What is the main purpose of OSI model

At the dawn of networks, most devices used proprietary software and protocols that allowed communication only with other devices of the same manufacturer or those that had access to those protocols. There were no real means of interacting outside of your organization at that time, so this wasn’t a big issue since most organizations purchased their equipment from the same manufacturer. In recent years, this has changed, and there is now a need to communicate with systems owned by other organizations. Because this equipment was unlikely to be made by the same company, it couldn’t communicate with the other organization’s devices. In order to address this, a standard model was requested that would be made publicly available for everyone to use. These two models became the standards:

• OSI (Open Systems Interconnection) model
• TCP/IP model

Networking technologies can be classified based on the OSI model layer (or layers) at which they operate. At a certain layer of the OSI reference model, knowing how that technology performs a particular function helps you determine whether or not the device will be able to communicate with another device using a similar technology at that layer. Data flows in a network from one device to another in accordance with the OSI model, which is a conceptual model. In 1984, the International Organization for Standardization (ISO) created the OSI model, and it was updated in 1994 to coordinate the development of standards for interconnected information-processing systems. The model describes seven layers, beginning with the physical connection and ending with the application. As show in the figure below, there are seven layers in OSI model.

Those are Physical Layer, Datalink Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer and Application Layer. The top three layers (Application, Presentation, and Session) are known as the upper layers. Normally, the four bottom layers (Transport, Network, Datalink, Physical) are referred to as the lower layers. For remembering the order of the layers, there are two common mnemonics: