topic Wow thanks ! in Wireless

High Channel utilization but no RX or TX utilisation

derobbacher — Sun, 04 Jul 2021 00:11:47 GMT

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

Re: High Channel utilization but no RX or TX utilisation

dennischolmes — Thu, 19 Feb 2009 13:33:15 GMT

Channel utilization can occur from broadcast beacons as well as data transmitted and received. I be you have 1 and 2mb datarates enabled on your controllers.

Re: High Channel utilization but no RX or TX utilisation

George Stefanick — Sat, 21 Feb 2009 16:59:47 GMT

High utilization can be caused by the following:

High density of access points on channel or co- channel.

Example- excessive access points on the same channel that contribute to interference, beacons, probe responses and probe request. All of which takes up medium.

Excessive use of SSIDs

if you broadcast for example 10 SSIDS you increase your management over head as above - broadcast, probe responses, and request. I did a study and found that by adding a single SSID you could increase over head by 3-7% (w/ 1Mb frames)

Low data rates enabled (1/2 mb)

By standard your managment frames (broadcast) are transmitted on the lowest basic PHY rate. If you enable 1/2Mb frames you are allowing these to go out in a very slow manner. Disabling 1/2 rates you can improve utilization significantly. In most you can see utilzation at 40-50% with no traffic be lowered to 5%.

High TX power is always a big problem. If your APs are at 100mW. They are far extending and could be adding to other same channel APs utilization. So those beacons are going further and clients are responding to them .. smaller cells are better ...

And of course data transmissions...

I would use a protocol analyzer like airmagnet. The controllers dont always do a good job in showing utilization.

I hope you find this helpful ...

Hi :

Victor900502 — Wed, 25 May 2016 23:42:55 GMT

Hi :

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

Thanks a lot.

Hi :

Victor900502 — Wed, 25 May 2016 23:43:23 GMT

Hi :

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

Thanks a lot.

Hi :

Victor900502 — Wed, 25 May 2016 23:47:48 GMT

Hi :

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

Thanks a lot.

Hello

George Stefanick — Thu, 26 May 2016 00:20:35 GMT

Hello

under the wirlees tab on the WLC. Left hand side you will see your 2 networks. 802.11bgn and 802.11anac

click on 802.21gbn and hit network. You will see the phy rates where you can disable.

Thanks a lot.

Victor900502 — Thu, 26 May 2016 18:43:56 GMT

Thanks a lot.

For improving the channel utilization, is your suggestion turning of 1Mbps and 2Mbps of 11b or the 1/2 FEC coding like following : ?

In 11ac MCS 0, MCS 1 and MCS 3 are 1/2 rate codes

In 11n this is

MCS 0, 8, 16

MCS 1, 9, 17

MCS 3, 11, 19

It's my advice if your deisgn

George Stefanick — Thu, 26 May 2016 18:47:24 GMT

It's my advice if your deisgn can support higher rates you should disabled everything below 12. Don't mess with other rates. Again, if your deisgn supports it.

Your 12 means "12Mbps", am I

Victor900502 — Thu, 26 May 2016 18:51:41 GMT

Your 12 means "12Mbps", am I right ?

You are not talking about the FEC rate (1/2, 3/4 etc...), right?

Yup ! 12 PHY. Don't mess with

George Stefanick — Thu, 26 May 2016 18:54:29 GMT

Yup ! 12 PHY. Don't mess with anything higher ..

I've had a lot of success with 12 supported and 24 mandatory. Rest supported .. Keep in mind you need to insure your RF will support it .. If it doesn't you will create issues for yourself ..

Thanks a lot! Got it!

Victor900502 — Thu, 26 May 2016 19:03:41 GMT

Thanks a lot!

Got it!

If you found this helpful

George Stefanick — Thu, 26 May 2016 19:06:45 GMT

If you found this helpful please consider rating helpful post ! Thanks !

Wow thanks !

George Stefanick — Thu, 26 May 2016 19:13:13 GMT

Wow thanks !

Hi, I see 50 clients

TM13 — Mon, 30 May 2016 07:46:25 GMT

Hi, I see 50 clients connected to 1 AP, sounds ridiculous i know, but when i check Channel Utilization = 40%, AP uplink is around 10Mb/5Mb and our computers couldn't download 10MB file from our file server, is that related with this? how to measure and check it? we have PI and WLC but still couldn't find related stuff

Check the channel utilization

Scott Fella — Mon, 30 May 2016 08:27:38 GMT

Check the channel utilization while downloading the file, but look at it from the controller CLI (show ap auto-rf 802.11a <ap name>) you can also look at the 802.11b. This command will show you the utilization real time and you will see how downloading a file can also increase the utilization. This is why you need to determine how many clients can connect and still have good user experience. The long time recommend number is 25, but again, it will depend on the clients and their activity on the wireless. I have found the 30 is a safe number before the experience starts to fall fast.

-Scott

*** Please rate helpful posts ***

Hi,George:

Victor900502 — Wed, 01 Jun 2016 16:44:34 GMT

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.

That is typical as channel

Scott Fella — Wed, 01 Jun 2016 17:02:40 GMT

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

*** Please rate helpful posts ***

So, the beacons and probe

Victor900502 — Wed, 01 Jun 2016 17:06:12 GMT

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%.

Hey Victor,

dennischolmes — Wed, 01 Jun 2016 17:18:27 GMT

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.