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1 - Two basic cable designs are:
Loose-tube cable, used in the majority of outside-plant
installations in North America, and tight-buffered cable,
primarily used inside buildings.
The modular design of loose-tube cables typically
holds up to 12 fibers per buffer tube with a maximum
per cable fiber count of more than 200 fibers. Loose-tube
cables can be all-dielectric or optionally armored.
The modular buffer-tube design permits easy drop-off
of groups of fibers at intermediate points, without
interfering with other protected buffer tubes being
routed to other locations. The loose-tube design also
helps in the identification and administration of fibers
in the system.
Single-fiber tight-buffered cables are used ase pigtails,
patch cords and jumpers to terminate loose-tube cables
directly into opto-electronic transmitters, receivers
and other active and passive components.
Multi-fiber tight-buffered cables also are available
and are used primarily for alternative routing and handling
flexibility and ease within buildings.
2 - Loose-Tube Cable
In a loose-tube cable design, color-coded plastic
buffer tubes house and protect optical fibers. A gel
filling compound impedes water penetration. Excess fiber
length (relative to buffer tube length) insulates fibers
from stresses of installation and environmental loading.
Buffer tubes are stranded around a dielectric or steel
central member, which serves as an anti-buckling element.
The cable core, typically surrounded by aramid yarn,
is the primary tensile strength member. The outer polyethylene
jacket is extruded over the core. If armoring is required,
a corrugated steel tape is formed around a single jacketed
cable with an additional jacket extruded over the armor.
Loose-tube cables typically are used for outside-plant
installation in aerial, duct and direct-buried applications.
3 - Tight-Buffered Cable
With tight-buffered cable designs, the buffering material
is in direct contat with the fiber. This design is suited
for "jumper cables" which connect outside plant cables
to terminal equipment, and also for linking various
devices in a premises network.
Multi-fiber, tight-buffered cables often are used
for intra-building, risers, general building and plenum
applications.
The tight-buffered design provides a rugged cable
structure to protect individual fibers during handling,
routing and connectorization. Yarn strength members
keep the tensile load away from the fiber.
As with loose-tube cables, optical specifications
for tight-buffered cables also should include the maximum
performance of all fibers over the operating temperature
range and life of the cable. Averages should not be
acceptable.
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Basic Cable Design