Now that you have a firm understanding of data flow through the OSI model, along with Layer 1 and 2 concepts and technologies, you are ready to start learning how to design networks. Network design takes many technologies into consideration (e.g. token-ring, FDDI, and Ethernet). For example, a Layer 1 LAN topology must be developed, and the type of cable, and the physical (wiring) topology must be determined. 

In this chapter you will learn how the network's physical and logical topologies should be designed and documented. You will also learn to document brainstormed ideas, problem solving matrices, and other notes used in making your determinations. In addition, you will learn wiring closet specifications used in LANs, as well as wiring and electrical techniques used in network building.

This lesson includes a more comprehensive list of the steps you must follow in order to design a network. You will not go through all of these steps when you do your structured cabling project. Many of the decisions have already been made by the existing network design and network administrator, however this is the process that you will eventually follow.

Your network design could take into consideration many technologies such as Token Ring, FDDI, and Ethernet. This design will focus on the Ethernet technology as that is the technology you will most likely encounter when you plan future designs. Ethernet has a logical bus topology, which leads to collision domains; however, you will try to keep them small by using the process called segmentation. Once you have settled on Ethernet, you must develop a Layer 1 LAN topology. You must determine the type of cable, and the physical (wiring) topology that you will use. The most common choice is CAT 5 UTP as the medium, and an extended star topology as the physical (wiring) topology. Then you must decide on which one, of the several types of Ethernet topologies, you need to use. Two common types of Ethernet are 10BASE-T and 100BASE-TX (Fast Ethernet). If you have the resources, you might run 100BASE-TX throughout the network. If not, you might use Fast Ethernet to connect the main distribution facility (central control point of our network) to other intermediate distribution facilities. You might use hubs, repeaters, and transceivers in your design, along with other Layer 1 components such as plugs, cable, jacks, and patch panels. To finish Layer 1 design, you must generate both a logical and a physical topology. (Note: As always, an important part of your design involves documenting your work.)

The next step is to develop a Layer 2 LAN topology, that is, to add Layer 2 devices to your topology to improve its capabilities. You could add switches to reduce congestion and collision domain size. In the future, you may be able to afford to replace hubs with switches, and other less intelligent Layer 1 devices with more intelligent Layer 2 devices.

The next step, then, is to develop a Layer 3 topology; that is, to add Layer 3 devices that will add to the topology's capabilities. Layer 3 is where routing is implemented. You could use routers to build scalable internetworks such as LANs, WANs, or networks of networks. Routers will impose logical structure on the network you are designing. They can also be used for segmentation. Routers, unlike bridges, switches, and hubs, break up both collision and broadcast domains.

The LAN's link to WANs and to the Internet must also be considered. As always, you should document your network design's physical and logical topologies. Your documentation should include any brainstormed ideas, problem-solving matrices, and any other notes you made while making your determinations.

In order for a LAN to be effective and serve the needs of its users, it should be implemented according to a systematic series of planned steps. While you are learning about the design process, and creating your own designs, you should use your engineering journal extensively.

Your first step in the process is to gather information about the organization. This information should include:

1. organization's history and current status
2. projected growth
3. operating policies and management procedures
4. office systems and procedures
5. viewpoints of the people who will be using the LAN

Hopefully, this step will also help you identify and define any issues or problems that need to be addressed (e.g. you may find that a remote room in the building may not have network access.)

The second step is to make a detailed analysis and assessment of the current and projected requirements of those people who will be using the network.

The third step is to identify the resources and constraints of the organization. Organization resources that can affect the implementation of a new LAN system fall into two main categories - computer hardware and software resources, and human resources. You must document an organization's existing computer hardware and software, and identify and define its projected hardware and software needs. The answers to some of these questions will also help you determine how much training will be required, and how many people will be needed to support the LAN. The questions you ask should include:

1. What financial resources does the organization have available?
2. How are these resources currently linked and shared?
3. How many people will be using the network?
4. What are the computer skill levels of the network users?
5. What are their attitudes toward computers and computer applications?

Following these steps, and documenting the information in the framework of a formal report, will help you estimate costs and develop a budget for the implementation of a LAN.

In technical fields, such as engineering, the design process includes:

• designer - person doing the design
• client - person who has requested, and is probably paying for, the design
• user(s) - person(s) who will be using the product
• brainstorming - generation of creative ideas for the design
• specifications development - usually numbers which will measure how well the design works
• building and testing - to meet client objectives and satisfy certain standards

One of the methods you can use in the process of creating a design is the problem solving cycle. This is a process that you use repeatedly until you finish a design problem.

One of the methods that engineers use to organize their ideas and plans when doing a design is to use the problem-solving matrix. This matrix lists alternatives and various choices, or options, from which you can choose.

The following list includes some of the documentation that you should create as you design a network:

• engineering journal
• logical topology
• physical topology
• cut sheets
• problem-solving matrices
• labeled outlets
• labeled cable runs
• summary of outlets and cable runs
• summary of devices, MAC addresses, and IP addresses

You might also ask your instructor if there is any other documentation that is relevant to your project. Perhaps the most important part of the network design process is designing according to the ANSI/EIA/TIA and ISO/IEC industry standards. For an excellent introduction to these standards (with PDF downloads available), see the Siemon Company Guide to Industry Standards @ http://www.siemon.com/standards/homepage.html