OSI Model (Quick Summary)

OSI Model (Open Systems Interconnection) is a conceptual model that divides the functions of a network into 7 layers so that hardware and software from different manufacturers can communicate properly.

The 7 Layers (Top to Bottom)

1. L7 - Application Layer: The layer that directly interacts with users through applications (Protocols: HTTP, HTTPS, FTP, SMTP, DNS)
2. L6 - Presentation Layer: Responsible for translation, encryption, and data compression so other systems can understand (Formats: JSON, JPEG, SSL/TLS)
3. L5 - Session Layer: Establishes, manages, and terminates the connection (Session) between two applications
4. L4 - Transport Layer: Ensures data delivery (End-to-End Communication) by breaking data into small pieces called Segments (Protocols: TCP, UDP)
5. L3 - Network Layer: Responsible for finding the optimal path (Routing) to send data across the network using Packets (Protocols: IPv4, IPv6, ICMP / Devices: Router)
6. L2 - Data Link Layer: Transmits data between directly connected nodes (Node-to-Node) using Frames and handles physical-level errors (Addressing: MAC Address / Devices: Switch)
7. L1 - Physical Layer: Transmits raw data as electrical currents or electromagnetic waves (Bits 0 and 1) over cables or Wi-Fi signals