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CCNA Certification All-In-One For Dummies by Silviu Angelescu

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Chapter 4: Data Encapsulation

Exam Objectives

Describing data encapsulation

Describing how data encapsulation relates to the OSI network reference model

Describing how data encapsulation enables the layers of the OSI network reference model to be independent of each other

Describing protocol data units (PDUs) and showing how they relate to data encapsulation

Read this chapter to find out about data encapsulation: what it is, how it works, and what its purpose is. You also read about protocol data units (PDUs) and see how they relate to data encapsulation. Diagrams illustrate data encapsulation and wrapping and unwrapping of PDUs at each OSI layer.

Introducing Data Encapsulation

Network models, including TCP/IP, use encapsulation and very clearly defined interfaces between layers to achieve independence of layer functionality.

Independence of layer functionality is crucial because it allows layers to evolve internally without impacting other layers. As long as a layer continues to interact the same way with upper and lower layers, it can change internally to adapt to new technologies and needs.

Independence of layer functionality also divides the network communication process into several precise specialized subprocesses. Each network model layer handles a specific subprocess. This eases management of the whole network communication process. It also allows each layer to specialize to specific network communication contexts, even to new unforeseen contexts. For example, the physical ...

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