Report on NW Indian Railway

1. SUMMER TRAINING REPORT
on
NORTH-WEST INDIAN RAILWAYS
Submitted by
RAM NIWAS BAJYA
(VII Sem ECE)
SESSION 2013-2014
Submitted for the partial fulfillment for the award of the degree of
B.Tech (Electronics & Communication Engg.) of
Rajasthan Technical University, Kota
Submitted To:
Submitted By:
Mr. Ravi Goyal
Ram Niwas Bajya
(Asst. Prof., Deptt. Of ECE)
B.Tech, 4thYEAR
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
GOVT. ENGINEERING COLLEGE AJMER
(An Autonomous Institute of Government of Rajasthan)
Badliya Chouraha, N.H.-8, Bypass, Ajmer – 305002

2. SUMMER TRAINING REPORT
on
NORTH-WEST INDIAN RAILWAYS
Submitted by
RAM NIWAS BAJYA
(VII Sem ECE)
SESSION 2013-2014
Submitted for the partial fulfillment for the award of the degree of
B.Tech (Electronics & Communication Engg.) of
Rajasthan Technical University, Kota
Mr. Ravi Goyal
Mrs. Rekha Mehra
Seminar Coordinator
HOD, Deptt. Of ECE
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
GOVT. ENGINEERING COLLEGE AJMER
(An Autonomous Institute of Government of Rajasthan)
Badliya Chouraha, N.H.-8, Bypass, Ajmer

3. RAM NIWAS BAJYA
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4. ACKNOWLEDGEMENT
I have also taken training at Supervisors Training Centre (North. Western.
Railway, Ajmer Division), Ajmer.
It was highly educative and interactive to take training at this center. In technical
field, theoretical knowledge is incomplete without practical knowledge and I
couldn’t find any place better than this to update myself. I am highly thankful to our
training Coordinator as well Principal of STC
Mr. Sanjay Bijawat Sir to grant me permission to take training at such a
coveted industry. And there was always a friendly guidance from Mr. Shakti
Singh Sir, for the better management of the project. I would also like to take
this opportunity to acknowledge the guidance and support from Mrs. Rekha
Mehra (H.O.D. of EC Engg.) and Mr. Ravi Goyal sir (Seminar
coordinator) for undergoing training at a reputed public sector company like
S.T.C.
RAM NIWAS BAJYA
B.TECH, VII SEM (10EC67)
RAM NIWAS BAJYA
ii

5. ABSTRACT
I have done my Summer Training under Indian Railways Supervisor Training
Center, Electronics & Signal telecom Department, Ajmer Division.
We have learn many things like passenger reservation system, Network Topology
and categories, working of Exchange, Microwave communication system, deep
concept of OFC . We learn about Railnet, which provide computer
connectivity between Railway Board, Zonal Railways, Production units,
RDSO, Centralized Training Institutes, CORE, MTP/Kolkata etc. The course
is mostly focused on communication system.
The training at North. Western. Railway, Ajmer was a great experience and
very useful to bridge the gap between theoretical knowledge and industrial
working.
RAM NIWAS BAJYA
iii

6. TABLE OF CONTENTS
S.
Contents
NO.
1.
Acknowledgement
Page No.
2.
Abstract
iii
3.
List of Tables
4.
List of
figures
A
B
C
D
E
F
2.1a
2.3a
3.3a
3.4a
3.4b
3.4c
3.5
3.6
4.3a
4.5a
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
ii
Training Labs
Medium Index of Refraction
Advantage of OFC communication
TX parameters & their meaning
Optical parameters & their meaning
RX parameters & their meaning
Interconnection of PRS & UTS Servers
CONCERT APPLICATION ARCHITECTURE
Railnet General Arrangement
Railnet Phase I
Railnet Phase II
Railnet Phase IIl
Network Topology
a Mesh topology
b Star topology
c Bus topology
d Ring topology
Classification of
a LAN
Networks
b MAN
c WAN
RCP card
tone generator card
bare fiber and OFC cable
light travel in strong field
light rays and its angles
Snell’s law
Total internal reflection
Optical fibre mode
Optical fibre index profile
acceptance angle
Frequency Vs Attenuation In Various Types
of Cable
5.10 parts of optic fibre cable
4
30
34
44
45
46
5
6
9
11
12
13
14
15
16
16
17
18
18
21
23
27
28
29
31
32
33
33
34
35
36
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7. 5.11
5.12
5.13
5.14
5.15
Fusion Splice
mechanical splice
transmitter with internal modulator
transmitter with external modulator
Digital Optical receiver with components and
sections
5.16 Multiplexer & De-multiplexer
5.
Chapter 1
Introduction To Northern Western Railway and
STC Office Ajmer
1.1
Northern Western Railway
Aims
Need Of Training
Objectives
Labs
1.2
1.3
1.4
1.5
6.
43
43
47
48
49
52
1
2
3
3
4
4
PRS & UTS Network
Chapter 2
2.1
Introduction
5
2.2
Interconnection of PRS & UTS Servers
5
2.3
PREVIOUS SET UP AT PRS/DELHI
6
2.4
CONCERT APPLICATION ARCHITECTURE
6
2.5
Other aspects of PRS
7
7
7
7
2.5A
2.5B
2.6
Use of Radio Frequency modems
2.6A to the Passengers
Benefits of
2.6B to the Railways
PRS
Technology used
Future Enhancements
New challenges
Railnet – An Overview
7
8
9
3.2
Introduction
Objectives
3.3
Railnet General Arrangement
9
2.7
2.8
2.9
7.
Use of satellite data links
Chapter 3
3.1
8
8
9
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8. 3.4
The Railnet Work
3.5
Network
Topology
3.6
3.7
Categories
of
Networks
3.5A
3.5B
3.5C
3.5D
3.6A
3.6B
3.6C
10
Mesh topology
Star topology
Bus topology
Ring topology
14
15
16
LAN (Local Area Network)
17
MAN (Metropolitan Area
Network)
WAN (Wide Area Network)
18
16
18
19
4.1
PROTOCOL
Exchange
Introduction
4.2
4.3
4.4
4.5
4.6
4.7
Power Supply Unit card
RAX Control processor(RCP)
Switching Network(TIC)
Tone generator with Diagnostic card(TGS)
Signal Processor (SP) card
Subscriber line card(SLC) or line circuit card(LCC)
Chapter 5
OPTICAL FIBRE
5.1
5.2
Need for OFC
OFC propagation fundamental
27
27
5.3
Propagation Modes
32
5.4
Numerical Aperture
34
5.5
Merit & Demerit of OFC and its Application
34
5.6
36
5.9
Nomenclature & Sizes of OFC
Signal Attenuation in Optical Fibber
Construction of Optical Fibre Cable
Jointing and termination of OFC
5.10
Fiber Breaks Grating
50
5.11
Characteristics of FBG
51
5.12
Multiplexer & De-multiplexer for OFC
52
10
Conclusion
54
11
BIBLOGRAPHY & REFRENCES
55
8
9
CHAPTER 4
5.7
5.8
20
20
21
22
23
24
25
37
40
42
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9. Chapter 1
INTRODUCTION TO NORTH-WESTERN RAILWAYS AND STC,
AJMER
1.1
NORTH WESTERN RAILWAYS:
North Western Railways which is overseen by the Ministry of Railways of the
Government of India came being on 1st October, 2002. It was carved out of 2 divisions
each from Northern and Western Railways.
