CWNA-108 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.

What is always required to establish a high quality 2.4 GHz RF link at a distance of 3 miles (5 kilometers) is a Fresnel Zone that is at least 60% clear of obstructions. The Fresnel Zone is an elliptical-shaped area around the line-of-sight path between two antennas that reflects and refracts the RF waves. The Fresnel Zone radius depends on the frequency of the RF signal and the distance between the antennas. For optimal performance, the Fresnel Zone should be at least 60% clear of any obstructions that may cause interference, attenuation, or multipath fading. The minimum output power level, antenna gain, and antenna type may vary depending on the environmental conditions and regulatory constraints, but they are not always required for a high quality RF link. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 75; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 65.

The error in administration that could be the cause of this security concern is that HTTP is in use instead of HTTPS. HTTP is an unencrypted protocol that transfers data in plain text over the network. This means that anyone who captures the traffic can see the HTML code of the Web pages used for access point management, as well as any sensitive information such as passwords or configuration settings. HTTPS is an encrypted protocol that uses SSL/TLS to secure the data transmission between the Web browser and the Web server. HTTPS prevents anyone from snooping on or tampering with the Web traffic. Therefore, HTTPS should always be used for Web based management of wireless access points, especially in autonomous mode where there is no centralized controller to enforce security policies. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 431; [HTTP vs HTTPS: What’s The Difference And Why Should You Care?].

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: Exam CWNA-107], page 299; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 289.

The BSSID (Basic Service Set Identifier) is typically mapped to an AP’s MAC address if a single BSS is implemented. The BSSID is a unique identifier that distinguishes one BSS from another within the same RF medium. It is usually derived from the MAC address of the AP’s radio interface, but it can also be manually configured or randomly generated by some vendors. The BSSID is used by client stations to associate with an AP and to send and receive frames within a BSS. References: , Chapter 1, page 24; , Section 1.2

The power level at the Intentional Radiator (IR) is 250 mW. The IR is the point where the RF signal leaves the transmitter and enters the antenna system. To calculate the power level at the IR, we need to consider the output power level of the transmitter, the loss of the cable, and the gain of the antenna. The formula is:

Power level at IR (dBm) = Output power level (dBm) - Cable loss (dB) + Antenna gain (dBi)

We can convert the output power level of 50 mW to dBm by using the formula:

Power level (dBm) = 10 * log10(Power level (mW))

Therefore, 50 mW = 10 * log10(50) = 16.99 dBm

We can plug in the values into the formula:

Power level at IR (dBm) = 16.99 - 3 + 16 = 29.99 dBm

We can convert the power level at IR from dBm to mW by using the inverse formula:

Power level (mW) = 10^(Power level (dBm) / 10)

Therefore, 29.99 dBm = 10^(29.99 / 10) = 999.96 mW

However, since we need to round off the answer to the nearest integer value, we get:

Power level at IR (mW) = 1000 mW

References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 67; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 57.

PoE stands for Power over Ethernet, which is a technology that allows network devices to receive power and data over the same Ethernet cable. PoE eliminates the need for separate power adapters or outlets for devices such as IP phones, cameras, or APs. PoE requires two types of devices: PSE (Power Sourcing Equipment) and PD (Powered Device). A PSE is a device that provides power to the Ethernet cable, such as a switch, injector, or splitter. A PD is a device that receives power from the Ethernet cable, such as an IP phone, camera, or AP. When implementing PoE, a switch plays the role of a PSE910. References: CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 293; CWNA-108 Study Guide, Chapter 7: Power over Ethernet (PoE), page 287.

A probe request frame is a management frame that is sent by a client station to discover available wireless networks in its vicinity. A probe request can be either unicast or broadcast, depending on whether it specifies a particular SSID (Service Set Identifier) or a wildcard SSID. A broadcast probe request with a wildcard SSID is used to solicit responses from all APs within range, regardless of their SSIDs. Each AP that receives a broadcast probe request prepares a probe response frame that contains information about its network, such as SSID, supported rates, channel, security, etc. However, before sending the probe response, each AP must contend for the medium using the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol, which is the basic access method for 802.11 WLANs. This means that each AP must sense the channel for a DIFS (Distributed Interframe Space) interval, which is longer than a SIFS interval, and then generate a random backoff time before transmitting. This reduces the probability of collisions and ensures fair access to the medium among multiple APs. Therefore, each AP responds in turn after preparing a probe response and winning contention . References: [CWNA-109 Study Guide], Chapter 5: IEEE 802.11 Medium Access, page 215; [CWNA-108 Study Guide], Chapter 5: IEEE 802.11 Medium Access, page 209; [CWNA-109 Study Guide], Chapter 6: Wireless LAN Devices and Topologies, page 255.

