Certified Wireless Network Professional (CWNA) Quiz

The correct answer is two spatial streams because the AP-1 is a 3x3:2 AP, which means it has three transmit antennas and two spatial streams. The STA-3 client is a 3x3:3 client, which means it has three transmit antennas and three spatial streams. However, the maximum number of spatial streams that can be used for a downlink HT-OFDM transmission from AP-1 to STA-3 is determined by the capabilities of the AP. Since the AP is capable of only two spatial streams, that is the maximum number that can be used for the transmission.

802.11 client devices can measure and use the signal strength of access point beacons received to select the optimal access point for association. This is because the signal strength indicates the quality of the wireless connection between the client device and the access point. By selecting the access point with the strongest signal, the client device can ensure a more stable and reliable connection.

An impedance mismatch in the RF cables and connectors can cause an excessively high VSWR in a WLAN RF transmission line. When there is a mismatch between the impedance of the transmission line and the impedance of the connected devices, a portion of the RF signal is reflected back towards the source. This reflection can result in standing waves along the transmission line, leading to an increase in VSWR.

The phrase "Equivalent Isotropically Radiated Power (EIRP)" refers to the highest RF signal strength that is transmitted from a given antenna.

When choosing an antenna with higher gain, the beamwidth will also always change. Beamwidth refers to the angle of coverage of the antenna's main lobe. A higher gain antenna will have a narrower beamwidth, meaning it will focus its energy in a more concentrated direction. This can be beneficial in situations where a specific area needs to be targeted with a stronger signal. However, it also means that the antenna's coverage area will be reduced, as the signal will be less dispersed.

The statement that is true about the IEEE 802.11e QoS facility is that 802.11 QoS is achieved by giving high priority queues a statistical advantage at winning contention. This means that the high priority queues have a higher chance of accessing the wireless medium and transmitting their data compared to lower priority queues. This ensures that important and time-sensitive data, such as voice or video, can be transmitted with minimal delay and higher reliability.

The EIRP (Effective Isotropic Radiated Power) is calculated by adding the transmitter power output (in this case, 50 mW) with the gain of the antenna (in this case, 16 dBi) and subtracting the loss of the cable (in this case, 3 dB). Converting the gain from dBi to dBd (decibels relative to a dipole), the calculation becomes: EIRP = Transmitter power output + Antenna gain - Cable loss = 50 mW + 16 dBd - 3 dB = 1000 mW. Therefore, the EIRP power output is 1000 mW.

When replacing the antenna of a WLAN device with a similar antenna type that has a higher passive gain, the beam width will decrease. Beam width refers to the angle between the half-power points of the main lobe in the radiation pattern of the antenna. A higher passive gain means that the antenna focuses more of its energy in a narrower beam, resulting in a smaller beam width. This narrower beam width can lead to a more concentrated signal, but it may also reduce the coverage area or range of the WLAN device.

The given question is asking about the term that correctly completes the sentence regarding guard intervals (GI) in OFDM. The sentence states that guard intervals are necessary in OFDM to reduce the likelihood of interference between two consecutive ________. Since OFDM divides a data stream into multiple subcarriers, the term that correctly completes the sentence is "Symbols." Guard intervals are used to separate symbols in OFDM to avoid interference between them.

Through loss refers to the loss of signal strength that occurs when using an RF splitter to connect one transceiver to sector antennas. This loss is a result of the signal being divided among multiple antennas, leading to a decrease in overall signal strength.

Dynamic Rate Switching is the correct term used to describe the functionality of a station changing its data rate as it moves away from the access point. This term refers to the ability of the station to automatically adjust its data rate based on the signal strength and quality of the wireless connection. By dynamically switching to lower data rates, the station can maintain a more reliable and stable connection even at longer distances from the access point. This functionality is an important feature in IEEE 802.11 wireless networks to optimize the performance and reliability of the wireless communication.

The EIRP (Effective Isotropic Radiated Power) is calculated by adding the transmitter power, cable loss, and antenna gain. In this case, the transmitter emits a 200 mW signal (23 dBm), the cable has a 3 dB loss, and the antenna has a 10 dBi gain. Adding these values together, we get 23 dBm - 3 dB + 10 dBi = 30 dBm. Therefore, the EIRP at the antenna element is 30 dBm.

To establish a high-quality 2.4 GHz RF link at a distance of 3 miles (5 kilometers), it is important to have a Fresnel Zone that is at least 60% clear of obstructions. The Fresnel Zone is an elliptical area around the direct line of sight between the transmitter and receiver. Obstructions within this zone can cause signal degradation and interference. By ensuring that at least 60% of the Fresnel Zone is clear, the RF signal can propagate with minimal interference, resulting in a high-quality link.

