Because networking is complex, communication tasks are divided into modular layers where each layer performs a specific job and relies on the layer beneath it. This separation allows individual protocols and technologies to evolve independently.

The theoretical benchmark is the seven-layer OSI Model:

1. Physical: Transmits raw physical signals, cables, radio waves, and voltages.
2. Data Link: Moves data between directly connected devices using MAC addresses.
3. Network: Routes packets across multiple networks using IP addresses.
4. Transport: Manages end-to-end communication between programs (e.g., TCP and UDP).
5. Session: Manages ongoing communication sessions between applications.
6. Presentation: Handles data formatting, translation, and encryption.
7. Application: Interfaces directly with user-facing software such as browsers and email clients.

In practical Internet implementations, the simplified four-layer TCP/IP Model is used, comprising the Link, Internet, Transport, and Application layers. Communication relies on encapsulation: as data moves down the protocol stack on the sending device, each layer attaches its own header. Upon arrival at the receiving host, data moves upward through the stack as each header is inspected and stripped away in turn.