Summary The 5GHz “Problem” For Wi-Fi Networks: DFS wifinigel.blogspot.com
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This text discusses the use of Dynamic Frequency Selection (DFS) to minimize the impact of channel changes on wireless networks and the use of Microsoft NPS as a RADIUS server.
Key Points
- Microsoft NPS is a RADIUS server for WiFi networks, providing authentication and authorization for users in a Windows Active Directory environment.
- To ensure the requirements of a WLAN design are not compromised, it is important to understand and verify the impact of radar detection.
- Non-latency-sensitive applications such as web browsing, email and streaming video files should not be affected by Dynamic Frequency Selection (DFS).
- To minimize the impact of DFS events, there are several options such as static channel planning and auto-RF exclusion of affected channels.
- Channels in the 5GHz band that are not subject to DFS are exempt from disruptions from local radar equipment and other sources of RF interference.
- When powering up an AP, the 5GHz radio may take another minute due to the AP performing a Dynamic Frequency Selection (DFS) “Channel Availability Check” to check for radar signals.
Summaries
170 word summary
My 802.11 WLAN resources include Ekahau Blog, CWNP Blog, Eddie Forero, Devin Aiken, Revolution WiFi, Wi-Fi For Beginners Podcast, my LinkedIn profile, GitHub repositories and YouTube channel. My white papers cover Licence-Exempt Spectrum, 802.11 Roaming Variations and DFS for 5GHz networks. Microsoft NPS is a RADIUS server for WiFi networks that provides authentication and authorization for users in a Windows Active Directory environment.
Dynamic Frequency Selection (DFS) can affect a wireless network, causing clients to transition to a new channel. This may have an impact on end-users depending on their applications. To minimize the impact of DFS events, static channel planning can be used to avoid affected channels. When radar signals are detected, a channel change is required and a Non-Occupancy Period of 30 minutes begins. Channels in the 5GHz band that are not subject to DFS are exempt from disruptions. When powering up an AP, the 2.4GHz radio becomes available immediately, while the 5GHz radio may take another minute due to the AP performing a DFS “Channel Availability Check”.
748 word summary
My 802.11 WLAN resources include Ekahau Blog, CWNP Blog, Eddie Forero, Devin Aiken, Revolution WiFi, Wi-Fi For Beginners Podcast, my LinkedIn profile, GitHub repositories and YouTube channel. Useful Links include my podcast, Amazon Ads and IT Blog Awards. I have written white papers on Licence-Exempt Spectrum, 802.11 Roaming Variations and DFS for 5GHz networks. Archive of blog posts from 2011 to 2020. Microsoft NPS is a RADIUS server for WiFi networks, providing authentication and authorization for users in a Windows Active Directory environment. This article looks at how to use NPS to authenticate users across multiple SSIDs, based on policy decisions. For example, in a school setting, students would only be able to authenticate using the "Student_Net" SSID, and staff would only be able to connect using the "Staff_Net" SSID.
In order to increase capacity and mitigate co-channel interference, many Enterprise wireless WLANs require the use of unique 5GHz channels. To ensure the requirements of a WLAN design are not compromised, it is important to understand and verify the impact of radar detection. This article provides useful information on Dynamic Frequency Selection (DFS) and how it can affect a wireless network. Real-time applications such as voice and video will be negatively impacted when clients transition to a new channel on a WLAN, as the process can take a while. However, non-latency-sensitive applications such as web browsing, email and streaming video files should not be affected. The actual impact on end-users depends on what they are doing.
To minimize the impact of DFS events, there are several options. If you have sufficient non-DFS channels, don't use DFS channels in your channel planning. If using static channel planning, avoid affected channels. If using auto-RF, exclude affected channels from the configuration. To tell the difference between real DFS events and false positives, look for events limited to a specific subset of channels in the 5GHz band that are consistent throughout the day; false positives tend to be spread across a wide portion of the band and vary throughout the day. Finally, work with your vendor or VAR to identify any local sources of interference causing false positives. Radar events can be monitored to look for patterns of behaviour (e.g. sites, event times, and channels). Logs from the AP, wireless controller, or management system can indicate when a radar hit is detected. False positives are more likely during times of increased user presence. Possible causes include local non-Wi-Fi equipment interference, co-channel interference from distant APs on the same channel, bad client drivers, and transient conditions due to high client densities.
When a radar signal is detected, a channel change is required which may have varying impacts on clients depending on their applications. A channel switch announcement (CSA) is sent to clients, instructing them to move to a new channel. If no CSA is received or is lost in transit, the client will have to go through its own AP discovery process. The time to re-associate with the network will vary depending on network configuration and client capabilities. Channels in the 5GHz band that are not subject to DFS (Dynamic Frequency Selection) are exempt from disruptions from local radar equipment and other sources of RF interference. The channels that are exempt vary from country to country. In the UK/EU, channels 36, 40, 44 and 48 are not subject to DFS; in the USA, channels 36 - 48 and 149 - 165 are exempt.
WLAN equipment must reliably detect radar signals to prevent false-positive detection. Radar signals are short duration pulses of RF energy with no specific framing format, making their identification challenging. When radar is detected on a channel, the Non-Occupancy Period begins (30 minutes), within which no transmissions will be made by the AP on the affected channel. The AP must continuously monitor its channel for the presence of radar signals. In some regions, an extended channel availability check of 10 minutes may be required due to weather radar restrictions on certain channels. When powering up an AP, the 2.4GHz radio becomes available immediately, while the 5GHz radio may take another minute due to the AP performing a Dynamic Frequency Selection (DFS) “Channel Availability Check” to check for radar signals. DFS is required to mitigate interference from radar networks in the 5GHz band that Wi-Fi networks use. All wireless services must adhere to technical restrictions to minimize interference, including RF transmit power levels and channel widths used. The 5GHz band has more channels available, fewer devices per channel, and lower non-Wi-Fi interference.