Pass the CWNP CWNA CWNA-109 Questions and answers with CertsForce

TVHT stands for Television Very High Throughput and it is a PHY defined by the 802.11af amendment. It uses the TV white space (TVWS) spectrum in the VHF and UHF bands between 54 and 790 MHz, which are not in use by broadcast video signals at the time. It can provide long-range and low-power connectivity for WLAN devices.

Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading. It is the difference between the receiver’s sensitivity and the actual received signal level. A higher Fade Margin indicates a more robust link that can withstand interference, attenuation, or other factors that may reduce the signal strength. A lower Fade Margin means that the link is more susceptible to failure or performance degradation. Fade Margin is usually expressed in decibels (dB) and can be calculated by subtracting the receiver sensitivity from the received signal level. References: 1, Chapter 2, page 51; 2, Section 2.1

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

The power level at the Intentional Radiator (IR) is 250 mW. The IR is the point where the RF signal leaves the transmitter and enters the antenna system. To calculate the power level at the IR, we need to consider the output power level of the transmitter, the loss of the cable, and the gain of the antenna. The formula is:

Power level at IR (dBm) = Output power level (dBm) - Cable loss (dB) + Antenna gain (dBi)

We can convert the output power level of 50 mW to dBm by using the formula:

Power level (dBm) = 10 * log10(Power level (mW))

Therefore, 50 mW = 10 * log10(50) = 16.99 dBm

We can plug in the values into the formula:

Power level at IR (dBm) = 16.99 - 3 + 16 = 29.99 dBm

We can convert the power level at IR from dBm to mW by using the inverse formula:

Power level (mW) = 10^(Power level (dBm) / 10)

Therefore, 29.99 dBm = 10^(29.99 / 10) = 999.96 mW

However, since we need to round off the answer to the nearest integer value, we get:

Power level at IR (mW) = 1000 mW

References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 67; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 57.

The likely cause of the problem is that the external hard drive is USB 3.0 and is causing a significant increase in the noise floor when in use. USB 3.0 devices are known to generate radio frequency interference (RFI) in the 2.4 GHz band due to their high data transfer rates and harmonics. This RFI can increase the noise floor and degrade the signal-to-noise ratio (SNR) of WLAN devices operating in the same band. This can result in lower data rates, reduced throughput, increased retransmissions, and poor performance. The problem may not occur outside of business hours or on the user’s home network because of different usage patterns or environmental factors. References: [CWNP Certified Wireless Network Administrator Official StudyGuide: ExamCWNA-109], page 527; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 497.

 The data rate of a signal is the speed that the data bits in individual 802.11 data frames are sent, but it does not account for the actual amount of data that can be transmitted over time. The throughput of a connection is the flow of information over time, which is affected by various factors such as data encoding, modulation, encryption, airtime utilization, noise levels, interference, etc. Therefore, the throughput is always lower than the data rate. According to one of the web search results1, the actual throughput is normally 60-70 percent of the supported data rates. So, for a connection with a data rate of 150 Mbps, the expected throughput would be around 90-105 Mbps.

CCI is still a possibility in this network because the client devices connected to one of the channel 1 APs will transmit frames that reach the other channel 1 AP as well as clients connected to the other channel 1 AP. CCI stands for co-channel interference, which is a type of interference that occurs when two or more devices transmit on the same channel within range of each other. CCI reduces performance and capacity because it causes contention and collisions on the wireless medium, which leads to retransmissions and delays. CCI can be mitigated by increasing physical separation between devices using the same channel or byreducing transmit power levels to limit coverage area. In this scenario, three access points are used within a facility. One access point is on channel 11 and the other two are on channel 1. The two access points using channel 1 are on either side of the access point using channel 11 and sufficiently apart so that they do not interfere with each other when they transmit frames. However, this does not prevent CCI from occurring between their client devices that are connected on channel 1. For example, if a client device connected to one of the channel 1 APs sends a frame to another device on the wired network or on another wireless network (such as an Internet server or a VoIP phone), that frame will be heard by both channel 1 APs as well as any other client devices connected to either of them on channel 1. This will cause CCI because these devices will have to wait for the channel to be clear before they can transmit their own frames. The answer that CCI only occurs in the 5 GHz frequency band is incorrect; CCI can occur in any frequency band where devices use the same channel. The answer that channel 11 loops around and causes CCI with channel 1 is also incorrect; channel 11 does not loop around and it operates in a different frequency band than channel 1. References: CWNA-109 Study Guide, Chapter 5: Radio Frequency Signal and Antenna Concepts, page 147

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

 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.

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.