this is a summer internship or training report at DMRC. if you encounter any error then please comment below

1. SUMMER INTERNSHIP REPORT
(18th June’16 to 16th July’16)
On
Signaling and Telecommunication
At
Submitted in the partial fulfilment of requirements for the degree
Of
Bachelor of Technology
in
Electronics and Communication Engineering
Hindu College of Engineering
Industrial area, Sonipat
Submitted to: Submitted by:
Ms. Aruna Tyagi Nalini Ranjan Panday
Assistant Professor 14011003010
Department of ECE ECE 5th
Sem.

2. Preface
This report documents the work done during the summer training at Training
Institute, Delhi Metro Rail Corporation Limited, Shastri Park, Delhi under the
guidance of Mrs. Aarti Gupta. The report first shall give the overview of tasks
performed during the period of training.
Report shall also elaborate about the concept of signalling and telecommunication
used in DMRC.
I have tried my best to keep the report simple yet technically correct. I hope I succeed
in my attempt.
Nalini Ranjan Panday

3. ACKNOWLEDGEMENT
It is a great pleasure to present this report of Summer Training about Delhi Metro
Rail Corporation in partial fulfilment of B. Tech. Program under Deenbandhu
Chhoturam University of Science and Technology, Murthal.
At the Outset, I would like to express my immense gratitude to my training guide,
Mrs. Aarti Gupta, for providing me with the opportunities of studying, learning and
gaining practical experience in various fields during the period of training. Her
invaluable suggestions not only helped me to reach the successful completion of the
tasks assigned, but also made me learn a lot. I am falling short of words for
expressing my feelings of gratitude towards her for extending her valuable guidance,
through critical reviews of project and the report and above all the moral support she
had provided me with all stages of this training.
Nalini Ranjan Panday
14011003010
ECE 5th
SEM.
Hindu College of Engineering

4. Table of Contents
1. Abstract……………………………………………………………1
2. Introduction to DMRC…………………………………………….2
3. Signalling………………………………………………………….4
 Introduction
 Types of signal
 Signalling System Components
4. Telecommunication in DMRC……………………………………12
 Telecommunication
 OCC
 FOTS
 PIDS/PAS
 Master clock
 EPABX
5. Radio Communication…………………………………………….18
 Radio waves
 Technology in use (TETRA)
 Modes of Communication
 Types of radio used in DMRC
 Advantages of TETRA
 Disadvantages of TETRA
6. Reference………………………………………………………….25

5. Page | 1
Abstract
The Delhi Metro Rail Corporation Ltd. is a metro system serving Delhi and its satellite cities
of Faridabad, Gurgaon, Noida and Ghaziabad in National Capital Region in India. DMRC is a
very vast and huge industry and it has a large number of ECE opportunities. Some of them are
Signaling and its components, telecommunication system, automatic fare collection system etc.
But this report tells only about signaling and telecommunication in DMRC.
Signaling is used to control the traffic on the railway tracks, to control the movement and speed of
the metro trains on various lines. There are many types of signals used in DMRC which convey
their own different message. The signaling system is controlled and managed by the Operation
Control Center (OCC) which are situated at Barakhamba Road and Shastri Park.
After that comes the telecommunication. It is the backbone of DMRC. If somehow the
communication system fails all the operations and movement of trains will be stopped
immediately.
Telecommunication means the exchange of information and data between two or more points.
There are basically six components of telecommunication system in DMRC which are explained
in this report.

