TELECOM COMBINED

 All about OFC

SM fibre ( Single mode fibre)-

It is a type of fibre optics cable that has smaller core diameter compared to multimode fibre.

This means only a single mode of light can travel through it,resulting less signal loss and higher bandwidth.

It transmits a single ray of light,which has higher bandwidth capabilities and preferred in longer distance applications.

Multi mode Fibre Optic Cable-

Large diameter core that allows multiple modes of light to propogate.

As the core increases,more data passes through a given time.

Quality of signal reduced over long distances.

Typically used for short distances,data and audio/video applications in LANs.

Windows of OFC -

1 st window - 850 nm - Short wavelength region

2 nd window - 1310 nm - Medium wavelength (O band)

3rd window - 1550 nm - Long Wavelength (C band)

Attenuation is minimum at 3 rd window.

2nd and 3rd window are used in Single Mode Fibre.

1st and 2nd in Multi mode Fibre.

Max speed of Cable laying in OFC - 15 meter/ min.

Link power budget analysis in OFC Link performed to ensure 

1. Sufficient System operations margin 

2. Link operational feasibility 

3. Minimum power available at receiver. 

10 m of ofc is to be coiled on each end in the jointing pit.

Dead Zone in OTDR - Distance along ofc cable where OTDR can not detect or measure events such as splices or connectors.

Excessive pulse width in OTDR causes increase in dead zone length.

Numerical Aperture of an OFC is its light gathering ability.

LSPM - ( Light Source Power Meter)

This meter is superior to OTDR for  measures power loss.

only.

Overall OTDR is much superior because it power loss,location of faults or faulty connectors.

Counter allowance in OFC laying- 2.5 %

Extra length for track cross in OFC - 2.5 m on each side

Bridge and culvert - 10 m each side 

Major Steel bridge - 5 m both sides.

Short Bridge - 2.5 m both side

At every cable joint - 10 m 

Telecom cable laying - 01 m inside Railway boundary 

Minimum bending radius is 30 time the radius of OFC diameter 

Pulling tension - 1.1 times of weight of OFC.

Pulling speed - 15 m/second.

After OFC laying,bitumen compound is poured in early hours or late hours when Ambient temperature is around 18 degrees or less so that temperature of cable does not increase beyond 55 degrees Celsius.

Bitumen compound should be filled upto height of 60 mm.

Cable marker should be placed at 50 m and at places where route ranges.

At track crossing depth should not less than 1.2 mm.

At 500 depth a PVC warning tape shall be provided continuously running in trench.

Mechanical and Fusion splicing 

All about Passenger Information System

System that facilitates dissemination of train related information to passengers are passenger Information System ( PIS)

System that provides information at Railway station Premises -

1. Audio : The train related information like arrival/ departure announced through PA system.

2. Video: The information provided through video system.This is of two types.

a. Interactive Video system: 

It is Graphic user interface ( GUI) based touch screen directly operated by passenger to get information.

These are called Passenger operated Enquiry Terminals (POET) or Touch Screen Display system.

b. Non Interactive Video system -

Provided train related information on CCTV monitors. These systems also display intertainment program like TV channel broadcasting.

3. Alphanumeric display systems- 

Gives information in different languages on platform.This information guides the passengers to go to correct platform and in time.

System that provides information at Passenger end-

Two types -

Interactive and non Interactive 

a) Interactive - System that provides information through interactive process.

ICVRS

Call Centre

Internet 

b) Non Interactive - Through text messages on the Public Land Mobile Network customers

Integrated Passenger Information System Rev 4.0 -

It will consist of following hardware

1) CDC ( Central Data Controller) loaded with software for announcement 

2) Platform data Controller( PDC)

3) MLDB ( Multiline Display Board)

4) Platform Display Board ( PDB)

5) At a glance display board (AGDB)

6) Coach Guidance Display Board ( CGDB)

7) LED/LCD display 

In video surveillance system the recording shall be stored for 30 days at full HD resolution of full HD cameras.

IP addressing is used in IPIS revision 4 display boards.

Call centre fetches train arrival/ departure data from NTES server.

In video surveillance system at Stations the recording shall be stored for 30 days at 25 FPS Full HD resolution of full HD camera

Max length of RS232 in IPIS is 15 m.

Redundant Array of Independent disks used in IP based surveillance system that has storage capacity of TETRA bits.

UTS Was developed using C++ for front end interface and SYBASE for backend database. It runs on UNIX operating system.

NeTS ( Network enabled Terminal System)- Standard solution for connecting dumb terminal and thin clients at remote site for PRS - UTS integration.

Used to facilitate ticket booking and management. This system allows seamless exchange of data between booking terminal and central server.

PRS and UTS are Integrated,allows operators to book tickets, check availability, cancel tickets and other functions related to train reservations and unreserved ticketing.

Topology used for PRS and UTS unification- Mesh.

UTS Application is Divided into modules 

1. Ticket Subsystem 

2. Fare

3. UDM/ TDM

Passenger can cancel UTS ticket one day in Advance.

Regional Centres for PRS -

1. New Delhi 

2. Mumbai

3. Kolkata 

4. Chennai 

5. Secunderabad

All about Telecom Cables 

Size of Cable-

The various size of conductors used in Cable are - 0.4 mm,0.51 mm,0.63 mm,0.9 mm and 1.2 mm.

Twisting is done to avoid crosstalk.

Distortionless condition-

If there is no phase Distortion, the velocity of propogation must be same for different Frequency components and should be independent of Frequency.

GL=RC is distortionless condition 

Loading of Underground cable -

When diameter of conductor increases,  value of R decreases . This is not possible due to its increased cost.

If the value of G increases, transmission loss will increase which is also not acceptable.

Therefore there is only one way to increase the value of GL by increasing L.This is achieved by using the coils of suitable inductance value wound on dust cores are placed in series with line on suitable intervals.

This is called coil loading or lump loading.Value of each coil connected in each limb of a quad cable is 59 mh.

V.F.balancing of underground cable-

V. F balancing of underground cable is done to reduce noise and crosstalk in cables.

This is necessary in RE cables because the cables carry important circuits and they are having repeaters at every 40-50 km.

The process of measuring the capacitance unbalances between various quads and earth,within the quad and with adjacent quads and minimising the unbalances by connecting condensor is called V.F balancing .

6 Quad Colour and Allocation 

Quad 1- Orange,White,Red,Slate - 

Quad 2- Blue,White,Red,Slate 

Quad 3- Brown,White,Red,Slate 

Quad 4 - Green ,White,Red,Slate 

Quad 5-  Yellow,White,Red,Slate 

Quad 6 - Black ,White,Red,Slate 

Section control - Quad 2 is used.                                                 

PIJF Cable-

Widely used for local loop and other networks.

IRS Specification - IRSTC - 41/97.

NO of pairs -

Vary from 10 to  200 pair.

Conductor Diameter-

0.5 mm,0.63 mm,0.9 mm

4/6 Quads -

Characteristics impedance- 470 Ohms ( unloaded)

                                                  1120 ohms ( loaded)

Cross sectional diameter  - 0.9 mm

Transmission loss - 0.25 dB ( loaded)

                                    0.63 dB ( Unloaded)

Permitted transmission loss per km for BPAC/SSDAC/MSDAC application - 1.2 dB

Attenuation in PIJF Cable is greater than Quad cable in dB/Km.

RDSO Specification of 4/6 Quad cable of 0.9 mm dia is IRS: TC 30/2005 ver.2

6 Quad cable ( Non RE)-

Quad 1 - Section controller

Quad 2- Emergency control 

Quad 3- Dy control

Quad 4- Test Quad

Quad 5- Block

Quad 6 - Lc gate and Spare.

Data Communication Cables-

For data communication,two types of cables are used for LAN.

UTP - Unshielded twisted pair

STP - Shielded Twisted pair

UTP-

Less expensive than STP.

Economical alternative of Eathernet.

Each conductor is made up of annealed copper of dia 0.9 mm.

Connected with RJ 45 connector.

STP - 

For high speed data,STP cables are used.

Each conductor is made up of annealed copper of dia 0.9 mm or 0.6 mm.

Size and Length of main cable length-

Contour Allowance- 2.5%

Jointing Allowance- 1%

At level crossing gates minimum 3 m of loose cable should be coiled to meet future need.

In Non RE Area distance of distance of 2.75 m and in RE Area distance of 5.75 m from centre of track to be maintained while laying the cable.

Cable route markers to be provided at every 20 m in straight and at joints with proper marking.

PIJF cable Jointing -

Available in 20,50 and 100 pairs of 500m drum length.

For straight jointing of PIJF cables, TSF-1,TSF-2,TSF-3 and TSF-4 jointing kits are used.Same kits are used for branch joint also.

Jointing of Quad Cable -

A) Straight Jointing 

TSF 1 - Used for 4 Quad 0.9 mm

TSF 2-  Used for 6 Quad 0.9 mm.

As per latest RDSO Specification RTSF Jointing kit is used for quad cable.

In the RTSF Jointing kit- 

Tinned copper braid is used to provide continuity between Aluminum Screening of both the cables.

Sealant tap in RTSF kit is used to cover metallic projections.

B) Derivation Joint-

This kit is used where Derivation cable is connected with Emergency Socket.

On steel girder bridge 10 m of cable is to be left on both sides while laying.

Laying of telecom cables outside the station limit-

Laid 10 m from centre of track.

T2,T3,T4,T6,T7

Connectors-

Two most common connectors used for professional audio are 3 pin XLR and 1/4 phone connectors.

RCA Connectors-

A round,press on connector used for audio and video connections.

F connectors- used for television and antenna applications.

N connectors- used by  cable TV industry.N means Navy.

C connectors- Similar to N connector. However they are Bayonet locking.

BNC Connector-( Bayonet Neil Conelment connector)

RF connector used for terminating coaxial cable.

Used in video and RF applications to 2 GHz.

TNC connector-

Threaded version of BNC connector 

Used in cellular telephone RF antenna connections.

Waveguide Tees-

Waveguide Tees are Waveguide junctions.

1. E type T junction 

2. H type T junction. 

Attenuator -

Used to Control the amount of power transferred between the  points on a transmission line by absorbing or reflecting some of Microwave power.

Directional Coupler-

It is four port component in which two transmission lines are employed in such way that output at port of transmission line depend on the propogation in other.

Modulation-

Modulation is the process in which amplitude, Frequency or phase of a high frequency wave called carrier is changed in accordance with instantaneous value of low frequency wave, called modulating signal.

Type of Analog Modulation-

1. Amplitude Modulation 

2. Angle Modulation ( frequency modulation and phase Modulation) 

Modulation index-

K= Em/Ec 

It is a number lying between 0 and 1

Digital Modulation Techniques-

1) Digital Amplitude Modulation or Ampitude Shift Keying ( ASK)

2) Frequency Shift Keying ( FSK)

3) Phase Shift Keying ( PSK)

Earth Electrodes-

There  are three types of earth electrodes. 

1) Plate type

2) Rod or pipe

3) Strip type 

Chemical Treatment of Soil-

Artificial reduction of Earthing resistance by treatment of soil with salt or similar compounds is generally not recommended except as last resort to improve specific resistivity.

