A dark fiber or unlit fiber
is an unused optical fiber, available for use in fiber-optic
communication. The term dark fiber was originally used when
referring to the potential network capacity of telecommunication
infrastructure, but now also refers to the increasingly common practice of
leasing fiber optic cables from a network
service provider, or, generally,
to the fiber installations not owned or controlled by traditional carriers.
For capacity expansion
One reason that dark fiber exists in well-planned
networks is that much of the cost of installing cables is in the civil engineering work required. This
includes planning and routing, obtaining permissions, creating ducts and
channels for the cables, and finally installation and connection. This work
usually accounts for more than 60% of the cost of developing fiber networks.
For example, in Amsterdam's city-wide installation of a fiber network, roughly
80% of the costs involved were labour, with only 10% being fiber. It therefore
makes sense to plan for, and install, significantly more fiber than is needed
for current demand, to provide for future expansion and provide for network redundancy in case any of the cables fail.
Many fiber optic cable owners such as railroads or
power utilities have always added additional fibers for lease to other
carriers.
In common vernacular, dark fiber may sometimes
still be called "dark" if it has been lit by a fiber lessee and
not the cable's owner.
Overcapacity
In the dot-com
bubble, a large number of telephone companies built optical fiber
networks, each with the business plan of cornering the market in telecommunications by
providing a network with sufficient capacity to take all existing and forecast
traffic for the entire region served. This was based on the assumption that
telecoms traffic, particularly data traffic, would continue to grow exponentially for the foreseeable future.
The availability of wavelength-division multiplexing
further reduced the demand for fiber by increasing the capacity that could be
placed on a single fiber by a factor of as much as 100. As a result, the
wholesale price of data traffic collapsed. A number of these companies filed
for bankruptcy
protection as a result. Global Crossing and Worldcom are two high profile examples.
Just as with the Railway
Mania, the misfortune of one market
sector became the good fortune of another, and this overcapacity created a
new telecommunications market sector.
Market
For many years incumbent local exchange carriers
would not sell dark fiber to end users, because they believed selling access to
this core asset would cannibalise their other, more lucrative services.
Incumbent carriers in the US were required to sell dark fiber to competitive local exchange carriers
as Unbundled Network Elements (UNE), but
they have successfully lobbied to reduce these provisions for existing fiber,
and eliminated it completely for new fiber placed for fiber to the premises (FTTP)
deployments.
Competitive local carriers were not required to
sell dark fiber, and many do not, although fiber swaps between competitive
carriers are quite common. This increases the reach of their networks in places
where their competitor has a presence, in exchange for provision of fiber capacity
on places where that competitor has no presence. This is a practice known in
the industry as "coopetition".
Meanwhile, other companies arose specialising as
dark fiber providers. Dark fiber became more available when there was enormous
overcapacity after the boom years of the late 1990s through 2001. The market
for dark fiber tightened up with the return of capital investment to light up
existing fiber, and with mergers and acquisitions resulting in consolidation of
dark fiber providers.
Dark fiber capacity is typically used by network
operators to build SONET
and dense wavelength division multiplexing (DWDM) networks, usually
involving meshes of self-healing rings. Now, it is also used by
end-user enterprises to expand Ethernet local area networks, especially since the adoption
of IEEE standards
for Gigabit Ethernet and 10 Gigabit Ethernet over single-mode fiber. Running Ethernet
networks between geographically separated buildings is a practice known as
"WAN elimination".
Emerging markets
In the last decade, many higher education
institutions have bought up large quantities of existing fiber optics sitting
dormant. Starting in 1999, Larry Starr, a technology director from the
University of Illinois, connected the Urbana-Champaign campus to major
academic, research, and telecommunications facilities in the Chicago area. At
the same time, other schools began creating large urban networks to directly
connect their school campuses with hospitals and large telecommunications
companies in metropolitan areas. Since then, the U.S. research and education
(R&E) community have been aggressively pursuing a revolutionary new means
for delivering advanced networking capabilities. With the plummeting prices of
fiber due to the over abundance, the option to own fiber networks has stomped
out the competition leasing of commercial circuits elsewhere. Experts say that
a mile of dark fiber that in the past would sell for $1,200 has sold, for as
low $200 or less. The downturn in telecommunications has offered significant
savings to schools, since intercity networks may include several hundred to
several thousand miles of fiber optic cable.
