What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM) modulation method in IEEE 802.11 WLANs?
Answer(s): B
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 .
[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?
Answer(s): C
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.
, 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?
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 SetIdentifier), 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.
, 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?
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.
, Chapter 9, page 367; , Section 6.3
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Quentin commented on November 14, 2024 I noticed that some comments were related to answers not being 100% correct. But for me as long as questions are real and same as the actual exam I was okay. Mexico upvote
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