CWNP CWNA-109 - Certified Wireless Network Administrator

 The frame type that is used to reserve the wireless medium for the transmission of high data rate frames that may not be understood by all clients connected to the BSS is RTS. RTS stands for Request to Send and is a control frame that is sent by a station to request access to the medium for a specified duration. The RTS frame contains the source and destination MAC addresses, as well as a Network Allocation Vector (NAV) value that indicates how long the medium will be occupied. The destination station responds with a Clear to Send (CTS) frame that echoes the NAV value and grants permission to the source station. All other stations in the BSS hear either the RTS or CTS frame and update their NAV timers accordingly, deferring their transmissions until the medium is free. The RTS/CTS mechanism can be used to prevent hidden node problems, reduce collisions, and protect high data rate frames that use features such as 802.11n or 802.11ac that may not be compatible with legacy stations. ACK, Beacon, and PS-Poll are not used to reserve the medium for high data rate frames. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 112; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 102.

The solution that you recommend is an Overlay WLAN monitoring solution. An Overlay WLAN monitoring solution is a system that uses dedicated sensors or probes to monitor the WLAN performance over time. The sensors are deployed throughout the WLAN coverage area and collect data on various metrics such as signal strength, noise level, channel utilization, interference, throughput, latency, packet loss, and QoS. The sensors send the data to a centralized server or appliance that analyzes the data and provides a single pane of glass for administration and monitoring of the solution. An Overlay WLAN monitoring solution can help to detect and troubleshoot WLAN issues, optimize WLAN performance, and generate reports and alerts. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 538; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 508.

Patch and panel antennas are directional antenna types that are commonly used by indoor Wi-Fi devices in a MIMO multiple spatial stream implementation. These antennas have a flat rectangular shape and can be mounted on walls or ceilings to provide coverage in a specific direction. They have a moderate gain and a relatively wide beamwidth, making them suitable for multipath environments where signals can reflect off different surfaces and create multiple spatial streams. Patch and panel antennas can also support polarization diversity, which means they can transmit and receive both horizontally and vertically polarized waves, increasing the MIMO performance. References: 1, Chapter 2, page 72; 2, Section 2.4

Refraction is the bending of an RF signal as it passes through a medium with a different density than free space. This can cause the signal to change its direction and speed, which can affect the accuracy and reliability of wireless communication. Refraction is influenced by factors such as temperature, humidity, and atmospheric pressure12. References: CWNA-109 Study Guide, Chapter 2: Radio Frequency Fundamentals, page 72; CWNA-109 Study Guide, Chapter 2: Radio Frequency Fundamentals, page 67.

In a public Wi-Fi hotspot, like the one Lynne runs in his hotel, ensuring customer security against active attacks is crucial. Active attacks involve unauthorized access, eavesdropping, or manipulation of the network traffic. To mitigate such threats, an effective and practical step is:

Station-to-Station Traffic Blocking: Also known as client isolation, this feature prevents direct communication between devices connected to the Wi-Fi network. By enabling this on the access points, Lynne can significantly decrease the likelihood of active attacks like man-in-the-middle (MITM) attacks, where an attacker intercepts and possibly alters the communication between two parties.

The other options, while beneficial for network security, might not be as straightforward or practical for Lynne's situation:

Network Access Control (NAC) requires a more complex infrastructure and management, which might not be ideal for a small hotel setup.

Implementing an SSL VPN adds an extra layer of security but might complicate the login process for users, potentially affecting the user experience.

Requiring EAP-FAST authentication provides secure authentication but may not be feasible for transient customers who expect quick and easy network access.

Therefore, enabling station-to-station traffic blocking is a practical and efficient measure that Lynne can implement to enhance customer security on the Wi-Fi network.

Refraction is the bending of an RF signal as it passes through a material of different density. Refraction can cause the signal to change its direction and angle of arrival. For example, when a light beam passes from air to water, it bends because of the difference in the refractive index of the two mediums. Similarly, when an RF signal passes from one medium to another, such as from air to glass, it can bend due to the change in the dielectric constant of the materials12. References: 1: CWNA-109 Official Study Guide, page 67 2: Refraction

In the 802.11ax (High Efficiency, HE) amendment, one of the key features introduced is BSS (Basic Service Set) Coloring. This feature is designed to mitigate issues arising from overlapping BSSs (OBSS), which can lead to contention and interference in dense wireless environments. BSS Coloring works by:

Assigning a "color" (a small number) to each BSS: This helps devices differentiate between frames from their own BSS and those from neighboring BSSs.

Reducing Inter-BSS Interference: Devices can ignore frames from different BSSs (with a different "color") under certain conditions, reducing the impact of OBSS interference.

Improving Spatial Reuse: By distinguishing between transmissions from different BSSs, devices can make more informed decisions about when to transmit, improving the efficiency of spatial reuse and reducing unnecessary contention.

This feature directly impacts design decisions related to AP placement and the spacing between same-channel BSS cells, as it allows for closer placement of APs on the same channel without significantly increasing interference, thus improving overall network capacity and efficiency.

The other options, while features of 802.11ax, do not directly pertain to reducing overlapping BSS contention in the same manner:

TWT (Target Wake Time) optimizes device sleep schedules to conserve power.

Uplink MU-MIMO enhances uplink data transmission capabilities but doesn't specifically address OBSS contention.

6 GHz Band Support introduces new spectrum for Wi-Fi use but is not a feature aimed at reducing OBSS contention within the 802.11ax framework.

Therefore, the correct answer is B, BSS Color.

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 . References: [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.