Lesson 4

Locating Network Resources

1-33

Locating Cables

The cable diagram is an important part of the network blueprint, because this part of

the network is likely to be invisible once the construction of the network is com-

pleted. To maintain and troubleshoot the network infrastructure, technicians must

know where the cables are located and how they are arranged. In addition to the

cable runs themselves, the blueprint should also specify the locations of obstacles

that cables must detour around and the location of each cable terminus, either at a

wall plate or a patch panel.

Part of selecting a network medium involves determining how the cables will be

installed, based on the physical characteristics of the site. Typically, the cable installa-

tion for a medium-to-large office network is internal, meaning that the cables run

inside walls and drop ceilings or sometimes under raised floors. In this type of instal-

lation, you should know the exact layout and construction of the site. If it is necessary

to run cables down from the ceiling in the center of a room, the plan should note the

exact location of a utility pole that will contain the cables.

Creating the cabling diagram requires more than a simple floor plan of the site. To

route the cables properly, the network designers must be aware of any obstacles that

can interfere with the cable’s installation or performance, and these obstacles often do

not appear on standard floor plans. For example, when using copper-based cable such

as UTP, you must know the locations of fluorescent light fixtures and other possible

sources of electromagnetic interference so that the installer knows to route the cables

around them. You should also document the locations of heating and air conditioning

ducts, plenums, firewalls, and other obstacles that the installer might have to route

cables around or through. In most cases, this requires the network designer to carefully

examine the site.

Another factor you should consider is that wiring diagrams are typically two-dimen-

sional overviews of the site while cables often have to travel in three dimensions. For

example, when you install cable runs in a drop ceiling and terminate them at wall

plates, the diagram should specify exactly where the cable goes down from the ceil-

ing space into the wall. The diagram should also specify how high the wall plate

should be off the floor and note whether the vertical wall itself contains any barriers

that installers might have to work around. If the installation should include telephone

as well as data cables, the plan should differentiate between the two and contain the

codes that the installers will use to mark the cables so that they can be located later.

A diagram for an external cable installation requires other details, particularly where

the cables are to be secured and how—such as using staples, raceways, or cable ties.