Transcript the osi model

THE OSI MODEL
KUDIRAT FAWEHINMI
96385
COSC 541
CONTENTS
What is OSI?
 Characteristics of the OSI layers
 The 7 OSI Layers
 Interaction between the OSI layers
 Conclusion
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What is OSI?
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The Open Systems Interconnection (OSI) is a
model that was developed by the ISO
(International Organization for Standards )
and it describes how information from a
software application in one computer, moves
through a network medium to a software
application in another computer.
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Characteristics of the OSI
Upper layers
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7 Layers
Lower layers
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The Upper Layers: This deals with Application
issues and generally are implemented only in
software. The highest layer, application layer
is closest to the end user. This layer is where
communication from one end user to another
begins through the interaction between the
application layer processes and the end user.
The Lower layers: This handles Data
transport issues. The physical layer and Data
link layers are implemented in hardware and
software.
The 7 OSI Layers
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The OSI model consists of 7 layers they are:
Application layer
Presentation layer
Session layer
Transportation layer
Network layer
Data-link layer
Physical layer
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Physical layer: This layer defines the
hardware means of sending and
receiving data through a medium.
Example of devices that work at this
layer include repeaters and Hubs
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Data-link: At this layer Data error
Checking and Media Access Control
takes place. It consists of two
– Network Layer: This layer deals with
the routing of packets over the
network. It decides the best path in
which to transmit a packet, using
routing protocols. E.g IP (Internet
Protocol), IPX (Internet Protocol
Exchange).
– Transport Layer : The Transport layer
ensures reliable service. It breaks
the message (from sessions layer)
into smaller packets, assigns
sequence number and sends
them.E.g of protocols that work at
this level are TCP(Transport Control
Protocol) and SPX (Sequence Packet
Exchange).
– Session Layer: This layer sets up,
coordinates, and terminates
conversations, exchanges, and
dialogs between the applications at
each end. It deals with session and
connection coordination Highlight any
procedural differences from regular
projects of this type.
– Presentation Layer: This layer
provides a variety of coding and
conversion functions that are applied
to the application layer. These
functions ensure that information
sent from the application layer of one
system will be readable by the
application layer of another system.
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Application Layer: This OSI layer, is the
closest to the end user, which means
that both the OSI application layer and
the end user, interact directly with the
software application. Some of the
protocols that work at this layer include
FTP(File Transfer Protocol) and SMTP
(Simple Mail Transfer Protocol).
Interaction Between OSI
Model Layers
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Information sent from a software
application in one system to a software
application in another, must pass
through each of the OSI layers. An
example of this is shown in the diagram
below:
DATA TRANSMISSION THROUGH THE
OSI LAYERS
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A given layer within the OSI model
communicates with three other
layers:the layer directly above it, the
layer directly below it and it’s peer layer
in other networked computer system. In
the diagram below, the data link layer
in system A, communicates with the
network layer and physical layer of
system A. It also communicates with
the data link layer of system B.
Conclusion
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Overall, this presentation has tried to
describe the OSI model,what it is all
about and how communication occurs
through the layers of the model from
one user to another .