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Question 261.

Which WLAN metric most directly indicates the difference between the strength of a received signal and the background RF noise?

1. EIRP
   2. SNR
   3. Antenna gain
   4. Channel width

Correct Answer: 2. SNR

Explanation:

Signal-to-noise ratio, or SNR, represents the difference between the desired received signal and the surrounding noise floor. For example, a signal at -60 dBm with a noise floor of -90 dBm provides an SNR of approximately 30 dB. Higher SNR generally allows a receiver to distinguish more complex modulation states and maintain higher data rates with fewer errors. EIRP describes effective transmitted power, antenna gain describes directional concentration of RF energy, and channel width defines the amount of spectrum used. SNR is therefore one of the most useful measurements when evaluating whether a WLAN signal is not merely strong, but actually usable in the surrounding RF environment.

Question 262.

Which antenna characteristic determines the directional shape in which RF energy is transmitted and received?

1. DHCP scope
   2. SSID
   3. Radiation pattern
   4. Beacon interval

Correct Answer: 3. Radiation pattern

Explanation:

An antenna’s radiation pattern describes how RF energy is distributed through space. Omnidirectional antennas provide broad horizontal coverage, while directional antennas concentrate more energy toward a particular area. The radiation pattern is critical when selecting antennas for offices, warehouses, outdoor bridges, corridors, or other specialized environments. DHCP scopes, SSIDs, and beacon intervals are unrelated to physical antenna behavior. A high-gain antenna does not simply create additional RF power; instead, it reshapes the radiation pattern so more energy is directed in some directions and less in others. WLAN engineers should evaluate both gain and pattern when selecting antennas.

Question 263.

Which antenna type would generally be most suitable for providing 360-degree horizontal coverage from a centrally located indoor access point?

1. Omnidirectional antenna
   2. Highly directional dish antenna
   3. Yagi antenna aimed down a corridor
   4. Point-to-point panel antenna

Correct Answer: 1. Omnidirectional antenna

Explanation:

An omnidirectional antenna is designed to provide broad coverage around the antenna in the horizontal plane, making it suitable for centrally located access points serving users in multiple directions. It does not radiate equally in every three-dimensional direction, but the horizontal pattern is generally close to 360 degrees. Directional antennas such as Yagi, panel, or dish designs concentrate energy toward a narrower area and are better suited to corridors, outdoor links, or focused coverage. Antenna selection should match the intended coverage geometry rather than simply choosing the device with the highest gain specification.

Question 264.

Which RF phenomenon can reduce signal strength because electromagnetic energy is converted into another form when passing through a material?

1. Reflection
   2. Refraction
   3. Diffraction
   4. Absorption**

Correct Answer: 4. Absorption

Explanation:

Absorption occurs when RF energy enters a material and part of that energy is converted into another form, commonly heat. Building materials, people, water, and other objects can absorb different amounts of RF energy depending on their physical properties and the operating frequency. Reflection redirects energy, diffraction bends it around obstacles, and refraction changes its direction as it enters another medium. Absorption contributes directly to attenuation and is one reason signal levels drop when Wi-Fi passes through walls, floors, furniture, or crowded spaces. Accurate WLAN design therefore considers real construction materials rather than relying only on distance.

Question 265.

Which value represents the actual RF power measured relative to 1 milliwatt?

1. dBm
   2. dBi
   3. dB
   4. SNR

Correct Answer: 1. dBm

Explanation:

dBm is an absolute power measurement referenced to 1 milliwatt. A value of 0 dBm equals 1 mW, 10 dBm equals 10 mW, 20 dBm equals 100 mW, and 30 dBm equals 1 watt. dBi measures antenna gain relative to an isotropic radiator, while dB expresses a relative gain or loss. SNR is also a relative measurement expressed in dB. WLAN professionals regularly use dBm for transmit power, receive signal levels, receiver sensitivity, and link budgets. Understanding logarithmic RF measurements is fundamental because wireless power spans a very large range that is easier to manage in decibel-based units.

Question 266.

Which statement correctly describes a decrease of approximately 3 dB in RF power?

1. Power increases by ten times
   2. Power is approximately halved
   3. Power approximately doubles
   4. Power becomes zero

Correct Answer: 2. Power is approximately halved

Explanation:

The Rule of 3s states that a 3 dB increase approximately doubles power, while a 3 dB decrease approximately halves power. For example, reducing 100 mW by about 3 dB results in approximately 50 mW. The Rule of 10s states that a 10 dB increase multiplies power by ten and a 10 dB decrease divides it by ten. These shortcuts are valuable when performing quick WLAN link-budget calculations involving transmit power, cable loss, and antenna gain. Because dB is logarithmic, equal changes in dB represent multiplicative rather than linear changes in power.

Question 267.

Which 802.11 architecture term describes multiple BSSs connected through a distribution system and generally using the same SSID?