Jaipur Division:
This division was formed after merging parts of BB&CI, Jaipur State Railways and
Rajputana Malwa Railway. Jaipur Division serves the states of Rajasthan, Uttar Pradesh
and Haryana. The total no. of stations on this division are 128 and the total no. of trains
run are 146. Jaipur station alone deals with 88 BG & 22 MG trains and
35,000passengers in a day.
Bikaner Division:
This division was established in 1924 and it serves the states of Rajasthan, Punjab and
Haryana. The total no. of situations in these divisions is 198 and the total no. of trains
dealt with are 142 including the rail bus and BG and MG mail/exp and passenger trains.
Bikaner division has 12 Computerized Passenger Reservation System functioning. The
staff strength of this division in all categories is 13728.
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10. Jodhpur Division:
This division was up in the year 1882 and it consists primarily of semi–urban
districts of Rajasthan. It covers areas of Jodhpur, Pali Marwar, Nagaur Jalore, Barmer,
Jaisalmer. It also covers certain districts of Gujarat state. This division also serves certain
sensitive areas of Rajasthan such as Jaisalmer, Barmer and Pokaran. This division has a
total of 144 stations and deals with 92 trains in the inward and outward directions.
Fifteen Computerized Passenger Reservation System Centers exist over this division. The
staff strength of this division in all categories is 10231.
Ajmer Division:
This division is spread over the states of Rajasthan and Gujarat. It is predominantly
a cement loading division as many cement plants of Rajasthan are located within
the jurisdiction of Ajmer. This division has 130 stations and the total no. of
trains run over the division amounts to 36 in both the passenger and mail/exp category.
At present there are 12 Computerized Passenger Reservation System Centers functioning
over this division. The staff strength of this division in all categories is 9046.
1.2 SYSTEM TECHNICAL SCHOOL, AJMER
System Technical School Ajmer, renamed as Supervisors Training Centre, was
inaugurated on 10th of July 1957. Ajmer City was chosen for establishing a Supervisor straining
Centre, as it is the only city where all the important workshops of the then Western Railway are
situated i.e. Diesel Locomotive workshop, Wagon shop, Carriage shop, Electrical Power House,
Electric Production Workshop and Signal workshop. Supervisors Training Centre, Ajmer is one
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11. of the most prestigious training center of Indian Railways. It has the pride of imparting training to
all Supervisors of Northwestern Railway and Western Railway of Mechanical & Electrical
Departments.
1.3 AIMS
Our country has a tremendous scope for continuous growth in the field of Railway transportation
that too with the positive competition with road transportation. Hence technology up-gradation,
improved productivity, enhanced safety etc. are the keys to take over the challenge of growth in
the true spirit. The training is the only mode which can prepare the newly inducted railway
supervisors for making them a positive asset to the organization. More over the refresher courses
are meant for updating the knowledge of the supervisors representing the middle management as
per the latest technical instructions from R.D.S.O. and Railway Board from time to time. The
supervisors can even have an idea that why and on what ground the instructions have been issued
to enable them to implement the same in the field in the best of its sprit.
Further the field units are having their own needs for imparting training in various fields like
Welding Technology, Supervisors Development Program, Computer know how, Internal Audit
Course plan for ISO as well as pre-selection training of the reserved candidates appearing in
LDCE examination.
1.4 NEED FOR TRAINING
Training is an investment and not expenditure: A trained man is an asset. The need of training
has become more essential with the development of Electric locomotive, Diesel locomotives,
Super-Fast Trains, Introduction of rolling stocks with Air brake system etc. Training is always
carried out for a purpose. It is the means of maintenance and improving the level of performance
of a trainee by systematically increasing the ability and aptitude of the trainee by giving him
planned tasks, coupled with continuous appraisal, advice and counseling. Growing transportation
needs of our country, productivity of manpower employed, modern technologies, knowledge of
safety knowledge of our production system and Railway Organization Present Status of Railways
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12. are all correlated terms, which need a proper and serially organized and systematized training.
Such training can only be imparted if we have a plan for this.
1.5 OBJECTIVES
The following are the main objectives of Supervisors Training Centre, Ajmer:To impart induction training to newly recruited supervisor from RRBs.
To impart training to the candidates inducted as supervisors on the basis of departmental
examination.
To conduct courses as per need of the divisions and workshops like supervisor development
courses, courses of contract management, courses on stores procurement, courses on computer,
pre-selection courses for the reserved candidates.
To conduct refresher courses for the posted supervisors to update their knowledge on the basis of
recent technological developments induced in the system.
1.6 Labs
So to manage all information of various labs and trainees Computerized System is required which
keeps all records of labs and faculties, trainees.
SN
1
2
3
4
5
LAB & TRAINING CENTER
UTS and PRS at Railway station
Railnet
Control office
Exchange
Microwave station
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13. Chapter 2
PRS & UTS Network
2.1
Introduction:-
With the implementation of computerized passenger reservation system on Northern Railway in
year 1985-86 at New Delhi, a modest beginning was made which has completely revolutionized
the process of passenger reservation service on Indian Railways. To begin with the computerized
reservation at Delhi was implemented on small VAX-750 computer with just 30 terminals. Today
it is a matter of great pride and satisfaction that highly complex but successful network of
computerized reservation is available at more than 20 major towns including 4 metros of India,
covering almost 25% of the reservation facility available on IR. PRS is equipped with latest state
of art technology both in the field of computer and data communication systems.
As a matter of policy and due to technical reasons, it was decided to have PRS computers only
at Delhi, Bombay, Madras, Calcutta and Secunderabad which cover bulk of reservation volume
and to have remote terminals at other major cities connected to host PRS computers through data
links. Today all PRS hosts are CRIS to network all the computers to provide an integrated
reservation system on IR.
Unreservation Ticketing System (UTS) is like as PRS but it have an external devise which store
ticketing information and upload on server.
2.2 Interconnection of PRS & UTS Servers:
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14. 2.3 PREVIOUS SET UP AT PRS/DELHI:
2.4 CONCERT APPLICATION ARCHITECTURE:
Fig. 2.3a
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15. 2.5 Other aspects of PRS:
(a) Use of satellite data links-
The Remote Area Business Messaging Network (RABMN) of Dot
commissioned recently may be tried for linking remote stations where normal BSNL links may not
be available or are unreliable. (E.g. North frontier areas from Calcutta PRS) Direct terminals or
teleprinter interfaces might be used sharing one VSAT link working at 1200 bps, provided the
rental and other maintenance costs do not become prohibitive.
(b)
Use of Radio Frequency modems- Trials have been conducted using Radio frequency
modems interfaced to VHF half duplex sets and connecting PRS terminals through this data link.
1200 and 2400 bps speeds have been found to be quite successful on WEBEL make VHF sets.
Extension of 1 or 2 terminals at a radius of 8 to 10 Kms with a reasonable line of sight will be
possible at a cheap cost through these modems.
2.6 Benefits of PRS:
(a) To the PassengersTransparency
Universal counters for booking
Instant update of status
Instantaneous enquiry
Reduced waiting time
Reservation available at a number of locations in the country
Customer satisfaction
(b) To the RailwaysIncreased efficiency
Optimal utilization of berths
Real time availability of Accounting Reports
Planning through MIS reports
Analysis of traffic pattern for better overall planning
Reduction in Revenue losses
Saving on Manpower
Eliminate possibilities of fraud
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16. 2.7 Technology used:
Hardware
DS20 Alpha machines under Tru 64 Unix 4.0 f
Software
C,RTR 3.2
Sybase with Replication
2.8 Future Enhancements:
Improvements in the response time in the Dynamic (PNR and Seat availability)
enquiries.
Other transport information (Road/Air/Water) for major tourist locations
Dynamic Enquiries in Hindi
Providing dynamic enquiries for 24 hours.
