OSI (Open Systems Interconnection) Model: 7 Layers
Physical -> Data Link -> Network -> Transport -> Session -> Presentation -> Application
- Layer 1 (Physical) agrees on how to transmit and receive data in a physical medium; the medium, the voltage, and RF details.
- Layer 2 (Data Link) adds MAC addresses, which can be used for named communication on the local network.
- Layer 3 (Network) allows the packets to pass through different networks – Routing.
- Layer 4 (Transport) adds TCP (reliability) or UDP (Speed)
- TCP ensured data is transmitted in the correct order and adds error checking.
- Ports allow different communication to the same host.
- Layer 5 (Session) adds the concept of sessions between client and server.
- Layer 6 (Presentation) adds the data conversion, encapsulation, and compression – TLS.
- Layer 7 (Application) is where protocols (HTTP, SSH, FTP) are added.