OSI for CCNA Layer 1: Physical
The CCNA exam has extensive coverage of
hardware. That's the physical layer. The physical
layer provides the electrical, optical, or over-the-
air connection between the sending host device
and the receiving host device. This typically
involves copper or fiber-optic cabling, or wireless
radio connections, patch panels, signal repeaters,
submarine cables, or satellites.
CCNA certification does not require you to be a
space science expert. However, you do need to
understand that data is always converted into
bits that can be transmitted over a medium using
electrical current or optical signals that simulate
a 1 (signal) or a 0 (no signal).
In a nutshell, the physical layer defines
mechanical, electrical, optical, radio, procedural,
and functional standards to enable the
transmission of data-link (Layer 2) frames over a
certain transmission medium.
These standards define how a physical link is
built, activated, maintained, and deactivated to
enable transmissions between DTE (data terminal
equipment) and DCE (data communications
equipment).
DTEs are host devices. DCEs are network
devices, that is, any device that stands between
two host devices.
Most hubs are amplifying the electrical signal;
therefore, they are really repeaters with several
ports. Hubs and repeaters are Layer 1 (physical
layer) devices
hardware. That's the physical layer. The physical
layer provides the electrical, optical, or over-the-
air connection between the sending host device
and the receiving host device. This typically
involves copper or fiber-optic cabling, or wireless
radio connections, patch panels, signal repeaters,
submarine cables, or satellites.
CCNA certification does not require you to be a
space science expert. However, you do need to
understand that data is always converted into
bits that can be transmitted over a medium using
electrical current or optical signals that simulate
a 1 (signal) or a 0 (no signal).
In a nutshell, the physical layer defines
mechanical, electrical, optical, radio, procedural,
and functional standards to enable the
transmission of data-link (Layer 2) frames over a
certain transmission medium.
These standards define how a physical link is
built, activated, maintained, and deactivated to
enable transmissions between DTE (data terminal
equipment) and DCE (data communications
equipment).
DTEs are host devices. DCEs are network
devices, that is, any device that stands between
two host devices.
Most hubs are amplifying the electrical signal;
therefore, they are really repeaters with several
ports. Hubs and repeaters are Layer 1 (physical
layer) devices
OSI for CCNA Layer 2: Data Link
The CCNA exam has extensive coverage of data
routing. Data routing is handled by the data link
layer of the OSI. The data link layer does the
following:
Transmits the data on the physical
medium.
Routes the data locally on the physical
network medium. The data link layer uses
physical addresses assigned to each
physical network device in the local
network to route data from one physical
device to another.
Receives each packet from the network
layer on the sending host and wraps it up
in a data frame along with local routing
data.
Sends each data frame down to the
physical layer to code an electrical or
optical signal to transmit the data frame
over a wire or over the air (wireless
transmission).
On the receiving host, the data link layer
unwraps the data frame received to extract
the packet and sends it up to the network
layer.
Cisco switches are Layer 2 (data link layer)
devices.
routing. Data routing is handled by the data link
layer of the OSI. The data link layer does the
following:
Transmits the data on the physical
medium.
Routes the data locally on the physical
network medium. The data link layer uses
physical addresses assigned to each
physical network device in the local
network to route data from one physical
device to another.
Receives each packet from the network
layer on the sending host and wraps it up
in a data frame along with local routing
data.
Sends each data frame down to the
physical layer to code an electrical or
optical signal to transmit the data frame
over a wire or over the air (wireless
transmission).
On the receiving host, the data link layer
unwraps the data frame received to extract
the packet and sends it up to the network
layer.
Cisco switches are Layer 2 (data link layer)
devices.
.
OSI for CCNA Layer 3: Network
The CCNA exam covers data packets; the
network layer routes data packets across
networks that link the sending and the receiving
host. In a nutshell, the network layer does the
following:
Chooses the best route to send packets
between hosts.
Assigns logical addresses to all devices in
the network to be able to identify each
source host and each destination host, as
well as each network through which
packets need to be routed.
Logical addresses are assigned at the
network protocol level. Physical addresses
are assigned on a physical device, such as
a network card.
Receives each data segment from the
transport layer on the sending host and
wraps it up in a data packet along with
routing data. The packet is sent down to
the data link layer to send it over the
network physical medium.
On the receiving host, the network layer
unwraps the packet received to extract the
data segment and sends it up to the
transport layer.
Several protocols operate at the network layer,
such as IP, IPX, AppleTalk, and SNA, but the
CCNA test is only concerned with IP.
network layer routes data packets across
networks that link the sending and the receiving
host. In a nutshell, the network layer does the
following:
Chooses the best route to send packets
between hosts.
Assigns logical addresses to all devices in
the network to be able to identify each
source host and each destination host, as
well as each network through which
packets need to be routed.
Logical addresses are assigned at the
network protocol level. Physical addresses
are assigned on a physical device, such as
a network card.
Receives each data segment from the
transport layer on the sending host and
wraps it up in a data packet along with
routing data. The packet is sent down to
the data link layer to send it over the
network physical medium.