6. Page | 2
Introduction to DMRC
The Delhi Metro Rail Corporation Ltd. is a metro system serving Delhi and its satellite cities
of Faridabad, Gurgaon, Noida and Ghaziabad in National Capital Region in India. Delhi Metro is
the world's 12th largest metro system in terms of both length and number of stations. A member
of Nova Group of Metros, the network consists of five color-coded regular lines and the
faster Airport Express line, with a total length of 213 kilometers serving 160 stations (including 6
on Airport Express line). The system has a mix of underground, at-grade, and elevated stations
using both broad-gauge and standard-gauge. The metro has an average daily ridership of 2.661
million passengers, and, as of August 2010, had already carried over 1.25 billion passengers since
its inception
The Delhi Metro Rail Corporation Limited (DMRC) was registered on 3rd
May 1995 under the
Companies Act, 1956 with equal equity participation of the Government of the National Capital
Territory of Delhi (GNCTD) and the Central Government to implement the dream of construction
and operation of a world-class Mass Rapid Transport System (MRTS). The Delhi Metro Rail
Corporation has been certified by the United Nations as the first metro rail and rail-based system
in the world to get "carbon credits for reducing greenhouse gas emissions" and helping in reducing
pollution levels in the city by 630,000 tons every year.
Having constructed a massive network of over 190 kilometres in record time, the DMRC today
stands out as a shining example of how a mammoth technically complex infrastructure project can
be completed before time and within budgeted cost by a Government agency. The first foundation
was laid on 1st
October 1998. The DMRC opened its first corridor between Shahdara and Tis
Hazari on the 25th
of December, 2002.
DMRC operates around 2800 trips daily between 05:30 till 11:30 running with a headway varying
between 1–2 minutes and 4–10 minutes. The trains are usually of four, six and eight-coach. The
power output is supplied by 25-kilovolt, 50 hertz alternating current through overhead catenary.
About 2.6 million peoples, on an average on working day, travels in metro train. DMRC get its
20% non- operational revenue through activities like Property Development, Advertising, etc.
Delhi Metro’s Phase 1:
The first phase of construction worth 65 kilometres of Metro lines was finished two years and nine
months ahead of schedule in 2005. Project of Phase 1 Corridor covered 3 lines Shahadra to Rithala
(Red Line), Vishwa Vidyalya to Central Secretariat (Yellow Line) and Dwarka Sec 9 to
Indraprastha (Blue Line). The first phase of construction covers total 58 stations: 18 stations under
Red Line, 10 stations under Yellow Line and 30 stations under Blue Line.

7. Page | 3
Delhi Metro’s Phase 2:
Keeping the Commonwealth Games, 2010 in mind, massive expansion of the Metro network was
planned across the National Capital Region (NCR) in Phase II. 125 Km of new Metro lines were
to be added and the Metro was set to enter the satellite cities of NOIDA, Ghaziabad and Gurgaon
for the first time. Though the quantum of work of Phase II was double the target set for Phase I, it
was completed in only four and a half years well on time before the commencement of the
Commonwealth Games.
In Phase 2 of construction, the Red, Yellow and Blue Lines were expanded and three new lines
(Green, Violet and Airport Express Line) were introduced. This project contained the construction
of 125 new stations.
Delhi Metro’s Phase 3:
In the third phase of Delhi Metro’s construction, the DMRC is in the process of building another
160 kilometers (approx.) of Metro lines which will weave a web of Metro corridors along the city’s
Ring Road besides connecting with many other localities. Metro services have reached Faridabad
and will also reach Bahadurgarh in Haryana for the first time.
The construction work of this phase is expected to be completed by the mid of 2017. Construction
work has started on all the proposed corridors and the ITO – Kashmere Gate corridor is expected
to open by December 2016.

8. Page | 4
SIGNALLING
Introduction:
A Signal is a medium to convey a particular pre-determined meaning in non-verbal form. Various
methods are used to convey the meaning of signals in non-verbal convey a definite information.
This concept of conveying a meaningful message with the help of signals is known as ‘signalling’.
In DMRC, signals are used to move, diverge or stop the metro train. Here mainly light signals are
used to communicate with train.
Types of Signals:
There are basic three types of signals used in DMRC:
1. Fixed signal
2. Cab signal
3. Hand signal
Fixed Signal:
Fixed signals are those signals which are installed at particular fix locations conveying different
messages for different signals at a particular place which controls the movement of trains, like at
the diversions on tracks, in depots etc.
Types of Fixed Signal:
Fixed signals are of two types:
A. Positon Light Signal or Shunt Signal
B. Color Light Signal
A. Position Light Signal: Positon Light Signals are also known as Shunt signals. These
signals are used in the depots to shunt down the metro train. Shunt down means that the
metro trains are bringing to the depots at rest. Position Light signals are mainly a set of
three white lights which are arranged in such a way that they form a triangle. This
arrangement is shown in the following figure. In the following figure when white lights of
set 1 glows it means ON, which means the train will stop at the instant. And when white
lights of set 2 glows it means OFF, which means the train will move or will remain in
motion in the depot. And thus these signals control the movement of trains in the depot. In
these signal one light is common.

