Free CWNP CWNA-109 Practice Exams - Page 27 of 38

Question #261

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?

A . The noise caused by elevators, microwave ovens, and video transmitters.
B . The extra energy radiated by access points and client devices beyond that intended for the signal.
C . The energy radiated by flooring materials that causes interference in the 2.4 GHz and 5 GHz bands.
D . 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.

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Correct Answer: D
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

Question #262

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 . The clients that must support OFDMA must also be upgraded to 802.11ax
B . OFDMA is an optional feature of 802.11ax and most APs don’t even support it
C . All 5 GHz PHYs use OFDM modulation, so you will achieve OFDMA everywhere in 5 GHz
D . If the devices support 802.11ac, they can be updated to support OFDMA through driver upgrades

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Question #263

When using a hotspot, you should do which of the following to ensure security back to your corporate network?

A . Enable WEP.
B . Enable 802.1X/EAP.
C . Use an IPsec VPN.
D . Security cannot be provided because you do not control the access point.

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Question #264

A VoIP telephone is connected to a 24-port PoE midspan PSE.

If the telephone does not provide a classification signature, how much power will the PSE provide to the telephone?

A . 12.95 watts
B . 4.0 watts
C . 7.0 watts
D . 15.4 watts

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Question #265

What is the main cause of co-channel interference?

A . Microwave interference on the same channel within hearing range
B . APs on the same channel within hearing range
C . APs on a different channel within hearing range
D . Clients on the same channel within hearing range
E . Clients on a different channel within hearing range

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Question #266

When implementing an 802.1X/EAP RSN network with a VoWiFi solution, what is needed to avoid latency issues during roaming?

A . Inter-Access Point Protocol
B . Fast BSS Transition
C . Distributed Coordination Function
D . Roaming Coordination Function
E . Lightweight APs

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Question #267

The IEEE 802.11-2012 standard defines communication mechanisms at which layers of the OSI model? (Choose all that apply.)

A . Network
B . Physical
C . Transport
D . Application
E . Data-Link
F . Session

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Question #268

When a client station sends a broadcast probe request frame with a wildcard SSID, how do APs respond?

A . Each AP responds in turn after preparing a probe response and winning contention.
B . For each probe request frame, only one AP may reply with a probe response.
C . Each AP checks with the DHCP server to see if it can respond and then acts accordingly.
D . After waiting a SIFS, all APs reply at the same time with a probe response.

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Question #269

What scenarios might result in a hidden node problem? (Choose all that apply.)

A . Distributed antenna system
B . Coverage cells that are too large
C . Coverage cells that are too small
D . Physical obstruction
E . Co-channel interference

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Question #270

Which of the following are objectives of fixed mobile convergence? (Choose all that apply.)

A . Have a single phone number.
B . Have a single device.
C . Always use the best-performing network.
D . Use the lowest-cost network.

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