CWNA-109 Certified Wireless Network Administrator Questions and Answers

The term used to describe the problem in this configuration is Co-Channel Interference (CCI)1. CCI occurs when multiple access points are on the same or overlapping channels, causing interference and degradation in network performance1. In this case, one AP is on channel 1 and the other is on channel 2, which are overlapping channels, leading to CCI1.

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-109Official Study Guide, page 67 2: Refraction

WLAN bridges must use a channel with acceptable SNR at both transceivers to maintain the desired data rate bi-directionally. A WLAN bridge is a device that connects two or more networks using the 802.11 protocol. A WLAN bridge must have a clear and strong signal between the two endpoints to ensure reliable and fast data transmission. The signal-to-noise ratio (SNR) is a measure of the quality of the signal, which depends on the distance, interference, obstacles, and antenna gain between the transceivers. A higher SNR means a better signal quality and a higher data rate. A lower SNR means a worse signal quality and a lower data rate. Therefore, a WLAN bridge must use a channel with acceptable SNR at both transceivers to maintain the desired data rate bi-directionally1.

The short guard interval is an optional feature of 802.11n and 802.11ac that reduces the time between OFDM symbols from 800 ns to 400 ns. This can increase the data rate by about 11%, but also requires more precise timing and synchronization between the transmitter and the receiver. The short guard interval is only used when both the AP and the client support it and agree to use it . References: [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 163; [CWNA-109Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 157.

A common feature of MDM solutions that can be used to protect enterprise data on mobile devices is containerization. Containerization is a technique that creates a separate and secure environment on the mobile device where enterprise data and applications are stored and accessed. Containerization isolates the enterprise data from the personal data and prevents unauthorized access, leakage, or loss of sensitive information. Containerization can also enforce security policies, encryption, authentication, and remote wipe on the enterprise data and applications. Over-the-air registration, onboarding, and self-registration are features of MDM solutions that facilitate the enrollment and management of mobile devices, but they do not directly protect enterprise data on mobile devices. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 336; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 326.

An isotropic radiator is a theoretical point source of electromagnetic radiation that radiates equally in all directions. It has no physical dimensions and no preferred direction of radiation. It is used as a reference for antenna gain because it represents the ideal case of a perfect omnidirectional antenna12

Antenna gain is a measure of how well an antenna concentrates its radiated power in a certain direction. It is expressed in decibels (dB) relative to a reference antenna. Whenthe reference antenna is an isotropic radiator, the antenna gain is denoted by dBi, which stands for decibels relative to isotropic12

For example, an antenna with a gain of 3 dBi means that it radiates 3 dB more power in its main direction than an isotropic radiator would. Conversely, an antenna with a gain of -3 dBi means that it radiates 3 dB less power in its main direction than an isotropic radiator would12

Granting access to specific network services or resources according to a user profile describes the authorization component of a AAA implementation. AAA stands for Authentication, Authorization, and Accounting, which are three functions that are used to control and monitor access to network resources and services. Authentication is the process of verifying that a user is who he says he is, by using credentials such as username, password, certificate, token, or biometric data. Authorization is the process of granting access to specific network services or resources according to a user profile, which defines the user’s role, privileges, and permissions. Accounting is the process of recording and reporting the usage of network services or resources by a user, such as the duration, volume, type, and location of the access. AAA can be implemented by using different protocols andservers, such as RADIUS, TACACS+, LDAP, Kerberos, or Active Directory. References: 1, Chapter 11, page 449; 2, Section 7.1

The authentication method that is referenced in the 802.11-2016 and 802.11-2020 specifications and is recommended for robust WLAN client security is 802.1X/EAP. 802.1X/EAP stands for IEEE 802.1X Port-Based Network Access Control with Extensible Authentication Protocol and is a framework that provides strong authentication and dynamic encryption key generation for WLAN clients. 802.1X/EAP involves three parties: the supplicant (the client), the authenticator (the AP or the controller), and the authentication server (usually a RADIUS server). The supplicant sends its credentials (such as username and password, certificate, or token) to the authenticator, which forwards them to the authentication server. The authentication server verifies the credentials and sends a response to the authenticator, which grants or denies access to the supplicant. The authentication server also generates a master key that is used to derive encryption keys for the data frames between the supplicant and the authenticator. 802.1X/EAP supports various EAP methods that offer different levels of security and flexibility, such as EAP-TLS, EAP-PEAP, EAP-TTLS, EAP-FAST, and EAP-SIM. SSL, IPSec, and WEP are not authentication methods, but rather encryption or security protocols that are not specific to WLANs or referenced in the 802.11 specifications. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 299; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 289.

