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| DISCLAIMER |
The information provided
on this page as is without any express or implied
warranties. Although, every effort has been taken
to ensure the accuracy of the information contained
in this page, the company assumes no responsibility
for errors or omissions, or for damages resulting
from the use of the information contained herein.
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| Q.5.
What is the transmission capacity of single mode fiber? |
A.
The transmission capacity i.e. bit rate, of a optical
fiber is dependent upon dispersion characteristics
of an optical fiber. This parameter varies with wavelengths.
The dispersion is further divided in two type i.e.
chromatic dispersion and polarization mode dispersion.
The polarization mode dispersion is more prominent
for data rates above 10 Gbps. The chromatic dispersion,
which is defined in ps/nm-km, is further divided in
two different types i.e. material dispersion and waveguide
dispersion. The Chromatic dispersion causes broadening
of light pulse as it travels along the core of optical
fiber. Because of this Bit Error Rate (BER) is generated
in digital transmission systems. With the help of
linear imperical formula (with 1 dB power penalty),
it is possible to find out the maximum bit rate transmission
for a given repeater distance and dispersion. The
formula is as follows:
B2 L D < 104,000
Where,
B= Bit Rate in Gb/s
L= Distance in Km
D= Dispersion in ps/nm-km
From the above formula, it can be that with a dispersion
of 18 ps/nm-km, 2.5 Gbps signal can be transmitted
over a distance of 800 Km between the repeater station.
The polarization mode dispersion (PMD) also limits
the transmission capacity of fiber but more prominently
for data rates above 10 Gbps. The PMD of a fiber is
measured in ps/Ökm. As a rule of thumb, the total
PMD of a fiber link should be less than one tenth
of bit period of a given data rate. For example, a
fiber optic link with PMD of 0.5 ps/Ökm would be able
to transmit 10 Gbps signal over a distance of 400
Km comfortably. |
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| Q.6.
What is splicing and which equipment are used for splicing? |
A.:
Optical
fibers are made of glass and these fibers are protected
from external forces by cabling. The process of jointing
two finite lengths of optical fibers is called splicing,
to be more precise 'fusion splicing'. The optical
are provided with first level of protection by the
use of acrylic coating, followed by coloring for identification
and then by either placing in single or multiple tubes.
The splicing (more simply jointing) of fibers consists
of following set of activities:
1. Accessing fibers
2. Removing coating of fibers
3. Cleaning of fibers
4. Cleaving of fibers
5. And finally splicing of fibers with the help of
splicing machine. Various different technologies adopted
by splicing machine are such as Local Injection and
Detection (LID) and profile alignment system (PAS).
Various equipment and tools used in splicing process
are Fiber Stripper, Fiber Cleaver and Fusion Splicing
machine. |
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| Q.7.
What do we mean transmission at 1310 nm and 1550 nm
? |
| A.:
The optical fibers transport the light (lasers) modulated
with the signal. 1310 and 1550 nm refers to the specific
wavelength used for transmission. The single mode
fibers were initially optimized for transmission at
1310 nm and 1550 nm, however with the advances in
the fiber manufacturing technology, today's' fibers
can transmit wavelengths from 1530 to 1565 nm (called
as C band), from 1565 to 1620 nm (called as L band)
and even wavelengths in 1440 nm region. |
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| Q.8.
What is the difference between unarmoured, armoured,
ADSS,and OPGW cables? |
A.
The optical fiber cables are installed in various
different ways in the Outside Plant (OSP). Based on
the way, the cables are installed different cable
constructions have been devised. The unarmoured cable
or alternatively called metal free cables do not have
any metallic components used in the cable construction.
These cables are installed in ducts.
The armoured cables have metallic components such
as corrugated metal tape and metal strength members
(generally used in central tube type cable). The presence
of corrugated metal tape provides strength to the
construction and has superior mechanical characteristics
than unarmoured cable. These types of cables are directly
buried.
ADSS stands for All Dielectric Self-Supporting cable.
These types of cables have superior tensile properties
such that they can be installed directly over the
supporting poles with necessary fixing hardware. These
type of cables do not have any metallic components
instead they use aramid yarns for extra tensile strength.
OPGW stands for Optical Ground Wire cable. The fibers
in this type of cable are placed in the slots provided
and the complete cable is made of metal. These type
of cable serve dual purpose of housing and protecting
the fibers and act as a ground wire for high power
transmission system. |
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| Q.9.
What does PDH & SDH stand for? |
A.
PDH stands Plesiosynchronous Digital Hierarchy and
SDH stands for Synchronous Digital Hierarchy. Both
PDH & SDH use Time Division Multiplexing technique.
Further, there are different levels in each hierarchy.
PDH has 4 levels viz. 2 Mbps, 8 Mbps, 34 Mbps and
140 Mbps. The basic multiplexing frame in PDH is 2
Mbps (also called as E1 in European market) which
consists of 30 x 64Kb time slots (channels). Each
64Kb channel is required for transmission one voice
channel. 8 Mbps system is realized by using four (4)
2 Mbps, 34 Mbps is realized by using four (4) 8 Mbps
system and 140 Mbps system is realized by using four
(4) 34 Mbps system.
SDH has four levels viz. STM-1 (155 Mbps), STM-4 (625
Mbps), STM-16 (2.5 Gbps) and STM-64 (10 Gbps). The
basic multiplexing rate in this hierarchy is STM-1,
which is 155 Mbps, and this is equivalent to 63 E1s.
Similar to PDH, higher levels of SDH are realized
by using multiple immediate lower levels. In SDH,
it possible to extract an E1, unlike in PDH which
requires down conversion of higher level signal to
lower level. |
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