Variations
·Managed dark fiber is a
form of wavelength-division multiplexed access to otherwise dark fiber where a
simple "pilot" signal is beamed into the fiber by the fiber provider
for management purposes using a transponder tuned to the assigned wavelength.
DWDM systems generally require central management because their closely spaced
wavelengths are subject to disruption by signals on adjacent wavelengths that
are not within tightly controlled parameters, especially if amplification is
required for signal transmission over 100 km.
·Virtual dark fiber
using wavelength multiplexing allows a
service provider to offer individual wavelengths ("lambdas" (λ)
or "colors"), where access to a dark narrowband
wavelength-division multiplexing (WDM) optical channel is provided
over a wavelength division multiplexed fiber network that is managed at the
physical level, but unlit by the network provider. This is typically done using
coarse wavelength division multiplexing CWDM because the wider
20 nm spacing of the wave bands makes these systems much less susceptible to
interference.
Rate of expansion
According to Gerry Butters, the former head of
Lucent's Optical Networking Group at Bell Labs, Moore's
law holds true with fiber optics. The amount of data coming out of an
optical fiber is doubling every nine months. Thus, excluding the transmission
equipment upgrades, the cost of transmitting a bit over an optical network
decreases by half every nine months. The availability of dense
wavelength-division multiplexing DWDM and coarse wavelength division multiplexing CWDM is rapidly
bringing down the cost of networking, and further progress seems assured.
Terra firma links between cities and cables that run alongside roads and
into houses and officers are certainly impressive — and without them we
wouldn’t have an internet!
— but sinking a cable into the Pacific, Atlantic, Indian, and even Arctic
Oceans requires a billion-dollar logistical feat that requires months or even
years to enact.
Across these cables, which span distances of up to 13,000 km (8,000 miles)
and have total lengths over 21,000 km (13,000 miles), terabits of information
squirt from one side of the planet to another.
To get from London to Tokyo, your packets can traverse Europe, the
Mediterranean, the Red Sea, the Arabian Sea, the Indian Ocean, and finally the
South China Sea — or they can hop across the Atlantic, the entirety of
continental North America, and then long haul over the Pacific.
These cables are just three inches thick, carry just a few
optic fibers, and have total capacities of between 40Gbps and 10Tbps, and
latencies that are close to the speed of light and just a few milliseconds in
duration.
628Q.What are the differences between a rich man
and a poor man?See 172Q
RICH MAN
POOR MAN
1] He buys the “time” of a poor man.
2] “Money” works for him.
3] He invests money for his development
4] He has a vision.
5] Mostly they are not so educated.
6] He has dreams.
7] He makes the law.
8] He plans.
1] He sells his “time” to the rich man
2] He works for money.
3] Tomeet his family maintenance.
4] He has no vision.
5] They are educated.
6] He has needs.
7] He follows the law.
8] He implements.
In September 2011, OPERA researchers reported that muon
neutrinos were apparently traveling apparently at faster
than light
speed.
This is a contradiction to special theory of light.
630Q. Is there really an anti-universe? Theoretically, yes. Our universe is almost entirely matter, but
cosmologists say that the Big Bang must have produced an equal amount of
anti-matter. The problem of where that anti-matter has gone is known as the
"baryon
assymetry." One theory goes that an entire universe of
anti-matter could exist on the edge of our own.
631Q. How could we possibly find it? Using an Alpha Magnetic Spectrometer. One of these futuristic-sounding
devices is set to be installed at the International Space Station next year.
The 8.5 ton instrument is designed to detect dark matter in our own universe,
but it "may also answer questions not yet asked," says Robert
Evans at ABC News.