9. Page | 5
Fig1: Diagram of Shunt Signal
B. Color Light Signal: In this type of signal, the indications are given by the color of a signal.
A particular color signal or a particular sequence of signals convey its own message. Color
signals are of four types:
a. Block Signal
b. Repeater Signal
c. Buffer Stop Signal
d. Main/ Route Signal
Block Signal: It contains a set of three color signals; RED, VIOLET and GREEN. The
operation of these signals are similar to road traffic signals, the only difference is that it
contains a violet signal instead of yellow signal, otherwise the operations are same. These
signals are installed at the both ends of the metro stations.
Fig2: Diagram of Block Signal
Repeater Signal: These signals are installed at the beginning and end of a tunnel. It contains
only two signals: GREEN and Violet. Green light indicates that the track or line is clear
and the Violet light signal indicates that the line is busy and wait for green light to turn
ON.

10. Page | 6
Buffer Stop Signal: A fixed red signal is required for the ends of line, the ends of siding in
the line and in the depot and the ends of the test track in the depot. For e.g. the Samaypur
Badli and the Huda City Centre stations are the ends of yellow line, so the buffer stop
signals are displayed at the ends of these stations because there are no more stations ahead
these stations. Fixed Red signals are permanently displayed.
Main/Route Signal: These signals are installed at the diversions. Each Route signal has five
lamps, at least three must glow at one time. In the following figure, there is a diversion
after Yamuna Bank, so a sequence of lights will glow which will tell the metro driver where
to move and with which parameters.
(a) (b)
Fig3: (a) diversion on blue line and (b) diagram of route signal
Cab Signal:
Cab Signal means visual indication displayed as speed code on the Train Operator’s console
granting him the authority to proceed under Automatic Train Operation or Automatic Train
Protection mode of driving.
Cab Signals are provided in the cab of a metro train where a train operator or driver operates the
metro train. These signals are given on the operating panel of the cab of the metro train.
Cab signals display the three speed codes:
1. Maximum speed that could be attained by the train.
2. Current speed at which the train is running.
3. The prescribed speed at which the train should run presently.
Cab Signals indicate the metro operator or driver to set the speed on a particular value, so that
there must not be any kind of mishap and the train’s schedule must not be late and the train run on
its time.

11. Page | 7
Fig4: a picture of cab signal displayed on the control panel of a cab.
Hand Signal:
Hand signals are the signals which are displayed or indicated to the metro drivers or operators,
using a color light torch or a colored flag in hands.
These signals are mainly used in emergencies and in the depots to stop or move the train. A Hand
Signal could be a color light torch or colored flags of RED and GREEN.
The messages conveyed by different Hand Signals are given below:
 “STOP” shall be indicated by a Red lamp or raising of both arms above the head or
waving a white light rapidly from side to side or a Red flag.
 “PROCEED” shall be indicated by a Green lamp or green flag held steadily.
 Any light other than “Green” or any object waived violently shall be interpreted
as a stop signal.
Fig5: a flagman is indicating a stop signal to the train operator using
a red flag.

12. Page | 8
Signalling System Components:
Following components or equipment of signalling are used in DMRC:
• Signal (The concept of signal has been explained in previous pages)
• Point Machine
• Track Circuit
• Computer Based Interlocking
• Automatic Train Supervision
• Automatic Train Control
• Emergency Stop Plunger
A. Point Machine:
Point machine is an electromechanical equipment provided near the points of operating them
electrically to the required position of the train movement.
Point position: Point has two positions ‘NORMAL’ & ‘REVERSE’.
 Normal point: It means that position of a point which set the trains for the straight path.
 Reverse point: It means that position of a point which cause diversion of train from one
line to another
Fig6. Schematic Point Diagram
Fig7. Picture of a Point machine

13. Page | 9
B. Track Circuit:
Track Circuit is an electrical circuit, which is used to detect the presence of a railway vehicle on
a portion of track forming part of the circuit.
Functions of Track Circuit in DMRC:
 To Detect presence of vehicle on a track
 Telegram Transmission from Track to Train
There are basically three types of track circuit:
1. Berth Track Circuit: It is the track circuit which is installed or joined just before the
origin signal.
2. First Track Circuit: It is the track circuit which is situated just after the origin signal.
3. Last Track Circuit: It is the track circuit which is situated just before the destination
signal.
Fig8. Electrical joint S-shape circuit.
C. Computer Based Interlocking (CBI):
CBI is an equipment, which provides an arrangement between signaling gears interconnected by
electronic locking so that signaling gear operation must take place in proper sequence to ensure
safety.

