Similarities and Differences between OSI and TCP/IP model

The TCP/IP and OSI models are foundational network reference models. Development of both began in the early 1970s and finished in the late 1970s, with publication occurring in the early 1980s. During the 1990s, manufacturers produced devices compatible with either model. However, by the late 1990s, the TCP/IP model became predominant, as a slower standardization process hindered the OSI model. In the 2000s, leading manufacturers transitioned from proprietary networking models to TCP/IP. Currently, the TCP/IP model is universally adopted, serving as the basis for nearly all modern computer networks and networking devices.

Why is the OSI model still part of the networking courses?

The OSI model is recognized for its comprehensive explanation and documentation, surpassing the TCP/IP model in clarity. It effectively describes complex networking concepts, protocols, and terminology in a manner that is both accessible and memorable. Both models were developed to achieve similar objectives and utilize comparable sets of standard protocols, resulting in analogous descriptions of networking concepts. Mastery of one model facilitates understanding of the other.

Consequently, although the OSI model is not supported or implemented by hardware manufacturers, it remains a core component of most networking curricula. Instruction typically begins with the OSI model, providing foundational knowledge and a layered approach that simplifies subsequent learning of the TCP/IP model.

Similarities between the TCP/IP model and the OSI model

• Both are logical models.
• Both define standards for networking.
• Both provide a framework for creating and implementing networking standards and devices.
• Both divide the network communication process into layers.
• In both models, a single layer defines a specific functionality and sets standards for it alone.
• Both models allow a manufacturer to produce devices and network components that can coexist with and work with devices and components from other manufacturers.
• Both models simplify the troubleshooting process by dividing complex functions into simpler components.
• Instead of defining the already defined standards and protocols, both models referenced them. For example, the Ethernet standards were already defined by the IEEE before these models were created. So instead of defining them again, both models used them as IEEE Ethernet standards.

Differences between the OSI model and the TCP/IP model

• The OSI model has seven layers, while the TCP/IP model has four.
• The OSI model is no longer used, while TCP/IP is still used in computer networking.
• To define the functionality of the upper layers, the OSI model uses three separate layers (Application, Presentation, and Session), whereas the TCP/IP model uses a single layer (Application).
• Just as in the upper layers, the OSI model uses two separate layers (Physical and Data-link) to define the functionality of the bottom layers, whereas TCP/IP uses a single layer (Link layer) for the same.
• To define the routing protocols and standards, the OSI model uses the Network layer, while the TCP/IP model uses the Internet layer.
• The OSI model is better documented than the TCP/IP model.
• The OSI model explains every standard and protocol in detail, while the TCP/IP model provides a summarized version of the same.

Differences between the original TCP/IP model and the updated TCP/IP model

• The TCP/IP model we use today is slightly different from the original TCP/IP model. The original TCP/IP model has four layers, while the updated TCP/IP model has five.
• The original version uses a single layer (Link layer) to define the functionality and components responsible for data transmission. The updated version uses two layers (Data Link and Physical) for the same. It defines the functions directly related to data transmission in the Physical layer and those indirectly related to data transmission in the Data-link layer.
• In the updated version, the Internet layer is renamed the Network layer.

The following figure compares the OSI reference model, the original TCP/IP model, and the updated TCP/IP model.

No matter which model you study or learn first, once you learned one, you can easily correlate it with another. Generally, the updated TCP/IP model is much or less similar to the OSI model except for the Application layer. For learning, you can think that the Application layer of the TCP/IP model does what the top three layers (Application, Presentation, and Session) of the OSI model do. The remaining layers have similar functions in both models.

Conclusion

Although the OSI and TCP/IP models differ in structure and historical adoption, both provide essential frameworks for understanding network communication. The OSI model is particularly valuable for its pedagogical clarity, while the TCP/IP model underpins contemporary networking. Studying both models offers a comprehensive perspective on network operations and interconnections, thereby facilitating understanding of current technologies and effective troubleshooting.