CWNP CWNP Certifications CWNA-109 Questions & Answers

• Question 121:

  An 802.11-based network uses an AP and has several connecting clients. The clients include iPhones, iPads, laptops and one desktop. What WLAN use case is represented?

  A. Ad-hoc

  B. WPAN

  C. BSS

  D. IBSS

  Correct Answer: C

  A BSS (Basic Service Set) is a WLAN use case that represents an 802.11- based network that uses an AP (Access Point) and has several connecting clients. The AP acts as a central point of coordination and communication for the clients, which can include iPhones, iPads, laptops, desktops, or any other devices that have Wi-Fi capabilities. A BSS can be identified by a unique BSSID (Basic Service Set Identifier), which is usually the MAC address of the AP's radio interface. A BSS can also be associated with an SSID (Service Set Identifier), which is a human-readable name that identifies the network. References: , Chapter 1, page 23; , Section 1.1

• Question 122:

  You are troubleshooting a problem with a new 802.11ax AP. While the AP supports four spatial streams, most clients are only achieving maximum data rates of 150 Mbps. What is the likely cause?

  A. The clients are 802.11n devices

  B. The clients are only two stream 802.11ax clients

  C. Contention caused by an overlapping BSS

  D. Non-Wi-Fi interference in the channel

  Correct Answer: A

  The scenario described suggests that while the Access Point (AP) is capable of 802.11ax (Wi-Fi 6) with four spatial streams, the clients are only achieving data rates typical of 802.11n (Wi-Fi 4) devices, which indicates that the clients are

  likely 802.11n devices. Here's why this is the most plausible explanation:

  802.11n Limitations: Devices that adhere to the 802.11n standard have lower maximum data rates compared to 802.11ax devices due to differences in technology such as modulation, spatial streams, and channel bandwidth. An 802.11n

  device with a single spatial stream operating on a 20 MHz channel can achieve a maximum data rate of 72.2 Mbps. Even with two spatial streams under ideal conditions, this would only double to approximately 144.4 Mbps, which is close to

  the 150 Mbps mentioned.

  Spatial Stream Capability: The fact that the AP supports four spatial streams suggests it can achieve much higher data rates with 802.11ax clients that also support multiple spatial streams. However, if the clients are 802.11n devices, they

  may not be capable of using more than two spatial streams, and many earlier 802.11n devices were limited to just one.

  The other options are less likely to be the primary cause based on the information provided:

  B. Two Stream 802.11ax Clients: If the clients were 802.11ax with only two spatial streams, they would likely achieve higher data rates than 150 Mbps due to the efficiency improvements in 802.11ax.

  C. Contention and D. Non-Wi-Fi Interference: While these could affect performance, they would not inherently limit clients to 150 Mbps,especially in the context of an 802.11ax environment where mechanisms to handle interference and

  contention are more advanced.

  References:

  IEEE 802.11n-2009: Enhancements for Higher Throughput. CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0- 105, by David D. Coleman and David A. Westcott.