2.9 New challenges:
Maintenance by remote login by vpn
By HP engineers in US or Bangalore
Regular proactive patch updation
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17. Chapter 3
Railnet – An Overview
3.1 Introduction:
Railnet is the name of the Corporate Wide Information System (CWIS) of Indian Railways. It is
aimed to provide computer connectivity between Railway Board, Zonal Railways, Production
units, RDSO, Centralized Training Institutes, CORE, MTP/Kolkata etc.
3.2 Objectives:
Railnet has been established with these objectives in mind:
●Eliminate
●Change
the need to move paper documents between different documents and
from “Periodic Reporting” to “Information on Demand.”
Railnet will expedite and facilitate quick and efficient automatic status update between Railway
Board and Zonal Railway, as well as between divisions and Zonal Railway. Internet gateways
have been established at Delhi, Mumbai, Chennai, Kolkatta and Secunderabad for access of
Internet through Railnet.
3.3 Railnet General Arrangement:
Fig. 3.3(a)
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18. The general arrangement of the equipment’s used in Railnet is shown in the diagram above. The
WAN link (or the Railnet link) terminates at the router. The router in turn is connected to the switch.
All the computers including the server is connected to the switch. Additional hubs/switches may
be connected to this switch so as to extend the Railnet LAN further.
Railnet users can exchange emails on the Internet. Commercial Dept. is extensively using Railnet
for their “Complaint Center.” Railways have launched their web pages and they keep up to date
information in these web pages. A Railnet authorized user can browse the Internet through
Railnet. A Railnet user can share resources with a co-user on Railnet.
3.4 The Railnet Work:
The Railnet Work was proposed to be completed in three phases. Phase I is planned to connect
all the zonal Railway and production units with Railway Board. Phase II consists of connecting
the divisions to the zonal Railways as well as connection the following to the Railway board.
●RDSO/LKO
●CORE/ALD
●MTP/CAL
●CTIs
viz. IRISET, IREEN, IRICEN, RSC, IRMEE
●Major
Training centers
Phase III will connect the divisions with the important places like important stations, stores depot
etc.
Phase I of Railnet was commissioned by IRCOT1 through a contract agreement with Tata
Infotech. IRCOT had done the following:
1 .Procurement, Installation and commissioning of Server, Router, switches, modems etc.
2. Testing and commissioning of Data Links.
3. Loading and configuration of system software.
4. Training of Railway personnel.
The maintenance of Railnet infrastructure and the web pages is done by the concerned Railways.
IRCOT has arranged proper training for officers as well as supervisors so that the maintenance
becomes easy.
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19. Railnet Phase I (Connectivity Diagram).
Fig. 3.4(a)
The connectivity diagram of Railnet Phase I is shown above. This constitute the backbone of
Railnet. This phase connects the zonal headquarters of WR, ER, SR, NR to the Railway Board.
The zonal HQ of SER, NFR, NER, CR and SCR are connected to one of the zonal HQ so as to
get connectivity with Railway Board. The production units are also connected to the zones nearest
to then so as to get connected with railway Board.
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20. Railnet Phase II (Connectivity Diagram).
Fig. 3.4(b)
The Railnet Phase II connectivity diagram is shown below. The backbone was further extended
in this phase by a direct connection between SCR Hqs and Railway Board. The zonal Railways
were connected to their divisions in this phase. The CTIs were connected to zones nearest to
them in this phase. The major training centres were also connected to Railnet in this phase. With
the completion of Railnet Phase II, the major portion of Railnet is in place and working. The Phase
III that aims at extending it further to stores depot etc. is being done at present.
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21. Railnet Phase IIl (Connectivity Diagram).
Fig. 3.4(c)
The diagram above shows the planned Railnet connectivity after Phase III. Almost all of Indian
Railways will be connected to Railnet after this phase.
3.5 Network Topology:
The network in which the terminals are interconnected with each other for inter communication
within and outside the network is called as Topology.
Basically the Topology is categorized in following four types of designs.
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22. (a) Mesh topologyIn mesh topology every device has a dedicated point to point to every
other device. Every device must have (n-1) I/O ports. All WAN is mesh topology.
Fig. 3.5a Fully connected mesh topology (for five devices)
Advantages are:
• It is robust.
• Each link can carry its own data load.
• It has privacy or secrecy.
• Fault identification is easy
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23. Mesh disadvantages are larger number of cables & I/O ports are required for each device.
Also the bulk of the wires can be greater than the available space.
(b) Star topologyIn star topology each device has a dedicated point to point link only to central
controller called as HUB as shown. If one device wants to send data to another device, it sends
through the HUB.
Fig. 3.5b Star topology
Advantages are
• It is easy to install and reconfigure.
• Each device needs only one link. Hence it is less expensive.
• If a link fails, only that link has to be attended. All other links remain active.
• It is easy to identify fault.
• It is also robust.
(c) Bus topologyA BUS topology is multipoint. One long cable acts as a backbone to link all
devices in a network. The advantage is the installation is easy.
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24. Fig. 3.5c Bus topology
Disadvantages are
• Difficult in fault isolation and reconnection.
• Difficult to add device to an exsisting system.
• A fault or break in bus cable stops all transmission.
(d) Ring topologyIn a ring topology, each has a dedicated point to point connection only with two
devices on either side of it. A data is passed along the ring in one direction, from device to device
until it reaches its destination. Each device in a ring incorporates a repeater.
Fig. 3.5d Ring topology
The advantages are
• It is easy to install & configure.
• The disadvantages are unidirectional traffic and a break in the ring can disable entire
network.
• To add or delete a device requires only changing two connections.
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25. 3.6 Categories of Networks:
Networks are categorized in three different categories as
• LAN (Local Area Network)
• MAN (Metropolitan Area Network)
• WAN (Wide Area Network)
Fig. 3.6a Classification of Networks
(a) LAN (Local Area Network)Local Area Networks (LANs) are networks that connect computers
and resources together in a building or buildings close together. The computers share resources
such as hard-drives, printers, data, CPU power, fax/modem, applications, etc... They usually have
distributed processing - means that there is many desktop computers distributed around the
network and that there is no central processor machine (mainframe).
Fig. 3.6a Local Area Network
Location: In a building or individual rooms or floors of buildings or connecting nearby buildings
together like a campus wide network like a college or university.
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26. (b) MAN (Metropolitan Area Network)Metropolitan Area Networks (MANs) are networks that
connect LANs together within a city. From The Big Picture, we see that telecommunication
services provide the connection (storm clouds) between networks. A local telecommunication
service provides the external connection for joining networks across cities.
Fig. 3.6b Metro Area networks
Location: Separate buildings distributed throughout a city. Examples of companies that use
MANs are universities, colleges, grocery chains, gas stations, department stores and banks.
(c) WAN (Wide Area Network)Wide Area Networks (WAN) are a communication system linking
LANs between cities, countries and continents. The main difference between a MAN and a WAN
is that the WAN uses Long Distance Carriers rather than Local Exchange carriers. Otherwise the
same protocols and equipment are used as a MAN.
Fig. 3.6c Wide area network
Location: City to city, across a country or across a continent. Wide Area Networks (WANs)
connect LANs together between cities or across a country.
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27. 3.7 PROTOCOL:
A protocol is a set of rules, which governs how data is sent from one point to another. In data
communications, there are widely accepted protocols for sending data. Both the sender and
receiver must use the same protocol when communicating. One such rule is. ...
