What is the OSI Model- Explained 7 Layers of OSI Model

Introduction

The ISO – ‘International Organization for Standardization’, developed the popular OSI model in the year 1984. It has a seven-layer architecture, with each layer carrying out a specific job. Additionally, all 7 of these layers cooperate to transport data from one person to another across the world.

Let's dive deep into the topic through this blog on OSI. Know about the popular 7 layers in OSI and their role.

Definition of OSI Reference Model

The OSI full form is the Open Systems Interconnection Model. It is a conceptual framework that helps describe the operations of a networking system. Moreover, this model categorizes computing functions into a universal set of guidelines and requirements. This facilitates interoperability across various goods and software.

Furthermore, in this model, the communications between a computing system are split into 7 different abstraction layers.

What is OSI Model in Computer Network?

Users of computer networks are spread out all over the world. Thus it is crucial to develop systems that can communicate with each other. It will ensure national and international data communication. The creator of this system is the International Organization for Standardization or ISO. This system is now popular as the OSI reference model.

The architecture of the ISO-OSI paradigm has seven layers. It outlines the seven tiers or layers making a whole communication system.

7 Layers of OSI Model

Layer 1: Physical Layer

This is the lowest layer of the OSI reference model. It takes care of the actual physical connection between the devices. This layer of OSI stores information in the bits format. It is in charge of sending specific bits from one node to the next.  On receiving the data, this layer takes the signal and converts it into 0s and 1s. Then it sends them to the Data Link layer, which rejoins the frame.

Layer 2: Data Link Layer (DLL)

The data link layer delivers the message from the node-to-node. This OSI model layer provides error-free data flow from one node to another over the physical layer. It also transmits a packet to the host using its MAC address when it enters a network.

Layer 3: Network Layer

The network layer allows the transfer of data between hosts that are part of various networks. It also handles packet routing via the shortest route from various options to transmit the packet. The network layer inserts the IP addresses of the sender and receiver in the header. 

Layer 4: Transport Layer

The network layer transfers services to the application layer through this layer of the OSI. ‘Segments’ is the name of the data in OSI’s transport layer. It is in charge of ensuring that the entire message arrives from beginning to end. Additionally, this layer confirms the successful data transmission and retransmits the data if an error occurs.

Layer 5: Session Layer

The next OSI model layers is the session layer. It controls the conversations between different computers. It sets up, manages, and terminates the connection between machines. This layer's services also include authentication and reconnections.

Layer 6: Presentation Layer

This layer prepares data for the application layer. It specifies how two devices should compress, encrypt, and encode data such that it appears correctly on the other end. Any data sent by the application layer gets ready for transmission over the session layer by the presentation layer.

Layer 7: Application Layer

In the 7 OSI layers, the layer "closest to the end user" is the Application Layer. Thus, it shows incoming data to the user after receiving input from the user directly. However, apps do not exist at the application layer themselves. The layer instead makes links with apps on the other end by allowing communication across lower layers.

How does OSI Model Work?

The basic concept behind OSI is that there are seven different categories of linked functions or levels. These levels help in classifying how two endpoints in a network communicate with one another. So, every program or user that communicates uses a device that supports seven layers.

Each layer in this layout provides services to the layers above it and receives services from the layers below it. Therefore, in a given message between users, the data will move via the levels of the source computer across the network. It will then move up through the layers of the receiving computer. The only layer in the stack that does not offer services to a lower-level layer is the application layer at the top.

OSI Reference Model Advantages and Disadvantages

The following are a few benefits of the OSI model:
 

1. It supports both connection-oriented and connectionless services. Users may use connectionless services to send data over the internet more quickly. Whereas when they need reliability, they can use the connection-oriented model.
2. The model is adaptable to many different protocols.
3. In comparison to bundling all services into one layer, the model is more flexible and safe.
4. The OSI reference model also serves as a standard model for computer networking.

The following are some of the OSI’s drawbacks:
 

1. It doesn't specify a specific protocol.
2. The presentation layer deals with user interaction. Whereas the session layer is useful for session management. But, both are less useful than other OSI layers.
3. The transport and data-link layers, for example, duplicate some services at different layers.
4. Each layer must wait to receive data from the one before it; layers cannot operate in parallel.

Conclusion

OSI model is a conceptual framework to explain the operations of a networking system. The model also categorizes computing functions into a global set of rules and requirements. Hence, it promotes interoperability between various hardware and applications.  The connections between computing systems fall into seven distinct abstraction levels in the OSI reference model. They are Physical, DLL, Network, Transport, Session, Presentation, and Application.