--- title: What Is DFS in Wi-Fi? DFS Channels Explained for 5GHz description: What DFS means in Wi-Fi, how many 5GHz channels you gain in Australia (9 non-DFS, 21 in total), when to avoid DFS for voice and how to plan around radar. image: https://blog.iptel.com.au/hubfs/Blogs/Reduce%20Wi-Fi%20Congestion%20-%20DFS/Reduce%20Wi-Fi%20Congestion%20with%20DFS%20(Instagram).gif --- [![IPTellogo-byline-2020-dark-v2-pnd-optimised-500 (1)](https://blog.iptel.com.au/hs-fs/hubfs/IPTellogo-byline-2020-dark-v2-pnd-optimised-500%20(1).png?width=200&height=59&name=IPTellogo-byline-2020-dark-v2-pnd-optimised-500%20(1).png "IPTellogo-byline-2020-dark-v2-pnd-optimised-500 (1)")](https://iptel.com.au) - [Home](https://iptel.com.au/) - [Solutions](https://iptel.com.au/solutions) Technologies - [Cisco Access Manager](https://iptel.com.au/technologies/cisco-access-manager) - [Cisco Catalyst Centre](https://iptel.com.au/technologies/cisco-catalyst-center) - [Cisco Meraki](https://iptel.com.au/technologies/cisco-meraki) - [Cisco SDA Fabric](https://iptel.com.au/technologies/cisco-sda-fabric) - 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There are no suggestions because the search field is empty. ## Reduce Wi-Fi Congestion with DFS June 19, 2025 Wi-Fi can be crippled by too many devices competing for airtime, creating a slower experience for everyone. In this blog, we'll explain how Dynamic Frequency Selection (DFS) channels can more than double your 5GHz channels, when to avoid them, and how to plan around nearby radar. ![Reducing Wi-Fi congestion with DFS channels](https://blog.iptel.com.au/hs-fs/hubfs/Blogs/Reduce%20Wi-Fi%20Congestion%20-%20DFS/Reduce%20Wi-Fi%20Congestion%20with%20DFS-still.jpg?width=1440&height=810&name=Reduce%20Wi-Fi%20Congestion%20with%20DFS-still.jpg) --- ## DFS Channels: What Are They and Why Use Them? [![Wi-Fi and the Problem With RADAR (DFS)](https://blog.iptel.com.au/hs-fs/hubfs/Blogs/Wi-Fi%20and%20the%20problem%20with%20RADAR/Wi-Fi%20and%20the%20problem%20with%20RADAR%20(Instagram).gif?width=173&height=173&name=Wi-Fi%20and%20the%20problem%20with%20RADAR%20(Instagram).gif)](https://blog.iptel.com.au/wifi-and-the-problem-with-radar)Dynamic Frequency Selection (DFS) is the mechanism that stops Wi-Fi interfering with radar. Some 5GHz channels share spectrum with radar, so Wi-Fi networks can take those channels out of service dynamically when radar is detected. Used well, DFS channels give you more channels, less contention and more throughput for each user. One way to reduce the number of devices competing for airtime is to increase the number of channels in use. DFS channels can be part of your 5GHz channel plan, and more channel diversity means less contention. Improper use of DFS channels can cause unexpected dropouts. Implemented correctly, they can more than double the number of channels available. For the background on how radar detection works, see [Wi-Fi and the Problem With RADAR](https://blog.iptel.com.au/wifi-and-the-problem-with-radar). Related reading - [Wi-Fi and the Problem With RADAR (DFS)](https://blog.iptel.com.au/wifi-and-the-problem-with-radar) - [Wi-Fi Terminology](https://blog.iptel.com.au/wi-fi-terminology) --- ## Channel Count: How Many 5GHz Channels Do You Have? In Australia there are nine 5GHz Wi-Fi channels that don't need DFS: 36–48 and 149–165. Once your deployment extends beyond nine access points, you need to reuse channels, which means more devices competing for airtime on each channel. Channel bonding cuts that number down quickly. Bond channels to 40MHz and those nine become four (channel 165 is left over). Go to 80MHz and you're down to two. Here's what radar events look like in practice. ![Example of DFS radar events on 5GHz Wi-Fi channels](https://blog.iptel.com.au/hs-fs/hubfs/Imported_Blog_Media/RadarEvents.png?width=700&height=83&name=RadarEvents.png) That's why the channel plan matters so much on larger sites, and why it's a core part of any [Wi-Fi predictive design](https://blog.iptel.com.au/wifi-predictive-design-wifi-heatmaps). Related reading - [Wi-Fi Predictive Design: Wi-Fi Heatmaps](https://blog.iptel.com.au/wifi-predictive-design-wifi-heatmaps) - [Cisco RX-SOP: How to Turn Down the Noise](https://blog.iptel.com.au/cisco-rx-sop-how-to-turn-down-the-noise) --- ## Channel Utilisation: Why Is Airtime the Limit? ![Flowchart of devices competing for Wi-Fi airtime](https://blog.iptel.com.au/hs-fs/hubfs/Imported_Blog_Media/FlowChart.png?width=173&height=152&name=FlowChart.png)The one thing you can't adjust in Wi-Fi is how much airtime (channel utilisation) is available. Unfortunately, you're at the mercy of the laws of physics. What you can change is how many devices compete for that airtime, by spreading your access points across more channels. Generally, depending on the application, you want to keep airtime utilisation below 30–40%. Once you get up around 70%, the Wi-Fi becomes unusable. Put all your access points on one channel and every device is competing with every other device for airtime. Give each AP its own channel and each device competes only with the other devices associated to the same AP. Transmit power plays a part too, because it sets how far each AP's channel reaches. Our posts on [EIRP vs transmit power](https://blog.iptel.com.au/what-is-eirp-eirp-vs-transmit-power) and [access point power caps](https://blog.iptel.com.au/access-point-power-caps) cover the detail. Related reading - [What Is EIRP: EIRP vs Transmit Power](https://blog.iptel.com.au/what-is-eirp-eirp-vs-transmit-power) - [RF Tuning: Access Point Power Caps](https://blog.iptel.com.au/access-point-power-caps) --- ## Voice Over Wi-Fi: When Should You Avoid DFS? DFS channels aren't recommended where voice over Wi-Fi is critical. Client devices need extra time to scan for access points on DFS channels, which can result in dropped packets during a call. If voice over Wi-Fi isn't a critical service, though, DFS channels can add an extra twelve channels to an Australian indoor WLAN. The other catch is what happens when radar turns up. When an access point detects a radar event that its transmissions could interfere with, it changes channel immediately, and client devices often aren't warned in time, which causes unexpected dropouts. At this point, you're probably thinking "That sounds like a nightmare!" If voice is a priority on your network, our [Wi-Fi Phone Dropouts](https://blog.iptel.com.au/wifi-phone-dropouts) post covers what else to check. Related reading - [Wi-Fi Phone Dropouts](https://blog.iptel.com.au/wifi-phone-dropouts) - [Wi-Fi Troubleshooting Part 1: How to Review a Wi-Fi Installation](https://blog.iptel.com.au/how-to-review-a-wifi-installation-part-1) --- ## Radar Planning: How Do You Work Around Radar? [![Introduction to Cisco AI-Enhanced RRM](https://blog.iptel.com.au/hs-fs/hubfs/Blogs/Cisco%20AI-RRM/Cisco%20Ai-RRM%20(Instagram).gif?width=173&height=173&name=Cisco%20Ai-RRM%20(Instagram).gif)](https://blog.iptel.com.au/cisco-ai-enhanced-rrm)Hang in there, the payoff is coming. Any radar near your WLAN will use a consistent part of the spectrum, and may knock out one or two Wi-Fi channels. Plan around those and you may still have ten or eleven of the twelve extra channels, which means more airtime and more throughput for each device. The chart below shows the indoor 5GHz channels, including the DFS channels. ![Indoor 5GHz Wi-Fi channels in Australia, including DFS channels](https://blog.iptel.com.au/hs-fs/hubfs/Imported_Blog_Media/Indoor5GHzChannels1.png?width=700&height=152&name=Indoor5GHzChannels1.png) So how do you plan around nearby radar? The simplest answer is: you don't — at least not initially. Enabling all the DFS channels increases your channel count to 21, possibly including some that overlap with a nearby radar and so are unusable. Cisco Catalyst Center (which replaces Prime Infrastructure) can be configured to alert you any time