The OSI model (Open Systems Interconnection) describes networking in seven layers, from physical cables up to applications. Data moves down the layers on the sender and back up on the receiver.
| Layer | Name | Examples |
|---|---|---|
| 7 | Application | HTTP, FTP, DNS, SMTP — apps and APIs |
| 6 | Presentation | Encryption, compression, encoding (TLS, JPEG) |
| 5 | Session | Sessions and connections (sockets) |
| 4 | Transport | TCP, UDP — segments, ports, reliability |
| 3 | Network | IP — routing, packets, addresses |
| 2 | Data Link | MAC, switches, frames (Ethernet) |
| 1 | Physical | Cables, signals, bits |
Mnemonic
Top to bottom: "All People Seem To Need Data Processing" (Application, Presentation, Session, Transport, Network, Data Link, Physical).