Prepare Smarter for the CWNA-109 Exam

An isotropic radiator is a theoretical point source of electromagnetic radiation that radiates equally in all directions. It has no physical dimensions and no preferred direction of radiation.  It is used as a reference for antenna gain because it represents the ideal case of a perfect omnidirectional antenna 1 2

Antenna gain is a measure of how well an antenna concentrates its radiated power in a certain direction. It is expressed in decibels (dB) relative to a reference antenna.  When the reference antenna is an isotropic radiator, the antenna gain is denoted by dBi, which stands for decibels relative to isotropic 1 2

For example, an antenna with a gain of 3 dBi means that it radiates 3 dB more power in its main direction than an isotropic radiator would.  Conversely, an antenna with a gain of -3 dBi means that it radiates 3 dB less power in its main direction than an isotropic radiator would 1 2

In the 2.4 GHz frequency band used for 802.11 wireless networks, the channel bandwidth is typically 20 MHz, but the actual frequency spread of each channel is about 22 MHz due to the modulation techniques used. This spread causes overlap between adjacent channels, which can lead to interference and degrade network performance. To avoid this, it ' s essential to use non-overlapping channels.

The three non-overlapping channels in the 2.4 GHz band are 1, 6, and 11. Each of these channels is spaced sufficiently apart to avoid interference with each other:

Channel 1 : Centered at 2.412 GHz.

Channel 6 : Centered at 2.437 GHz.

Channel 11 : Centered at 2.462 GHz.

Given the options provided, option C (1 and 5) is the closest to a pair of non-overlapping channels, although in practice, channel 5 would still cause some interference with channel 1 due to the 22 MHz spread. The ideal choice for non-overlapping channels would be any two channels among 1, 6, and 11, but this is not an option provided. Therefore, within the given options, 1 and 5 are the best choice, understanding that in a real-world scenario, 1 and 6 or 6 and 11 would be preferred to avoid overlap.

[References:, CWNA Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109, by David D. Coleman and David A. Westcott., Understanding 2.4 GHz channel arrangement and interference patterns in 802.11 wireless networks., , , , ]

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 .  References:  [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.

VHT stands for Very High Throughput, which is a physical layer (PHY) specification that supports the 5 GHz frequency band and supports 80 MHz channels. VHT is used by the IEEE 802.11ac standard, which is also known as Wi-Fi 5. VHT allows for higher data rates and more spatial streams than the previous HT (High Throughput) PHY, which is used by the IEEE 802.11n standard, also known as Wi-Fi 4.  HT supports the 2.4 GHz and 5 GHz bands, but only supports up to 40 MHz channels 1 2

The other options are not correct because:

ERP (option C) stands for Extended Rate PHY, which is a physical layer specification that supports the 2.4 GHz frequency band and supports up to 20 MHz channels. ERP is used by the IEEE 802.11g standard, which is also known as Wi-Fi 3.  ERP allows for higher data rates than the previous DSSS (Direct Sequence Spread Spectrum) PHY, which is used by the IEEE 802.11b standard, also known as Wi-Fi 2 3 4

OFDM (option D) stands for Orthogonal Frequency Division Multiplexing, which is a modulation technique that divides a signal into multiple subcarriers that are spaced orthogonally to each other. OFDM is not a physical layer specification, but a common feature of many PHY specifications, including ERP, HT, and VHT.  OFDM allows for higher spectral efficiency and robustness against multipath interference than the previous CCK (Complementary Code Keying) modulation technique used by DSSS 3 4

The cipher suite specified by the 802.11-2016 standard and is not deprecated is  Counter Mode with CBC-MAC Protocol (CCMP) . CCMP is an encryption protocol that uses  Advanced Encryption Standard (AES)  as the underlying cipher and provides  confidentiality, integrity, and origin authentication  for wireless data. CCMP is the mandatory encryption protocol for  WPA2  and  WPA3 .  References:  [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 295; [IEEE Standard for Information technology–Telecommunications and information exchange between systems Local and metropolitan area networks–Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications] , page 1560.