2. OUTLINE
• Summer Training at Signal and Telecommunication
Department North Eastern Railways, Izatnagar, Bareilly from
15th June, 2015 to 11th July, 2015.
• An amazing experience as I got to see, how exactly the
communication system works for Indian Railways.
• Main Objective was to learn Optical Fiber Communication In
Railways.
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3. OPTIC FIBER
• An optical fiber is a cylindrical
dielectric waveguide made of low-
loss materials such as silica glass.
• It has two main component layers: A
Core & A Cladding.
• It has a central core in which the light
is guided, embedded in an outer
cladding of slightly lower refractive
index.
• It works on the principle of total
internal reflection
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4. INSIDE OPTICAL FIBER CABLE
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• Core – thin glass center of the fiber where light
travels.
• Cladding – outer optical material surrounding
the core
• Buffer Coating – plastic coating that protects the
fiber.
5. TYPES OF OPTICAL FIBER
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OPTICAL FIBERS
MULTIMODE
FIBERS
STEP INDEX GRADED INDEX OM1/OM2/OM3
SINGLEMODE
FIBERS
STEP INDEX
6. TYPES OF OPTICAL FIBER(conti…)
SINGLE MODE FIBER
• Used to transmit one signal per
fiber.
• Used in telephone and cable TV.
• They have small cores(9 microns
in diameter) .
• Transmit infra-red light from
laser.
MULTI MODE STEP INDEX FIBER
• Used to transmit many signals
per fiber.
• Used in computer networks.
• They have larger cores(62.5/50
microns in diameter)
• Transmit infra-red light from LED.
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MULTI MODE GRADED INDEX FIBER
• Core diameter : 50/62.5 microns.
• Cladding size: 125-140 microns.
• Refractive index changes
continuously.
• Low dispersion.
• Core refractive index is made to
vary as a function of the radial
distance from the center of the
fiber
OM1: refer to the commonly used 62.5/125
multimode fiber.
OM2: refer to the commonly used 50/125
cable.
Both OM1 and OM2 easily supports
applications ranging from Ethernet to gigabit
Ethernet.
OM3: Typically this fiber optic patch cable is
with 50/125 multimode fiber, with aqua jacket.
They support bandwidth up to 10GB upto
300 meters.
9. Fiber geometry parameters
• The three fiber geometry
parameters that have
the greatest impact on
splicing performance
include the following:
• Cladding diameter
• Core/clad concentricity
(or core-to- cladding
offset)
• Fiber curl
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12. COMPARATIVE STATEMENT
ADVANTAGES
• Wide bandwidth
• Light weight and small
size
• Immunity to
electromagnetic
interference
• Lack of EMI cross talk
between channels
• Lack of sparking
• Compatibility with solid
state sources
• No emission licenses
DISADVANTAGES
• High investment cost
• Need for more expensive
transmitters and
receivers
• Fragility
• Opaqueness
• Requires special skills
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13. AREAS WHERE WE CAN USE IT
• Medical
Used as light guides, imaging tools and also as lasers for surgeries
• Defence/Government
Used as hydrophones for seismic and SONAR uses, as wiring in
aircraft, submarines and other vehicles and also for field networking
• Data Storage
Used for data transmission
• Telecommunications
Fiber is laid and used for transmitting and receiving purposes
• Networking
Used to connect users and servers in a variety of network settings
and help increase the speed and accuracy of data transmission
• Industrial/Commercial
Used for imaging in hard to reach areas, as wiring where EMI is an
issue, as sensory devices to make temperature, pressure and other
measurements, and as wiring in automobiles and in industrial
settings 13
14. JOINING OF FIBER- SPLICING
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Mechanical splicing Fusion splicing
Reflection losses
(-45 db to -55 db)
No reflection losses
Insertion loss
(0.2 db)
Very low insertion
loss
(0.1 db to .15 db)
cost – high Comparatively less
18. TIME DIVISION MULTIPLEXING
• Time on the information channel, or fiber, is shared among the many
data sources
• The multiplexer MUX can be described as a type of ―rotary switch,
which rotates at a very high speed, individually connecting each input
to the communication channel for a fixed period of time
• The process is reversed on the output with a device known as a
demultiplexer, or DEMUX
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19. WAVELENGTH DIVISION MULTIPLEXING
• Data from each TDM channel is loaded on one optical frequency (or
wavelength, λ) of a particular wavelength band
• These wavelengths are then multiplexed onto one fiber with the help
of WDM multiplexers
• Other side of the network these wavelengths are demultiplexed by
using either optical filters, gratings or WDM demultiplexer
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20. PLESIOCHRONOUSDIGITALHIERARCHY(PDH)
• In Europe a standard was adopted where thirty-two,
64kbit/s channels were combined to produce a structure
with a bit rate of 2.048 Mbit/s (usually referred to as 2
Mbit/s)
• Four, 2 Mbit/s signals were combined together to form an 8
Mbit/s signal (actually 8.448 Mbit/s).
• As the need arose further levels of multiplexing structure
were added to include rates of 34 Mbit/s (34.368), 140
Mbit/s (139.264) and 565 Mbit/s (564.992).
• These transmission speeds are called Plesiochronous Digital
Hierarchy or PDH rates
• Although each of the systems works fine as a stand-alone
hierarchy, it does make international inter-connection very
difficult and costly
• This was the major reason for the development of a new
internationally agreed standard
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22. DEMISE OF PDH
1. Bit interleaving multiplexing
2. Lack of Flexibility
3. Lack of consensus on standards
4. Limited Network
Management/debugging
5. Defined for selected topologies
6. Mode of Transmission
7. Less bandwidth compared to SDH
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23. SYNCHRONOUS DIGITAL HIERARCHY (SDH)
• SYNCHRONOUS :ONE MASTER CLOCK & ALL ELEMENTS SYNCHRONISE WITH
IT.
• DIGITAL: INFORMATION IN BINARY.
• HIERARCHY: SET OF BIT RATES IN A HIERARCHIAL ORDER
At each hierarchical level, synchronous transport module is formed with
information pay-load and overhead bits and a synchronizing mechanism is in-
built to ensure all network elements work to a master clock reference
All the limitations of PDH are removed in SDH
• High transmission rates
• Simplified add & drop function
• High availability and capacity matching
• Reliability
• Future-proof platform for new services
• Interconnection
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26. ADVANTAGES OF SDH
• SDH permits the mixing of the existing European and North American PDH bit rates
• All SDH equipment is based on the use of a single master reference clock source & hence
SDH is synchronous
• Compatible with the majority of existing PDH bit rates
• SDH provides for extraction/insertion, of a lower order bit rate from a higher order
aggregate stream, without the need to de-multiplex in stages.
• SDH provides for a standard optical interface thus allowing the inter-working of different
manufacturer’s equipment
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