14. Page | 10
D. Automatic Train Supervision System:
ATS is a subsystem of Continuous Automatic Train Control system (CATC) which automatically
monitors the entire system and directs train running so as to provide scheduled service under
normal circumstances.
ATS system monitors the System Status continuously and provides the appropriate Controls to
direct the Operation of Trains in order to maintain intended Traffic Patterns and minimize the
effect of Train Delays on the Operating Schedule. The System also has the capability to organize
the Train Movements in an optimum manner in case of Abnormalities.
Using Networked Computers and Automated Functions, ATS ensures efficient Rail Operation,
Automatic Monitoring and Control of Interlocking through Automatic Train Tracking to
Automatic Route Setting. ATS assigns Identification Numbers to Trains and provides all necessary
Real Time Train Information to the Operator. ATS also caters for Tools for Time Table Generation
& Modification as also for the Management of Signalling Equipment.
ATS Function:
 To monitor and control traffic through CATC equipment.
 To perform ARS (Automatic Route setting) and ATR (Automatic Train Regulation).
 To display info on Passenger Information Display System.
 To synchronize the system time with a master clock.
 To generate alarms and events messages.
ATS Components:
There are three basic components of ATS System:
1. Centralised Automatic Train Supervision (CATS)
2. Local Automatic Train Supervision (LATS)
3. Depot Automatic Train Supervision (DATS)
All these components are interconnected with each other and this interconnection is known as ATS
Wan.

15. Page | 11
1. CATS: It is located at the OCC (Operation Control Centre) in Telecom Equipment Room.
It communicates with the radio system, Master Clock, PIDS/PAS etc. to provide
centrallised monitoring and controlling of traffic.
2. LATS: It is located in SER (Signalling Equipment Room). It communicates with PIDS/
PAS and ATC (Automatic Train Control) to provide local monitoring and controlling of
traffic.
3. DATS: It is located in Depot SER (Signalling Equipment Room). It communicates with
ATC to provide local monitoring and controlling of traffic.
E. Automatic Train Control System (ATC);
It is a Safety system for railways, which guides the train operator to regulate the movement of
trains for the purpose of safety and efficiency by making use of cab signals instead of fixed signals.
In DMRC, the metro trains are semi automtic, it means that the trains move automatically. The
work of the train driver is just to start and stop the metro train. This auomation in metro trains are
controlled by ATC.
F. Emergency Stop Plunger (ESP):
ESP is a safety equipment provided at platform and Station Control System (SCR) to prevent the
entry of train to the ESP zone area.
It is used in case of Emergency, suppose, if a person wants to commit suicide by jumping off in
front of the metro train and on the same instant if another person uses the Emergency Stop Plunger
then the Metro train, which is coming on the platform, will be stopped immediately.
When the Emergency Stop Plunger is activated then the platform becomes the ESP zone area.
These ESP’s are given at each and every platform of all stations.
Fig: Emergency Stop Plunger

16. Page | 12
TELECOMMUNICATION IN DMRC
Telecommunication:
Telecommunication is the exchange of information over significant distances by electronic means
and refers to all types of voice, data and video transmission. This is a broad term that includes a
wide range of information transmitting technologies such as telephones (wired and wireless),
microwave communications, fiber optics, satellites, radio and television broadcasting, the internet
and telegraphs.
In DMRC, the basic components of telecommunication system are:
1. FOTS ( Fiber Optic Transmission System)
2. PIDS (Public Information Display System)
3. PAS (Public Address System)
4. Master Clock
5. EPABX (Electronic Private Automatic Branch Exchange)
6. Radio System
Befor discussing about the above components, let me tell you about the OCC (Operation Control
Centre). So, the first question is what is an OCC? The answer to this question is given in below
topic.
Operation Control Centre (OCC):
OCC is a centre where all the operations of metro trains, stations, platforms and their conditions
are supervised and controled. All the system monitoring equipment are installed in OCC. It
controls both rail and metro corridor.
From OCC, every aspect of Delhi metro system is monitored: the time table, speed, security,
traction or electricity, the trains, auxiliary equipments like air conditioning, ventilation system in
underground tunnels and even the crowd in the stations.
DMRC has two OCCs, one is situated at the Barakhamba Road and another is situated at the Shastri
Park.