Chemical used include Sodium chloride,Calcium chloride.Magnisium sulphate,copper sulphate.

Decibel -

Decibel is one tenth of bel (B), I.e 1B= 10dB

Although Decibel  measurement are always relative to reference level,if the numerical value of that reference is exactly stated ,then the decibel measurement is called absolute measurement.

dBm indicates power measurement relative to  1 milliwatt, 

0 dBm means no change from 1mW.

Thus 0 dBm is the power level corresponding to a power of exactly 1 mW.

3 dBm means 3 dB greater than 0 dBm.

Absolute measurement of Power-

dBm or dBmW

dB(1mW) - Power measurement relative to 1 milliwatt.

X dBm = X dBW + 30

dBW

dB(1 W) - Similar to dBm but the reference level is 1 Watt.

0 dBW = + 30 dBm

-30 dBW = 0 dBm

Cable Fault Locator-

Cable fault locator are of two types.

1. Pulse Echo Method

2. Time domain Reflectometry 

Transmission Measuring Sets ( TMS)-

Specially designed for maintenance of Telecommunication lines in telephone exchanges & on the field.

TMS is used for following measurements.

1. Signal Levels 

2. Insertion Losses

3. Transmission losses 

4. Return Losses

Insertion loss is the loss of signal power resulting from Insertion of a device in a transmission loss.

Measurements used in OFC

Visual Fault Locator-

It is also called Laser fault locator.

It uses 650 nm or 635 nm visible laser that emits a bright beam of Laser light into a fibre,allowing the user to visually detect a fibre fault upto 5 km.

It is used for following.

1. To locate breaks 

2. To locate macro bends

3. To locate faults in connectors.

4. To find end to end identification.

Optical Power Meter-

It is used to determine how much attenuation ( loss) the light emitted from a light source suffers,while it travels through a given length of fibre.

Optical Time Domain Reflectometer ( OTDR) -

It is a key instrument used in field of fibre optics communication for testing the integrity and performance of fibre optics cable.It works on the principle of sending a series of optical pulses into fibre and analyzing the reflected light to evaluate fibre's characteristics.

OTDR measures the time it takes for the back scattered light to return and intensity of the returned light.

This device analyzes the returning light to create a trace, a geographical representation of fibres performance.

Following can be measured with OTDR.

1. Fibre Attenuation Characteristics 

2. Insertion Loss ( connector)

3. Splice loss.

4. End to end loss measurement.

5. Break point.

Micro bending in OFC

1. Microbending losses occur when an optical fibre bends on a small scale,causing light to scatter and reducing transmission quality.

2. This is loss induced by physical stress on the fibre.

3. The loss which exists when an optical fibre undergoes bending is called bending losses.

4. It affects both,attenuation and loss.

FSK - Two frequencies are used

Telecom Manual

PTCC - Power and Telecommunication Co-ordination Committe.

Central standing committee for co-ordination of Power and Telecommunication system.

Local Telephone Equipment ( LTE).

LTE is used to provide 20 local telephones at HQ.

Types of cables 

A) Quad Cable 0.9 mm or 1.4 mm dia.

1.4 dia Quad used for Block Section more than 12 kms.

Suitable for underground laying.

Used for control Circuits and block interfaces.

IRS Specifications IRS: TC 30/05

B) PIJF cable-

 Multi pair ( from 10 pairs to 200) Multi dia ( 0.5 mm/0.63 mm/0.9 mm)

Suitable for underground laying.

Used for exchange subscriber lines or branch cables branching off from main quad cable.

C) Twisted Pair Switch Board Cable ( 0.5 mm/0.6 mm)

Not designed for underground laying.

Used for indoor applications such as distribution to various telephone subscribers in a building.

Jointing Kit-

For quad cable jointing- RTSF ( Reinforced Thermo Shrink Jelly Filled kit) type jointing kit to be used.

Laying -

Quad cable should be laid 10 meter inside railway boundary outside station limit.

Inside station limit, it is 5.75 m.

Cable Markers should be provided at 50 m intervals.

Quad cable should be laid 1 meter below surface of ground.

When the depth of cable trench exceeds 0.5 mm near the OHE Mast. It shall be ensured that nearest edge of cable trench is at least 3m away from OHE mast.

When independent earth is provided for an OHE structure, the cables shall be laid 01 m away from the earth.

In the vicinity of Traction sub station, the cable shall be laid at least one meter away from any metallic body of sub station, which is fixed in ground.

Further, this cable should be laid in concrete pipes for a length of 300 m,on either side of sub station.

As far as possible, cable shall be laid on the side of track opposite to the sub station.

In the vicinity of OHE switching Station , the cable shall be laid at least one meter away from any metallic body of sub station, which is fixed in ground and 5 m away from station Earthing. This distance can be reduced 1 m, provided cables are laid in concrete pipes. 

Outside station limit,cable shall be laid 10 m distance from centre of nearest track.

When signal and telecom both cables laid in the same trench, a distance of 100 mm to be maintained between them.

While laying cables shall not be subjected to sharp bends.The bending radius of cable shall not be less than 40 times the dia of cable.

IP MPLS ( Multi Protocol Label Switching)-

It is networking technique used to improve speed and management of IP network.

MPLS assigns a short fixed length label to packets.

Labels are used by Routers to forward packets through network without looking IP header.

MPLS is widely used for creating secure VPN.

Facilitates the transport of voice,video and data over a single network.

MPLS works in between Data link layer and network layer and often summarized as layer 2.5.

Cost of MPLS is more than Eathernet.

MPLS header is 32 bit.

 VHF Communication-

Frequency band is 30 Mhz to 300 Mhz.

Frequency alloted by WPC to Railway is 146.2 Mhz to 167.95 Mhz

Type of operation- Simplex,Duplex 

Type of Equipment-

5W set - Guard,driver

25W set - ASM room ( operating on 12 V battery)

Range - max 25 kms.

Feeder cable - 50 ohms unbalanced.

ART- 147.975 Mhz

Cable Length-

a) Route length as per actual measurement plus contour Allowance of 2.5%.

b) Extra length for track crossing- 2.5 m loop on each side.

c) Bridge/culvert crossing- 10 m extra on each side.

d) Major steel bridges - 5 m on either side.

e) Short bridges - 2.5 m on either side.

f) At every joint - 10 m on either side

g) Cable huts- 10 m in the cable pit.

Blowing of OFC Cable-

Cable will be blown into pre lubricated HDPE duct with help of compressor and blowing equipment.Blowing method involves feeding of optical fibre cable into duct with help of consistent high pressure airflow,equally distributed along the entire cable throughout the duct.

Loss in OFC -

End to end loss should not exceed 0.25 db/km at 1550 nm.

End to end loss should not exceed 0.40 db/km at 1310 nm.

RCC marker color-

Red path of ofc quad

Yellow quad joint

Green Ofc joint

Duct integrity test of OFC-

Synchronus Transport Module ( STM) -

Fundamental unit in SDH framework,which is used for high speed Telecommunication transmission over Optical fiber.

STM defines the basic transmission rate for SDH.

The base level is STM 1,which operates at transmission rate of 155.52 Mbps.

Higher levels are STM-4,STM-16,STM-64 and STM -256.

In railway STM-1 and STM-4 are used.STM1 can accommodate max 63 E1s

Used for high speed internet and Telecommunication services.

Supports various types of traffic such as voice,data and video.

STM 1 - 155.52 Mbps bit rate

STM 4- 622 Mbps bit rate

STM 16- 2488 Mbps bit rate.

Data Network -

Indian Railways has three major data networks.

1. Railnet

2. UTN ( unified ticketing network)

3. FOIS network ( freight operations information System)

The various applications are as under:

* PRS( Passenger Reservation system)

* UTS ( Unreserved ticketing system)

* COIS ( Coaching operation information system)

* COA ( Control Office Automation)

* CMS ( Crew Management System)

* MMIS ( Material Management information system)

* PMS ( Parcel Management System)

* E Drishti ( A dashboard for Indian Railway)

* SMMS ( Signalling maintenance management system)

* RTIS ( Real time train information system)

The general purpose wide area intranet of IR is known as Railnet.Railnet is also widely used for accessing Internet.

Railnet is built by Railway own transport network, utilizing bandwidth from RCIL ( Railtel cooperation of India) or leasing bandwidth from BSNL.

Communication Media-

The communication links making up the data network are combination of media like OFC,GSM- R/LTE,VSAT and twisted pair copper cable.

Network Security -

a) Firewall -

First level of defense at Network perimeter.

b) UTM ( Unified Threat Management)-

It consists firewall as well as key security features.

ART:-

Complete testing by JE/SSE - Once in 15 days

ADSTE/ DSTE- Once in 3 months 

Sr DSTE - Once in year.

Mobile Train Radio Communications - GSM - R

MTRC is digital wireless network based on GSM-R ( Global System for Mobile Communication).

LTE( long term evolution)

It is a standard for wireless broadband communication for mobile devices and data terminals.

LTE is often marked as 4G LTE.

LTE is fully IP based ,enhancing IP based,enhancing the efficiency and integration of voice,video and data services.

EPC ( Evolved Packet Core) is core Network in LTE.

Spectrum alloted to Railway for LTE is 5 Mhz paired in 700 Mhz band.

OFDMA

Uses of LTE -R

1) TCAS 

2) Video surveillance system in Locomotives 

3) Internet of things ( IoT) based asset reliability monitoring.

4) On board video surveillance for passenger security.

5) Broadband internet on running train ( on Board wi fi facility through LTE)

Indian Railways is migrating from GSM -R to LTE for railway automation system and Broadband services.

Passenger Information system -

Following types of Passenger information system are provided by telecom department of Railway 

1) Interactive Voice Response System (IVRS)

2) Prerecorded Announcement and Auto Announcement system

3) Train indicator 

4) Coach Guidance system 

5) GPS Clock/ Master slave Clock. 

Satellite communication System -

VSAT( Very small Aperture Terminal) Network 

It provides point to point or point to  multipoint data connectivity using Geostationary Satellite as repeater location.

VSAT network is used for UTS/PRS & FOIS connectivity and as accident site communication for voice,data and video transmission.

Frequency for satellite communication in the range of gigahertz 

IR VSAT Network Components-

It works and consists of  

i) Hub Earth Station 

ii) Remote Earth Station 

iii) Satellite transponder & Space link

iv) Network control centre

v) Interface Equipment 

It works on Star and Mesh and Hybrid Topology 

Master earth station of VSAT has 6 m large Antenna.

IR Satelite network operates on Ku Band and operates on up link frequency of 13.75 to 14.5 Ghz and down link frequency of 10.70 to 12.75 Ghz.

Up link frequency- Carrier frequency on which Hub or remote earth station transmits the signal to satellite.

Dn link frequency- Carrier frequency on which Satellite transmits the signal to Hub or remote earth station.

VSAT supports frequency band of Ku Band, C band and Extended C band.

IR 's present Earth Station is situated at New Delhi.

It is heart of entire network.

THE NDLS Satellite Hub has now been upgraded to latest HX Satellite technology.

