Information Technology Reference
In-Depth Information
dards have been developed to help the LAN user plan a wiring system that stays
within the maximum wiring distance for various LAN topologies.
For example, in the case of 100BaseT, this cable must be no more than 100 m
(328 ft), including patch and equipment cords. This same “structure” works for 10
and 1000BaseT, as well.
We achieve the needed wiring concentration by placing telecommunications
rooms (wiring centers) at appropriate locations in a building and then interconnect-
ing those wiring closets as needed to provide the total network connectivity for the
building. Typically, a model of a multistory building is used to illustrate this struc-
tured concept, as shown in Fig. 1.1.
On each floor of our model, a telecommunications room (TR) concentrates all
of the station cables for that floor. Each workstation location has a wall or surface-
mounted jack. The network cable is terminated at that jack and runs directly to the
wire center. This is called a
home run
, as there are no intermediate connections,
splices, taps, or daisy-chains.
The wire may run in wire trays or conduit, or be draped over supports (run-
ning over a drop ceiling; the type with push-up ceiling tiles is no longer permitted).
Larger floors may require more than one TR per floor.
At the TR, each station wire is terminated on an appropriate punchdown ter-
mination, or directly onto a patch panel location. The punchdowns or patch panels
may be mounted to a wall or in a freestanding rack or cabinet. In the telecommuni-
cations room, some type of network device, such as a hub or concentrator, is con-
nected to each station cable and electrically terminates the cable run.
The hub passes the LAN signals on to other stations or wire centers for ulti-
mate connectivity with the entire network. The process is essentially the same for
different network topologies, although Token-Ring uses passive wiring concentra-
tors called multistation access units (MSAUs), rather than the active hubs of 10/100/
1000BaseT.
A TR is typically connected to the TRs on other floors. This center-to-center
wiring is usually done from floor to floor to floor, as a backbone, with LAN hubs on
each floor. In some cases, it may be more effective to connect TRs on several floors
to a single backbone concentrator on one of the floors. Ideally, TRs should be located
directly above one another, to minimize the cable runs between them, but that varies
from building to building. Fiber-optic cable is sometimes a good choice for wiring
between TRs, as it totally eliminates grounding and bonding concerns that exist with
metallic cable and can often be run longer distances than copper cable.
Obviously, there are differences between the wiring considerations for station
wiring on a single floor and for TR-to-TR wiring between floors. For one thing, the
fire protection requirements may be different for the vertical riser cabling used
