The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer
Let’s take a practical example so that we understand it better.
Layer 7 = Application Layer
You open your Internet browser and type in the name of the website of your target which you want to visit.
Layer 6 = Presentation Layer
Your browser knows how to show pictures from different format, such as JPG, PNG…
Your browser knows how to handle different file types, for example if the target’s web site is created using HTML or ASP, your browser know how to open these file types.
Also if the web page is encrypted, and you have the authority to open this page, then your browser will know how decrypt the page and show a readable format.
Layer 5 = Session Layer
This is the first step of networking, where your browser establishes a session between your computer and the Web Server, and terminates the session at the end.
Layer 4 = Transport Layer
The web page you requested needs to be divided into small chunks to be transferred, and arranged in order to be sent through the network.
Layer 3 = Network Layer
Now, the page is ready, but it doesn’t know how to reach you because your address is xxx.xxx.xxx.xxx, which is wired for the web server because it doesn’t know where this address is located, so in this step Addressing occurs and data is sent to the Network Card.
Layer 2 = Data Link Layer
Now, the data is ready to be transferred out of the computer, so the Data Link Layer starts packaging the data + the address of delivery
Layer 1 = Physical layer
This is the step when data is transferred into electrical signals that is understood by the network cables and devices