Well, take Cisco routers for instance. You configure the interface to use
either 802.3 or Ethernet II (or 802.2 or SNAP). So in this case it is you
that decides which encapsulation to use and the router just follows your
instructions. In other cases a program might be explicitly set up to only
use one certain encapsulation but generally they let you choose which one
you want to use.
At 10:19 AM 2/4/01 -0800, you wrote:
>Thanks.
>I mean, during encapsulation how IEEE 802.3 or Ethernet will be selected ?
>"Who" decides that ?
>
>
>"Curtis Call" <[EMAIL PROTECTED]> wrote in message
>4.3.2.7.0.20010204110556.00ab6100@mail">news:4.3.2.7.0.20010204110556.00ab6100@mail...
> > 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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>
>
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