The Open System Interconnection model was the first standard model for communication and adopted in 1980 by all major computer and telecommunication companies.

But the modern internet is not based on OSI, modern internet is based on the TCP/IP model. However, the OSI model has seven layers.

OSI Model Seven Layers Top to Down

OSI Model Explained: The OSI seven layers

7- Application Layer

6- Presentation Layer

5- Session Layer

4- Transport Layer

3- Network Layer

2- Data Link Layer

1- Physical Layer

Application Layer:-

This application layer is used by end-user software such as web browsers and email clients. it provides a protocol that allow the software to send and present meaningful data to users. For Example- Hypertext transfer protocol (HTTP), File Transfer Protocol (FTP), etc.

Presentation Layer:-

This presentation layer prepares data for the application layer. it defines how two devices should encode, encrypt, and compressed data so it is received correctly on the other end.

Session Layer:-

The session layer provides a session for the communication between devices. it is responsible for the opening session, ensuring they remain open and functional while data is being transferred, and closing the session when communication end. this layer also sets the checkpoint during a data transfer and if the session is interrupted, the device can resume data transfer from the last checkpoint.

Transport Layer:-

This transport layer transfer data to the session layer and break it to segments on the transferring end.

Network Layer:-

This network layer has two main functions. one is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network.

Datalink Layer:-

This data link layer established and terminate a connection between two physically-connected nodes on a network.

Physical Layer:-

This physical layer is responsible for the physical cable or wireless connection between network nodes.