632Q. What's the difference between dark matter and anti-matter? Dark matter exists in our universe — in fact, scientists think it may make up
23 percent of it — but it's incredibly difficult to detect as it
does not reflect light. Anti-matter is the opposite of matter, and barely
exists in our universe at all. Matter and anti-matter annihilate each other on
contact, creating energy.
633Q. How easy will the anti-universe be to detect? Not easy. Both matter and anti-matter will produce light in the same way,
so scientists say the only way to detect an anti-matter region is to identify
the boundary that keeps it separate from a matter-dominated region. The
annihilation reactions within that boundary would produce gamma rays, and it is
these that the Alpha Magnetic Spectrometer may be able to detect from
deep space.
634Q. What would the anti-universe contain? We have no idea. Science fiction writers have long imagined it to be a mirror image of our own universe,
with the capacity to produce life — a theory that some scientists actually subscribe
to. In any case, so little is known about it that no theory is too far-fetched.
NPR's Ron Elving, for example, claims the
anti-universe exists in Alaska, though his proof — Tea Partier Joe
Miller's primary win over Sen. Lisa Murkowski (R-AK) — is unscientific, to say
the least.
635Q. What is Cherenkov radiation?
Cherenkov radiation (also spelled Čerenkov) is electromagnetic radiation emitted when a chargedparticle (such as an electron)
passes through a dielectric medium at a speed greater than
the phase velocity of light
in that medium. The charged particles polarize the molecules of that medium,
which then turn back rapidly to their ground state, emitting radiation in the
process. The characteristic blue glow of nuclear
reactors is due to Cherenkov radiation.
636Q. Whyare there more cyclones in Arabian Sea
recently?
A more familiar phenomenon El Nino was found to suppress cyclones formation
in the Arabian Sea.
The reason why El Nino Modoki brings only fewer number of cyclones in the
Bay Bengal is because on e of the two descending limbs of the Walker Cell
onthe other hand brings over the
western Pacific and Bay of Bengal.
The descending limb causes dry conditions not conductive for cyclone
formation.
The sea surface temperatures are too low for cyclogenesis.
Cyclones usually do not form during monsoon season.
Few reasons for this are
Atmospheric parameters
Low level relative vorticity
Mid-tropospheric relative humidity
Vertical wind shear
637Q. When
does development is possible?
If you are a prochanger
If you have guts to change
If you are dare enough
If you are an introvert
If you can expand
If you have confidence
If you have aim
If you ca n experiment
Live every second.
638Q. What
are the learning percentages?
20% of what we read
30% of what we hear
40% of what we see
50% of what we say
60% of what we do
Further improvement is possible if we frequently practise them.
639Q. What
things effect our personality?
Fear of poverty
Fear of death
Fear of ill-health
Fear of loss of love
Fear of old age
Fear of criticism
Poverty alone is sufficient to kill our ambition, confidence, hope….
Fear leads to superstition, hypocrisy, dogmas,…
640Q. What do
we need to come up?
Home work
Hard work
Smart work
Team work
Net work
Secondly
Power of imagination
Power of voice
Power of language
Power of giving
Thirdly say always “I can do” but not “Can I do?”
Fourthly there is enough in this world. You need not exploit other.
641Q. What are the evidences
of continental drift theory?
Geophysicist Jack Oliver is credited with providing
seismologic evidence supporting plate tectonics which encompassed and
superseded continental drift with “Seismology and the New Global Tectonics,”
published in 1968, using data collected from seismologic stations, including
those he set up in the South Pacific.
It is now known that there are two kinds of crust, continental crust and oceanic
crust. Continental crust is inherently lighter and of a different
composition to oceanic crust, but both kinds reside above a much deeper fluid
mantle.
Oceanic crust is created at spreading centers, and this, along
with subduction,
drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas
of isostatic imbalance.
The theory of plate tectonics explains all this,
including the movement of the continents, better than Wegener's theory.
642Q.Homeopathicpotency scale?
