Abstract:

The prime objective of the training was to enhance the

knowledge of communication technology and various

network used across worldwide for data transmission. The

motive of the training not only was to build up various

concepts of the telecommunication world but also to

experience the troubleshooting procedures practically.

ACKNOWLEDGEMENT

I would like to thank the Management of RAILTEL

CORPORATION OF INDIA (KOLKATA) for giving me this

wonderful opportunity to work with highly knowledgeable

people on a project of great importance. I sincerely acknowledge the help and guidance received

from Mr. Pradeep Kumar without whom it would have been

difficult to complete this project work. His constant

encouragement and words of motivation have been a

source of inspiration for me. His guidance from the very

first day helped me develop an understanding of the project I owe my deepest gratitude to the engineers of RailTel

Corporation f o r the valuable inputs provided by him at each

and every step of the project and this project would have

been incomplete without his help.

I convey my deep appreciation to all the technical and

administrative staffs at RailTel Office, Kolkata

ANIKET BANDYOPADHYAY

DEPT. OF ETCE

JADAVPUR UNIVERSITY

CHAPTER 1: Introduction

Objective:

To enhance the knowledge of communication

technology and various network used across worldwide

for data transmission.

Scope:

The training was carried out in the regional

operation centre of RailTel Corporation of India Ltd.

Which gave us a tremendous advantage of being

accustomed with the real world scenario of

telecommunication. The engineers were of huge help

with their knowledge and experiences.

Duration:

14 Days

CHAPTER 2: The Training Organization

ABOUT RAILTEL CORPORATION OF INDIA

RailTel Corporation “A Mini Ratna (Category-I) PSU” is one of

the largest neutral telecom infrastructure providers in the country

owning a Pan-India optic fibre network on exclusive Right of Way

(ROW) along Railway track. The OFC network covers all important

towns & cities of the country and several rural areas covering 70% of

India’s population. RailTel with strong nationwide presence is

committed to bring cutting edge technology and offer innovative

services to the Indian Telecom market. RailTel is in the forefront in

providing nationwide Broadband Telecom & Multimedia Network in

all parts of the country in addition to modernization of Train operations

and administration network systems. With its Pan India high capacity

network, RailTel is working towards creating a knowledge society at

various fronts. Presently, RailTel has created over 45000 RKm of fibre

network connecting over 4500 cities/towns on the network including

several rural areas. The network is supported by multiple of 10G/2.5G

based STM-64/16 system rings. In addition, RailTel has also provided

over 10500 KM of network with DWDM systems with 100G/400G

capacity which is targeted to be further expanded to additional 14000

KM within a year to cover all major cities of the country. RailTel also

has a MPLS network with core on 10G capacity along with NGN

system to support various IP enabled services.

Equipped with an ISO 9001:2008 certification, RailTel offers a wide

gamut of managed telecom services to Indian Telecom market. The

service includes Managed lease lines, Tower colocation, MPLS based

IP-VPN, Internet and NGN based voice carriage services to Telecom

Operators, Internet Service Providers, MSOs, Enterprises, Banks,

Govt. Institutions/dept., Educational Institutions/Universities, etc.

RailTel is aggressively entering into Enterprise services market with

launch of its various services like Data Centre, Rail wire,

Telepresence, etc.

In addition, RailTel with its rich experience in the domain of Telecom

& ICT field have been selected for implementation of various

mission-mode Govt. projects in the telecom field. Under such

initiatives, RailTel is rolling out National Knowledge Network

(NKN), National Optical Fibre Network (NOFN) and North East OFC

project under USOF scheme.

EVOLUTION OF RAILTEL

Since communication is key to transportation, Indian Railways (IR)

was earlier solely dependent on Department of Telecom (now BSNL)

for their Control & Administrative Communication circuits. To

increase circuit efficiency, Railways started building up their own

communication systems from early 70’s based on overhead telephone

lines, quad cables and MW.

In 1983, Railway Reforms Committee decided to introduce OFC

based communications in IR for reasons of Safety, Reliability, and

Availability & Serviceability through using a dedicated network. This

decision was taken to create network independent of DoT (BSNL) &

replace existing MW telecom systems (60% of which have achieved

end of life) with OFC.

