THE OSI MODELTHE OSI MODEL

KUDIRAT FAWEHINMIKUDIRAT FAWEHINMI

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CONTENTSCONTENTS

What is OSI?What is OSI? Characteristics of the OSI layers Characteristics of the OSI layers The 7 OSI LayersThe 7 OSI Layers Interaction between the OSI layers Interaction between the OSI layers ConclusionConclusion

What is OSI? What is OSI?

The Open Systems Interconnection (OSI) The Open Systems Interconnection (OSI) is a model that was developed by the ISO is a model that was developed by the ISO (International Organization for Standards ) (International Organization for Standards ) and it describes how information from a and it describes how information from a software application in one computer, software application in one computer, moves through a network medium to a moves through a network medium to a software application in another computer.software application in another computer.

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Characteristics of the OSICharacteristics of the OSI

Upper layersUpper layers 7 Layers 7 Layers Lower layers Lower layers

The Upper LayersThe Upper Layers: This deals with Application issues and generally are : This deals with Application issues and generally are implemented only in software. The highest layer, application layer is implemented only in software. The highest layer, application layer is closest to the end user. This layer is where communication from one end closest to the end user. This layer is where communication from one end user to another begins through the interaction between the application user to another begins through the interaction between the application layer processes and the end user. layer processes and the end user.

The Lower layersThe Lower layers: This handles Data transport issues. The physical layer : This handles Data transport issues. The physical layer and Data link layers are implemented in hardware and software. and Data link layers are implemented in hardware and software.

The 7 OSI LayersThe 7 OSI Layers

The OSI model consists of 7 layers they are:The OSI model consists of 7 layers they are: Application layerApplication layer Presentation layerPresentation layer Session layerSession layer Transportation layerTransportation layer Network layerNetwork layer Data-link layerData-link layer Physical layerPhysical layer

Physical layer: 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

Data-link:Data-link: At this layer Data error Checking and Media At this layer Data error Checking and Media Access Control takes place. It cAccess Control takes place. It consists of two sublayers:

Logical Link Control (LLC) defines how data is transferred over the cable and provides data link service to the higher layers.

Medium Access Control (MAC) defines who can use the network when multiple computers are trying to access it simultaneously (i.e. Token passing, Ethernet [CSMA/CD

– Network Layer:Network Layer: This layer deals This layer deals with the routing of packets over with the routing of packets over the network. It decides the best the network. It decides the best path in which to transmit a path in which to transmit a packet, using routing protocols. packet, using routing protocols. E.g IP (Internet Protocol), IPX E.g IP (Internet Protocol), IPX (Internet Protocol Exchange).(Internet Protocol Exchange).

– Transport LayerTransport Layer : The : 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 Highlight any procedural differences from regular projects of this differences from regular projects of this type.type.

– Presentation Layer: Presentation Layer: This layer This layer provides a variety of coding and provides a variety of coding and conversion functions that are conversion functions that are applied to the application layer. applied to the application layer. These functions ensure that These functions ensure that information sent from the information sent from the application layer of one system will application layer of one system will be readable by the application be readable by the application layer of another system.layer of another system.

Application LayerApplication Layer: This OSI layer, is : This OSI layer, is the closest to the end user, which the closest to the end user, which means that both the OSI application means that both the OSI application layer and the end user, interact layer and the end user, interact directly with the software application. directly with the software application. Some of the protocols that work at Some of the protocols that work at this layer include FTP(File Transfer this layer include FTP(File Transfer Protocol) and SMTP (Simple Mail Protocol) and SMTP (Simple Mail Transfer Protocol).Transfer Protocol).

Interaction Between OSI Interaction Between OSI Model LayersModel Layers

Information sent from a software Information sent from a software application in one system to a application in one system to a software application in another, software application in another, must pass through each of the OSI must pass through each of the OSI layers. An example of this is shown layers. An example of this is shown in the diagram below:in the diagram below:

DATA TRANSMISSION THROUGH THE DATA TRANSMISSION THROUGH THE OSI LAYERSOSI LAYERS

A given layer within the OSI model A given layer within the OSI model communicates with three other layers:the communicates with three other layers:the layer directly above it, the layer directly layer directly above it, the layer directly below it and it’s peer layer in other below it and it’s peer layer in other networked computer system. In the networked computer system. In the diagram below, the data link layer in diagram below, the data link layer in system A, communicates with the network system A, communicates with the network layer and physical layer of system A. It layer and physical layer of system A. It also communicates with the data link layer also communicates with the data link layer of system B.of system B.

Conclusion Conclusion

Overall, this presentation has tried Overall, this presentation has tried to describe the OSI model,what it to describe the OSI model,what it is all about and how is all about and how communication occurs through the communication occurs through the layers of the model from one user layers of the model from one user to another . to another .