Questions for the CWNA-109 were updated on : Nov 21 ,2025
Which IEEE 802.11 physical layer (PHY) specification includes support for operation in the 2.4 GHz, 5
GHz, and 6 GHz bands?
D
Explanation:
The IEEE 802.11ax standard, also known as High-Efficiency Wireless (HEW) or simply HE, includes
support for operation across multiple frequency bands: 2.4 GHz, 5 GHz, and, with the appropriate
regulatory approvals, the 6 GHz band. This makes option D the correct answer. Here's how it
compares to the other options:
HE (802.11ax): Introduced as an enhancement over previous standards, 802.11ax is designed to
improve efficiency, especially in dense environments. It supports operation in the 2.4 GHz, 5 GHz,
and 6 GHz bands (the latter pending regulatory approval in various regions), making it highly
versatile and future-proof.
VHT (802.11ac): Very High Throughput, or 802.11ac, operates exclusively in the 5 GHz band. It
introduced significant speed improvements over its predecessor (802.11n) but does not support the
2.4 GHz or 6 GHz bands.
HT (802.11n): High Throughput, or 802.11n, supports operation in both the 2.4 GHz and 5 GHz bands.
However, it does not include support for the 6 GHz band.
HR/DSSS (802.11b): High-Rate Direct Sequence Spread Spectrum, or 802.11b, operates only in the
2.4 GHz band. It was one of the early Wi-Fi standards and does not support 5 GHz or 6 GHz bands.
Given these distinctions, only 802.11ax (option D) supports operation across all three mentioned
bands, aligning with the requirements stated in the question.
Reference:
IEEE 802.11ax-2021: High-Efficiency Wireless LAN Medium Access Control (MAC) and Physical Layer
(PHY) Specifications.
Understanding the 802.11ax (Wi-Fi 6) standard and its implications for modern wireless networking.
You have implemented an 802.11ax WLAN for a customer. All APs are four stream HE APs. The
customer states that it is essential that most of the clients can use the OFDMA modulation scheme.
What do you tell the customer?
A
Explanation:
OFDMA is a new modulation scheme introduced in 802.11ax that allows multiple users to share the
same channel by dividing it into smaller subchannels called resource units (RUs). This improves the
efficiency and capacity of the WLAN by reducing contention and overhead. However, to use OFDMA,
both the AP and the client must support 802.11ax and negotiate the parameters of the subchannel
allocation.
Therefore, the customer needs to upgrade the clients that require OFDMA to 802.11ax
devices12
.
The other options are not correct because they do not reflect the reality of OFDMA.
Option B is
incorrect because OFDMA is a mandatory feature of 802.11ax for both downlink and uplink
transmissions, and all 802.11ax APs must support it1
. Option C is incorrect because OFDM and
OFDMA are different modulation schemes, and OFDM does not allow multiple users to share the
same channel.
Option D is incorrect because 802.11ac devices cannot support OFDMA through driver
upgrades, as they lack the hardware and firmware capabilities to do so2
.
Reference: 1: CWNA-109 Official Study Guide, page 144 2
:
OFDMA
You are troubleshooting a problem with a new 802.11ax AP. While the AP supports four spatial
streams, most clients are only achieving maximum data rates of 150 Mbps. What is the likely cause?
A
Explanation:
The scenario described suggests that while the Access Point (AP) is capable of 802.11ax (Wi-Fi 6) with
four spatial streams, the clients are only achieving data rates typical of 802.11n (Wi-Fi 4) devices,
which indicates that the clients are likely 802.11n devices. Here's why this is the most plausible
explanation:
802.11n Limitations: Devices that adhere to the 802.11n standard have lower maximum data rates
compared to 802.11ax devices due to differences in technology such as modulation, spatial streams,
and channel bandwidth. An 802.11n device with a single spatial stream operating on a 20 MHz
channel can achieve a maximum data rate of 72.2 Mbps. Even with two spatial streams under ideal
conditions, this would only double to approximately 144.4 Mbps, which is close to the 150 Mbps
mentioned.
Spatial Stream Capability: The fact that the AP supports four spatial streams suggests it can achieve
much higher data rates with 802.11ax clients that also support multiple spatial streams. However, if
the clients are 802.11n devices, they may not be capable of using more than two spatial streams, and
many earlier 802.11n devices were limited to just one.
The other options are less likely to be the primary cause based on the information provided:
B . Two Stream 802.11ax Clients: If the clients were 802.11ax with only two spatial streams, they
would likely achieve higher data rates than 150 Mbps due to the efficiency improvements in
802.11ax.
C . Contention and D. Non-Wi-Fi Interference: While these could affect performance, they would not
inherently limit clients to 150 Mbps, especially in the context of an 802.11ax environment where
mechanisms to handle interference and contention are more advanced.
Reference:
IEEE 802.11n-2009: Enhancements for Higher Throughput.
CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, by David D.
Coleman and David A. Westcott.
What can cause excessive VSWR in RF cables used to connect a radio to an antenna?
D
Explanation:
Impedance is the measure of opposition to the flow of alternating current (AC) in a circuit.
Impedance mismatch occurs when the impedance of the radio does not match the impedance of the
antenna or the cable. This causes some of the transmitted or received signal to be reflected back,
resulting in a loss of power and efficiency. The voltage standing wave ratio (VSWR) is a metric that
indicates the amount of impedance mismatch in a transmission line. A higher VSWR means a higher
impedance mismatch and a lower signal quality. A VSWR of 1:1 is ideal, meaning there is no
impedance mismatch and no reflected power.
A VSWR of 2:1 means that for every 2 units of forward
power, there is 1 unit of reflected power12
.
The other options are not correct because they do not affect the VSWR in RF cables. A high gain yagi
antenna or a high gain parabolic dish antenna can increase the signal strength and directionality, but
they do not cause impedance mismatch in the cable.
Radio output power above 100 mW but below
400 mW is within the acceptable range for most WLAN devices and does not cause excessive VSWR
in the cable3
.
Reference: 1: CWNA-109 Official Study Guide, page 77 2
:
VSWR 3
: CWNA-109 Official Study Guide,
page 81
An RF signal sometimes bends as it passes through a material rather than around an obstacle. What
is the RF behavior that this statement best describes?
B
Explanation:
Refraction is the bending of an RF signal as it passes through a material of different density.
Refraction can cause the signal to change its direction and angle of arrival. For example, when a light
beam passes from air to water, it bends because of the difference in the refractive index of the two
mediums.
Similarly, when an RF signal passes from one medium to another, such as from air to glass,
it can bend due to the change in the dielectric constant of the materials12. Reference: 1: CWNA-109
Official Study Guide, page 67 2
:
Refraction
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?
D
Explanation:
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 and cookies, 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. Reference: [CWNP Certified
Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 343; [CWNA: Certified
Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 333.
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?
B
Explanation:
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. Reference: [CWNP Certified Wireless Network Administrator Official Study
Guide: Exam CWNA-109], page 562; [CWNA: Certified Wireless Network Administrator Official Study
Guide: Exam CWNA-109], page 532.
You administer a small WLAN with nine access point. As a small business, you do not rum a RADIUS
server and use WPA2-Personal for security. Recently, you changed the passphrase for WPA2-personal
in all Aps and clients. Several users are now reporting the inability to connect to the network at time
and it is constrained to one area of the building. When using scanner, you see that the AP covering
that area is online
B
Explanation:
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 match with 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
You are attempting to explain RF shadow and how it can cause lack of coverage. What common
building item frequently causes RF shadow and must be accounted for in coverage plans?
C
Explanation:
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. Reference: CWNA-109 Study Guide, Chapter 13: Wireless LAN Site Surveys - Types &
Processes , page 433
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?
D
Explanation:
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. Reference: CWNA-109 Study Guide, Chapter 5: Radio Frequency Signal and Antenna
Concepts, page 139
When using a spectrum to look for non Wi-Fi interference sources, you notice significant interference
across the entire 2.4 GHz band (not on a few select frequencies) within the desktop area of a users
workspace, but the interference disappears quickly after just 2 meters. What is the most likely cause
of this interference?
A
Explanation:
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,
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.
C
Explanation:
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. Reference: CWNA-109 Study Guide, Chapter 14:
Troubleshooting Wireless LANs, page 4831
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?
B
Explanation:
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. Reference: [CWNP Certified Wireless Network Administrator
Official Study Guide: Exam CWNA-109], page 81; [CWNA: Certified Wireless Network Administrator
Official Study Guide: Exam CWNA-109], page 71.
802. 11ax (HE) introduces Resource Units that can be used to allow communications with multiple
devices at the same time, on the same channel, in the same BSS. What feature of 802.1 lax provides
this functionality?
D
Explanation:
The feature of 802.11ax (HE) that provides this functionality is OFDM
A . OFDMA stands for Orthogonal Frequency Division Multiple Access and is a technology that allows
multiple devices to communicate simultaneously on the same channel in the same BSS. OFDMA
works by dividing a channel into smaller subchannels called Resource Units (RUs), which are
composed of groups of subcarriers or tones. Each RU can be assigned to a different device based on
its bandwidth requirement and signal quality. This way, OFDMA can increase the efficiency and
capacity of the channel by reducing overhead, contention, and latency. OFDMA can also support
both uplink and downlink multi-user transmissions using trigger frames and buffer status reports. 6
GHz support, TWT, and Wi-Fi-LTE are not features of 802.11ax that provide this
functionality. Reference: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam
CWNA-109], page 226; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam
CWNA-109], page 216.
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
Explanation:
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. Reference: [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.