In Dec’1988, Indian Railways commissioned first OFC on

Churchgate - Virar section (in Mumbai) for Train operation & control

purpose which comprised of 60 KM of network across 28 stations.

Later the network was expanded in Central India with the

commissioning of 900 KM of OFC network in 1991-92 across Durg -

Nagpur, Nagpur – Itarsi and Itarsi - Bhusaval sections and in Eastern

India with the commissioning of 60 RKM of OFC network in Tata

nagar – Chakradhrapur section. In 1994, DoT issued 1st National

Telecom policy (NTP) which introduced Mobile Licenses to private

operators in India under the license system. However in 1999, 2nd

NTP was introduced which opened the NLD segment under

favourable license in conditions with revenue share to assist Telcos

spread network across India including in rural areas.

In Railway Budget of 2000, announcement was made for formation of

a telecom corporation to build a Nation-wide Broadband Multimedia

Telecom Network. RailTel formed as a PSU fully owned by Railways

in Sept, 2000 with authorized capital of Rs. 1000 crore with a

mandate to modernize Railways Communication network and to

significantly contribute to the realization of goals and objectives of

the National Telecom Policy 1999.

It was also decided that Railway’s existing telecom OFC assets

(approx. 4500 RKM) shall be transferred to RailTel for commercial

exploitation. RailTel initiated roll out of OFC across the country

along Railway routes from 2001 and created over 25000 RKM of

OFC network equipped with SDH based systems by March 2006.

OFC NETWORK OF

RAILTEL

RailTel has more than 42,000 Route Km of Optical Fibre Cable

running along Indian Railway Track in many part of the country.

RailTel is having fibres at every station enroot, spaced at 8-10 km to

meet Railway operations. RailTel is laying fibres in uncovered

sections & shall complete 54,000Km of Rail route & covering most of

the stations & commercial requirement (5000+) on its backbone.

This network is designed in a Layered for its efficient utilization and

management. The three layers viz. Access Layer, Edge Layer &

Backbone layer enables required capacity with desired granularity.

Access layer provides of STM-1 (155Mbps) capacity at stations,

spaced at every 8-10 km. The traffic from access layer is aggregated

on to the Edge layer having STM-16 connectivity, which is available

in important locations at every 50-60 Km. Collecting the traffic from

edge layer is finally aggregated on to the Backbone layer with

DWDM/STM-16/64 available in big cities/towns situated at every 60-

70 Km.

Over that RailTel has built “state of the art” backbone network using

latest SDH & DWDM technology. Presently, 400 cities covering over

30,000 RKm are connected on backbone network with STM-16 (2.5

GBPS) connectivity across the country. We have implemented

DWDM network over 10,000 RKM to provide 100mbps, which may

be further augmented, to 400 GBPS as & when required. RailTel

plans to cover complete CORE network on DWDM network within a

year.

For Trouble Free Service to our customers, Backbone Network have

been configured in multiple ‘Self-Healing’ ring architecture which

provides redundancy by automatically redirecting traffic away from

failed/ de-graded route .It supports SNCP and MS-Spring protection

schemes. It is designed in such a way that full redundancy is available

for bandwidth between any two points.

RailTel is servicing all Telco’s in the country through its OFC

network. RailTel also serves some Enterprises customer through its

MPLS, IBW network. RailTel’s strength is in providing access to

rural & remote areas and with commissioning of OFC in new sections

everywhere; we enable digital connectivity to unconnected.

CHAPTER 3: Formal Training

ABOUT OPTICAL FIBRE CABLE (OFC)

An optical fibre cable is a cable containing one or more optical fibres

that are used to carry light. The optical fibre elements are typically

individually coated with plastic layers and contained in a protective

tube suitable for the environment where the cable will be deployed.

Different types of cable are used for different applications, for

example long distance telecommunication, or providing a high-speed

data connection between different parts of a building.

