Roaming between 2 APs with WDS

Dan Williams dcbw at redhat.com
Fri Oct 10 14:22:12 EDT 2014


On Fri, 2014-10-10 at 23:03 +0530, Avinash Patil wrote:
> Hi Dan,
> 
> SD8787 does not support interleaved scanning i.e. scanning one channel and
> then coming back to operating channel for TX/RX.

Ouch.  I guess background scanning won't work in this situation then, as
long as (mostly) continuous data transmission is required...  I wonder
if/how the BG_SCAN_QUERY/BG_SCAN_CONFIG could be worked in to provide
background scanning if not under control of the supplicant.  Probably
more work than it's worth though.

> We have recently added channel scan gap support to mwifiex driver; but that
> is applicable only for newer chipsets.

Good to hear.

Dan

> http://git.kernel.org/cgit/linux/kernel/git/linville/wireless-testing.git/commit/drivers/net/wireless/mwifiex?id=cb91be87e12c079fcf25069a21123756c0931dd6
> 
> Thanks,
> Avinash
> 
> On Fri, Oct 10, 2014 at 10:59 PM, Dan Williams <dcbw at redhat.com> wrote:
> 
> > 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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