While the OSI model is heavily used for theoretical understanding and troubleshooting, the TCP/IP Model is a more practical framework that closely maps to how the modern Internet actually functions.
The 4 Layers of TCP/IP
- Network Access (or Link) Layer: Roughly corresponds to OSI Layers 1 and 2. It handles the physical transmission of data across a single link (e.g., Ethernet, Wi-Fi).
- Internet Layer: Corresponds to OSI Layer 3. It uses IP addresses to route packets across multiple interconnected networks.
- Transport Layer: Corresponds to OSI Layer 4. It provides host-to-host communication services using protocols like TCP (reliable) and UDP (unreliable).
- Application Layer: Corresponds to OSI Layers 5, 6, and 7 combined. It represents the protocols that end-user applications use to interact, such as HTTP, DNS, and SSH.
TCP/IP vs OSI
It is important to remember that these models are just frameworks. They do not dictate how software must be written, but rather help us categorize how it works. The TCP/IP model is simpler because it groups presentation, session, and application logic into one broad Application Layer, which accurately reflects how most modern software is developed.