Design

Optical fibre consists of a core and a cladding layer, selected for total

internal reflection due to the difference in the refractive index

between the two. In practical fibres, the cladding is usually coated

with a layer of acrylate polymer or polyimide. This coating protects

the fibre from damage but does not contribute to its optical waveguide

properties. Individual coated fibres (or fibres formed into ribbons or

bundles) then have a tough resin buffer layer and/or core tube(s)

extruded around them to form the cable core. Several layers of

protective sheathing, depending on the application, are added to form

the cable. Rigid fibre assemblies sometimes put light-absorbing

("dark") glass between the fibres, to prevent light that leaks out of one

fibre from entering another. This reduces cross-talk between the

fibres, or reduces flare in fibre bundle imaging applications.

ADVANTAGES OF OPTICAL FIBRE

Bandwidth - Fibre optic cables have a much greater bandwidth than

metal cables. The amount of information that can be transmitted per

unit time of fibre over other transmission media is its most significant

advantage. With the high performance single mode cable used by

telephone industries for long distance telecommunication, the

bandwidth surpasses the needs of today's applications and gives room

for growth tomorrow.

Low Power Loss - An optical fibre offers low power loss. This

allows for longer transmission distances. In comparison to copper; in

a network, the longest recommended copper distance is 100m while

with fibre, it is 2000m.

Interference - Fibre optic cables are immune to electromagnetic

interference. It can also be run in electrically noisy environments

without concern as electrical noise will not affect fibre.

Size - In comparison to copper, a fibre optic cable has nearly 4.5

times as much capacity as the wire cable has and a cross sectional

area that is 30 times less.

Weight - Fibre optic cables are much thinner and lighter than metal

wires. They also occupy less space with cables of the same

information capacity. Lighter weight makes fibre easier to install.

Safety - Since the fibre is a dielectric, it does not present a spark

hazard.

Security - Optical fibres are difficult to tap. As they do not radiate

electromagnetic energy, emissions cannot be intercepted. As

physically tapping the fibre takes great skill to do undetected, fibre is

the most secure medium available for carrying sensitive data.

Flexibility - An optical fibre has greater tensile strength than copper

or steel fibres of the same diameter. It is flexible, bends easily and

resists most corrosive elements that attack copper cable.

Cost - The raw materials for glass are plentiful, unlike copper. This

means glass can be made more cheaply than copper.

DISADVANTAGES OF OPTICAL

FIBRE

Cost - Cables are expensive to install but last longer than copper

cables.

Transmission - transmission on optical fibre requires repeating at

distance intervals.

Fragile - Fibres can be broken or have transmission loses when

wrapped around curves of only a few centimetres radius. However by

encasing fibres in a plastic sheath, it is difficult to bend the cable into

a small enough radius to break the fibre.

Protection - Optical fibres require more protection around the cable

compared to copper.

OPTICAL

FIRBE

PLESIOCHRONOUS DIGITAL

HIERARCHY

The PDH system effectively develops the idea of primary

multiplexing using time division multiplexing (TDM) to generate

faster signals. This is done in stages by first combining (multiplexing)

E1 or T1 links into what are known as E2 or T2 links, and if required,

going even further by combining (multiplexing) E2 or T2 links, etc.

This multiplexing hierarchy is known as the Plesiochronous Digital

Hierarchy (PDH). Plesiochronous, meaning “almost synchronous,”

relates to the inputs that can be of slightly varying speeds relative to

each other and the system’s ability to cope with the differences.

These groups of signals can be transmitted as an electrical signal over

a coaxial cable, as radio signals, or optically via fibre-optic systems.

As such, PDH formed the backbone of early optical networks.

The aggregate signal can be sent to line at any stage of the hierarchy,

using the appropriate transmission medium and modulation

techniques.

PDH Network Operation — PDH network equipment is now quite

physically small, allowing for its deployment in locations other than a

telephone exchange.

Network operators are able to house such equipment in street

cabinets; enough equipment to supply 120 telephone lines can be

stored in an enclosure measuring 1.5 meter by 1 meter high. This has

removed the need for many of the smaller telephone exchange

buildings that we used to see in fixed networks.

PDH systems are generally used only for point-to-point

communications systems because the signals must be fully

demultiplexed to access a single information channel. In addition,

proprietary alarm configuration and management means that

equipment at either end of a PDH system must be from the same

manufacturer.