802.11 QoS is achieved by giving high priority queues a statistical advantage at winning contention. 802.11 QoS is based on the Enhanced Distributed Channel Access (EDCA) mechanism, which defines four access categories (ACs) for different types of traffic: Voice, Video, Best Effort, and Background. Each AC has its own transmit queue and contention parameters, such as Arbitration Interframe Space (AIFS), Contention Window (CW), and Transmission Opportunity (TXOP). These parameters determine how long a station has to wait before transmitting a frame and how long it can occupy the channel. Higher priority ACs have shorter AIFS, smaller CW, and longer TXOP, which means they have more chances to access the channel and send more data than lower priority ACs. However, this does not guarantee that higher priority ACs will always win the contention, as there is still a random backoff process involved. Therefore, 802.11 QoS is a statistical service that provides different levels of service quality based on traffic categories. References: , Chapter 10, page 403; , Section 6.1

Station-to-station traffic blocking is a security feature that prevents wireless clients from communicating with each other on the same network. This can prevent active attacks such as man-in-the-middle, ARP spoofing, or denial-of-service that hackers may launch from their devices against other users in a public Wi-Fi hotspot. By enabling station-to-station traffic blocking by the access points in the hotel, Lynne can decrease the likelihood of such attacks on his customers’ wireless computers. This feature can be configured on most wireless APs or controllers345. References: CWNA-109 Study Guide, Chapter 10: Wireless LAN Security, page 427; CWNA-108 Study Guide, Chapter 10: Wireless LAN Security, page 417; Wireless Station-to-Station Traffic Being Blocked.

When performing a post-deployment validation survey for voice over Wi-Fi (VoWiFi), an action that must be performed is Application analysis with an active phone call on a VoWiFi handset. Application analysis is a method of testing the performance of a specific application over the WLAN by measuring parameters such as throughput, latency, jitter, packet loss, MOS score, and R-value. Application analysis with an active phone call on a VoWiFi handset can help to evaluate the quality of service (QoS) and user experience of VoWiFi calls over the WLAN. It can also help to identify any issues or bottlenecks that may affect VoWiFi calls such as interference, roaming delays, or insufficient coverage. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 549; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 519.

Discovering the scale of the problem is the next logical step in the troubleshooting process after identifying the problem of poor wireless connections on the third floor of a building under your administration. Troubleshooting is a systematic process of finding and resolving problems or issues in a network or a system. Troubleshooting usually follows a general methodology that consists of several steps or phases, such as:

• Identifying the problem: This step involves defining and describing the problem clearly and accurately based on the symptoms and evidence observed or reported by users or administrators. For example, in this case, the problem is that three individuals have reported poor wireless connections on the third floor of a building.
• Discovering the scale of the problem: This step involves determining how widespread and severe the problem is by gathering more information and data from different sources and perspectives. For example, in this case, this step could involve checking if other users or devices on the third floor or other floors are experiencing similar issues, verifying if there are any changes or updates in the network configuration or environment that could affect the wireless connections, testing if there are any differences in performance or quality between different access points or channels on the third floor, etc.
• Performing corrective actions: This step involves applying possible solutions or fixes to resolve or mitigate the problem based on logical reasoning and analysis. For example, in this case, this step could involve adjusting the output power or channel assignment of the access points on the third floor, relocating or reorienting some access points or antennas to improve coverage or reduce interference, updating or replacing some faulty or outdated hardware or software components, etc.
• Verifying the solution: This step involves confirming that the problem is solved or improved by testing and monitoring the network performance and user satisfaction after applying corrective actions. For example, in this case, this step could involve measuring and comparing the signal strength and throughput of wireless connections on the third floor before and after performing corrective actions, asking for feedback from users who reported poor wireless connections to see if their issues are resolved or reduced, etc.
• Creating a plan of action or escalating the problem: This step involves documenting and reporting the problem and its solution for future reference and improvement purposes. It also involves deciding whether to close or escalate the problem depending on its status and severity. For example, in this case, this step could involve creating a report that summarizes what was done to troubleshoot and fix poor wireless connections on the third floor with relevant data and evidence to support it. It could also involve escalating poor wireless connections to higher-level administrators if they persist or worsen despite performing corrective actions.