VoIP (Voice over Internet Protocol) is an application that is likely used that demands the requirements of unidirectional delays of less than 150 ms and the signal strength at all receivers can be no lower than -67 dBm. VoIP is an application that allows users to make and receive voice calls over a network, such as the Internet or a WLAN. VoIP is a real-time and interactive application that requires high quality of service (QoS) to ensure good user experience and satisfaction. One of the QoS metrics for VoIP is delay, which is the time it takes for a voice packet to travel from the sender to the receiver. Delay can affect the quality and intelligibility of the voice conversation, as well as the synchronization and naturalness of the dialogue. The ITU-T G.114 recommendation suggests that the maximum acceptable one-way delay for VoIP should be less than 150 ms, as anything higher than that can cause noticeable degradation and annoyance to the users. Another QoS metric for VoIP is signal strength, which is the measure of how strong the RF signal is at the receiver. Signal strength can affect the reliability and performance of the wireless connection, as well as the data rate and throughput of the VoIP traffic. The CWNA Official Study Guide recommends that the minimum signal strength for VoIP should be -67 dBm, as anything lower than that can cause packet loss, retries, jitter, and other issues that can impair the voice quality. References: 1, Chapter 10, page 398; 2, Section 6.1

The client drivers are faulty and should be upgraded is the likely problem for the laptop that can see and connect to 2.4 GHz APs, but does not even see 5 GHz APs. The client drivers are the software components that enable the wireless adapter of the laptop to communicate with the operating system and the network. The client drivers are responsible for scanning the available wireless channels, detecting and connecting to the access points, negotiating the security and data rate parameters, and transmitting and receiving data frames. If the client drivers are faulty, outdated, or incompatible, they may cause various issues with the wireless performance and functionality, such as low data rates, poor signal strength, frequent disconnections, or inability to see or connect to certain access points or channels.

One of the possible causes of faulty client drivers is that they do not support or recognize some of the features or standards of the 802.11ac technology, such as wider channel bandwidths, higher modulation schemes, or DFS (Dynamic Frequency Selection) channels. This could explain why the laptop can see and connect to 2.4 GHz APs, but not 5 GHz APs, as 802.11ac operates only in the 5 GHz band and uses channels that are wider (up to 160 MHz) and higher (up to channel 165) than those used by previous standards. Moreover, some of the 5 GHz channels are subject to DFS rules, which require the access points and client stations to monitor and avoid using channels that are occupied by radar systems or other primary users. If the client drivers do not support or comply with DFS rules, they may not be able to see or connect to access points that use DFS channels.

To solve this problem, the client drivers should be upgraded to the latest version that supports and is compatible with 802.11ac features and standards. This can be done by downloading and installing the updated driver software from the manufacturer’s website or using a device manager tool. Upgrading the client drivers may also improve other aspects of wireless performance and functionality, such as data rates, signal strength, security, and stability. References: 1, Chapter 12, page 493; 2, Section 8.1

The RF energy that exists in the environment from intentional and unintentional RF radiators that forms the baseline above which the intentional signal of your WLAN must exist is the best explanation of the noise floor noted in the report. The noise floor is a term that describes the level of background noise or interference in a wireless channel or band. The noise floor is measured in dBm (decibel-milliwatts) and it represents the minimum signal strength that can be detected or received by a wireless device. The noise floor is influenced by various factors, such as the sensitivity of the receiver, the antenna gain, the cable loss, and the ambient RF environment. The ambient RF environment consists of intentional and unintentional RF radiators that emit RF energy in the wireless spectrum. Intentional RF radiators are devices that are designed to transmit RF signals for communication purposes, such as Wi-Fi access points, Bluetooth devices, microwave ovens, or cordless phones. Unintentional RF radiators are devices that are not designed to transmit RF signals but generate electromagnetic radiation as a by-product of their operation, such as USB 3 devices, PC power supplies, or fluorescent lights. The noise floor affects WLAN performance and quality because it determines the minimum signal-to-noise ratio (SNR) that is required for a successful wireless transmission. SNR is the difference between the signal strength of the desired signal and the noise floor of the channel. SNR is also measured in dB and it indicates how much the signal stands out from the noise. A higher SNR means a better signal quality and a lower bit error rate. A lower SNR means a worse signal quality and a higher bit error rate. Therefore, to achieve a reliable WLAN connection, the intentional signal of your WLAN must exist above the noise floor by a certain margin that depends on the data rate and modulation scheme used. The other options are not accurate or complete explanations of the noise floor noted in the report. The noise caused by elevators, microwave ovens, and video transmitters is not the noise floor but rather examples of interference sources that contribute to the noise floor. The extra energy radiated by access points and client devices beyond that intended for the signal is not the noise floor but rather an example of spurious emissions that cause interference to other devices or channels. The energy radiated by flooring materials that causes interference in the 2.4 GHz and 5 GHz bands is not the noise floor but rather an example of attenuation or reflection that reduces or changes the direction of the signal. References: CWNA-109 Study Guide, Chapter 5: Radio Frequency Signal and Antenna Concepts, page 139