Refraction is the correct answer because it refers to the bending of an RF signal as it passes through a medium with a varying density from that of free space. When the signal encounters a change in the density of the medium, such as when it passes from air to water or from one type of material to another, it bends or changes direction. This phenomenon is known as refraction.

The key difference between an independent basic service set (IBSS) and an infrastructure basic service set (BSS) is the presence of a distribution system (DS). An IBSS does not have a DS, which means that it operates in an ad-hoc mode where devices communicate directly with each other. On the other hand, a BSS has a DS, which is typically a wireless access point (AP) that acts as a central hub for devices to connect to. The DS in a BSS enables devices to communicate with each other and also provides connectivity to other networks, such as the internet.

The specified frequency ranges for use by IEEE 802.11 radios are 2.4000 – 2.4835 GHz, 5.15 – 5.25 GHz, 5.470 – 5.725 GHz, and 5.725 – 5.875 GHz. These frequency ranges are within the commonly used 2.4 GHz and 5 GHz bands for Wi-Fi communication. The IEEE 802.11 standard defines these frequency ranges to ensure compatibility and avoid interference between different Wi-Fi devices operating in the same area.

An impedance mismatch between components in the RF system can cause high return loss in an RF transmission system. When there is a mismatch in impedance between different components, such as the radio, cables, connectors, and antenna, some of the power from the forward energy gets reflected back towards the transmitter, resulting in a high return loss. This can lead to signal degradation and reduced efficiency in the transmission system.

When the antenna is moved to a new location using an extension cable, the Equivalent Isotropically Radiated Power (EIRP) will decrease. EIRP is a measure of the power radiated by an antenna in a specific direction. By adding an extension cable, there will be additional cable losses, resulting in a decrease in the power radiated by the antenna. This decrease in EIRP can lead to a weaker signal and potentially lower data throughput rate.

Spatial multiplexing is a technology that requires MIMO (Multiple-Input Multiple-Output) support on both the transmitter and receiver. MIMO involves the use of multiple antennas to transmit and receive multiple data streams simultaneously. Spatial multiplexing takes advantage of the multiple antennas to transmit different parts of the data simultaneously, increasing the overall data rate. Therefore, in order to utilize spatial multiplexing, both the transmitter and receiver must support MIMO technology.

dBm is the correct answer because it is an absolute unit of measurement used to quantify power levels on a linear scale. It is a logarithmic unit that represents power relative to a reference level of 1 milliwatt (mW). dBm is commonly used in telecommunications and electronics to express power levels in a more convenient and manageable way.

Fade Margin is an additional pad of signal strength that is intentionally added to the RF system. It is designed to compensate for unpredictable signal fading, which can occur due to various factors such as atmospheric conditions, interference, and obstacles in the signal path. By having a higher signal strength than what is actually required for reliable communication, the fade margin ensures that even if the signal weakens temporarily, it will still remain above the minimum threshold for successful transmission. This helps to maintain a reliable and stable long-distance RF link.

The given statement is false because the question states that the device is certified as a/b/g/n, which means it supports up to 600 Mbps data rate for 2.4 GHz band and up to 1300 Mbps data rate for 5.0 GHz band. Therefore, the maximum supported data rate for this device is not 300 Mbps.

If the SSID of the current AP does not match the SSID of the new AP, it will prevent a dual-band VHT/HT client device from performing a fast and seamless transition between the two access points. This is because the client device needs to authenticate and associate with the new AP, and if the SSID does not match, the client device will not be able to connect to the new AP. As a result, latency-sensitive applications may be disrupted during the transition.

The 802.11n (High Throughput) PHY specifies two channel modes: 20 MHz and 20/40 MHz. These channel modes determine the available bandwidth for wireless communication. The 20 MHz channel mode provides a single 20 MHz wide channel for data transmission. The 20/40 MHz channel mode allows for the aggregation of two 20 MHz channels to provide a wider bandwidth of 40 MHz, which can increase the data throughput.

Dipole and Patch antennas are commonly used by indoor Wi-Fi devices in a MIMO diversity implementation. Dipole antennas are simple and omnidirectional, meaning they radiate signals in all directions. Patch antennas, on the other hand, are directional and provide a focused signal in a specific direction. Using a combination of these two antenna types allows for improved signal coverage and diversity, which helps to enhance the overall performance and reliability of the Wi-Fi network in indoor environments.

