Telecom
Basics of Telecom
STM - Synchronus Transport Module
STM 1 link has 63 E1.
1 E1 = 30 Channel
E1 stream has bandwidth of 2 Mbps.E2 stream has bandwidth of 8 Mbps
STM 4 can accommodate 252 E1.
Difference between PDH and SDH
PDH stands for plesiochronus digital Hierarchy.PCM multiplexer used in PDH.
It is Telecommunications network transmission technology designed for the transport of large data volumes across large scale digital networks. In PDH, multixiplexing of 2 Mbit/s signals into high order multixiplexied signals. The laying cables between switch sites is very expensive.It increases traffic capacity of a cable by increasing bit rate.Used to transmit voice conversations.Use Time division multiplexing.It has 4 type of frames. E1,E2,E3 and E4.Use coaxial cable or twisted pair copper wire.
SDH stands for Synchronus digital Hierarchy.Used to transmit voice and data over Optical Fibre. It refers to as multiplexed technology used in Telecommunications.It uses time division multiplexing to transmit constant stream of data.SDH was developed to overcome the disadvantages of PDH.
In SDH, multiplexing is done by byte interleaving process.SDH allows different types of signal formats to be transmitted over OFC.
In PDH, multiplexing is done by bit interleaving process.
Uses basic rate 155.52 Mbps which is called STM 1( Synchronus Transport Module).
STM1 is basic unit of framing in SDH.for branching in STM , LI card is used.
SDH Signal Data rate
STM 1 155.52 Mbps
STM-4 622.08 Mbps
STM -16 2488 Mbps (2.5 GBPS)
STM -64 9953 Mbps (10 GBPS)
STM -256 40 GBps
Generally STM 1 and STM 4 are used in Indian Railways
Advantage-
Simple,support different topologies, Allow quick recovery from failure, Optical Fibre bandwidth can be increased without limit.
Disadvantages-
Lower bandwidth utilization ratio as compared to PDH.Vanurable to computer viruses,Requires complicated Equipments.
STM 4 -252 E1
VHF Frequency alloted to Railway is (146.2-167.95) Mhz.
Mobile Service Switching Centre
The switching between networks is controlled by the Mobile Service Switching Centre.
Control Communication
Railway control Circuits are Omnibus telephone circuits.
Open System Interconnection Model (OSI)-
It has 7 layer
1. Physical layer
2. Data Link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer
Physical layer contains information in the form of bits.It is responsible for transmitting individual bits from one node to another.While receiving data this layer will convert it into 0s and 1s and send them to data link layer.
Data link layer is responsible for node to node delivery of message.The main function of this layer is to make some sure that data transfer is error free from one node to another,over physical layer.
VLANs operate in Layer 2 of OSI model.
Presentation layer is responsible for encryption and descryption of user data.
HTTP is a example of Application layer
Voice Over Internet Protocol
SIP ( Session Initiation Protocol) has been specified in VOIP in Indian Railways.
Subnetting
Dividing a network into logical sub networks is called subnetting.
Contour Allowance in case of Quad Cable
2.5 % of route length.
Characteristics Impedence
470 ohms for unloaded 0.9 mm dia Quad cable.
Omnibus Circuit is used control Communication at way side Stations.
Ip Addressing -
An Internet protocol address ( IP Address) is essential to each device connected to a computer network that uses the internet protocol for communication.
IP Address serves both network interface identification and location addressing.
IP address space is managed globally by Internet Assigned Numbers Authority ( IANA) and five regional internet registries ( RIRs).
Two versions of IP addressing are common use in internet today. IPv 4 and IPv 6.
Address length of IPV4- 32 bits which limits the address space to around 4.29 billion (2 to the power 32).
Address length of IPv6 - 128 bits
Jitter is the time interval between sending and receiving of data packets in data communication.It is time interval error.
Wander- Long term
Jitter - Short term
Sub Network
IP network may be divided into sub networks.
IP address has two parts.
Higher order bits are called network prefix.
Remaining bits are called Rest field or host identifier used for host numbering within a network.
The subnet mask notation determines how the IP address is divided into network and host parts.
Subnet mask
It is a number that identifies the number of bits used for network part of IP address.
Subnet mask is 32 bit number.
If n number of bits represent network part of address, it's 32 bit representation is n ones followed by ( 32-n) zeros.
