What is OSI Model?

What is OSI Model?


The OSI (Open Systems Interconnection) model is a theoretical framework that describes the process of communication between two end devices in a network. It consists of seven layers, each of which performs specific functions and represents a different aspect of communication.


Layers in Detail of OSI Model

The following are the 7 layers of the OSI model:-

  1. Physical Layer (Layer 1) - This layer is concerned with the transmission of raw bits over a physical medium, such as copper or fiber-optic cables. It defines the electrical, mechanical, and functional specifications of the interface between the devices and the physical media.

  2. Data Link Layer (Layer 2) - This layer takes care of the reliable transmission of data frames over the physical layer. It performs functions such as error detection and correction, flow control, and media access control.

  3. Network Layer (Layer 3) - This layer is responsible for routing data packets from the source to the destination. It performs functions such as network addressing, routing, and forwarding.

  4. Transport Layer (Layer 4) - This layer is responsible for end-to-end communication between the applications. It performs functions such as error-free transmission, flow control, and reliability.

  5. Session Layer (Layer 5) - This layer establishes, maintains, and terminates connections between applications. It provides synchronization, checkpointing, and recovery services.

  6. Presentation Layer (Layer 6) - This layer provides a common format for data representation, encryption, and compression. It is responsible for data translation and code conversion.

  7. Application Layer (Layer 7) - This layer is the top layer of the OSI model and interacts directly with the applications. It provides services such as file transfer, remote file access, and email services.

Note: The OSI model is a theoretical construct and is not strictly followed by all network protocols. However, it is a useful reference for understanding the different aspects of network communication and how they are organized.


The OSI model was developed by the International Organization for Standardization (ISO) in the late 1970s and early 1980s. The development of the OSI model was motivated by the need for a common reference model for communication between different computer systems. The model was designed to provide a framework for understanding how different protocols and technologies interacted with each other, and to serve as a basis for the development of open, vendor-independent communication standards. The OSI model was created through a collaborative effort involving experts from various countries and organizations. The development process involved extensive discussions, negotiations, and agreements among participating experts to define the functions and responsibilities of each layer of the model. The final result was a seven-layer model that provided a comprehensive and structured description of the communication process between end devices in a network.

The OSI model has since become widely recognized and widely used as a reference model for network communication. It has served as the basis for the development of many communication protocols, including TCP/IP, and has been instrumental in facilitating communication between different computer systems and networks. The OSI model continues to be a relevant and useful reference for understanding and designing communication systems in the modern digital age.