The two IEEE amendments that should be supported to provide the management frame protection and fast secure roaming security features are 802.11r and 802.11w12.

• 802.11r (Fast BSS Transition): This amendment to the IEEE 802.11 standard permits continuous connectivity aboard wireless devices in motion, with fast and secure client transitions from one Basic Service Set to another1.
• 802.11w (Management Frame Protection): This amendment increases the security of its management frames2.

 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: ExamCWNA-109], page 112; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 102.

Weak signal strength is the likely cause of the low data rate issue for the client that has a signal strength of -84 dBm and a noise floor of -96 dBm. The client is an 802.11ac client and connects to an 802.11ac AP. Both the client and AP are 2x2:2 devices. Signal strength is the measure of how strong the RF signal is at the receiver. Signal strength can affect the reliability and performance of the wireless connection, as well as the data rate and throughput of the traffic. The higher the signal strength, the better the signal quality and the higher the data rate. The lower the signal strength, the worse the signal quality and the lower the data rate.

The data rate of an 802.11ac connection depends on several factors, such as channel bandwidth, modulation and coding scheme (MCS), spatial streams, guard interval, and beamforming. However, these factors are also influenced by the signal strength, as they require a certain signal-to-noise ratio (SNR) to operate properly. SNR is the ratio of the signal strength to the noise floor, which is the measure of the background noise or interference in the RF environment. The higher the SNR, the more robust and efficient the communication. The lower the SNR, the more prone and vulnerable to errors and retries.

According to the CWNA Official Study Guide , Table 3.7, page 112, an 802.11ac connection with a channel bandwidth of 80 MHz, an MCS of 9, two spatial streams, a short guard interval, and no beamforming can achieve a maximum data rate of 867 Mbps. However, this data rate requires a minimum SNR of 30 dB to maintain a sufficient signal quality. If the signal strength is -84 dBm and the noise floor is -96 dBm, then the SNR is only 12 dB (-84 dBm - (-96 dBm) = 12 dB), which is far below the required SNR for this data rate. Therefore, the data rate will drop significantly to match the lower SNR and signal quality.

To solve this problem, the signal strength should be increased to improve the SNR and data rate. This can be done by adjusting the output power or channel assignment of the AP or client, relocating or reorienting some APs or antennas to reduce attenuation or interference, updating or replacing some faulty oroutdated hardware or software components, etc. References: , Chapter 3, page 112; , Section 3.2

The tool described is a WLAN (Wireless Local Area Network) scanner tool. WLAN scanner tools are designed to provide information about the wireless networks in a given area, including:

• Signal Strength: They show the signal strength of all access points (APs) in the vicinity, which is crucial for understanding the coverage area and potential interference.
• SSID Visualization: These tools display the SSIDs (Service Set Identifiers) of available networks, allowing users to identify different wireless networks easily.
• Security Settings Information: WLAN scanner tools often show the type of security implemented on each network, such as WPA2, WEP, etc.
• Frequency Band Filtering: They allow users to filter and view networks based on the frequency band (2.4 GHz or 5 GHz), which is useful for analyzing network distribution and planning.

While protocol analyzers, site survey utilities, and spectrum analyzers are also used in wireless networking, their functions are distinct from what is described:

• Protocol Analyzersare more sophisticated and are used to capture and analyze network traffic.
• Site Survey Utilitiesare used to map signal coverage and plan network layouts, often with more advanced features for detailed site surveys.
• Spectrum Analyzersprovide a detailed view of the frequency spectrum and non-Wi-Fi interference but don't typically focus on SSIDs or security settings.

Thus, the correct answer is D, a WLAN scanner tool, based on the functionalities described.

