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Date:      Fri, 15 Feb 2002 08:59:49 -0800
From:      "Kevin Oberman" <oberman@es.net>
To:        Vinod Namboodiri <geekvinod@yahoo.com>
Cc:        Jason Hunt <leth@primus.ca>, freebsd-net@freebsd.org, freebsd-mobile@freebsd.org
Subject:   Re: MAC Layer of TCP/IP stack 
Message-ID:  <20020215165949.E92E05D09@ptavv.es.net>
In-Reply-To: Your message of "Fri, 15 Feb 2002 08:20:56 PST." <20020215162056.49296.qmail@web21106.mail.yahoo.com> 

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> Date: Fri, 15 Feb 2002 08:20:56 -0800 (PST)
> From: Vinod Namboodiri <geekvinod@yahoo.com>
> Sender: owner-freebsd-net@FreeBSD.ORG
> 
> Not actually.Its more to run QoS experiments and need
> to customize some medium access protocols like csma/ca
> e.t.c.Guess i cant get to the csma protocol from the
> freebsd tcp/ip stack source code.

CSMA/CD is ALWAYS implemented on the card in microcode, usually in ROM
and is totally untouchable from the standard API, let alone TCP or
IP. The closest you can come is a total reload of the code and many
cards don't support this. 

In the world of full-duplex Ethernet, there is no CSMA/CD and
virtually no MAC. Only cards running half-duplex still use
CSMA/CD. The specifics of CSMA/CD were in the original 802.3
specification and the rules have never changed since then (although
they are broken).

In wireless (802.11) protocols there is also no CSMA/CD as it is not
applicable to wireless although there IS a MAC and it is usually
loadable, though documentation and source is proprietary and general
hard to get.

R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman@es.net			Phone: +1 510 486-8634

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