THE OSI MODEL

A brief introduction

Salvador Moreno Carrillo

The OSI model 

Conceptual model created in 1978 to standarize network comunications. 

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

Provides protocols that allow software to send and receive information and present meaningful data to users.

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The presentation layer prepares data for the application layer.

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The session layer creates communication channels, called sessions, between devices

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The transport layer takes data transferred in the session layer and breaks it into “segments” on the transmitting end. It is responsible for reassembling the segments on the receiving end.

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The network layer breaks up the segments of the transport layer into packets  and looks for the best path to the destination.

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The data link layer establishes and terminates a connection between two physically connected nodes on a network.

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The OSI model 

Application

Presentation

Session

Transport

Network

Data Link

Physical

The physical layer is responsible for the physical signals and conections of the network.

Comunication using the OSI model

Application

Presentation

Session

Transport

Network

Data Link

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Application

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Data Link

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Application

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Data Link

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Application

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Application

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USER A

USER B

Application

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Application

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USER A

USER B

User A generates an e-mail

Application

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Data Link

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Application

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USER A

USER B

Analises the data and prepares it.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

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Transport

Network

Data Link

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USER A

USER B

Creates a session with user B

Application

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Transport

Network

Data Link

Physical

Application

Presentation

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Network

Data Link

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USER A

USER B

Breaks  the message into fragments and lables each one

Application

Presentation

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Transport

Network

Data Link

Physical

Application

Presentation

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Data Link

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USER A

USER B

Breaks  the fragments into packets and routes them

Application

Presentation

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Data Link

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Application

Presentation

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USER A

USER B

Indicates the physical devices that should recieve it

Application

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Data Link

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Application

Presentation

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USER A

USER B

Sends the frames

Application

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Network

Data Link

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Application

Presentation

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Transport

Network

Data Link

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USER A

USER B

Application

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Data Link

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Application

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USER A

USER B

Recives the frames

Application

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Application

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Data Link

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USER A

USER B

Accepts the frames 

Application

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Transport

Network

Data Link

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Application

Presentation

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Data Link

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USER A

USER B

Reassembles the packets

Application

Presentation

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Transport

Network

Data Link

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Application

Presentation

Session

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Network

Data Link

Physical

USER A

USER B

Reassembles the fragments

Application

Presentation

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Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

USER A

USER B

Reassembles the message

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

USER A

USER B

Prepares and presents the information to the application

Application

Presentation

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Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

USER A

USER B

User B recive and read their message

To sum up...

- Divides the necesary tasks for network comunication 

- It standardises  processes

- Simplifies troubleshooting