17. Page | 13
Now we will discuss about the components of telecommunication system.
1. Fiber Optic Transmission System (FOTS):
Fiber-optic communication is a method of transmitting information from one place to another by
sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave
that is modulated to carry information.
Because of its advantages over electrical transmission, optical fibers have largely replaced copper
wire communications in core networks in the developed world. Optical fiber is used by many
telecommunications companies to transmit telephone signals, Internet communication, and cable
television signals. They are largely used for telephony but also for internet traffic, long high-speed
local area networks (LANs), cable TV, and also increasingly for shorter distances.
Types of Optical Fiber Cable:
There are two types of Optical Fiber Cables:
 Single Mode Fiber: It is an optical fiber designed to carry light only directly down the fiber -
the transverse mode. These modes define the way the wave travels through space, i.e. how the
wave is distributed in space. Single mode optical fibers are used over large distances.
 Multi Mode Fiber: Multi-mode optical fiber is a type of optical fiber mostly used for
communication over short distances, such as within a building or on a campus. Typical
multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters
(2000 feet).
Fiber optic relay system:
Fiber optic relay system consists of the following:
 Transmitter - Produces and encodes the light signals.
 Optical fiber - Conducts the light signals over a distance.
 Optical regenerator - May be necessary to boost the light signal (for long distances).
 Optical receiver - Receives and decodes the light signals.
In DMRC, the minimum distance between two station is about 1.2 km, so, here single mode optical
fiber cables are used because it has a lower power loss characteristic than multimode fiber, which
means light can travel longer distances through it than it can through multimode fiber. The multi-
mode fiber has much larger core diameter than single mode fiber. The core diameter of multimode
fiber is typically 50–100 micrometers, while that of single mode fiber is between 8 and 10.5
micrometers.

18. Page | 14
In DMRC, the optical fiber cables are laid under the railway tracks between two stations in both
UP and DOWN directions, so that if one optic fiber cable is damaged somehow then the
communication can be carried by the second optic fiber cable and the communication will not
break. DMRC used to use copper wires for communication, but near about 1200 meter of copper
wire was stolen daily. So, DMRC replaces the copper wires with the optical fiber cables because
a used optical fiber cable is of no worth in the market and it is also very cheap.
Advantages of Fiber Optics:
Compared to conventional metal wire (copper wire), optical fibers are:
 Less expensive: Several miles of optical cable can be made cheaper than equivalent lengths of
copper wire. This saves your provider (cable TV, Internet) and your money.
 Thinner: Optical fibers can be drawn to smaller diameters than copper wire.
 Less signal degradation: The loss of signal in optical fiber is less than in copper wire.
 Non-flammable: Because no electricity is passed through optical fibers, there is no fire hazard.
 Higher carrying capacity: Because optical fibers are thinner than copper wires, more fibers
can be bundled into a given-diameter cable than copper wires. This allows more phone lines
to go over the same cable or more channels to come through the cable into your cable TV box.
 Light signals: Unlike electrical signals in copper wires, light signals from one fiber do not
interfere with those of other fibers in the same cable. This means clearer phone conversations
or TV reception.
 Low power Transmitters: Because signals in optical fibers degrade less, lower-power
transmitters can be used instead of the high-voltage electrical transmitters needed for copper
wires. Again, this saves your provider and you money.
 Digital signals: Optical fibers are ideally suited for carrying digital information, which is
especially useful in computer networks.
 Lightweight: An optical cable weighs less than a comparable copper wire cable. Fiber-optic
cables take up less space in the ground.
 Flexible: Because fiber optics are so flexible and can transmit and receive light, they are used
in many flexible digital cameras for the following purposes:

19. Page | 15
2. Public Information Display System (PIDS):
Public Information Display System is used to display traffic & train scheduling information also
data related to arrival & departure time and other information along the station and various
platform areas. It helps the passengers by providing information about the arrival of the next train.
It is fixed at the both ends of the platform and also on the concourse.
The Public Information Display System is made up of a set of orange LED lights. PIDS are
controlled and supervised by the OCC as well as the Station Control Room.
Following is a picture of the public information display system.
3. Public Address System (PAS):
Public Address System is basically a speaker and it is used to broadcast voice messages to
passengers/staff in all stations, depots, OCC and DMRC Headquarter. Public address system is
used in the emergency case. It is operated mainly by the Station Control Room to address the
passengers or staff members to call them or to do an announcement.

