University of Michigan - Ann Arbor

Networking is broken into layers where each layer handles a single specific job and relies on the layer directly below it. This modular separation allows each layer to be designed and modified independently without disrupting the entire system.

The classic teaching framework is the Open Systems Interconnection (OSI) model, which organizes network communication into seven layers from the physical medium at the bottom to user-facing software at the top:

1. **Physical:** Transmits raw signals over physical media, including actual cables, radio waves, and electrical voltages.
2. **Data Link:** Moves data between two directly connected devices on a local segment using MAC addresses.
3. **Network:** Moves packets across multiple interconnected networks using logical IP addresses.
4. **Transport:** Provides end-to-end delivery between specific programs (such as via TCP and UDP).
5. **Session:** Manages and coordinates ongoing conversations between applications.
6. **Presentation:** Formats and encrypts data for presentation or transmission.
7. **Application:** Represents the software interface that users directly interact with, such as web browsers and email clients.

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