DCS Enhancement

Zyxel_Lynn

DCS Enhancement: Optimized 5GHz Spectrum Utilization

Starting with Nebula 20.00, Zyxel has introduced a significant shift in Dynamic Channel Selection (DCS) behavior, where the "Avoid 5G DFS channel" option is now disabled by default for all new sites. This enhancement is designed to improve channel availability and ensure maximum utilization of the 5GHz spectrum.

The Advantage of DFS Channels

Previously, 5G DFS channels (ranging from 52 to 64 and 100 to 144) were often excluded by default. By including these channels, administrators can access a much larger pool of available frequencies, which significantly reduces congestion on standard non-DFS channels like 36, 40, and 44.

Managing the Channel Availability Check (CAC)

The use of DFS channels requires a Channel Availability Check (CAC) to ensure the spectrum is not being used by weather or military radar. During this check, the AP must temporarily stop broadcasting SSIDs for 1 to 10 minutes, leading to a brief wireless service disruption.

Roaming Strategies for Connectivity

To mitigate service downtime, Zyxel recommends a multiple-AP deployment strategy. This allows clients to roam to a nearby neighbor AP while the original AP is undergoing its CAC. Successful roaming requires identical SSID and security settings across APs, with a coverage overlap signal strength stronger than -75 dBm. Administrators can utilize the Neighbor Scan tool to verify the availability of neighboring APs for roaming. 

While DFS is highly effective in multi-AP environments, it is generally not recommended for single-AP deployments due to the unavoidable service interruptions.