Analyze requirements. In this phase, the network analyst interviews users and technical personnel to gain an understanding of the business and technical goals for a new or enhanced system. The task of characterizing the existing network, including the logical and physical topology and network performance, follows. The last step in this phase is to analyze current and future network traffic, including traffic flow and load, protocol behavior, and quality of service (QoS) requirements.

Develop the logical design. This phase deals with a logical topology for the new or enhanced network, network layer addressing, naming, and switching and routing protocols. Logical design also includes security planning, network management design, and the initial investigation into which service providers can meet WAN and remote access requirements.

Develop the physical design. During the physical design phase, specific technologies and products to realize the logical design are selected. Also, the investigation into service providers, which begin during the logical design phase, must be completed during this phase.

Test, optimize, and document the design. The final steps in top-down network design are to write and implement a test plan, build a prototype or pilot, optimize the network design, and document our work with a network design proposal.

• Plan. Network requirements are identified in this phase. This phase also includes an analysis of areas where the network will be installed and an identification of users who will require network services.
• Design. In this phase, the network designers accomplish the bulk of the logical and physical design, according to requirements gathered during the plan phase.
• Implement. After the design has been approved, implementation begins. The network is built according to the design specifications. Implementation also serves to verify the design.
• Operate. Operation is the final test of the effectiveness of the design. The network is monitored during this phase for performance problems and any faults, to provide input into the optimize phase of the network life cycle.
• Optimize. The optimize phase is based on proactive network management which identifies and resolves problems before network disruptions arise. The optimize phase may lead to a network redesign if too many problems arise due to design errors or as network performance degrades over time as actual use and capabilities diverge. Redesign may also be required when requirements change significantly.