X Scale
C Scale
Ratio
Note
1X
—
1:10
described as low potency
2X
1C
1:100
called higher potency than 1X by homeopaths
6X
3C
10−6
8X
4C
10−8
allowable concentration of arsenic in U.S. drinking water[11]
If pure water was used
as the diluent, no molecules of the original solution remain in the water.
60X
30C
10−60
Dilution advocated by Hahnemann for most purposes: on
average, this would require giving two billion doses per second to six
billion people for 4 billion years to deliver a single molecule of the
original material to any patient.
Note: the "X scale" is also called "D
scale". 1X = 1D, 2X = 2D, etc.
643Q. What
are the Seven Seas?
There seem to be about as many answers to this question as there are, well,
combinations of seas and oceans. The New Grolier Multimedia Encyclopedia
[1993], for example, says that in the Age of Discovery, the seven navigable
seas of the world were the Atlantic, Pacific, Arctic, and Indian Oceans, as
well as the Mediterranean Sea, the Caribbean Sea, and the Gulf of Mexico.
Not so says Don Groves in The Oceans [John Wiley, 1989]. He lists the
seven ancient seas as the Mediterranean, the Red, the Black, the Adriatic, and
the Caspian, plus the Persian Gulf and the Indian Ocean. And Robert Hendrickson
in The Ocean Almanac [Doubleday, 1984] maintains yet another compendium. He
agrees with Groves on the Mediterranean and Red Seas, the Indian Ocean, and the
Persian Gulf, but adds the China Sea and the West and East African Seas to top
off his list.
One less confusing note: Both Groves and Hendrickson agree on a list of the
modern seven seas: The North and South Atlantic, the North and South Pacific,
the Arctic and Antarctic, and the Indian.
644Q. What causes the Gulf Stream?
The Gulf Stream is a jetlike current of warm ocean water that meanders
northeastward from the Straits of Florida to the coast of northwestern Europe.
Off Florida, where the current is strongest, it has been affecting sailors
since the Spanish explorer Ponce de Le\227n first noticed it in the early
1500s.
Several factors work together to generate the stream. In the equatorial
Atlantic Ocean, the prevailing winds blow west (toward the Americas); but
farther north, they blow east (toward Europe). The combined effect creates a
clockwise circulation of water in the North Atlantic. The so-called Coriolis
effect - a rightward deflection of the water in the north Atlantic due to
Earth's rotation and the curvature of the planet's surface - makes the
northward flow narrower and swifter than that of the water heading southward.
What happens is that the Coriolis forces water to build up in the center of the
ocean; this water mass then drifts west, squeezing the northward current into a
narrow area along the U.S. coast. Hence the Gulf Stream.
(Why the water mass drifts west and not some other direction appears to be a
question that even oceanographers have trouble explaining. When we asked one
researcher, he gave a nervous chuckle and mumbled something to the effect that
he'd explain it if we had time for an hour-long lecture on geophysics. We
passed on his offer.)
In the narrow Straits of Florida, the Gulf Stream reaches a maximum speed of
four knots, and its transport encompasses a volume of 1.1 billion cubic feet of
water per second - or approximately 1,800 times that of the Mississippi River.
But the Stream diffuses as it continues eastward. The water returning southward
- called the Canaries current - plods at mere hundredths of a knot.
645Q. Why is the ocean salty?
When Earth was still young, its atmosphere contained a nasty mix of hydrogen
chloride, hydrogen bromide, and other noxious emissions from volcanoes. Some of
these gases dissolved in the primitive ocean, making it salty, oceanographers
believe.
Today, however, most of the salt in the oceans comes from the continual
rinsing of the earth. Rain falling on the land dissolves the salts in eroding
rocks, and these salts are carried down the rivers and out to sea. The salts
accumulate in the ocean as water evaporates to form clouds. The oceans are
getting saltier every day, but the rate of increase is so slow that it is
virtually immeasurable.
Ocean water is currently about 3.5 percent salt. If the oceans dried up,
enough salt would be left behind to build a 180-mile-tall, one- mile-thick wall
around the equator. More than 90 percent of that salt would be sodium chloride,
or ordinary table salt.
