The OSI Model -7 Layers[Explained]

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OSI stands for Open System Interconnection. It is a well-organized structure which enables many systems to connect with each other and share the data. This structure contains 7 different layers to be specific and each layer has its own functions to perform. These layers are nothing but a set of protocols which provides a base to perform or execute various processes. This conceptual model was introduced by ISO (International Organization for Standardization) in 1984.

The 7 layers are Application layer, Presentation layer, Session Layer, Transport layer, Network layer, Data link layer and physical layer. Now let us see all of these layers in detail.

Application Layer:

This layer of the network system contains protocols which executes the function of network applications on the system. Network applications are the applications that use the internet, for example google chrome, Firefox, Microsoft edge, Skype etc. This layer forms the base for various networking services such as Web surfing, File transfer, Emails etc.

This layer contains many protocols, some of these are FTP, HTTP, HTTPs, TELNET, SMTP etc.

Service Protocol Used
Web SurfingHTTP, HTTPs
File TransferFTP

Presentation Layer:

This layer works with the information passed from the application layer. This layer has three important functions.

  • Translation: This layer converts the data from the application layer into the binary language (0s and 1s).
  • Data Compression: Now the converted data is compressed so that it could engage less space. This also makes the data transmission easy.
  • Encryption:  In this process the reduced data is encrypted with a code so that it is now not accessible to any third party person, this enhances the security of the model. This encrypted data is decrypted at the receiver’s side. The encryption and decryption ouccers through SSL(Secure Sockets Layer) protocol.

Session Layer:

Let us understand this layer with an example,

You are now at our webpage of the terminal stack, when you open the webpage your system asks the server to load the information, the server then verifies your system’s identity this process is called as authentication. After authentication the server checks whether you are allowed to access the information or not, this process is called authorization. Now the server sends the information in the form of data packets in which the categories(images, text etc) of data are sorted. This sorting is called session management.

All of these three functions are performed by the session layer.

Transport Layer:

This layer also performs three important functions:

  • Segmentation: The data from the session layer is divided into different segments which helps in locating the receiver application and tracking the data transfer.
  • Flow Control: This layer has some protocols which maintain the exact rate of data transmission which gives the fastest transfer.
  • Error control: If the data in the process is lost this layer tells the sender to resend the lost data.

Network Layer:

The segments from the transport layer are merged with the senders and receivers IP addresses to form packets. This helps in locating the exact locations. The packets are then sent through routers; this transport process is called routing. This layer also executes an important function of path determination in which it chooses the shortest and fastest path for the data transfer; it uses some protocols such as OSF,BGP,IS-IS etc. to execute its functions.

Data Link Layer:

The system is connected to a router from where it transfers data to another router, the data packets formed in the network layer are now upgraded with the addition of head and tail to form frames. These heads and tails are strings of 0s and 1s, these are added for smooth transmission between the system and the router. At the router this frame is again decapsulated to form packets and sent through the network layer. Another function of this layer is to control the data flow to the router.

There can be many systems connected to the router if the frame, if the frame and some other data reach the router at the same time the combined data will be a total waste. This layer doesn’t allow this to happen.

Physical Layer:

This layer converts the data from the Data link layer to signals. The Frame which was a binary number is now converted to signals using this layer. These signals are then transmitted and received by the receiver. The receiver’s system converts these signals to BITs and then the application layer helps to display the data in the receiver’s system.

The OSI Model

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Now you know how a web page is loaded, how you download a movie, how you share data and how this intense network works. If this was helpful for you please let me know in the comment section.

Thank you for reading!!


This Post Has 2 Comments

  1. Samaksh

    Wow this was interesting 👍

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