ADVANTAGES OF PDH

Equipment small enough for use in street cabinets

Good for point-to-point connections

Cost-effective support for access networks

DISADVANTAGES OF PDH

Manufacturer-specific systems

Multiplexer mountains

No integrated network management

Limited management available

SDH NETWORK OF RAILTEL RailTel has built state of the art backbone network using latest SDH

technology. More than 400 important cities covering over 28,000

RKMs across the country are connected on backbone network with

STM-16 (2.5 GBPS) connectivity presently.

Backbone network have been configured in multiple ‘self-healing’

ring architecture which provide for redundancy by automatically

redirecting traffic away from failed/ de-graded route for fault-free

service. The network supports SNCP and MS-Spring protection

schemes. The network has been designed in such a way that full

redundancy is available for bandwidth between any two points.

The complete network is managed by centralized network

management system (NMS) located at New Delhi with back up at

Secunderabad / Kolkata. RailTel has got the unique advantage to

meet the quality bandwidth and service requirements from single

network. The state of art network enables point and click provisioning

of the bandwidth from anywhere to anywhere in the country. It

enables provisioning of traffic of any granularity with the extensive

reach from any part of the country to any other part.

RailTel network is managed and monitored by RailTel Engineer from

four Regional NOC at New Delhi, Kolkata, and Mumbai &

Secundrabad.

Synchronous Digital Hierarchy

(SDH)

Although it is a reliable system, PDH has a number of obvious

shortcomings. When designing the next generation of transmission

systems, consideration was given to overcoming these shortcomings.

The Synchronous Digital Hierarchy (SDH) was developed from the

American SONET (Synchronous Optical Network) and is designed to

provide an effective, well-managed, reliable, and efficient system for

use with optical-fibre (high-bandwidth) links. It was developed to be

compatible with existing systems and can therefore carry PDH

channels as well as other formats. Although seen as an expensive

option compared to the tried and trusted PDH alternative, the

advantages of SDH are well recognized, and SDH is now the accepted

standard for digital transmission around the world. SDH has many

advantages over PDH, most notably:

It is designed to get the best out of high-capacity fibre-optic cables.

It is compatible with many other accepted standards such as E1 and

T1. It has built-in network performance monitoring and management

facilities. It is compatible with both European and American

standards.

SDH can multiplex together a variety of different digital signal types,

including those that are already multiplexed using PDH, or even SDH

These signals are arranged by the system onto a standard frame,

called a synchronous transport module (STM), ready for transmission.

SYNCHRONOUS TRANSPORT

MODULE (STM)

The smallest of these is STM-1, which operates at 155 Mbps. There

are larger frames, denoted STM-x. The x merely implies the number

of STM-1 equivalents transmitted (systems can employ STM- 4,

STM-16, STM-64, or even higher). The inputs are known as

tributaries.

STM-1 is equivalent to 63 × E1 links, or 1890 telephone channels.

The common implementation throughout Europe is a 155.52-Mbps

link (carrying many multiplexed channels) in STM-1 (synchronous

transfer module) format, which can itself be multiplexed into higher

capacity levels (mainly STM-4, STM- 16, and STM-64). These

signals are typically transmitted over optical fibre, although it is

possible to send STM-1 over modest distances using coaxial cable or

radio.

SDH Network Operation

Every voice or data channel is identifiable in the STM-x and allows

selective demultiplexing.

This has the advantage of eliminating the multiplexer mountains of

PDH and allows new network structures beyond simple point-to-point

connections. This also allows some or all of the channels to be

effectively protected in case of a network failure. The ability to

automatically protect traffic is an inherent feature of SDH. SDH has

inherent management capabilities built into its structure. It is possible

to control and configure an entire network remotely. This has given

rise to large NOCs (network operation centres) where an operator can

monitor, identify, and react to any fault in a network within minutes.

Protection and management systems work best where the fibre optic

(or other medium on which SDH is running) is organized in ring

structures to provide alternative reconfigurable routes, and therefore

more reliable connections for the user.

