What is OSI Model? 7 layers of the OSI Model Explained (2023)

Imagine you are on your computer and you want to send an image to your friend who is on a different computer. You can use a wire and connect both computers to transfer this image. But wait! There are some problems with this. How do you guarantee that the computer which your friend has can make sense of the data which is being sent to him? The cable will send data in the form of electric signals (0s and 1s). You need to follow a set of rules to convert your file data to a transferable form of 0s and 1s. Your friend's computer would also need to follow the same set of rules to recreate the image from the received binary data. This set of rules is what the OSI Model is all about.

You might be wondering - "Hey Gourav, Why did you include this in your Backend Development Series? We don't care about the OSI model in the backend. The OSI model is all about computer networks". Well, you are partly correct. As a software developer or software architect, there are actually situations where you can implement certain parts of code or design your system in a better way if you are aware of the underlying technology and how things work in computer networks, even though you do not actually use these inner details. So if you are someone who is a software developer or a computer networks engineer or someone who wants to know about about the OSI model, this blog is for you.

So, let's dive right in -

1. What is the OSI Model?

2. Who Developed The OSI Model?

3. The 7 layers of the OSI Model Explained

4. What is a layer?

5. OSI Model Layer 7: Application Layer

6. OSI Model Layer 6: Presentation Layer

7. OSI Model Layer 5: Session Layer

8. OSI Model Layer 4: Transport Layer

9. OSI Model Layer 3: Network Layer

10. OSI Model Layer 2: Data Link Layer

11. OSI Model Layer 1: Physical Layer

12. Comparison of the OSI model to the TCP/IP model

13. How to remember the OSI Model 7 layers – Mnemonic tricks

14. My thoughts and Conclusion - Why does the OSI model matter?

1. What is the OSI Model?

OSI Model in computer networks

OSI stands for Open Systems Interconnection. It can be defined as a conceptual framework that maps the various functions of a communication system in seven layers. The International Organization for Standardization (ISO) defines these layers and what each layer does. In layman's terms, the OSI model basically ensures that different computer systems send information to each other in a standardized way. Once you learn the OSI model, you will be able to relate to and appreciate more how the Internet works.

2. Who Developed The OSI Model?

The OSI (or Open Systems Interconnection) model was invented in 1984 by the International Standardization Organization - ISO and contains 7 layers namely- The physical layer, Data Link layer, Network layer, Transport layer, Session layer, Presentation layer, and Application layer.

Each layer can have its own set of protocols. The OSI (or Open Systems Interconnection) model is an industry effort that aims to get participants in the industry (hosting vendors, ISPs, and even individuals) to agree on common network standards. Luckily, this standardization also means that there is a higher chance of seamless interoperability across different vendors' networks - which helps everyone!

3. The 7 layers of the OSI Model Explained

OSI Model 7-layered Architecture

What is a layer?

A layer can be thought of as a logical way of grouping behaviors of the network. In the OSI model, the layers are organized from the least physical or tangible to the most tangible form.

Every layer actually comprises a set of protocols that help to ensure standardization while data transferring.

Just to be clear, the OSI model is the conceptualization of how communication should happen, and not the actual strict rules. As mentioned, the OSI model consists of 7 layers. Let's look at them one by one as to how data flows through the OSI Model.

Spoiler Alert! These are the 7 layers of the OSI model.