What is OSI Model | 7 Layers Explained

OSI, or Open Systems Interconnection, was introduced by the ISO (International Organization for Standardization) in 1984. The OSI model has a 7-layer architecture, with every layer having individual functionalities. The different layers collaborate to transmit data from one individual to another worldwide. Dive into this article to gather more details about the OSI reference model and its seven layers. 

What is the OSI Model?

The OSI model is conceptual and logical in nature. It helps define network communication utilized by different systems suited for communication and interconnection with different systems. The OSI model can also efficiently describe computer packet transfer with the help of different protocol layers.  

The modern internet does not follow the OSI reference model. Instead, it follows the much simpler TCP/IP model. But the OSI model is still quite popular and helps with visualizing and communicating the operational mechanism of networks. The OSI model also helps isolate and fix networking issues.

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The OSI reference model offers the following advantages to computer network users and operators:

• Find out the necessary hardware and software for building the network
• Comprehending and conveying the process followed by different components in a network
• Performing troubleshooting and identifying which networking layer is causing an issue to resolve it quickly

The OSI reference model provides networking software vendors and network device manufacturers with the following advantages:

• Build devices and software to communicate with products from other vendors to support interoperability
• Define different parts of the network that the products should be compatible with
• Convey users at which layer their products should operate

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Characteristics of the OSI Model

A few key characteristics of the OSI reference model are as follows:

• A layer can be created where definite levels of abstraction are necessary.
• The function of every layer must be chosen according to standard international protocols. 
• Multiple layers should be present to ensure that separate functions are not found in the same layer. But the architecture also should be small enough to handle complications.
• Every layer in the OSI model depends on the next lower layer to complete primitive operations. All levels offer services to the next higher level.
• When changes are made in one layer, you don’t need to make alterations in other layers. 

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Why Use the OSI Model?

The purpose of using the OSI reference model is as follows:

• Enables you to understand communication inside a network
• Allows you to comprehend how different technologies are developed
• Separating functions into different network layers makes troubleshooting easier.
• Helps you to compare primary functional relationships available on different network layers 

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Different Layers in the OSI Model 

The seven different layers in the OSI reference model are as follows:

1. Layer 1: Physical Layer

The physical layer enables you to describe the physical and electrical characteristics of the data connection. This level develops the relationship between a transmission medium and a device. The physical layer is not concerned about the higher-layer items or protocols. 

The Primary Rate Interface is a key example of a technology operating in the physical layer. A few pieces of hardware necessary in the physical layer include networking hubs, ethernet repeaters, and network adapters.

Layer 2: Data Link Layer

The data link layer present in the OSI reference model can rectify errors present in the physical layer. This layer helps you to build a connection between two connected network devices. Using the data link layer, you will be able to describe logical addressing for easy identification of endpoints.

The data link layer found in the OSI reference model will help with the implementation of packet routing through a network. It enables you to define the best path for transmitting data from the source to the destination.

Layer 3: Network Layer

The network layer in the OSI reference model delivers procedural and functional means of transferring variable-length data sequences across different nodes connected in various networks. Every node comes with a specific address, and the network layer guarantees that the data reaches the destination address. The data is transmitted in the form of multiple fragments so that they can be connected to one another after processing.  

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Layer 4: Transport Layer

The transport layer present in the OSI model is responsible for managing the delivery of data packets. It helps with the management of data flow, error control, and segmentation and desegmentation. The different classes of the transport protocol start at TP0 and end at TP4. This stage in the OSI model is involved with the fragmentation and reassembly of data packets.

Layer 5: Session Layer

The session layer in the OSI model manages the connection between different computers in a network. This layer of the OSI model revolves around the establishment, management, and termination of remote and local applications. The session layer also looks after authentication and authorization in the OSI model. Additionally, it is responsible for ending a session or transmission after its completion.

Layer 6: Presentation Layer

The presentation layer in the OSI model ensures that the syntax and semantics can be converted into what an application understands. The data gets formatted at this stage of the OSI model before it proceeds further. Some common functions performed at this level of the OSI model include compression, compatible character code setting, and encryption. The basic purpose of the presentation layer is to serve as the network’s data translator. 

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Layer 7: Application Layer

The application layer present in the OSI model is all about interaction with the user or the user application. The application layer can determine the availability and identity of communication partners. A few key functions of the application layer in the OSI model are as follows:

Identifying communication partners, determining resource availability, and synchronizing communication

• Enabling users to log on to a remote host
• Supports different email services
• Provides distributed database sources
• Offers access to global information related to different services and objects

Learn more about OSI layers here. 

Conclusion

All layers inside the OSI model communicate with the two other layers below it. Additionally, the layers also communicate with peer layers in other networked computing systems. The OSI model facilitates interface standardization and modular engineering and minimizes complexity. Therefore, it can be a standard model in a computer networking system that can help you flexibly adapt to different protocols.