OSI Layers

In short: The seven OSI layers divide network communication into levels that build on each other.

In more detail: Each layer does one job and uses the services of the layer below. The model was developed by the ISO.

In Depth

The seven layers

1. Physical (Physical): cables, radio, signals.
2. Data link (Data link): frames, MAC addresses, switches.
3. Network (Network): IP, routing.
4. Transport (Transport): TCP, UDP.
5. Session (Session): manage connections.
6. Presentation (Presentation): format, encoding, encryption.
7. Application (Application): HTTP, DNS, SMTP.

Mnemonic

Mnemonic for 7 to 1: “All People Seem To Need Data Processing.” See OSI model.

See also: OSI Model, OSI Layer: Transport, OSI Layer: Application