Network Design

Design Goals

Good network designs should:

• Deliver services requested by users.
• Ensure acceptable throughput and response times.
• Be within budget and maximize cost efficiency.
• Be reliable and resilient.
• Be expandable without major redesign.
• Be manageable by support and maintenance staff.
• Be well-documented for future reference.

Design Choices

Key factors to consider in network design include:

• Balance of distribution: Centralized or decentralized systems.
• Level of transparency: How seamless the user experience is across networks.
• Security: How to secure data, devices, and communications.
• Connectivity technology: Selecting appropriate technologies.
• Green technology: Emphasizing low power consumption and eco-friendliness.

Design Approaches

There are two main methods:

• Traditional Analytic Design: Detailed analysis of needs and technical solutions.
• Building Block Approach: A modular approach where components are integrated progressively.

Both methods follow an iterative design process.

The Design Process

Design Stages - Agree Requirements

• Engage end-users to understand business objectives and technical specifications.
• Translate business goals into phased technical requirements.

Design Stages - Designing Requirements

• Complete the design and ensure nothing is missed.
• Use a priority system:
  • [M] Mandatory
  • [H] Highly desirable
  • [D] Desirable
  • [N] Note

Design Stages - Assessing Requirements

• Consider costs over the network’s lifecycle, such as support, maintenance, upgrades, and project management.
• Use a weighted matrix system to rank suppliers, assigning higher multipliers for critical features.

Design Stages - Information Gathering

• Collect detailed data on:
  • User location and behavior.
  • Site constraints (security, costs, traffic).
  • Servers, WAN/backbone traffic, and service needs.
  • Legacy systems and specific availability needs.
  • Greenfield or existing site.

Design Stages - Site Constraints

• Greenfield sites: No legacy constraints but require simulations to predict network performance.
• Existing sites: Easier to assess due to observable bottlenecks but limited by current infrastructure.

Design Stages - Planning

• Information on hosts, users, and services forms the foundation of the iterative process:
  • Conceptual design, analysis, refinement, and review.
  • Use brainstorming, modelling tools, and design reviews.

Connectivity Options

• Technology choices include LANs (Ethernet, Token Ring), MANs (MPLS, ATM), WANs (IP routing, ISDN), and wireless options (802.11, Bluetooth, GSM).
• Factors determining the choice include:
  • Packet, cell, or circuit switching.
  • Wired vs. wireless.
  • Distance, bandwidth, performance, and Quality of Service (QoS).

Capacity Planning

Capacity Planning - Outline

Capacity planning ensures:

• Minimizing downtime.
• Maximizing service delivery to users.
• Minimizing procurement and maintenance costs.
• Avoiding costly upgrades or bad publicity due to poor performance.

Capacity Planning - Stages

1. Form discussion groups with users and stakeholders.
2. Quantify user behavior and location.
3. Quantify application behavior, performance characteristics, and impact on the network.
4. Baseline the existing network to analyze current performance.
5. Make traffic projections using tools and simulations.
6. Summarize data to inform the design process, considering budget, user populations, and applications.

Good Design Principles

• Network design should be:
  • Iterative: Continuous refinement.
  • Logical and consistent.
  • Focused on performance and cost metrics.
  • More than just technology selection. It should consider user needs and system sustainability.