BY CONVENTION, THE LEAST SIGNIFICANT BIT IS TRANSMITTED FIRST
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28. Chapter 4
Exchange
4.1 Introduction:
C-DOT
128P
RAX
is
a
Telephone
exchange
designed
to
meet
the
telecommunication needs of small sized rural areas. These exchanges are also suitable for Indian
Railway applications where the telephone line capacity is less than 100. Provision is made in the
design to expand the line capacity up to 400 subscribers roughly.
C-DOT (Centre for Development of Telematics) is a Central government organization of India set
up to develop the necessary equipment’s (infrastructure) suitable for Indian climate and
environmental conditions. The system is designed to offer uninterrupted services by using
duplicating methods for control and power supply circuits. Tone generator circuit is also
duplicated.
4.2 Power Supply Unit card:
The input voltage is –48+/-4V. The RAX system requires various internal working voltage sources.
PSU card provides the following output voltages for internal working.
1) +5V-8A – For microprocessor and other digital components.
2) –9V-0.5A – Codec
3) +12V-1A – Relays
4) –5V-0.1A – For other digital components.
5) –48V – For speech
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29. 4.3 RAX Control processor (RCP):
This card uses 65C02 Micro Processor and has 12K RAM, 48K EPROM & 16K EEPROM
memories. This contains the information pertaining to peripheral cards, metering and other
administrative functions to be performed. Maintenance panel is connected directly to RCP by
which any changes in the data of the exchange can be made (adding, deleting, modifying of
subscriber or trunks etc.).
The main functions RCP are Call processing, Administration and Maintenance. The functional
block diagram is shown in fig 4.3a.
Fig. 4.3a Functional Block diagram of RCP card
1. FUNCTIONAL BLOCKS a. Processor and Memory.
b. Clock Generation.
c. Address Decoder and Read/Write Generator.
d. Asynchronous Communication and Timer.
e. Error Monitor.
f.
EEPROM and Real Time Clock.
g. High Level Data Link Control.
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30. 4.4 Switching Network (TIC):
The TIC/SN is essentially a generic card. It switches voice between the 128 ports, controls
signalling, support diagnostics and duplication under the intelligence of RCP. It can be understood
this way also. The signalling of the termination cards is handled by the signal processor (SP) and
voice by the Switching Network (SN). Both SP and SN are under the control of Terminal Interface
Controller (TIC) which works under instruction from RCP.
1. FUNCTIONS1) TIC/SN Switches the PCM (Pulse Code Modulation) digital voice information. This
is to enable the subscribers to converse with each other and to be fed with different
tones at different stages of the call.
2) TIC (Terminal Interface Controller) derives the identities of the calling and called
terminals and establishes a path through SN (Switching Network) between these
terminals. TIC communicates with RCP on HDLC (High Level Data Link Control)
for call related information.
3) Using SPC (Signal Processor Card) it receives status indication for all the 128 port
(terminals) i.e. scan signalling information. This information is passed on to RCP. Also
it gets the message from RCP to drive events on terminals and passes the Drive
signalling information to signal processor. Note: (HDLC) is to ensure that data is
transferred quickly and correctly.
4) It keeps on doing periodic diagnostic on the terminal cards including itself and
informing RCP through HDLC messages.
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31. 4.5 Tone generator with Diagnostic card (TGS):
Tone Generator card is used to generate call supervisory and test tones for system like
PABX and RAX. It has also capability to diagnosis the tones it produces and thereby can conform
sanity check of the voice path.
Figure 4.5a TG
(a) A tone is a simple audio signal having distinct frequency or set of frequencies (usually a voice
frequency i.e. between 20 Hz to 20 KHz).
(b) A tone may be continuous or may have cadence i.e. signal has certain ON – OFF period.
(c) A tone consists of one or more tone components.
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32. (d) A tone component may mean a single frequency signal (400 Hz) or a modulated frequency
signal (400 Hz modulated by 25 Hz) or it can be an addition of two sine waves of different
frequencies as well.
(e) These tone components which contain the PCM samples of a particular frequency or group of
frequencies reside in a bank of memory called tone memory.
(f) Each bank of this tone memory consist s one tone component.
(g) When a tone consists of more than one tone component the second tone component may be
just silence (regarded as inaudible d. c. signal).
(h) If in a tone (like RBT) there is one tone component followed by silence then the tone is said to
have cadence.
4.6 Signal Processor (SP) card:
Signal processor exchanges signalling information between Termination cards and Terminal
interface controller. The SP card acts as an interface between the terminal cards and Terminal
interface controller cum Switching Network (TIC / SN) card. This interface is primarily for
supervisory, control and data signal.
1. Main functionsThe Signal processor card performs the following functions:
(a) Receiving supervisory signals such as on - hook / off – hook/ hook switch flash
and decadic (dial) pulses from termination and also for transient validation (noise
rejection).
(b) Controlling ringing towards subscriber and providing automatic ring trip when
the called subscriber goes off - hook.
(c) Controlling metering signals.
(d) Recognising incoming ring from incoming junction calls.
(e) Controlling out pulsing towards junction calls.
(f) Channel associated signalling on digital trunks.
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33. 4.7 Subscriber line card (SLC) or line circuit card (LCC):
Line circuit card is one of the termination cards and It is the first link in the chain of cards
comprising the exchange.
Line circuit card (LCC) is the direct interface between the exchange and subscriber. Each card
has 8 identical circuits on which it receives 8 pairs of subscriber telephone wires. Each of these
circuits does the following function.
1. MAIN FUNCTIONS1. D.C feed to subscriber for signalling and energising handset microphone.
2. Detects the status of the corresponding subscriber telephone handset i.e. on –
hook (idle or ringing) or off – hook (call initialisation or ring trip).
3. Enables the voice of the subscriber to reach a point within the exchange for
onward Transmission to the called party or vice-versa.
4. Through control logic, subscriber line card (SLC) performs a diagnostic check
on the basic health of the card.
5. It has provision to operate from any of the two sets of the input signals i.e. copy
– 0 or copy - 1(copy selection).
6. The subscriber line card communicates with the Terminal Interface Controller &
Switching Network (TIC / SN) for voice switching.
7. The subscriber line card communicates with signal processor card (SPC) for
Signalling data.
8. Operates Test Access Rely for a particular subscriber line.
The basic function of Line Circuit Card (Termination cards) is collectively termed as BORSCHT
an acronym for –
B - Battery Feed.( -48v, 35 mA)
O - Over Voltage Protection.
R - Ringing.
S - Supervision.
C - Coding & Decoding
H - Hybrid Conversion ( 2 / 4 wire conversion)
T - Testing.
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34. 2. POWER REQUIREMENTSThe LCC gets several power inputs from the back plane (generally known as mother
board) through connector. These are supplied by the PSU 0/1 card. These are:
+ 12 V, for relay operation,
- 48 V, for Battery feed circuits.
75 V rms, for ringer signal.
- 5 V, for Codecs and Op-Amps.
+ 5 V, for digital logic circuits, codecs and Op-Amps.
The (LCC) Line circuit card receives + 12 v and - 48 v supplies from PSU 1 card of the Unit
through back plane connector. +5v and - 5v are generated by using 3 terminal Voltage regulators
from input voltage of + 12 V and - 9 V respectively.
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35. Chapter 5
OPTICAL FIBRE
5.1 Need for OFC:
a. IntroductionThe demand for bandwidth on transmission networks is increasing rapidly because video and
graphical rich contents are exchanged through the corporate network or the Internet. The Gigabit
Ethernet became commonly used in the corporate network backbone, and 10Gbit Ethernet will
be adopted in the near future. Meanwhile in the home, the demand for high-speed network
becomes popular as the wide spread of broadband access, e.g. CATV, xDSL, and FTTH. The
transmission medium with capability to transmit high bit rate signal is necessary to satisfy these
requirements. The telecommunication transport technologies move from copper based networks
to optical fibre, from timeslot based transport to wave length based transport, from traditional
circuit switching to terabit router and all optical based networks entering into a new era of optical
networking.