20. Page | 16
4. Master Clock:
Clock system is used to provide accurate time to staff, passengers and time reference to systems
at DMRC. Accurate and synchronized time information is obtained from Global Positioning
System (GPS) by Master Clock at OCC, i.e. , there is a master clock system situated at the OCC
which uses the GPS technology to provide the accurate and same time to each and every clock
which is fixed at the stations.
GPS: GPS or Global Positioning System is a network of orbiting satellites that send precise
details of their position in space back to earth. The signals are obtained by GPS receivers, such as
navigation devices and are used to calculate the exact position, speed and time at the vehicles
location.
Fig. Master Clock Device
Three clocks are fixed at the platforms in which two clocks are digital and they have one sided
display while the other is the analog clock which has a double sided display.
The digital clocks are installed at the both end of the platform while the analog clock is fixed at
the center of the platform. So that, wherever a passenger is standing at the platform, he/she is able
to watch the time clearly and it is one of the best services provided by DMRC at the platforms.
This clock system in DMRC is managed and controlled by the Operation Control Centers so that
there must not be any kind of variation in time at different stations at the same instant.

21. Page | 17
5. Electronic Private Automatic Branch Exchange (EPABX):
A private branch exchange (PBX) is a telephone exchange that serves a particular business or
office, as opposed to one that a common carrier or telephone company operates for many
businesses or for the general public. PBXs are also referred to as PABX – private automatic branch
exchange and EPABX.
EPABX network is used for the administrative communication purposes, including
communication with outside DMRC. This includes extensions for the staff concerned with
administration, digital phones, and analog phones. The EPABX Switch Network will use
ALCATEL 4400 PABX system and also ALCATEL Transmission Equipment between the
stations, using 2 Mbps links to fiber optic transmission system.
The purpose of Telephone system is to provide voice and data communication for DMRC. At each
station, communication is provided through EPABX. All the telephone systems are connected
together to form a telephone network over FOTS.
The DMRC uses its own EPABX and it does not hire exchanges of other telecom companies, so
that the communication in DMRC will be secure and private.
Key Functions of EPABX:
 Establishing connections (circuits) between the telephone sets of two users (e.g. mapping
a dialed number to a physical phone, ensuring the phone is not already busy).
 Maintaining such connections as long as the users require them (i.e. channeling voice
signals between the users).
 Disconnecting those connections as per the user’s requirement.
 Providing information for accounting purpose (e.g. metering calls).
EPABX System at OCC:
Telephone system should interface to the radio system to enable radio users to initiate and receive
calls to/from EPABX extension.

22. Page | 18
Communication in DMRC through
Radio System
Radio Waves:
Radio is the technology of using radio waves to carry information, such as sound, by
systematically modulating some property of electromagnetic energy waves transmitted through
space, such as their amplitude, frequency, phase, or pulse width. When radio waves strike
an electrical conductor, the oscillating fields induce an alternating current in the conductor. The
information in the waves can be extracted and transformed back into its original form.
A radio communication system sends signals by radio. The radio equipment involved
in communication systems includes a transmitter and a receiver, each having an antenna and
appropriate terminal equipment such as a microphone at the transmitter and a loudspeaker at the
receiver in the case of a voice-communication system.
Technology in use:
DMRC is using TETRA technology for radio communication. Terrestrial Trunked Radio
(TETRA) (formerly known as Trans European Trunked Radio) is a special professional Mobile
Radio and two-way transceiver specification. This standard was developed by the ETSI (European
Telecommunication Standard Institute) for private mobile radio. Open standard for private mobile
radio. It defines radio services and interface. The TETRA standard defines the air interface
between mobile stations and the infrastructure.
TETRA uses Time Division Multiple Access (TDMA) with four user channels on one
radio carrier and 25 kHz spacing between carriers. Both point-to-point and point-to-multipoint
transfer can be used. Digital data transmission is also included in the standard though at a low data
rate.
TETRA Mobile Stations (MS) can communicate direct-mode operation (DMO) or using trunked-
mode operation (TMO) using switching and management infrastructure (SwMI) made of TETRA
base stations (TBS). As well as allowing direct communications in situations where network
coverage is not available, DMO also includes the possibility of using a sequence of one or more
TETRA terminals as relays. This functionality is called DMO gateway (from DMO to TMO) or
DMO repeater (from DMO to DMO). In emergency situations this feature allows direct
communications underground or in areas of bad coverage.
In addition to voice and dispatch services, the TETRA system supports several types of data
communication. Status messages and short data services (SDS) are provided over the system's
main control channel, while packet-switched data or circuit-switched data communication uses
specifically assigned channels.

