About link-layer handoff

张 yf zyf73518
Wed Jul 20 18:00:37 PDT 2005

I have made a test-bed, two AP made with hostap driver, a terminal with XP, 
NTP for synchronization, airopeek NX for sniffing. simulate the handoff 
process by shut down an AP, 
Open system used. the detect result shows a complete handoff process takes 
about 3.5 seconds. probe process take about 3.4 seconds, and auth and 
associate take just less than 10 ms.

I have test for about 6 times, and the result is very similar. also I take 
a notebook walking around our lab. The APs and pc card used come from 
Cisco, and I notice there happened a handover as I walk from AP 1 to AP 2. 
I didnot sniff the result, but I find a ping packet is lost (it's just a 
link-layer handover, no network-layer handover takes place, and the two 
real AP connect to the same switch), so the latency is about 2~3 seconds.

But from all the papers I have read, all authors claim the latency is about 
200ms ~ 500ms, There is a big gap. WHY??

to be mentioned, I have found from a Sweden university's website, a guy 
also got the same result with me.

>From: JIE XIONG <g00220008 at gmail.com>
>Reply-To: JIE XIONG <g00220008 at gmail.com>
>To: ? yf <zyf73518 at hotmail.com>
>CC: hostap at shmoo.com
>Subject: Re: About link-layer handoff
>Date: Wed, 20 Jul 2005 18:50:59 +0800
>i also want to ask about it...
>Anyone can give a definition about what layer 2 handover is (no IP
>address change?)
>And how long it will take for a normal layer handover
>How can we decrease the layer 2 handover (it depends on OS, kernel,
>driver, wireless card??)
>please help, thanks!
>On 7/20/05, ? yf <zyf73518 at hotmail.com> wrote:
> > Can anyone give me some answer about what is the least time link-layer
> > handoff needs to finish with hostap driver, even the driver is modified 
> > crosslayer information is used?
> >
> > Thanks
> >
> > Mark Hsueh
> >
> > _________________________________________________________________
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>Xiong Jie

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