5.2. Basic physics of OFC1. Optical Fibre CableOFC have Fibres which are long, thin strands made with pure glass about the diameter of a
human hair. OFC consists of Core, Cladding Buffers and Jacket as shown in figure :
Figure 5.1 bare fibre and OFC cable
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36. 2. Monochromatic light, or single color lightLight or visible light is electromagnetic radiation of a wavelength that is visible to the human eye
( about 400 – 700 nm). The word light is sometimes used to refer to the entire electromagnetic
spectrum. Light is composed of elementary particles called photons. Three primary properties of
light are:
• Intensity or brightness
• Frequency or wavelength and
• Polarization or direction of the wave oscillation
Light can exhibit properties of both waves and particles. This property is referred to as waveparticle duality. The study of light, known as optics. In free space, light (of all wavelengths)
travels in a straight path at a constant maximum speed. However, the speed of light changes
when it travels in a medium, and this change is not the same for all media or for all wavelengths.
By free space it is meant space that is free from matter (vacuum) and/or free from
electromagnetic fields.
Thus, the speed of light in free space is defined by Einstein’s equation:
E = mc^2
Frequency (ν), speed of light in free space (c),
are interrelated by:
ν = c/λ
and wavelength (λ),
From the energy relationships
E = mc2 = hν
and the last one, an interesting relationship is obtained, the equivalent mass of a photon
m = hν/c^2
When light is in the vicinity of a strong electromagnetic field, it interacts with it. From this
interaction and other influences, its trajectory changes direction as shown in figure : 1.2
Figure 5.2 light travel in strong field
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37. 3. Incident ray, Reflected ray and Refracted ray-
An incident ray is a ray of light that strikes a surface. The angle between this ray and the
perpendicular or normal to the surface is the angle of incidence. Reflection is the change in
direction of a wave front at an interface between two different media so that the wave front returns
into the medium from which it originated. Common examples include the reflection of light, sound
and water waves. The reflected ray corresponding to a given incident ray, is the ray that
represents the light reflected by the surface. The angle between the surface normal and the
reflected ray is known as the angle of reflection. The Law of Reflection says that for a specular
(non-scattering) surface, the angle of reflection always equals the angle of incidence. The
refracted ray or transmitted ray corresponding to a given incident ray represents the light that is
transmitted through the surface. The angle between this ray and the normal is known as the angle
of refraction, and it is given by Snell's Law. The figure:1.3 shows Incident ray, Reflected ray,
Refracted ray , the angle of incidence and angle of refraction.
Figure 5.3 light rays and its angles
4. Refractive indexRefractive index is the speed of light in a vacuum ( c =299,792.458km/second) divided by the
speed of light in a material ( v ). Refractive index measures how much a material refracts light.
Refractive index of a material, abbreviated as ‘n ‘, is defined as ‘n=c/v ‘. Light travels slower in
physical media than it does when transmitted through the air. Refractive index (n): is a function of
molecular structure of matter; optical frequency, optical intensity; determines optical propagation
properties of each wavelength (λ) may not be distributed equally in all directions, is affected by
external temperature, pressure, and fields.
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38. Refractive index of a medium is a measure for how much the speed of light is reduced inside the
medium. For example, typical glass has a refractive index of 1.5, which means that light travels
at 1 / 1.5 = 0.67 times the speed in air or vacuum. Two common properties of glass and other
transparent materials are directly related to their refractive index. First, light rays change direction
when they cross the interface from air to the material, and effect that is used in lenses and glasses.
Second, light reflects partially from surfaces that have a refractive index different
From that of their surroundings.
The indices of refraction of various Medias are shown in table below.
5. Medium Index of RefractionVacuum
Air ( actual )
Air ( accepted )
Water
Ethyl alcohol
Oil
Glass
Polystyrene plastic
Zircon
Diamond
Silicon
1.00
1.0003
1.00
1.33
1.36
1.46
1.50
1.59
1.96
2.41
3.50
6. Snell’s lawIn 1621, a Dutch physicist named Willebrord Snell derived the relationship between the
different angles of light as it passes from one transparent medium to another. When light passes
from one transparent material to another, it bends according to Snell's law which is defined as:
n1sin(θ1) = n2sin(θ2)
Where:
n1 is the refractive index of the medium the light is leaving
θ1 is the incident angle between the light beam and the normal (normal is 90° to the interface
between two materials)
n2 is the refractive index of the material the light is entering
θ2 is the refractive angle between the light ray and the normal
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39. Snell’s law (see figure 1.4) gives the relationship between angle of incidence and angle of
refraction.
Figure 5.4 Snell’s law
For the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0°
regardless of the values of n1 and n2. That means a ray entering a medium perpendicular to the
surface is never bent.
The above is also valid for light going from a dense (higher n) to a less dense (lower n) material;
the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.
7. Total internal reflectionWhen a light ray crosses an interface into a medium with a higher refractive index, it bends
towards the normal. Conversely, light traveling cross an interface from a higher refractive index
medium to a lower refractive index medium will bend away from the normal.
This has an interesting implication: at some angle, known as the critical angle θc, light
traveling from a higher refractive index medium to a lower refractive index medium will be
refracted at 90°; in other words, refracted alon g the interface.
If the light hits the interface at any angle larger than this critical angle, it will not pass through to
the second medium at all. Instead, all of it will be reflected back into the first medium, a process
known as total internal reflection ( see figure 1.5 ) .
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40. Figure 5.5 Total internal reflection
The critical angle can be calculated from Snell's law, putting in an angle of 90° for the angle of the
refracted ray θ2. This gives θ1:
Since
θ2 = 90°
So
sin(θ2) = 1
Then
θc = θ1 = arcsin(n2/n1)
For example, with light trying to emerge from glass with n1=1.5 into air (n2 =1), the critical angle
θc is arcsin(1/1.5), or 41.8°.
For any angle of incidence larger than the critical angle, Snell's law will not be able to be solved
for the angle of refraction, because it will show that the refracted angle has a sine larger than 1,
which is not possible. In that case all the light is totally reflected off the interface, obeying the
law of reflection.
5.3 Optical fibre mode:
An optical fibre guides light waves in distinct patterns called modes (see figure 1.6 ). Mode
describes the distribution of light energy across the fibre. The precise patterns Depend on the
wavelength of light transmitted and on the variation in refractive index that shapes the core. In
essence, the variations in refractive index create boundary conditions that shape how light waves
travel through the fibre, like the walls of a tunnel affect how sounds echo inside.
We can take a look at large-core step-index fibres. Light rays enter the fibre at a range of
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41. angles, and rays at different angles can all stably travel down the length of the fibre as long as
they hit the core-cladding interface at an angle larger than critical angle. These rays are different
modes.
Fibbers that carry more than one mode at a specific light wavelength are called multimode
fibres. Some fibres have very small diameter core that they can carry only one mode which travels
as a straight line at the centre of the core. These fibres are single mode fibres. This is illustrated
in the following picture.
Figure 5.6 Optical fibre mode
Optical fibre index profile
Index profile (see figure 1.7) is the refractive index distribution across the core and the cladding
of a fibre. Some optical fibre has a step index profile, in which the core has one uniformly
distributed index and the cladding has a lower uniformly distributed index. Other optical fibre has
a graded index profile, in which refractive index varies gradually as a function of radial distance
from the fibre centre. Graded-index profiles include power-law index profiles and parabolic index
profiles. The following figure shows some common types of index profiles for single mode and
multimode fibres.