1. IBSS
   2. BSSID
   3. ESS
   4. PHY

Correct Answer: 3. ESS

Explanation:

An Extended Service Set, or ESS, consists of multiple infrastructure Basic Service Sets connected through a distribution system. The BSSs typically use the same SSID and compatible security configuration so clients can move throughout a larger area while remaining on the same logical WLAN. A BSSID identifies one individual BSS, while an IBSS refers to an older ad hoc WLAN topology. PHY refers to the physical-layer technology rather than a network topology. Most enterprise WLANs operate as ESS environments containing many access points and BSSs providing continuous coverage throughout buildings or campuses.

Question 268.

Which address is normally used to identify one particular Basic Service Set?

1. Default gateway
   2. IP broadcast address
   3. SSID
   4. BSSID**

Correct Answer: 4. BSSID

Explanation:

The BSSID identifies a specific Basic Service Set. In an infrastructure WLAN, it is commonly associated with a MAC address used by an access point radio for that BSS. The SSID is the logical network name and can be shared across many BSSs in one ESS. A default gateway and IP broadcast address operate at the network layer and do not identify an 802.11 BSS. Understanding BSSID versus SSID is important when analyzing roaming because a client can remain on the same SSID while moving between different BSSIDs as it associates with different access points.

Question 269.

Which frame type is responsible for Beacon, Probe Request, Authentication, and Association messages?

1. Management frames
   2. Data frames
   3. Ethernet frames
   4. TCP frames

Correct Answer: 1. Management frames

Explanation:

802.11 management frames handle WLAN discovery, connection establishment, maintenance, and termination. Examples include Beacon, Probe Request, Probe Response, Authentication, Association Request, Association Response, Reassociation, Disassociation, and Deauthentication frames. Data frames transport higher-layer payloads, while control frames provide functions such as acknowledgments and medium reservation. Ethernet and TCP use different framing or protocol structures. Management-frame analysis is important during troubleshooting because many client connection failures occur before normal data transfer begins. A protocol analyzer can reveal status codes and reason codes associated with these exchanges.

Question 270.

Which frame type includes ACK, RTS, and CTS frames?

1. Management
   2. Control
   3. Application
   4. Network-layer

Correct Answer: 2. Control

Explanation:

ACK, RTS, and CTS are examples of 802.11 control frames. ACK confirms successful reception of many unicast frames, while RTS and CTS can reserve the medium and help reduce collisions in some hidden-node scenarios. Management frames support network discovery and association, and data frames transport higher-layer information. Application and network-layer terminology refers to higher layers and does not describe 802.11 MAC frame categories. Understanding control frames is essential because they play a major role in the timing, reliability, and efficiency of Wi-Fi communication even though they do not carry normal user application data.

Question 271.

Which mechanism allows a station to defer transmission based on duration information even when it does not physically detect every transmission involved in the exchange?

1. DHCP snooping
   2. VLAN tagging
   3. Virtual carrier sensing
   4. NAT

Correct Answer: 3. Virtual carrier sensing

Explanation:

Virtual carrier sensing uses duration information carried in 802.11 frames to determine how long the medium is expected to remain reserved. Stations maintain a Network Allocation Vector, or NAV, and defer transmission while the NAV indicates that another frame exchange is still in progress. This complements physical carrier sensing, where a station listens directly for RF energy or valid Wi-Fi transmissions. DHCP snooping, VLAN tagging, and NAT are unrelated network functions. Virtual carrier sensing is especially important in RTS/CTS exchanges and helps reduce collisions among stations sharing the wireless medium.

Question 272.

Which value is maintained by a Wi-Fi station to track virtual medium reservation?

1. DNS cache
   2. ARP table
   3. DHCP lease
   4. NAV**

Correct Answer: 4. NAV

Explanation:

The Network Allocation Vector, or NAV, is maintained by an 802.11 station as part of virtual carrier sensing. When a station receives a frame containing a duration value, it can update the NAV to indicate how long the channel should be treated as virtually busy. While that timer is active, the station generally defers transmission. DNS caches, ARP tables, and DHCP leases operate at higher networking layers and are unrelated to Wi-Fi medium reservation. NAV behavior is an important part of CSMA/CA and helps stations coordinate access even when they cannot hear every individual component of a transmission exchange.

Question 273.

Which mechanism is intended specifically to improve performance in environments affected by hidden nodes?

1. RTS/CTS
   2. DHCP relay
   3. WPA Personal
   4. DNS caching

Correct Answer: 1. RTS/CTS

Explanation:

RTS/CTS can help in hidden-node environments by providing a short medium-reservation exchange before the actual data transmission. The transmitter sends Request to Send, and the receiver responds with Clear to Send. Other stations that hear the exchange update their NAV and defer transmission. This helps when two clients cannot hear each other but can both reach the same access point. RTS/CTS adds overhead and should therefore not be enabled aggressively without reason. DHCP, WPA, and DNS do not address medium-access collisions caused by hidden nodes.

Question 274.

Which condition best describes a hidden node?

1. An AP that does not advertise an SSID
   2. Two stations that cannot hear one another but can both communicate with the same receiver
   3. A client with no DHCP address
   4. A radio with disabled encryption

Correct Answer: 2. Two stations that cannot hear one another but can both communicate with the same receiver

Explanation:

A hidden node occurs when two stations cannot detect each other’s transmissions yet both communicate with the same access point or receiver. Because one station may believe the channel is idle while the other is transmitting, their frames can overlap at the receiver and require retransmission. This problem is unrelated to hidden SSIDs, DHCP addressing, or encryption settings. Hidden-node conditions may be created by physical obstacles, directional antennas, large cells, or unusual layouts. RTS/CTS can help by allowing the receiver’s CTS frame to notify both hidden stations that the medium is reserved.