802.11g radios support a data rate of 11 Mbps, which is not supported by 802.11a radios. The 802.11a standard supports data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, while the 802.11g standard supports data rates of 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36, 48, and 54 Mbps. Therefore, the correct answer is 11 Mbps.

Passive Gain describes the effect of increasing the intensity of an RF wave with an antenna by focusing the energy in a specific direction. This term refers to the process of using passive elements such as reflectors or directors to shape the radiation pattern of the antenna, resulting in increased signal strength in the desired direction.

The WLAN hardware known as a pole or mast mount unit is intended to be used for mounting an omnidirectional antenna to a mast. This type of hardware allows for secure installation of the antenna on top of a mast or pole, providing optimal coverage and signal distribution in all directions.

The SSID must be included in an association request frame because it is used to identify the network that the client wants to connect to. The SSID is an alphanumeric value with a maximum length of 32 octets, which means it can consist of both letters and numbers and cannot exceed 32 characters in length. This is the standard limit set by the IEEE for SSID values.

The center frequency of channel 4 can be determined by adding 5 to the center frequency of channel 1. Since the center frequency of channel 1 is 2.412 GHz, adding 5 to it gives us 2.417 GHz. Therefore, the center frequency of channel 4 is 2.417 GHz.

802.11 enterprise-class WLAN controllers are designed to support various features that are essential for enterprise networks. Link aggregation / port trunking is a feature that allows multiple physical links to be combined into a single logical link, increasing bandwidth and providing redundancy. 802.1p and DSCP QoS are Quality of Service mechanisms that prioritize and manage network traffic, ensuring that critical data receives higher priority and better performance. Captive web portals are used for guest authentication and access control, allowing organizations to provide secure Wi-Fi access to visitors. IGMP snooping is a feature that monitors and manages multicast traffic, optimizing network performance by forwarding multicast packets only to the devices that have subscribed to them.

The beacons are from an IBSS instead of a BSS. In an Independent Basic Service Set (IBSS), also known as an ad hoc network, the devices communicate directly with each other without the need for an access point (AP). In this case, the BSSID (Basic Service Set Identifier) remains the same for all beacons, but the source address varies between three different addresses because each device in the ad hoc network takes turns broadcasting the beacons. This is different from a Basic Service Set (BSS) where the beacons would typically have the same BSSID and source address.

The number of client stations associated to the BSS will have a significant impact on the amount of wireless bandwidth available to each station because as the number of client stations increases, the available bandwidth needs to be divided among more devices, resulting in reduced bandwidth per station.

The data rates at which nearby client stations are transmitting and receiving data will also have a significant impact on the available wireless bandwidth. If nearby client stations are transmitting and receiving data at high data rates, it can consume a significant portion of the available bandwidth, leaving less bandwidth for other stations in the BSS.

The first statement is true because the gain of an antenna is inversely proportional to the beamwidth. A lower gain antenna will have a narrower beamwidth.

The second statement is also true because the beamwidth patterns on an antenna polar chart indicate the boundaries at which the RF signal stops propagating. These patterns show the extent of the antenna's coverage area.

Therefore, the correct answer is that horizontal and vertical beamwidth are calculated at the points in which the main lobe decreases power by 3 dB, and horizontal beamwidth is displayed (in degrees) on the antenna's Azimuth Chart.

Virtual and Physical carrier sense functions are used to determine if the wireless medium is busy. Virtual carrier sense involves monitoring the wireless channel for any ongoing transmissions from other devices, while physical carrier sense involves detecting the presence of any energy or signals on the wireless medium. Both functions are necessary to ensure that a device can accurately determine if the medium is busy before transmitting data.

The term that describes the rate at which the expansion of the wave front happens is the inverse square law. According to this law, the intensity of the wave decreases as the square of the distance from the source increases. This means that as the RF wave propagates through space, the signal strength diminishes rapidly with distance.

The three factors that influence the distance that an RF signal can be effectively received are Free Space Path Loss, Transmitting station’s output power, and Receiving station’s radio sensitivity. Free Space Path Loss refers to the loss of power as the signal travels through space. The Transmitting station’s output power determines the strength of the signal being transmitted. The Receiving station’s radio sensitivity indicates how well the station can detect and interpret the incoming signal. These factors collectively determine the effective range of an RF signal.

VHT TXOP power save improves battery life for devices on a WLAN by using the partial AID in the preamble to allow clients to identify frames targeted for them. This means that devices can selectively wake up from sleep mode only when there are frames specifically meant for them, reducing the amount of time spent in active mode and conserving battery power.

