Wireless Access

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Occasional Contributor I

Channel changes

Hi

I was looking at an Airwave report that showed an AP was struggling with interference and had changed 2.4 GHz channels 179 times over a 24 hour period.  I was trying to work out what would instigate a channel change and was told that an AP would change channels if it had an intf_idx(Total) of 25 or less than its existing channel. I have absolutely no reason to doubt this, I am just not sure how the calculation is made.

 

I can see that the AP last changed channels over five hours ago  -

 

Interface :wifi1
ARM History
-----------
Time of Change Old Channel New Channel Old Power New Power Reason Result
-------------- ----------- ----------- --------- --------- ------ ------
2017-12-13 09:53:08 1 13 15 15 I Configured
2017-12-13 09:46:16 13 1 15 15 N Configured

 

And the AP has remanined on channel 13

 

From looking at the output of show ap arm rf-summary channels 1 and 5 have a far greater quality and noise floor but a small ammount of non 802.11 interference 

 

Channel Summary
---------------
channel retry phy-err mac-err noise util(Qual) cov-idx(Total) intf_idx(Total)

1 0 0 0                                       94    8/7/0/0/99 8/0(8) 44/32//0/0(76)
5 0 0 0                                       90    4/4/0/0/100 13/0(13) 99/14//0/0(113)
13 0 0 0                                     76    1/1/0/0/72 5/0(5) 11/0//0/0(11)

 

 

 

 Channel quality history:wifi1
1:Q: 99 99 99 99 99 99 99 99 99 98 98 98 98 98 98 99 99 99 99 99 99 99 99 98
:c: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
:N: 94 94 94 94 94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94 *94
:s: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
:U: 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2


5:Q: 100 100 100 100 36 99 99 100 100 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99
:c: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
:N: 90 90 90 90 90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90 *90
:s: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
:U: 0 0 0 0 0 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1


13:Q: 72 72 72 72 72 72 72 72 72 72 72 69 69 69 69 69 69 69 69 69 69 75 75 75
:c: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
:N: *76 *76 *76 *76 *76 *76 *76 *76 *76 *76 *76 *75 *75 *75 *75 *75 *75 *75 *75 *75 *75 *75 *75 *77
:s: 28 28 28 28 28 28 28 28 28 28 28 31 31 31 31 31 31 31 31 31 31 31 31 25
:U: 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 1 1 20 20 0
:R: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

 

 

I am just curious as to why this AP has not changed channels further as it would seem to me (and I am no expert) that it has better alternatives.

 

 

Thank you,

 

Jonathan

Guru Elite

Re: Channel changes

What regulatory domain is this?

 

If you are using 3 channels, it should be 1, 6, 11 typically.  If you use different channels you it could cause more interference and make interference detection/mitigation more difficult.  The edges of channels 1 and 5 overlap a little, believe it or not and that would create issues.

 

The AP might not have changed channels because the potential channel has to be a certain factor better than the existing channel.  You need to start with proper design, however, otherwise you will have issues that you cannot figure out.

******************
Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.
******************
Occasional Contributor I

Re: Channel changes

Hi and thanks for your reply.  We had to use 1,5 and 13 on the 2.4 range due to a large ammount of interference on channels 6 and 11.  This did go through design and with Aruba engineers - we all agree that it is less than ideal though :)  I was just trying to work out what the factors are on when tha IAP would change channel.  It will just help with troubleshooting in the futire.  It looked like there were better channels to use.

 

Thanks,

 

Jonathan

Guru Elite

Re: Channel changes

If you only have APs on channel 1,6,11 outside of your network, you need to match that so that energy/interference detection works correctly.  Adding in those channels will allow energy/interference detection to work correctly.  Just because you share a channel with foreign access points does not mean that there is high utilization or even interference on those channels.  You should match the channels and allow the controller to properly detect and avoid channels with real interference.  Make sure that you have "client aware" off, so that the controller will change AP channels even when users are associated.

 

I honestly don't have any good advice for you if you don't align your channels.

******************
Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.
******************
Occasional Contributor I

Re: Channel changes

Hi, we did use 1,6 and 11 but the IAPs just did not cope well with the interference.  We even had custom code written for the access points.   I was just trying to work out how  I can determin from show ap arm-summary when an IAP will chnage channel as it seems that this should have done.

Guru Elite

Re: Channel changes

If you have a c-build and it is to fix RF, you should honestly be contacting working very closely with the engineers you got the c-build from.

******************
Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.
******************
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