Features of (GSM- R)
Global System for Mobile Communication- Railways
1. Point to point call
2. Voice Broadcast call
3. Voice Group call
4. Emergency Call
5. Functional Addressing
6.Location Dependent Addressing
7. eMLPP ( Enhanced multilevel Precedence and Preemption)
8. Compatible upto speed of 500 km/ h
In 0.9 mm Quad cable, transmission loss in VF range is 0.63 db/km (unloaded) and 0.25 db/km (loaded).
Mandatory tests to be conducted before Commissioning of BPAC in Quad Cables
A) Conduction test - 56 ohms/ loop km ( to be done monthly)
B) Insulation Resistance- 10 M ohms ( to be done yearly)
C) Transmission loss test - At 2khz/600 ohms, Transmission loss should not be more than 30 db for full length of quad cable.Loading of quad is to avoid TX loss.Tx loss test is done using 800 c/s tone frequency using TMS kit. To be done monthly.
D) Near end crosstalk- Should be better than -55 dbm at 155 khz & -61 dbm at 1khz
E) Far end crosstalk - Should be better -55 dbm at 155 khz & -65 dbm at 1khz.
F) Psophpmetric Noise - Should not be more than 2mv.( to be checked Quarterly)
G) Isolation transformer is placed at interval of 17 kms.It is used to minimise induced voltage.Generally provided at cable huts.
H) Induced voltage is 8.75 V/ Km.
I) Maximum induced voltage in an U/G telecom cables is 150 volt.Under normal conditions,it is 60 volts.
J) In digital cable fault locator, Pulse echo reflector mode is used to find open/short circuit fault.
Crosstalk of BPAC CKTs checked using is 155 khz freq
GSM (Global System for Mobile) and GPRS- General Packet Radio Services -
GPRS is upgradation of GSM system for better speed of data.
GSM is 2G technology and GPRS is 2.5 G technology.
GSM is circuit switched type network and GPRS is a packet switched type network.
GSM - R (Global System for Mobile communications -Railway)
Mobile Train Radio Communication is a digital wireless network based on GSM - R designed on EIRENE ( European Integrated Railway Radio enhanced network) Functional requirement specification ( FRS) and System Requirement Specification (SRS).
Video calling is not possible in GSM -R.
DSLAM ( Digital subscriber line access multiplexer)
It is network device, often located in telephone exchanges,that connects multiple customer digital subscriber line (DSL) interfaces to a high speed digital channel using multiplexing techniques.it uses ASDL( Asymmetric digital subscriber line) modem.In ADSL, upload width is always less than download bandwidth.
ADSL is connected to High Pass filter .
Piconet uses Bluetooth technology for wireless connectivity.
Intranet-
Extranet -
It helps an organization connect with its suppliers and customers using VPN technology over the level of Internal Medium security.Multiple organizations can own it.
Psophometric Noise
When cable is in close proximity of the strong electromagnetic field.Unwanted current and voltage may be induced on it.This Noise will be measured with psopho meter.In a circuit this noise shall not be more than 2 mV.
In the vicinity of Traction sub station, the quad shall be laid in concrete pipes or enclosed bricks channels for a length of 300 m on either side of the track opposite the sub station side.
Attenuation percentage reduction calculator
if attenuation is 3db, percentage reduction in power is 50%
If attenuation is 6db, percentage reduction in power is 25%
ISDN ( Integrated Service Digital Network)
It is a circuit switched telephone network system that transmits both data and voice Over a digital line.These data lines could be of copper lines.It provides better speeds and higher quality than traditional connections.Faster speeds and better connections allow data transmissions to travel more reliably.
To access through ISDN,users had to connect through a digital modem.It is still used for internet where Broadband is not available otherwise for internet purpose ISDN has been phased out.Cost of ISDN is higher than Broadband.One popular alternative is VoIP. Signalling used in ISDN is CCS7.
It is a dial up Service .There are two types of ISDN Networks
BRI- Basic Rate Interface
PRI - Primary Rate Interface
BRI is lower tier of service. It only provides basic needs at lower cost
BRI has 2 B channel, 1 D channel and 1 OH channel . B or Bearer channel is 64 Kbps, D is 16 kbps and OH is 48 Kbps.
2B+1 D+1 OH = 2*64 + 1*16+ 1*48 = 192 Kbps
PRI is main service. It provides a better connection,more reliable service and faster speeds.PRI cards are used in telephone exchanges.
Both BRI and PRI use B channels for sending data and D channel for other forms of communication.BRI uses only two B channels and one D channel.BRI has max speed of 128 kbps.
PRI varies in the no of channels.Data transmission rate in PRI-ISDN is 2048 Kbps(2.048 Mbps).
