About link-layer handoff
maccari-thisaintpartofmyaddress- at lenst.det.unifi.it
Wed Jul 20 09:47:07 EDT 2005
On Wed, Jul 20, 2005 at 06:50:59PM +0800, JIE XIONG wrote:
> How can we decrease the layer 2 handover (it depends on OS, kernel,
> driver, wireless card??)
a couple of documents I suggest over the topic:
expecially the second document gives an insight view of the phases of
handoff in 802.11b networks. Actually they have made an experiment with a
prism 2.5 card as a client and prism 2.5 with hostap driver as AP and they
measured average handoff time around 200 ms.
I still have to read it in deep (it looks a too little gap).
basically it depends on a mix of the causes you named, for example, the
protocol doesn' really specify when to leave current AP and pass to a new
one, it should happen when the signal strenght goes under a certain value,
but it is not clear how to measure that value. So as reported from first
document different nics perform differently. Then there is a scan phase,
to select new AP, this is controlled normally by firmware (see
host_roaming options in hostap driver) and then authentication,
association, eventually 802.1X stuff, llc layer procedures ...
see also http://www.drizzle.com/~aboba/IEEE/ there are some links to
documentation on handoff procedures.
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