OSI (Open Systems Interconnection) Model is one of the fundamental and prominent concepts of Computer Networks. It is basically a 7 layer architecture, developed by ISO (International Organization of Standardization), with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe. In simple words, it is like a reference model for how applications communicate over a network. The OSI Model consists of a total of seven layers namely Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, and Application Layer. Undoubtedly, to understand various basic and advanced level underlying mechanisms of Computer Networks, you're first required to understand the OSI Model well.

What is OSI Model in Computer Networking? :  https://www.geeksforgeeks.org/osi-model-full-form-in-computer-networking/