Explanation/Reference:
Section: Design Methodologies Explanation
Explanation:
Most likely, you will analyze the company application requirements during the initial phase of the top-down network design approach. The top-down network design approach is typically used to ensure that the eventual network build will properly support the needs of the network's use cases. For example, a dedicated customer service call center might first evaluate communications and knowledgebase requirements prior to designing and building out the call center's network infrastructure. In other words, a top-down design approach typically begins at the Application layer, or Layer 7, of the Open Systems Interconnection (OSI) reference model and works down the model to the Physical layer, or Layer 1.
The top three layers of the OSI reference model-which are the Application layer, Presentation layer, and Session layer-should be analyzed in order to determine the design requirements. The infrastructure that is needed for the Transport layer, Network layer, Data Link layer, and Physical layer is thus determined by this analysis.
You would not route cables from a server room to workstations. This action would fall into the Physical layer of the OSI reference model. Therefore, you might start with this action if you were following a bottom- up network design approach. In contrast to the top-down approach, the bottom-up approach begins at the bottom of the OSI reference model. Decisions about network infrastructure are made first, and application requirements are considered last. This approach to network design can often lead to frequent network redesigns to account for requirements that have not been met by the initial infrastructure.
You would not license operating systems (OSes) to host network services during the initial phase of the top-down network design approach. Licensing OSes to host network services would most likely be performed in the Transport layer. In addition, you would not select switches to build out the LAN. This action would fall within the lower three layers of the OSI reference model.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 1, Top-Down Approach, pp. 24-25 Cisco: Using the TopDown Approach to Network Design (Flash)