CWNP CWNA-107 Exam Questions

What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM) modulation method in IEEE 802.11 WLANs?

OFDM was used by Frequency Hopping Spread Spectrum (FHSS) PHY devices.

OFDM was first introduced in 802.11 and is used by the ERP, HT and VHT PHYs as well.

OFDM implement BPSK modulation to allow for data rates up to 7 Gbps.

OFDM modulation is used only in 5 GHz 802.11 transmissions.

Correct Answer: B

Orthogonal Frequency Division Multiplexing (OFDM) was first introduced in the IEEE 802.11a standard and is utilized by Enhanced Rate PHY (ERP), High Throughput (HT), and Very High Throughput (VHT) PHYs. This means that OFDM is not limited to just 5 GHz transmissions but is also used in the 2.4 GHz band. These uses help achieve higher data rates and improve performance in IEEE 802.11 WLANs.

What factor is likely to cause the least impact on the application layer throughput of an 802.11n client station in a 2.4 GHz HT BSS?

Increasing or decreasing the number of spatial streams in use by the client station and AP

Implementation of several other clients in the same BSS using 802.11 g radios

Implementing Fast BSS Transition (FT) for roaming

RF interface from more than 10 nearby Bluetooth transmitters

Correct Answer: C

Implementing Fast BSS Transition (FT) for roaming is likely to cause the least impact on the application layer throughput of an 802.11n client station in a 2.4 GHz HT BSS. FT is designed to improve the efficiency of roaming between access points, but under typical usage, it does not significantly affect the application layer throughput when the client station is not in the process of roaming. On the other hand, the number of spatial streams, presence of other 802.11g clients, and interference from Bluetooth transmitters can have a more direct and substantial impact on throughput.

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

For each probe request frame, only one AP may reply with a probe response.

Each AP responds in turn after preparing a probe response and winning contention.

Each AP checks with the DHCP server to see if it can respond and then acts accordingly.

After waiting a SIFS, all APs reply at the same time with a probe response.

Correct Answer: B

When a client station sends a broadcast probe request frame with a wildcard SSID, each AP that receives the request will respond independently. The APs will prepare their probe responses and then attempt to transmit them after competing for access to the medium using the standard contention process. This ensures that the APs do not transmit their responses simultaneously, which would result in collisions.

You are reconfiguring an AP to use the short guard interval. How long will the new guard interval duration be after the change?

Correct Answer: A

When reconfiguring an Access Point (AP) to use the short guard interval, the new guard interval duration will be 400 nanoseconds (ns). This is standard for many modern wireless networks, including 802.11n, where the short guard interval helps to increase data throughput by reducing the delay between symbol transmissions.

You manage a WLAN with 100 802.11ac access points. All access points are configured to use 80 MHz channels. In a particular BSS, only 40 MHz communications are seen. What is the likely cause of this behavior?

The short guard interval is also enabled.

The clients are all 802.11n STAs or lower

The AP is improperly configured to use only 40 MHz of the 80 MHz allocated bandwidth

All clients implement single spatial stream radios

Correct Answer: B

In a WLAN using 802.11ac access points configured for 80 MHz channels, if only 40 MHz communications are seen, it is likely because the clients connected to that Basic Service Set (BSS) are all 802.11n STAs or lower. 802.11n clients support up to 40 MHz channels, whereas 802.11ac clients can support wider channels like 80 MHz. Therefore, the presence of only 40 MHz communications suggests that the connected devices are unable to utilize the 80 MHz channels typical of more advanced 802.11ac devices.