On the receiving host, the network layer
unwraps the packet received to extract the
data segment and sends it up to the
transport layer.
Several protocols operate at the network layer,
such as IP, IPX, AppleTalk, and SNA, but the
CCNA test is only concerned with IP.
OSI for CCNA Layer 4: Transport
On the CCNA exam, you'll work with hosts. The
transport layer manages the transport of data
between two hosts communicating over a
network. In a nutshell, the transport layer does
the following:
Slices up the data to be transmitted into
small chunks called data segments that can
be easily sent over the network medium.
Reassembles the data in order on the
receiving host:
Some transport protocols send the
segments in order.
Other protocols, such as Transmission
Control Protocol (TCP), send the data
segments in any order and
reassemble them in the correct order
on the receiving host.
Provides some error-detection
mechanisms.
transport layer manages the transport of data
between two hosts communicating over a
network. In a nutshell, the transport layer does
the following:
Slices up the data to be transmitted into
small chunks called data segments that can
be easily sent over the network medium.
Reassembles the data in order on the
receiving host:
Some transport protocols send the
segments in order.
Other protocols, such as Transmission
Control Protocol (TCP), send the data
segments in any order and
reassemble them in the correct order
on the receiving host.
Provides some error-detection
mechanisms.
OSI for CCNA Layer 5: Session
As a certified CCNA, you'll work in
communications between applications. Some
applications need to open logical communication
channels between the computer hosts. Logical
communication channels (sessions) maintain
data about the communication established
between the network application running on the
sending host and the network application running
on the receiving host. The session layer does
the following:
Opens and maintains logical communication
channels between network applications
running on the sending host and network
applications running on the receiving host.
Handles authentication: Some network
applications use authentication
mechanisms before they open a logical
communication channel (session) with a
remote host.
communications between applications. Some
applications need to open logical communication
channels between the computer hosts. Logical
communication channels (sessions) maintain
data about the communication established
between the network application running on the
sending host and the network application running
on the receiving host. The session layer does
the following:
Opens and maintains logical communication
channels between network applications
running on the sending host and network
applications running on the receiving host.
Handles authentication: Some network
applications use authentication
mechanisms before they open a logical
communication channel (session) with a
remote host.
OSI for CCNA Layer 6: Presentation
As you prepare for the CCNA exam, the
presentation layer is mostly concerned with data
format. It converts the data between different
formats so that both the sender and the receiver
can use heterogeneous data. For example, mail
messages contain various data formats: text,
application attachments, video, audio, and
graphical signature.
The presentation layer on the sending host
receives the data payload from the
application layer.
The presentation layer on the sending host
converts the data into a format that is
easily transportable over the network.
The presentation layer on the receiving
host converts the data from the network
format back to its native format that can
be easily interpreted, used, and displayed
by the application layer above
presentation layer is mostly concerned with data
format. It converts the data between different
formats so that both the sender and the receiver
can use heterogeneous data. For example, mail
messages contain various data formats: text,
application attachments, video, audio, and
graphical signature.
The presentation layer on the sending host
receives the data payload from the
application layer.
The presentation layer on the sending host
converts the data into a format that is
easily transportable over the network.
The presentation layer on the receiving
host converts the data from the network
format back to its native format that can
be easily interpreted, used, and displayed
by the application layer above
OSI for CCNA Layer 7: Application
The CCNA exam requires knowledge of the OSI
reference model's application layer. This layer
represents the various network applications such
as e-mail reader, Web browser, Hypertext
Transfer Protocol (HTTP), File Transfer Protocol
(FTP), and Network File System (NFS).
The application layer provides a user
interface and processes network data.
The application layer on the sending host
produces the network data to be
transmitted from the sender host.
The application layer on the receiving host
consumes the network data produced and
transmitted by the sender host.
reference model's application layer. This layer
represents the various network applications such
as e-mail reader, Web browser, Hypertext
Transfer Protocol (HTTP), File Transfer Protocol
(FTP), and Network File System (NFS).
The application layer provides a user
interface and processes network data.
The application layer on the sending host
produces the network data to be
transmitted from the sender host.
The application layer on the receiving host
consumes the network data produced and
transmitted by the sender host.
OSI for CCNA Layer 7: Application
The CCNA exam requires knowledge of the OSI
reference model's application layer. This layer
represents the various network applications such
as e-mail reader, Web browser, Hypertext
Transfer Protocol (HTTP), File Transfer Protocol
(FTP), and Network File System (NFS).
The application layer provides a user
interface and processes network data.
The application layer on the sending host
produces the network data to be
transmitted from the sender host.
The application layer on the receiving host
consumes the network data produced and
transmitted by the sender host.
reference model's application layer. This layer
represents the various network applications such
as e-mail reader, Web browser, Hypertext
Transfer Protocol (HTTP), File Transfer Protocol
(FTP), and Network File System (NFS).
The application layer provides a user
interface and processes network data.
The application layer on the sending host
produces the network data to be
transmitted from the sender host.
The application layer on the receiving host
consumes the network data produced and
transmitted by the sender host.