Calculation of Earth Resistence- 

Approximate Earth Resistence of the rod/pipe

R= 0.75 × o/L    if 25< L/d < 100

R = o/L                if 100 < L/d < 600

R = 1.2 o/L          if  600 < L/d < 3000

where o = Resistivity of earth in Ohm meter.

              L =     Length of electrode in meter

              d =      Diameter of electrode in meter

If Resistence of single pipe is R and desirable earth Resistence is R(d). Then

R(d) = (1.5/ N) × R

N is no of electrodes in parallel at a distance of 3 to 4 m intervals.

Types of Fire -

A Class:-

Wood,charcoal,jute etc - water is sufficient to extinguish the fire.

B Class-

Oil, petrol,  paint etc- Foam is sufficient to extinguish the fire.

C class - 

Electric fire- Water not used,only CO2 used.

Wi Fi-

Railnet is general purpose Enterprise Wide Area Network of Indian Railways. Wi fi network is allowed to be established as a part of network.

Wi fi network operates using Radio frequency ( RF) technology in the free band mostly at 2.4 GHz and 5GHz in public band.

An access point (AP) is used for providing a wireless network. The access point is connected to the wired network( Railnet)  to provide internet services to its clients.

An access point works as combination of Router,switch and wireless radio in one device.

The closer to an access point,the stronger is the Signal and faster is connection speed.

Following security measures are used for improved security of networks using Wi-Fi

a. SSID hiding 

b. Mac filtering 

c. Static IP Addressing 

d. Use of strong passwords for admin as well as wi fi access

e. Use of strong end to end encryption standard like WPA.

f. Changing default IP address and password of the access point.

IP Addressing ( Internet protocol)-

IANA- Internet Assigned Number Authority 

IP address is essential to each device connected to a network that uses IP for communication.It serves both network interface identification and location addressing.

Two versions of IP addressing are common today.Original version is IPv4 and next version is IPv6.

IPv4 address has a size of 32 bits.

IPv4 addresses are represented in dot decimal notation, consisting four decimals. each ranging from 0 to 255.

E.g.     172.16.244.1

Each decimal digit can be denoted by 8 bits binary number. Thus total no bits = 32.

Sub Networks-( Subnet)

Sub Network is also called Subnet 

IP network may be divided into sub networks.

A subnet is smaller,segmented portion of larger network. 

Subnetting involves Dividing a network into multiple smaller,more manageable sections,which improves network performance and enhances security.

For this purpose, an IP Address consists of two parts :

The Network prefix in the high order bits 

and remaining bits called Rest field or host identifier used for hosting numbering within network.

The subnet mask notation determines how the IP address is divided into networks and host parts.

Subnet Mask-

It is also 32 bit number used in IPv4 network to divide IP address into Network and Host Portion.

It defines which part of IP address defines network and which parts defines Host.

It's binary form consists a series of 1s followed by 0s

1s represent network Portion 

0s represent Host Portion.

E. g.

For an IP Address 192.168.1.1 with a subnet mask 255.255.255.0 (11111111.11111111.11111111.00000000)

Network Portion is 192.168.1

Private IP Address-

A private IP  address is an IP Address used within private network ( home , office, enterprise network) to identify devices.These addresses are not accessible directly from public internet.

An Internet service provider (ISP) is a company that provides internet access to organizations and home users.

At present RCIL is ISP of Indian Railways.

IPv6 Addressing Scheme -

Address size increases to 128 bits. Thus providing 2 to the power 128 addresses.

Important features of IPV6

1. Sufficient address space for the near future.

2. Enhanced security.

3. No need for NAT.Since every device has a globally unique IPv6 Address, there is no need for NAT.

4. IPv6 hosts can automatically configure themselves with an IPv6 Address even without a DHCP server.

5. The 128 bits of IPv6 are arranged in 8 quartets of 4 hexadecimal digit separated by a colon (:).

Not case sensitive for A,B,C,D,E and F

Leading zeros in any quartet can be omitted.

Methods from Migration from IPv4 to IPv6

Dual Stack method-

This will allow both IPv4 and IPv6 to co exist and gradual transition of IPv4 to IPv6 can happen.

Tunneling-

It allows IPv6 hosts to communicate over IPV4 infrastructure.

Transmission loss Per KM on 4/6  Quad Cable for BPAC/ SSDAC/ MSDAC application - 1.2 dB.

Sound power and Ambient Noise Level-

In waiting room - Sound level should be higher than 5 dB.

Railway platform- Sound level should be higher than 10 dB

Closed Auditorium- 5 to 10 dB

Loco sheds,outdoor stadium- 12 to 15 dB.

Telecom Radio towers

Painted at 5 years intervals 

Orange and white,orange at top

Inspection of Control Office and test room-

Monthly by DSTE/ADSTE.

FRMC - LTE technology .

Exchange-

IP Exchange shall be worked on 230 V AC/48 V DC.

For provision of 230 V AC, 2 sets of UPS along with 2 sets of batteries of Adequate capacity shall be provided at each location.

For provision of 48V DC,2 sets of Telecom chargers along with 2 sets of batteries shall be provided to ensure 12 hours of back up at each location. 

Inspection by DSTE/ADSTE

Exchange- yearly 

Control Office- monthly 

Outdoor OFC/ quad/ EC sockets- Inspection of 100% in a year.

Indoor OFC/Quad - All station in a year.

No of 5W VHF Walkie Talkie sets in ART =30

Ec socket -once in year painting.

EC socket pin 1 and 6 used for trans signal.

CCEO ( Control Communication for OFC)

Works on -48 volts

Components of CCEO-

1. CRE - Control Room equipment 

2 . LTE - Local Telephone Equipment- provides 20 local telephones at hq.

3. MTWE - Multi telephone way station equipment- provided at every way side stations.  Connected to VF channel from PD mux on OFc system. It can connect maximum 4 control telephones.

4. TWA - Three Way Amplifier- Used when maximum no of telephones required is more than 4.

5. TDCT - Two wire dialing control telephone 

Standard telephone instrument with a handset and numeric dial.

Each TDCT is connected to MTWE with a twisted pair having loop resistance less than  1200 ohms. 

6. RPE- Remote patching Equipment 

Provide patching between two 4 wire VF control Circuits available on OFC system.

MOV - Arrangement done in telephone instrument to arrest the high voltage like lightening on the line.

4m - Distance between any two earths.

No of UTS locations per area shall not exceed 70.

Average range of Walkie talkie - 1 to 2 kms.

Data bandwidth of out route and in route of IR VSAT Network- 12Mbps and 7.4 Mbps.

As per telecom manual cable distant from 

OHE mast -

If depth limited to 0.5m without concrete pipe, distance 1 m.

If depth limited to 0.5m with concrete pipe, distance 0.5 m.

If depth exceed 0.5 m, distance 3 m.

Traction Sub Station -

1 m from nearest metalic part and 1 m from Earthing. Concrete pipe of enclosed bricks for 300 m.

UTS developed through Sybase, C++ and Unix.

UTS - Network Architecture is 4 tire. 

Frequency alloted by WPC to Indian Railway is 146.2 - 167.95 Mhz

VHF -

Line of sight,Reflection, Scattering.

Type of operation : Half Duplex ( for present Railway operations)

Equipment- Walkie-talkie set,Base radio

Antenna- Whip, Ground Plane 

Feeder cable- 50 Ohms Unbalanced Coaxial cable 

Mobile Station 

The Mobile station represents the terminal equipment used by cellular subscriber by GSM system.

Mobile system has two entities.

Mobile Equipment (ME)

Subscriber Identify Module ( SIM)

Functions of SIM card-

User authentication 

Storage of subscriber related information. 

Base Station Subsystem ( BSS)

BSS has two entities.

1. Base Transceiver Station( BTS)

2. Base Station Controller ( BSC)

BTS- It facilitates wireless communication between User equipment( mobile)  and network.

Antenna is also part of BTS.

It serves as Accesss point for Mobile devices to connect to network.

Transmit and receive radio signals to and from mobile devices.

Each BTS has a defined coverage area called Cell.

Size of cell depends upon various factors.

BTS generates carrier frequency for voice and data transmission.It modulates these carriers with the information from mobile devices,creating radio signals that can be received by mobile stations. These signals are then transmitted over air to mobile devices.

At reception end BTS demodulates these signals to extract transmitted voice/ data content.

Signal will reach from mobile to BTS , then BTS to BSC.

BSC-

Controls Call hand over between BTS stations under its jurdiction.

Manages multiple BTSs within a given area.

Monitors and controls BTS Hardware.

It ensures efficient use of radio frequency spectrum by allocating and releasing radio channels to mobile devices.

Connection to MSC for calls.

BSC provides authentication and encryption services to ensure security of communication between Mobile and network.

BSC records call details such as call duration,called number and other information for billing and accounting purposes.

MSC-

Gateway for all mobile communications 

Overseeing both inter BSC and Inter MSC handovers.

Network and Switching Subsystem ( NSS)

Manage communication between Mobile station and other users of the cellular network.

Home Location Register ( HLR)-

Subscriber relevant data are kept in database called Home Location Register ( HLR)

GSM radio spectrum-

Three main frequency bands 

GSM -900,GSM-1800,GSM -1900

IMEI ( International Mobile subscriber equipment identity)

Each mobile Equipment has IMEI number for its authentication and identification.

IMEI is 15 digit number.

EIREN - European Integrated Railway Enhanced Network 

GSM (R) is communication standard choosen by EIREN to meet the Railway requirements.

Enhanced Multilevel Precedence and Preemption ( eMLPP)

1. A telecom feature that provides prioritized Call handling in mobile and fixed network.

2. Often used in emergency Communication system to ensure high priority calls are connected even during network congestion.

3. Assigns priority level to each call based on its importance.

4. High priority calls are given preference.

5. Allows high priority calls to interrupt lower priority calls if network resources are scare.( Preemption)

6. Used in emergency services ( police,fire,medical).

PCM TDM -

PCM is a technique used to represent analog  signal into digital.

In practice many PCM signals representing different messages and transmitting them over same channel using TDM ( Time division multiplexing).

With PCM TDM system,two or more voice channels sampled,converted to PCM codes and then time division multiplied into onto a single metallic or optical fibre cable.

HDB3 Line Encoding used in PCM TDM-

It does not have any DC components in encoded signal.

It doesn't increase or decrease data rate.

Suitable for high data rate transmission over long distances 

It has the built in error detection facility.

LTE standard-

Developed by 3GPP ( 3rd Generation Partnership Project)

MAC address-6 bytes( 48 bits)

Spectrum alloted to IR for LTE - 5MHz of Spectrum in 700 MHz band.

Evolved packet core ( EPC) is core network of LTE.

Root Bridge-

Switch which has lowest bridge ID in Spanning tree process is Root Bridge.It is first Bridge elected in spanning tree process.

LTE downlink multiplexing - OFDM (Orthogonal Frequency Division Multiplexing).

2 G Technology 

Data speed - 64 kbps

Uses digital signal in place of Analog 

Bandwidth 30-200 khz

Enables services such as SMS and MMS.

Provides better voice calls

Technology- GSM

Internet - Narrow band

3 G Technology 

Data speed- 2 Mbps

Bandwidth 15-20  Mhz

Used for GPS and video calls 

Technology- WCDMA

Internet - Broad band

Mobile Communication

Very low frequency ( VLF) - 3 to 30 khz.

