CWNP Updated CWNA-108 Exam Questions and Answers by idrees

The clients are 802.11n devices. 802.11n devices can only support a maximum of four spatial streams, and the maximum data rate for a single spatial stream is 150 Mbps. Therefore, if most clients are only achieving 150 Mbps, it means they are using only one spatial stream, which is typical for 802.11n devices. To achieve higher data rates, the clients would need to support more spatial streams, which is possible with 802.11ax devices12.

The other options are not correct because they do not explain why most clients are only achieving 150 Mbps. Option B is incorrect because two stream 802.11ax clients can achieve data rates of up to 574 Mbps in a 20 MHz channel1. Option C is incorrect because contention caused by an overlapping BSS would affect all clients, not just most of them, and it would also reduce the throughput, not the data rate. Option D is incorrect because non-Wi-Fi interference in the channel would also affect all clients, not just most of them, and it would also cause errors and retransmissions, not lower data rates.

References: 1: CWNA-108 Official Study Guide, page 144 2: 802.11ax data rates

An IBSS is used instead of a BSS is a network configuration that would result in multiple stations broadcasting Beacon frames with the same BSSID but with different source addresses. An IBSS (Independent Basic Service Set) is a type of WLAN that does not use an AP but rather allows stations to communicate directly with each other in a peer-to-peer manner. An IBSS is also known as an ad-hoc network or a peer-to-peer network. In an IBSS, each station generates its own Beacon frames to announce its presence and capabilities to other stations within range. The Beacon frames have the same BSSID, which is randomly generated by one of the stations when creating the IBSS, but they have different source addresses, which are the MAC addresses of each station’s radio interface. The BSSID is used to identify the IBSS and prevent stations from joining other IBSSs with different BSSIDs. References: , Chapter 1, page 25; , Section 1.1

When a station scans for available wireless networks, it listens for beacon frames sent by APs. A beacon frame contains information about the BSS, such as SSID, supported rates, channel, security, etc. The station also measures the signal strength of the beacon frames, which indicates how well the station can communicate with the AP. The signal strength is usually expressed in dBm or RSSI units. The higher the signal strength, the better the connection quality and performance. Therefore, the station can use the signal strength of AP beacons as the primary metric to select the best AP for connectivity to the desired BSS12. References: CWNA-109 Study Guide, Chapter 6: Wireless LAN Devices and Topologies, page 249; CWNA-108 Study Guide, Chapter 6: Wireless LAN Devices and Topologies, page 243.

OFDM is a modulation method that divides the channel bandwidth into multiple subcarriers, each carrying a single data symbol. This allows for higher data rates and more robust transmissions in multipath environments. OFDM was first introduced in the 802.11a standard, which operates in the 5 GHz band and supports data rates up to 54 Mbps. Later, the 802.11g standard adopted OFDM for the 2.4 GHz band, and the 802.11n and 802.11ac standards enhanced OFDM with features such as MIMO (Multiple Input Multiple Output), channel bonding, and higher-order modulation schemes to achieve data rates up to 600 Mbps and 6.9 Gbps, respectively. These standards are collectively known as the ERP (Extended Rate PHY), HT (High Throughput), and VHT (Very High Throughput) PHYs . References: [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 163; [CWNA-108 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 157.