OSI Model — 7-layer networking model.
Seven Layers:
7. Application — HTTP, FTP, SMTP
6. Presentation — SSL/TLS, encryption
5. Session — session management
4. Transport — TCP, UDP
3. Network — IP, routing
2. Data Link — Ethernet, MAC
1. Physical — cables, signals
Data Flow:
Sender: Application → Physical
Receiver: Physical → Application
Each layer adds/removes header
Mnemonic: "Please Do Not Throw Sausage Pizza Away"
TCP/IP Model (4 layers):
4. Application (5,6,7)
3. Transport (4)
2. Internet (3)
1. Network Access (1,2)