(1/2) ACS testing and some potential improvements...
David Littell
david.littell
Mon Feb 18 09:25:05 PST 2013
Hi all,
I've been looking at the ACS implementation and running some tests in
our environment (~90 AP's on both 2.4 and 5 GHz) with hostapd-1.0 over
ath9k (compat-wireless-3.6.8-1). In general it appears that ACS does
indeed select a channel... ;-) However, I've seen some curious things
and I'm hoping for some feedback from the group.
Odd/Questionable Survey Results: (ACS is configured for 7 surveys with a
30 mSec ROC duration.) I've gotten some survey results that don't seem
quite right. Here are the survey results for 5 GHz (sorry for any silly
wrapping):
1358873457.934770: nl80211: Freq survey dump event (freq=5180 MHz
noise=-88 channel_time=26 busy_time=0 tx_time=0 rx_time=0)
1358873457.964729: nl80211: Freq survey dump event (freq=5200 MHz
noise=-89 channel_time=26 busy_time=2 tx_time=2 rx_time=0)
1358873457.994732: nl80211: Freq survey dump event (freq=5220 MHz
noise=-89 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.024741: nl80211: Freq survey dump event (freq=5240 MHz
noise=-87 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.054800: nl80211: Freq survey dump event (freq=5745 MHz
noise=-88 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.084816: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=26 busy_time=2 tx_time=1 rx_time=0)
1358873458.111970: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109723 busy_time=73415 tx_time=155741
rx_time=85709)
1358873458.144813: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=29 busy_time=13 tx_time=12 rx_time=0)
1358873458.174819: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=26 busy_time=2 tx_time=2 rx_time=0)
1358873458.204732: nl80211: Freq survey dump event (freq=5180 MHz
noise=-90 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.234737: nl80211: Freq survey dump event (freq=5200 MHz
noise=-89 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.264754: nl80211: Freq survey dump event (freq=5220 MHz
noise=-89 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.294752: nl80211: Freq survey dump event (freq=5240 MHz
noise=-90 channel_time=26 busy_time=0 tx_time=0 rx_time=0)
1358873458.324797: nl80211: Freq survey dump event (freq=5745 MHz
noise=-88 channel_time=26 busy_time=0 tx_time=0 rx_time=0)
1358873458.354810: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=26 busy_time=3 tx_time=2 rx_time=0)
1358873458.381973: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109766 busy_time=73448 tx_time=155757
rx_time=85709)
1358873458.414813: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=29 busy_time=12 tx_time=11 rx_time=0)
1358873458.444813: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=26 busy_time=3 tx_time=2 rx_time=0)
1358873458.474743: nl80211: Freq survey dump event (freq=5180 MHz
noise=-90 channel_time=26 busy_time=2 tx_time=2 rx_time=0)
1358873458.504733: nl80211: Freq survey dump event (freq=5200 MHz
noise=-90 channel_time=26 busy_time=2 tx_time=2 rx_time=0)
1358873458.534748: nl80211: Freq survey dump event (freq=5220 MHz
noise=-88 channel_time=26 busy_time=2 tx_time=2 rx_time=0)
1358873458.564753: nl80211: Freq survey dump event (freq=5240 MHz
noise=-89 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.594801: nl80211: Freq survey dump event (freq=5745 MHz
noise=-88 channel_time=26 busy_time=0 tx_time=0 rx_time=0)
1358873458.624807: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=26 busy_time=4 tx_time=3 rx_time=0)
1358873458.651966: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109809 busy_time=73480 tx_time=155772
rx_time=85709)
1358873458.684819: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=29 busy_time=6 tx_time=4 rx_time=0)
1358873458.714813: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=26 busy_time=11 tx_time=11 rx_time=0)
1358873458.744738: nl80211: Freq survey dump event (freq=5180 MHz
noise=-88 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.774744: nl80211: Freq survey dump event (freq=5200 MHz
noise=-91 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.804751: nl80211: Freq survey dump event (freq=5220 MHz
noise=-89 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.834887: nl80211: Freq survey dump event (freq=5240 MHz
noise=-87 channel_time=26 busy_time=0 tx_time=0 rx_time=0)
1358873458.862549: nl80211: Freq survey dump event (freq=5745 MHz
noise=-88 channel_time=26 busy_time=1 tx_time=1 rx_time=0)
1358873458.892240: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=84933 busy_time=3 tx_time=2 rx_time=0)
1358873458.921971: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109852 busy_time=73514 tx_time=155790
rx_time=85709)
1358873458.952248: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=84936 busy_time=8 tx_time=7 rx_time=0)
1358873458.982246: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=84933 busy_time=2 tx_time=2 rx_time=0)
1358873459.012124: nl80211: Freq survey dump event (freq=5180 MHz
noise=-90 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.042145: nl80211: Freq survey dump event (freq=5200 MHz
