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The Open Systems Interconnection model is a conceptual model that characterises and standardises the communication functions of a telecommunication system without regard to its underlying internal structure and technology. It is quite abstract, and each layer may not have a clear equivalent (or instance) in every context, especially in embedded systems. A layer serves the layer above it and is served by the layer below it (above = higher layer number).
| Layer | Unit | Description | |
|---|---|---|---|
| 7: Application Layer | Data | ||
| 6: Presentation Layer | The presentation layer transforms data into the form that the application accepts | ||
| 5: Session Layer | |||
| 4: Transport Layer | |||
| 3: Network Layer | |||
| 2: Data Link Layer | |||
| 1: Physical Layer | Defines the physical medium that carries the signal. |