PRI has 30 B channel,1D channel and 1 OH (overhead or supervisory) channel .D is signalling data channel and B ie bearer channel.
Bit rate of B,D and OH channel in PRI is 64 Kbps( kilo bits per second)
Equipment side (TLBI & telephone) -1120 ohms
Unloaded Quad Cable Characteristics Impedance- 470 ohms .
Loaded Quad cable Characteristics - 1120 ohms
UFsbi - 600 ohms
quad cable is screened, screen factor - 0.1 ohm
Permitted transmission loss in 4/6 quad - 1.2 dB/Km
EC sockets - 06 pin holes in line, impedance ratio of EC socket is 470:1120
Characteristics impedance of Switch board cable - 600 ohms
In data communication,Jitter is time interval error.
Leaky coaxial cable is adopted for providing wireless communication in tunnels.
Inspection schedule of telecom equipments in ART by ADSTE is quarterly.
OSPF routing protocol is used in UTS ( unreserved ticketing system)
RTSF jointing kit is used for joining quad cable.
Error message is ICMP ( internet control messaging protocol)
COA is used in Automation of train control charting at Divisional Control Office.
Spectrum alloted to Indian railways for long term evolution (LTE). - 5 Mhz paired in 700 Mhz band.
Data rate of GPRS - 56 kbps to 171 kbps
GSM to GPRS - pcu is required.
GSM 900 band - uplink frequency 890-915 Mhz and downlink frequency is 935-960 Mhz
Cable marker - 50 m distance
Emergency control runs over 3rd quad.
Characteristics impedance of PIJF pair cable and switch board cable is 600 ohms.
In PIJF ,jelly is used to prevent entry of water
Screening is done to avoid induced voltage
Twisting done to avoid crosstalk.To check the Crosstalk for VF ckt 1000 c/sec frequency tone is used.Perodicity is quarterly
Periodicity of Conduction test is monthly.
Periodicity of Insulation Resistance yearly.
Psophometric test is done quarterly
Supply voltage of CCEO system - -48 volt.
Max no of control telephone in MTWE - 4
IWCCE - 30 telephone
Loss in case of fusion splicing - 0.2 dB.
Most corrosion resistance - Copper.
River bed is not suitable place for placing earth electrode.
Earth Enhancement material s are-
Bentonite,Bonding Resins,Graphite & Portland,
Class C SPD between phase and neutral .
PDH - MUX
64 conductors are used for in /out channel of PD MUX.
ART frequency - 149.975 Mhz
ART INSP by ADSTE - Quarterly
30 min after ART siren 🚨 at day and 45 min at night - Turn out must occur
For ARME it 15 min for day and 25 min for night.
Railway disaster no -1072
Mega phone required at accident site
Time slots in PCM frame -32
In Voltage Matching Technique,
1) Line matching transformer (LMT) is used.
2) Loudspeaker is connected in parallel.
IEEE standard for WLAN - 802.11
When a person is in contact with both earth and with conductor of a telecommunication line.During normal functioning of the power line, Max Longitudinal induced voltage in telecom cable - 60 v (normally)
During abnormal functioning of the traction power line.Max permitted longitudinal induced voltage ⚡ in underground telecom cable is 150 volts.
There is possibility that after every 17 kms parallel to underground cable,this 150 V is induced in the cable.To avoid this induced voltage, isolation transformer is used at every 17 kms.
TETRA- Terrestrial trunk radio. It has two parts.
Radio access and Network layer transport
Frequency alloted to TETRA is (380- 400 ) Mhz and (410-430) Mhz.TETRA does not support signalling applications like AWS etc.
Voltage to time converter is used in A to D converter.
Sensitivity =1/ Current, unit is ohms/volt
CCITT - Consultative committee for international telephony and telegraphy.
Transducer is an input element.
ITU - International Telecommunication Unions.
33 dbm is equal to 2 watts.
If 3 dB power loss - 50% power loss
If 10 dB power loss - 90% power loss
Megger is moving coil instrument.
Transmission measuring sets - Signal level and Transmission loss, Return loss and Insertion loss.
OSPF - Open shortest path first, is a dynamic Routing protocol.
Integrated cable path diagram- To protect cables
Open/ short ckt fault - Digital cable fault locator ( pulse echo reflection)
Quad cable testing by Je /tel - monthly
POET - Passenger operated enquiry terminal
DVR - Digital video recorder-Analog based CCTV Surveillance system.
Depth of Telecom cable- 1 m
Drum of quad- 1 km
Drum of OFC - 3 km
VF frequency band is from 300 hz to 3400 hz.
