Overview Now that you 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 design's physical and logical topologies should be designed and documented, as well as any brainstormed ideas, problem-solving matrices, and any other notes you made while making your determinations. You will also learn about wiring closet specifications used in LANs. In addition, you will learn about wiring and electrical techniques used in building networks. Note: In this chapter, you may need to convert units of measurements. A small utility to help you make the conversions is available here. You can access it from anywhere in this chapter via the Index button below. 8.1 Basic Network Design and Documentation 8.1.1 General design process Instructor Note The purpose of this target indicator is to present an overview of layer 1, 2, and 3 design issues. The actual design activities in the semester 1 project in chapters 8 and 9 are primarily layer 1 issues. Layer 2 and layer 3 design issues are paramount in the Threaded Case Study in semester 3. First, a layer 1 topology is decided upon. This is the part of the design process the students will be implementing in their structured cabling project. The process continues on, adding a layer 2 topology (primarily switching) to the layer 1 topology. Finally, a layer 3 topology a network layer addressing scheme would be implemented. The layer 3 topology also involves the placement of routers for segmentation of collision domains, segmentation of broadcast domains, and connection to WAN links. Again, the emphasis for the students should be on contextualizing their structured cabling project within the OSI model. 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. Web Links Cabling Glossary 8.1 Basic Network Design and Documentation 8.1.3 General network design process Instructor Note The purpose of this target indicator is to introduce the students to a general approach to design. There are many general design methodologies. A method taught by Dartmouth as a particularly good problem-solving approach for high school students is briefly introduced. There are three key aspects to the "Dartmouth method". First, there is the problem solving cycle, which consists of:Original problem statement. Redefine problem. Develop general specifications. Brainstorm alternatives. Select most viable alternative. Check problem definition. Redefine and add specifications. Brainstorm again if necessary. Reiterate until problem is appropriate. The key here is iteration -- engineering and technical design proceeds over and over again until the problem is adequately solved. The second key aspect to their approach is the problem-solving matrix. This is a graphical organizer; it need not be an obstacle to students learning. Simply list alternatives (choices) down the horizontal rows; list specifications across the vertical columns. In a real design process, many of these matrices would be created. You can teach the creation of these matrices with some simple choices the students would have to make, such as buying a car or choosing a college. The car or college with the highest score would presumably be the one they choose. If they still choose something with a lower score, that simply means there is a specification (a preference) that they have not made explicit. The matrix is a graphical organizer to help the design process and also serves as documentation of how a given design decision was reached.A third key aspect of design is brainstorming. This word is greatly overused; by brainstorming we mean a special 2 to 10 minute session which follows these rules:quantity of ideas no censorship of ideas building upon others ideas wildest ideas possible While the students will not use the full design method until semesters 3 and 4, they will be planning a structured cabling project and some of these techniques may prove useful.One activity relating to design is to brainstorm the meaning of the word design -- which means everything from fashion to architecture to aircraft to computer networks. 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 meets client objectives and satisfies 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. Web Links What is Engineering Problem Solving? Cabling Glossary 8.1 Basic Network Design and Documentation 8.1.4 Network design documents Instructor Note As the instructor, you will ultimately have to decide what written (or electronic) work you want from your students. Here are some suggestions as to what you might want from a structured cabling installation. engineering journal -- preliminary documentation of user needs, preliminary sketches of cable runs, pin outs, color codes, special safety precautions, reflections on key points in the installation are some of what might be kept in an engineering journal logical topology -- how does data flow? What is the location of key networking devices? physical topology -- how is the network actually wired? A series of diagrams, from floor-plan views of cable runs and patch cords to PCs to detailed diagrams of patch panels would all be considered part of the physical topology documentation cut sheets -- in the selection of wiring closet location, catchment areas must be drawn to see where repeaters and hubs might be needed problem-solving matrices -- a matrix should ideally be created everytime there is a choice with several options to be made. Placement of wiring closets, the use of Cat 5 versus fiber versus coax for a given network segment, and paths to IDFs and MDFs for specific cable runs are all common decisions when doing a structured cabling installation labeled outlets -- actual outlets should be labeled in a consistent manner labeled cable runs -- cable runs should be labeled in a consistent manner summary of outlets and cable runs -- a database or spreadsheet of outlets and cable runs should be created summary of devices, MAC addresses, and IP addresses -- once devices are attached, IP and MAC addresses should be recorded for the various networking devices We strongly recommend a rubric for documentation be created. This way every student group knows exactly what is expected of them. You cannot overemphasize the importance of documentation to the students. It is an integral