Good catch Richard, I forgot about the stale association problem.
Actually, my note about having the 'new AP' wlan stack generate a
bcast frame in reponse to the association event should take care of
this problem as well. When the old AP's wlan stack sees a frame
coming in from above (i.e. off the wire) with a source address equal
to one of its associated stations, it _should_ immediately disassoc
that station thus breaking the mac-level STA-to-STA frame path.
I think this 'send a bcast to the wire upon assoc' behavior is listed
in a recommended-practices somewhere (been a long time). It's
basically a trick to enforce the 'STA shall be associated to
one-and-only-one BSS within an ESS' rule.
-Mark
Quoting "richardvoigt@xxxxxxxxx" <richardvoigt@xxxxxxxxx>:
On 9/28/07, Dennis Borgmann <dennis.borgmann@xxxxxxxxxxxxxx> wrote:
Dear list-members!
I am using OpenWRT (www.openwrt.org) on two accesspoints. Within
OpenWRT, the wireless interface and the ethernet interface are bridged
to one interface (br0).
Those two accesspoints are standing quite far from one another. Their
WLAN-cells do not cross each other, meaning I have an area in between
the two accesspoints, where there is no accesspoint of the two
accessible: a dead spot.
Now I use two WLAN-telephones (Cisco 7920). I start calling one of the
phones inside the same radio cell and I answer this call. Now I start
moving away to the other accesspoint. As soon as I see myself assiciated
to the "new" accesspoint, I am able to hear my mate on the other phone
in the "old" cell, but he cannot hear me. This stays this way, until a
This seems not to be a bridging problem then, since your pal didn't move to
a new access point, his information should be correct in all bridges (either
correct interface or no entry). Therefore packets sent to him should be
correctly delivered. OTOH his outgoing packets could be blocked by his
access point as long as it thinks you are locally attached (the first packet
coming in via the other access point should disillusion it without need for
a timer).
The behavior you are seeing is opposite, therefore I think you have
misidentified the cause. Can you use VOIP software on a real computer, and
run packet capture software? It might be very informative to have a
connection phone <-> computer and also computer <-> computer in order to see
if any packets are actually being missed, and in which direction.
Most likely your phone clears the routing table when you dissociate from the
other access point, and the routing table isn't rebuilt until dhcp runs at
the new location. This affects outgoing packets more than incoming, since
your adapter still may honor packets destined to your MAC address and
broadcast within its range. Of course it may not be the routing table
either.
certain point of time is reached. In our tests, he has been able to hear
my voice recurring at :30 each minute. Take these examples:
05:40:20 I roamed to the "new" AP
05:40:30 my mate could hear me
05:43:35 I roamed to the "new" AP
05:44:30 my mate could hear me
05:47:03 I roamed to the "new" AP
05:47:30 my mate could hear me
...and so on.
So at a certain point of time, there seems to be a flushing of some
bridge-tables, but I don't know, how I could influence this behaviour.
Is this "flushing" somehow to be done manually? Or is there a timer,
which sets this behaviour?
I sniffed the WLAN a little while my tests have been done and the result
is, that the "old" accesspoint seems to still believe me in his radio
cell. So he sends out data for me all of the time, but since my
telephone has moved away, there is no more client to ACK these packages.
After the time mentioned before has passed, these packet are away and
the communication goes on the way it should. So I assume, there is a
timeout, that tells the AP to flush its old bridge-MAC tables of
clients, that he did not hear of since XX seconds...
Any help would be appreciated. Thanks a lot in advance,
Dennis
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Mark S. Mathews
AbsoluteValue Systems Web: http://www.linux-wlan.com
721-D North Drive e-mail: mark@xxxxxxxxxxxxxx
Melbourne, FL 32934 Phone: 321.259.0737
USA Fax: 321.259.0286
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