DTMF ( dual tone multi frequency), frequencies lie in VF band. In DTMF dialing 4 frequencies are used.DTMF works on 12 volts. DTMF uses frequency combination of two ( row and column)
IP telephone transmit voice data using digital form by VOIP.
NVR is able to record 64 videos simultaneously.
IPV 4 uses 32 bit address.Mostly computer networks use IPV 4
E1 is 30 channel PCM - bit rate is 2 Mbps.
Emergency Socket at 01 km
NEXT and FEXT is measured from crosstalk meter.
OTDR - Optical time domain reflectometer.
For connecting POTS(PBT) in VoIP requires 8FXS gateways.
Manchester digital encoding is used in baseband signal in Ethernet
Initial charging and boost charging - Constant current method
Trickle charging and float charging are constant voltage method. Rate of trickle charging 1mA/AH.
Sources used in 1310 nm light is LED or LASER .
LCR meter can measure all the three resistance, capacitance and inductance.
FOIS network is a Star topology with mesh at zonal level.
Condensor joints are provided in middle of loading section.( Used for balancing).
Railnet uses the TCP/IP protocol
Max no of station codes in DTMF system - 99.
SPG - Stored program control - used in Electronic exchange
Screening factor must be less than 1
RS 232 - 50 feet
Underground cables - 4 Wire system is used for longer distance circuits.
Overhead cables - 2 wire system is used for longer distance circuits.
Break down voltage suggested for LD ( lightening discharger) - 230 volt in the MDF of telephone exchange.GD tube is used in MDF
CCTV - close circuit television
MDCH- Main data communication hub.
PDCH - Platform data communication hub.
Adapter is not a networking device.
Switch and Hub are networking devices.
Topologies-
Bus, Ring,Star, Mesh,Tree,Daisy Chain, Hybrid and point to point.
Mesh is costliest network topology.No of links in Mesh topology= n(n-1)/2, n is no of nodes.
Internet is WAN ( wide area network) type of network.
ASDL - Asymetric Digital subscriber Line.
Threshold of pain - 130 dB
Threshold of discomfort -110 dB
In CCEO, LTE can provide 20 nos of two wire telephones
Mutual capacitance (800 Hz) of quad is 50 pF/km.
LMT ( Line matching transformer) is used to match voltage.
Isotopic antenna radiates equal power in all directions.
IWCCE (Integrated way station control communication equipment) - 30 control telephone can be connected.
UTN - Unified ticketing network.
Loudspeaker used in low frequency-
Woofer ( below 2 khz).
Sub woofer- 2-20 khz
Above it Tweeter.
Twitter is connected to High Pass filter
Shortest frame in HDLC protocol - supervisory .
HDLC - High level data link control.
Duration of E1 multi frame- 2 milli second . No of frames in one multiframe is 16.Duration of one slot is 3.9 micro second.Duration of one sample is 125 micro second.
Transmission mode in Coaxial Ethernet- Half duplex
In Linux ,single dot for current directory. Double dot for parent directory .
T flop flop used for Frequency divider and counter design.It divides clock frequency by two
D flip flop - for resistor , output follows input.
1.4 mm 6 quad used when distance between block sections more than 25 kms.
Characteristics impedance of 1.4 mm quad is 310 mm.
Loop resistance of 1.4 mm quad is 23.2 ohm/ km . Transmission loss is 0.3 dB/km(unloaded).Loop resistance is same greater than 100.
Class of IP -
Class A - 0 to 126,
Class B - 128 to 191,
Class C - 192 to 223.
Class D - 224 to 239
Class E - 240 to 254
Horn type speaker not used in Auditorium.
RTP - Real type transport protocol
Dialing facility not provided at way side stations.
IEEE standard for WLAN - 802.11 and For eathernet it is 802.3.
Short haul -15 kms
Long haul - 40 kms for 1310 mm and 60 kms for 1550 mm window.
VPN ( Virtual Private Network)- It extends a private network over Public network and enables users to send and receive data across shared or public network.
Electronics exchange works on SPC ( stored program control).
Antenna in 5 W walkie talkie set- Whip/ helical. Motorola uses Helical antenna.5 W walkie talkie set is used for driver and guard communication on 160.150 Mhz.It works on Half duplex.
A router controls the data though IP address or logical address.
A switch controls the data though MAC address.
IPV6 - 128 bits
RF power meter - used to measure power in VHF communication.
No of channels in 25 W VHF set -16.