23. Page | 19
Radio Systems in DMRC:
The Radio system is a digital trunked radio system, operating in 380-400 MHz band and
confirming to TETRA standards. The Radio system have central control equipment installed in
OCC. The Radio system uses EBTS (Enhance Base Transceiver System) towers for
communication in rail corridor & leaky coaxial cable along each track in the tunnels for
communication with train borne mobile radio (in metro corridor).
Trunking:
Trunking is a method for a system to provide network access to many clients by sharing a set of
lines or frequencies instead of providing them individually. This is analogous to the structure of a
tree with one trunk and many branches. Examples of this include telephone systems and the two-
way radios commonly used by police agencies. More recently port trunking has been applied in
computer networking as well.
A trunk is a single transmission channel between two points, each point being either
the switching center or the node.
The trunking concept allows channels or other resources to be made available to users as they are
needed. It allows all the channels to be pooled together. As a channel is needed, the controller
grants an available channel from its pool of channels.
In two-way radio communications, trunking refers to the ability of transmissions to be served by
free channels whose availability is determined by algorithmic protocols. In conventional (i.e., not
trunked) radio, users of a single service share one or more exclusive radio channels and must wait
their turn to use them, analogous to the operation of a group of cashiers in a grocery store, where
each cashier serves his/her own line of customers. The cashier represents each radio channel, and
each customer represents a radio user transmitting on their radio.
Trunked radio systems (TRS) pool all of the cashiers (channels) into one group and use a store
manager (site controller) that assigns incoming shoppers to free cashiers as determined by the
store's policies (TRS protocols).
In a TRS, individual transmissions in any conversation may take place on several different
channels. In the shopping analogy, this is as if a family of shoppers checks out all at once and are
assigned different cashiers by the traffic manager. Similarly, if a single shopper checks out more
than once, they may be assigned a different cashier each time.
Trunked radio systems provide greater efficiency at the cost of greater management overhead. The
store manager's orders must be conveyed to all the shoppers. This is done by assigning one or more
radio channels as the "control channel". The control channel transmits data from the site controller
that runs the TRS, and is continuously monitored by all of the field radios in the system so that
they know how to follow the various conversations between members of their talkgroups (families)
and other talkgroups as they hop from radio channel to radio channel.

24. Page | 20
Talk Group:
In most organizations, radio users work in groups that are based on their functions and
responsibilities. These groups of radio users can be assigned to communication talkgroups that
reflect their function or responsibilities.
Types of Modes of Communication:
There are two modes of communication used in DMRC:
1. Trunk Mode Communication
2. Direct Mode communication
A. Trunk Mode Communication:
It represents communication between two or more TETRA mobile stations with the use of trunking
network infrastructure.
It is if four types:
a. Group mode
b. Private mode
c. Phone mode
d. Emergency mode
Group Mode:
It is a half-duplex communication mode in which many users can communicate with each other
by selecting a common talk group.
Half-Duplex means allowing the transmission of signals in both directions but not simultaneously.
For example, on a local area network using a technology that has half-duplex transmission, one
workstation can send data on the line and then immediately receive data on the line from the same
direction in which data was just transmitted.
In DMRC, OCC is able to have a group mode of communication with the Station Controllers of
different stations at the same time.

