An IEEE 802.11 amendment is in the daft state. What impact does this draft amendment have on the
802.11 standard?
B
Explanation:
An IEEE 802.11 amendment is a proposed change or addition to the existing 802.11 standard, which
defines the specifications and protocols for wireless LANs. An amendment goes through several
stages of development, such as draft, sponsor ballot, and final approval, before it is ratified by the
IEEE Standards Association and becomes part of the standard. Until then, it has no official impact on
the standard, although some vendors may release products based on draft amendments to gain a
competitive edge or to influence the final outcome of the amendment . Reference: [CWNA-109 Study
Guide], Chapter 1: Overview of Wireless Standards, Organizations, and Fundamentals, page 25;
[CWNA-109 Study Guide], Chapter 1: Overview of Wireless Standards, Organizations, and
Fundamentals, page 23; [IEEE website], IEEE-SA Standards Development Process.
You are implementing a VHT-capable AP. Which one of the following channels is available in the
802.11-2016 standard that was not available before the ratification of 802.11 ac?
D
Explanation:
Channel 144 is a new channel that was added to the 5 GHz band by the 802.11ac amendment, which
defines the VHT (Very High Throughput) PHY for WLANs. Channel 144 has a center frequency of 5720
MHz and a bandwidth of 20 MHz. It can also be combined with adjacent channels to form wider
channels of 40 MHz, 80 MHz, or 160 MHz. Channel 144 is available in some regions, such as North
America and Europe, but not in others, such as Japan and China . Reference: [CWNA-109 Study
Guide], Chapter 3: Antennas and Accessories, page 121; [CWNA-109 Study Guide], Chapter 3:
Antennas and Accessories, page 115; [Wikipedia], List of WLAN channels.
What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM)
modulation method in IEEE 802.11 WLANs?
B
Explanation:
OFDM is a modulation method that divides the channel bandwidth into multiple subcarriers, each
carrying a single data symbol. This allows for higher data rates and more robust transmissions in
multipath environments. OFDM was first introduced in the 802.11a standard, which operates in the 5
GHz band and supports data rates up to 54 Mbps. Later, the 802.11g standard adopted OFDM for the
2.4 GHz band, and the 802.11n and 802.11ac standards enhanced OFDM with features such as MIMO
(Multiple Input Multiple Output), channel bonding, and higher-order modulation schemes to achieve
data rates up to 600 Mbps and 6.9 Gbps, respectively. These standards are collectively known as the
ERP (Extended Rate PHY), HT (High Throughput), and VHT (Very High Throughput) PHYs
. Reference: [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts,
page 163; [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page
157.
Which IEEE 802.11 physical layer (PHY) specification includes support for and compatibility with both
ERP and HR/DSSS?
C
Explanation:
The HT (802.11n) physical layer (PHY) specification includes support for and compatibility with both
ERP and HR/DSSS. ERP stands for Extended Rate PHY, which is an extension of the original DSSS
(Direct Sequence Spread Spectrum) PHY that supports data rates up to 54 Mbps in the 2.4 GHz band.
HR/DSSS stands for High Rate/Direct Sequence Spread Spectrum, which is another extension of DSSS
that supports data rates up to 11 Mbps in the 2.4 GHz band. HT stands for High Throughput, which is
a new PHY that supports data rates up to 600 Mbps in both the 2.4 GHz and 5 GHz bands. HT uses
OFDM (Orthogonal Frequency Division Multiplexing) as its modulation scheme, but it also supports
legacy DSSS and ERP devices by using a dual preamble and header structure that allows backward
compatibility. Reference: , Chapter 3, page 103; , Section 3.1
An 802.11-based network uses an AP and has several connecting clients. The clients include iPhones,
iPads, laptops and one desktop. What WLAN use case is represented?