References: 1, Chapter 12, page

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-107], page 133; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 123.

A high-density deployment is a wireless network that is designed to support a large number of users and devices in a relatively small area. This type of deployment is often used in enterprise environments, such as offices, schools, and hospitals.

The use of semi-directional antennas in the deployment described in the question is a good indication that it is a high-density deployment. Semi-directional antennas can be used to focus the signal from an access point in a specific direction. This can help to reduce interference and improve performance in high-density environments.

The other answer choices are less likely to be correct for the following reasons:

• SOHO (small office/home office) deployments are typically smaller and less complex than high-density deployments.
• Residential deployments are typically even smaller and less complex than SOHO deployments.
• Standard office deployments may be high-density, but they may also be lower-density.

It is important to note that the type of deployment is not determined solely by the output power of the access points. However, the use of 10 mW of output power on the 2.4 GHz radios and 20 mW of output power on the 5GHz radios is also consistent with a high-density deployment.

Here are some additional tips for deploying a high-density wireless network:

• Use a site survey to determine the optimal placement of access points.
• Configure the access points to use non-overlapping channels.
• Use semi-directional or directional antennas to focus the signal and reduce interference.
• Implement a wireless intrusion prevention system (WIPS) to detect and mitigate rogue access points and other security threats.

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

 A Wi-Fi scanner is a basic tool that can be used to easily locate areas of high co-channel interference. A Wi-Fi scanner is a software application that can run on a laptop, tablet, smartphone, or other device that has a Wi-Fi adapter. A Wi-Fi scanner can scan the wireless environment and display information about the detected access points and client stations, such as their SSID, BSSID, channel, signal strength, security, and data rate. A Wi-Fi scanner can also show the channel utilization and overlap of different access points, which can indicate the level of co-channel interference. Co-channel interference is a type of interference that occurs when multiple access points use the same or adjacent channels within the same coverage area. Co-channel interference can reduce the throughput and performance of the WLAN, as the access points and client stations have to contend for the channel access and avoid collisions. To identify areas of high co-channel interference, a Wi-Fi scanner can be used to measure the signal strength and channel utilization of different access points and compare them with a threshold or a baseline. Alternatively, a Wi-Fi scanner can also use a color-coded heat map to visualize the co-channel interference level in different locations. References: 1, Chapter 7, page 279; 2, Section 4.3

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

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.

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.

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: Exam CWNA-107], page 234; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 224.

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: Exam CWNA-107], page 336; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 326.

PoE has different standards that define different power levels for PSEs and PDs. The original standard, IEEE 802.3af, defines two classes of PSEs: Class 3 (15.4 W) and Class 4 (30 W). The newer standard, IEEE 802.3at, also known as PoE+, defines four classes of PSEs: Class 0 (15.4 W), Class 1 (4 W), Class 2 (7 W), and Class 3 (12.95 W). The power level received at the PD is always lower than the power level provided by the PSE, due to cable resistance and power dissipation. The IEEE standards specify the minimum power level that must be received at the PD for each class of PSE. For a Class 4 PSE, the minimum power level received at the PD is 25.5 W910. References: CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 295; CWNA-108 Study Guide, Chapter 7: Power over Ethernet (PoE), page 289.

VHT TXOP power save uses the partial AID in the preamble to allow clients to identify frames targeted for them. VHT TXOP power save is a feature introduced in the 802.11ac amendment that improves battery life for devices on a WLAN by allowing them to enter sleep mode more frequently and for longer periods of time. It works by using a new field called partial AID in the preamble of VHT frames that indicates which stations are addressed by the frame. This allows stations to quickly determine if they need to wake up and receive the frame or stay in sleep mode and save power. This reduces the overhead and latency of legacy Power Save mode, which requires stations to wake up periodically and listen to Beacon frames or other control frames to check if there are any buffered frames for them at the AP. References: , Chapter 3, page 117; , Section 3.2

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.

