High Channel utilization but no RX or TX utilisation

[derobbacher]

Hello WLAN experts,

looking at our Top-Ten Access Points statistics, I often see APs with the following Load statistics:

RX Utilisation : 0

TX Utilisation : 0

Channel Utilisation : 18

Do You have any explanation for the high Channel utilisation ?

What is causing this ?

Detailed traffic statistics contain the following figures:

TX Frame count: 380606

RX Frame Count: 77222980

FCS Error Count: 3281837

TX Failed count: 157979

Retry Count: 145735

Noise vs. Channel: -98

Interference: -90

Thank You in advance

[George Stefanick]

Wow thanks ! 

[Victor900502]

Hi,George:

Another thing is very strange,  from the report I found the Channel Utilization are much higher than the sum of Rx and Tx. In both band for all of the AP. 

From my understanding, Rx+Tx reflecting the traffic on the AP. So , all of the others are interference ? You can refer to the attached picture.

Thanks.

[Scott Fella]

That is typical as channel utilization has various number of things in the calculation.  Traffic, co-channel, broadcast, beacons all affect the channel utilization.

-Scott 

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[Victor900502]

So, the beacons and probe(from own AP) are not parts of Rx /Tx ?

In my reports, Rx and Tx always very low (less than 5%) but channel utilization sometimes are higher like 70%.

[dennischolmes]

Hey Victor,

Remember that high channel utilization can come from a lot of different places. Client devices, APs, and even a high level of the noise floor (causing excessive retries) can be the source of the issue. If you have a copy of Airmagnet WiFi Analyzer Pro you can dig deep into what is happening. Depending solely on the WLC tools is difficult at best to determine the issue. Airmagnet looks at the basic stuff and then allows you to dig down all the way to the packet level if necessary.

[George Stefanick]

Hey look who is back! The old thread kicked started Dennis! LOL Hi Dennis...

Vic, Think of it this way. I just validated this with my Cisco guy. Utilization it the sum of all WiFi and non WiFI traffic, say 70%. The TX/RX is specific to the ap radio you are looking at. That is why you see the difference. 

Does that help ?

[Victor900502]

thanks George.

I understood that, I have checked non-wifi interference too via clean air. The non-wifi percentage is very low,around 2%.

So , most of contributor should be the co-channel interference . But what I cannot understand is the similar things happening on 5GHz band. I believe we should have few co-channel interference in 5GHz.

Again, are the beacon and probe considered as Rx or Tx ?

[George Stefanick]

Are you bonding on 5 Ghz and what channels are you using UNII1,2,2E and 3 ?

[Victor900502]

No bonding.

We are using all the channels, UNII 1, 2, 2E and 3.   DCA enabled

[Scott Fella]

That is also what we see all around the world. The channel utilization is what we look at to determine end user experience and the ability to make changes to lower overall channel utilization throughout the day.  Every site is different and we treat them differently because of what the users are doing on the wireless.

The best way is to be onsite and test for yourself.  Everyone's experience is different and the number of clients on a given AP or radio and utilization will vary.  This is how you can determine what is the threshold for your environment.

-Scott

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[Victor900502]

Hi :

Do you know how can I disable 1/2 rate via PI or WLC ?

Thanks a lot.