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CWNP CWNA-109 Exam
Certified Wireless Network Administrator (Page 11 )

Updated On: 7-Feb-2026
Page 5 of 26
PDF with 122 Questions

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?

  1. Increasing or decreasing the number of spatial streams in use by the client station and AP
  2. Implementing Fast BSS Transition (FT) for roaming
  3. Implementation of several other clients in the same BSS using 802.11g radios
  4. RF interference from more than 10 nearby Bluetooth transmitters

Answer(s): B

Explanation:

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 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 application layer throughput. FT is defined in the IEEE 802.11r amendment and is also known as Fast Roaming or Fast Secure Roaming.


Reference:

, Chapter 9, page 367; , Section 6.3



What ID is typically mapped to an AP's MAC address if a single BSS is implemented?

  1. SSID
  2. Device ID
  3. VLAN ID
  4. BSSID

Answer(s): D

Explanation:

The BSSID (Basic Service Set Identifier) is typically mapped to an AP's MAC address if a single BSS is implemented. The BSSID is a unique identifier that distinguishes one BSS from another within the same RF medium. It is usually derived from the MAC address of the AP's radio interface, but it can also be manually configured or randomly generated by some vendors. The BSSID is used by client stations to associate with an AP and to send and receive frames within a BSS.


Reference:

Chapter 1, page 24; , Section 1.2



What is appended to the end of each 802.11 data frame after the payload?

  1. Preamble
  2. MAC header
  3. PHY header
  4. FCS

Answer(s): D

Explanation:

The FCS (Frame Check Sequence) is appended to the end of each 802.11 data frame after the payload. The FCS is a 4-byte field that contains a CRC-32 (Cyclic Redundancy Check) value that is calculated based on the contents of the MAC header and the payload of the frame. The FCS is used by the receiver to verify the integrity of the frame and to detect any errors or corruption that may have occurred during transmission. If the FCS does not match with the expected value, the frame is discarded by the receiver.


Reference:

Chapter 4, page 139; , Section 4.2



When an ACK frame is not received by the transmitting STA, what is assumed?

  1. The receiver processed the frame, but did not respond with an ACK frame because 802.11w is enabled
  2. The frame was correctly delivered
  3. The frame was not delivered and must be retransmitted
  4. The receiver is offline

Answer(s): C

Explanation:

An ACK (Acknowledgement) frame is a short control frame that is sent by the receiver of a data or management frame to confirm that the frame was received correctly. The ACK frame is sent after a SIFS (Short Interframe Space) interval, which is the shortest time gap between frames in 802.11. If the transmitter does not receive an ACK frame within a specified time, it assumes that the frame was not delivered and must be retransmitted. This is part of the 802.11 reliability mechanism that ensures reliable data delivery over an unreliable wireless medium .


Reference:

[CWNA-109 Study Guide], Chapter 5: IEEE 802.11 Medium Access, page 209; [CWNA-109 Study Guide], Chapter 5: IEEE 802.11 Medium Access, page 203.



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

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

Answer(s): A

Explanation:

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.


Reference:

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.



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