Features and Advantages of SDH

In previous pages we have seen the limitations of PDH. Now let us

see the advantages of SDH.

SDH permits the mixing of the existing European and North

American PDH bit rates.

All SDH equipment is based on the use of a single master reference

clock source & hence SDH is synchronous.

Compatible with the majority of existing PDH bit rates

SDH provides for extraction/insertion, of a lower order bit rate from a

higher order aggregate stream, without the need to de-multiplex in

stages.

SDH allows for integrated management using a centralised network

control.

SDH provides for a standard optical interface thus allowing the inter-

working of different manufacturers’ equipment.

Increase in network reliability due to reduction of necessary

equipment/jumpering.

Frame structure of SDH

The STM-1 frame is the basic transmission format for SDH

(Synchronous Digital Hierarchy). A STM-1 frame has a byte-oriented

structure with 9 rows and 270 columns of bytes, for a total of 2,430

bytes (9 rows * 270 columns = 2430 bytes). Each byte corresponds to

a 64kbit/s channel.

TOH: Transport

Overhead (RSOH + AU4P + MSOH)

MSOH: Multiplex Section Overhead

RSOH: Regeneration Section Overhead

AU4P: AU-4 Pointers

VC4: Virtual Container-4 payload (POH + VC-4 Data)

POH: Path Overhead

Frame characteristics

The STM-1 base frame is structured with the following

characteristics:

Length: 270 column × 9 row = 2430 bytes

Byte: 1-byte = 64kbit/s speech channel

Duration (Frame repetition time): 125 μs i.e. 8000 frame/s

Rate (Frame capacity): 2430 × 8 × 8000 = 155.520 Mbit/s

Payload = 2349bytes × 8bits × 8000frames/sec = 150.336 Mbit/s

RSOH (REGENERATOR SECTION

OVERHEAD)

1st row = Unscrambled bytes. Their contents should therefore be

monitored

X = Bytes reserved for national use

D = Bytes depending on the medium (satellite, radio relay system …)

The Regenerator Section Overhead uses the first three rows & nine

columns in the STM-1 frame

A1, A2 the Frame Alignment Word is used to recognize the beginning

of an STM-N frame

A1: 1111 0110 = F6 (HEX)

A2: 0010 1000 = 28 (HEX)

J0: Path Trace. It is used to give a path through an SDH Network a

"Name". This message (Name) enables the receiver to check the

continuity of its connection with the desired transmitter

B1: Bit Error Monitoring. The B1 Byte contains the result of the

parity check of the previous STM frame, after scrambling of the

actual STM frame. This check is carried out with a Bit Interleaved

Parity check (BIP-8).

E1 Engineering Order wire (EOW). It can be used to transmit speech

signals between Regenerator Sections for operating and maintenance

purposes

F1 User Channel. It is used to transmit data and speech for service

and maintenance

D1 to D3 Data Communication Channel at 192 Kbit/s (DCCR). This

channel is used to transmit management information via the STM-N

frames

MSOH (multiplex section overhead)

X = Bytes reserved for national use.

The Multiplex Section Overhead uses

the 5th through 9th rows, and first 9

columns in the STM-1 frame.

B2: Bit Error Monitoring. The B2 Bytes contains the result of the

parity check of the previous STM frame, except the RSOH, before

scrambling of the actual STM frame. This check is carried out with a

Bit Interleaved Parity check (BIP24)

K1, K2 Automatic Protection Switching (APS). In case of a failure,

the STM frames can be routed new with the help of the K1, K2 Bytes

through the SDH Network. Assigned to the multiplexing section

protection (MSP) protocol

K2 (Bit6, 7, 8) MS_RDI: Multiplex Section Remote Defect Indication

(former MS_FERF: Multiplex Section Far End Receive Failure)

D4 to D12 Data Communication Channel at 576 Kbit/s (DCCM). (See

also D1-D3 in RSOH above)

S1 (Bit 5 - 8) Synchronization quality level:

E2 Engineering Order wire (EOW). Same function as E1 in RSOH

M1 MS_REI: Multiplex Section Remote Error Indicator, number of

interleaved bits which have been detected to be erroneous in the

received B2 bytes. (Former MS_FEBE: Multiplexing Section Far End

Block Errored)

