CWNP CWAP-404 Online Practice Questions and Exam Preparation

CWNP CWAP-404 Online Questions & Answers

• Question 41:

  Given: The Frame Check Sequence (FCS) is a 32 CRC used for error detection.

  The CRC is calculated over what?

  A. Mac Header and Frame Body only
  B. Frame Body only
  C. PHY Header, MAC Header and Frame Body
  D. PHY Header and Mac Header only
  A. Mac Header and Frame Body only

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  Explanation/Reference:

  The CRC is calculated over the MAC Header and Frame Body only. The CRC (Cyclic Redundancy Check) is a 32-bit value that is used for error detection in wireless transmissions. The CRC is calculated over the MAC Header and Frame Body of a PSDU, which are the parts of the data unit that contain information such as source and destination addresses, frame type, frame control, sequence number, payload, etc. The CRC is appended to the end of the PSDU as a FCS (Frame Check Sequence) field. The CRC is not calculated over the PHY Header or PHY Preamble, which are parts of the PPDU that contain information such as modulation, coding, data rate, etc. The PHY Header and PHY Preamble are added or removed by the PHY layer during the conversion between PSDU and PPDU. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 4: 802.11 Physical Layer, page 97-98

• Question 42:

  Where, in a protocol analyzer, would you find an indication that a frame was transmitted as part of an A-MPDU?

  A. The HT Operation Element
  B. A-MPDU flag in the QoS Control Field
  C. A-MPDU flag in the Frame Control Field
  D. The Aggregation flag in the Radio Tap Header
  D. The Aggregation flag in the Radio Tap Header

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  Explanation/Reference:

  In a protocol analyzer, you would find an indication that a frame was transmitted as part of an A-MPDU by looking at the Aggregation flag in the Radio Tap Header. The Radio Tap Header is a pseudo-header that is added by some wireless capture devices to provide additional information about the physical layer characteristics of a frame. The Aggregation flag is one of the fields in this header, and it indicates whether the frame belongs to an A-MPDU or not. If the flag is set to 1, it means that the frame is part of an A- MPDU; if it is set to 0, it means that the frame is not part of an A-MPDU . References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter

  9: PHY Layer Frame Formats andTechnologies, page 303; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 9: PHY Layer Frame Formats and Technologies, page 304.

• Question 43:

  Prior to a retransmission what happens to the CWmax value?

  A. Increases by 1
  B. Reset to 0
  C. Set to the value of the AIFSN
  D. Doubles and increases by 1
  D. Doubles and increases by 1

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  Explanation/Reference:

  Before a retransmission, the CWmax (Contention Window maximum) value doubles and increases by 1. The CWmax is a parameter that determines the upper limit of the random backoff time that a STA (station) has to wait before attempting to access the medium. The random backoff time is chosen from a range of values between CWmin (Contention Window minimum) and CWmax. The CWmin and CWmax values depend on the AC (Access Category) of the traffic and the PHY type of the STA. If a transmission fails due to a collision or an error, the STA has to retransmit the frame after waiting for another random backoff time. However, to reduce the probability of another collision, the STA increases its CWmax value by doubling it and adding 1. This increases the range of possible backoff values and spreads out the STAs more evenly. The STA resets its CWmax value to its original value after a successful transmission or after reaching a predefined limit. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 7: QoS Analysis, page 196-197

• Question 44:

  You are analyzing a packet decode of a Probe Request and notice the SSID element has a length of zero. What do you conclude about the transmitting STA?

  A. The WLAN adaptor is configured in promiscuous mode
  B. The STA is operating in Ad-Hoc mode
  C. The STA's WLAN adaptor is disabled
  D. The STA is discovering a list of available BSSs
  D. The STA is discovering a list of available BSSs

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  Explanation/Reference:

  The STA is discovering a list of available BSSs by sending a Probe Request with an empty SSID element. This is also known as a broadcast Probe Request, as it does not specify any particular SSID to probe for. Any AP that receives this Probe Request will respond with a Probe Response containing its own SSID and other information about its BSS. This way, the STA can learn about all the BSSs in its vicinity and choose which one to associate with . References: CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter 6: MAC Sublayer Frame Exchanges, page 191; CWAP-404 Certified Wireless Analysis Professional Study and Reference Guide, Chapter

  6: MAC Sublayer Frame Exchanges, page 193.

