Information Technology Reference
In-Depth Information
This construction is shown in Fig. 5.4. The buffer is rather like the insulation
that surrounds a copper wire in a conventional cable. The strength fibers are added
to prevent stretching of the cable, which would fracture the optical fiber.
Optical fiber is made of extruded glass (silica) or plastic, specially formulated to
pass light of specific wavelengths with very little loss. Most fiber-optic LAN wiring
is used for backbone wiring and uses glass fiber. Plastic step-index fiber is available
from a few sources, but has traditionally suffered from high attenuation and limited
bandwidth, factors that are critical to the deployment of fiber technology.
Recent developments in graded-index plastic optical fiber (GIPOF) may offer
increased bandwidths in the future, perhaps with lower cost and suitable attenua-
tion when compared to glass fiber. Plastic fiber construction is not yet blessed by the
standards for LAN wiring, so the rest of this section will concentrate on the charac-
teristics of standard glass fiber.
The Fiber Debate
The choice between installing copper wiring and fiber-optic cable to the workstation
is the subject of much debate—an important issue, particularly in new cabling
installations where the cable plant is expected to have a useful life of 15 to 20 years.
Few would suggest that anything but fiber should be used for campus wiring or for
longer high-speed cable runs between wiring closets. The controversy centers on
whether fiber should be used from the wiring closet to the workstation—so-called
“fiber to the desktop.” Current estimates for horizontal fiber range from 5% to
15% of all installations. Copper wiring installations still dwarf fiber installations,
yet there is much disagreement on the issue.
What are the two sides to the debate? The proponents of fiber argue that it
offers greater signal bandwidth, runs longer distances, offers future growth, costs
nearly the same, and is now easy to install and more rugged than generally thought.
Proponents of copper over fiber argue that expanded bandwidth is being imple-
mented for copper, that network switching equipment often does not support fiber,
that the installed cost of fiber is greater than copper, and that fiber is subject to
breaks that are expensive to repair. In general, the most avid fiber supporters are
either those companies that offer fiber-optic cable, connectors, and related hard-
ware, or they are installers and users who have made a significant investment in
fiber-optic technology and very naturally defend their decision. Please do not con-
strue this statement to mean that either of these two groups is wrong, but simply
that they have a certain bias that leads them to the conclusion that fiber is always
the best choice. In some circumstances, fiber cabling may clearly be the best, if not
the only reasonable choice. But, in many other situations, the issue is less clear.