Figure 5.7 Optical fibre index profile
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42. 5.4 Optical fibber’s Numerical aperture (NA)
Multimode optical fibre will only propagate light that enters the fibre within a certain cone, known
as the acceptance cone of the fibre. The half-angle of this cone is called the acceptance angle
(see figure 1.8), θ max. For step-index multimode fibre, the acceptance angle is determined only
by the indices of refraction:
Where
n is the refractive index of the medium light is traveling before entering the fibre
nf is the refractive index of the fibre core
nc is the refractive index of the cladding
Figure 5.8 acceptance angle
5.5 Merit & Demerit of OFC and its Application:
1. Advantage of OFC communication
• More information carrying capacity fibbers can handle much higher data rates than
copper. More information can be sent in a second.
Information Carrying Capacities of various media are:
Medium / Link
Copper Cable
(short distance)
Coaxial Cable
(Repeater every 4.5 km)
UHF Link
MW Link
(Repeater every 40 km)
OFC
Carrier
1 MHz
100 MHz
2 GHz
7 GHz
1550 nm
Information Capacity
1 Mbps
(ADSL Modem)
140 Mbps (BSNL)
8 Mbps (BSNL)
2 Mbps (Rly.)
140 Mbps (BSNL)
34 Mbps (Rly.)
2.5 Gbps(STM-16 – Rly.)
10 Gbps (STM-64)
1.28 Tbps (128 Ch. DWDM)
20 Tbps (Possible)
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43. • Free from Electromagnetic and Electrostatic interference
.
Being insulator no electric current flows through the fibre and due to this reason fibres neither
radiate nor pick up electro - magnetic radiation. So WPC CLEARANCE is not required.
• Low attenuation: 0.25 dB/km at 1550 nm
Loss in twisted pair and coaxial cable increases with frequency, whereas, loss in the
optical fibre cable remains flat over a wide range of frequencies (See figure:1.9 ).
Figure 5.9 Frequency Vs Attenuation In Various Types of Cable
Use of WDM – Switching / routing at Optical signal level
• Self-healing rings under NMS control
• Small size makes fibre cable lighter in weight. So easy to handle. Optic fibre cable weight
(approx.) 500 kg / km Copper cable weight (approx.) 1000 kg/km
• Fibres not effected by power surges and corrosive chemicals.
The reasons are photons of light in a fibre do not affect each other as they have no electrical
charge and they are not affected by stray photons outside the fibre. But incase of copper,
electrons move through the cable and these are affected by each other.
• Safety Optical fibre does not carry any electricity even if the cable is damaged or short circuited
it does not cause any spark or fire hazard.
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44. • Signal security as the fibre do not radiate energy it cannot be detected by any nearby antenna
or any other detector. The fibres are difficult to tap and therefore excellent for security.
• No cross talk as the signal transmission is by digital modulation there is no chance of cross talk
in between channels.
• Less prone to theft as the fibre does not have resale value in the market.
• Flexibility in system up gradation only by adding a few additional terminal and repeater
equipments the capacity of the system can be increased, at any time once the cable is laid.
• High resistance to chemical effects and temperature variations.
2. Limitations of OFC
• Difficulty in jointing (splicing)
• Highly skilled staff would be required for maintenance
• Precision and costly instruments are required
• Tapping for emergency and gate communication is difficult.
• Costly if under- utilised
• Special interface equipment’s required for Block working
• Accept unipolar codes i.e. return to zero codes only.
3. Application in Signal and Telecommunications
• Long haul circuits for administrative branch and data transmission circuits
• Short -haul circuits for linking of telephone exchanges.
• Control communication & Signalling application for fail safe transmission
• Electronic interlocking systems installations
5.6 Nomenclature & Sizes of OFC:
1. Optical Fibre Sizes
• To ensure compatibility among splices/connectors, sizes of
Core & cladding have been standardized
• International standards for SM fibre
– Cladding diameter: 125 microns (micro meter)
– Cladding + coating: 245 microns (micro meter)
– Core diameter: 7 to 10 micro meter
• International standards for MM fibres
– Cladding diameter: 125 microns (micro meter)
– Cladding + coating: 245 microns (micro meter)
– Core diameter: 50 to 62.5 micro meter
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45. 2. Nomenclature for Optical Interface
Optical Interface specified as X.Y.Z
• X can be I or S or L or V or U & denotes haul
– I for intra station (up to 2 km)
– S for short haul (15 km)
– L for long haul (40 km at 1310 nm & 80 km at 1550 nm)
– V for very long haul (60 km at 1310 nm & 120 km at 1550 nm)
– U for ultra-long haul (160 km at 1550 nm)
• Y can be 1 or 4 or 16 or 64 & denotes STM Level
– 1 for STM-1
– 4 for STM-4
– 16 for STM-16
– 64 for STM-64
• Z can be 1 or 2 or 3 & denotes fibre type
– 1 for 1310 nm over NDSF (G.652 fibre)
– 2 for 1550 nm over NDSF (G.652 fibre)
– 3 for 1550 nm over DSF (G.653 fibre)
– 5 for 1550 nm over NZDSF (G.655 fibre)
Examples of Nomenclature for Optical Interface
• I.16.1 – Intra station STM-16 link on 1310 nm fibre
• S.16.2 – Short haul STM-16 link on 1550 nm fibre (G.652)
• L.16.2 & L.16.3 – Long haul STM-16 link on 1550 nm fibre (G.652 & G.653)
• S.4.1 – Short haul STM-4 link on 1310 nm fibre
• L.4.1 – Long haul STM-4 link on 1310 nm fibre (40 km)
• S.1.1 – Short haul STM-1 link on 1310 nm fibre
• L.1.1 – Long haul STM-1 link on 1310 nm fibre (40 km)
5.7 Signal Attenuation in Optical Fibber
• Attenuation has three components:
- Bending loss (Macro / Micro)
- Absorption loss
- Scattering loss
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46. • In bending loss, there are 2 categories
- Macro bending loss (specified by manufacturer)
- Micro bending loss (not specified but included in total attenuation accountable by
manufacturer)
Macro-bending loss
• Macro-bending loss is caused by bending of the entire fibre axis
• The bending radius shall not be sharper than ‘30d’ where d is diameter of cable
• One single bend sharper than 30d can cause loss of 0.5 dB
• If bending is even sharper, fibre may break.
Micro-bending loss
• Micro-bending loss is caused by micro deformations of fibre axis which leads to failures
in achieving total internal reflection conditions
• Micro-bends are small-scale perturbations along the fibre axis, the amplitude of which
are on the order of microns. These distortions can cause light to leak out of a fibre.
• Micro-bending may be induced at very cold temperatures because the glass has a different
coefficient of thermal expansion from the coating and cabling materials. At low
temperatures, the coating and cable become more rigid and may contract more than the
glass. Consequently, enough load may be exerted on the glass to cause micro bends.
• Coating material is selected by manufacturers to minimize loss due to micro-bending.
The linear thermal expansion coefficient of coating material shall be compatible with that
of fibre.
Factors causing absorption & attenuation
• Scattering of light due to molecular level irregularities in the glass
• Light absorption due to presence of residual materials, such as metals or
water ions, within the fibre core and inner cladding.
• These water ions that cause the “water peak” region on the attenuation curve,
typically around 1380 nm.
