basic rate set / response frame rate

[Johannes Berg <johannes@sipsolutions.net>]

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Hi,

How does hardware currently handle the control response (ACK/CTS) frame
rate? In 802.11 clause 9.6 talks about this, and we implement basic rate
handling in mac80211 to calculate the control response duration, but we
never tell drivers what bitrate to transmit control response frames at.

I suspect this is broken in all drivers (except maybe iwlwifi which
probably does it all in firmware.) The problem then is that if the AP
has basic rates higher than your firmware/hardware default, the control
response takes too long and the NAV isn't updated correctly in other
STAs.

How should we fix this?

The most straight-forward way would be to include a map of rate -> basic
rate into ieee80211_bss_conf, but that isn't easy because the size of
the map isn't known.

Another way would be to just give the driver the basic rate set, but
that means it has to calculate the mapping itself, subject to all the
rules in 802.11 clause 9.6.

Therefore, I prefer the former way, or giving the driver a function to
call for each rate on bss_info_changed to calculate the mapping.

johannes

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