Actually CSMA/CD is still required. When communicating through a switch,
the TX (towards the switch) is guaranteed the full bandwidth towards the
switch. However the inbound (RX from the switch) may be carrying traffic
from more than one originating host. As such, collisions may still occur if
more than on of these hosts tries to talk to the same destination at the
same time.
A basic switch (without VLANS and fancy Layer 3 functionality) creates
bandwidth domains but NOT broadcast domains. As such it will still flood
broadcasts and multicasts to all ports - again creating opportunity for
collisions that require CSMA/CD arbitration.
Full duplex increases throughput as less traffic is forwarded to end devices
(cuts out unicasts not addressed to the attached devices) but does not
guarantee collisionless connectivity. CSMA/CD is required to handle the
collisions that do occur.
Keith
""Joe Martin"" <[EMAIL PROTECTED]> wrote in message
8fbq4s$80t$[EMAIL PROTECTED]">news:8fbq4s$80t$[EMAIL PROTECTED]...
> Full duplex transmission requires a point to point connection between two
> devices. This is achieved using a switch. Since the connection is
between
> two and only two devices at a time, this allows them to transmit and
receive
> at the same time. Thus a collision would never occur and CSMA/CD is
> unnecessary.
>
> JOE
> CCNP, CCDP, and a few other things...
>
>
> "Dan West" <[EMAIL PROTECTED]> wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Sorry to ask such a simple question--but the CCNA book
> > is still unclear as to what's going on.
> >
> > Half-duplex ethernet uses CSMA/CD for arbitration on
> > the link. Does full duplex use it as well for
> > arbitration? The book makes it sound like if you are
> > running full-duplex that the CSMA/CD is not necessary.
> > It mentions half-duplex looping a duplicate frame onto
> > the recieve wire from the transmit wire.
> >
> > Thanks.
> >
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