Passed Exam Today CWNA-109

The IEEE 802.11ax standard, also known as High-Efficiency Wireless (HEW) or simply HE, includes support for operation across multiple frequency bands: 2.4 GHz, 5 GHz, and, with the appropriate regulatory approvals, the 6 GHz band. This makes option D the correct answer. Here's how it compares to the other options:

HE (802.11ax): Introduced as an enhancement over previous standards, 802.11ax is designed to improve efficiency, especially in dense environments. It supports operation in the 2.4 GHz, 5 GHz, and 6 GHz bands (the latter pending regulatory approval in various regions), making it highly versatile and future-proof.

VHT (802.11ac): Very High Throughput, or 802.11ac, operates exclusively in the 5 GHz band. It introduced significant speed improvements over its predecessor (802.11n) but does not support the 2.4 GHz or 6 GHz bands.

HT (802.11n): High Throughput, or 802.11n, supports operation in both the 2.4 GHz and 5 GHz bands. However, it does not include support for the 6 GHz band.

HR/DSSS (802.11b): High-Rate Direct Sequence Spread Spectrum, or 802.11b, operates only in the 2.4 GHz band. It was one of the early Wi-Fi standards and does not support 5 GHz or 6 GHz bands.

Given these distinctions, only 802.11ax (option D) supports operation across all three mentioned bands, aligning with the requirements stated in the question.

The client STA can use Beacon frames transmitted by the AP to verify that an AP supports the same data rates that it supports. Beacon frames are management frames that are periodically broadcasted by the APs to announce their presence, capabilities, and parameters. One of the information elements contained in the Beacon frames is the Supported Rates or Extended Supported Rates, which lists the data rates that the AP can use for communication. The client STA can compare its own data rates with those advertised by the AP to determine if they are compatible. Data frames, authentication frames, and probe request frames do not contain information about data rates. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 133; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 123.

DHCP (Dynamic Host Configuration Protocol) is a commonly used method to locate the controllers by the APs in a WLAN that is implemented using wireless controllers. DHCP is a protocol that allows a device to obtain an IP address and other network configuration parameters from a server. In a wireless controller scenario, the APs can use DHCP to request an IP address from a DHCP server, which can also provide the IP address or hostname of the wireless controller as an option in the DHCP response. This way, the APs can discover the wireless controller and establish a connection with it. Alternatively, the APs can also use other methods to locate the wireless controller, such as DNS (Domain Name System), broadcast or multicast discovery, or manual configuration. References: 1, Chapter 8, page 309; 2, Section 5.2

The feature of 802.11ax (HE) that provides this functionality is OFDMA. OFDMA stands for Orthogonal Frequency Division Multiple Access and is a technology that allows multiple devices to communicate simultaneously on the same channel in the same BSS. OFDMA works by dividing a channel into smaller subchannels called Resource Units (RUs), which are composed of groups of subcarriers or tones. Each RU can be assigned to a different device based on its bandwidth requirement and signal quality. This way, OFDMA can increase the efficiency and capacity of the channel by reducing overhead, contention, and latency. OFDMA can also support both uplink and downlink multi-user transmissions using trigger frames and buffer status reports. 6 GHz support, TWT, and Wi-Fi-LTE are not features of 802.11ax that provide this functionality. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 226; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 216.