802.11a support

Jouni Malinen j
Mon Sep 1 09:28:47 PDT 2008

On Fri, Aug 29, 2008 at 03:43:52PM -0500, Nils Bagge wrote:

> I am working with the ath9k device driver (consequently using
> driver_nl80211, I am not yet sure of all the terminology), and have
> recently been able to get hostapd to work nicely in 802.11g mode. I just
> tried putting the NIC in 802.11a mode and encountered an error, which
> eventually led me to the following code:
> hw_features.c: hostapd_get_hw_features(), ~ line 81: 
> feature->channels[j].flag &= ~HOSTAPD_CHAN_W_SCAN
> Being unfamiliar with this code, it is not yet entirely clear to me the
> purpose of HOSTAPD_CHAN_W_SCAN, or furthermore any of the channel flags
> themselves CHAN_W_XXXX flags. 

In practice, this flag is to indicate which channels can be used.

> Regardless, that flag (HOSTAPD_CHAN_W_SCAN) needs to be set in order for
> the desired channel to be configured. I saw a TODO in the code about
> adding regulatory domain lookup. Does the setting of this flag depend on
> regulatory domain? After seeing this code, it would seem like 802.11a
> support in hostapd has never worked! I just turned the bit on, and was
> able to start moving data in 11a.

Yes, that is indeed related to the TODO comment about regulatory domain
information. The open source version of hostapd does not yet have proper
data available about allowed channels and related regulatory limitation.
Because of this, only the safest channels (most likely to be available
everywhere) are enabled. 5 GHz band has much more variance based on the
location, so 802.11a channel are currently disabled. Once proper
regulatory data is available, hostapd will start marking these channels
enabled based on the location of the device.

Jouni Malinen                                            PGP id EFC895FA

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