They are different standards for ethernet. They both use CSMA/CD. 802.3
was defined by the IEEE and Ethernet was defined by Xerox I believe.
The difference is in the packet format:
Ethernet:
Destination Address (6 octets) - Source Address (6) - Protocol (2) - Data
(Variable) - FCS (4)
802.3
Destination Address (6 octets) - Source Address (6) - Length (2) - Data
(Variable) - FCS (4)
A node can tell the difference between the two protocols because the Length
of a packet can never be more than 1518 bytes so if that value is more than
1518 the node can tell that it is an Ethernet packet and that that
particular spot is the protocol type field not the length.
Given that 802.3 packets don't contain the protocol type field they cannot
transport different network layer protocols without using additional
information which is why 802.2 and SNAP was defined. The 802.2 or SNAP
fields occur at the beginning of the Data portion of the packet and are
used to specify which protocol is sending the packet.
Did that answer your question?
At 09:43 AM 2/4/01 -0800, you wrote:
>I see a description of the differences between them but I can't really
>understand that in practical terms.
>Is the IEEE 802.3 the CSMA/CD ?
>
>
>
>
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