References:

• CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, by David D. Coleman and David A. Westcott.
• Tools and techniques for wireless network analysis and troubleshooting.

An immediate concern that you note after hearing this information is that the power budget in the edge switches must be carefully planned and monitored based on the number of supported PoE devices. PoE stands for Power over Ethernet and is a technology that allows Ethernet switches to deliver power along with data to devices such as VoIP phones and 802.11 access points. PoE devices are classified into different classes based on their power consumption and output. The edge switches have a limited power budget that determines how many PoE devices they can support simultaneously. If the power budget is exceeded, some PoE devices may not receive enough power or may shut down unexpectedly. Therefore,it is important to plan and monitor the power budget in the edge switches based on the number and class of PoE devices connected to them. Using Ether-channel, placing switches in optimal locations, or avoiding distortion are not immediate concerns related to PoE devices. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 234; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 224.

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

VHT TXOP (Very High Throughput Transmit Opportunity) power save is a feature introduced with the 802.11ac amendment, which is designed to improve the power efficiency of devices connected to a WLAN. This feature enhances battery life in several ways, compared to the legacy Power Save mode:

• Enhanced Power Saving: VHT TXOP power save allows devices to disable more components of the WLAN transceiver when they are in a low power state. This reduces the power consumption during periods when the device is not actively transmitting or receiving data.
• Intelligent Wake-Up Mechanisms: It employs more sophisticated mechanisms for devices to determine when they need to wake up and listen to the channel, further reducing unnecessary power usage.
• Optimized Operation: This power save mode is optimized for the high-throughput environment of 802.11ac networks, allowing devices to efficiently manage power while maintaining high performance.

Legacy Power Save mode, introduced in earlier versions of the 802.11 standards, does not provide the same level of component disablement or the intelligent wake-up mechanisms found in VHT TXOP power save, making option B the correct answer.

References:

• IEEE 802.11ac-2013 Amendment: Enhancements for Very High Throughput for Operation in Bands below 6 GHz.
• CWNA Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109, by David D. Coleman and David A. Westcott.

An access point is configured by a WLAN controller in the management plane of the three networking planes. The management plane is responsible for the configuration, administration, and monitoring of network devices, such as access points, switches, routers, and controllers. The WLAN controller communicates with the access point using a management protocol, such as CAPWAP or SNMP, to send configuration commands and receive status information. The control plane is responsible for the routing, switching, and forwarding of network traffic, such as data frames and control frames. The WLAN controller may also participate in the control plane by performing functions such as authentication, encryption, roaming, and load balancing. The security plane is responsible for the protection of network devices and data from unauthorized access, modification, or disclosure. The WLAN controller may also participate in the security plane by implementing features such as firewall, VPN, IDS/IPS, and WIPS. The data plane is responsible for the transmission and reception of user data, such as voice, video, or web traffic. The WLAN controller may or may not participate in the data plane depending on the architecture of the WLAN. In some cases, the access point forwards the user data directly to the wired network without involving the WLAN controller (distributed data forwarding). In other cases, the access point tunnels the user data to the WLAN controller before forwarding it to the wired network (centralized data forwarding). References: CWNA-109 Study Guide, Chapter 9: Wireless LAN Architecture, page 279

The device in the bridge implementation that acts as the 802.1X Authenticator is the root bridge. The root bridge is the bridge that connects to the wired network and acts as the central point for all other bridges in the point-to-multipoint topology. The root bridge authenticates the non-root bridges using 802.1X/EAP and forwards their authentication requests to the RADIUS server. The non-root bridges act as the 802.1X Supplicants and use EAP methods such as EAP-TLS or EAP-PEAP to authenticate with the root bridge. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 459; [Cisco Aironet Wireless Bridges FAQ], question 29.

Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading. It is the difference between the receiver’s sensitivity and the actual received signal level. A higher Fade Margin indicates a more robust link that can withstand interference, attenuation, or other factors that may reduce the signal strength. A lower Fade Margin means that the link is more susceptible to failure or performance degradation. Fade Margin is usually expressed in decibels (dB) and can be calculated by subtracting the receiver sensitivity from the received signal level. References: 1, Chapter 2, page 51; 2, Section 2.1

