layer correlates to OSI Layers 5 through 7, the Network File System (NFS) implements
elements matching all three layers. Likewise, the 802.3, 802.5, and Ethernet standards define
details for the data link and physical layers.
layers are not as important to CCNAs. In addition, most networking people know what the OSI
model is but do not need to memorize everything about it. Table 3-2 shows plenty of detail and
explanation for a more in-depth idea of the OSI model components. If you are daunted by the
task of memorizing all the examples in Table 3-2, you can refer to Table 3-3, which offers a
(Layer 2)
getting data across one particular link or medium. The
data link protocols define delivery across an individual
link. These protocols are necessarily concerned with the
type of media in question; for example, 802.3 and 802.2
are specifications from the IEEE, which are referenced
by OSI as valid data link (Layer 2) protocols. These
specifications define how Ethernet works. Other
protocols, such as High-Level Data Link Control
(HDLC) for a point-to-point WAN link, deal with the
different details of a WAN link. As with other protocol
specifications, OSI often does not create any original
specification for the data link layer but instead relies on
other standards bodies such as IEEE to create new
standards for the data link layer and the physical layer.
HDLC, Frame Relay,
PPP, FDDI, ATM, IEEE
802.5/ 802.2
(Layer 1)
also typically standards from other organizations that are
referred to by OSI, deal with the physical characteristics
of the transmission medium. Connectors, pins, use of
pins, electrical currents, encoding, and light modulation
are all part of different physical layer specifications.
Multiple specifications are sometimes used to complete
all details of the physical layer. For example, RJ-45
defines the shape of the connector and the number of
wires or pins in the cable. Ethernet and 802.3 define the
use of wires or pins 1, 2, 3, and 6. So, to use a category 5
cable, with an RJ-45 connector for an Ethernet
connection, Ethernet and RJ-45 physical layer
specifications are used.
EIA/TIA- 449, V.24,
RJ45, Ethernet, 802.3,
802.5, FDDI, NRZI,
NRZ, B8ZS