[Sugar-devel] ESSIDs and BSSIDs, NM and Sugar

[Andrés Nacelle]

Hello again people, I´m really happy to see you gave me some feedback.
Lets see if I can clear out all points you've mentioned and put a beet more
clear some other which I mentioned before with some lack of details

>On 11 Aug 2009 James Cameron
>The instantaneous signal strengths change very quickly, as a result of
>micromovements of metallic objects, and the movement of people within
>the signal area.

First of all thanks James for taking your time and reading the stuff I send
and giving me such a complete response. Getting into what you were saying,
I'm aware of the high dynamics under the signal sensing and reception,
because of that I managed to run the test in a big storehouse 65 meters long
and 35 meters wide, completely empty (except because of me and the
equipment). In addition is in a place where there's almost no interference
from other wireless devises. This way I tried to minimise the influence of
variables out of my management.

>The firmware in the wireless components of the XO can and will make
>decisions about which AP to use at a rate which is dependent on the
>changing conditions.  The rate at which you can obtain and perceive the
>signal strength value is much lower.

>If one were to place objects in the near field of one AP's antennas,
>reducing the signal strength, then it would be expected and beneficial
>for all XOs to swap to the other AP.  Surely this is what you want.

The concept of the XO taking the decision to connect to the "best" AP is
what we are chasing. But the definition of best is not that easy and the
behavior of the XO is not that as desired. What I'm saying here is that best
AP also means no overloading a single AP when there is another one nearby
with a reasonable quality. In the other hand the XO doesn't stay in the same
AP, it changes all the time even when there's 14 dBm power difference
between each signal instead of staying connected to the same AP. There
should be a way to make those  connections more stable.

>Also, it isn't just signal strength, but also noise level that matters.
>The noise level changes dynamically with activity.

As I was saying at the beginning the noise level was really low (I'm talking
of -94 dBm) and uniform in all the testing room so it shouldn't bother, but
then again if a difference of 1 dBm makes the XO change from AP the minimum
change in noise level may do something (and that it's almost unbelievable).

>On Mon, Aug 10, 2009 at 12:40:15PM -0300, Andr?s Nacelle wrote:
>> I wasn?t able to find data witch allow me to say if the throughput was
>> affected because of this behavior (I suspect that would be some
>> decrease on congested nets), but I don?t like to have in a school half
>> of the XO moving from an AP to another all the time. This kind of
>> behavior I think would produce dynamical congestion in the net,
>> basically because when many XO jumps to the same AP this is not going
>> to be able to manage all that much connections and throughput, then
>> the XO are going to keep trying and suddenly they will start
>> connecting to the other. What I?m afraid of is a mass effect, in witch
>> big blocks of XO go from one to another AP sub-employing one of the AP
>> and overcharging the other.

>These are rational fears, but you need to validate your theory, by
>measuring the congestion and load on each AP.

In this first stage I was measuring the congestion from the net in general
trying to see if any effect could be sensed in this fashion mainly because I
had some data from other tests done in this was a few month ago, so I would
compare them. There were enough differences to run deeper examinations but
no to say nothing for sure on throughput topic. Next time I'm planing to put
an script in the AP to save a log of incoming connections, MAC and time to
see if the jumps occur in group or are independent between XO.

>How are you measuring signal strength in your test area?  Is it a
>once-off reading using "iwconfig eth0", or do you average several
>samples and capture a standard deviation?

I've been using two different ways for doing this. The first is running 15
times the iwlist eth0 sc, and doing the average. This I did it in different
regions of the testing area. The other system was using a WI-Spy with an
Aser Laptop, witch gives me a dynamic lecture of the electromagnetic fields
on the wireless frequencies. This way I was able to see if a non wireless
interference was taking place in the area (which didn't occur)

>--
>James Cameron
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