OSI Model vs. TCP/IP Model

 The OSI Model (Open Systems Interconnection) is essentially a reference model that helps IT technicians understand the different layers. For the TCP/IP Model, this is the Transmission Control Protocol/ Internet Protocol that is a functional model and is how the layers actually work. There are seven OSI layers compared to the four TCP/IP layers. The OSI model was made by the International Organization for Standardization as a conceptual model.

OSI Model

The best way to think about the OSI Model is to break it down into layers. These are from the bottom to the top and starts with layer 1 which is the Physical layer, layer two is the Data Link layer, the Network layer, Transport layer, Session, Presentation and layer 7 which is the Application layer. By using the Please Do Not Throw Sausage Pizza Away mnemonic you can remember these layers.

The Physical layer is the actual hardware, cabling, and wireless mediums and uses encapsulation to go to the Data Link layer which are frames. The Network layer uses packets and encapsulates the frames into packets. By the fourth layer, the Transport layer, the packets are encapsulated by ports.

With the Session layer, the ports are encapsulated by sessions which interact with layer six to allow for encryption and then the Application layer which is by that point data. By understanding these layers, you can understand more about what the TCP/IP Model is about and why it is easier to troubleshoot with the OSI model. The OSI model is also used by vendors that create hardware and software to be interoperable.

TCP/IP Model

In the TCP/IP Model there are four layers which are the Network Access layer that corresponds to Layer 1 and 2 of the OSI Model, the Internet layer for Layer 3, Transport layer for layer 4, and the Application layer which corresponds with layers 5, 6, and 7 of the OSI Model. This model was developed by the Department of Defense and is a practical standard for internet communications.

Conclusion

By learning more about the OSI and TCP/IP models you can understand how to troubleshoot more effectively. There are some encapsulation and decapsulation items going up and down the TCP/IP stack at the same time. This allows for effective communication across systems. When you understand this at a deeper level you can go for more advanced certifications like the CCNP or even the CCNA.