In order to learn how multiple earth grounds can impact a LAN's wiring scheme, assume that you have been asked to prepare a wiring plan for a twenty-story building. Three companies occupy the building:

• Company A occupies the first fifteen floors.
• Company B occupies the sixteenth, seventeenth, and eighteenth floors.
• Company C occupies the nineteenth and twentieth floors.

The description of the building is as follows:

• The building has three separate supplies of power.
• Each has its own earth ground.
• None of the earth grounds is identical.
• The height of each story is 4.9 m.
• Only one wiring closet is needed on each floor, to supply horizontal cabling runs to the work areas located there.
• The POP is located on the first floor.

You have been directed to develop a wiring plan for company A. A study has been conducted and all work areas have been mapped on a plan of each floor. The plans include the selections for the wiring closet on each floor. These are shown in the building profile in the Figure .

In multi-story buildings the MDF is usually located on one of the middle floors of the building because it is the center of an Ethernet star topology. A middle floor is the best location even though the POP may be located on the first floor. On which floor would you locate the MDF?

This will be a new installation; therefore, the networking media for the horizontal cabling will be CAT 5 UTP. Now you must determine which types of networking media you should use for the backbone cabling. After a preliminary study, you have narrowed the choices to two types - CAT 5 UTP and 62.6/125 µ fiber-optic cable. Because of the high cost of installation, you would like to avoid using fiber-optic cable unless absolutely necessary. However, based on your preliminary study and projections, you have determined that it may not be necessary to use fiber-optic cable because UTP could sufficiently carry all anticipated network data for the next ten years. There are, however, two more factors that could influence your decision - safety and distance. In light of this, you must consider the following points:

1. The building has three different earth grounds. Could this present any safety problems for company A's network?
2. The maximum distance specified by TIA/EIA-568-A for CAT 5 cable is 100 m. Because the height of each floor is 4.9 m, you will need to exceed this distance if you use this for the backbone cabling. Can you think of a way to solve the problem of distance between the POP and the MDF?
3. Can you think of a way to solve the problem of distance between the MDF and the IDFs?
4. The repeating hubs will be located in IDFs.

To determine which IDFs will be ICCs, multiply each floor by its height as you move away from the MDF. Assuming that the backbone cabling runs will all be vertical, from the MDF to the IDF on the ninth floor, the distance would be 4.9 m. The distance from the MDF to the tenth floor would be 9.8 m. Then answer the following questions:

1. What would be the distance to the eleventh floor IDF, from the MDF?
2. What would be the distance to the twelfth floor IDF, from the MDF?
3. What would be the distance to the thirteenth floor IDF, from the MDF?
4. What would be the distance to the fourteenth floor IDF, from the MDF?
5. What would be the distance to the fifteenth floor IDF, from the MDF?

(Note: Backbone cabling must also run from the MDF to each of the floors below it.)

IDFs that are connected to the work areas by horizontal cabling runs are called horizontal cross-connects (HCCs). Can you determine where the HCCs for company A's network will be located?

Use blue ink, or a blue pencil, to draw the horizontal cabling runs on each floor. Use red ink, or a red pencil, to draw the backbone cabling for company A's Ethernet star topology LAN.

You have been directed to develop a wiring plan for company B, which occupies the sixteenth, seventeenth, and eighteenth floors of the same building as company A. A study has been conducted and all work areas have been mapped on a plan of each floor. The plans include the selections for the wiring closet on each floor. These are shown in the building profile in the graphic.

Because company B only occupies three floors of the building, and because it is so far from the POP, you have made the decision to locate the MDF on the sixteenth floor. The remaining wiring closets, located on the seventeenth and eighteenth floors, will be IDFs.

This will be a new installation; therefore, the networking media for the horizontal cabling will be CAT 5 UTP. Now you must determine which types of networking media you should use for the backbone cabling. After a preliminary study, you have narrowed the choices to two types - CAT 5 UTP and 62.6/125 µ fiber-optic cable. There are, however, two more factors that could influence your decision - safety, and distance. In light of this, you must consider the following points:

1. The building has three different earth grounds. Could this present any safety problems for company B's network?

Use blue ink, or a blue pencil, to draw the horizontal cabling runs on each floor. Use red ink, or a red pencil, to draw the backbone cabling for company B's Ethernet star topology LAN.