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Very High Density Football Arena: DFS problem during match

Hi Guys,

 

we have a VHD scenario with 200 AP in a football arena. We had some critical issue with DFS only during match. 

 

The configuration is following the VRD for VHD Scenario suggested by Aruba.

 

After the RF planning and static channel allocation, we have tested the overall RF behaviour. We have identified that some channels were subject to frequent DFS events (probably weather radar on ch 120,124). In order to avoid trouble we have modified our RF planning excluding those channels.


The RF part was running fine until a lot of people began to connect to the infrastructure. When the number of people connected increased, the cases of radar detect increased dramaticallly and we had about 40 radio in Radar Detect and, due to static allocation, moved  into AM mode so not working on 5 Ghz!

 

Before/after the match we had this rate:  

==============================

 

RATE: 1 Radar Detect/hour 
AP involved: 1 AP
Channel hitted: 112
 
During match
===========
 
RATE: 120+ Radar Detect/hours
AP involved: about 60
Channel hitted: 52-56-60-64-100-104-108-112-116-(120-124)-128-132-140
 
We are thinking that are  related to  various frames  and other craps that are generated in a High Density environment and they trigger signal pattern masks set on the DFS analysis.
 
We have also tested that during match also indoor AP are experiencing Radar Detect.
 
Do you have any suggestions? We already open a support ticket but I was wondering if there is a way to inhibit DFS working only during match. 
 
Thanks !!
 

 

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Occasional Contributor II

Re: Very High Density Football Arena: DFS problem during match

Hello stefanob,

This is a long-known Issue in the Aruba-Universe. We are experiencing the same issue in the auditoriums of our university. When the rooms are empty everything is fine, when there are students the APs change channel all the time.

The reason for this are false-positive radar-detects. When lots of clients enter the area of a wifi and start connecting they all send probe requests, due to the hidden node problem they might even send at the same time. Those frames are not recognized as 802.11 frames by the chipset and sometimes even are recognized as radar. The drivers are coded in a way that they prefer switching the channel, even if it's a false-positive, than staying on the channel and risk causing interference.

Aruba did a lot in the past to lower the amount of those detections, but this is a problem that will never be resolved totally. As the AP sends a channel-switch-announcement before actually changing the channel there should be no loss for the client.

I hope this helps you a bit, even tho the propably best solution is to accept it.

 

Kind Regards,
Hendrik

~~~
WiFi Enthusiast | ACMP
New Contributor

Re: Very High Density Football Arena: DFS problem during match

Thanks Hendrik for your complete answer!

In our scenario, due to Very High Density RF planning, we have statical
channel allocation..so Radar Detect means go to AM Mode for 10 min.

I don't know which Firmware implementation Radar Detect pattern mask t are
used during scanning period: probably huge number of probes creates
frankenstein RF packets- ) which match pattern mask as you described.

I hope that will be some countermeasures to reduce this effect.

Thanks!

Stefano
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