Re: Netgear WPN824v2 (MIMO) router...

On 7/3/06, Robert G. Brown <rgb phy duke edu> wrote:

I run a set of system monitor panels at the top of my screen that
includes the network.  I noticed that my network load (which was zero a
lot of the time before as I work on local files etc) starts off at zero
but then creeps up over time to end up in a range anywhere from 4% to
100%, sustained, when I'm not typing and nothing at all is happening on
the system.  This is enough that the system load average sometimes bumps
up to a few percent when nothing is happening, and the system fan kicks
on as heat is generated from the load.

I used tcpdump/top to try to figure out just what was happening.  top is
unremarkable -- hald accumulates a bit of time, NM accumulates a minute
or so a day, X of course accumlates time, but nothing looks like it is
running away or unreasonable.

tcpdump is interesting, though.  I see a steady stream of packets like
the one below -- typically 3-5 almost-full-MTU frames/sec.  Note that
they are "from" the router and "to" the wireless interface on my laptop.
Note also that they are completely empty past the ethernet header itself
(or if there ever was data, it was stripped off upstream by the wireless
I'm wondering if this is an artifact of netgear's implementation of MIMO
-- perhaps what is making it through to the OS from a "sounding frame".
In order to tune the multiple antennae dynamically, tuning frames are
(supposedly) periodically sent with some complex encoded information.
It MAY be that these frames are supposed to be isolated by the wireless
client device and not passed back to the recipient network interface --
if you have a MIMO compliant device receiving, which is of course pretty
much impossible at this point.  Perhaps the radio pulls off the tuning
information correctly but is still forwarding the packet headers and an
empty frame to the bus, I don't know.  Does anybody on this list know
what's going on ?  Is this perhaps an artifact instead of a NM feature,
perhaps in response to these odd no-protocol packets?  Is there any way
to shut them off or regulate them to drop the network "load" back down
to sane idle levels?

I would connect to your AP by stopping NM and starting WPA_Supplicant
manually and see if you observe the same behavior.  I haven't
witnessed what you are describing personally but I wonder if what you
are seeing is just noise caused by the MIMO router hopping channels...

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