• Question 45:

  Which one of the following is required for Wi-Fi integration in laptop-based Spectrum Analyzer software in addition to the spectrum analysis adapter?

  A. An 802.11 wireless adaptor
  B. A firmware upgrade for the spectrum analysis adapter
  C. A directional antenna
  D. SNMP read credentials to the WLAN controller or APs
  A. An 802.11 wireless adaptor

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  Explanation/Reference:

  An 802.11 wireless adaptor is required for Wi-Fi integration in laptop-based spectrum analyzer software in addition to the spectrum analysis adapter. The spectrum analysis adapter is a hardware device that captures the RF signals in the wireless environment and sends them to the spectrum analyzer software for analysis and display. The 802.11 wireless adapter is a hardware device that connects the laptop to the wireless network and allows the spectrum analyzer software to correlate the RF data with the Wi-Fi data, such as SSID, channel, and BSSID. This enables the spectrum analyzer software to provide more context and insight into the spectrum activity and its impact on the Wi-Fi network. A firmware upgrade for the spectrum analysis adapter is not required for Wi-Fi integration, but it may be needed to fix bugs or add features to the device. A directional antenna is an antenna that focuses the RF energy in a specific direction and has a high gain and a narrow beamwidth. A directional antenna can be used with a spectrum analysis adapter to pinpoint the location or source of interference or noise in the wireless environment, but it is not required for Wi-Fi integration. SNMP read credentials to the WLAN controller or APs are not required for Wi-Fi integration, but they may be useful for obtaining additional information about the wireless network configuration and performance from the network devices.References: CWAP-404 Study Guide, Chapter 4: Spectrum Analysis and Troubleshooting, page 123 CWAP-404 Objectives, Section 4.2: Integrate Wi-Fi data with spectrum analysis data CWAP-404 Study Guide, Chapter 4: Spectrum Analysis and Troubleshooting, page 131

• Question 46:

  When performing protocol analysis, you capture an 802.1 lac data frame on channel 52, transmitted at MCS 8. At what data rate was the PHY Preamble transmitted?

  A. 54 Mbps
  B. 86.7 Mbps
  C. 6 Mbps
  D. 78 Mbps
  C. 6 Mbps

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  Explanation/Reference:

  The data rate at which the PHY preamble was transmitted is 6 Mbps. The PHY preamble is a part of the PPDU that is transmitted before the PHY header and the PSDU. The PHY preamble consists of a series of training fields that help the receiver to detect and synchronize with the signal. The PHY preamble is always transmitted at a fixed data rate that depends on the type of PPDU (e.g., OFDM, HT, VHT, HE). For an 802.1 lac data frame on channel 52, which uses VHT PPDUs, the data rate for the PHY preamble is 6 Mbps. This data rate does not depend on MCS (Modulation and Coding Scheme), which only affects the data rate for the PSDU. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 4: 802.11 Physical Layer, page 99-100

• Question 47:

  How does a VoIP Phone, using WMM Power Save, request data frames buffered at the AP?

  A. The VoIP phone transmits a PS-Poll frame
  B. The VoIP phone sets the More Data bit in the MAC Header to 1
  C. The VoIP phone transmits a WMM Action frame
  D. The VoIP phone transmits a trigger frame, which is a QoS Null frame or a QoS Data frame
  D. The VoIP phone transmits a trigger frame, which is a QoS Null frame or a QoS Data frame

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  Explanation/Reference:

  A VoIP phone, using WMM Power Save, requests data frames buffered at the AP by transmitting a trigger frame, which is a QoS Null frame or a QoS Data frame. WMM Power Save is a power saving mode that allows a STA (station) to conserve battery power by periodically sleeping and waking up. WMM Power Save is based on WMM (Wi-Fi Multimedia), which is a QoS (Quality of Service) enhancement that provides prioritized and differentiated access to the medium fordifferent types of traffic. When a STA sleeps, it cannot receive any data frames from the AP, so it informs the AP of its power save status by setting a bit in its MAC header. The AP then buffers any data frames destined for the sleeping STA until it wakes up. When a STA wakes up, it sends a trigger frame to the AP, indicating its AC (Access Category), which is a logical queue that corresponds to its QoS level. A trigger frame can be either a QoS Null frame or a QoS Data frame, depending on whether it has any payload or not. The AP then responds with one or more data frames from the same AC as the trigger frame, followed by an ACK or BA (Block Acknowledgement) frame from the STA. The other options are not correct, as they are not used by a VoIP phone using WMM Power Save to request data frames buffered at the AP. A PS-Poll (Power Save Poll) frame is used by a STA using legacy power save mode, not WMM Power Save mode, to request data frames buffered at the AP. A PS-Poll frame does not indicate any AC or QoS information. Setting the More Data bit in the MAC header to 1 does not request any data frames from the AP, but indicates that there are more data frames to be sent by the STA or received by the STA. Transmitting a WMM Action frame does not request any data frames from the AP, but performs various management actions related to WMM features, such as admission control, parameter update, etc. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 7: QoS Analysis, page 198-199

• Question 48:

  Which one of the these is the most important in the WLAN troubleshooting methodology among those listed?

  A. Obtain detailed -knowledge of the wireless vendors debug and logging options
  B. Interview the network manager about the issues being experienced
  C. Observe the problem
  D. Talk to the end users about their experiences
  C. Observe the problem

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  Explanation/Reference:

  Observing the problem is the most important step in the WLAN troubleshooting methodology among those listed. This step involves capturing and analyzing the relevant data from the wireless network, such as packets, frames,

  spectrum, and performance metrics. Observing the problem helps to verify the existence and scope of the issue, identify the root cause and possible solutions, and validate the results of any actions taken. The other steps are also important,

  but they are not as critical as observing the problem12 References:

  CWAP-404 Study Guide, Chapter 1: Troubleshooting Methodology, page 15 CWAP-404 Objectives, Section 1.2: Observe the problem

• Question 49:

  A client is operating in an unstable RF environment. Out of five data frames transmitted to the client it only receives four. The client sends a Block Ack to acknowledge the receipt of these four frames but due to frame corruption the Block Ack

  is not received by the AP.

  Which frames will be retransmitted?

  A. All data frames
  B. Both the corrupted data and Block Ack
  C. Only the data frame which was corrupted
  D. Only the Block Ack
  A. All data frames

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  Explanation/Reference:

  All data frames will be retransmitted in this scenario. This is because the AP uses a Block Ack (BA) mechanism to acknowledge the receipt of multiple data frames from a client in a single frame. The BA contains a bitmap that indicates which data frames were received correctly and which were not. If the BA is not received by the AP due to frame corruption, the AP will assume that none of the data frames were received by the client and will retransmit all of them. The other options are not correct, as they do not account for the loss of the BA or the use of the bitmap. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 6: 802.11 Frame Exchanges, page 167-168

• Question 50:

  Which common feature of a Spectrum Analyzer would be the best to help you locate a non- 802.11 interference source?

  A. Max hold
  B. Min hold
  C. Location filter
  D. Device finder
  D. Device finder

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  Explanation/Reference:

  The device finder is a common feature of a spectrum analyzer that helps locate a non-802.11 interference source. The device finder uses a directional antenna to measure the signal strength of a specific frequency or signal source. By pointing the antenna in different directions, the device finder can indicate the direction and distance of the interference source. The device finder can also filter out other signals that are not related to the interference source. The other options are not correct, as they do not help locate a non-802.11 interference source. Max hold and min hold are features that show the maximum and minimum RF power levels over time,respectively. Location filter is a feature that filters out signals that are not from a specific location or area. References: [Wireless Analysis Professional Study Guide CWAP-404], Chapter 3: Spectrum Analysis, page 77-78