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Introduction to Top-Down Design Approach

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While the topic may sound boring and analytical, top-down network design is actually more intricate, involving not only the technical requirements but also understanding the various business factors that affect the network you are designing. In this article, Sean Wilkins walks through this approach to designing networks and examines the many factors that go into an effective system that puts the needs of the organization first.
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For all those people already bored by the title of this article, I will attempt to make this concise enough to be interesting and help in everyday network designs. Network design, to many people, is something that sounds interesting but can also be construed into a boring, analytical task that is less interesting to the “typical” network engineer who wants to get their hands dirty. Some of this is true; the design phase of most projects does require a level of analysis and analytical tasks that require an understanding of not only the technical aspects of the networks but also the business factors that affect the network.

This article takes a look at the concept of Top-Down network design. This is one common method used to design networks where the focus is put on the needs of the business first. Top-Down design is not a process that is limited to network design; it is a concept that can be used for many other applications. Top-Down network design is simply the analysis of the needs of companies from a high level. Instead of starting a design by choosing the equipment, the design starts by taking the company requirements and needs analysis information and using it to derive a design based on high-level functional requirements.

The following sections will offer a brief review of the different phases that are used with Top-Down network design; these include:

  • Analyzing Business Goals and Constraints
  • Analyzing Technical Goals and Tradeoffs
  • Characterizing the Existing Internetwork
  • Characterizing Network Traffic

Analyzing business goals and constraints

One of the most important parts of designing a network includes a careful review of the existing business goals and constraints. Often when these are not taken into account early in a project, unneeded changes must occur mid-project that can greatly affect the schedule and budget of a project.

When reviewing the business’s goals, it is important that as much information be gathered from as many sources as possible in order to have a complete picture of the business from multiple angles. For example, if the view is only from above, many things that happen in the trenches that are important can be missed, and vice versa.

It is at this part of the project that the scope of the project must also be calculated. How the project is being handled and whether it is supported by all departments within the company that will be affected are important questions. If not, it is important that any interdepartmental issues be addressed before the project starts; this will ensure a smoother project transition. These issues are also addressed below as business constraints.

It is also important during this phase of the project to get a detailed understanding of the current network applications, as well as any additional network applications that will be sought in the future. This information is vital as part of the design process from a business and technical perspective.

Another equally important part of this phase is analyzing business constraints. There are different aspects of network design that must be carefully completed; these include a careful accounting of the politics within the company. Many projects are hindered or halted by different political factions within a company. It is vital that each of these factions be happy when a project affects their areas of operation. Budget, staffing, and scheduling issues must also be carefully addressed in order to ensure that the project has the resources available to successfully complete the project.

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