Information Technology Reference
In-Depth Information
The concept of an orderly system of telecommunications cabling has actually been
around for many years. In a way, it was inspired by the hierarchical system of outside-
plant cabling for the telephone industry. The concept was (and is still) simple: From
wiring centers (central offices), large pair-count cables run to outdoor subscriber-line
interface cabinets, where smaller multi-pair cables interconnect. These smaller cables
then run to nearby neighborhoods or business areas, where the subscriber lines (drops)
are connected to individual users. Inside the central offices, a similar hierarchical sys-
tem of main and intermediate distribution frames fan out the connections to the cen-
tral switch. Finally, between these wiring centers, the network equivalent of backbone
cables interconnect central offices, and ultimately the long-distance system (PSTN).
Inside multi-tenant and larger commercial buildings, a similar hierarchical sys-
tem of main and intermediate wiring rooms is used to distribute telephone service
first to every company (or physical floor or wing) in the building, and then to every
telephone. This building-wire system formed the core concept of modern structured
cabling, because data distribution has a very similar topology to telephone distribu-
tion. Structured cabling was developed to standardize the media and connection sys-
tems so that high-speed LAN data could travel the infrastructure.
We will describe several LAN cabling systems in this chapter. These systems
define the characteristics of cable, connectors, and general wiring schemes without
regard to any of the specific LAN topologies that were described in Chapter 2, and
all of them also use some form of twisted-pair wire as their basis. The general pur-
pose TIA-568-C cabling system will be described, as will several of the proprietary
cabling systems that are in wide use.
Many proprietary cabling plans have been offered over the history of LAN
wiring technology. Early on, the direction of LAN cabling was uncertain and several
major equipment vendors devised detailed cabling systems that met the needs of
their equipment. Any customer who followed their guidelines could be reasonably
assured of a LAN cable plant that would operate well with that vendor's products.
Of course, use of a particular vendor's products also frequently implied use of a par-
ticular LAN topology.
Over time, many LAN technologists have learned that the use of a particular
vendor's cabling plan might actually limit the utility of their cable plant for other
uses. In some cases, adherence to a cabling system might significantly increase sys-
tem cost over other methods. However, a few cable plans offered wide connectivity
of both voice and data. Out of those plans, a universal cabling system finally
emerged, EIA/TIA 568, now revised as TIA/EIA-568-C (the “/EIA” portion of the
standard number is often omitted, even in official documents from the TIA).