Low frequency- 30 to 300 khz

High frequency- 3 to 30 Mhz 

Vhf - 30 to 300 Mhz 

Uhf- 300 Mhz to 3 Ghz

LTE -

For downlink - OFDMA ( orthogonal frequency division Multiple Access)

and for uplink SC FDMA ( Single Carrier Frequency Division Multiple Access )is used which is also known as DFT ( Discrete Fourier Transform) spread over OFDMA.

LTE support both Time division duplex technology ( TDD) as well as Frequency Division duplex ( FDD).

Dia up Connection -

Internet is connected through telephone lines using PSTN ( public switched telephone Network).

It uses a Dial up modem to change from digital to analog audio to transmit on telephone lines. Dial up Modem is Asynchronous.

Data transfer rate is 56 kbps in Dial up connection.

Less expensive and easy to set up.

Slow data rate, less reliable.

Could not make or receive calls while using internet.Outdated technology. 

UHF - Frequencies in UHF rmeans propogates by means of Space wave.

90 kbps - Minimum bandwidth for good Voip call signal quality.

Internal backbone of GPRS network- IP based network 

Data Communication & Networking 

Data Components -

A data communication system has five components.

1.  Receiver 

2. Sender

3. Message 

4. Transmission media- Path by which message travels. Ex Twisted pair wires, Coaxial cable,fibre optic cable and radio waves

5. Protocol 

Protocol is set of rules used by computers to communicate with each other across network. 

Protocols can be classified as

Proprietary Protocol ( specific make)

Open source Protocol ( Any make).

Bandwidth- 

It is defined as amount of data that can be transmitted into a fixed amount of time.

Usually expressed in bps ( bits per  second)

Fundamental Characteristics of Data Communication 

1. Delivery- System must deliver data to correct destination 

2. Accuracy- System must deliver data accurately 

3. Timeliness- System must deliver data in a timely manner 

4. Jitter- Jitter refers to variation in packet arrival time. It is uneven delay in the delivery of audio and video packets,which results in degradation of the quality.Hence Jitter is to be minimized.

5. Data flow- Communication between two devices can be unidirectional,half duplex or full duplex.

Simplex- 

Only one of Two devices can transmit,the other can receive only. Key board and traditional monitor are examples of Simplex.  Keyboards can only  introduce digital input and monitor can accept output.

Simplex mode can use entire channel capacity to send data in one direction.

Half duplex- 

Both devices can transmit and receive but not at same time. Entire channel capacity is taken over by whichever of the two devices is transmitting at a time. Ex. Walkie Talkie

Full Duplex- 

Also called Duplex.  Both can transmit and receive simultaneously.Channel capacity is shared between two devices.

Ex. - Telephone network 

Data Transmission-

There are two types

Parallel and Series

In parallel mode multiple bits are sent with each clock tick. In serial mode ,1 bit is send with each clock tip.

Parallel- 

1) Fast Transfer Rates

2) Used for short Distance only

3) Multiple bits are sent.

Serial-

1) Slow transfer rate

2) Used for long distance  

3) Single bit is sent

Serial Communication has two sub classes 

1. Asynchronous                          2. Synchronus 

Asynchronous Transmission:-

We send One start bit at  Beginning and one or more stop bit at end of each byte.Suitable for slow speed.Does not contain error detection information,and is susceptible to errors.

Additional bits are required be sent.So this method is inefficient mean of sending large data.

Synchronous Transmission:-

No start or stop bits or gaps. We send bits one after another.Greater efficiency. User data is prefixed with a header field and suffixed with a tailor field which includes a checksum value.

Network:-

Network is a set of devices ( often referred as nodes) connected by communication link. A node can be a computer, printer or other device capable of sending and receiving data generated by other nodes of network.

Main advantage of Network is sharing of resources.  Resources can be hardware or software.

Categories of network-

1. LAN

2. WAN

3. Intranet and Internet 

LAN :-

A group of computers and network communities devices interconnected within a geographically limited area,such as building or campus.

Transfer data at high rate ( higher bandwidth)

Can be in single building or in multiple buildings in a campus area.

WAN :-

WAN is collection of many seperate networks.

They exist in unlimited geographical area.

Interconnect multiple LANs.

Linkup of LANs is often shown as cloud.

Transfer data at lower speeds ( lower bandwidth)

Intranet:-

Multiple PCs are connected to each other.

These PCs are not available to world outside the intranet. 

Each organization has its own Intranet network and members/employees of that organization can access the computers in the intranet.

Each computer in intranet is identified by an unique  IP Address.

Internet:-

Internet is network of networks.It is worldwide collection of multiple computer networks.

Speed is very fast.

Accessible to every user in world.

Similarities between Intranet and Internet 

Intranet uses internet protocols such as TCP/IP and FTP.

In intranet, own instant messengers can be used as similar to Yahoo messenger/gtalk over internet.

Difference between Intranet and Internet 

Internet is not safe as intranet. Intranet can be safely privatized as per need.

Security in internet is low,configured under 0 security level in firewall. Security in Intranet is high, configured under 100 security levels in  firewall.

Internet is regulated by Internet Architecture Board ( IAB).Intranet is regulated by an organization.

Topology 

A network in which terminals are interconnected with each other for inter communication within and outside the network is called as Topology.

1. Mesh topology 

2. Star topology 

3. Bus topology 

4. Ring topology 

Mesh topology -

In Mesh topology every device has a dedicated point to point connectivity to every other device. Each device must has (n-1) I/O ports.

Eg . If 5 computers are to be connected in Mesh Topology,  each computer must have 4 input/output ports.

Each link can carry its own data load.

It has privacy or secrecy. Fault identification is easy.

It's disadvantages are large no of cables and I/O ports.

Star topology -

Each device has a dedicated point, which links to central controller only.This controller is called HUB  . All the devices are connected through HUB only. 

Generally used in LAN only.

Easy to install and reconfigure.

Each device needs only one link.Hence it is less expensive.

If a link fails,only that link to be attended.

Easy to identify fault.

Eathernet network typically found in star topology.

Bus topology -

Bus topology is multipoint 

One long cable acts as backbone to link all devices in a network.

Installation is easy.

Generally used in LAN network.

Disadvantages- Difficult in fault isolation and reconnection.  Difficult to add device in an existing system.A fault or break in bus cable stop all transmission.

Ring Topology :-

Each has a dedicated point to point connection only with two devices on either side of it.Data is passed along the ring in one direction, from device to device until it reaches its destination.Each device acts as repeater.

Generally used in LAN.

Easy to install and configure.

Unidirectional traffic and a break in the ring can disable entire network.

Standard Organisations :-

ISO ( International Organization for Standards)

Non Government Organization

Based in Geneva

Maintain standard for Quality assurance.

Most significant activities are its work on open System, which define Protocols.

ÌTUT ( International Telecommunication Unions)

Agency of United Nations

Sets standard for Modems and Switching network.

Co ordinates international communications and recommend standard interface.

ÀNSI ( American National Standard Institute)

Represents a number of US Standards organizations

Private Agency 

Sets up standard for FDDI and ASCEE.

OSI Model:-

Established in 1947,by ISO.

Purpose of OSI is to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software.

Seven layer framework that allows communication between all types of computer systems.

It is a theoretical model.Not a protocol,technology, program or software.

1) Physical Layer :-

It is responsible for transmission of digital data bits from physical layer of Sending device to physical layer of receiving device.

At physical layer,  data is transmitted using type of signaling supported by physical mediam : electric voltage,radio frequencies,or pulses of infrared or ordinary light.

Physical  layer provides the means to transmit the web page request to the default gateway.

Physical layer provides a physical mediam through which bits are transmitted.

2) Data link layer :-

After physical layer ,Data link layer

1) checks physical transmission error like CRC Checks.

2) Packages bits into data frames.This layer is responsible for moving frames from one node to next.

4) At data link layer, the web request is inserted inside a network request to the default gateway.

5) It is used for error free transfer of data frames.

Trqditional simple LAN and VLAN operate in Data link layer.Bridge works in Layer 2.

3) Network Layer :-

When data arrives at Network layer,source and destination addresses contained inside each frame are examined to determine if data has reached its final destination.

Formats data into packets delivered upto transport layer.

Network layer maintains logical addresses such as IP address for device on Network.

The network layer also manages mapping between logical address and physical address.

It is responsible for moving the packets from source to destination.

Router  and Layer 3 switch operates primarily on the network layer of OSI Model.

OSPF message is produced by Network layer.

Eg - IP( internet protocol)

Data units in networking are called packets.

Functions of network layer

1) Logical addressing 

2) Path determination ( Finding the correct path)

3) Routing 

4) Transport Layer:-

It delivers data across network connections.

It helps in error control.TCP and UDP are used.

TCP is most common example.TCP connection breaks up the web page  into manageable chunks,levels them numbers so they can be reassembled in correct order and transport the pieces.

It provides reliable message delivery from process to process.

Process to process delivery of the entire message is the responsibility of the Transport layer.

Transport layer does

Segmentation 

Flow control 

Error control

5) Session Layer :-

It helps in setting and managing connections. It manages sequence and flow of events.

It is built to support multiple types of connections that can be created dynamically and run over individual networks.

Session layer keeps track of a file that are downloaded.

Session layer helps in session management. 

6) Presentation Layer :-

It handles syntax  processing of message such as format conversations ( like ASCII to EBCDIC ) and encryption/descryption needed to support the application layer above it.

Sender side data is encrypted and receiver side data is decrypted.

Conversation of data from one form to another is the job of Presentation layer.

SSL ( secured socket layer) protocol is used in this process 

7) Application Layer :-

It supplies network services to end user's applications. Network services are protocols that work with user's data. 

Application layer provides the service to user.Mail services are available to network users through the application layer.

Application layer provides file transfer,web surfing Emails etc.

Eg. - Web browser  such as Internet Explorer or Netscape,HTTP,FTP,Telnet

Data and Signal -

Both data and signal can be Analog and Digital.

Baseband Transmission-

Data is sent as digital signal through media as single channel that uses entire bandwidth of the media.

Bi directional 

Broadband Transmission-

Sent in the form of Analog signal,which flows as electromagnetic waves or optical waves.

Each transmission is assigned to a portion of bandwidth.

Hence multiple transmissions are possible at the same time.

Unidirectional 

Frequency division multiplexing is possible.

Transmission Impairment -

Signal at Beginning of the medium is not same at the end of medium.What is sent is not what is received.Three causes of Impairment are Attenuation,Distortion and noise.

Attenuation -

It means loss of energy in overcoming the resistence of the medium.To compensate this loss,amplifiers are uses to amplify the Signal.

Signal loses strength due to different propogation speeds of each frequency that makes up the Signal.

The decibel ( DB) measures

i) Relative strength of two signals at a point.

ii) Relative strength of one  signals at two points

dB = 10 log P2/P1

If this value is negative- Signal is attenuated.

If this value is positive- Signal is Amplified.

Distortion -

Distortion means that signal changes its form and shape.