C
Explanation:
A BSS (Basic Service Set) is a WLAN use case that represents an 802.11-based network that uses an
AP (Access Point) and has several connecting clients. The AP acts as a central point of coordination
and communication for the clients, which can include iPhones, iPads, laptops, desktops, or any other
devices that have Wi-Fi capabilities. A BSS can be identified by a unique BSSID (Basic Service Set
Identifier), which is usually the MAC address of the AP’s radio interface. A BSS can also be associated
with an SSID (Service Set Identifier), which is a human-readable name that identifies the
network. Reference: , Chapter 1, page 23; , Section 1.1
What factor is likely to cause the least impact on the application layer throughput of an 802.11n
client station in a 2.4 GHz HT BSS?
B
Explanation:
Implementing Fast BSS Transition (FT) for roaming is likely to cause the least impact on the
application layer throughput of an 802.11n client station in a 2.4 GHz HT BSS. 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 application layer throughput. FT is defined in the IEEE 802.11r amendment and is
also known as Fast Roaming or Fast Secure Roaming. Reference: , Chapter 9, page 367; , Section 6.3
What ID is typically mapped to an AP’s MAC address if a single BSS is implemented?
D
Explanation:
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. Reference: , Chapter 1,
page 24; , Section 1.2
What is appended to the end of each 802.11 data frame after the payload?
D
Explanation:
The FCS (Frame Check Sequence) is appended to the end of each 802.11 data frame after the
payload. The FCS is a 4-byte field that contains a CRC-32 (Cyclic Redundancy Check) value that is
calculated based on the contents of the MAC header and the payload of the frame. The FCS is used
by the receiver to verify the integrity of the frame and to detect any errors or corruption that may
have occurred during transmission. If the FCS does not match with the expected value, the frame is
discarded by the receiver. Reference: , Chapter 4, page 139; , Section 4.2
When an ACK frame is not received by the transmitting STA, what is assumed?
C
Explanation:
An ACK (Acknowledgement) frame is a short control frame that is sent by the receiver of a data or
management frame to confirm that the frame was received correctly. The ACK frame is sent after a
SIFS (Short Interframe Space) interval, which is the shortest time gap between frames in 802.11. If
the transmitter does not receive an ACK frame within a specified time, it assumes that the frame was
not delivered and must be retransmitted. This is part of the 802.11 reliability mechanism that
ensures reliable data delivery over an unreliable wireless medium . Reference: [CWNA-109 Study
Guide], Chapter 5: IEEE 802.11 Medium Access, page 209; [CWNA-109 Study Guide], Chapter 5: IEEE
802.11 Medium Access, page 203.
When a client station sends a broadcast probe request frame with a wildcard SSID, how do APs
respond?
A
Explanation:
In the 802.11 wireless networking protocols, when a client station sends a broadcast probe request
frame with a wildcard SSID (Service Set Identifier), it is essentially asking for any nearby access points
(APs) to identify themselves. The way APs respond to such a probe request is governed by standard
802.11 behavior, which includes:
Probe Request Handling: Upon receiving a broadcast probe request, each AP that can serve the client
prepares a probe response. The response includes information about the AP, such as its SSID,
supported data rates, and other capabilities.
Contention-Based Mechanism: Wireless networks use a contention-based mechanism (CSMA/CA -
Carrier Sense Multiple Access with Collision Avoidance) for medium access. Each AP must wait for a
clear channel and win the contention process before it can send its probe response.
Independent Responses: Each AP operates independently in responding to the probe request. There
is no coordination between APs to decide which one responds first or at all, leading to multiple APs
sending probe responses, each after winning the contention for the medium.
Option A accurately reflects this process, indicating that each AP prepares and sends a probe
response in turn, contingent upon winning the medium contention. The other options suggest
mechanisms (such as coordination with a DHCP server or simultaneous responses after a Short
Interframe Space (SIFS)) that do not align with standard 802.11 procedures for handling broadcast
probe requests.
Reference:
IEEE 802.11 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.
CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, by David D.
Coleman and David A. Westcott.