Explanation/Reference:
Section: Design Methodologies Explanation
Explanation:
Most likely, you will consider business goals, existing and future network services, technical objectives, and applications if you are using structured design principles to generate a model of the completed system if that system is being planned by using the top-down design method. 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. 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. In order for the designer and the organization to obtain a complete picture of the design, the designer should create models that represent the logical functionality of the system, the physical functionality of the system, and the hierarchical layered functionality of the system.
Because a top-down design model of the completed system is intended to provide an overview of how the system functions, lower OSI-layer specifics such as network protocols should not be included in the model.
Therefore, you should not consider the network protocols that will be implemented. Nor should you consider the network topologies or network hardware components. Those components of the design should be assessed in more specific detail in the lower layers of the OSI reference model.
Reference:
Cisco: Using the Top-Down Approach to Network Design: Structured Design Principles (Flash)