Wi-Fi adapter and a GPS receiver. A site survey tool can scan the wireless environment and collect information about the detected access points and client stations, such as their SSID, BSSID, channel, signal strength, security, and data rate. A site survey tool can also measure and display various metrics of network performance, such as throughput, jitter, packet loss, delay, and SNR. A site survey tool can also use a floor plan to visualize the wirelesscoverage and quality in different locations on a map. A floor plan is an image file that shows the layout and dimensions of a building or an area where the WLAN is deployed. A floor plan can be imported from various sources, such as a CAD file, a PDF file, an image file, or a Google Maps screenshot. After importing a floor plan into a site survey tool, it is necessary to calibrate the floor plan before gathering survey data. Calibrating the floor plan means adjusting the scale and orientation of the floor plan to match the actual size and direction of the area. Calibrating the floor plan can be done by using a reference point or a reference line that has a known distance or angle in the real world. Calibrating the floor plan ensures that the survey data is accurate and consistent with the physical environment. References: 1, Chapter 7, page 290; 2, Section 4.3

The common spectrum analyzer view that you should use for this analysis is the Waterfall/Spectrogram view. The Waterfall/Spectrogram view shows the signal from the interfering device over time on a three-dimensional graph. The x-axis represents frequency, the y-axis represents time, and the z-axis represents amplitude or power. The color of each pixel indicates the signal strength at a given frequency and time. The Waterfall/Spectrogram view can help you identify the characteristics of the interference source, such as its frequency range, duty cycle, modulation type, and pattern. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 524; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 494.

An isotropic radiator is a theoretical point source of electromagnetic radiation that radiates equally in all directions. It has no physical dimensions and no preferred direction of radiation. It is used as a reference for antenna gain because it represents the ideal case of a perfect omnidirectional antenna12

Antenna gain is a measure of how well an antenna concentrates its radiated power in a certain direction. It is expressed in decibels (dB) relative to a reference antenna. Whenthe reference antenna is an isotropic radiator, the antenna gain is denoted by dBi, which stands for decibels relative to isotropic12

For example, an antenna with a gain of 3 dBi means that it radiates 3 dB more power in its main direction than an isotropic radiator would. Conversely, an antenna with a gain of -3 dBi means that it radiates 3 dB less power in its main direction than an isotropic radiator would12

SAE (Simultaneous Authentication of Equals) is required when operating 802.11ax APs in the 6 GHz band using passphrase-based authentication. SAE is a secure and robust authentication method that is defined in the IEEE 802.11s amendment and is also known as WPA3-Personal or WPA3-SAE. SAE is based on a cryptographic technique called Dragonfly Key Exchange, which allows two parties to establish a shared secret key using a passphrase, without revealing the passphrase or the key to an eavesdropper or an attacker. SAE also provides forward secrecy, which means that if the passphrase or the key is compromised in the future, it does not affect the security of past communications.

SAE is required when operating 802.11ax APs in the 6 GHz band using passphrase-based authentication because of the new regulations and standards that apply to this band. The 6 GHz band is a new frequency band that was opened for unlicensed use by the FCC and other regulatory bodies in 2020. The 6 GHz band offers more spectrum and less interference than the existing 2.4 GHz and 5 GHz bands, which can enable higher performance and efficiency for Wi-Fi devices. However, the 6 GHz band also has some restrictions and requirements that are different from the other bands, such as:

The 6 GHz band is divided into two sub-bands: U-NII-5 (5925-6425 MHz) and U-NII-7 (6525-6875 MHz). The U-NII-5 sub-band is subject to DFS (Dynamic Frequency Selection) rules, which require Wi-Fi devices to monitor and avoid using channels that are occupied by radar systems or other primary users. The U-NII-7 sub-band is not subject to DFS rules, but it has a lower maximum transmit power limit than the U-NII-5 sub-band.

The Wi-Fi devices that operate in the 6 GHz band are called 6E devices, which stands for Extended Spectrum. 6E devices must support 802.11ax technology, which is also known as Wi-Fi 6 or High Efficiency (HE). 802.11ax is a new standard that improves the performance and efficiency of Wi-Fi networks by using features such as OFDMA (Orthogonal Frequency Division Multiple Access), MU-MIMO (Multi-User Multiple Input Multiple Output), BSS Coloring, TWT (Target Wake Time), and HE PHY and MAC enhancements.

