Roaming between 2 APs with WDS

Dan Williams dcbw at redhat.com
Tue Oct 14 11:58:25 EDT 2014


On Tue, 2014-10-14 at 09:44 +0200, Víctor Andrés wrote:
> Hi Dan,
> 
> If I set the search in one channel, it's out of transmitting for 110 ms 
> (more or less). But if I set in the configuration for search only for 
> the channel in use, it will scan in 2 channels, and the time searching 
> (not transmitting) will be for 200 ms (more or less).

That sounds like it's using passive scans.  If active scans are used,
the dwell time on each channel should be about 20 - 30ms plus a bit for
switching and the nullfunc frames to stop/start data flow.  Note that
some channels in the 5GHz range cannot be active scanned due to
regulatory restrictions though.

> I need to transmit data at 1000 Hz, so with this time searching, I have 
> small breaks in the flow data. The data aren't lost, but in the flow 
> data you can see that small stops.
> Any other alternative? I think less than 100 ms of searching and 
> transmitting is not possible, isn't it?

No, it certainly is possible with active scanning.  Can you confirm that
active scanning is not being used, and if so, try to enable that?

Dan

> Wpa_supplicant log, for scanning only in channel 2412 MHz (cannel 1):
> ...
> 1413272106.062501: nl80211: Scan frequency 2412 MHz
> 1413272106.064362: Scan requested (ret=0) - scan timeout 30 seconds
> 1413272106.065553: nl80211: Event message available
> 1413272106.066987: nl80211: Drv Event 33 (NL80211_CMD_TRIGGER_SCAN) 
> received for mlan0
> 1413272106.067902: mlan0: nl80211: Scan trigger
> 1413272106.068665: mlan0: Event SCAN_STARTED (49) received
> 1413272106.069001: mlan0: Own scan request started a scan in 0.003479 
> seconds
> 1413272106.069733: mlan0: CTRL-EVENT-SCAN-STARTED
> 1413272106.180420: nl80211: Event message available
> 1413272106.180694: nl80211: Drv Event 34 (NL80211_CMD_NEW_SCAN_RESULTS) 
> received for mlan0
> 1413272106.180847: mlan0: nl80211: New scan results available
> 1413272106.180908: nl80211: Scan probed for SSID 'WIRELES1'
> 1413272106.181000: nl80211: Scan included frequencies: 2412
> 1413272106.181091: mlan0: Event SCAN_RESULTS (3) received
> 1413272106.181183: mlan0: Scan completed in 0.112213 seconds
> ...
> 
> Thanks
> 
> El 10/10/2014 19:29, Dan Williams escribió:
> > On Fri, 2014-10-10 at 11:56 +0200, Víctor Andrés wrote:
> >> Hi Avinash,
> >>
> >> I'm using the firmware version 14.66.9.p192
> >> (http://git.marvell.com/?p=mwifiex-firmware.git;a=commit;h=633d06edab7a2b82efaa134ec5591cd20f9ac0a3)
> >> and testing the recent commit p52 version
> >> (http://git.marvell.com/?p=mwifiex-firmware.git;a=commit;h=3f45b8c4cc1eb1d102bc3486b19677332dd215ab),
> >> but I'm not sure of this last commit, becauseeven if it was posted more
> >> recent, it's a previous versionof the FW.
> >>
> >> Yes, the roaming is working now. I'm trying to reduce the scanning
> >> timein order toscan only the channel in use or only for the known bssid.
> >> When the interface is scanning it isn't transmitting data, and what I
> >> need is a continuous flow of data.
> > Scanning only the channel-in-use doesn't work very well for roaming,
> > because close-by APs are quite likely to be on a different channel to
> > ensure they don't interfere with each other.  Scanning for a known BSSID
> > doesn't work very well because you still have to scan a bunch of
> > channels to find the BSSID you're looking for.  The driver/mac80211
> > should be capable of partial scans (send PS, scan 2 or 3 channels, jump
> > back to operating channel for a while), is that not happening?  How long
> > is the card off the operating channel for, and what are your latency
> > requirements?  Is 100ms too long to pause data transmission?
> >
> > Dan
> >
> >
> 




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