2. The OSI Model has seven different layers. This presentation will
describe and explain each one of the layers, Starting with highest in
the hierarchy (The Application Layer) proceeding to the lowest (The
Physical Layer).
This is how the layers look:
Layers 7 – 4 focus on end to
end communication of data
source and destination
Layers 3 – 1 provide consistent
communication between the
network devices.
3. The application layer is the
closest to the end user. It is the
layer that provides the interface
between the applications we
use to communicate and the
underlying network over which
our messages are transmitted.
The application layer protocols
are used to exchange data
between programs running on
the source and destination
hosts. There are many
application layer protocols
including HTTP, FTP, TFTP,
IMAP, DNS protocol.
4. Layer 6 - Presentation
The presentation layer or sometimes
referred to as the syntax layer, serves
as a data translator for the network. It is
responsible for the delivery and
formatting of information to the
application layer for further processing
display.
Encryption is typically done at this layer
too, although it can be done at the
application, session and transport
layers. Decryption is also handled at
this layer. For example when logging on
to bank account sites the presentation
layer will decrypt the data as it is
received.
5. Allows to applications to establish and terminate
communicate to each other, known as a session.
Provides services like:
Dialog management- what decides which end point talks at
what time
6. Ensures data sent does no receive errors, like
duplication, lost or corruption.
It Provides:
Message segmentation- what splits messages into smaller
pieces, for fewer losses, and then passes to the network
layer. The receiving transport layer reassembles the
segments into the full data.
Error checking and data recovery
7. This layer forwards PDUs between hosts
It uses four process to do this:
1. Addressing end devices- this process configures
end devices with a unique IP address
2. Encapsulation – this layer receives the data from
the transport layer and then adds an IP header to
the data, what includes the source and
destination IP address.
8. 3. Routing - a router selects paths to direct
the packet towards to the destination.
4. De-encapsulation – when receiving a packet
the network layer reads the IP address, if
the destination IP address is the same as its
own it will remove the header and send the
data up to the transport layer.
9. The Data link layer is responsible for the moving of data
across the a physical link in a network.
The data link has two sublayers:
Media Access Control (MAC)
Logical Link Control (LLC)
The Data link ensures that initial connection has been set up, It
also divides output data into frames. It ensures that incoming
has been received.
10. This layer transmit the data, in bits form, to
the destination physical layer.
The data is transmitted using signals, the
signal used is determined by the medium
used.
Electrical voltage, radio frequencies and
pulses of light or infrared are types of
signalling.