The 6E devices that operate in the 6 GHz band must also support WPA3 security, which is a new security protocol that replaces WPA2 and provides stronger encryption and authentication for Wi-Fi networks. WPA3 has two modes: WPA3-Personal and WPA3-Enterprise. WPA3-Personal uses SAE as its authentication method, which requires a passphrase to establish a secure connection between two devices. WPA3-Enterprise uses EAP (Extensible Authentication Protocol) as its authentication method, which requires a certificate or a credential to authenticate with a server.

Therefore, SAE is required when operating 802.11ax APs in the 6 GHz band using passphrase-based authentication because it is part of WPA3-Personal security, which is mandatory for 6E devices in this band. References: , Chapter 3, page 120; , Section 3.2

9of30

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.

Granting access to specific network services or resources according to a user profile describes the authorization component of a AAA implementation. AAA stands for Authentication, Authorization, and Accounting, which are three functions that are used to control and monitor access to network resources and services. Authentication is the process of verifying that a user is who he says he is, by using credentials such as username, password, certificate, token, or biometric data. Authorization is the process of granting access to specific network services or resources according to a user profile, which defines the user’s role, privileges, and permissions. Accounting is the process of recording and reporting the usage of network services or resources by a user, such as the duration, volume, type, and location of the access. AAA can be implemented by using different protocols andservers, such as RADIUS, TACACS+, LDAP, Kerberos, or Active Directory. References: 1, Chapter 11, page 449; 2, Section 7.1

Passive Gain is the increase of RF energy in an intentional direction with the use of an antenna. It is achieved by focusing the same amount of power into a smaller area, resulting in a higher power density and a stronger signal. Passive Gain does not require any additional power or amplification, but rather depends on the antenna’s physical characteristics, such as size, shape, and orientation. Passive Gain is also expressed in decibels (dB) and is related to the antenna’s beamwidth and directivity. References: 1, Chapter 2, page 63; 2, Section 2.3

 This is because the passphrase for WPA2-Personal is case-sensitive and must match exactly on both the AP and the client. If the passphrase is entered incorrectly on the client, the client will not be able to authenticate with the AP and connect to the network. The AP that covers the problem area is not likely to require a firmware update, fail, or be improperly configured, as it is online and works with other clients that have the correct passphrase. To troubleshoot this issue, you can check the passphrase settings on the clients and make sure they matchwith the AP. You can also try to reconnect the clients to the network or reboot them if necessary. For more information on how to configure WPA2-Personal on your router

WPA2 (Wi-Fi Protected Access 2) is a security certification program developed by the Wi-Fi Alliance to secure wireless computer networks. It is important to understand the following:

WPA2 and the 802.11 Standard: While WPA2 is based on elements of the 802.11i amendment to the 802.11 standard, it is not itself a standard but rather a certification to ensure devices comply with certain security criteria, including the correct implementation of CCMP (Counter Mode Cipher Block Chaining Message Authentication Code Protocol) and AES (Advanced Encryption Standard).

CCMP/AES Implementation: WPA2 enhances the security of wireless networks by using CCMP for encryption, which is based on AES, a robust encryption algorithm. This represents a significant security improvement over WEP (Wired Equivalent Privacy) and WPA (Wi-Fi Protected Access) that used TKIP (Temporal Key Integrity Protocol).

WPA vs. WPA2: WPA was the interim security enhancement over WEP, utilizing TKIP for encryption. WPA2, however, moved to the more secure AES-based encryption method. Contrary to option C, WPA2 does not enhance security by using TKIP; it uses CCMP/AES.

Therefore, option B correctly describes WPA2 as a certification program ensuring devices properly implement the more secure CCMP/AES encryption methods.

References:

Wi-Fi Alliance website for WPA2 certification details.

IEEE 802.11i-2004: Amendment for Enhanced Security.

