Roaming between 2 APs with WDS

Dan Williams dcbw at redhat.com
Fri Oct 10 13:29:12 EDT 2014


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

> Víctor
> 
> El 10/10/2014 10:55, Avinash Patil escribió:
> > Hi Victor,
> >
> > What is SD8787 FW version you are using?  As I understand from your 
> > last email, roaming is now working fine, right?
> >
> > Thanks,
> > Avinash
> >
> > On Fri, Oct 10, 2014 at 12:38 PM, Víctor Andrés <victor at cymonline.com 
> > <mailto:victor at cymonline.com>> wrote:
> >
> >     Hi Dan.
> >     Thanks by your help.
> >
> >     I tested it in a different board and the signal level of the APs
> >     were correct. At least, not all the same and with a value of -101.
> >     May be a problem of the chip wifi of that board, I don't know. I
> >     use the same antenna for the 2 tests, and the boards were in the
> >     same position (more or less) for the 2 tests (with the same AP
> >     locations). I'll continue with the tests. I don't understand how
> >     can I connect with these APs that the wifi have detected with that
> >     poor signal.
> >
> >     I've compiled Wpa-supplicant with bgscan option enabled and tested
> >     in a different board, and now I have roaming between that 2 APs
> >     (with bgscan:learn). Now I'm trying to reduce the searching time,
> >     because when the wireless is searching network it can't transmit
> >     data, isn't it?
> >
> >     Víctor
> >
> >
> >     El 08/10/2014 19:33, Dan Williams escribió:
> >
> >         On Wed, 2014-10-08 at 12:35 +0200, Víctor Andrés Andrés wrote:
> >
> >         First, roaming works better with "bgscan" options enabled. 
> >         This option
> >         tells the supplicant to periodically scan looking for a better
> >         AP.  If
> >         scans don't happen (either through "bgscan" or manually via
> >         the control
> >         interface) the supplicant will stick with the current AP until the
> >         connection is broken.  The only way the supplicant knows which
> >         AP is
> >         better is if a scan has taken place and it knows the RSSI of
> >         each AP.
> >
> >         Second, it looks like the driver is broken for signal strength
> >         reporting.  -100dBm signal level is quite awful, and the fact
> >         that it
> >         shows *all* APs at that level is pretty much a smoking gun. 
> >         This is the
> >         reason the supplicant won't switch APs even if you do trigger
> >         a manual
> >         scan, because no AP really has a better signal level than the
> >         current
> >         one.
> >
> >         (one other slight possibility: your antenna isn't connected
> >         very well,
> >         or isn't connected at all, and you're close to the APs...)
> >
> >         Dan
> >
> >
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> >
> >
> 




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