Channel in HT40 and VHT80

Jouni Malinen j at w1.fi
Mon Jun 16 17:14:39 EDT 2014


On Fri, Jun 13, 2014 at 10:00:48AM +0200, Vu Hai NGUYEN wrote:
> Can someone explain to me that why hostapd use 802.11n Annex J to set up channel like this way:
> 	HT40-		                                           HT40+
> 	40,48,56,64,104,112,..                               36,44,52,60,100,108,...
> It is not the same information as debugfs file "ht40allow_map". For example, If I set channel for a monitor 
> interface using "iw", I can have:
> channel 44 (5220 MHz), width: 40 MHz, center1: 5210 MHz 
> channel 44 (5220 MHz), width: 40 MHz, center1: 5230 MHz
> But if I set up an AP using hostapd I can only have the 2nd one as channel 44 allowed only in HT40+.

hostapd uses the HT40 channels as defined in the standard. The
regulatory rules may allow other options within the same frequency
ranges, but the channels defined in IEEE 802.11 are the ones that get
deployed in practice.

> I also have another questions: I can set up channel from 36 to 128 for 802.11ac mode using ath10k and
> hostapd. But both channels 132 and 136 is automatically converted to another channel (100,116 or whatever..)
> Is this normal???. And channel 140 is only enabled in HT20 (not HT40 and VHT80) for Atheros card?
> 

I'm not completely sure I understood the exact question, but VHT has a
bit different way of configuring channels. Regulatory rules have affect
on how different channel bandwidths can be used especially near either
end of each operating class.

-- 
Jouni Malinen                                            PGP id EFC895FA


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