Re: CVS-2-2 NMApplet empty bar explained

[Dan Williams <dcbw redhat com>]

On Fri, 2005-02-04 at 10:53 -0500, Sven wrote:
> iwlib.c in WEXT says (in the example) 
>    * 2) value is -54dBm. noise floor of the radio is -104dBm.
>    *    qual->value = -54 = 202 ; range->max_qual.value = -104 = 152
> i'm confused. why is the max value the noise floor??? in Atheros chips,
> given the value in dBm comes from RSSI, should max_qual.value not be
> MAX_RSSI (converted into dBm)?

I think this is actually wrong...  What I _think_ it should say is:

   * 2) level is -54dBm. noise floor of the radio is -104dBm.
   *    qual->level = -54 = 202 ; range->max_qual.noise = -104 = 152

Noise levels _do_ change dynamically, which is something else that the
drivers don't do (ahem, atmel, madwifi, and airo for starters).  When
you turn on your microwave, that totally screws the 2.4GHz frequency
range and impacts 802.11 communications.  Since the microwave is random
energy, it is extra noise and therefore decreases the Signal to Noise
ratio (ie, the noise value increases, say from -95dBm -> -85dBm, due to
the extra energy from the microwave, while the signal may stay the
same).

You _always_ have a noise floor, which is the normal value where in good
conditions the card can no longer distinguish the usable radio energy
from background energy, but most drivers at this time use that noise
floor level in the "qual.noise" field and not the "max_qual.noise"
field, because they evidentally don't sample noise on each channel
dynamically, or don't know how to pull that value off the card.

Jean: can you give some clarification on that statement in iwlib.c?

Dan