646Q. What is the temperature of the bottom
of the ocean at the equator?
The ocean bottom temperature is more or less the same everywhere in the
world, generally 33 F to 36 F. Why? Because cold water is heavier than warm
water. Like spilt molasses, cold arctic and antarctic water slowly spreads out
underneath warmer surface waters around the globe, eventually reaching the
equator.
647Q. What is the remotest inhabited island?
Tristan da Cunha, a 38-square-mile volcanic outpost, is the remotest
inhabited island in the world, according to the Guinness Book of Records.
It's situated 1,510 miles southwest of its nearest neighbor, St. Helena, and
1,950 miles west of Africa. Discovered by the Portuguese admiral of the same
name in 1506, and settled in 1810, the isle belongs to Great Britain and has a
few hundred residents.
Coming in a close second - and often wrongly cited as the most distant land
- is Easter Island, located 1,260 miles east of its nearest neighbor, Pitcairn
Island, and 2,300 miles west of South America.
The mountainous 64-square-mile island was settled around the 5th century,
supposedly by people who were lost at sea. They had no contact with the outside
world for more than a millennium, giving them plenty of time to construct more
than 1,000 enormous stone figures, called moai, for which the island is most
famous.
On Easter Sunday, 1722, however, Dutch settlers moved in and gave the island
its name. Today, 2,000 people inhabit the Chilean territory. They share one
paved road, a small airport, and a few hours of television per day.
648Q. How deep can a human dive on a lungful
of air?
On December 16, 1994, a lad from Key Largo nicknamed "Pipin" (his
real name is Francisco Ferreras), rode a lead sled 417 feet down, then shot
back to the surface 2 minutes, 24.45 seconds later to break his own world
record for deep-diving on a lungful of air. Afterward, Pipin was pretty
nonchalant about the whole thing, telling reporters, "It's just one more
step on the way to 500 feet."
Had he been wearing standard scuba gear, Pipin could descend to about 350
feet before suffering "rapture of the deep," a narcotic like stupor
caused by compressed nitrogen. If Pipin worked for a commercial diving outfit
that serviced oil rigs, he'd spend weeks in pressurized nodules so he could
work at a depth of 1,000 feet. Some test dives using oxygen mixed with various
exotic gases have enabled people to survive at 2,400 feet, but that seems about
the limit for unprotected humans.
649Q. Do fish ever get thirsty?
A book conveniently titled Do Fishes Get Thirsty? [Franklin Watts,
1991] provides the answer to this question. It explains that fish living in the
ocean need to drink a lot to avoid shriveling up like prunes.
"Water flows in and out of a fish's body through a process called
osmosis," the authors explain. "In osmosis, water moves from where
there is less dissolved salt to where there is more. Since seawater is saltier
than the liquids in a fish's body, water inside the fish is constantly flowing
out." The fish drinks to replace the lost water.
650Q. What causes tidal waves?
First, tidal waves have
nothing to do with tides. Tidal waves - here's where you wish you hadn't napped
in physics class - are the dissipation of energy in a viscous fluid over an inclined
plane. To translate this into
plain English: The energy source usually is an under-sea earthquake (although
it could also be a meteor strike or under-sea explosion); the viscous fluid is
the ocean; and the inclined plane is the ocean floor sloping up toward land. Let's take the case of an
earthquake. When the earth thrusts up and down, it also moves all water above
it up and down. This generates a huge wave traveling outward in a series of
concentric rings. In deep water, most of the tidal wave, or tsunami, remains
hidden beneath the surface. But as the tsunami moves toward more shallow water,
its enormous energy is forced to the surface. What makes a tidal wave so
destructive is not so much its height (it can reach more than 100 feet), but
its speed and tremendous volume of water. In the open ocean, tsunami are hundreds
of miles wide and travel at jetliner speeds. Near land they slow down to mere
freeway speeds, but even a five-foot tsunami can dump harborfuls of water on a
unlucky seaside town.