Noise -

Signal to noise ratio (SNR)-

SNR =  Signal Power/ Average Noise Power

In decibel

SNR ( In db) = 10 log SNR

High SNR means signal  less corrupted by noise.

Nyquist Bit Rate( noiseless channel)

For a noiseless channel,  the nyquist Bit Rate is the theoretical maximum bit rate is

Bit rate = 2× bandwidth of channel × log L base 2.

L is the number of signal levels used to represent data

Shannon capacity ( noisy channel)

The theoretical maximum bit rate of a noisy channel 

   Bit rate = Bandwidth of channel × log (1 + SNR)

Baud Rate-

Baud rate refers to signal ( symbol) rate,how many signal changes are transmitted per second.

Goal of data communication is to increase the data rate while decreasing signal rate.

Increase data rate -- Increase the speed of transmission

Decrease the Signal rate ----- decreases bandwidth requirement.

Bit rate ---- No of bits per second 

Baud rate ---- No of signal elements per second.

(Bit per Second)BPS = Baud per second × the no of bits per Baud.

Digital to Analog conversion -

There are three types of D to A conversion techniques

1. Amplitude Shift Keying(ASK)

2. Frequency Shift Keying(FSK)

3.  Phase Shift Keying(FSK)

Analog to Analog conversion -

1. Amplitude Modulation 

2. Frequency Modulation 

3. Phase Modulation 

Transmission Media-

Two basic categories 

a. Un guided transmission media

Wireless communication,  transports electromagnetic waves without using a physical conductor.

Three types

Radio waves - used in wireless LANs

Microwave- used for Terrestrial and satellite communication 

Infrared waves - used for controlling devices like remote control

b. Guided transmission media

Open wire

Coaxial wire

Optical Fibre

Twisted pair

Open wire - not used in data communication.

Coaxial cable - 

Thick net ( RG -8 and RG - 11)

Thin net ( RG -58)

Optical Fibre Cables 

High speed alternative to Copper wire

Uses glass or plastic filaments to move data.

Provides greater bandwidth.

Twisted Pair Cables

LAN cables are generally called twisted pair.

Two types-

UTP - Unshielded Twisted pair - Indoor areas

STP - Shielded Twisted pair - Outdoors Areas

Error Detection & Correction-

Data can be corrupted during transmission. Some applications required that errors to be detected and corrected. 

Single bit Error-

Only one bit of data changes during transmission.

Burst Error- 

Two or more bits of data have changed during transmission

To detect errors we need to send Extra( redundant) bits with data.

Popular methods of Error detection methods are Parity checking,Block coding, CRC( Cyclic Redundancy Check) and Checksum.

Checksum uses ones complement arithmetic.

Simple Parity Check - 

Basic error detection technique used to identify single error in data transmission.

It adds an extra bit, called an Parity bit to the data to ensure that total no of 1s or 0s in the data meets a specific condition.

Even Parity  - Ensures that total no of 1s in data is even.

Odd Parity - Ensures that total no of 1s in data is odd.

The party bit is calculated based on type of Parity.  Parity bit may be 0 or 1.The data and Parity bit are transmitted together. 

The receiver checks the data and Parity bit.If the Parity condition is not met, an error is detected.

This method is used for just one redundant bit per data unit.

Cyclic Redundancy Check (CRC)-

CRC is robust error detection method to ensure data integrity during transmission. 

It uses polynomial division to generate checksum,which is appended to data. Receiver uses same polynomial to verify data's integrity.

LAN Protocols-

For data transmissions on LAN, protocols are used to form frames. Basically there are two types of protocols are used.

There are two types of protocols 

● Character Oriented protocols 

● Bit Oriented protocols 

For the purpose of sending data on link, there are two types of stations.

■ Primary Station( Issue Commands)

■ Secondary Station ( Responds to commands)

NIC ( Network interface Card)-

Computer hardware component that connects a computer to a network.

Located on motherboard.

It provides physical connection between networking cable and computer internal bus. NIC comes in three basic varieties,8 bit,16 bit and 32 bit. 

MAC address is burnt on ROM part of NIC.

Two types of NICs.

Wired and wireless. 

MAC - Media Access Control

MC is unique identifier assigned to a network interface card.

■  The IEEE 802.3 MAC is Physically located in the ROM of the Network Interface Card.

■ Link between Data link layer and physical layer.

Most popular IEEE 802.3 MAC Protocol is Ethernet Protocol.

Ethernet -

It is a protocol in TCP/IP stack,describing how networked device can format data for transmission to other network segments and how to put tht data on Network connection.

Eathernet technology suffers from Broadcast/ collision 

 IEEE 802.3  is standard of Eathernet.

Eathernet provides Network using CSMA/CD

Eathernet LAN can support data rates  1 to 100 Mbps.

Cables used for Eathernet for LAN are generally called twisted pair cables. There are of two types UTP and STP.

UTP for indoor areas 

STP for outdoor and special areas.

Maximum distance supported by UTP/STP - 100 m

PoE ( Power over Eathernet)

It allows a single cable to provide data connection and electrical power to the devices.

This technology is applicable for network products such as Accesss points, Routers, Modems ,switches,etc.

Power over Eathernet is defined by Standard IEEE 802.3 af/ 15.4 W.

IEEE 802.3 is standard of Eathernet.

IEEE 802.11 is standard of wifi or wireless LAN.

IEEE 802.15 is standard of Bluetooth.

Networking Devices-

(HUBs, Switches, Routers  & Gateways)

Repeater -

It is an electronics device that receives a signal and retransmits it.Its job is to regenerate the signal over the same network before signal becomes two weak or corrupted.

Hubs -

It is a multiport repeater.

Connects multiple wires coming from different branches.

HUBs come in three types.

Passive 

Active

Switching.

HUBs are used in star Technology.

Bridge-

It connects two LANs working on same network protocols so that they can exchange data.

Switches-

Switch is multiport bridge. The switch can perform error checking before forwarding data . It forwards good packets selectively to correct port.

Computer networking device that connects network segments.

Switches may operate at one or more OSI layers,including physical, data link,network or transport.

A device that operates simultaneously at more than of these layers is called multilayer switch.

Switches provide many facilities not offered by old devices such as HUBS and Bridges.

Router -

Router is networking device that forwards data packets between computer networks.

Gateway - 

It acts as an entrance between two different networks. Gateway device is used to connect two different networks.

Gateway in organization is the computer that routes traffic from a work stn to outside network that is sending web pages.

It is passage to connect two networks together that may work upon differernt networking models.

VLAN ( Virtual LAN)-

VLAN has same attributes as a physical LAN,but it allows for end stations to grouped together even if they they are not located on same network switch.

Network configuration can be done through software instead of physically relocating them.

VLAN is also called wimax.

VLAN 0 and  VLAN 1 -

VLAN 0 and VLAN 1 are two different networks on Eathernet network.

VLAN 0 is often used for  management and traffic.Access to VLAN 0 is usually restricted for security reasons.VLAN ID  is 0.

VLAN 1 is standard VLAN with a VLAN ID 1. Default VLAN for new connections.

WAN- 

WAN can be intranet or internet otherwise called Private or public network.

Majority of applications use TCP( transmission control protocol) and Internet Protocol ( IP) together.

WAN is established with the help of Routers & long distance communication links and suitable for Network layer protocol ( Ex . IP)

Data units are packets.

Packets are routed through networks with help of IP routing,static and Dynamic.

IEEE standard of WAN is 802.11

TCP-

Responsible for end to end delivery of segments. Segments are terms that is used to describe the data that is transmitted and received at transport layer of OSI model where TCP resides.

User Datagram protocol ( UDP)-

1) Unreliable and contactless.Uses random path in network channel.

2) Operate at  transport layer of the OSI model for providing internet service.

3) No acknowledgement is received.

Major uses of this protocol are DNS and TFTP.

Session Initiation Protocol ( SIP) -

1) A protocol used for initiating ,maintaining and terminating communication session that include voice,video and message.

2) A set of rules that allows users

to make and manage voice,video and messaging calls over the internet.

3) Used in internet telephony,mobile calling over LTE ( VoLTE).

4) Protocol of Application layer.

Internet Protocol (IP)

A piece of software that operates at Network Layer and provides the following.

Unique Addresses

Connectionless communication 

Routing 

Data Transmission on IP

There are three types of data transmission on Internet Protocol.

1) Unicast - Communication from single host to another single host.

2) Broadcast - Single device transmitting a message to all other devices in a given address range.

3) Multicast- Single device to communicate with specific sets of hosts.

IP Addresses-

Computer gets its address one of Two wayes. Either the computer administrator enters it into computer manually(Static  IP address) or it is learned by computer dynamically using a protocol called DHCP ( Dynamic IP).

DHCP( Dynamic host Configuration Protocol)

Network management Protocol used to automate the process of assigning IP address and other network configuration details on a network.

Information provided by DHCP are-

IP address

Subnet mask

Default gateway 

DNS service. 

 

IP address are of two types

IPv4 ( IP version 4) and IPv6 ( IP Version 6)

IPv4 Address 

An IP Address is a number used to identify the logical connection of computer to a physical network.

IPv4 is 32 bit binary address ( Composed by four,8 bit binary numbers).

IP address is represented as four decimal numbers ( between 0 and 255) seperated by dots.It is called dotted decimal notation.Eg. 199.232.66.20

These addresses are always unique and software configured.

It is easy to move hosts from one network to another simply by changing the IP address or the Network Mask. This process is called Renumbering.

Network and Host Portion of an IP Address-

Left most portion of address- Which network the machine (Host) belongs to.

Right most portion - Address of Host itself. 

Eg IP address- 199.233.66.20 then 

Network Address- 199.233.61

Host Address - 20

All the computers on same local network - Same network number in their address. Host Portion will be different and unique for each host on the network.

Classes of IP Address -

IP Addresses are divided into classes : A,B,C,D and E.

Classful-

First addressing scheme developed. Wasted a lot of address space so new scheme was developed called CLASSLESS.

Source Address- IP address of HOST sent on DATAGRAM.

Destination Address- IP address of host

Mask - 

Mask is a value that is stored in the configuration of a computer along with IP address. 

Mask gives the computer a simple way to figure out whether the IP address of another computer is on same local network or on a different local network.

 Subnet Mask-

A subnet mask is a 32 bit number used in networking to divide an IP address into network and its host Portion.It is primarily used to determine which part of an IP Address represents the network and which part represents the devices( host) within the network.

Written in dotted decimal notation,similar to an IP Address.(e.g 255.255.255.0)

Each octet ( 8 bits) can range from 0 to 255.

Subnet mask ANDed with IP address gives the Network address.

E.g.

IP Address: 192.168.1.10

Subnet mask: 255.255.255.0 (Default)

Default address point of  access point : 192.168.1.1 and 192.168.0.1

Classes of IP Addresses -

The entire IP address is between-  0.0.0.0 to 255.255.255.255

The different classes of IP Addresses are Class A, Class B,Class C,Class D & Class E. Example

Class A - 0.0.0.0 to 127.255.255.255 , subnet - 255.0.0.0

Class B - 128.0.0.0 to 191.255.255.255,subnet - 255.255.0.0

Class C - 192.0.0.0 to 223.255.255.255,Subnet - 255.255.255.0

Class D - 224.0.0.0 to 239.255.255.255

Class E - 224.0.0.0 to 255.255.255.255

Class A B and C used for Host purpose.

