Basics of the OSI model

Today we are going to look at one of the fundamental concepts in the world of computer networking – the OSI model. Let’s not hesitate, but dive straight into the fascinating world of network protocols and communication layers.

What is the OSI model: basic principles

The OSI (Open Systems Interconnection) model is a structured approach to organizing the work of network protocols and devices. Developed by the International Organization for Standardization (ISO), this model defines seven layers of communication, each of which performs a specific function. Here is what these seven layers look like:

OSI model layers and their functions

Layer 1: Physical Layer

The physical layer provides the physical transmission of data over the communication medium. It defines the characteristics of cables, connectors, transmission protocols, and other aspects of physical communication. This layer is responsible for converting data into signals that can be transmitted over the physical medium. Examples include Ethernet cables for wired data transmission, fiber optics for transmitting data over light signals, USB for connecting devices to a computer.

The data link layer is where data is transferred between neighboring devices on the network. It is responsible for framing, addressing devices, controlling access to the medium, and detecting errors. This layer ensures that data is successfully delivered between devices on the same network. Examples are Ethernet for wired network data transmission, Wi-Fi for wireless data transmission.

Layer 3: Network Layer

The network layer deals with the routing of data on the network. It determines the best path for data to travel between different networks and devices. It also manages data flow and error control within the network. Examples of protocols are IP (Internet Protocol) for routing data between networks, ICMP (Internet Control Message Protocol) for error reporting and network control.


Layer 4: Transport Layer

The Transport Layer ensures reliable delivery of data from one node to another. It is responsible for dividing data into packets, controlling errors, managing the flow of data, and ensuring delivery in the correct sequence. At this layer, protocols provide mechanisms for establishing, maintaining and terminating connections. Examples of protocols are TCP (Transmission Control Protocol) for reliable delivery of data in the correct sequence and error control, UDP (User Datagram Protocol) for transmitting data WITHOUT guaranteeing delivery.

Layer 5: Session Layer

The session layer establishes, maintains, and terminates communication sessions between applications. This layer controls communication and synchronization between applications by providing the means to manage sessions. It is also responsible for managing dialogs and ensuring that communication is restored when failures occur. Examples: NetBIOS for session management on Windows networks, SSH for secure remote access.

Layer 6: Presentation Layer

The Presentation Layer converts data into an exchangeable format. It provides data compression, encoding, decoding and encryption. It allows for compatibility between different data formats because applications can use different formats to represent information. Examples are JPEG for image compression, MPEG for video compression, and technologies for data security SSL (Secure Sockets Layer) and TLS (Transport Layer Security).

Layer 7: Application Layer

The application layer is where user applications interact with network services. This layer provides an interface to applications that allows programs to communicate over the network. The protocols that allow data to be exchanged between programs and users work here. Examples of protocols are HTTP for transmitting web pages, SMTP for sending e-mail.

Application of the OSI model in modern networks

The OSI model serves as a framework for understanding the interaction of devices in computer networks. Network engineers use the model to design, configure, and maintain complex network infrastructures. It helps them better understand how different protocols work and their impact on network performance and security.


The OSI model remains an integral part of the computer networking world. Understanding it allows network professionals to build efficient and reliable networks, as well as successfully diagnose and solve problems in network infrastructures. I hope that this article has helped you gain a better understanding of this important topic.

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