Question 275.

Which 802.11 amendment introduced QoS enhancements that became the foundation for WMM?

1. 802.11i
   2. 802.11k
   3. 802.11e
   4. 802.11h

Correct Answer: 3. 802.11e

Explanation:

IEEE 802.11e introduced quality-of-service enhancements for WLANs, including mechanisms that became the technical foundation for Wi-Fi Multimedia, or WMM. WMM defines differentiated access categories for voice, video, best effort, and background traffic. 802.11i focuses on security, 802.11k provides radio-resource measurement capabilities, and 802.11h includes spectrum-management mechanisms. QoS is important for real-time applications, but it does not create unlimited capacity. A WLAN still requires sufficient airtime, low interference, good signal quality, and appropriate channel reuse for WMM prioritization to provide useful results.

Question 276.

Which access category generally receives lower priority than Best Effort in WMM?

1. Voice
   2. Video
   3. Network control
   4. Background**

Correct Answer: 4. Background

Explanation:

The Background access category receives the least favorable contention parameters among the standard WMM access categories. It is intended for delay-tolerant traffic such as non-urgent synchronization or background transfers. Best Effort receives normal priority, while Video and Voice receive increasingly favorable access parameters. WMM changes how traffic competes for the wireless medium but does not reserve fixed bandwidth. Background traffic can therefore wait longer when higher-priority traffic is present. Correct QoS classification should also be maintained across the wired network to preserve end-to-end application treatment.

Question 277.

Which security protocol should be considered obsolete and unsuitable for protecting modern WLAN traffic?

1. WEP
   2. WPA3
   3. WPA2 with AES-based protection
   4. 802.1X/EAP

Correct Answer: 1. WEP

Explanation:

Wired Equivalent Privacy, or WEP, is obsolete because its cryptographic design contains serious weaknesses that allow attackers to recover keys and decrypt traffic using well-known techniques. WPA and WPA2 were introduced to improve WLAN security, and newer WPA3 mechanisms provide further enhancements. 802.1X/EAP supports enterprise authentication and is widely used in secure corporate WLANs. Legacy compatibility should not be used as justification for retaining WEP because supporting fundamentally insecure encryption can expose the entire network to compromise. Older devices that require WEP should generally be replaced or isolated from sensitive infrastructure.

Question 278.

Which enterprise WLAN authentication design provides individualized credentials and centralized authentication?

1. Open System only
   2. 802.1X/EAP with RADIUS
   3. One shared PSK for all employees
   4. MAC filtering only

Correct Answer: 2. 802.1X/EAP with RADIUS

Explanation:

802.1X/EAP with a centralized RADIUS infrastructure allows individual users or devices to authenticate using unique credentials or certificates. This provides better accountability, policy control, and credential lifecycle management than using a single shared pre-shared key. Open authentication does not provide meaningful identity validation, and MAC filtering is easily bypassed because MAC addresses can be observed and spoofed. Enterprise WLANs should also use proper certificate validation, authentication-server redundancy, and secure identity infrastructure. The exact EAP method should be selected based on organizational security requirements and client capabilities.

Question 279.

Which survey method is most appropriate for confirming that actual deployed coverage matches the requirements defined during WLAN design?

1. Post-deployment validation survey
   2. Predictive design only
   3. Inventory check only
   4. DHCP lease review

Correct Answer: 1. Post-deployment validation survey

Explanation:

A post-deployment validation survey measures the real installed WLAN and compares the results with the original design requirements. Depending on the use case, validation can include RSSI, SNR, channel utilization, channel reuse, roaming, throughput, retries, interference, and application performance. Predictive models are valuable before installation but rely on assumptions about construction materials, RF behavior, and client capabilities. Inventory checks and DHCP records do not prove that wireless coverage or capacity goals have been achieved. Validation is therefore the strongest method for confirming whether the installed WLAN actually performs as intended.

Question 280.

Users report excellent RSSI but poor performance during busy periods. Which troubleshooting approach is most appropriate?

1. Increase transmit power on every AP
   2. Replace all access points immediately
   3. Disable WLAN security
   4. Analyze channel utilization, client density, retries, interference, and co-channel contention**

Correct Answer: 4. Analyze channel utilization, client density, retries, interference, and co-channel contention

Explanation:

Excellent RSSI confirms that clients receive a strong signal, but it does not indicate whether adequate airtime is available. Poor performance during busy periods strongly suggests capacity, contention, or interference problems. The investigation should examine channel utilization, active client counts, retry rates, neighboring same-channel cells, application demand, channel width, data rates, and non-Wi-Fi interference. Increasing power can worsen contention, while replacing APs or disabling security without evidence does not address the root cause. Effective WLAN troubleshooting considers the shared-medium nature of Wi-Fi and uses multiple measurements rather than relying on RSSI alone.