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47. Absorption loss & Scattering loss
The three peaks & troughs
• Three peaks in attenuation
– 1050 nm
– 1250 nm
– 1380 nm
• Three troughs in attenuation (Performance windows)
– 850 nm: 2 dB/km
– 1310 nm: 0.35 dB/km
– 1550 nm: 0.25 dB/km
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48. 5.8 Construction of Optical Fibre Cable
The main parts of an optical fibre cable are shown in figure: 4.14 in a cross section of
armoured loose tube optic fibre cable:
Figure:5.10 parts of optic fibre cable
Legends:
A HDPE outer jacket 2.0 mm thickness minimum
B Corrugated stainless steel armour (.6mm mini.)
C Inner PE Sheath of 1.m mm mini thickness
D Secondary coating tube nylon/PBTP of 2.5 mm
E Primary coated fibre of 125 micro mm max dia
F Central strength member of FRP to comply with 2w of specification
G Wrapping armide yarn
H Water blocking jelly thixotropic
I Water blocking thixotropic jelly
J Rip card mini. Two at 1800C part
• Core
Core is a central portion of the cable, in form of very thin tube size (approximately 8 um)
made up of glass and carries light signals from transmitter to receiver.
• Cladding
It surrounds core cylindrically and is having lower refractive index as compared to the core.
• Buffers
a. Primary coating Acrylate, silicon rubber or lecquer is applied as primary coating. It works as
mechanical protection
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49. b. Secondary coating An additional buffer (secondary coating) is also added during manufacturing
process.
• Jacketing
Normally outer most sheath which is called jacketing provides protection from chemical
acids, alkalis, solvents etc. Material used are high density polyethylene with anti termite
compound, polyurethane, PVC, nylon etc.
StrengthThe common misconception about optical fibre is that it must be fragile because it
is made of glass. The ultra-pure glass of optical fibres exhibits both high tensile strength
and extreme durability, even though traditional bulk glass is brittle. The Tensile strength
is of the order of 44000 to 60000 kg per sq.cm. The tensile strength of copper is only 7500
kg per sq.cm.
Bending ParametersThe optical fibre and cable are easy to install because it is lightweight, small in size and
flexible. But precautions are needed to avoid tight bends, which may cause loss of light or
premature fibre failure. The bending radius should be greater than '30d', where'd' is the diameter
of the cable. The splice trays and other fibre handling equipment’s (racks) are designed in such
way that the fibre installation losses can be prevented
Specifications of Optical Fibre Cable used in Indian RailwaysIn Indian Railways, 24 Fibre armoured Optical Fibre Cable as per RDSO Spec. IRS: TC
55-2006 is used.
Overall DiameterThe overall diameter of the cable shall not be more than 20 mm and uniform through out
the length from top to end.
Fibre & Unit IdentificationFibres are coloured with readily distinguishable durable colours. In case of four fibres in a
tube the order of coloured fibres are Blue, Orange, Green and Natural. The 6 loose tubes have
the following colours:
Loose Tube number Colour of loose tube
1 Blue
2 Orange
3 Green
4 Brown
5 Slate
6 White
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50. 5.9 JOINTING AND TERMINATION OF OFC:
There are two methods for jointing Optical fibre cable.
They are splicing or by using connectors.
Splicing is permanent connection of two pieces of fibre. Splicing is the process of
connecting two bare fibres directly without any connectors. Both methods provide much
lower insertion loss compared to fibre connectors.
• Two techniques of splicing
– Mechanical splicing
– Fusion splicing
• Fibre mechanical splicing – Insertion loss < 0.5dB
• Fibre optic cable fusion splicing – Insertion loss < 0.1dB
• Two types of splices:
– Mid-span splicing of two fibres
• Fibbers from two cables are spliced after laying drum by drum
• Cuts in fibre run are attended by splicing certain minimum length cable piece at
either end.
– Pig-tail splicing
• Pig-tail is fibre with factory installed connector at one end
• The free fibre of pig-tail is spliced connected to cable.
1a. Fusion SplicingThis is accomplished by applying localized heating (i.e. by electric arc or flame) at the
interface between two butted, pre-aligned fibre ends, causing them to soften and fuse together
During initial installation, fusion splicing should be adopted at all locations of fibre optic cable.
• Fusion splicing provides a fast, reliable, low-loss, fibre-to-fibre connection by
creating a homogenous joint between the two fibre ends.
• The fibres are melted or fused together by heating the fibre ends, typically using
an electric arc.
• Fusion splices provide a high-quality joint with the lowest loss (in the range of 0.01
dB to 0.10 dB for single-mode fibres) and are practically non-reflective.
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51. Figure 5.11 Fusion Splice
1b. Mechanical Splicing
This aligns the axis of the two fibres to be jointed and physically hold them together Mechanical
splicing can be used for temporary splicing of fibres or where fusion splicing is not possible or
undesirable.
• Mechanical splicing is of slightly higher losses (about 0.2 db) and less-reliable
performance
• System operators use mechanical splicing for emergency restoration because it is
fast, inexpensive, and easy.
• Mechanical splices are reflective and non-homogenous
Figure 5.12 mechanical splice
2. Basics about connectors• Fibre optic connector facilitates re-mateable connection i.e. disconnection /
reconnection of fibre
• Connectors are used in applications where – Flexibility is required in routing an
optical signal from lasers to receivers
– Reconfiguration is necessary
– Termination of cables is required
• Connector consists of 4 parts:
– Ferrule
– Connector body
– Cable
– Coupling device
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52. TX parameters & their meaning
TX parameters & their meaning Meaning
Wavelength range
Though operation is at 1310 nm or 1550 nm,
a range is specified to signify WDM
compatibility
Optical source
Laser diode – SLM / MLM Single
longitudinal mode/Multi longitudinal mode
Emission
Spectral width in nm of sustainable
Spectrum Width
longitudinal modes of MLM
20 db spectral
Separation in ‘nm’ between -20 dB points on
width
either side of peak emission wavelength of
SLM
SMSR (Side mode
Ratio of intensities of main (single) mode and
suppression ratio)
largest side mode for SLM laser diode
Launched power
Power output of laser diode
EX or ER
Extinction Ratio is the ratio of max. to min.
light power representing logic 1 and logic 0
Introduction to Optical sources
1. Introduction
An optical source is a major component of optical transmitters. Fibre optic communication
systems often use semiconductor optical sources such as Light emitting diodes ( LEDs) and
semiconductor lasers. Some of the advantages are:
• Compact in size
• High efficiency
• Good reliability
• Right wavelength range
• Small emissive area compatible with fibre core dimensions
• Possibility of direct emulation at relatively high frequencies
2. Light emitting diodes
• Light emitting Technique in LEDs
A forward biased p-n junction emits light through spontaneous emission, a phenomenon called
as electroluminescence. A LED is a forward biased p-n junction. Radiative recombination of
electron – hole pairs in the depletion region generates light, only light emitted (see figure 8.2)
within a cone of angle ( θc ) is the critical angle for the semiconductor-air interface. A fraction of
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53. light escapes from the device and can be coupled into an optical fibre. The emitted light is
incoherent with a relatively wide spectral width (30-60nm) and a relatively large angular spread.
Power current characteristic the output power of LEDs is 10 microwatt or less, even though the
internal power can easily exceed 10 mill watt. This is due to internal absorption and total internal
reflection at the semiconductor-air interface. Internal absorption can be avoided by using
heterostructure LEDs in which the cladding layers surrounding the active layer are transparent to
the radiation generated.
