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CWNP CWNA-109 Exam
Certified Wireless Network Administrator (Page 4 )

Updated On: 1-Feb-2026
Page 4 of 26
PDF with 122 Questions

When considering data rates available in HT and VHT PHY devices, in addition to the modulation, coding, channel width, and spatial streams, what impacts the data rate according to the MCS tables?

  1. Frequency band in use
  2. client drivers
  3. guard interval
  4. Antenna Height

Answer(s): C

Explanation:

The guard interval is a short period of time inserted between the symbols of an OFDM signal to prevent inter-symbol interference and improve the robustness of the transmission1. The guard interval can have different values depending on the 802.11 standard and the configuration of the device. For example, 802.11n supports two guard intervals: 800 ns (normal) and 400 ns (short)2. 802.11ac supports the same guard intervals as 802.11n, plus an optional 200 ns guard interval for 80 MHz and 160 MHz channels3. 802.11ax supports three guard intervals: 800 ns, 1600 ns, and 3200 ns4.
The guard interval affects the data rate because it determines the duration of each symbol. A shorter guard interval means more symbols can be transmitted in a given time, resulting in a higher data rate. However, a shorter guard interval also means less protection against inter-symbol interference, which may degrade the signal quality and increase the error rate. Therefore, there is a trade-off between data rate and reliability when choosing the guard interval. The MCS tables for HT and VHT PHY devices show the data rates for different combinations of modulation, coding, channel width, spatial streams, and guard intervals. For example, for a VHT device using MCS 9 with QAM-256 modulation, 5/6 coding rate, 80 MHz channel width, and one spatial stream, the data rate is 433.3 Mbps with a normal guard interval (800 ns) and 486.7 Mbps with a short guard interval (400 ns)2. Therefore, the guard interval impacts the data rate according to the MCS tables.



A string of characters and digits is entered into an AP and a client STA for WPA2 security. The string is

8 characters long.
What is this string called?

  1. MSK
  2. WEP key
  3. Passphrase
  4. PSK

Answer(s): C

Explanation:

The string of characters and digits that is entered into an AP and a client STA for WPA2 security and is 8 characters long is called a passphrase. A passphrase is a human-readable text that is used to generate a Pre-Shared Key (PSK) for WPA2-Personal security. A passphrase can be between 8 and 63 characters long and can include any ASCII character. The PSK is a 256-bit key that is derived from the passphrase using a hashing algorithm called PBKDF2. The PSK is used to encrypt and decrypt the data frames between the AP and the client STA. A MSK is a Master Session Key that is generated by an authentication server for WPA2-Enterprise security. A WEP key is a 40-bit or 104-bit key that is used for Wired Equivalent Privacy (WEP) security, which is deprecated and insecure. A PSK is not a string of characters and digits, but a binary key.


Reference:

[CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 303; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 293.



When a STA has authenticated to an AP (AP-1), but still maintains a connection with another AP (AP-
2), what is the state of the STA on AP-1?

  1. Transitional
  2. Unauthenticated and Unassociated
  3. Authenticated and Unassociated
  4. Authenticated and Associated

Answer(s): C

Explanation:

Authenticated and Unassociated. According to one of the web search results1, a STA can be authenticated to multiple APs, but it can only be associated to one AP at a time. Association is the process of establishing a logical link between the STA and the AP, which allows the STA to send and receive data frames through the AP2. Therefore, when a STA has authenticated to an AP-1, but still maintains a connection with another AP-2, it means that the STA is authenticated to both APs, but only associated to AP-2. The state of the STA on AP-1 is authenticated and unassociated, which means that the STA can switch to AP-1 without repeating the authentication process, but it cannot send or receive data frames through AP-1 until it becomes associated.



What statement about 802.11 WLAN performance is true?

  1. In modem networks, both centralized and distributed data forwarding work well for most standard office deployments
  2. In most WLANs, no special skill or tuning is required to get peak performance
  3. WLANs perform better as more wireless clients connect with each AP
  4. To get the best performance out of an AP, you should disable data rates of 72 Mbps and lower

Answer(s): A

Explanation:

The statement that in modern networks, both centralized and distributed data forwarding work well for most standard office deployments is true about WLAN performance. Data forwarding refers to how wireless frames are transmitted from wireless clients to wired networks or vice versa through wireless access points (APs). Centralized data forwarding means that all wireless frames are sent to a central controller or gateway before being forwarded to their destinations. Distributed data forwarding means that wireless frames are forwarded directly by the APs to their destinations without going through a central controller or gateway. Both methods have their advantages and disadvantages, depending on the network size, topology, traffic pattern, security, and management requirements. However, in modern networks, both methods can achieve high performance and scalability for most standard office deployments, as they can leverage advanced features such as fast roaming, load balancing, quality of service, and encryption. The other statements about WLAN

performance are false. In most WLANs, special skill or tuning is required to get peak performance, such as selecting the appropriate channel, power, data rate, and antenna settings. WLANs perform worse as more wireless clients connect with each AP, as they cause more contention and interference on the wireless medium. To get the best performance out of an AP, you should not disable data rates of 72 Mbps and lower, as they are needed for backward compatibility and range extension.


Reference:

CWNA-109 Study Guide, Chapter 9: Wireless LAN Architecture, page 2811



In an 802.11n (H T) 2.4 GHz BSS, what prevents each station from using all the airtime when other client stations are actively communicating in the same BSS?

  1. 802.11 DOS prevention
  2. OFDMA
  3. CSMA/CD
  4. CSMA/CA

Answer(s): D

Explanation:

What prevents each station from using all the airtime when other client stations are actively communicating in the same BSS is CSMA/C
A . CSMA/CA stands for Carrier Sense Multiple Access with Collision Avoidance and is a media access control method used by WLAN devices to share the wireless medium. CSMA/CA works by having each station sense the medium before transmitting a frame. If the medium is busy (i.e., another station is transmitting), the station defers its transmission until the medium is idle. If the medium is idle, the station waits for a random backoff period before transmitting. This way, CSMA/CA reduces the chances of collisions and ensures fair access to the medium for all stations. CSMA/CA also uses positive acknowledgements to confirm successful transmissions and retransmissions to recover from errors. CSMA/CD, DOS prevention, and OFDMA are not used by WLAN devices in a BSS.


Reference:

[CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA- 109], page 108; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA- 109], page 98.



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