Class A - 

No of networks 256, No of hosts 16777214.Railnet  uses Class A

Class B - 

No of networks 65536, No of hosts 65536

Class C -

No of networks 16777216, No of hosts 256

Subnetting- 

Subnetting is process used in networking to divide a large network into smaller manageable sub networks.

This is done to improve the efficiency of IP address allocation,enhance network performance and improve security. 

Subnet mask determines how the IP address is divided into Network and host Portion.

For Eg. in IPv4,the subnet mask 255.255.255.0 means the first 24 bits are for the network ,  and remaining 8 bits are for hosts.

Purpose of Subnetting-

Reduces waste of IP address by allocating only necessary number of IPs for each subnet.

Limits the size of Broadcast domains,reducing network congestion.

Super netting-

Process of combining multiple smaller networks into a larger network.

Reverse of Subnetting.

IP Routing-

IP Routing is the process of moving data packets from one network to another based on their destination addresses.

It involves determining best path for data to travel across interconnected networks using Routers.

Static Routing - non adapting routing 

Routers are manually configured by the network administrator.

Used in small or simple networks where topology does not change frequently.

Default Routing Protocol -

When destination address is unknown to router, router uses default Route and sends data packets to single hop device, regardless of network.

Dynamic Routing-

Adapting routing 

Routers automatically discover and maintain routes in network using Routing Protocols.

It adapts changes in Network Topology,such as link failures or new routes without manual intervention.

Routing Protocols are of two types. Intra domain and Inter domain.

Intra domain(Interior Gateway Protocol) has three types.

1) Distance Vector, e.g. RIP, IGRP - calculate the best path based on number of hops.

2) Link State e.g. OSPF,IS-IS - Use complex algorithm to calculate the shortest path to a destination.

3) Hybrid Routing Protocol - EIGRP.

RIP - Routing information Protocol 

1) RIP is Intra domain Distance Vector Protocol based on hop count matrix.

2) The maximum hop count allowed for RIP is 15.

IGRP - Interior Gateway Routing Protocol 

1) IRGP Protocol is Cisco proprietary protocol.

2) Distance Vector Routing protocol.

3) It supports max 100 hops. 100 Routers can be connected.

4) Products data security and data reliability.

5)  Classful Routing protocol 

6) consumes more bandwidth than EIGRP.

7) Supports only IP Routing.

OSPF - Open Shortest Path First

1) Routing Protocol

2) Standard protocol- works with any company router.

3) Link State Protocol 

4) Unlimited hop count ( Unlimited Routers can be connected)

5) Classless routing protocol

6) Used in UTS Network 

IS-IS - Intermediate System to Intermediate System

Another link state protocol that operates similarly to OSPF.

EIGRP - Enhanced Interior Gateway Routing protocol 

1) Hybrid Routing protocol 

2) It has both characteristics,distance Vector and link state

3) Cisco proprietary protocol

4) Successor of IGRP

5) Classless Routing protocol 

Exterior ( Inter domain)-

BGP ( Border gateway Protocol)

Router-

Router is specialized computer connected to more than one network. Router receive data packets from one network, read their destination IP address and forward them to appropriate next address.

Uses Routing Protocols like RIP,OSPF or BGP is used.

Router operates at layer 3 ( Network layer) of OSI model.

Gateway -

Gateway is a device that acts as a gate between two different networks.

It is used to connect networks that use different network protocols ensuring that data can flow smoothly between them.

Gateway operates at layer 4 of OSI Model.

Network Address Translation-

A technique used in networking to modify the source or destination IP Address of packets as they pass through a router or firewall.

Very important aspect of firewall security.It conserves the number of public addresses used within an organization. 

MPLS( Multi Protocol Label Switching)-

It is a a networking technology used to improve the speed,efficiency and management of network traffic.

Key features-

Label Switching: Instead of solely relying on IP address for Routing, MPLS assigns short path labels to packets,enabling faster and most efficient forwarding.

In MPLS data packets are assigned labels.

Designs to work in large complex networks.

Works with various network protocols, Eg. IPv4,IPv6, Eathernet. 

Commonly used to create VPN for secure communication.

MPLS header - 32 bits

Comparison of MPLS versus IP-

MPLS uses labels for forwarding packets,bypassing traditional Routing while IP Routing uses IP Addresses for packet forwarding.

Speed in MPLS is faster than IP Routing. 

MPLS is ideal for large scale network which needs high performance while IP Routing is simpler and more cost effective.

VPN ( Virtual Private Network)-

It extends a private network across public network and enable users to send and receive data across shared or public network.

VPN allows users to securely access a private network and share data remotely through public network.

VPN protects your data on line.

It uses two security protocols.

PPTP - point to point tunneling protocol

L2TP

Modem -

A hardware device that enables computers or other devices to connect to the internet by converting digital data into signals that can be transmitted over telephone lines,cable systems etc.

LAN extender-

A device or technology used to expand LAN beyond its Normal physical or geographical limitations. It enables users to connect to LAN over greater distances than would be possible with standard Eathernet or wireless connections.

Use fibre optics,DSL ( Digital Subscriber line) or wireless connections.

Media Converter-

Media converter is a networking device used to connect two different type of media or transmission technologies.such as copper ( Ethernet) and fibre optics within a LAN.

WLAN -( Wireless Local Area Network)

Uses wireless communication to connect devices within a limited area such as Home,office or school.

Devices connect using Radio waves instead of Physical cables.

Wi fi ( Wireless fidelity) belongs to WLAN.

Access points are specially configured nodes on WLAN.  They act as central transmission and receiver of WLAN radio signals.Access points support Wi Fi wireless communication standards.

IEEE standard of WLAN is 802.11

Bandwidth available in 802.11a WLAN is 54 Mbps.

Access protocol for WLAN is CSMA/CA.

RF band used in WLAN is 2.4 GHz.

WAP ( Wireless Access Point)-

Hardware device that allows Wi Fi devices to  to a wired device.

Acts as bridge between wired  and wireless devices,providing connectivity

IPv6 Address-

Latest version of Internet Protocol. 

Developed by Internet Engineering Task Force (IETF)

Most recent version of Internet Protocol.

IPv6 addresse is represented by 8 groups of 16 bit value.(128 bit addresses).

IPv6 addresses are represented by Colon Hex notation.

Leading zeros in the Quartet are omitted to simplify the representation of the address.

Consucative sections of zeros are omitted using Double colon (::) 

Provides better support for Mobile devices.

Uses hexadecimal numbers in address format while IPv4 uses Decimal numbers.

IPv6 Address Classification 

IPv6 Address are classified as Unicast Addressing,  Anycast addressing and Multicast addressing.

Dual Stack Deployment -

Strategy used to enable the co existence of IPv4 and IPv6. It allows devices and applications to communicate using both IPv4 and IPv6 protocols,ensuring a smooth transition to IPv6 while maintaining compatability  with IPv4 systems.

Tunneling Approaches -

Techniques used to facilitate communication between IPv4 and IPv6 networks during transition to IPv6.

Manual Tunnneling -

Network administrator manually configure tunnel between specific IPv4 and IPv6 end points.

Automatic Tunnneling-

Tunnels are dynamically created as needed without requiring manual configuration of each end point.

QOS( Quality of Service)-

Ability of network to provide better service to selected traffic over various technologies.It is essential for applications requiring consistent and reliable performance, such as video streaming,  VoIP, online gaming etc.

Bluetooth-

Bluetooth is open wireless protocol designed for short range data exchange between devices.

Operates at 2.4 GHz ISM

Typical range - 10 m

Quick sharing of files between devices.

Data transfer speed is slower compare to Wi Fi.

Radio over IP- 

Radio over internet protocol is a method of transmitting and receiving radio communications via Internet Protocol.

RoIP is similar to  VoIP. It uses standard VoIP techniques to transfer analog audio.

This provides a method of linking two or more radios.

Connectors & Interfaces 

EIA RS 232- C- Standard 

This standard is used to connect serial devices like Modem to Personal Computer.

25 pin connector

V.35 Interface -

Standard for Synchronus data transmission.

Commonly used in WAN.

High speed Synchronus data transmission.

34 pin rectangular connector.

Speed is upto 2 Mbps.

Used in past. Have been phased out in favor of Eathernet based solution due to advancement in technology.

E1 Interface-

Digital transmission format for transmitting voice and data.

Data rate of E1 is 2.048 Mbps.

Transmission medium is Coaxial, twisted pair or optical fibre.

BNC connector is used for Coaxial cable

RJ 45 connctor  for twisted pair. 

Being replaced by Broadband and IP based technology.

Data Communication Equipment ( DCE) 

Device or hardware that establish a connection between Data source and its destination.

Fitted with 25 pin female connector. 

Examples are Modems,Network switches and Multiplexers

Data Communication Equipment ( DTE) 

Device or equipment that serves as source or destination data in a communication system.

Originate or terminate data communication.

Interfaces with DCE to transmit or receive data over a network.

Example- Computer, printer etc

RJ 45 Connector-

Standard type of physical connector commonly used  for Eathernet networking.

8 pin connector designed to connect computers,Modems,Routers and other networking devices Via Ethernet cables.

HDMI ( High Definition Multimedia Interface) -

A standard for transmitting uncompressed video and audio data between devices.

Widely used for connecting audio visual equipment such as TV, monitor etc.

Supports High definition video resolutions

Combines audio and video transmission in a single cable.

19 pin connector is used.

HDMI cable is composed of four Shielded Twisted pair.

Syntax - 

Syntax refers to the structure or format of the data,meaning the order in which they are presented.

Header and trailer - 

Header and trailer added to data during network communications.

Header-

Header is added to the beginning of data by sending device.It contains control information such as-

Source Address 

Destination Address 

Protocol Information

Sequence number 

Error checking 

As data packets move from uppar to lower layers, Headers are added.

Trailer-

Trailer is added at end of the data by sending device.It contains following information 

Error checking code ( e.g. CRC)

Purpose of Header and trailer 

Ensure proper delivery

Data integrity 

Flow control and segmentation 

HDLC - High level data link Control

Dial up Modems are Asynchronous.

DSLAM- Digital subscriber line access multiplexer 

ADSL - Asymmetric digital subscriber line 

Link Local Address- 

It is a type of IP address that is automatically assigned to network interface for communication within single link or segment. It is used for local communication when there is no external router or DHCP server.

MAC address -

An identifier that every network device uses to identify itself on computer.No two devices will have same MAC address.

6 byte ( 48 bits)  number or 12 digit hexadecimal number.

First 6 hexadecimal will represent manufacturer,the next 6 digit hexadecimal represents NIC.

It is called physical or hardware address.

Used when two network devices communicate with each other.

IP address can be changed but MAC address can not be changed , it is decided by manufacturer.

IP address is used to find final destination while MAC address is used at each step on its way to final destination.

Switches have one MAC Address for each port.Switch controls flow of datadata using MAC address. 

Collision Domain-

It is a part of network where data packets can collide with each other.Collission can slow down network.Collission network is bound by Switches.

