| Q: What are Fiber
Optics? |
Fiber optics (optical fibers) are long, thin strands
of very pure glass about the diameter of a human hair.
They are arranged in bundles called optical cables and
used to transmit light signals over long distances.
If you look closely at a single optical fiber, you will
see that it has the following parts:
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Core - Thin glass center of the
fiber where the light travels.
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Cladding - Outer optical material surrounding the core
that reflects the light back into the core.
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Buffer coating - Plastic coating that protects the fiber from
damage and moisture.
Hundreds or thousands of these optical fibers
are arranged in bundles in optical cables. The
bundles are protected by the cable's outer covering,
called a jacket.
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Optical fibers come in two types:
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Single-mode fibers - Used to transmit one signal per fiber (used
in telephones and cable TV)
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Multi-mode fibers - Used to transmit many signals per fiber (used
in computer networks, local area networks)
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Single-mode fibers have small cores (about 3.5 x 10-4
inches or 9 microns in diameter) and transmit infrared
laser light (wavelength = 1,300 to 1,550 nanometers).
Multi-mode fibers have larger cores (about 2.5 x 10-3
inches or 62.5 microns in diameter) and transmit infrared
light (wavelength = 850 to 1,300 nm) from light-emitting
diodes (LEDs).
Some optical fibers can be made from plastic. These
fibers have a large core (0.04 inches or 1 mm diameter)
and transmit visible red light (wavelength = 650 nm)
from LEDs.
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| Q: Advantages of
Fiber Optics? |
Compared to conventional metal wire (copper wire), optical
fibers are:
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Less expensive - Several
miles of optical cable can be made cheaper than
equivalent lengths of copper wire. This saves
your provider (cable TV, Internet) and you money.
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Thinner - Optical fibers can be drawn to smaller
diameters than copper wire.
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Higher carrying capacity
- Because optical fibers are thinner than copper
wires, more fibers can be bundled into a given-diameter
cable than copper wires. This allows more phone
lines to go over the same cable or more channels
to come through the cable into your cable TV box.
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| • |
Less signal degradation -
The loss of signal in optical fiber is less than
in copper wire.
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Light signals - Unlike electrical
signals in copper wires, light signals from one
fiber do not interfere with those of other fibers
in the same cable. This means clearer phone conversations
or TV reception.
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Low power - Because signals
in optical fibers degrade less, lower-power transmitters
can be used instead of the high-voltage electrical
transmitters needed for copper wires. Again, this
saves your provider and you money.
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| • |
Digital signals - Optical
fibers are ideally suited for carrying digital
information, which is especially useful in computer
networks.
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Non-flammable - Because no
electricity is passed through optical fibers,
there is no fire hazard.
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| • |
Lightweight - An optical
cable weighs less than a comparable copper wire
cable. Fiber-optic cables take up less space in
the ground.
Because of these advantages, you see fiber optics
in many industries, most notably telecommunications
and computer networks.
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| Q: What does it
cost to use fiber vs. conventional cat 5 cabling
for a LAN? |
Fiber will cary any speed imaginable its not limited,
and CAT5 carries only 100 mbit. The expense is about
1000 times CAT5 for fiber. It's VERY expensive to lay
fiber. We are talking low 6 figures per about 100 feet
of cable. Typical cost of multimode fiber per foot is
around $0.75 compared to $0.10 for Cat5e Gigabit certified
copper cable.
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| Q: FTTB, FTTC, FTTH,
and FTTN technologies |
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"Fiber to the Building" (FTTB) refers to installing optical
fiber from the telephone company central office
to a specific building such as a business or apartment
house.
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| • |
"Fiber to the Curb" (FTTC) refers to the installation
and use of optical fiber cable directly to the
curbs near homes or any business environment as
a replacement for "plain old telephone service"
(POTS) Fiber to the curb implies that coaxial
cable or another medium might carry the signals
the very short distance between the curb and the
user inside the home or business.
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"Fiber to the Home" (FTTH) is a network technology
that deploys fiber optic cable directly to the
home or business to deliver voice, video and data
services. By leveraging the extremely high bandwidth
capacity of fiber, FTTH can deliver more bandwidth
capacity than competing copper-based technologies
such as twisted pair, HFC and xDSL.
Fiber to the home is deployed
in two primary architectures - point-to-point
and passive optical network (PON). While both
have their place in solving the last-mile bottleneck,
a point-to-point architecture is generally deployed
to businesses in metro and urban areas, while
a PON is a more cost-effective solution for small-
to medium-sized businesses and residences. A PON
architecture allows a single fiber from the central
office (CO) or headend to be split up to 32 ways,
delivering high-bandwidth converged services to
multiple residences or businesses, using a single
optical transceiver in the CO. In a point-to-point
configuration, an optical transceiver for each
subscriber is required in the CO, thus substantially
increasing the total cost of deployment.
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"Fiber to the neighborhood" (FTTN) refers to installing it
generally to all curbs or buildings in a neighborhood.
Hybrid Fiber Coax (HFC) is an
example of a distribution concept in which optical
fiber is used as the backbone medium in a given
environment and coaxial cable is used between
the backbone and individual users (such as those
in a small corporation or a college environment).
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| Q: DFITL, IFITL
and FITL technologies |
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DFITL is in short adsl over
FITL (fiber in to loop/fiber to the curb). The
way it works is it sends the dsl signal over fiber
to the ONU thur the DISCS system and connects
to the ATM in the CO. The card in the ONU acts
like the DSLAM since the signal runs over copper
from the ONU to the house.
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IFITL is an implementation
of FTTC by Marconi Communications which delivers
integrated voice, Digital TV, and high-speed data
(PCDATA).
PCDATA which is simply 10Mbps
Ethernet delivered to your doorstep. You can't
buy "PCDATA" itself because there are
no tarrifs for that class of service. Instead
Bellsouth sells a throttled version (1.5Mbps down/
256Kbps up) of PCDATA as "Fast Access".
Some call this "DSL over Fiber", but
this is a misnomer as there is no DSL signalling
involved at all...it's Ethernet, period.
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FITL = IFITL without the video and data services
(e.g. no PCDATA).
If you are in the unfortunate
circumstance of being located in a sub-division
serviced by FITL, you are ironically, at a major
disadvantage. Remember, DSL requires copper cabling,
a DSL modem in your home AND a DSL modem on the
other end of the copper (a DSLAM). Since FITL
pushes fiber to the curb, the only copper that
exists is between your home and the pedestal....and
their ain't no DSLAMS in the pedestals.
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| Q: What is Hybrid
Fiber Coax (HFC)? |
Hybrid Fiber Coax is a way of delivering video, voice
telephony, data, and other interactive services over
coaxial and fiber optic cables.
An HFC network works consists of a
headend office, distribution center, fiber nodes, and
network interface units.
The headend office receives information
such as television signals, Internet packets, and streaming
media, then delivers them through a SONET ring to distibution
centers. The distribution centers then send the signals
to neighborhood fiber nodes, which convert the optical
signals to electrical signals and redistributes them
on coaxial cables to residents' homes where network
interface units send the appropriate signals to the
appropriate devices (i.e. television, computer, telelphone).
An HFC network provides the necessary
bandwidth for home broadband applications, using the
spectrum from 5 MHz to 450 MHz for conventional downstream
analog information, and the spectrum from 450 MHz to
750 MHz for digital broadcast services such as voice
and video telephony, video-on-demand, and interactive
television.
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