You are configuring an access point to use channel 128. What important fact should be considered about this channel?

It is a channel that may require DFS when used is an important fact that should be considered about

channel 128. Channel 128 is a 5 GHz frequency band 20 MHz channel that has a center frequency of

5.64 GHz. Channel 128 is one of the channels that are subject to DFS (Dynamic Frequency Selection)

rules, which require Wi-Fi devices to monitor and avoid using channels that are occupied by radar

systems or other primary users. DFS is a feature that is defined in the IEEE 802.11h amendment and

is mandated by some regulatory bodies, such as the FCC and the ETSI, to protect the licensed users

of the 5 GHz band from interference by unlicensed Wi-Fi devices. DFS works by using a mechanism

called channel availability check (CAC), which requires Wi-Fi devices to scan a channel for a certain

period of time before using it. If a radar signal is detected during the CAC or while using the channel,

the Wi-Fi devices must switch to another channel that is free from radar interference.

When configuring an access point to use channel 128, it is important to consider the implications of

DFS rules, such as:

The access point must support DFS and comply with the local regulations and standards that apply to

DFS channels.

The access point may experience delays or interruptions in its operation due to CAC or channel

switching.

The access point may have limited channel selection or availability due to radar interference or other

Wi-Fi devices using DFS channels.

The access point may have compatibility or interoperability issues with some client devices that do

not support DFS or use different DFS parameters.

The access point may have performance or quality issues due to co-channel or adjacent-channel

interference from other Wi-Fi devices using non-DFS channels.

Therefore, it is advisable to use channel 128 only when necessary and after performing a thorough

site survey and spectrum analysis to determine the best channel for the access point. Reference: 1,

Chapter 3, page 117; 2, Section 3.2