On 16 August 2014 01:42, Avery Pennarun <apenwarr@xxxxxxxxx> wrote: > Hi all, > > I'm pretty confused about how to select the "primary" channel when > using wide channels with 802.11ac (and also 802.11n, really). My > hostapd contains a section like this: > > hw_mode=a > channel=149 > country_code=US > ieee80211d=1 > ieee80211h=1 > ieee80211n=1 > ieee80211ac=1 > ht_capab=[HT20][HT40+][RX-STBC1] There is no such thing as [HT20] in ht_capab in hostapd. You can just remove it. It has no effect. > vht_capab=[MAX-A-MPDU-LEN-EXP4] > vht_oper_chwidth=1 > vht_oper_centr_freq_seg0_idx=155 > > If I understand correctly, this will have the following results: > - at 20 MHz, it will use channel 149 > - at 40 MHz, it will use channels 149+153 (HT40+) > - at 80 MHz, it will use channels 149+153+157+161 (centr_freq_seg0_idx) Basically, yes. > > This is fine when I'm the only AP around. But let's imagine I'm in a > crowded apartment building with lots of APs, and various clients > support only 20 MHz channel width (increasingly rare), or 20/40, or > 20/40/80. In such a situation, we'd like to spread around the APs so > that clients that can only do 20 or 40 don't always fall back to > channel 149 or 149+153; otherwise we're just wasting tons of empty > space on channels 157 and 161. > > The obvious way to do this would be to try a configuration like this (HT40-): > > channel=153 > ht_capab=[HT20][HT40-][RX-STBC1] > vht_capab=[MAX-A-MPDU-LEN-EXP4] > vht_oper_chwidth=1 > vht_oper_centr_freq_seg0_idx=155 > > or perhaps this (40 Mhz uses upper half instead of lower half): > > channel=157 > ht_capab=[HT20][HT40+][RX-STBC1] > vht_capab=[MAX-A-MPDU-LEN-EXP4] > vht_oper_chwidth=1 > vht_oper_centr_freq_seg0_idx=155 > > But when I try to do this, hostapd seems to abort and claim it can't > register to use the channels. Am I doing something wrong? Is it > hostapd version related? All following configs work for me: http://pastebin.com/w1LKTDGn http://pastebin.com/McquAcCf http://pastebin.com/1RNWHAAS http://pastebin.com/kDd2RybJ My hostapd is at 6d00ab04302df257cb3092b2b31b4eac42e77569. > > Also, hostapd contains code to swap the primary/secondary 20 MHz > channels in the 40 MHz channel, based on what other APs are around. > If I read correctly, it seems to want to use the same primary channel > as everyone else. Wouldn't it be better to equailze things to try to > get about half the APs using each sub channel? That would break 20/40 coex, wouldn't it? Michał -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
