THE OSI MODEL KUDIRAT FAWEHINMI COSC 541

CONTENTS CONTENTS n What is OSI? n Characteristics of the OSI layers n The 7 OSI Layers n Interaction between the OSI layers n Conclusion

What is OSI? n 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. List location or contact for specification (or other related documents) here FOR MORE INFO...

Characteristics of the OSI n Upper layers n 7 Layers n Lower layers

n 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. n 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 n The OSI model consists of 7 layers they are: n Application layer n Presentation layer n Session layer n Transportation layer n Network layer n Data-link layer n Physical layer

n Physical layer: n 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 n Data-link: At this layer Data error Checking and Media Access Control takes place. It c n Data-link: At this layer Data error Checking and Media Access 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: 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 : 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).

– Highlight any procedural differences from regular projects of this type. –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.

 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 n 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

n 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 n 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.