Z1, Z2 Spare bytes

SMALL FORM FACTOR PLUGGABLE

TRANSCIEVER (SFP)

The small form-factor pluggable (SFP) is a compact, hot-pluggable

transceiver used for both telecommunication and data

communications applications. The form factor and electrical interface

are specified by a multi-source agreement (MSA). It interfaces a

network device motherboard (for a switch, router, media converter or

similar device) to a fibre optic or copper networking cable. It is a

popular industry format jointly developed and supported by many

network component vendors. SFP transceivers are designed to support

SONET, gigabit Ethernet, Fibre Channel, and other communications

standards. Due to its smaller size, SFP obsolesces the formerly

ubiquitous gigabit interface converter (GBIC); the SFP is sometimes

referred to as a Mini-GBIC although no device with this name has

ever been defined in the MSAs.

TYPES OF SFP

SFP transceivers are available with a variety of transmitter and

receiver types, allowing users to select the appropriate transceiver for

each link to provide the required optical reach over the available

optical fibre type (e.g. multi-mode fibre or single-mode fibre). Optical

SFP modules are commonly available in several different categories:

For multi-mode fibre, with black or beige extraction lever

SX - 850 nm, for a maximum of 550 m at 1.25 GBPS (gigabit

Ethernet) or 150m at 4.25 GBPS (Fibre Channel)

For single-mode fibre, with blue extraction lever

LX - 1310 nm, for distances up to 10 km

EX - 1310 nm, for distances up to 40 km

ZX - 1550 nm, for distances up to 80 km, with green extraction lever

EZX - 1550 nm, for distances up to 160 km

BX - 1490 nm/1310 nm, Single Fibre Bi-Directional Gigabit SFP

Transceivers, paired as BS-U and BS-D for Uplink and Downlink

respectively, also for distances up to 10 km. Variations of

bidirectional SFPs are also manufactured which use 1550 nm in one

direction.

1550 nm 40 km (XD), 80 km (ZX), 120 km (EX or EZX)

SFSW – Single Fibre Single Wavelength transceivers, for bi-

directional traffic on a single fibre. Coupled with CWDM, these

double the traffic density of fibre links.

CWDM and DWDM transceivers at various wavelengths achieving

various maximum distances

For copper twisted pair cabling

1000BASE-T - these modules incorporate significant interface

circuitry and can only be used for gigabit Ethernet, as that is the

interface they implement. They are not compatible with (or rather: do

not have equivalents for) Fibre channel or SONET.

DWDM NETWORK OF RAILTEL

RailTel has created countrywide state of the art SDH/DWDM

backbone optical transport network using latest cutting edge

technology. More than 400 cities covering over 37,000 RKMs across

the country are connected on the network with multiple STM-16 (n X

2.5 GBPS) connectivity. RailTel has also implemented ultra-high

capacity DWDM network over 10,000 RKM to provide 400 GBPS

which is further up gradable to 800 GBPS in future. The PAN India

DWDM network will be made operational soon...

RailTel’s Backbone Transport Network has been configured in which

provide for redundancy by automatically redirecting and switching

traffic from failed/ de-graded routes for un-interrupted service

ensuring maximum up time and service reliability. The network

supports multiple ring protection schemes. The network has been

designed in such a way that full redundancy is available for

bandwidth between any two points. The whole network is managed

by centralized network management/operation system (NMS)

centrally located at New Delhi with back up facilities at Secunderabad

/ Kolkata/Mumbai. RailTel has got the unique advantage to offer the

best quality of service (QOS) from a single unified network with PAN

India presence. This state of art network enables point and click

provisioning of the bandwidth and other services from anywhere to

anywhere in the country. It enables provisioning of traffic in any

granularity from 2MBPS to multiple of GBPS (n x 10GBPS) from its

country wide strong backbone network.

Dense wavelength division multiplexing

(DWDM)

Dense wavelength division multiplexing (DWDM) is a technology

that puts data from different sources together on an optical fibre, with

each signal carried at the same time on its own separate light

wavelength.

