A dual-band 802.11ac AP must be powered by PoE. As a class 4 device, what power level should be received at the AP?
Answer(s): C
PoE has different standards that define different power levels for PSEs and PDs. The original standard, IEEE 802.3af, defines two classes of PSEs: Class 3 (15.4 W) and Class 4 (30 W). The newer standard, IEEE 802.3at, also known as PoE+, defines four classes of PSEs: Class 0 (15.4 W), Class 1 (4 W), Class 2 (7 W), and Class 3 (12.95 W). The power level received at the PD is always lower than the power level provided by the PSE, due to cable resistance and power dissipation. The IEEE standards specify the minimum power level that must be received at the PD for each class of PSE. For a Class 4 PSE, the minimum power level received at the PD is 25.5 W910.
CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 295; CWNA-109 Study Guide, Chapter 7: Power over Ethernet (PoE), page 289.
A WLAN is implemented using wireless controllers. The APs must locate the controllers when powered on and connected to the network. Which one of the following methods is commonly used to locate the controllers by the APs?
Answer(s): B
DHCP (Dynamic Host Configuration Protocol) is a commonly used method to locate the controllers by the APs in a WLAN that is implemented using wireless controllers. DHCP is a protocol that allows a device to obtain an IP address and other network configuration parameters from a server. In a wireless controller scenario, the APs can use DHCP to request an IP address from a DHCP server, which can also provide the IP address or hostname of the wireless controller as an option in the DHCP response. This way, the APs can discover the wireless controller and establish a connection with it. Alternatively, the APs can also use other methods to locate the wireless controller, such as DNS (Domain Name System), broadcast or multicast discovery, or manual configuration.
1, Chapter 8, page 309; 2, Section 5.2
You are implementing a multi-AP WLAN and fast secure roaming is essential. Which one of the following methods is an IEEE 802.11 standard method for fast roaming?
Answer(s): A
FT (Fast Transition) is an IEEE 802.11 standard method for fast roaming. FT is defined in the IEEE 802.11r amendment and is also known as Fast BSS Transition (FBT) or Fast Secure Roaming. 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 security of the connection. FT works by using pre-authentication and key caching mechanisms that allow the client station and the APs to exchange security information before the actual roaming occurs. This way, when the client station decides to roam to a new AP, it can use a fast reassociation request and response that contain only a few fields, instead of a full authentication and association exchange that require more time and data.
1, Chapter 9, page 367; 2, Section 6.3
In an 802.11 2.4 GHz system, what 22 MHz channels are considered non-overlapping?
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.
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.
The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz). What is the center frequency of channel 4?
The center frequency of channel 4 in the 2.4 GHz band is 2.427 GHz (2427 MHz). The center frequency of a channel is the midpoint of its frequency range, where the signal strength is highest and most concentrated. The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz), as given in the question. The center frequency of each subsequent channel is obtained by adding 5 MHz to the previous channel's center frequency, since the channels are spaced 5 MHz apart from each other in this band. Therefore, to find the center frequency of channel 4, we need to add 15 MHz (5 MHz x 3) to the center frequency of channel 1:2.412 GHz + 0.015 GHz = 2.427 GHzAlternatively, we can use a formula to calculate the center frequency of any channel in the 2.4 GHz band:Center frequency (GHz) = 2.407 + (0.005 x Channel number) Using this formula for channel 4, we get:Center frequency (GHz) = 2.407 + (0.005 x 4)Center frequency (GHz) = 2.407 + 0.02Center frequency (GHz) = 2.427
1, Chapter 3, page 85; 2, Section 3.2
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