Network Models

In this second chapter in this Exam Cram, you learn about the basics of internetworking. This chapter also introduces you to the different network models used to maintain, organize, and troubleshoot Cisco systems.

In this chapter, you learn about three network models, the OSI Reference model, the Troubleshooting model, and the Cisco Hierarchical model. You need to know about one other model, the TCP/IP Internetworking Model. That model is covered extensively in the next chapter.

Reference models provide many advantages to system engineers by dividing the complexities of network operations into a more manageable set of individual layers. Reference models also allow changes to occur in one layer without having an impact on, or disabling the responsibilities of, other layers . This enables specialization in development for equipment and application developers by allowing new features for old products and new products to be developed. As a result, using reference models allows you to conceptually take a part from one vendor and replace it with a part from another vendor. In a way, a network model defines standard interfaces for "plug and play" multivendor integration.

The Open Systems Interconnection (OSI) model is the primary architectural model used in creating standards in today's networks. This model has seven hierarchical layers. Each of the layers help companies in the industry create a standard method to communicate between disparate systems.

Cisco also supplemented the OSI model with its own three-layer hierarchical network model that should be used to build, implement, troubleshoot, and maintain any size network that uses Cisco equipment. This model allows you to effectively build, maintain, and troubleshoot any size network.