noise=-90 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.072140: nl80211: Freq survey dump event (freq=5220 MHz
noise=-87 channel_time=84933 busy_time=0 tx_time=0 rx_time=0)
1358873459.102146: nl80211: Freq survey dump event (freq=5240 MHz
noise=-89 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.132229: nl80211: Freq survey dump event (freq=5745 MHz
noise=-89 channel_time=84933 busy_time=0 tx_time=0 rx_time=0)
1358873459.162249: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=84933 busy_time=7 tx_time=4 rx_time=0)
1358873459.191958: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109895 busy_time=73547 tx_time=155806
rx_time=85709)
1358873459.222252: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=84936 busy_time=5 tx_time=4 rx_time=0)
1358873459.252252: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=84933 busy_time=2 tx_time=2 rx_time=0)
1358873459.282117: nl80211: Freq survey dump event (freq=5180 MHz
noise=-90 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.312143: nl80211: Freq survey dump event (freq=5200 MHz
noise=-88 channel_time=84933 busy_time=2 tx_time=2 rx_time=0)
1358873459.342144: nl80211: Freq survey dump event (freq=5220 MHz
noise=-90 channel_time=84933 busy_time=2 tx_time=2 rx_time=0)
1358873459.372162: nl80211: Freq survey dump event (freq=5240 MHz
noise=-89 channel_time=84933 busy_time=2 tx_time=2 rx_time=0)
1358873459.402225: nl80211: Freq survey dump event (freq=5745 MHz
noise=-88 channel_time=84933 busy_time=0 tx_time=0 rx_time=0)
1358873459.432248: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=84933 busy_time=3 tx_time=2 rx_time=0)
1358873459.461961: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109938 busy_time=73580 tx_time=155822
rx_time=85709)
1358873459.492246: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=84936 busy_time=6 tx_time=5 rx_time=0)
1358873459.522272: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=84933 busy_time=3 tx_time=3 rx_time=0)
1358873459.552132: nl80211: Freq survey dump event (freq=5180 MHz
noise=-89 channel_time=84933 busy_time=4 tx_time=4 rx_time=0)
1358873459.582139: nl80211: Freq survey dump event (freq=5200 MHz
noise=-90 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.612149: nl80211: Freq survey dump event (freq=5220 MHz
noise=-88 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.642145: nl80211: Freq survey dump event (freq=5240 MHz
noise=-87 channel_time=84933 busy_time=0 tx_time=0 rx_time=0)
1358873459.672228: nl80211: Freq survey dump event (freq=5745 MHz
noise=-88 channel_time=84933 busy_time=1 tx_time=1 rx_time=0)
1358873459.702631: nl80211: Freq survey dump event (freq=5765 MHz
noise=-87 channel_time=84933 busy_time=2 tx_time=1 rx_time=0)
1358873459.731962: nl80211: Freq survey dump event (freq=5785 MHz
noise=-80 channel_time=109981 busy_time=73620 tx_time=155845
rx_time=85709)
1358873459.762254: nl80211: Freq survey dump event (freq=5805 MHz
noise=-80 channel_time=84936 busy_time=8 tx_time=7 rx_time=0)
1358873459.792248: nl80211: Freq survey dump event (freq=5825 MHz
noise=-80 channel_time=84933 busy_time=2 tx_time=2 rx_time=0)
Questions, queries, and puzzlers: The survey event-to-event timing looks
good, but...
1. I would have expected channel_time to never exceed the config
file's acs_roc_duration_ms and yet there are numerous instances of some
seriously bogus times. Is it reasonable to expect channel_time to be <=
acs_roc_duration_ms?
2. What do huge values of channel_time indicate?
3. I would have expected busy_time to also never exceed
acs_roc_duration_ms, but there it is again. Is it reasonable to expect
busy_time to be <= acs_roc_duration_ms?
4. What do huge values of busy_time indicate?
5. There are surveys above where tx_time is far beyond
acs_roc_duration_ms and in some cases even larger than channel_time.
Shouldn't tx_time always be <= busy_time?
6. There seem to be two rx_time values: 0 and impossible. What
does a 0-valued rx_time indicate?
Certainly the completely bogus surveys would skew the channel's
interference factor, so I would think that some sanity checks should be
applied to a survey to determine if it's valid or not. If I'm guessing
correctly about the relationship among the survey result components,
here's what I came up with:
acs.c::acs_chan_interference_factor(...)
...
dl_list_for_each(...)
/* Look for some excuses to throw out this survey. */
if( (survey->nf > 0.0) ||
(survey->nf < -120.0) ||
(survey->channel_time > SurveyDwellTime_ms) ||
(survey->channel_time_busy > SurveyDwellTime_ms) ||
(survey->channel_time_tx > SurveyDwellTime_ms) ||
(survey->channel_time_busy > survey->channel_time) ||
(survey->channel_time_tx > survey->channel_time_busy) )
{
wpa_printf( MSG_DEBUG, "--->> survey abandoned: "
"nf %d channel_time %lld busy_time %lld tx_time
%lld",
survey->nf,
survey->channel_time,
survey->channel_time_busy,
survey->channel_time_tx );
continue;
} /* close if( ... */
...
where SurveyDwellTime_ms is acs_roc_duration_ms. Comments?
(Part II to follow...)
Thanks,
Dave
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