a DFS event occurs. Getting DFS events that are kicking APs off channel 112? Disable channel 112. It's as simple as that. If you get lucky, you may see no DFS events at all, leaving you with every channel to play with. Cisco's [AI-Enhanced RRM](https://blog.iptel.com.au/cisco-ai-enhanced-rrm) then manages channel assignment across the channels you've allowed. Related reading - [Introduction to Cisco AI-Enhanced RRM](https://blog.iptel.com.au/cisco-ai-enhanced-rrm) - [Wi-Fi Surveys](https://blog.iptel.com.au/wi-fi-surveys) --- ### How Many Access Points Do You Need? More channels only pay off when your access point count matches the space and the people in it. Our free [Wi-Fi Access Point Calculator](https://iptel.com.au/resources/wifi-access-point-estimator?utm_source=blog&utm_medium=cta&utm_campaign=dfs-congestion) gives you a quick estimate for your building: enter each floor’s area and how many people use it, and it works out the access points, PoE budget and switch ports you’ll need, then emails you a full report. ## Dynamic Frequency Selection: FAQs ### What Are DFS Channels in Wi-Fi? DFS channels are 5GHz Wi-Fi channels that share spectrum with radar. Access points using them listen for radar and move off the channel if radar is detected. In Australia, they add twelve channels to the nine non-DFS channels. ### Are DFS Channels Safe to Use? Yes, for most networks. The risk is unexpected dropouts when an AP leaves a channel after detecting radar. Enable them, monitor for DFS events in Catalyst Center, and disable any channel that a nearby radar keeps knocking out. ### Should I Use DFS Channels for Voice Over Wi-Fi? Not where voice is critical. Client devices take longer to scan for APs on DFS channels, which can drop packets during a call. If voice isn't a critical service, the extra channels are usually worth it. ### How Many 5GHz Channels Can I Use Indoors in Australia? Nine 5GHz channels in Australia don't need DFS, and DFS adds twelve more, for 21 channels in total at 20MHz. Channel bonding to 40MHz or 80MHz reduces that count, so plan channel width and DFS use together. --- ## Dynamic Frequency Selection: Summary Don't be afraid to use DFS channels in your WLAN! Ignore them and you're ignoring over half of the potential channels you have available. Enable them, watch for DFS events, disable any channel a nearby radar keeps hitting, and think twice where voice over Wi-Fi is critical. You'll get more channel diversity, less contention and more throughput for every user. ### Need Help With DFS and Your Wi-Fi Channel Plan? Our [Wi-Fi survey and design team](https://iptel.com.au/services/wi-fi-surveys) can help you implement DFS channels and configure the event logging that reduces your risk of unexpected dropouts. If that's useful, [get in touch with the IPTel team](https://iptel.com.au/contact-us) or email [sales@iptel.com.au](mailto:sales@iptel.com.au). #### Related Articles ###### [Wi-Fi and The Problem With RADAR (DFS)](https://blog.iptel.com.au/wifi-and-the-problem-with-radar) July 21, 2025 ###### [What is EIRP: EIRP vs Transmit Power](https://blog.iptel.com.au/what-is-eirp-eirp-vs-transmit-power) May 23, 2025 ###### [Effect of Trees on Wi-Fi](https://blog.iptel.com.au/effect-of-trees-on-wi-fi) Dec 9, 2025 Free tool ### How Many Wi-Fi Access Points Do You Need? Work out APs, PoE and switch ports floor by floor, using the same survey grades our Cisco wireless engineers design to. Takes under a minute. [Try the AP Estimator →](https://iptel.com.au/resources/wifi-access-point-estimator?utm_source=blog&utm_medium=cta&utm_campaign=ap-estimator) ```json { "@context" : "https://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "IPTel Solutions", "url" : "https://blog.iptel.com.au/author/iptel-solutions" }, "dateModified" : "2026-10-11T05:24:24.667Z", "datePublished" : "2025-06-19T05:23:38.000Z", "headline" : "What Is DFS in Wi-Fi? 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