Writing a Design Document


Role of the Design Document.  Regardless of whether or not your customer gave you a detailed RFP- Request for Proposal you are going to need to give them some sort of document detailing your design decisions.  If the customer gave you an RFP your document should follow the format specified in the request, though this depends mostly on the degree of strictness represented in the proposal.

If you didn't receive a  detailed RFP with a lot of well specified requirements then you are likely to want to follow the steps outlined in Teare.  The content of the Design Document should contain the following sections.

  • Executive Summary
  • Design Requirements
  • Design Solution
  • Summary
  • Appendixes
  • The cost of the proposed design
    • this may be provided separately

The following sections give more detail and correspond to the sections listed above.

Section 1 - Executive Summary.  The executive summary is directed at the key decision makers for the project.  It should be no more than two pages.  Make sure to elucidate benefits that you can offer.

  • Purpose of the Project - including one or two paragraphs that state the purpose of this document as it relates to the company's strategic objectives
  • Strategic Recommendations - including one or two paragraphs that outline your internetworking design strategy
  • Implementation Considerations - including one paragraph that lists implementation considerations for the project, such as integration issues, training, support and transition issues
  • Benefits of the Solution - summarizing the overall benefits of your solution while making sure they relate to the overall corporate strategic objectives

Section 2 - Design Requirements.  This section is likely to include your characterization of the existing network in addition to what you perceive as the new requirements.  The two most likely subsections may well be the following.

Characterization of the Existing Network - including the following items and more

  • A description of the existing network, including a topology map if available
  • Current applications, protocols, topology, and number of users
  • Business issues relevant to the network design project
  • Health of the customer's existing network

Customer Requirements - likely to include the following items and more

  • Requirements for performance, security, capacity and scalability to support new applications
  • Flow of information for new applications

Section 3 - Design Solution.  Describe the recommended solution along with its benefits and major features.  Make sure to prioritize the presentation according to the customer's needs.  The following list contains the most frequently used components.

  • Proposed Network Topology - Including a topology map and the advantages offered by the new network topology.
  • Hardware and Media Recommended for the LAN - Including features and benefits of each component, related to the customer's needs for performance, security, capacity and scalability.
  • Hardware and Media Recommended for the WAN - Including features and benefits of each component, related to the customer's needs for performance, security, capacity and scalability.
  • Network Layer Addressing Model - Including an addressing model and naming model for all components on the network, related to the customer's needs for performance, security, capacity and scalability.
  • Routing and Bridging Protocols Recommended for the Network - Including recommended routing and bridging protocols related to the customer's needs for performance, security and capacity.
  • Software Features Recommended for the Network - Include things such a access lists, proxy services, encryption, compression and queueing.  Relate your selection of software features to the customer's needs for performance, security, capacity and scalability.
  • Network Management Strategy - Including recommended products and protocols related to the customer needs.  Include a description of a proactive network management strategy.

Section 4 - Summary.  This section includes a summery of the proposed solution and reiterates how it meets the customer's needs.

Section 5 - Appendixes.  Include as many appendices as required to provide necessary detailed information.  Be sure to consider how much content your customer will be able to read and comprehend.  Always keep in mind the customer's capacity for considering large amounts of information.

Appendixes may include the following content.

  • A list of contacts for your firm and the customer's site.
  • A project implementation or time schedule
  • Details of addressing and naming schemes that you developed for the customer
  • Details of strategies for managing the network that is being developed
  • Results of prototype tests
  • Test results of any performance measurements you performed on the customer's current network.

Section 6 - Cost.  The cost of your design should be presented in enough detail so that the customer can understand how the total cost was determined.  It may be important to itemize equipment costs and installation costs.

If appropriate, ongoing network operation costs should also be specified.

This section may well be provided separately from the rest of the document for any number of reasons, so make sure to find out how the customer wants this organized.