part of their professional training. Virtually every institution and every network has a horror story to tell as the result of improper or nonexistent documentation.What follows are a set of activities, which could be done at once or spread out over several weeks, to address some of the drawing and model-making techniques which might help students visualize various networking issues.Architectural Drawings for the Networking Technician Objectives:Students will be able to:Draw the floor plan of an existing room to scale Visualize a room or a set of rooms expressed in an architectural floor plan Estimate the length of a cable run using only a floor plan (optional) Rationale:Many networking students usually have little drawing experience and no experience with standard architectural drawing projections. This is a disadvantage to a practicing Technician, as they must be able to accurately interpret floor plans and cross sections of the building that contains the network. This is so that they can make informed decisions about network topologies, the amount of materials needed for a particular job, and the equipment required for installation. Furthermore, they must be able to accurately annotate such drawings for future reference.Abstract:During this activity, students will measure for and build a three-dimensional model of their networking classroom using simple materials. They will then draw a scaled floorplan, and will use their model as a guide. The model and drawing can then be used to stimulate discussion about means of representing in two dimensions the complex three-dimensional path that a networking cable must follow. If time permits, there is the opportunity to link together many students' models to help them see the horizontal and vertical wire routing problems that must be solved in setting up a network in a large building with dozens of computers, multiple servers, and a variety of networking equipment.Procedure:Give students, in small groups, access to a full-scale architectural floor plans of a whole-building network installation to provide them a context for their lesson Have them locate the drawings legend and identify as many of the symbols and lines on the drawing as they can Have student groups measure the outline shape of the room using a variety of methods (tape measure, ruler, heel-to-toe, counting floor tiles, string, etc.). Students should then draw on a sheet of cardboard (at least 10" by 12") using the scale of 1 inch = 3 feet. Provide them with rulers and stress the accuracy of their drawing. Have students cut out their cardboard along the outlines they have drawn. Provide the students with 3"x5" index cards, transparent tape, and scissors so that they may construct the walls around the edge of the outline (use the card's 3" dimension to represent the height of the walls). Be sure that they cut out doors and windows and construct large features of their room like columns, tables, equipment racks, etc. Check that their models are well attached to the cardboard bases and that all cuts are clean and accurate. Provide the students with a sheet of overhead transparency and a transparency marker. Have them cover the top of their models completely with the transparent sheet and have them tape it to the walls (from underneath) temporarily in two places. Using the transparency pens and looking down from above, students should draw the traces where the tops of the walls touch the sheet. Next they should draw other features that they see, such as tables and racks. Also have them note the locations and extent of door openings and windows (show them examples of this from the professional drawings). Have students remove the floor plans that they have thus produced, and compare them with the professional drawings. Point out similarities and differences, including scale, level of detail, and wall thickness. Also have students compare their drawings with each other, and discuss issues of accuracy of measurement and care and precision of drawing. Optional Activities.Arrange the students "rooms" on a tabletop as they would be in a real building. Allow space for corridors, and stack some vertically to help illustrate vertical wiring problems. You may wish to fasten them to the tabletop with tape. Pose networking problems for students to solve by suggesting the locations of PCs, wiring closets, networking equipment, jacks and the like. Their solutions could be expressed by drawing cable routes directly on the models with a felt tip pen, or for more realism, by having them tape lengths of string, scaled to the maximum possible run for the particular medium (UTP, coax, fiber) along their proposed cable routes. For showing runs across ceilings, have the students attach transparent sheets to the top of their room; these sheets should be hinged with tape along one side for easy access to the interior. Orienting Students to Orthographic Projections (top, front, and side views at a minimum)Show students examples of orthographic drawings of familiar objects. Some good objects are a car, a person standing, a person sitting, a basketball, or a house. Have students make an orthographic drawing (with at least a top, a side, and a front view) of a simple object they have with them, such as a book, pen, key, ring, or trinket. Point out the limitations that external views have in representing the entirety of an object. Show examples of section views and cut-away views. Have students make some cross-sectional views using objects they are familiar with or that you have on hand to be disassembled. Good examples are a house, an egg, an orange, a person (MRI and CAT scans are good examples of cross-sections), a marking pen, a computer, or a sneaker. Show students the x, y, and z axes Show students how to draw three dimensional cubes Show students how to draw three dimensional rectangular boxes Show students how to draw multi-tiered three dimensional rectangular objects Show students how to remove cubic and rectangular volumes from already drawn rectangular objects Show students how use of shading can enhance these basic drawing techniques. 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. Web Links Siemon Guidelines to Industry Standards Cabling Glossary
