Understanding Network Layer Models: OSI Model
In our opening module, we talked about how there are lots of competing network layer models. We've been working from a five-layer model, but you'll probably run into various other models during your career as an IT support specialist. Some models might combine the physical and data link layers into one and only talk about four layers. But you might remember a certain model we called out specifically in a reading section back in the first module. This is the OSI or Open Systems Interconnection model.
🧩 The Seven Layers of the OSI Model
This model is important to understand alongside our five-layer model because it's the most rigorously defined. That means it's often used in academic settings or by various network certification organizations. The OSI model has seven layers and introduces two additional layers between our transport layer and our application layer.
Physical Layer: Deals with the physical transmission of data through media such as cables or wireless signals.
Data Link Layer: Handles the reliable transmission of data frames between nodes on a network.
Network Layer: Manages the addressing and routing of data packets between different networks using IP.
Transport Layer: Ensures reliable delivery of data by providing end-to-end communication channels using protocols like TCP and UDP.
Session Layer: Facilitates communication between applications and the transport layer, managing session establishment, maintenance, and termination.
Presentation Layer: Ensures that data from the application layer is properly formatted, encrypted, or compressed for successful transmission.
Application Layer: Provides interfaces and protocols for different applications to access network services.
🔄 The Relationship with the Five-Layer Model
While the OSI model introduces the session and presentation layers, our five-layer model combines these functions into the application layer. We believe a five-layer model is the most useful for understanding day-to-day networking. However, the seven-layer OSI model is also prevalent in certain contexts.
No networking education would be complete without understanding the basics of the OSI model.
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The OSI model provides a comprehensive framework for understanding network protocols and communication. While the five-layer model is more practical for everyday networking, the OSI model remains an important reference in academic and certification settings.
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