Open Systems Interconnection model (OSI model)

Introduction To OSI Model

When we talk about about Internet it looks simple, just put the domain in the address bar of the browser and it takes you to the desired page. But when we dig deeper into networking, we get to know a lot of things and it starts to get complicated to understand the process.
But there is a model to describe and easily understand what happens when one computer connects to another computer, it is called OSI Model.
It consists of 7 layers named

Layer 1: Physical Layer
Layer 2: Data Link Layer
Layer 3: Network Layer
Layer 4: Transport Layer
Layer 5: Session Layer
Layer 6: Presentation Layer
Layer 7: Application Layer

Confused? Don’t worry I am not Wikipedia 😉 I don’t tell things which can not be understood by humans.
So first of all take a look at this picture which shows these 7 layers:

Now lets see what these layers mean:

7. Application Layer:

This is the closest layer to the user. This layer contains the program which is using the Internet. For example your internet browser comes into layer 7 but it doesn’t connects to the Internet itself. Other 6 layers help it to send and receive data over Internet.

6. Presentation Layer:

This layer represents tasks of Operating System. Network drivers reside here, this layer deals with the encryption/decryption and compression of the data as well character encoding.
If you are using a VPN, the data gets encrypted/decrypted here.

5. Session Layer:

When two computers are connected to each other they form a “Session”. Session may represent continuity like when you are talking on phone its a session. Its the reason you and the other person are interacting. This layer manages sessions, it starts sessions and terminates sessions. When you go to a website then you open a session with their server, you send and receive data and all this happens in Session Layer.

4. Transport Layer:

I personally call it Rulebook Of Packets and this is what it means. As we have previously discussed in How Data Travels Over Network? that when we have to upload/download a file it is first broken down into smaller parts called Data Packets. So this layer decides what should be the size of packets, how much should we wait before sending another packet etc.
Simply deals with the “Transport Of Data”

3. Network Layer:

This is where an IP Address reside. Everything which happens with TCP/UDP protocols happens in this layer. So basically Network Layer moves packets from source to destination.

2. Data Link Layer:

This layer is the home of MAC Addresses (Media Access Control) and Logical Link Control (LLC).
Logical Link Control identifies the protocols and helps in transmission of data as the rules of the protocol in use. It plays a very important role in LAN.

1. Physical Layer:

As its name indicates it contains things which we can touch like your broadband cable. You can basically call it the source of Internet. The layer which has the medium to connect to the Internet like your router, dial up modem, broadband cables etc.

Thanks for reading, This article ends here.
For further reading read this Wikipedia article.

Also Read: UltimaOS Skin For Windows By D3V

About the author


I am Somdev Sangwan also known as D3V. I am n00b and I love computers and hacking. I am a python freak and your friendly neighborhood hacker.


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