Network DesignMethodology

As network expectations have changed, so have design principles. Enterprises no longer rely on a single vendor, technology, or protocol. The design strategy has changed dramatically to include security and scalability as primary criteria. Security has a large impact on network design.

There is greater redundancy in network designs. Since the events of September 11, 2001, business continuity has become a priority. Organizations are focusing on increased levels of redundancy, and disaster-recovery planning is becoming a necessity. Redundancy takes many forms, including separate power sources, multiple WAN carriers, alternate cable routes, and redundant hardware. Network connectivity and services are critical components of enterprise operations. The cost of downtime is increasing at a phenomenal rate.

Enterprises are no longer locked into using a single vendor, technology, or protocol; many technologies have standardized. But designing a network is still not a trivial factor. Assessing the design criteria enables you to understand the network and what it was meant to do. Network designs must easily adapt to implement the next generation of technology. Many network designers are planning for IP telephony; these network design plans are not just for new networks but are improvements on existing ones. Properly planning networks based on sound architecture makes necessary network redesigns easier at a later stage.

Stages of the Network

Design is just one component of a network life cycle. Planning, design, implementation, operation, and optimization (PDIOO) are the stages of the network life cycle. Each stage builds on its predecessor to create a sound network that maintains its effectiveness despite changing business needs. You can apply the PDIOO methodology to all technologies. During the PDIOO process, you define key deliverables and associated actions with a direct correlation to the added value and benefit for the client's network. For example, understanding business goals, usage characteristics, and network requirements helps you avoid unnecessary upgrades and network redesigns, thereby reducing the time it takes to introduce new services in the network.

Planning Phase

During the planning stage, you can test the logic of your future design for flaws. Planning helps you avoid replicating a logical mistake in a network design that you might use as a template across a number of locations. The planning stage focuses on technical as well as financial criteria and takes into account all the requirements and constraints that were discussed in the previous section. During this phase, it is important to identify all the stakeholders in order to make this process a success. The stakeholders are people or organizations who have a vested interest in the environment, performance, and outcome of the project.

Design Phase

After completing the planning stage, you have enough information to develop a network design. If a network is already in place, use this phase to review and validate the network design as it is currently implemented. At this stage, you choose products, protocols, and features based on criteria defined in the planning stage. You develop network diagrams to illustrate what changes will occur in the network to achieve the desired results. The more detailed the network diagram and plan, the better you can anticipate the challenges during implementation.

Implementation Phase

The implementation stage provides detailed, customized deliverables to help avoid risks and meet expectations. A sound implementation plan ensures smooth deployment even when issues arise. Communicating the implementation plan to all stakeholders provides you with an opportunity to assess the viability of the plan. It is better to find mistakes on the drawing board than during implementation.

Good processes, such as change control, can effectively handle issues that occur during deployment. Change control provides flexibility because it is impossible to plan for every contingency, especially if the implementation has a long duration.

Operation Phase

The operation phase, also known as the operational-support phase, is designed to protect your network investment and help your staff prevent problems, maximize system utility, and accelerate problem resolution.

Optimization Phase

The last step in the PDIOO process is the optimization of the network. A sound design still requires optimization and tweaking to reach its full potential. The optimization of the network can be as simple as hardening servers against security threats or adding QoS to the network for latency-sensitive traffic. Hardening servers is discussed in Chapter 7, "Web Security." Figure 6-1 illustrates the PDIOO process, in which each stage builds on its predecessor.

Optimization can even lead to a redesign of the network, so the cycle would begin again.