Full duplex does not require CSMA/CD. Full duplex requires a switch.
Transmit and receive are done on separate wires to a switch. The switch
then performs all arbitration internally. This theoretically makes 200Mbps
possible, if the transmit and receive pipes are both kept full at 100Mbps.
Half duplex was originally done on a single wire (10base5 and 10base2) so
the receive wire and the transmit wire were the same wire. 10baseT only
changed the physical media but it still "acts" like a single wire if it is
attached to a hub rather than a switch. In this case, CSMA/CD (Carrier
Sense Multiple Access with Collision Detect) must be used by all users of
the 10baseT hub, 10base2 or 10base5.
Vern Stitt, AE, ASE, CCNA, MCSE
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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