Information Technology Reference
In-Depth Information
The concept of a series of interconnected telecommunications rooms (TR) is central
to structured cabling system design. The planning and placement of these telecom-
munications rooms is a subject sufficiently important for the Telecommunications
Industry Association (TIA) to devote an entire standard to it, TIA 569-B,
Commercial Building Standard for Telecommunications Pathways and Spaces .
In this chapter, we will discuss the placement of telecommunications rooms in
modern telecommunications installations. Naturally, this discussion will center
around designing a wiring system for LAN use. This will impose some additional
considerations on the location of our telecommunications rooms, primarily because
of the distance restrictions of LAN wiring.
Defining the Telecommunications Room (TR)
The telecommunications room is more broadly defined in TIA 569-B as a hierarchi-
cal system of telecommunication spaces that are used for the concentration and con-
nection of a building's telecommunications wiring. This standard covers wiring
spaces for all telecommunications activities and actually includes telephone as well
as computer wiring.
Because of the much lower operating frequency, telephone wiring is not sub-
ject to the severe distance limitations of LAN wiring. For example, the standard
allows a total distance of 800 m (2624 ft) for an unshielded twisted-pair circuit run
through a combination of telecommunications rooms—far beyond that allowed for
a single LAN leg, which is limited to 100 m (328 ft) without passing through a
repeater or bridge. So, we will concentrate on criteria appropriate for LANs, and
assume that the telephone wiring will either easily meet its requirements or be sep-
arately handled.
Traditional Cabling Heirarchy
In this hierarchical telecommunications room system (so-called structured wiring),
there are three types of wiring closets: the telecommunications room (TR), the inter-
mediate cross-connect (IC), and the main cross-connect (MC). Figure 14.1 shows
this hierarchy. The structure does not assume that any of these telecommunications
rooms necessarily contain equipment (such as hubs or telephone gear), but allows
for any telecommunications room to be collocated with an equipment room (ER).
In the traditional structured wiring installation for telephones, a cable from the local
exchange carrier (LEC) would enter the building and run to the MC, which would
generally also house the user's telephone switching equipment (a PABX or EKTS).
This would be a combination MC/ER.
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