What is Open System Interconnection(OSI) Model ?

The Open Systems Interconnection (OSI) model is a conceptual framework for network communication that was developed by the International Organization for Standardization (ISO) in the 1980s. The OSI model provides a way to understand how data is transmitted over a network by breaking down the process into seven layers. Each layer has a specific function, and the layers work together to ensure reliable communication.

The OSI model provides a standardized way of describing network communication, which allows different network technologies and devices to communicate with each other. For example, a device that uses Ethernet can communicate with a device that uses Wi-Fi because they both follow the same OSI model. The OSI model also allows for easier troubleshooting of network issues because each layer has a specific function that can be tested independently.

However, the OSI model is a theoretical framework and does not correspond directly to the actual implementation of network protocols. In practice, network protocols are often a combination of multiple OSI layers, and some layers may be merged or omitted entirely. Nonetheless, the OSI model remains a useful tool for understanding the complex process of network communication.

Source - https://www.real-sec.com/

The seven layers of the OSI model are:

1. Physical Layer: The physical layer is responsible for transmitting raw data bits over a physical medium such as copper wires, optical fibers, or radio waves. It deals with the electrical, mechanical, and physical characteristics of the physical medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur.

2. Data Link Layer: The data link layer is responsible for the reliable transfer of data frames over a physical medium. It establishes and terminates connections between network devices, performs error detection and correction, and manages flow control.

3. Network Layer: The network layer is responsible for routing data packets from the source to the destination network. It determines the best path for data to travel and manages congestion control.

4. Transport Layer: The transport layer is responsible for ensuring reliable end-to-end communication between applications. It segments and reassembles data into packets and provides error recovery and flow control.

5. Session Layer: The session layer is responsible for managing communication sessions between applications. It establishes, maintains, and terminates sessions and provides synchronization and recovery in case of failures.

6. Presentation Layer: The presentation layer is responsible for ensuring that data is presented in a format that can be understood by the application layer. It provides data encryption, compression, and decryption.

7. Application Layer: The application layer is responsible for providing network services to user applications. It provides a user interface and manages application-level protocols such as HTTP, FTP, and SMTP.