OSI (Open Systems Interconnection) Model

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers. Each layer serves a specific purpose and interacts with adjacent layers to provide a structured approach to network design and communication. The model was developed by the International Organization for Standardization (ISO) to facilitate communication between different systems and vendors.

<> Here are the seven layers of the OSI model, from the lowest to the highest:

> Physical Layer:

Concerned with the physical connection between devices. It deals with the transmission and reception of raw data bits over a physical medium, such as cables or wireless signals.

> Data Link Layer:

Responsible for the reliable transmission of data frames between devices on the same network. It handles issues like framing, error detection, and media access control.

> Network Layer:

Focuses on logical addressing and routing of data between devices on different networks. It determines the best path for data to travel from the source to the destination across multiple networks.

> Transport Layer:

Ensures reliable communication between devices by providing error detection, flow control, and segmentation of large messages into smaller segments. It also manages end-to-end communication and can operate in connection-oriented (like TCP) or connectionless (like UDP) modes.

> Session Layer:

Manages sessions or connections between applications on different devices. It establishes, maintains, and terminates communication sessions, allowing for synchronization and coordination between applications.

> Presentation Layer:

Handles data translation, encryption, and compression to ensure that information sent from one system is properly understood by the receiving system. It also deals with character set conversions and data formatting.

> Application Layer:

Provides network services directly to end-users or applications. It encompasses the protocols and interfaces used by software applications to communicate over the network, such as HTTP for web browsing or SMTP for email.

The OSI model serves as a conceptual tool for understanding and discussing network interactions. In practice, the more commonly referenced model is the TCP/IP model, which has fewer layers (Application, Transport, Internet, and Link). The concepts, however, remain similar between the two models.