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Date:      Fri, 21 Dec 2001 14:46:32 -0500
From:      "Louis A. Mamakos" <louie@TransSys.COM>
To:        Alfred Perlstein <bright@mu.org>
Cc:        Christoph Kukulies <kuku@gilberto.physik.rwth-aachen.de>, freebsd-mobile@FreeBSD.ORG
Subject:   Re: access point vs. point to point 
Message-ID:  <200112211946.fBLJkW719107@whizzo.transsys.com>
In-Reply-To: Your message of "Fri, 21 Dec 2001 12:38:23 CST." <20011221123823.R48837@elvis.mu.org> 
References:  <200112211530.fBLFUBs03175@gilberto.physik.rwth-aachen.de> <20011221123823.R48837@elvis.mu.org> 

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> * Christoph Kukulies <kuku@gilberto.physik.rwth-aachen.de> [011221 09:30] wrote:
> > 
> > Just a question: What is peculiar to an accesspoint? Can a 
> > FreeBSD computer with a PCI card with a PCMCIA holding a wireless LAN
> > adapter serve multiple notebook computers?
> 
> An accesspoint typically acts as a bridge to ethernet.
> 
> You can use a PCI card in a freebsd box, but you won't be able to
> use "BSS" mode, just "adhoc".
> 
> I'm not really sure what that means exactly, but I switched from
> an PCI card to an access point (addtron) because I kept having
> difficulties with my PCI card version.

And for completeness, an 802.11 access point also acts at a bridge
between the wireless devices as well.  That is, in your example, the
traffic between the laptop computers would go via the access point, 
given a wider coverage area "centered" on the access point.  The
other stations need not be able to "hear" each other.

In addition, the access point arbitrates access to the RF channel,
preventing the "hidden terminal" problem.  That's when two stations
listen for a clear RF channel before they transmit; since they can't
hear each other, one might "step on" another station, and the
mutual interference might mean that neither gets through.  When the
station is associated with an access point, the access point polls each
of the stations for traffic so that two stations won't try to transmit
at the same time.

louie



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