MPLS - Multi Protocol Label Switching.In MPLS , customer side uses Edge Routers
Float charging voltage of VRLA - 2.25 V.
If temperature increases, battery capacity decreases.
Indian railways is alloted 5 Mhz spectrum for MTRC LTE in the frequency range of 700 Mhz.
Codal life of Quad -25 years .
NIC card is used for networking.
Point to point Ethernet radio - 2.4 GHz .
During installation of OFC, bending radius should be more than 30 times of cable outer dia.
In the case of Quad it is 40 times
VTAS - Very small aperture Terminal.
BTS is placed in the centre of Cellular cell.
WPC ( Wireless planning and Coordination) license is required for VHF set.
Output of Solar cell is DC.
Min distance between OHE mast and telecom cable is 5.75 m in block section.
Assembly language to machine language - Assembler
LASER - Light Amplification by stimulated Emission of Radiation.
10 mm Copper cable - Equipment to Sub Earth Equipotential busbar
16 sq mm - copper cable from Sub Earth Equipotential busbar to Main earth Equipotential busbar
35 sq mm - Main MEEB to earth electrode.
Primary protection in MDF is GDT ( gas discharge tube).
Hybrid circuit is used to convert 2 wire to wire or vice versa.
EC sockets - transformer used is having impedance ratio 470:1120.
Secunderabad PRS is now data recovery sever. Remaining fours are acting as Data Centres.(Delhi Mumbai, Kolkata, Chennai).
Mutual capacitance of 6 quad pair - 50 pF/Km.
Mutual capacitance of PJIF cable is - 50 nF/ km.
Dia of PJIF cable conductor - 0.63 mm.
Isotropic antenna- Equal power in all directions
Visual faul locator- Also called Laser fault locator , visible laser source emits a beam of Laser light into fibre, to detect a fibre fault upto 5 km.
RC (Remote control) circuit is used for implementing SCADA system.
OTDR ( optical time domain reflectometer)- finds losses in OFC.
HTTP - Hyper text transfer protocol , port no 80, Works in Application layer.
During On Hook, 48 V DC available at Rosette
During Off Hook, 12 V DC available at Rosette.
TPC phone is given at SSP.
Negative feedback used in an amplifier
PDH multiplexer - 30 voice and data channel .
Webfil mux station ID - NIM card
Sampling period of 30 channel PCM - 125 micro second
End point voltage of VRLA cell - 1.75 V/cell
End point voltage of Lead Acid cell - 1.85 V/cell.
NIC ( Network interface card ) is used for networking.
K factor of earth -1.33.
Characteristics impedance of 1.4 mm quad - 310 ohms ( unloaded)
Codal life of VRLA -04 years, for lead acid cell -05 year.
For Platform announcement - Voltage Matching method .
6 Quad used in block is
Orange - White- Red- Slate.
Positive terminal of power supply is connected to earth terminal in Electronic Exchange
CAT 6 cable - Data can be send 100 meters only.
SCADA - used for Traction power control system.
IPDSLAM - ADSL modem is required at users end.
TMS kit - to check Attenuation loss
LAN tester - to check continuity of CAT cable.
IRS Specifications of Quad cable - TC 30/05
PIJF (Polythene Insulated Jelly Filled) -
1) It is multi paired( from 10 to 200 pairs).
2) It is multi Dia ( 0.5 mm/ 0.63 mm/0.9 mm).
0.51 mm for Subscribers connection upto 5 kms
0.63 mm for Subscribers connection upto 10 kms
3) IRS Specifications - TC 41/97.
4) Suitable for underground laying.
5) Generally used for exchange subscriber lines or branch cables branching off from main quad cable.
6) Purpose of jelly is to stop humidity.
7) Characteristics Impedence is 600 ohms.
Twisted Pair Switch Board Cable
1) Size 0.5 mm/0.6 mm copper conductor.
0.5 mm - Subscribers connection in a building, MDF wiring etc.
0.6 mm- Trunk connections
2) Not designed for underground laying.
3) Used for indoor applications such as distribution to various telephone subscribers in a building.MDF to exchange wiring etc.
Size of telephone exchange cables
(1) 50 pair, 0.63 mm dia armoured polythene insulated polythene sheathed jelly filled armoured telephone cables as per IRS: TC- 41/1997
(2) In underground laying, only jelly filled armoured cable to be used.
Spare-
It will be generally desirable to leave 25% or more conductor spare for all cable carrying 5 or more pair of conductors for future expansion.