25. Page | 21
Private Mode:
It is a half as well as full duplex communication mode in which many users can communicate with
each other privately without interfering the talk group. It uses two frequencies.
In this mode of communication an OCC officer can talk privately with any other officer in the
building or to the Station Controller of any station or one Station Controller can talk to another
Station Controller.
Phone Mode:
It is a full duplex mode of communication in which a radio user can talk to any dialed phone
number within DMRC or external network connected to DMRC.
Here any staff member in DMRC, who is authorized to have a phone mode communication can
talk to another authorized person and also to a person who is not a part of DMRC using the same
EPABX system.
Emergency Mode:
The emergency key is provided on every radio equipment, an audio visual alarm will appear on
every radio unit in that talk group. The party who initiates the call has the highest priority for
calling. That means, if a staff member uses the emergency button then he is given the highest
priority to make the call and also if all the lines or channels are busy then the line would be cleared
immediately and his call will be taken.
B. Direct Mode Communication:
It represents direct communication between two or more TETRA mobile stations without the
use of trunking network infrastructure. It means that there is no need of any kind of towers to
communicate between two points. And Walky-Talky is a very good example of this mode of
communication and this mode is mostly used by the CISF officers or the Engineers present
within the premises of a metro station.
It is the Simplex mode of communication.

26. Page | 22
Enhanced Base Transceiver System (EBTS):
It provides RF interface from the master site to the mobile subscribers in a TETRA system. It can
be categorized in two configuration:
 Above ground (Rail corridor)
 Underground (Metro corridor)
Both are of same configuration & characteristics.
Types of Radio used in DMRC:
There are two types of radio used in DMRC:
1. Mobile Vehicle radioFixed
 RAU (Radio Access Unit) or Zetron radio set or Station radio
 Train radio set
 RCW (Radio console workstation)
2. Mobile Portable radio
Radio Access Unit (RAU):
It is located in the Station control room. It is placed in the best radio coverage and it is fixed & has
a functionality just like a telephone radio. It is ideally suited to radio operator dispatchers and
where office personnel need access to a radio system without wanting to have a radio placed into
the office environment.
The M390 is a robust telephone style desktop controller with a large, easy to read LCD display &
handset.
Train Radio:
 MTM700 Mobile radio is installed at front & rear cab for communication between the train
driver & designated station controllers at OCC & Depots.
 This radio unit is connected to different units e.g. TRIU, TRCP; these units are required to
communicate with RCW, TIMS, ATS and rear cab radio.
 Dome type omni directional antenna is located at top roof of train. This antenna is
connected through RF cable which is connected to radio unit.

27. Page | 23
Hand Portable Radio:
The hand portables come with 3x4 keypads, rotary switch dial, and LCD for number dialing and
maximum flexibility. Each hand portable is equipped with an ultra-high capacity batteries (Li ion
or Li Mgh.) for longest standby and talk-time of 24 hrs, that is 5% transmit, 5% Receive and 90%
standby.
Hand portable is suitable for all kinds of calls used in DMRC.
NOTE: Each radio has its radio identification which register itself in central system for its
function. The radio is programmed for its ID, frequency, network code, talk group and allowing
types of call. Radio consists of transmitter and receiver and frequency synthesizer circuit which
function along with DSP (Digital Signal Processor) for digital function.
Advantages of TETRA:
 The frequency used gives longer range, which permits high levels of geographic coverage
with a smaller number of transmitters, thus cutting infrastructure costs.
 Unlike the cellular technologies, TETRA is built to do one-to-one, one-to-many and many-
to-many.
 Rapid deployment (transportable) network solutions are available for disaster relief and
temporary capacity provision.
 In the absence of a network mobiles/portables can use 'direct mode' whereby they share
channels directly (walkie-talkie mode).

28. Page | 24
Disadvantages of TETRA:
 Requires a linear amplifier to meet the stringent RF specifications that allow it to exist
alongside other radio services.
 Handsets are more expensive than cellular.
 Handsets can sometimes interfere with badly designed (usually old) or sensitive electronic
devices such as broadcast (TV) receivers, hospital equipment, speed cameras.
End of Report

29. Page | 25
REFERRENCE
1. https://en.wikipedia.org/wiki/Delhi_Metro
2. https://en.wikipedia.org/wiki/Fiber-optic_communication
3. http://www.slideshare.net/rudyrishi003/telecommunacation-indmrc?qid=e11f9b94-5b9d-
47db-97d7-573d94678951&v=&b=&from_search=1
4. http://www.slideshare.net/Rish108/dmrc-telecom-epabx-system?qid=dcd911c9-8647-40a1-
bbf8-31d76c3d82d1&v=&b=&from_search=1
5. https://en.wikipedia.org/wiki/Base_transceiver_station