The IEEE 802.11-2012 standard specifically addresses the Physical Layer Convergence Procedure (PLCP) and Media Access Control (MAC) sublayers of the OSI model. These two sublayers are crucial in the functioning of a communication system as they handle the physical transmission of data and the access control to the medium, respectively. The PLCP sublayer is responsible for converting data into a format suitable for transmission, while the MAC sublayer manages the access to the shared communication medium.

802.11ac VHT-OFDM utilizes 256-QAM, which increases the data rate significantly over 64-QAM available in HT-OFDM. This means that 802.11ac VHT-OFDM can transmit more data per symbol, resulting in higher data rates compared to HT-OFDM. By using a higher order modulation scheme, more bits can be encoded into each symbol, allowing for faster transmission speeds. This improvement in data rate is a key advantage of 802.11ac VHT-OFDM over previous OFDM technologies.

The WMM certification, created by the Wi-Fi Alliance, is based on the hybrid coordination function with support for contention-based QoS priority. This means that the WMM certification utilizes a combination of both contention-based and scheduled access methods to prioritize quality of service. Contention-based access allows devices to compete for access to the network, while the hybrid coordination function ensures that QoS priorities are maintained.

RTS (Request to Send) and CTS (Clear to Send) frames are components of the 802.11 standard that allow stations to reserve access to the RF (Radio Frequency) medium for a specified period of time. When a station wants to transmit data, it sends an RTS frame to the intended recipient, requesting permission to transmit. The recipient responds with a CTS frame, granting permission and reserving the medium for the sender. This mechanism helps prevent collisions and ensures that only one station transmits at a time, improving the overall efficiency and reliability of the wireless network.

In an 802.11n WLAN with a heterogeneous set of associated client devices including 802.11b, 11g, and 11n, the BSS will use Mode 3: Non-HT mixed mode. This mode is used to protect the non-HT (802.11b/g) devices from interference caused by the HT (802.11n) devices. It allows the BSS to operate in mixed mode, supporting both HT and non-HT devices simultaneously. This ensures compatibility and optimal performance for all devices in the network.

When a client station sends a broadcast probe request frame with a wildcard SSID, all APs compete for the opportunity to respond. After waiting a SIFS (Short Interframe Space), each AP prepares a probe response and participates in contention to determine which AP will respond first. The AP that wins contention sends its probe response, and then other APs respond in a sequential manner, taking turns after preparing their own probe responses. This ensures that multiple APs do not reply simultaneously, preventing potential collisions and ensuring a more efficient communication process.

In the 802.11ac amendment to the 802.11-2012 standard, the channel 144 became available, which was not available in the standard before this amendment.

The factors that are taken into account when calculating the Link Budget of a point-to-point outdoor WLAN bridge link are the transmit antenna gain, transmit power, and operating frequency. The transmit antenna gain refers to the ability of the antenna to focus the transmitted signal in a specific direction, which can affect the signal strength and coverage. The transmit power is the amount of power that is being transmitted, which also affects the signal strength. The operating frequency is the frequency at which the wireless communication is taking place, and different frequencies can have different propagation characteristics and signal losses.

DFS (Dynamic Frequency Selection) may be required in some regulatory domains on some channels. The 5 GHz frequency band used by IEEE 802.11a/n/ac has a limited number of available channels. In order to avoid interference with radar systems, certain channels require DFS, which is a mechanism that allows devices to detect and avoid radar signals. However, not all regulatory domains require DFS on all channels, so it may only be required in certain regions on specific channels.

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In an IEEE 802.11 frame, the IP packet is considered by the MAC layer to be a(n) MAC Service Data Unit (MSDU). The MSDU is the data unit that is passed from the higher layers (such as the IP layer) to the MAC layer for transmission over the wireless network. It contains the payload data and any necessary headers or trailers added by the higher layers. The MAC layer then encapsulates the MSDU into a MAC Protocol Data Unit (MPDU) for transmission over the wireless medium. Therefore, the correct term to complete the sentence is MAC Service Data Unit (MSDU).

The AP may ignore the initial probe requests or 802.11 authentication requests sent in the 2.4 GHz band by dual-band clients. This means that when a client device sends a probe request or authentication request in the 2.4 GHz band, the AP will not respond to it. By doing this, the AP encourages the client to try connecting to the 5 GHz band instead. This helps to steer clients towards using the 5 GHz band, which generally provides better performance and less congestion compared to the 2.4 GHz band.