Definition
The OSI model, or Open Systems Interconnection model, is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. Each layer represents a specific set of protocols and services, progressing from the physical transmission of data to the user interface. This layered approach allows different network technologies and protocols to interoperate seamlessly. In practice, it helps network professionals troubleshoot connectivity issues by isolating problems to a specific layer. Understanding the OSI model is crucial for designing, implementing, and securing complex networks. For instance, when you browse a website, your request travels up through the application and presentation layers, then down through the network and physical layers to reach the server. It is often confused with the TCP/IP model, which is a more practical, four or five layer implementation of similar concepts. This model is frequently referenced in networking certifications like CompTIA Network+ and CCNA, as well as in security exams such as Security+ and CISSP.