A POE device that requires 47 W of power should use the 802.3bt specification. This is because 802.3bt is the latest POE standard that supports up to 90 W of power delivery over four pairs of wires in an Ethernet cable. The previous POE standards, such as 802.3af and 802.3at, only support up to 15.4 W and 30 W of power delivery over two pairs of wires in an Ethernet cable, respectively. Therefore, they are not sufficient for powering a device that requires 47 W of power. The 802.11at specification does not exist; it is a typo or confusion with the 802.3at specification. References: CWNA-109 Study Guide, Chapter 8: Wireless LAN Access Points, page 2431

Return loss is a measure of how well the components of an RF system are matched in terms of their impedance. Impedance is the opposition to the flow of alternating current in a circuit, and it depends on the frequency, resistance, capacitance, and inductance of the components. When the impedance of the source, the transmission line, and the load are not equal, some of the power is reflected back to the source, causing a loss of forward power. This loss is expressed in decibels (dB) as return loss. The higher the return loss, the lower the reflection and the better the impedance matching. Conversely, the lower the return loss, the higher the reflection and the worse the impedance matching.

VSWR (Voltage Standing Wave Ratio) is another way of expressing the same concept. It is the ratio of the maximum voltage to the minimum voltage along a transmission line due to the interference of the incident and reflected waves. A VSWR of 1:1 means that there is no reflection and perfect impedance matching. A VSWR higher than 1:1 means that there is some reflection and impedance mismatch. The higher the VSWR, the higher the reflection and the lower the return loss.

Therefore, a significant impedance mismatch between components in an RF system will cause high reflection, high VSWR, and low return loss.

USB 3 devices in the user’s work area are the most likely cause of this interference when using a spectrum analyzer to look for non-Wi-Fi interference sources. A spectrum analyzer is a tool that measures and visualizes the radio frequency activity and interference in the wireless environment. A spectrum analyzer can show the spectrum usage and energy levels on each frequency band or channel and help identify and locate the sources of interference. Interference is any unwanted signal that disrupts or degrades the intended signal on a wireless channel. Interference can be caused by various sources, such as other Wi-Fi devices, non-Wi-Fi devices, or natural phenomena. Interference can affect WLAN performance and quality by causing signal loss, noise, distortion, or errors. USB 3 devices are non-Wi-Fi devices that use USB 3.0 technology to transfer data at high speeds between computers and peripherals, such as hard drives, flash drives, cameras, or printers. USB 3 devices can generate electromagnetic radiation that interferes with Wi-Fi signals in the 2.4 GHz band, especially when they are close to Wi-Fi devices or antennas. USB 3 devices can cause significant interference across the entire 2.4 GHz band (not on a few select frequencies) within the desktop area of a user’s workspace, but the interference disappears quickly after just 2 meters. This is because USB 3 devices emit broadband interference that affects all channels in the 2.4 GHz band with a high intensity near the source but a low intensity at a distance due to attenuation. The other options are not likely to cause this interference pattern when using a spectrum analyzer to look for non-Wi-Fi interference sources. Bluetooth devices in the user’s work area are non-Wi-Fi devices that use Bluetooth technology to communicate wirelessly between computers and peripherals, such as keyboards, mice, headphones, or speakers. Bluetooth devices can cause interference with Wi-Fi signals in the 2.4 GHz band, but they use frequency hopping spread spectrum (FHSS) technique that changes frequencies rapidly and randomly within a range of 79 channels. Therefore, Bluetooth devices do not cause significant interference across the entire 2.4 GHz band (not on a few select frequencies), but rather intermittent interference on some channels at different times. Excess RF energy from a nearby AP is not a non-Wi-Fi interference source but rather a Wi-Fi interference source that occurs when an AP transmits more power than necessary for its coverage area. Excess RF energy from a nearby AP can cause co-channel interference (CCI) with other APs or client devices that use the same channel within range of each other. CCI reduces performance and capacity because it causes contention and collisions on the wireless medium,

The common spectrum analyzer view that you should use for this analysis is the Waterfall/Spectrogram view. The Waterfall/Spectrogram view shows the signal from the interfering device over time on a three-dimensional graph. The x-axis represents frequency, the y-axis represents time, and the z-axis represents amplitude or power. The color of each pixel indicates the signal strength at a given frequency and time. The Waterfall/Spectrogram view can help you identify the characteristics of the interference source, such as its frequency range, duty cycle, modulation type, and pattern. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 524; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 494.

