Re: Change wireless interface "sens" value how?

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On Sat, Feb 12, 2011 at 03:12:53PM +0000, mike cloaked wrote:
> I am trying to resolve some wireless issue with a laptop running F14,
> and I need to change the "sens" (i.e. Sensitivity) value for the
> wireless interface.
> 
> However when trying to run the following command as root it fails:
> 
> iwconfig wlan0 sens -65
> 
> gives output:
> Error for wireless request "Set Sensitivity" (8B08) :
>      SET failed on device wlan0 ; Operation not supported.
> 
> and yet the command "man iwconfig" gives for this section:
>        sens   Set the sensitivity threshold. This define how sensitive is  the
>               card  to  poor  operating conditions (low signal, interference).
>               Positive values are assumed to be the  raw  value  used  by  the
>               hardware or a percentage, negative values are assumed to be dBm.
>               Depending on the hardware  implementation,  this  parameter  may
>               control various functions.
>               On modern cards, this parameter usually control handover/roaming
>               threshold, the  lowest  signal  level  for  which  the  hardware
>               remains  associated with the current Access Point. When the sigâ
>               nal level goes below this threshold the card starts looking  for
>               a  new/better  Access  Point.  Some  cards may use the number of
>               missed beacons to trigger  this.  For  high  density  of  Access
>               Points,  a higher threshold make sure the card is always associâ
>               ated with the best AP, for low density of APs, a lower threshold
>               minimise the number of failed handoffs.
>               On  more  ancient card this parameter usually controls the defer
>               threshold, the lowest signal level for which the  hardware  conâ
>               siders the channel busy. Signal levels above this threshold make
>               the hardware  inhibits  its  own  transmission  whereas  signals
>               weaker  than this are ignored and the hardware is free to transâ
>               mit. This is usually strongly linked to the  receive  threshold,
>               the  lowest  signal level for which the hardware attempts packet
>               reception. Proper setting of these thresholds prevent  the  card
>               to  waste  time  on  background noise while still receiving weak
>               transmissions. Modern designs seems to control those  thresholds
>               automatically.
>               Example :
>                    iwconfig eth0 sens -80
>                    iwconfig eth0 sens 2
> 
> So the command should work according to the man command section above.

Heh...honestly, does that description seem clear to you?  This part
of the man page is the poster child for all that is wrong with the
wireless extensions API.

> Can someone tell me if there is some workaround for this or is this a bug?
> 
> I have already reported as https://bugzilla.redhat.com/show_bug.cgi?id=677008

Neither -- the driver (like all mac80211-based drivers) simply does
not support that setting.  mac80211-based drivers are simple, and
they don't do roaming by themselves.  Instead they rely on a userland
component (e.g. wpa_supplicant) to take care of roaming for them.

Unfortunately, I don't know of any roaming "knobs" to turn for
wpa_supplicant (or NetworkManager) -- maybe it would be nice to
have one.  Even if it were there, I suspect that control of that
"knob" would have to flow through NetworkManager if you are using it.

John
-- 
John W. Linville		The truth will set you free, but first it will
linville@xxxxxxxxxx			make you miserable. -- James A. Garfield
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