Dynamic Frequency Selection (DFS) regulations require wireless devices to prevent interference with incumbent radar systems operating in the 5 GHz band. Before an access point (AP) can transmit on a designated DFS channel, it must perform a mandatory Channel Availability Check (CAC). This process involves passively listening on the channel for a specific duration, typically 60 seconds, to detect any radar signals. If no radar is detected during this period, the AP can then begin broadcasting its SSIDs and servicing clients on that channel.

A. Client device support is a consideration for network performance and design, but it is not a regulatory requirement the AP must perform before transmitting on a DFS channel.

C. The AP must listen passively. Transmitting anything, especially radar-like pulses, before the channel is cleared would cause interference and is a direct violation of DFS regulations.

D. Validating non-DFS channels is part of the AP's broader channel selection algorithm or a fallback action if radar is detected, not the required initial step for an assigned DFS channel.

1. Juniper Mist Documentation, Radio Resource Management (RRM): In the "Dynamic Frequency Selection (DFS)" section, it states, "Before an AP can use a DFS channel, it must scan the channel for 60 seconds to make sure that no radar is present. This is known as the Channel Availability Check (CAC)."

Source: Juniper Networks, "Radio Resource Management (RRM)," Mist Wireless Assurance Documentation, Section: Dynamic Frequency Selection (DFS).

2. Juniper Mist™ Wi-Fi Assurance Feature Guide: This guide explains the operational principles of Mist APs. The section on RRM details the DFS compliance mechanism, emphasizing the listening period. "If RRM assigns a DFS channel to an AP, the AP must first listen on that channel for radar signals for one minute (or 10 minutes for weather radar channels) before it can begin transmitting."

Source: Juniper Networks, "Juniper Mist™ Wi-Fi Assurance Feature Guide," Page 12, Section: Radio Resource Management (RRM).