S1G is one of the 802.11 PHYs that is more likely to be used in an industrial deployment but not likely to be used in standard office deployments. This is because S1G stands for Sub-1 GHz, which means it operates in the frequency bands below 1 GHz, such as 900 MHz and 868 MHz. These bands offer better penetration and range than the higher frequency bands used by other 802.11 PHYs, such as 2.4 GHz and 5 GHz. This makes S1G suitable for industrial applications that require robust and reliable wireless communication in harsh environments, such as factories, warehouses, mines, and smart grids. S1G also supports low-power and low-data-rate devices, such as sensors, actuators, and meters, which are common in industrial Internet of Things (IoT) scenarios. VHT, OFDM, and HT are other 802.11 PHYs that are more commonly used in standard office deployments, as they offer higher data rates and capacity than S1G, but have lower range and penetration. References: CWNA-109 Study Guide, Chapter 3: Radio Frequency Technologies, page 751

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.

https://www.cablinginstall.com/articles/2012/08/cat-6a-vs-cat-5e-poe.html

The statement that the lowest voltage drop is achieved when using CAT6 cable instead of Cat5 or CAT5e is true about 802.3, Clause 33 Power over Ethernet. Power over Ethernet (PoE) is a technology that allows electrical power to be delivered over Ethernet cables along with data signals. PoE is defined by IEEE 802.3, Clause 33 and has several variants, such as PoE (802.3af), PoE+ (802.3at), and PoE++ (802.3bt). PoE works by using a device called PSE (Power Sourcing Equipment) that injects power into the Ethernet cable and a device called PD (Powered Device) that receives power from the Ethernet cable. The PSE can be either an endpoint device, such as a switch or a router, or a midspan device, such as an injector or a splitter, that is inserted between two Ethernet devices. The PD can be any device that requires power, such as an access point, a camera, or a phone.

One of the factors that affects PoE performance is voltage drop, which is the reduction of voltage that occurs as current flows through a cable due to its resistance. Voltage drop can cause power loss and inefficiency in PoE systems, as well as damage to PDs if the voltage falls below their minimum requirement. To minimize voltage drop, it is recommended to use high-quality cables with low resistance and short length. Among the common types of Ethernet cables, CAT6 has the lowest resistance and therefore the lowest voltage drop compared to Cat5 or CAT5e. CAT6 also has higher bandwidth and data rate than Cat5 or CAT5e, making it more suitable for PoE applications. References: 1, Chapter 7, page 263; 2, Section 4.4

WPA2 (Wi-Fi Protected Access 2) is a security certification program developed by the Wi-Fi Alliance to secure wireless computer networks. It is important to understand the following:

• WPA2 and the 802.11 Standard: While WPA2 is based on elements of the 802.11i amendment to the 802.11 standard, it is not itself a standard but rather a certification to ensure devices comply with certain security criteria, including the correct implementation of CCMP (Counter Mode Cipher Block Chaining Message Authentication Code Protocol) and AES (Advanced Encryption Standard).
• CCMP/AES Implementation: WPA2 enhances the security of wireless networks by using CCMP for encryption, which is based on AES, a robust encryption algorithm. This represents a significant security improvement over WEP (Wired Equivalent Privacy) and WPA (Wi-Fi Protected Access) that used TKIP (Temporal Key Integrity Protocol).
• WPA vs. WPA2: WPA was the interim security enhancement over WEP, utilizing TKIP for encryption. WPA2, however, moved to the more secure AES-based encryption method. Contrary to option C, WPA2 does not enhance security by using TKIP; it uses CCMP/AES.

Therefore, option B correctly describes WPA2 as a certification program ensuring devices properly implement the more secure CCMP/AES encryption methods.

References:

• Wi-Fi Alliance website for WPA2 certification details.
• IEEE 802.11i-2004: Amendment for Enhanced Security.

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.

The inverse square law states that the signal strength of an RF wave is inversely proportional to the square of the distance from the source. This means that as the distance from the transmitter increases, the signal strength decreases rapidly.

References: Wireless Network Administrator Official Study Guide, Chapter 3, page 64.

The beamwidth of an RF antenna is the angular measure of how wide the main lobe of radiation is. The main lobe is the area where the signal strength is highest and most concentrated. The beamwidth is calculated at the points where the main lobe decreases power by 3 dB, which means it is half of the maximum power. The beamwidth can be measured in both horizontal and vertical planes, depending on how the antenna is oriented. The horizontal beamwidth is also called azimuth, while the vertical beamwidth is also called elevation. The beamwidth patterns on an antenna polar chart indicate how the RF energy is distributed in different directions. References: 1, Chapter 2, page 66; 2, Section 2.3