Laying -
The telecom cables should normally be laid within 1 m inside the Railway boundary.It should be laid at least 2 m away from nearest track.The cable shall be laid 1 m below the surface of the ground.The trench shall be sufficiently wide to ensure smooth cleaning of trenches and laying of cables.
Cable Markers-
Cable marker shall be provided all along the route at a nominal interval of 50 m.Additional markers shall be provided to indicate important points like cable joints, water and sewage mains,power cable, crossing, alignment bends/ curves etc.
VHF Parameters -
30 - 300 MHz
Freq band used in Railway- 146.2 MHz to 167.95 MHz.
Type of operation - Simplex, Duplex
Channel capacity - 1/16/128/256 channel.
There are three types of VHF Equipments
1) Walkie Talkie set- 1W/2W to 5 W,used for communication between guard and driver.Range 1 to 2 kms
2) Portable 25 W VHF are used in loco and vehicles
Normally operated on 12 v battery set.Range 12 to 15 kms
3) Fixed 25 W VHF Sets- Installed in ASM office
Operated on AC mains or 12 V battery.Range upto 25 kms
Antenna used -
Whip antenna, Ground plane Antenna, Diapole, Low profile, Yogi Antenna
Feeder cable - 50 ohms unbalanced coaxial cable.
WPC License is required to be taken for each VHF set.
Inspection- fixed VHF set must be inspected monthly by JE,Six monthly by SSE and yearly by ADSTE/DSTE.
OFC-
OFC has 24 fibres.It is less costly and carries more data compared to Copper cable. Transmission in OFC is not affected by electric and magnetic field.
OFC cable has 6 loose tubes and 4 fibres in each loose tube
Single mode Fibre OFC is used in railway. In single mode Fibre only single ray of light travels while in Multi mode, multiple rays of light travels.
OFC cable drum - 3 Km
Bending permitted in OFC
Normal recommendation of Minimum bend radius under tension during pulling is 20 times the diameter of cable.
In Indian Railways, bending radius under tension should always be greater than 30 times of the diameter of the OFC.
During installation, a minimum of 10 meter of cable at each end is coiled in the jointing pit to provide for joining to be carried out at convenient location as well as spare length.
Transmission loss/km at 1550 nanometer is 0.25 dB/ km.
Transmission loss at 1310 mm is about 0.35 db/ km
Cladding - Low reflective index
Core - High refractive index.
FOIS- Freight operation information system.
It also hosts almost all the operational intelligence software that helps in train operations.ICMS , Crew Management System, Parcel Management System, Control Office Management etc. are hosted on this network.
NMS ( Network Management System)
Essential part of a data network to monitor the health of the network. It is an essential tool for managing complete data network using SNMP protocol based on open standards.
The policy for network access control shall be approved by PCSTE and should be reviewed periodically.
Inspection of ART -
Complete testing by ART SSE/JE -15 days
Inspection by ADSTE/DSTE - Once in 3 months
Inspection by Sr DSTE - Once every year
Wi fi operate using RF technology mostly in 2.4 GHz and 5 GHz.
Emergency Communication
Emergency Communication is provided by following means
a) Emergency Sockets
b) 5/25 Watt VHF sets
c) GSM - R ( very less percentile)
d) Mobile phones available with driver, guard and staff.
Disadvantage of above mode of Emergency Communication -
Section controller is not able to contact train crew in moving train
It can be initiated only in static condition
SOS facility is not available
Weight of emergency control phone is fairly heavy.
GSM - R is used at very less percentile.
To avoid these Shortcoming MTRC ( Mobile train radio communication) is implemented.
Accidents, unusual situation, robbery in train, Locomotive failure and chain pulling etc.
Features of MTRC
Driver to Control
Guard to Control
Driver to station master
Driver to guard
Guard to train crew
Train crew to gateman of gates enroute.
MTRC uses GSM-R technology.
MTRC has been designed on EIRENE ( European Integrated Railway Radio Enhanced Network), Function requirement specification (FRS) and System Requirement Specification ( SRS)
VHF Mobile Radio Communication
Frequency of VHF Communication is 30 to 300 MHz.
The frequency alloted by WPC ( wireless Planning and Coordination wing of ministry of communication) for 146-174 MHz.
Features of VHF Communication -
Mode of propogation is line of sight
Type of operation - Half Duplex
Channel Capacity - upto 16 channels
Type of equipment:
Walkie Talkie set
Base radio
Antenna used- Whip Antenna for portable sets, Ground Plane ( GP) for base radio equipment.
