Perhaps because of my background in drafting and interest in architecture, my conceptualization of a physical diagram is perhaps a little different than what I typically see elsewhere. To me, a physical diagram starts with a floor plan. Not just any floor plan but one that is essentially a lighter version of an architectural drawing. In other words, walls, dimensions, electrical outlets, etc need to be indicated on the drawing. Scale is important as this feeds into your wireless design as well. Some people might refer to this as a wiring schematic. But, to me, a physical diagram is like a wiring schematic on steroids.
If you've already got an architectural drawing, great. Otherwise, it takes a little more effort. Get out your tape measure and go to town documenting the physical space you are going to install your network. Make note of the materials the walls are made out of (brick, wood, sheet rock, etc...again, this will pay off when you go to develop your wireless diagram. Record all if this information on a sheet of paper and once complete, translate your scribbles to a Visio diagram. Take your time here to master Visio. There are lots of tutorial videos out there on Visio. If you are choosing networking as a profession, I would recommend that you all become Visio ninjas.
Now you can get started with the networking part of the diagram. Start placing your various components on the diagram, taking care to be consistent with the items you actually have (or will be getting). Far too often, I see students place clients, servers, or other networking node/components on their physical diagram that they did not account for on their logical diagrams or cost analyses. For the nodes and network components, scale is not quite as important as it is for the walls in your diagram. In other words, you want to make the nodes and network components easy to see and recognize for what they are.
Include reasonable layouts of your network cabling. How are you going to route your cables? Some of this has to do with whether or not this is a new facility, existing, and construction of the facility. If it is currently being built, it may be quite easy to run cabling through the walls. The end results look nice, requires less effort than some other approaches, but costs more in cabling. If you are installing in an existing facility, you may want to run it through the attic and drop it down inside the walls. This will cost less in cabling but will take more time and cost more in labor to install. With any luck, the facility may have a drop ceiling which will make things easier. You can run cables along the floor, along the edges of the room but this really should be avoided for any sort of permanent solution. The reason your decision regarding how you are going to route cables is important is that since you used scale in your drawing, you can now more accurately "guestimate" how much cabling you need. Without scale, you cannot do that. For a small facility, this is probably not important. But, as the size increases and the higher quality (more expensive) medium is used, the costs go up. The last thing regarding cabling, as it relates to your diagram includes color. Are there parts of the network that are on different subnets or different VLANs? Why not use color to differentiate one VLAN from another? It makes it more clear about how different nodes and parts of the network relate to one another.
Now, you are starting to get close to your final product. Again, I love to have configuration information included on diagrams. Things like Gateways, DNS servers, IP addresses, subnets, MAC addresses, etc. Careful here. As this is a physical diagram, you should focus on physical characteristics of your design. Things like IP addresses are logical in nature. Ideally, you would use Visio's layer feature because your drawing can get out of hand quite quickly with the level of detail. Layers allow you to selectively see different components of the diagram. Perhaps you have a "configuration information" layer so that it does not clutter up the rest of the diagram when you do not need that information. Figure 1 below is an example of a good physical diagram. This was submitted by a former student of mine who is quite skilled at using Visio. While it might a bit cluttered, it represents a nice job of using color to differentiate different security zones.
Figure 1: Physical Diagram
Not to be outdone by the diagram itself is the narrative used to describe the physical aspects of your diagram. The narrative, in which the diagram should be embedded somewhere in the middle, is your opportunity to discuss things that are perhaps a little more difficult to communicate in the diagram itself. For example, what type of wiring did you choose? Why? What are the pros and cons of that particular choice? Why is it a good solution in this particular case? Are you recommending UTP or STP? Why/why not? How much cabling will you need? Again, since your diagram is to scale, you should be able to articulate how your are going to route cables and approximate how much cabling you will need.
The key to this and the logical diagram is keeping it updated; treating it as a living document. If you are like me, you like documentation being in order. But, most people under the crunch of trying to keep the network up and going, tend to let documentation slide and it quickly loses its usefulness when that happens. The key is to set aside some time and actively engage in maintaining network documentation. This is a network management function which we will talk about in later posts.
So, I put it to you. What information do you feel is a must when it comes to physical diagrams? What absolutely has to be there for it to serve a useful purpose?
