Today we will be discussing different layers of the OSI model. This is the most important aspect of networking that you will ever learn. Let’s first understand what OSI model is.
Definition of the OSI model
The OSI Model, or open System Interconnection Model, is used to describe how data is transferred between computers in a computer network. Communication between computing devices can be broken down into seven layers in the OSI Reference Model: physical, data link and network, transport, session presentation, and application.
Two computers are connected to each other by a LAN Cable. Connectors share data with the help Network interface card (NIC). If one computer has Microsoft windows, the other computer has MAC OSI. How can these two computers communicate with each other?
In 1984, International organization for standardization introduced the 7 system or OSI model to ensure successful communication between computers, networks, or other architectures.
Below are the seven OSI layers:
Application Layer
Presentation Layer
Session Layer
Network Layer
Transport Layer
Data Link Layer
Physical Layer

Note: Each layer is a bundle of protocols. These layers do NOT include applications, unless they are taken as an example of an application layer. They contain protocols that are required to make these applications such as Chrome, Firefox, etc.
OSI Model description
The OSI model can be divided into two layers: the upper layers and the lower layers.
Let’s briefly talk about each layer in the OSI Model.
Application Layer: Network applications use this layer. Network applications are those that use internet, such as Google chrome, firefox and Outlook. Web browser is a network app that runs on your computer. It does not reside in an application layer, but uses application layer protocol like HTTP or HTTPs to surf the web. Other applications such as outlook and Skypee are also dependent on application layer protocols to function. There are many protocols that can perform different functions in application layers. These protocols are all used for different functions. File transfer FTP is used for web surfing, email SMTP for emails, and file transfer FTP for file transfers.
Presentation Layer: This layer receives data from the application layer. These data are in the form numbers and characters. These numbers and characters are converted into machine language or binary numbers by the presentation layer.
For example, conversion of ASCII code into EBCDIC code.
This function is known as translation. This bit reduction process, which reduces the number of bits used to represent original data before data is transmitted, is known as data compression.
This can be either lossy or non-existent.
Data compression is used in order to reduce the file size so that the compressed file can reach its destination in a shorter time. Data encryption is used to preserve the integrity of data before transcription. Protocol SSL (secure sockets Layer) is used to decrypt and encrypt data. The presentation layer serves three functions, namely: Translation, compression, and encryption are the three functions of presentation layer.
Session Layer: The session layer is used to manage, terminate and establish sessions. It also has its own helpers such as APIs or Application Programming Interfaces. NETBIOS, or network basic output system, is one example of an API that allows applications on different computers to communicate. Server performs authentication before a session is established. Authentication is the process of identifying yourself. After identifying yourself, every connection uses a password and a user name. The connection has been established with the server. After authentication process auth