Antenna used is directional and fixed at height of 15 to 20 metre
Feeder cable - 50 ohms unbalanced Coaxial cable
Communication Range-
Walkie Talkie Set ( Hand Held set)- 1 to 2 km
Base Station - upto 50 Kms
License is Mandatory.
VHF set of 25 W and walkie talkie sets of 5 W are being used.
25 W VHF is provided to ASMs at stations. This will be operated at the frequency of 161.15 MHz.
ART frequency ( 147.975 MHz) should be used for communication at disaster sites.Normally restricted to 30 sets.
GSM( Global System for Mobile Communication)
First mobile telephone service started in 1946 at St.Lousis USA.
ETSI ( European Telecommunication Standard Institute) is the body,which is primarily responsible for development of GSM.
Mobile Station -( MS)
Mobile station represents the terminal equipment used by cellular subscriber supported by GSM System.The MS consists of two entities.
a) Mobile Equipment ( ME)
b) Subscriber Identify Module( SIM)
Mobile Equipment ( ME) is called as Cell phone handset has a transceiver, which is capable of turning to all allocated channel within the traffic area.
Major components of the handset are - transmitter, Receiver, Number Alignment Module , logic unit, Frequency Synthesizer , Antenna and required software.
SIM is a smart card that holds information required to identify a particular subscription to a mobile service.The SIM card can be used with any approved GSM handset.
SIM card has following components
CPU
ROM
RAM
EEPROM.
Functions of MS
Radio Transmission/ reception
Radio Channel management
Speech coding/decoding
Radio link error protection
Flow control of data
Rate adaption of user data to the radio link
Mobility management
Base Station Subsystem ( BSS)
It consists of two entities,Base Transceiver Station ( BTS) and Base Station Controller( BSC)
Base Transceiver Station( BTS)
BTS is equipment which facilitate the wireless communication between user equipment( UE) and the network.
It may also have equipment for encrypting and decrypting communication and spectrum filtering tools (band pass filters)
Antenna is also considered a part of BTS.
BTS has several transceivers which allow it to serve different frequencies and different sectors sectors of the cell( in case of sectorised base stations)
Functions performed by BTS-
Radio Transmission in GSM format
Coding and decoding of radio channels
Transmission of signaling Message
Control of protocols
Operation and maintenance of BTS.
Network and Switching Subsystem ( NSS)
It performs switching function of GSM and consist of database needed for subscriber and mobility Management.
It's main feature is to manage communication between Mobile station and other users.
There are three main frequency bands used in GSM
GSM -900, GSM - 1800, GSM - 1900.
Multiple Access technique in GSM-
The objective of multiple access techniques is to combine signals from different sources into a common transmission medium in such a way that at destinations, the different channels can be seperated without mutual interference.
Frequency division multiple access( FDMA)
Time division multiple access( (TDMA)
Code divison multiple Access ( (CDMA)
FDMA users share the radio spectrum in frequency domain.
The user is allocated in the frequency band, which is used throughout conversation.Users are seperated in frequency.
In TDMA,the users share the radio spectrum in time domain.An individual user is allocated a time slot during which it accesses a part of frequency.Users are seperated in time.
In CDMA, each user is assigned a unique pseudorandom code and access the frequency time domain uniquely.
In GSM to achieve a high spectral efficiency in the network the coordination of FDMA and TDMA is used.
Duplexer-
A device which allows a transmitter operating on one frequency and a receiver on a different Frequency to share one common antenna with a minimum of interaction and degradation of the different RF signals.
Tetra based systems
Terrestrial Trunk Radio( TETRA) works on an international open standard architecture that improves performance heighten reliability and increases efficiency.It provides an infrastructure that is able to support both voice and data traffic.
Wireless Planning & coordination ( WPC)
It is national radio regulatory authority responsible for frequency spectrum management, including licensing and caters for the needs of all wireless users( govt and private) in the country.
General Packet Radio Service ( GPRS)
It is a third generation step towards internet access.
It is also called GSM- IP that is Global System Mobile Communications Internet Protocol
Even TDMA users get benefit from this system.
GPRS is an enhancement to existing GSM network and provides connectionless packet data service.
Wireless Local Loop( WLL)
In a telephone network, a wireless local loop is a generic term for an access system that uses wireless link to connect subscribers to their local exchange in place of conventional copper cable.Using a wireless link shortens the construction period and also reduces installation and operating costs.
Comparison of Technologies ( 1G,2G,3G,4G,5G)
G refers to generation
1G offers - 2.4 kbps speed
2 G - 64 Kbps
1G and 2G are based on GSM technology.
