WPA Supplicant causes timeouts
Jouni Malinen
j at w1.fi
Sun Nov 13 08:34:10 PST 2016
On Sun, Oct 30, 2016 at 08:01:19PM +0100, Nickolai Dobrynin wrote:
> Last February, the distro I was using - Gentoo - switched
> from WPA Supplicant v. 2.4 to v. 2.5, and recently to 2.6.
>
> After the upgrade, I started having frequent (every 2-4 mins)
> transient timeouts in all of my web browsers. I looked at the
> logs and found this:
>
> Oct 30 03:08:17 wpa_supplicant[335]: nl80211: Associated on 5500 MHz
> Oct 30 03:08:17 wpa_supplicant[335]: nl80211: Associated on 2462 MHz
>
> Why would it associate and instantly reassociate with the same AP on a different
> frequency? I am sending the relevant log snippet. Is there any way to stop
> these timeouts from happening?
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: Selecting BSS from priority group 0
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: 0: *** ssid='***'
> wpa_ie_len=0 rsn_ie_len=20 caps=0x411 level=-57 freq=2462 wps
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: selected based on RSN IE
This seems to indicate that the best BSS result in the last scan was
from the 2.4 GHz band.
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: Considering within-ESS
> reassociation
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: Current BSS: ***
> level=-68 snr=24 est_throughput=390001
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: Selected BSS: ***
> level=-57 snr=32 est_throughput=65000
However, the current BSS (on the 5 GHz band) has better estimated
throughput even though its signal strength is significantly lower.
> Oct 30 03:08:17 wpa_supplicant[335]: wlp3s0: Considering connect
> request: reassociate: 0 selected: *** bssid: *** pending:
But the roaming to the selected BSS is allowed.. This does not really
look reasonable in this specific case. It might be useful to check what
triggered the current BSS being selected (i.e., go through a longer log
snippet showing multiple roams between the BSSs). My guess is that there
would be "Allow reassociation - selected BSS has better estimated
throughput" somewhere there. This case was added to make it easier to
roam from a less capable AP (e.g., 2.4 GHz HT) to a more capable AP
(e.g., 5 GHz VHT) even if the signal strength would not allow that on
its own.
It looks like this change only applied in this lower throughput to
higher throughput direction and that could result in cases where a
significantly higher signal strength from the AP that has a lower
estimated throughput estimate would allow roaming back to the previous
AP on the next scan and then back to the higher throughput one on the
next scan, and so on..
The following changes could be tried to avoid this:
Use estimated throughput to avoid signal based roaming decision
Previously, the estimated throughput was used to enable roaming to a
better AP. However, this information was not used when considering a
roam to an AP that has better signal strength, but smaller estimated
throughput. This could result in allowing roaming from 5 GHz band to 2.4
GHz band in cases where 2.4 GHz band has significantly higher signal
strength, but still a lower throughput estimate.
Make this less likely to happen by increasing/reducing the minimum
required signal strength difference based on the estimated throughputs
of the current and selected AP. In addition, add more details about the
selection process to the debug log to make it easier to determine whaty
happened and why.
Signed-off-by: Jouni Malinen <j at w1.fi>
---
wpa_supplicant/events.c | 52 +++++++++++++++++++++++++++++++++++++++----------
1 file changed, 42 insertions(+), 10 deletions(-)
diff --git a/wpa_supplicant/events.c b/wpa_supplicant/events.c
index 17f057a..210b45c 100644
--- a/wpa_supplicant/events.c
+++ b/wpa_supplicant/events.c
@@ -1396,8 +1396,9 @@ static int wpa_supplicant_need_to_roam(struct wpa_supplicant *wpa_s,
{
struct wpa_bss *current_bss = NULL;
#ifndef CONFIG_NO_ROAMING
- int min_diff;
+ int min_diff, diff;
int to_5ghz;
+ int cur_est, sel_est;
#endif /* CONFIG_NO_ROAMING */
if (wpa_s->reassociate)
@@ -1431,12 +1432,13 @@ static int wpa_supplicant_need_to_roam(struct wpa_supplicant *wpa_s,
#ifndef CONFIG_NO_ROAMING
wpa_dbg(wpa_s, MSG_DEBUG, "Considering within-ESS reassociation");
wpa_dbg(wpa_s, MSG_DEBUG, "Current BSS: " MACSTR
- " level=%d snr=%d est_throughput=%u",
- MAC2STR(current_bss->bssid), current_bss->level,
+ " freq=%d level=%d snr=%d est_throughput=%u",
+ MAC2STR(current_bss->bssid),
+ current_bss->freq, current_bss->level,
current_bss->snr, current_bss->est_throughput);
wpa_dbg(wpa_s, MSG_DEBUG, "Selected BSS: " MACSTR
- " level=%d snr=%d est_throughput=%u",
- MAC2STR(selected->bssid), selected->level,
+ " freq=%d level=%d snr=%d est_throughput=%u",
+ MAC2STR(selected->bssid), selected->freq, selected->level,
selected->snr, selected->est_throughput);
if (wpa_s->current_ssid->bssid_set &&
@@ -1462,6 +1464,14 @@ static int wpa_supplicant_need_to_roam(struct wpa_supplicant *wpa_s,
return 0;
}
+ if (current_bss->est_throughput > selected->est_throughput + 5000) {
+ wpa_dbg(wpa_s, MSG_DEBUG,
+ "Skip roam - Current BSS has better estimated throughput");
+ return 1;
+ }
+
+ cur_est = current_bss->est_throughput;
+ sel_est = selected->est_throughput;
min_diff = 2;
if (current_bss->level < 0) {
if (current_bss->level < -85)
@@ -1474,20 +1484,42 @@ static int wpa_supplicant_need_to_roam(struct wpa_supplicant *wpa_s,
min_diff = 4;
else
min_diff = 5;
+ if (cur_est > sel_est * 1.5)
+ min_diff += 10;
+ else if (cur_est > sel_est * 1.2)
+ min_diff += 5;
+ else if (cur_est > sel_est * 1.1)
+ min_diff += 2;
+ else if (cur_est > sel_est)
+ min_diff++;
}
if (to_5ghz) {
+ int reduce = 2;
+
/* Make it easier to move to 5 GHz band */
- if (min_diff > 2)
- min_diff -= 2;
+ if (sel_est > cur_est * 1.5)
+ reduce = 5;
+ else if (sel_est > cur_est * 1.2)
+ reduce = 4;
+ else if (sel_est > cur_est * 1.1)
+ reduce = 3;
+
+ if (min_diff > reduce)
+ min_diff -= reduce;
else
min_diff = 0;
}
- if (abs(current_bss->level - selected->level) < min_diff) {
- wpa_dbg(wpa_s, MSG_DEBUG, "Skip roam - too small difference "
- "in signal level");
+ diff = abs(current_bss->level - selected->level);
+ if (diff < min_diff) {
+ wpa_dbg(wpa_s, MSG_DEBUG,
+ "Skip roam - too small difference in signal level (%d < %d)",
+ diff, min_diff);
return 0;
}
+ wpa_dbg(wpa_s, MSG_DEBUG,
+ "Allow reassociation due to difference in signal level (%d >= %d)",
+ diff, min_diff);
return 1;
#else /* CONFIG_NO_ROAMING */
return 0;
--
1.9.1
--
Jouni Malinen PGP id EFC895FA
More information about the Hostap
mailing list