Ethernet typically manifests both in hardware and software to collectively provide
the physical connectivity and processing capabilities just noted (more specific details
are in the next section).
More formally, Ethernet is defined by the IEEE 802.32 standard and enables
half-duplex (transmitting in one direction at a time over a shared physical medium)
as well as full-duplex (simultaneously transmitting in both directions) data communication,
and provides the underlying capabilities across three architectural layers:
Physical, Media Access Control (MAC) and the Logical Link Control (LLC) these are
discussed in some detail next. These capabilities correspond to those provided by the
first two layers in the OSI Reference Model3: Physical and Data-Link Layers, or Layer
1 and 2, respectively. This is shown in Figure 1.1 and it should be clear that the MAC
and LLC sub layers in the IEEE model are intended to have the same function as the
Data-Link Layer alone, in the OSI model.
Physical layer The Physical layer, at the bottom of the OSI/IEEE stack, is concerned
with the actual physical transmission of raw bits4 over the (physical5) media.
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