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woland
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Channel Selection vs. Channel Width

Mon Jun 13, 2022 6:05 pm

Hi,
Sorry for the basic question, but I don´t know if I got it right:
how does the Channel definition work on an interface and on CapsMan. Could someone please explain?
I did not find much documentation on this, maybe a pointer to some posts would suffice.

If I would like to use an 80MHz band, what should I configure? Let´s say I pick a channel with a center freq of 5210MHz and I configure this:
 channel-width=80mhz-eeeeCeee 
versus
channel-width=80mhz-eeeeeeCe
Should I have defined in both cases:
frequency=5210 
Or should I configure the frequency using 3x10MHz or 1x10MHZ offset?
I suppose C must be always the center and this is the frequency I am setting up with the "frequency=" setting.

And what about the 20/40/80/160mhz-XXXXXXXX setting, which chooses the control channel automatically?

What about CapsMan? It has:
channel.control-channel-width (40mhz-turbo | 20mhz | 10mhz | 5mhz; Default: )
channel.extension-channel (Ce | Ceee | eC | eCee | eeCe | eeeC | xx | xxxx | disabled; Default: )
channel.frequency (integer [0..4294967295]; Default: )

Like this?:
channel.control-channel-width 40mhz-turbo ; channel.extension-channel eCee; channel.frequency 5170
Then it goes from 5160 -5200 ?

There is no support for 80MHz on CapsMan?

Thanks!

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erlinden
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Re: Channel Selection vs. Channel Width

Mon Jun 13, 2022 6:18 pm

C stands for Control and is 20MHz width. And every e is also 20MHz width.
So, if you choose i.e. channel 5160 (which is 36) and Ceee you configure channels 5160 to 5240 (which is 80MHz width) where channel 5160 is control channel.
And, if you choose i.e. channel 5280 (which is 56) and eC you configure channels 5260 and 5280 (which is 40MHz width) where channel 5280 is control channel.

In the picture below you can see which channels are allowed:

Image
 
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woland
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Re: Channel Selection vs. Channel Width

Mon Jun 13, 2022 7:24 pm

C stands for Control and is 20MHz width. And every e is also 20MHz width.
So, if you choose i.e. channel 5160 (which is 36) and Ceee you configure channels 5160 to 5240 (which is 80MHz width) where channel 5160 is control channel.
And, if you choose i.e. channel 5280 (which is 56) and eC you configure channels 5260 and 5280 (which is 40MHz width) where channel 5280 is control channel.
Hi,

thanks! C is control that´s clear, but I think the "e" can´t stand for 20MHz, I think it must stand for 10MHz, as for 40M there are 3x "e" and for 80M there are 7x "e".

Apologies, I might not have described clearly enough my questions, but they really are for Wireless AP Interface:
Do you always define the C with the frequency parameter? If so what frequency should be used with the automatic control channel selection "XX" or "XXXX" or "XXXXXXXX" ?

About Capsman:
Why is there an additional parameter called "channel.control-channel-width" additionally to "channel.extension-channel" if by "Ceee" you already have set 4x10MHz?

BR

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mkx
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Re: Channel Selection vs. Channel Width

Mon Jun 13, 2022 11:34 pm

thanks! C is control that´s clear, but I think the "e" can´t stand for 20MHz, I think it must stand for 10MHz, as for 40M there are 3x "e" and for 80M there are 7x "e".

In ROS, all channels (specially on ac hardware) are exactly 20MHz wide ... either C, e or X. When seeing 8 letters (e.g. eeeCeeee), it's about 160MHz channel, supported by certain devices.

Some (mostly legacy) devices indeed support other channel widths. But those channel widths will not work with all wireless clients.

If you want to leave channel layout selection to AP's automagic (by setting it to X-es), then you may leave frequency selection to AP's magic as well. Because if you set control channel frequency manually and let AP decide about the rest, you might end up with AP selecting setup which is not entirely conformant to standards and some clients might not be able to connect.
 
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woland
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Re: Channel Selection vs. Channel Width

Tue Jun 14, 2022 10:56 am

thanks! C is control that´s clear, but I think the "e" can´t stand for 20MHz, I think it must stand for 10MHz, as for 40M there are 3x "e" and for 80M there are 7x "e".
In ROS, all channels (specially on ac hardware) are exactly 20MHz wide ... either C, e or X. When seeing 8 letters (e.g. eeeCeeee), it's about 160MHz channel, supported by certain devices.
Oh I see, my mistake! Thanks for explaining mkx and sorry erlinden!
However MT could have done a better job in the docs...
Some (mostly legacy) devices indeed support other channel widths. But those channel widths will not work with all wireless clients.

If you want to leave channel layout selection to AP's automagic (by setting it to X-es), then you may leave frequency selection to AP's magic as well. Because if you set control channel frequency manually and let AP decide about the rest, you might end up with AP selecting setup which is not entirely conformant to standards and some clients might not be able to connect.
So as I get it: channel.control-channel-width should not be changed at all?
Also I will leave the x-es alone.
So setting channel.extension-channel + channel.frequency shlould be enough on Capsman. By setting channel.extension-channel to disabled, I get 20MHz bandwidth.

I appreciate it! Happy to have this sorted out, this was a mess in my head since I did my first MT config! :)

BR
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gkowalchuk
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Re: Channel Selection vs. Channel Width

Sat Dec 10, 2022 9:16 pm

Thanks for your POST, which cleared up my problem!

My wAP_AC_BE PTP BRIDGE CPE used default 20/40/80n Ceee while the host router was 20/40/80n eeeC
Experienced erratic latency and dropped PINGs which had me confused until I read your POST.
Matched the wAP 20/40/80n eeeC with host router and everything cleared up.

Thanks again
:D

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