HUBs are Half duplex.Switch are better than hub.

Broadcast domain-

It is bound by Switches.

VTP - VLAN trunking protocol.

TCP Three way Handshake - there are three steps of Handshake 

Step 1. Client sends SYN( Synchronus) packets to the Server. This packet includes a sequence number that the Client chooses.

Step 2. Server sends SYN- ACK ( Synchronize- Acknowledge) packet  to the Client.This packets includes the server's sequence number and acknowledge client's sequence number.

Step 3. The client sends an ACK ( Acknowledge) packet  to Server.

Data Transmission on Internet Protocol-

Unicast -

Data Transmission from single host to another single host. There is one device transmitting a message to another receiver.

Broadcast-

Single device transmitting a message to all other devices in a given data range.

Broadcast represents one to many valid Eathernet transmissions.

Multicast-

Single device communicates with specific sets of hosts,not defined by any standard IP address and mask combination.

The speaker 's message is not broadcasted everywhere.

In TCP/IP max data packets length is 65535 bytes.

Collision Domain-

It is a network segment where data packets can collide with each other when being sent over a shared communication medium.

Collision can occur when data simultaneously on the same network segments.

Each port on a switch is a separate collision Domain,reducing network congestion.

Collision Domain is restricted by Switches.

ICMP ( Internet Control Message Protocol)

Network layer protocol used for sending error messages and operational information about network communications.

IP Routing-

Routing is the process of moving data from one network to another by forwarding packets via gateway.

With IP based networks,the Routing decision is based on the destination address in the IP packet header.

Routing is of two types

Static and Dynamic 

Static Routing -

Manual method used to set up Routing.

Administrator enters routes into the router using configuration commands.

This method is predictable and simple to set up.

Easy to manage small networks.

Does not scale well in large networks.

Dynamic Routing ( Using protocol)

Interior ( Intra Domain)

OSPF

IS -IS

IGRP

EIGRP 

Exterior ( Inter domain)

BGP

Default Administrative Distance (DAD) -

Value assigned to Routing protocol to determine the trustworthiness of a route.

Lower value indicates higher performance.

Default Administrative Distance of Static Route is 1

Routing Protocol-

Routing protocol is a set of rules used by by Routers to determine best path for forwarding data packets in a network.

Types of Routing Protocols 

1. Distance Vector Routing protocol 

Routes are selected based on hop count I.e. number of route between source and distance 

2. Link State Routing protocol 

Uses short path algorithm 

3. Hybrid Routing protocol 

Combine both distance Vector and link state

4. Path Vector Protocols

Used in large scale network like internet.

Primary Multipltiplexing equipment

1) Terminal MUX

It shall have one 2048 kbps port each for trans and receive side and shall be used as end multiplexer.

2) Primary drop/ insert mux -

This shall have two 2048 kbps ports ( P1 and P2) each for send and receive side.

3) Drop/ insert mux with Conference facility-

Similar to drop insert MUX above with additional facility of at least 3 party conference between any combination of time slots of either P1 port or P2 port and voice interface.

Port number -

Port number is a address used to identify Specific TCP/IP application.

Multiplexing-

Multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. 

It is of two types 

Analog and Digital 

FDM is Analog while TDM is digital multiplexing. 

Two types of mediums

Wired medium ( Guided Medium)

Wireless medium ( EM waves)

Wired Medium 

Three types.

Twisted pair - Slow (electrical Signal)

Coaxial cable- Fast (electrical Signal)

Fibre optic- Very fast ( light signal)

Eathernet not a network protocol 

ADSL - QAM +FDM

Modem pair for WAN - Synchronus  V.35 + G.703

Layer 3 ( L 3) switch has Eathernet ports only.  Layer 3 switch are designed for high speed forwarding within LAN.

Layer3 is often called multilayer switch.

Eathernet operates using star topology.

Default Routing -

Mask and destination address are both 0.0.0.0 in Routing table 

Piggy backing-

When data and acknowledgement are sent on the same frame.

Piggybacking is technique of delaying outgoing acknowledgement temporarily and attach it to next data packet.

Round trip time for smooth working between Client terminal and server - 130 - 150 msec.

In LTE- Radio modem works on 24 v.

WPA ( Wi Fi protected area)-

Encryption bit - 128 bit. 

WAP ( Wireless application protocol)

Uses wireless communication technologies such as GSM,4G,GPRS etc.

Flow control is needed to prevent overflow of receiver buffer.

Basics of Telecom

Mobile Communication 

Emergency Communication 

Emergency Communication is provided by following means

a) Emergency Socket

b) 5/25 Watt VHF sets

c) GSM - R ( very less percentile)

d) Mobile phones available with driver, guard and staff.

Emergency Socket- PT Set telephone is provided in Emergency Socket.

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 

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,Reflection and scattering.  

Type of operation - Half Duplex

Channel Capacity - upto 16 channels

Type of equipment:- 

i) Walkie Talkie set

ii) Base radio

Antenna used- Whip Antenna for portable sets, Ground Plane ( GP) for base radio equipment. 

Polarization in Gp Antenna- Vertical 

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 25 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.

25 W VHF set works on 12  Volt DC

EC sockets - 06 pin holes in line, impedance ratio of EC socket is 470:1120

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

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.

Mobile Service Switching Centre

The  switching between networks is controlled by the Mobile Service Switching Centre

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-

PDH stands for plesiochronus digital Hierarchy.

Used to transmit voice conversations.

Use Time division multiplexing.

Uses bit interleaving method

Has 3 standards ( European, American, Japanese)

It has 4 type of frames. E1,E2,E3 and E4.

E1 - 2 Mbps

E2 - 8 Mbps

E3 - 34 Mbps

E4 - 140 Mbps

Use coaxial cable or twisted pair copper wire.

SDH -

stands for Synchronus digital Hierarchy.

Used to transmit voice and data over Optical Fibre. 

It is a group of fibre optics transmission rates 

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.

SDH uses time division multiplexing.

SDH has two standards ( European and American)

European frame is called STM.

American frame is SONET.

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.

E2 is not supported in SDH multiplexing 

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 

Frame structures of SDH-

B2 bytes - used for Bit interleaved Parity.

K1 and K2-  Automatic protection Switching 

D4 - D12  Data Communication channel 

M1 -remote error indication

S1 - synchronization status byte

Z1 and Z2 - spare bytes.

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.

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.

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-

Private network used all the employees of a single organization.Used in telephone directories and many more.Highly secured in nature.Configured in the firewall under 100 security level.A single organization owns it.

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

1) BRI- Basic Rate Interface ( used for Home,Residential and small office)

2) PRI - Primary Rate Interface ( Used for large business)

BRI-

lower tier of service. It only provides basic needs at lower cost

02 Bearer  channel ( User information or Data information)

01 Data  channel ( Signalling information)

01 OH channel ( Supervisory and alarm monitoring)

 B or Bearer channel Operates at 64 Kbps,

 D or Data Channel operates at 16 kbps 

OH operates at  48 Kbps. 

2B+1 D+1 OH = 2*64 + 1*16+ 1*48 = 192 Kbps

BRI Speed - 192 Kbps

BRI Total bandwidth - 144 Kbps

PRI-

PRI is main service. It provides a better connection,more reliable service and faster speeds.PRI cards are used in telephone exchanges.

Bearer channel- 23

Data channel - 1

Both B and D channel operate at 64  kbps.

30 B + 1 D + 1 OH = 2048 Kbps.

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

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 in Block section and 20 m distance in Station Section.

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.

PD muxes are in star topology.

ART frequency - 147.975 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- Used in Analog based CCTV Surveillance system but not used in IP based CCTV Surveillance system.  It can accommodate  32 no of cameras.

Depth of Telecom cable- 1 m

Drum of quad- 1 km

Drum of OFC - 3 km

Drum of OFC duct -1 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.

Railnet uses Railtel MPLS.

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, GSM-R and LTE but not required for OFC.

Output of Solar cell is DC.

Min distance between OHE mast and telecom cable is 5.75 m in station section and 10 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.

-48 V is fed to subscriber line when it is Off hook,On Hook or talk mode.

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.

CAT 6 - 4 pairs

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.

4. Specifications -  GR/WIR/06/03. of March 2002

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 

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.

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.

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.

Conduction test -56 ohm/ loop km

Insulation Resistance Greater than 10 M ohms.

Transmission loss test- At 2 khz/600 ohms,loss is 1.2 dB/Km

Near end Crosstalk at 155 khz = Better than - 55 dB

Far end Crosstalk at 155 khz = Better than - 55 dB

Psophometric Noise = Not more than 2 mV

Schedule of Quad Cable testing 

Checking Attenuation-Monthly 

Loop resistance test - Monthly 

Checking Crosstalk level -Quarterly

Checking Noise level -  Quarterly 

Insulation Resistance Test - yearly 

Schedule of Quad Cable Inspections 

JE/SSE - Monthly 

SSE TEL incharge- Quarterly and yearly Schedules

ADSTE/DSTE/Sr.DSTE- Annual Inspection 

Switch Board Cable

1) Used in indoor cables.

2) The characteristics impedance is 600 ohms.

3) TEC Specification No GR/WIR/06/03 of March 2002

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.

Antenna Converts RF electrical current into EM Wave of same frequency.

Antenna gain = 17.8+ 20 log(f × dia)

f - frequency in GHz

Dia- Diameter of Microwave antenna

Absolute measurement of Power-

dBm or dbmW:- It refers to dB(1mW) i. e. Power measurement relative to 1miliwatt.

Insulation Resistance -

More than 5 M ohms for a pair is good. 

Less than 2 M  ohms for a pair Considered faulty.

Cable Route tracer - Used to trace the path of route of underground cables.

Cable Fault Locator- Used to locate various kinds of faults in UG  copper cables. They use Pulse Echo Method and Time Domain reflectometry.

Transmission Measuring Set ( TMS)

Used for following measurements

1. Signal levels

2. Insertion Loss

3. Transmission Loss

4. Return Loss

Visual Fault Locator-

Also called Laser fault locator.Using 650 nm or 635 nm visible laser source.Emits beam of Laser light into fibre,allowing users to visually detect a fibre fault upto 5 km.

OTDR (Optical Time domain reflectometer)

Used to measure attenuation (loss) of a whole optic fibre chain caused by splicing,connectors and bending.Wavelength settings are 1310 nm or 1550 nm.

Data Communication Cables

UTP - Unshielded Twisted Pair

STP - Shielded Twisted Pair 

V F repeaters - placed   at regular intervals of 40 - 50 kms 

PIJF telephone Pair cable -

Dia of conductors 0.5/0.6 mm

Characteristics impedance- 600 ohms

Thermo shrinkable jointing kit used in PIJF Telephone pair cable while Reinforced Thermo Shrinkable Jointing Kit used for 4/6 Quad Cables.

Services at Call Centre 139

Accommodation availability 

Reservation status

Arrival & Departure of Trains

Fare Structure 

Concessions 

Trains of different Destinations 

Summer specials 

Information on passenger Amenities 

Accident related queries 

Registration of complaints

Power supply 

Sp gravity of fully charged LA cell- 1.220

Sp gravity of fully discharged LA cell- 1.180

Sp gravity of pure water - 1

DOD of  a flooded type LA cell - 70%

DOD of low maintenance LA cell - 80%

DOD of low  VRLA CELL - 50%

VRLA is also called Sealed Lead Acid batteries.