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

The least expensive solution available for increasing throughput for these users without implementing configuration options that are not recommended is to use a 40 MHz channel on the 5 GHz radio. This solution can double the channel bandwidth and increase the data rates for the 5 GHz capable 802.11ac clients. Using a 40 MHz channel on the 5 GHz radio is also less likely to cause co-channel interference or overlap with other channels than using a 40 MHz channel on the 2.4 GHz radio, which has only three non-overlapping channels. Using a 160 MHz channel on the 5 GHzradio may provide even higher throughput, but it may also consume too much of the available spectrum and cause more interference with other devices or networks. Installing a second AP in the coverage area may also improve the throughput, but it may require additional costs and configuration. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 216; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 206.

The factors that will have the most significant impact on the amount of wireless bandwidth available to each station within a BSS are:

The number of client stations associated to the BSS

The presence of co-located (10m away) access points on non-overlapping channels

The number of client stations associated to the BSS affects the wireless bandwidth because each station shares the same channel and medium with other stations in the same BSS. The more stations there are, the more contention and collision there will be for the channel access, which reduces thethroughput and efficiency of the wireless communication. The wireless bandwidth available to each station depends on how the access point allocates the channel resources and how the stations use the channel time. For example, if the access point uses a round-robin scheduling algorithm, each station will get an equal share of the channel time regardless of its data rate or traffic demand. However, if the access point uses a proportional fair scheduling algorithm, each station will get a share of the channel time that is proportional to its data rate and traffic demand, which may result in higher or lower bandwidth for different stations.

The presence of co-located (10m away) access points on non-overlapping channels affects the wireless bandwidth because even though they use different channels, they may still cause interference and noise to each other due to channel leakage or imperfect filtering. The interference and noise can degrade the signal quality and SNR of the wireless communication, which reduces the data rate and throughput of the wireless communication. The wireless bandwidth available to each station depends on how well the access point and the station can cope with the interference and noise from other channels. For example, if the access point and the station support dynamic frequency selection (DFS) or adaptive radio management (ARM), they can switch to a less congested channel or adjust their output power or antenna gain to avoid or minimize interference from other channels.

References:1, Chapter 3, page 94;2, Section 3.2

The short guard interval is an optional feature of 802.11n and 802.11ac that reduces the time between OFDM symbols from 800 ns to 400 ns. This can increase the data rate by about 11%, but also requires more precise timing and synchronization between the transmitter and the receiver. The short guard interval is only used when both the AP and the client support it and agree to use it . References: [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 163; [CWNA-109Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 157.

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.

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.

 The most effective method for testing roaming in relation to 802.11 VoIP handsets is to place a call with the handset and move around the facility to test quality duringroaming. This method allows you to evaluate the actual performance and user experience of VoIP calls over wireless networks, as well as identify any potential issues such as signal strength, interference, latency, jitter, packet loss, or handoff delays. A spectrum analyzer can only show you the RF activity during a VoIP call, but not how it affects the voice quality or roaming behavior. A protocol analyzer can capture the traffic generated when a laptop roams, but it cannot simulate the characteristics of a VoIP handset such as battery life, antenna design, codec support, or QoS features. A built-in roaming monitor is not a common feature in all VoIP handsets, and it may not provide accurate or comprehensive information about the roaming process. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 487; [Voice over Wireless LAN 4.1 Design Guide], page 6-19.

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

When performing a post-deployment validation survey for voice over Wi-Fi (VoWiFi), an action that must be performed is Application analysis with an active phone call on a VoWiFi handset. Application analysis is a method of testing the performance of a specific application over the WLAN by measuring parameters such as throughput, latency, jitter, packet loss, MOS score, and R-value. Application analysis with an active phone call on a VoWiFi handset can help to evaluate the quality of service (QoS) and user experience of VoWiFi calls over the WLAN. It can also help to identify any issues or bottlenecks that may affect VoWiFi calls such as interference, roaming delays, or insufficient coverage. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 549; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 519.

