Open Systems Interconnection OSI Reference Model Explained For Beginners

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OSI reference model explained for beginners

1. Are you a beginner in the networking world?
2. Are you shifting your current IT career to become a networking expert?
3. Are you new to the networking world and want to start from the basics first?
4. Are you a fresher in the networking domain?
5. Do you want to know what is OSI model all about and how can you easily understand it and remember it through the rest of your networking career?
6. Do you want to understand the history of OSI model and the functions of the OSI model and the purpose of the OSI model in detail?
7. Have you started preparing for your CompTIA N+ or Cisco CCENT exam?

If your answer is yes then please read this article as the first thing that you will have to understand in the networking domain would be the OSI reference model.

This article is for all of you out there who have started your career in the networking domain.

All of you who are new to this networked world you must completely know and understand that if you want to understand the bits and pieces of networking than there is no other way to do this other than to study the OSI reference model first.

OSI reference model will give you the foundational basics and the core knowledge that you need in order to sustain your career in this networking world.

Whatever your end goal is whether you like to get certified in CompTIA N+ certificate or Cisco CCENT or Cisco CCNA for that matter, OSI reference model will build your basics from the scratch and there is no way you can bypass this important step and jump to hardcore commands and configurations directly.

Open Systems Interconnection Model OSI Model Explained

Now let us understand what exactly do we mean by OSI Reference Model.

• Open Systems Interconnection Model was developed by International Organization for Standardization (ISO).
• The main purpose of creating the OSI model is to create interoperability among different systems and to promote vendor-neutral network systems.
• It is used as a guide to understanding how data travels across the network.
• OSI reference model is a communication model.
• All these 7 layers play an important role in the actual network communication that happens between 2 hosts.
• OSI model describes how data from one host travels to another host across the network using the physical media.
• OSI is a model and not a protocol that you can install in your Windows or Linux machines or in any system for that matter, this is just a reference model to understand how actual network communication happens between 2 hosts.
• The layered approach helps you in isolating faults in the network quickly and also helps you to troubleshoot the network issues more easily.
• OSI model is used as a reference model to help in understanding how data flows between 2 systems.

What is a Host?

If you don’t know what a host is then let me explain that to you first before going ahead. A host can be a node on the network which means any system, server, client etc. can be referred to as a host.

1. The seven layers of the OSI model can be divided into 2 parts, upper layers part and lower layers part, where Layers 5, 6 and 7 come under the upper layers part and layers 1 to 4 come under lower layers.
2. Upper layers includes the application, presentation, session layers and lower layers include the transport, network, data link and physical layers
3. Upper layers are responsible for all the transactions that are happening at the host level or at the software or application level.
4. Lower layers are responsible for the physical transport of data and all the transactions that are taking place physically across the network.
5. The highest layer 7 is closest to the end user where the end user actually interfaces with the network using the application software.
6. Each layer in the OSI reference model has a specific role and responsibility that it is responsible for.
7. OSI model explains to us how hardware and software layers work together in integration to make the network communications possible between 2 hosts.

• Layer 7 also known as the Application layer.
• Layer 6 also known as the Presentation layer.
• Layer 5 also known as the Session layer.
• Layer 4 also known as the Transport layer.
• Layer 3 also known as the Network layer.
• Layer 2 also known as the Data Link layer.
• Layer 1 also known as the Physical layer.

Data communication in the OSI model starts from the application layer (top layer) of the layered stack at the sending side.

The data then travels down the stack to the sender’s physical layer (lowest, bottom) layer.

Then after that, the data traverses the physical network connection to the physical layer(bottom layer) on the receiving side, and then it goes up in its receivers OSI model stack.

I think that this data flow can be better explained below by the encapsulation and decapsulation process which I have described here for your reference.

Encapsulation and Decapsulation Process explained

All layers perform services to all the layers above them and below them, we will discuss these seven layers separately in different upcoming articles and videos, and also describe how actual data flow happens in the OSI reference model.

Data encapsulation and decapsulation is nothing but a process that specifies the actual transfer of data between the different layers.

Encapsulation happens at the transmitting end for the host who is sending data, and decapsulation happens at the receiving end for the host who is receiving the information.

In the encapsulation process the data goes down from layer 7 to layer 1 and is then sent to the receiving end and in decapsulation, this process is reversed.

Computer Networking Pdf

With the exception of the lowest layer in the OSI networking model, no layer can pass any data directly to its peer layers. On the contrary, all the data on the sending computer must be passed down through each successive layer until it reaches the physical layer and then passed back up at the receiving end of the receiving host.

We will discuss this in more detail in the upcoming articles when we will discuss the functionality of each layer in the OSI model in detail.

Conclusion

Believe it or not, almost all the networks in the world are based in some way or the other on the OSI model. This makes learning this topic more than worthwhile.

It is difficult to understand about the networking technology without making any references to the OSI model and its layers because the model’s framework actually helps you in developing your basic understanding about how these protocols work together at different layers.

By understanding the OSI model you can also then understand which protocols and devices can interoperate with each other when new technologies are developed and explained. I hope that feels good now!

If you have any questions about any of the topics that I have discussed here in terms of the OSI model then please feel free to comment below in case of any queries on what I have discussed here.

Do you still need more help on understanding OSI reference model explained for beginners ?

I hope that if you have read this far then this article and my Youtube video would have answered any questions that you may have by now, but still by any chance if you believe that any of the steps that I have mentioned in my post above is still not clear and is not making any sense to you then please watch this video that I have created wherein I discuss all these steps in depth.

If you still have any more questions then please feel free to contact me and I will make sure that I will personally respond back to your emails as soon as I can.

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Luv Johar is the founder-editor of Aaj Ka Tech.

Luv Johar is having “practical and hands-on expertise” for around a decade in the Information Technology domain.

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