Capacity of Cell = Load current × Back up time÷ DOD

Current rating of charger = Load current + AH  Capacity/10

Codal life of Rechargeable battery - 4 years

Constant Voltage Charging - 

Allows full current of charger to flow into battery until power supply reaches its preset voltage.The current will come down to a minimum value once voltage level is reached.

Constant Current Charging -

Charging Current is approximately 10% of maximum battery rating.Used for initial and Boost type of charging.

Sulphation -

It may occur if battery is stored for prolonged period in a completely discharged  state.  It increases internal resistance of the  battery.It can be connected by charging at low current.

Tickle charging -

Charging a fully charged battery under no load at a rate equal  to self discharge rate,thus enabling a battery to remain at fully charged level.Done at the rate of 2.25 to 2.30 V/cell.

Float Charging -

Done at the rate of 2.15 to 2.20 V/Cell . Battery is connected parallel to the charger.

Boost Charging -

Done at Higher rate for shorter duration in order to prevent over discharging of battery. 

Equalizing Charge - 

To overcharge a battery so that weaker cells are brought upto full charge.

Causes of Surge - 

Lighting discharges ( Major reason)

Switching ON/OFF inductive loads ( Transformer, coils etc)

Ignition and interruption of electric arcs ( Welding process)

Tripping of fuse and circuit breakers.

Short circuits 

External Protection ( Class A protection)

50% of lightening energy is transferred to ground.

Balance 50% enters building through Power/ Telecom cables.

Class B Protection 

First stage protection before the equipment (At Main Distribution Panel)

Spark Gap Technology-- Operates on Arc chopping principle.

SPD provided between each P-N and N-E

Class C protection 

Uses MOVR to provide surge Protection with low let through voltage.

Class D Protection System 

All external data/ Signalling (AC/DC ) lines connected to electronic equipment at either end is protected by Class D.

MOVR/Gas Discharge GDs used

Earthing 

Earth is ideal Equipotential surface.

Earth Resistence should be as low as possible.

It probably low impedance path to fault current.

Reduce shock hazard to personnel 

Provides protection free lightening 

Characteristics of Earth

Low resistance 

High corrosion resistance (Cu coating used)

Max Earth value of equipment in VF RPTR stations,cable huts & Telephone exchange - 5 Ohms 

Cable Size

Equipment to SEEB - 10 Sq mm

SEEB to MEEB - 16 Sq mm

MEEB to SPD - 16 Sq mm

MEEB to Main earth electrode- 35 sq mm

Main earth to other Earth - Copper tape of 25×2 mm

Control Communication 

This communication is provided between controller and Way side stations This is unique omnibus communication circuit in which controller and all station masters are connected to a common medium.

Conventional type VF repeater

This is provided at every 45 to  50 KM along the track to amplify the Signal and to compensate the loss of signal due to various reasons.

Equalizer type VF repeater

This is provided at every station. Provides equalization as well as Amplification of VF frequencies.

Control Room equipment 

4×4 matrix key board

DTMF Code Generater

Speech Amplifier 

Way station equipment-

DTMF Decoder

Control Telephone 

Power supply unit

2 Wire control Telephone 

Provided at way stations for providing communication from 2 wire Omnibus Control network 

4 Wire control Telephone 

Provided at way stations for providing communication from 4 wire Omnibus Control network 

Universal Control Telephone 

Suitable for both 4 W and 2W working.

2W/4W Portable Control Telephone

Provided with train crew for talking with controller in case of emergency from EC  socket provided at every km.

Inspection of Telephone Exchange

Once in a year by Sr.DSTE/ DSTE/ADSTE

Once in quarter by SSE

Once in month by JE

Local Call - Two subscribers in the same exchange 

Trunk Call - Two subscribers in the two different exchanges

Loop Signalling - It is referred to Off Hook condition of Telephone.  It is physically short of 2 wire analog signal 

DTMF Signalling-  It is a tone which uses two frequencies,generated by pressing a digit on  keypad normally used to dial an address of a subscriber.

Dial Tone -Tone extended from exchange to subscriber when handset is off hook,indicating that user can make an  outgoing call.

Ring Back Tone - Tone extended from exchange to calling subscriber,when ringing voltage is extended to called subscriber.

Busy Tone - Tone extended from exchange to calling subscriber when subscriber is busy.

IP Telephony-  VOIP ( Voice Over Internet Protocol) is a technology that allows telephone calls over an IP network.It is also called as IP telephony,internet telephony, Broadband telephony.

SIP ( Session Initiation Protocol)-

Used to create, manage and terminate sessions in the network. 

A session could be a simple two way telephone call or a multi media conference Session.

SIP takes the help of SDP ( Session Description Protocol) which describes sessions and RTP ( Real time transport protocol) Used for delivering voice and video over IP network.

Serial Data Communication- 

Only one bit can be transmitted at single instance of time , only one wire used.

Used for long distance.

Slow data transfer 

Parallel Data Communication 

More than one bit can be transmitted at single instance of time , 

more than one wire used.

Used for short Distance only

Fast data transfer.

MPLS ( Multi Protocol Label Switching)-

32 bits

STP cables - Aluminium foil is used as screen 

UTP cables transmits up to 10 Mbps - Cat 3

UTP cables transmits up to 16 Mbps - Cat 4.

CAT cables -RJ 45 Connector

Transmission loss and conduction  test in quad cable - monthly 

Cross talk test - quarterly 

PIjf telephone cable -  41/97

Emergency Control -It is used to establish instant communication from field or mid section in case of emergency or accident 

In Non RE area This circuit is provided with Dy chief controller and in RE area, it is provided with Traction power control.

This circuit is dropped and terminated at EC socket at every 1 Km.

Remote Control Circuits -

Used for remote operation of 25 kv traction equipment which works on SCADA ( Supervisory control and Data acquisition) principle.

Types of VF Repeater

Conventional type

Equalizer type

Equalizer type VF Repeater

12 v power supply 

Provided at every station

Loading joints not required 

Condenser joints not required Balancing can be done at every station.

Remote Monitoring 

8 way intercom

Automatic bypassing 

IP Telephony-

Integration of

Voice

Message 

Video

Data service over IP network 

Electronic LC Gate Telephone 

Meant for communication between ASM office and LC gate.

Works on Master and Slave principle.

One master can control 6 Slaves using omnibus 2 wire line.

24 Volt power supply extended through same omnibus speech line from master.

Master operates on 12 V supply derived from 24V 7 AH maintenance free battery. 

No need of any power supply at LC gate.

Master operates at 12 v and Slave LC gate phones operate with 24 V from dual power supply arrangement.

Master is provided with seperate push buttons for calling each slave.

Master telephone is provided with voice logging facility 

Integrated Way Control Communication Equipment ( IWCCE)

Eight 4 wire omnibus control circuits or channels at way stations.

Can connect 30 way station control telephone.

IWCCE has facility to generate ring back tone whenever a ring comes from control office.

IWCCE work on -48 v DC power supply.

Way side station do not need any power supply.

Way side telephone works on twisted pair having loop resistance of less than 1200 hrs.

Ringing voltage for analog phones in ISDN Exchange- 75 V @25 Hz.

Fault Detected by Electronic Exchange-

Loop and short circuit 

Fault can not be Detected by Electronic Exchange- Break 

Derivation- The technique of providing a number of circuits using a single transmission pair.

LI Card is used for  branching in  STM. 

Collision Domain-Swithes

Broadcast domain - Routers 

Type of OFC used in railways - 24 F

CAT cable supports - 100 m

Control telephone at way Station - No dialing facility .

Antenna - Metallic device for radiating or receiving radio waves.

Speed of Eathernet transmission 

> 100 Mbps

DWDM -Dense wavelength Division Multiplexing 

Technology used to increase the capacity of OFC 

Number of Quads required for ufsbi single line- 2 quad

BIOS - Basic interface output program 

Cable laid outside the  station section -10m from centre of nearest track. 

Max permitted line loop resistance in ISDN Exchange- 1200 ohms.

In Non Re area - Station limits -  Cable to be3from centre.laid at 3 m 

Clip stands - Calling line identification presentation 

Characteristics impedance of VF circuit in RE cable - 600

OFC cable laying- max speed is 10 mtrs/ day.

MONO MODE Fibre RDSO Specification TC 55/ 2006 Rev 1.0 follows ITU Specification ITU Recommendations Ģ.652 D

End point protection software in a system provides 

1.Anti virus software 

2. Device control- Software that prevents unauthorized end point use of connected mobile devices and removable media.

3. Anti malware software.

Selective fading-

A fading caused by phase difference between radio wave component of same transmission as experienced at receiving station.

Fluctuations at receiving end is called fading. 

TX and Rx frequency in MTRC is 338-355 Mhz 

NGN - New generation Network -works in layer 3

Impls level - 20 bit.

Bridge - Connects similar LANs with same protocol.Operates  on Data link layer. 

Router - Different LANs but same protocol 

Gateway - Different LAN and different Protocol 

IP phones are also alled SIP phone

Voice logger Unit -

No of speech channels - 04

Hard disc capacity - 40 GB.

Equalizer Amplifier-

Loading and balancing of quad is eliminated in Equalizer Amplifier system.

Remote monitoring and control from test room

8 way intercom facility for supervisors posted at stations with facility of call from control.

Upto 20 km distance, no Amplifier equalizer system is required.

Upto 12 km 0.9 mm 4/ 6 quad can be used without using any Equalizer system.

Between 12 km to 20 km,1.4 mm 4/6 quad will be used.

After 20 km, Equalizer Amplifier system will be used.

No need for seperate room to install it.It can be  installed in SM room,gate lodge or IB hut.

No loading or balancing in block section.

Repeater at all stations with active Equalizers to compensate unequal attenuation over voice frequency band.

Multi way conference hall at all stations 

Radio path facility at all stations 

Station bypass in case of Complete  failure of power supply.

Types of Telecom cables-

PCUT - Paper core unit twisted cables

PCQT - Paper core Quad twist/ Trunk cable 

Derivation cable ( Paper insulated quad cable)

Polythene Insulated twin twisted Corey for telephone ( for Telephone connection)

Polythene insulated jelly filled cable ( 4/6 quad)

Telecom switch board cable

UTP - Unshielded Twisted pair ( for data communication)

STP - shielded Twisted pair ( for data communication)

Co axial cable for data communication.

Common Modulation used in OFC - Intensity Modulation.

Troposphere scatter - UHF 

Recommended Cross talk level

NEXT - better than 61 dB

FEXT - better than 65 dB

Quad Cable insulation less than 2 Mega ohms - must be replaced 

4 faults -

Earth fault

Short circuit fault 

Open circuit fault 

Low insulation fault .

Speed of STM 1 - 20 Mbps, Bit rate - 155.52 Mbps

Speed of STM 4 - 100 MBPS, Bit rate - 622.08 Mbps

Speed of STM 16 - 1 GPS,Bit rate - 2488 Mbps