What is DFS, and Why Does It Matter?

Dynamic Frequency Selection (DFS) is FCC-required functionality when operating a WLAN on UNII-2a and UNII-2c channels. Compliance to DFS rules are obligatory, and manufacturers only implement this functionality correctly part of the time. Whether you realize it or not, this put your organization at risk. DFS implementations are based on specific access point hardware and firmware and differ widely even among same-vendor APs. Testing to date has shown a wide variety of out-of-compliance scenarios among all vendors. What is required to happen when a DFS (RADAR) event is observed in the spectrum? The AP must move to another channel, in a very specific way. To do otherwise either breaks the 802.11 standard, the FCC rules (the law), Wi-Fi client device/application behavior, or all of them. Observe below a DFS event causing an AP to move away from its native operating channel.

What Does Divergent Offer?

Divergent’s DFS Compliance Consulting service helps you understand:

1. whether your system meets FCC requirements,
2. if/how/when your system reacts to DFS events,
3. how your access points’ behavior impacts client devices and applications, and
4. whether your vendor’s marketing around its DFS feature set is truthful or just plain hype, give our service a try.

Proof of system behavior is saved, documented, and provided to our customers in a detailed report that can be presented to the equipment manufacturer.

How Is This Service Delivered?

Divergent’s DFS Compliance Consulting service incorporates state-of-the-art RADAR signature generation, across all DFS channels and all required FCC RADAR signatures. Our DFS validation processes have been developed in conjunction with the creation of the RADAR signature generation equipment so that WLAN systems can be fully validated. We can observe how access points react to DFS events in a live environment. Questions that should be asked by customers include:

1. When a DFS event is seen, does my AP move to a new channel in compliance with FCC rules?
   
   • To what channel does my AP move?
   • Does it choose the same channel each time?
2. When my AP has moved to a new channel, does it move back to its original channel?
   
   • If so, how long did it take?
   • If not, where did it go?
3. How long does it take my AP to move to the new channel? Do all of my APs take the same length of time?
4. Does my AP issue action frames and channel switch announcements (CSAs) according to the FCC and IEEE rules?
5. When my AP moves to a new channel, do the client devices follow the AP like they are supposed to?
6. When my AP moves to a new channel, does it maintain its channel width?
7. If there are “specialty” DFS features advertised by WLAN vendors, do they work? (e.g. Zero-wait DFS, Flex DFS, etc)

This service can be delivered by testing your APs in a lab or by visiting your site with the required diagnostic hardware and software. If you wish to know only how APs react to DFS events, then the testing can be done in a lab. If you wish to understand how DFS events impact your enterprise (other APs and client devices/applications), then the testing must be done on-site.

What Will This Service Deliver?

If you want to understand whether your system should be using DFS channels (52 – 144) in order to obtain the maximum possible capacity without client service disruption, this service is for you. An additional benefit of this testing is the ability to vet a WLAN infrastructure vendor’s automatic channel and power (AutoRF) algorithm. The equipment and processes used by Divergent can validate:

1. whether the AutoRF algorithm is working as advertised by the WLAN infrastructure vendor,
2. whether the AutoRF algorithm working according to design best practices, and
3. what impact any poor algorithmic decisions are having on client devices and applications.

The interplay between the DFS algorithm and AutoRF algorithm can also be observed and documented, showing the customer whether or not they should be using static channels within their network.

Give Divergent’s new DFS Compliance Consulting service a try, and understand if/how your system reacts to DFS events, whether your system is in compliance with FCC rules, and how DFS events impact your users’ devices and applications. If you are interested, please contact us for pricing.