 This is because the passphrase for WPA2-Personal is case-sensitive and must match exactly on both the AP and the client. If the passphrase is entered incorrectly on the client, the client will not be able to authenticate with the AP and connect to the network. The AP that covers the problem area is not likely to require a firmware update, fail, or be improperly configured, as it is online and works with other clients that have the correct passphrase. To troubleshoot this issue, you can check the passphrase settings on the clients and make sure they match with the AP. You can also try to reconnect the clients to the network or reboot them if necessary. For more information on how to configure WPA2-Personal on your router

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: Exam CWNA-107], page 524; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 494.

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 (Orthogonal Frequency Division Multiplexing) is the physical layer specification (PHY) that VHT capable devices must be backward compatible with according to the IEEE 802.11-2012 standard. VHT (Very High Throughput) is a PHY and MAC enhancement that is defined in the IEEE 802.11ac amendment and is also known as Wi-Fi 5. VHT operates only in the 5 GHz band and uses features such as wider channel bandwidths (up to 160 MHz), higher modulation schemes (up to 256-QAM), more spatial streams (up to eight), multi-user MIMO (MU-MIMO), beamforming, and VHT PHY and MAC enhancements. VHT can achieve data rates up to 6.9 Gbps.

According to the IEEE 802.11-2012 standard, VHT capable devices must be backward compatible with devices using OFDM PHY, which is defined in the IEEE 802.11a amendment and is also used by IEEE 802.11g, IEEE 802.11n, and IEEE 802.11h amendments. OFDM operates in both the 2.4 GHz and 5 GHz bands and uses features such as subcarriers, symbols, guard intervals, and OFDM PHY and MAC enhancements. OFDM can achieve data rates up to 54 Mbps.

Backward compatibility means that VHT capable devices can interoperate with OFDM devices on the same network by using common features and parameters that are supported by both PHYs. For example, VHT capable devices can use a channel bandwidth of 20 MHz, a modulation scheme of BPSK, QPSK, or 16-QAM, one spatial stream, no beamforming, and OFDM PHY and MAC headers when communicating with OFDM devices. Backward compatibility also means that VHT capable devices can fall back to OFDM mode when the signal quality or SNR is too low for VHT mode. References: 1, Chapter 3, page 123; 2, Section 3.2

The unit of measurement that is an absolute unit and is used to quantify received signal power levels on a logarithmic scale is dBm. dBm stands for decibel-milliwatt and represents the power level relative to 1 milliwatt (mW). dBm is an absolute unit because it has a fixed reference point and does not depend on the input power level. dBm is used to measure the received signal power levels on a logarithmic scale because it can express large variations in power levels with small numbers and make calculations easier. For example, a 10 dB increase in power level means a 10-fold increase in power, and a 20 dB increase means a 100-fold increase in power. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-107], page 66; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 56.

 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-107], page 112; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106], page 102.

FT (Fast Transition) is an IEEE 802.11 standard method for fast roaming. FT is defined in the IEEE 802.11r amendment and is also known as Fast BSS Transition (FBT) or Fast Secure Roaming. FT is a feature that allows a client station to quickly switch from one AP to another within the same ESS (Extended Service Set) without having to re-authenticate and re-associate with each AP. This reduces the latency and packet loss that may occur during roaming, thus improving the user experience and maintaining the security of the connection. FT works by using pre-authentication and key caching mechanisms that allow the client station and the APs to exchange security information before the actual roaming occurs. This way, when the client station decides to roam to a new AP, it can use a fast reassociation request and response that contain only a few fields, instead of a full authentication and association exchange that require more time and data. References: 1, Chapter 9, page 367; 2, Section 6.3

Passive Gain is the increase of RF energy in an intentional direction with the use of an antenna. It is achieved by focusing the same amount of power into a smaller area, resulting in a higher power density and a stronger signal. Passive Gain does not require any additional power or amplification, but rather depends on the antenna’s physical characteristics, such as size, shape, and orientation. Passive Gain is also expressed in decibels (dB) and is related to the antenna’s beamwidth and directivity. References: 1, Chapter 2, page 63; 2, Section 2.3