C27 1 hr
OSI and TCP/IP models
The two communication models and how they map to each other.
OSI model (7 layers)
| Layer | Purpose |
|---|---|
| Application | User-facing protocols |
| Presentation | Encoding and encryption |
| Session | Connection management |
| Transport | End-to-end delivery |
| Network | Addressing and routing |
| Data link | Local frame delivery |
| Physical | Bits on the medium |
TCP/IP model (4 layers)
- Application — combines OSI application, presentation, and session.
- Transport — TCP and UDP.
- Internet — IP addressing and routing.
- Network access — link and physical.
Why it matters for IoT
IoT devices often use lightweight protocols at the application layer, but they still rely on IP for addressing and transport for reliability. Understanding the layers helps you isolate faults: a cable problem is physical, an unreachable host is network, a missing port is transport.
Check your understanding
- Map the OSI transport layer to TCP/IP.
- Which layer would you investigate for a cable fault?