3G offers 144 kbps to 2 Mbps
4G offers 100 Mbps to 1 Gbps and based on LTE technology.
Loading of Cable
Process of Removal of Distortion is called Loading.
Condition of Distortion less cable
GL=RC
Loading Section of quad - 2000 m
Loading is done to reduce transmission loss.
Condenser Joint is done in the middle of the loading section of 6 quad cable at a distance of 1000 m.
Normal Joint can be done wherever required.
Permissible limit of capacitance unbalance - 40 pF for full section and 20 pF for half section
Capacitance unbalance exist between
A) Conductor of quad and sheath ( Earthed).This is called Earth Coupling.
B) Conductors of a quad and between adjacent quads.This is called Crosstalk Coupling.
Capacitive coupling cause cross- talk and earth coupling cause nose.
Ripcord
A non metallic suitable ripcord shall be laid longitudinally to facilitate removal of PVC sheath.
Data Communication Cables
For data communication, two types of cables are used for LAN work.
UTP - Unshielded twisted pair
Range is Maximum 100 metres
STP - Shielded Twisted pair- used for high speed data
CAT cable is terminated through RJ 45 connector.CAT cable has 4 pairs i.e 8 conductors
CAT 7 support Speed of 10 Gbps upto 100 metres.
Coaxial Cable
It is unbalanced cable.It has only one conductor.
The Coaxial cable comes in various forms.
Thin Ethernet or thin wire:- Can carry a signal for about 185 m.
Thin Ethernet LANs Coaxial cable is connected with BNC( Bayonet Neill Concelman) connector.
Thick Ethernet - It can carry signal farther than thinned cabling about 500m and thus often used as backbone connecting.
Screening factor of telecom cables is 0.1.
Screening factor= Voltage induced in conductor in presence of metallic sheath/ Voltage induced in conductor in the absence of metallic sheath
It is considered that field strength of 87.5 V/ Km exist in the vicinity of a telecom cables.This induces voltage of 8.75 V/Km in each conductor of cable because of screening factor 0.1.
Traditional simple LAN Switch operate at layer 2.
Parallel Communication
It allows fast data transfer between two devices.
Ethernet
Ethernet uses a physical address that is imprinted on the network interface card ( NIC).For the above physical address 48 bits are used.
VLAN ( Virtual Local Area Network)
VLAN in a switch is configured by Software.
NAT ( Network Address Translator)
It is the process of where private address is converted to public and public address to private.
Laying of Cable
If OFC and Quad are to be laid in same trench,then OFC will be at 120 cm and Quad will be at 100 cm depth.
6 Quad
Standard drum length is 1000 m.
Branch off Clip is used In derivation joint of 6 quad cable between main and derivative cable .
Impedence ratio of transformer used in EC socket is 470:1120.
IEEE standard for WiFi both 2.4 GHz and 5 GHz- 802.11n
In Electronic LC gate telephone no power supply is required at LC gate.
Switch Board Cable
1) Used in indoor cables.
2) The characteristics impedance is 600 ohms.
UEC System ( Universal Emergency Communication)
Operates on 146.2 Mhz to 151.45 Mhz and 159.6 Mhz to 162.45 Mhz
Data Network Analyzer is basically a protocol Analyzer, Packet Analyzer & sniffer.
Spectrum Analyzer examines the spectral composition of EM waves consisting of the following waveforms
Electrical, Optical & their power waveforms.
Spectrum Analyzer are used to examine Carrier levels, Side bands & Harmonics & Phase Noise.
Frequency counters used for Microwave application are of Heterodyne method type.
UTP - Unshielded twisted pair.
The Network Architecture for the Unified Ticketing System is of 4 Tier.
In UTS, the number of locations per OSPF are shall not exceed 70.
Branch office Clips are required in Derivation joint of Six quad cable.
Quad used for BPAC must be meggered with 100 V Megger.
In OFC cable at 1310 nm - Max end to end loss in DB per km is 0.40 DB/ Km.
Bending radius should be greater than 30 times the diameter of OFC cable.
Routers operate primarily on Network layer of the OSI model.
Core netbook in LTE - EPC ( evolved packets core)
Distance of underground telecom cable from track centre - 10 m.
Spare conductor required- 25%.
Internet service provider in Railway - CRIS, Relaince Jio, BSNL
Addressing in IPIS revision 4 - IP based addressing.
Ethernet is not network layer protocol .
Gateway - used to connect two or more different networks.
Telnet - Internet service to access the computer of office from remote location.
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