RTS/CTS not fully disabled?

Jouni Malinen j at w1.fi
Sat May 26 22:09:41 EDT 2007

On Tue, May 22, 2007 at 12:31:14PM +0200, ahuguet at cttc.es wrote:

> > If I remember correctly, there
> > were some changes to rate control algorithm in the firmware and it may
> > have involved use of RTS/CTS in some cases. If the firmware versions are
> > different, I would assume this would be reason for the behavior you are
> > seeing.
> >From what I've been able to read in the mailing list, it indeed seems to
> point to a rate control issue.
> It seems that, if the card fails for the 3rd time (IIRC) to send a packet
> (that is, doesn't receive an ACK for said packet) it tries to adapt its
> transmission rate, to the value immediately lower.

That is the default behavior in STA firmware. I looked at bit more
details on documentation and this behavior should actually be
configurable. I would assume that the cards you are using are setting
CNFFALLBACKCTRL (RID FCB5) to the default value 0x047C which is
requesting rate control algorithm to start using RTS/CTS on third retry.
I would suggest testing a value of 0x007C in that RID to prevent this
from happening.

You should be able to read the current value with 'hostap_rid wlan0 get
fcb5' and set the new value with 'hostap_rid wlan0 set fcb5 7c 00' (the
value is little endian, so swapped bytes here). Please let me know
whether this helps in your test setup.

Jouni Malinen                                            PGP id EFC895FA

More information about the HostAP mailing list