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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.
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