Using DWDM, up to 80 (and theoretically more) separate

wavelengths or channels of data can be multiplexed into a light stream

transmitted on a single optical fibre. Each channel carries a time

division multiplexed (TDM) signal. In a system with each channel

carrying 2.5 GBPS (billion bits per second), up to 200 billion bits can

be delivered a second by the optical fibre. DWDM is also sometimes

called wave division multiplexing (WDM).

Since each channel is demultiplexed at the end of the transmission

back into the original source, different data formats being transmitted

at different data rates can be transmitted together. Specifically,

Internet (IP) data, Synchronous Optical Network data (SONET), and

asynchronous transfer mode (ATM) data can all be travelling at the

same time within the optical fibre.

DWDM promises to solve the "fibre exhaust" problem and is

expected to be the central technology in the all-optical networks of the

future.

ADVANTAGES OF DWDM

Bandwidth multiplication

Provides extra resilience

1. Optical circuit protection around ring

2. Or use inter-switch trunking for each ring path

3. Faster fail over than spanning tee

New services

1. Intersite private interconnect

Improves scalability

Permits multiple logic topologies over single physical MAN

Can converse switched Bandwidth

OPTICAL TIME DOMAIN

REFLECTOMETER (OTDR)

An optical time-domain reflectometer (OTDR) is an optoelectronic

instrument used to characterize an optical fibre. An OTDR is the

optical equivalent of an electronic time domain reflectometer. It

injects a series of optical pulses into the fibre under test and extracts,

from the same end of the fibre, light that is scattered (Rayleigh

backscatter) or reflected back from points along the fibre. The

scattered or reflected light that is gathered back is used to characterize

the optical fibre. This is equivalent to the way that an electronic time-

domain reflectometer measures reflections caused by changes in the

impedance of the cable under test. The strength of the return pulses is

measured and integrated as a function of time, and plotted as a

function of fibre length.

TJ1500 (STM)

The TJ1500 is a cost-effective and compact STM- 1/4/16

SDH multiplexer equipment designed to manage and derive

services from the optical core to access. The product supports

end-to-end provisioning and management of services across

all segments of the optical network. It combines innovative

optical networking software with the resilience of SDH to

deliver a flexible solution to today’s service providers. The

product is well suited for backbone and high speed links. As

traffic demand grows, the product ensures a smooth upgrade

by allowing support for DWDM interfaces as well. The

TJ1500 can be configured as a Terminal Multiplexer

(TMUX), Add-Drop Multiplexer (ADM), or as a Regenerator

in various configurations with E1, E3/DS3, STM-1e/1o, STM-

4 and 10/100 Mbps Ethernet tributary interfaces and trunk

interfaces at STM-16 rates. The product has built-in non-

blocking cross-connect at VC-3, VC-4 and VC-12 granularity

and supports drop-and-continue functionality.

NETWORK TOPOLOGY

Network topology is the arrangement of the various elements (links,

nodes, etc.) of a computer network. Essentially, it is the topological

[3] structure of a network and may be depicted physically or logically.

Physical topology is the placement of the various components of a

network, including device location and cable installation, while

logical topology illustrates how data flows within a network,

regardless of its physical design. Distances between nodes, physical

interconnections, transmission rates, or signal types may differ

between two networks, yet their topologies may be identical.

TYPES OF NETWORK

The study of network topology recognizes eight basic topologies:

point-to-point, bus, star, ring or circular, mesh, tree, hybrid, or daisy

chain.

Point-to-point

The simplest topology with a permanent link between two endpoints.

Switched point-to-point topologies are the basic model of

conventional telephony. The value of a permanent point-to-point

network is unimpeded communications between the two endpoints.

The value of an on-demand point-to-point connection is proportional

to the number of potential pairs of subscribers and has been expressed

as Metcalfe's Law.

Bus

Bus network topology

In local area networks where bus topology is used, each node is

connected to a single cable. Each computer or server is

connected to the single bus cable. A signal from the source

travels in both directions to all machines connected on the bus

cable until it finds the intended recipient. If the machine address

does not match the intended address for the data, the machine

ignores the data. Alternatively, if the data matches the machine

address, the data is accepted. Because the bus topology consists

of only one wire, it is rather inexpensive to implement when

compared to other topologies. However, the low cost of

implementing the technology is offset by the high cost of

managing the network. Additionally, because only one cable is

utilized, it can be the single point of failure.

