On 11/07/2016 06:10 AM, Ashok Raj Nagarajan wrote:
On 2016-08-01 18:57, Ben Greear wrote:
On 08/01/2016 02:29 AM, Johannes Berg wrote:
Sure.. First use case will be to help with the problem of legacy
client devices that roam across multiple APs. It is a classic
enterprise Wi-Fi AP problem, often managed by a "network controller"
unit that is connected to all the APs.
The problem is how to handle seamless handoff of clients between
multiple APs while maximizing the client throughput and minimizing
disruption of IP application services like VoIP calls and video
streaming. A legacy client will often hold onto an AP association,
even down to 1 Mbps as it roams away. Instead, if the AP can
recognise that the client RSSI (and therefore throughput) is poor, it
can "drop" the Tx power significantly (just to that client) such that
it forcesthe client to look for a better, closer, and therefore
higher-throughputassociation. It would "give it a kick" without
blacklisting it. It just needsto hold the power low for the small
amount of time it takes to convince it to go away.
Not sure that *works* since implementations may just compare beacon
signal strength and hold on to the AP based on that, but it does seem
like a reasonable use case.
How is that better than just kicking the station deliberately and/or
refusing to send frames to it at all?
Ben, deliberately kicking out the station can potentially cause the black
listing behaviour on the client side and results in connection failures. Each
client handles the kickout logic differently. Reducing the tx power, causes the
station to trigger its roaming algorithm.
We tested some phones a year or so ago, and used a variable attenuator
to decrease the signal of one AP while ramping up signal of a second AP.
They did not roam until they lost connection, and since we were not using an
isolation
chamber, we could not get the AP signal less than around -75 DB, so in our test,
the phones often did not roam at all.
http://www.candelatech.com/cookbook.php?vol=wifire&book=Emulating+Station+Motion+with+Programmable+Attenuator
So, I am not sure you can assume much about scanning behaviour either. Maybe
newer
phones are better...
Thanks,
Ben
--
Ben Greear <gree...@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
