mapping "iw list" to ht_capab (to get past the 130 Mbps cap)

[Christian Lamparter]

On Saturday 28 July 2012 13:40:56 Wojtek Swiatek wrote:
> I have installed a  TP-LINK TL-WN821ND card on my Debian squeeze
> (3.2.0-3-686-pae) and it has been recognized out of the box. I use it
> in an AP mode with hostapd. The driver used is ath9k.
Isn't it ath9k_htc?

> It basically works except that the negotiated speed is always 130 Mbps
> (across several laptops). The /etc/hostapd/hostapd.conf file I use is:
> 
> interface=wlan3
> driver=nl80211
> ssid=MYSSID
> channel=7
> hw_mode=g
> wme_enabled=1
> ieee80211n=1
> ht_capab=[HT40+][SHORT-GI-40][DSSS_CCK-40]
This is just a hunch, but:

Your problem could be HT40+ with channel 7.
Have you a different channel or HT40-?
(If debian enabled MAC80211_DEBUG, then you
can take a look at the map in 
/sys/kernel/debug/ieee80211/phyX/ht40allow_map.
It tells you which HT40+/- mode is supported
at which frequency/channel)

However, don't get your hopes up, because
"According to 802.11-2012, APs and routers
must default to 20 MHz bandwidth mode in
the 2.4 GHz band. They may switch to 40 MHz
bandwidth mode only after satisfying
multiple criteria, including no "fat channel"
intolerant bit set and no interfering APs.

In addition, to meet spec, APs are not
allowed to have a "40 MHz only" mode 
in the 2.4 GHz band.

Note that some vendors, Apple and Intel most
notably, too matters into their own hands.
Intel initially initially didn't allow HT40
in the 2.4 GHz band, but has since relented.
Intel adapters now allow 40 MHz mode in
2.4 GHz to be set, but ship default set to
20 MHz only mode."
 
So, if you have just one "bad apple" in the
vicinity you can forget about it... Of course,
you can force hostapd to enable HT40, but
then you'll sacrifice interoperability.

your choice.

Regards,
	Chr