(2/2) ACS testing and some potential improvements...

[David Littell]

(Part 1/2 posted earlier)


Swapped channel_time_tx and channel_time_rx: While I was trying to
understand some of the odd values in the survey results I stumbled on a
wpa_printf() argument order problem in driver_nl80211.c's add_survey().
The wpa_printf() argument list has channel_time_tx and channel_time_rx
swapped relative to the format string.  Thought you'd like to know...


The Test Environment:  There are quite a few AP's around here:

2412 |   23 +++++++++++++++++++++++
2417 |    2 ++
2422 |    2 ++
2427 |    1 +
2432 |    2 ++
2437 |   17 +++++++++++++++++
2442 |    6 ++++++
2447 |    7 +++++++
2452 |    4 ++++
2457 |    2 ++
2462 |   26 ++++++++++++++++++++++++++

(The vendor's ACS mechanism on 2.4 GHz channels is disabled due to the
fact that it simply doesn't work.  So, all the AP's in 2.4 GHz currently
have specific, fixed channel assignments.)


5180 |   18 ++++++++++++++++++
5200 |   15 +++++++++++++++
5220 |   14 ++++++++++++++
5240 |   18 ++++++++++++++++++
5745 |    7 +++++++
5765 |    1 +
5785 |    6 ++++++
5805 |    6 ++++++
5825 |    4 ++++

(Note that within 5 GHz there's a preponderance of AP's on the lower
channels even though all AP's on 5 GHz are using the radio vendor's ACS
mechanism.  It turns out that more radios than I expected have the upper
channels explicitly disabled.)


Some testing results: If I apply the survey sanity filter above along
with the correction to add_survey(), I get channel selection
distributions that looks like this:

2.4 GHz, 100 ACS runs:

2417 |   45 +++++++++++++++++++++++++++++++++++++++++++++
2422 |    8 ++++++++
2427 |   34 ++++++++++++++++++++++++++++++++++
2432 |    1 +
2442 |    1 +
2457 |   11 +++++++++++


2.4 GHz, 1000 ACS runs:

2417 |  464
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2422 |    2
2427 |  481
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2432 |    1
2437 |    2
2442 |    8 +
2457 |   32 ++++
2462 |   10 +


5 GHz, 100 ACS runs:

5180 |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
5200 |   29 +++++++++++++++++++++++++++++
5220 |   20 ++++++++++++++++++++
5745 |    1 +


5 GHz, 1000 ACS runs:

5180 |  432
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
5200 |  443
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
5220 |  119 +++++++++++++++++
5240 |    5
5745 |    1


In glancing at the results it appears ACS makes some "interesting"
choices from time to time.  The 2.4 GHz choices seem to fall where I
might expect (given the AP/channel distribution), but I'm puzzled why
it's choosing the low 5 GHz channels the vast majority of the time.
That's where everybody else is!  Any ideas, anyone?


Thanks,
Dave




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