|  | 8.1 | Basic Network Design and Documentation
| 8.1.1 | General design process
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, because many of the decisions have already been made by the existing network design and network administrator, but this is the process that you will eventually follow. Your network design could take into consideration many technologies (e.g. Token Ring, FDDI, and Ethernet); however this design will focus on the Ethernet technology, since 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 (larger LANs, WANs, networks of networks), or to impose logical structure on the network you are designing, or use them for segmentation (i.e. routers break up both collision domains and broadcast domains, whereas bridges, switches, and hubs do not). Your network design should also consider the placement of such things as file servers, databases, and other shared resources, as well as the LANs link to WANs and to the Internet. Finally, you should document your network design's physical and logical topologies, as well as any brainstormed ideas, problem-solving matrices, and any other notes you made while making your determinations.
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