Star

Star network topology

In local area networks with a star topology, each network host is

connected to a central hub with a point-to-point connection. In

Star topology every node (computer workstation or any other

peripheral) is connected to a central node called hub or switch.

The switch is the server and the peripherals are the clients. The

network does not necessarily have to resemble a star to be

classified as a star network, but all of the nodes on the network

must be connected to one central device. All traffic that

traverses the network passes through the central hub. The hub

acts as a signal repeater. The star topology is considered the

easiest topology to design and implement. An advantage of the

star topology is the simplicity of adding additional nodes. The

primary disadvantage of the star topology is that the hub

represents a single point of failure.

Mesh

The value of fully meshed networks is proportional to the exponent of

the number of subscribers, assuming that communicating groups of

any two endpoints, up to and including all the endpoints, is

approximated by Reed's Law.

Fully connected network

A fully connected network is a communication network in

which each of the nodes is connected to each other. In graph

theory it known as a complete graph. A fully connected network

doesn't need to use switching or broadcasting. However, its

major disadvantage is that the number of connections grows

quadratically with the number of nodes, as per the formula

And so it is extremely impractical for large networks. A two-

node network is technically a fully connected network.

Tree

A tree topology is essentially a combination of bus topology and star

topology. The nodes of bus topology are replaced with standalone star

topology networks. This results in both disadvantages of bus topology

and advantages of star topology.

For example, if the connection between two groups of networks is

broken down due to breaking of the connection on the central linear

core, then those two groups cannot communicate, much like nodes of

a bus topology. However, the star topology nodes will effectively

communicate with each other.

Hybrid

Hybrid networks use a combination of any two or more topologies, in

such a way that the resulting network does not exhibit one of the

standard topologies (e.g., bus, star, ring, etc.). For example a tree

network connected to a tree network is still a tree network topology.

A hybrid topology is always produced when two different basic

network topologies are connected. Two common examples for Hybrid

network are: star ring network and star bus network

A Star ring network consists of two or more star topologies

connected using a multistation access unit (MAU) as a centralized

hub.

A Star Bus network consists of two or more star topologies

connected using a bus trunk (the bus trunk serves as the network's

backbone).

Daisy chain

Except for star-based networks, the easiest way to add more

computers into a network is by daisy-chaining, or connecting each

computer in series to the next. If a message is intended for a computer

partway down the line, each system bounces it along in sequence until

it reaches the destination. A daisy-chained network can take two basic

forms: linear and ring.

A linear topology puts a two-way link between one computer and

the next. However, this was expensive in the early days of

computing, since each computer (except for the ones at each end)

required two receivers and two transmitters.

By connecting the computers at each end, a ring topology can be

formed. An advantage of the ring is that the number of transmitters

and receivers can be cut in half, since a message will eventually

loop all of the way around. When a node sends a message, the

message is processed by each computer in the ring. If the ring

breaks at a particular link then the transmission can be sent via the

reverse path thereby ensuring that all nodes are always connected

in the case of a single failure.

CHAPTER 4: CONCLUSION

Our Experience of Industrial Visit ‘See & know’ is better motto

than ‘read & learn’. After completing the industrial visit, we have

upgraded our knowledge at a very great level. It was a good learning

experience. In each & every lab, we got some or the other new ideas

and new thinking which was very necessary for our course. We have

visited the entire department. They are using new technologies. They

are strictly following quality & safety aspects. It is desirable to review

various aspects & sum up the industrial visit. During industrial visit,

we felt very much satisfied by acquiring information of various labs &

knowing many new things. The industrial visit helps how to translate

theory into practical. We also want to thank Prof. Iti Saha Mishra, Head

of the Department, Electronics and Telecommunication Engineering,

Jadavpur University for her encouragement & support for making this

visit successful.

Prepared By:

ANIKET BANDYOPADHYAY