Lesson 19: Introducing the TCP/IP Model (Comparison to OSI)
While the OSI model is excellent for teaching networking concepts, the protocol standard actually used by the modern internet is the TCP/IP Protocol Suite (Transmission Control Protocol/Internet Protocol).
Why Two Models?
The TCP/IP model was developed earlier and is a practical standard defined by the IETF (Internet Engineering Task Force). It is more streamlined than the theoretical OSI model.
TCP/IP Layer Structure
The TCP/IP model simplifies the structure into four core layers:
| TCP/IP Layer Name | Corresponds to OSI Layers |
|---|---|
| 4. Application Layer | Application (7), Presentation (6), Session (5) |
| 3. Transport Layer | Transport (4) |
| 2. Internet Layer | Network (3) |
| 1. Network Access Layer | Data Link (2), Physical (1) |
Key Differences
- Layer Consolidation: TCP/IP combines the top three layers of OSI into one Application layer and the bottom two into one Network Access layer.
- Focus: OSI is conceptual, focusing on what needs to happen. TCP/IP is protocol-driven, focusing on how the protocols (TCP, IP) accomplish the task.
- Reliability: In TCP/IP, reliability functions (like error detection and sequencing) are handled at the Transport layer (TCP) and the Application layer, rather than strictly at the Data Link layer.
Conclusion: We use the OSI model to understand where functions occur, but we use the TCP/IP model to implement them.