Chapter 5: Network Design Basics

Whether you're constructing a complete network or simply renovating an existing network, the basic approach is the same. You begin by planning what you want to implement, and then you gather the ingredients necessary to realize your plans. Next, you have to execute those plans according to the blueprint that you devised. The execution of any successful plan involves bringing all the pieces together, applying solid organizational principles to your network, and documenting what you add (and what's already in place) to your network.

Begin at the Beginning: Requirements

Whenever you set forth on a network project, begin by analyzing your requirements. If you're building a network from scratch, this phase can take weeks or even months of effort; if you're simply extending or repairing an existing network, planning may take a day of your time or less.

Whatever your project's scope, your plan should contain the following:

• A brief statement of your overall objectives, plus a more lengthy statement of requirements that addresses the following: what applications and services users need to access; estimates of user -to-server bandwidth requirements; and estimates of server-to-server bandwidth requirements (where applicable ).

  For example: The new XYZ Inc. network will provide 60 users with access to Windows Server 2003 file and print services, plus access to a SQL Server sales and inventory database. Each user will require no more than 1-Mbps bandwidth, and there are no server-to-server bandwidth requirements during business hours because all backups are scheduled for after-hours and weekends.

• A complete list of all the elements that you must purchase or otherwise acquire to meet those objectives.

  For example: Three different department servers (Accounting, Manufacturing, and Sales) will act as routers to link two network segments of 10 users each, for a total of 6 user segments based on 10-Mbps Ethernet. The three servers will be connected with a 100-Mpbs Ethernet backbone using 100BaseT. We will purchase six 16-port 10/100 Ethernet hubs (one per user segment) to leave room for growth, and three two-CPU 500-MHz Intel Zeon Pentium II server machines, each with 512MB RAM and 24GB of disk space. The Accounting server will have an 80GB DLT tape drive attached so that we can back up all three servers across the backbone.

• A description of the role each element will play on the network, the location of each element on the network, the configuration of each element, and the time during the installation process in which you plan to add each element to the network.

  You should use a map or a set of plans to help you place cables, computers, and other components , and a timeline to indicate the order in which you have to install everything.

  For example: The Accounting server will handle users from the Accounting and Purchasing departments; the Manufacturing server will handle users from the Manufacturing and Engineering departments; the Sales server will handle users from Administration as well as from the Sales and Marketing departments. All servers, the backbone, and all hubs will be installed when the company is closed between Christmass and New Year. The network should be operational when normal business operations resume. A map of this network appears in Figure 5-1.

  
  Figure 5-1: A simple network map of the XYZ Inc. network shows all hubs, servers, and cable segments overlaid on a simple building floor plan.

• A test plan that describes how you plan to test individual elements, individual cable segments, and the entire network to make sure everything functions properly after you finish the installation.

  For example: The three servers will be installed first and tested individually the weekend before the Christmas break. On December 23 and 24, the 100-Mbps backbone will be installed. On December 28, the backbone will be tested. On December 28 and 29, the hubs will be installed and tested. On December 30, workstations on all existing 10-Mbps cable segments will be connected to the new 10/100 hubs and tested individually. From December 31 to January 2, automated testing software will exercise the entire network. On January 3, a network technician will visit our site with Bob, the site administrator, and any last-minute changes, repairs , and adjustments will be performed. We believe the network will be ready for use on January 4.

This plan helps you to decide where you must place key network elements - such as servers, hubs, and other network devices. More importantly, the plan also helps you determine what type of network technology and bandwidth you need to deploy to meet your objectives. Because most businesses work on a budget, building a plan also helps you make sure that you won't try to spend more than you're allowed to spend or incorporate more exotic technologies than you can afford.

Your network implementation plan should also help you evaluate your current network backbone or plan a new one to be able to carry all the traffic that normally comes together on such critical network segments. (We discuss backbones in more detail in Chapter 7.)