The OSI Model Explained: A Practical Guide for Developers

The OSI model can feel like academic fluff, but it's the map of the entire internet. Let's break down the layers from a developer's perspective.

Layers 7-5: The Application Space

This is where your code lives. Layer 7 (Application) is HTTP, DNS, and SSH. Layer 6 (Presentation) handles SSL/TLS and Data Formatting (JSON). Layer 5 (Session) manages the longevity of your connection.

Layer 4: Transport

This is the domain of TCP and UDP. It handles data integrity (retransmission) and port numbering.

Layer 3: Network

This is where IP Addresses and Routers live. It's responsible for finding the path between two different networks.

Layers 2-1: The Physical Space

Layer 2 (Data Link) is about MAC addresses and Ethernet frames. Layer 1 (Physical) is the actual electricity or light traveling through cables.