What should be inspected to verify proper configuration is DNS. DNS stands for Domain Name System and is a service that resolves hostnames to IP addresses. In a controller-based AP deployment, DNS can be used to help the AP locate the controller by using a predefined hostname such as CISCO-CAPWAP-CONTROLLER or aruba-master. The AP sends a DNS query for this hostname and receives an IP address of the controller as a response. Therefore, if DNS is not configured properly or if there is no DNS entry for the controller hostname, the AP may not be able to locate the controller. NTP, BOOTP, and AP hosts file are not relevant for this scenario. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 374; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 364.

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

a mesh portal is a device that connects a mesh BSS (MBSS) to an Ethernet network, such as the Internet. A mesh portal acts as a bridge between the wired and wireless domains, and allows the mesh stations to communicate with external networks. A mesh portal is also a mesh point, which means it can forward traffic within the MBSS.

The other options are not correct. Option A. Mesh Gate is a device that connects a mesh BSS (MBSS) to another mesh BSS or another wireless network, such as an infrastructure BSS or an ad hoc network2. A mesh gate acts as a gateway between different wireless domains, and allows the mesh stations to communicate with other wireless networks. A mesh gate is also a mesh point, which means it can forward traffic within the MBSS. Option B. Mesh Switch is not a valid term in the 802.11 standard. Option C. Mesh Router is also not a valid term in the 802.11 standard.

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.

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

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.

VHT stands for Very High Throughput, which is a physical layer (PHY) specification that supports the 5 GHz frequency band and supports 80 MHz channels. VHT is used by the IEEE 802.11ac standard, which is also known as Wi-Fi 5. VHT allows for higher data rates and more spatial streams than the previous HT (High Throughput) PHY, which is used by the IEEE 802.11n standard, also known as Wi-Fi 4. HT supports the 2.4 GHz and 5 GHz bands, but only supports up to 40 MHz channels12

The other options are not correct because:

ERP (option C) stands for Extended Rate PHY, which is a physical layer specification that supports the 2.4 GHz frequency band and supports up to 20 MHz channels. ERP is used by the IEEE 802.11g standard, which is also known as Wi-Fi 3. ERP allows for higher data rates than the previous DSSS (Direct Sequence Spread Spectrum) PHY, which is used by the IEEE 802.11b standard, also known as Wi-Fi 234

OFDM (option D) stands for Orthogonal Frequency Division Multiplexing, which is a modulation technique that divides a signal into multiple subcarriers that are spaced orthogonally to each other. OFDM is not a physical layer specification, but a common feature of many PHY specifications, including ERP, HT, and VHT. OFDM allows for higher spectral efficiency and robustness against multipath interference than the previous CCK (Complementary Code Keying) modulation technique used by DSSS34

Elevators are a common building item that frequently causes RF shadow and must be accounted for in coverage plans. RF shadow is a term that describes an area where wireless signals are blocked or significantly weakened by an obstacle or an object that absorbs or reflects RF energy. RF shadow can cause lack of coverage or poor performance in a WLAN because wireless devices in those areas may not be able to communicate with access points or other devices. RF shadow can be mitigated by adjusting access point placement, antenna orientation, transmit power level, or channel selection to avoid or overcome the obstacle or object that causes it. Elevators are a common building item that frequently causes RF shadow because they are made of metal and they move up and down within a shaft. Metal is a material that has high attenuation and reflection values, which means it can block or bounce off wireless signals very effectively. A moving elevator can create dynamic RF shadow that changes depending on its position and direction. Therefore, elevators must be accounted for in coverage plans to ensure adequate WLAN coverage and performance throughout the facility. The other options are not common building items that frequently cause RF shadow or must be accounted for in coverage plans. Wooden doors are not likely to cause RF shadow because they are made of wood, which is a material that has low attenuation and reflection values, which means it can pass through or slightly weaken wireless signals. Carpeted floors are not likely to cause RF shadow because they are made of fabric, which is a material that has low attenuation and reflection values, which means it can pass through or slightly weaken wireless signals. Cubicle partitions are not likely to cause RF shadow because they are made of thin plastic or cardboard, which are materials that have low attenuation and reflection values, which means they can pass through or slightly weaken wireless signals. References: CWNA-109 Study Guide, Chapter 13: Wireless LAN Site Surveys - Types & Processes , page 433

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

 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.

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: ExamCWNA-109], page 234; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 224.

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

 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.