A further loss occurs when emitted light is coupled into an optical fibre. Because of the incoherent
nature of the emitted light, an LED act as a Lambertian source. In view of the fact that numerical
aperture (NA) for optical fibre is in the range 0.1 to 0.3, only a few percentage of emitted power
is coupled into the fibre.
Essential difference between emissions by LEDs & LDs
• LEDs – Spontaneous emission
• LDs – Stimulated emission
Optical path (Equipment to external) parameters & their meaning
Parameter
Attenuation
Chromatic dispersion (PS/nm)
Optical return loss
Dispersion reflectance
Meaning
Attenuation in connectors, patch cords
Spreading of output pulse due to
different travel times of different
wavelengths in emitted signal
Ratio (in dB) of reflected power to
transmitted power; It is negative; More
negative the better
Spreading of reflected pulse
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54. RX parameters & their meaning
Parameter
Sensitivity
Overload
Power penalty
Reflectance
Meaning
Min. power required at receiver to detect
signal, for a particular data rate,
ensuring particular BER (usually BER
of 1X 10-12 )
Maximum input power that the receiver
can accept
Non-linear effects contribute to signal
impairment & hence additional amount
power will be needed at the receiver to
maintain the same BER as in their
absence.
This additional power required is known
as ‘Power penalty’ [Non-linear effects
are : Variations of RI , polarization
mode dispersion, non-uniform gain of
amplifiers, group velocity dispersion
and inelastic scattering (scattering due
to interaction between optical signals
and molecular or acoustic vibrations in
fibre) ]
Input power to reflected power ratio
Optical Detectors
1.
Introduction to Optical detectors-
The role of an optical receiver is to convert the optical signal back into electrical signal and recover
the data transmitted through the optical fibre communication system. Its vital component is a
photo detector that converts light into electricity through the photoelectric effect. Some the
advantages are:
• high sensitivity
• fast response
• low noise
• low cost
• high reliability
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55. 2. Light absorption techniqueThe fundamental mechanism behind the photo detection process is optical absorption. If the
energy ( hv) of incident photons exceeds the band gap energy, an electron-hole pair is generated
each time a photon is absorbed by the semiconductor. Under the influence of an electric field
setup by an applied voltage, electrons and holes are swept across the semiconductor, resulting
in a flow of electric current. The photocurrent (Ip) is directly proportional to the incident optical
power (Pin).
Ip = RPin
Where ' R ' is the responsivity of the photo detector
Optical TransmittersThe Optical transmitter consists of two main sub parts. They are light sources (LEDs and Laser)
and modulators. We recollect few seconds about sources. There are different types of LED
sources. They are Surface emitting LEDs and Edge emitting LEDs. Similarly we have two types
of laser sources. They are Febry – Perot and DFB.
There are two different types of transmitter. They are transmitter with Internal modulators or
Intensity modulators. The intensity of radiated power is varied between maximum and minimum
values. The block diagram of transmitter with internal modulators consists of different sub
components is shown in figure 9.1.
Figure 5.13 Block diagram of transmitter with internal modulator
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56. DisadvantagesThe bandwidth is restricted by LDs relaxation frequency. The fast variation of LDs radiating
frequency as per pulse or modulating current results in broadening of pulse known as ‘chirp’.
This severely affects the limits the high speed. Finally high driving current required to launch
high power into fibre for long-haul optical links.
The another type of transmitter is with External modulator. In this type, the Laser diode radiates
continuous light while change in power occurs outside laser diode (see figure 9.2)
Figure 5.14 Functional blocks of transmitter with external modulator
Advantages of external modulatorsThe LD circuit is not loaded with extra task of modulation. The feedback loop using photo diode
provides a very stable level of power radiated by the LD. This avoids chirp.
There are two types of external modulators. They are Mach-Zander External Modulator (MDM)
and Electro absorption modulator (EA).
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57. Optical ReceiversThe Digital Optical receiver has three major sections (see figure 9.4). The three major sections
are the front end, the liner channel and the decision circuit.
Figure: 5.15 Digital Optical receiver with components and sections
Wave Division Multiplexing (WDM) principles
WDM systems send signals from several sources over a single fibre on different wavelengths
closely spaced. A multiplexer, which takes optical wavelengths from multiple fibbers and
converges them into one beam. At the receiving end the system must be able to separate out the
components of the light so that they can be discreetly detected. Demultiplexers perform this
function by separating the received beam into its wavelength components and coupling them to
individual fibres.
Demultiplexing must be done before the light is detected, because photo detectors are inherently
broadband devices that cannot selectively detect a single wavelength. In a unidirectional system
(see Figure 9.7), there is a multiplexer at the sending end and a demultiplexer at the receiving
end. Two system would be required at each end for bidirectional communication, and two
separate fibres would be needed.
Multiplexers and demultiplexers can be either passive or active in design. Passive designs are
based on prisms, diffraction gratings, or filters, while active designs combine passive devices with
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58. tuneable filters. The primary challenges in these devices is to minimize cross-talk and maximize
channel separation. Cross-talk is a measure of how well the channels are separated, while
channel separation refers to the ability to distinguish each wavelength.
5.10 The fiber that Breaks Grading (FBG)
Fiber grating is made by periodically changing the refraction index in the glass core
of the fiber. The refraction changes are made by exposing the fiber to the UV-light
with a fixed pattern
When the grating period is half of the input light wavelength, this wavelength
signal will be reflected coherently to make a large reflection.
The Bragg Condition
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59. 5.11 Characteristics of FBG:
It is a reflective type filter
Not like to other types of filters, the demanded wavelength is
reflected instead of transmitted
It is very stable after annealing
The gratings are permanent on the fiber after proper annealing
process
The reflective spectrum is very stable over the time
It is transparent to through wavelength signals
The gratings are in fiber and do not degrade the through traffic
wavelengths, very low loss
It is an in-fiber component and easily integrates to other optical devices
Temperature Impact on FBG
The fiber gratings is generally sensitive to temperature change (10pm/°C)
mainly due to thermo-optic effect of glass.
A thermal packaging technique has to be used to compensate the
temperature drift
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60. Chart Title
1535.0
Center Wavelength (nm)
1534.8
1534.6
1534.4
1534.2
Athermal
1534.0
Normal
1533.8
-5
15
35
55
75
Temperature (℃)
• Possible Use of FBG in System-
5.12 Multiplexer & De-multiplexer:
•
ITU FBG Filter for DWDM-
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61. • ITU FBG Filter for OADM-
Figure 5.16 FBG Filter for OADM
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62. CONCLUSION
Engineering student will have to serve in the public and private sector
industries and workshop based training and teaching in classroom has its
own limitation .The lack of exposure real life, material express and
functioning of industrial organization is the measure hindrance in the
student employment. In the open economy era of fast modernization and
tough competition, technical industries Should procedure pass out as near
to job function as possible. Practical training is one of the major steps in
this direction. I did my training from NORTH-WESTERN
RAILWAY, AJMER.
The training helps me in gaining depth knowledge about technologies
used in development of real life projects. I gain the knowledge of working
as a team member in the team of developers and they give me very good
knowledge of how to work on different type of tools and
communicational environment. In the end, I hereby conclude that I have
successfully completed my industrial training on the above topics.
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63. BIBLOGRAPHY & REFRENCES
I.
BIBLOGRAPHY
Optical Fiber Communications: Principles and Practice (3rd Edition)
by JOHN M. SENIOR
Computer Networking for LANs to WANs: Hardware, Software and
Security By Kenneth C. Mansfield, Jr., James L. Antonakos
II.
REFERENCES:
http://www.indianrailways.gov.in
http://www.authorstream.com
http://www.amazon.com
http://books.google.co.in/
Study material provided by railway training center
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