ACKNOWLEDGEMENT

Behind the completion of any successful work there lies the contribution of not one but many individuals who may have directly or indirectly contributed to it.I first of all want to thank BHARAT SANCHAR NIGAM LIMITED (BSNL) for providing me this valuable opportunity to work and learn with them. I owe my personal thanks to my trainer in charge –Mr. R.P.Tiwari who extended full support and co-operation at every stage of my training period.

I am also thankful to my parents and friends for their constant encouragement and helping me in my endeavor.Last, but not the least, I would like to thank everyone who has contributed for the successful completion of my training.

SHASHI BHUSHAN

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PREFACE

Organizations are made up of people and function through people. Without people, organizations cannot exist. The resources of men, money, material, machinery, and mechanism are connected, coordinated and utilized through people. Engineers need to concentrate more on mechanism and the way in which things have been made. The need of training arises for doing things yourself, understanding its way.

Practical exposure for doing things makes a person conversant to the technicalities involved in any job. In view of such benefits, imparting of vocational training has been made an integral part of any academic structure.

In B.S.N.L., training is given to Engineering Aspirants to secure future in the dynamic world of telecommunications. Today telecommunication industry is one of the very fastest growing industries in the world.

In this order I have taken 28 days BSNL training. In my report I try to introduce Basic communication system, optical fiber, GSM concepts and CDMA etc.

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CONTENTS

• Acknowledgement

• Preface

• Introduction

• Basic Communication System

• Cellular Concept

• GSM

• GPRS

• CDMA

• Optical Fibre

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INTRODUCTION

India is the fourth largest telecom market in Asia after China, Japan and South Korea. The Indian telecom network is the eighth largest in the world.

TYPE: COMMUNICATION SERVICE PROVIDERCOUNTRY: INDIAAVAILABLITY: NATIONAL EXCEPT DELHI & MUMBAIOWNER: THE GOVERNMENT OF INDIAWEBSITE: www.bsnl.co.in

HOW BSNL CAME IN TELECOM MARKET:

The initial phase of telecom reforms began in 1984 with the creation of Center for Department of Telematics (C-DOT) for developing indigenous technologies and private manufacturing of customer premise equipment. Soon after, the Mahanagar Telephone Nigam Limited (MTNL) and Videsh Sanchar Nigam Limited (VSNL) were set up in 1986.The Telecom Commission was established in 1989. A crucial aspect of the institutional reform of the Indian telecom sector was setting up of an independent regulatory body in 1997 – the Telecom Regulatory Authority of India (TRAI), to assure investors that the sector would be regulated in a balanced and fair manner. In 2000, DoT corporatized its services wing and created Bharat Sanchar Nigam Limited.

BSNL CONTRIBUTION TO DEVELOPMENT OF TELECOM:

Bharat Sanchar Nigam Limited was formed in year 2000 and took over the serviceproviders role from DOT. BSNL’s roadmap for providing customer with access to the latest telecommunications services without losing sight of universal service access has been by way of utilizing optimally the existing infrastructure and accelerating advances in technological component by innovative absorption.

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BASIC TELECOMMUNICATION NETWORK

This section includes brief introduction of how a call is processed when we dial a call from basic telephone to another basic telephone or from basic to mobile or vice versa.

CALL SETUP:

• When a subscriber calls to another subscriber first its request goes to the nearest switching centre that is PSTN (Public Switching Telecommunication Network). Then it processes the caller and subscriber’s number if it exists in the same BSC then call setup is completed.

• If subscriber is not in the same BSC (Base Switching Centre) then call transfer to MSC (Main Switching Centre) then it transfers the call to prior BSC then call setup is completed.

• If Caller calls to a mobile subscriber then call transfer is done by MTSO now call transfer is done on BTSs (Base Transceiver Station) and call setup is completed.

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FUNCTION OF EXCHANGE:

• Exchange of information with subscriber lines with other exchange. This is done by two type of signaling:

1. Inchannel signaling2. Common channel signaling

• Processing of signaling information and controlling the operation of signaling network.

• Charging and billing.

ELECTRONIC EXCHANGE:

• All control functions by series of instructions are stored in memory.• Memories are modifiable and control program can always be

rewritten. For each call processing step decision is taken according to class of service.

CARRIER ROOM:

Leased line connectivity is provided in carrier room. This room has two parts:1. Conventional leased line system2. MLLN

CONVENTIONAL LEASED LINE SYSTEM:• It consists of modems and routers that are provided by the company

requesting for that network.• Connectivity of different ATM, banks etc. is provided by BSNL here.• For this, we have 4 modems (2 in Exchange, 1 at sender and 1 at

receiver)• Modems are used for short distances i.e. trans and receive part are

received here and local lead connection is given to the subscriber.• Local lead faults can be handled here but the trans and receive faults

can be handled by the department meant for it.• Accept 64Kbps or 2 Mbps.• For long distance communication we have MUXS and data is sent

through optical fibers. MUXS are present at both the ends.

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MDF(MAIN DISTRIBUTION FRAME):M.D.F. is a media between switching network and subscriber’s line. It is a termination point within the local telephone exchange where exchange equipment and terminations of local loops are connected by jumper wires.

MDFMANAGED LEASED LINE NETWORK:

The MLLN service is specially designed mainly for having effective control and monitoring on the leased line so that the down time is minimized and the circuit efficiency is increased. This mainly deals with data circuits ranging from 64 Kbps to 2048 Kbps

FUNCTIONS OF MDF:

• All cable copper wires supplying services through user telephone lines are terminated and distributed through MDF.

• The most common kind of large MDF is a long steel rack accessible from both sides. Each jumper is a twisted wire.

• It consists of local connection and broadband connection frames for the main Exchange area.

• The MDF usually holds central office protective devices including heat coils and functions as a test point between a line and the office.

• It provides testing of calls.• It checks whether fault is indoor or external.• All lines terminate individually.

MLLN ADVANTAGES:

1. 24 hrs Performance Monitoring of the circuit.

2. Circuit fault reports generated proactively.

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3. On Demand the Bandwidth can be increased.

4. Low lead time for new circuit provisioning.

POWER PLANT:

• It provides -48V to the switch rooms and 48V to the connections.• Batteries are artificially discharged once in a year for their

maintenance.• Cooling is provided through fans & AC.• There is earth region too for protection.

APPLICATION OF MLLN:

1. Corporate high speed internet access through Broadband.

2. LAN interconnection.

3. Hotline connectivity for voice.

4. Point to point connection for data circuit.

5. Point to multipoint connection.

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Cellular ConceptTraditional mobile service was structured similar to television broadcasting: One very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to fifty kilometers. The Cellular concept structured the mobile telephone network in a different way. Instead of using one powerful transmitter many low-powered transmitter were placed throughout a coverage area. For example, by dividing metropolitan region into one hundred different areas (cells) with low power transmitters using twelve conversations (channels) each, the system capacity could theoretically be increased from twelve conversations using one hundred low power transmitters.

Cells :A cell is the basic geographic unit of cellular system. The term cellular comes from the honeycomb areas into which a coverage region is divided. Cells are base stations transmitting over small geographic areas that are represented as hexagons. Each cell size varies depending upon landscape. Because of constraint imposed by natural terrain and man-made structures, the true shape of cell is not a perfect hexagon.A group of cells is called a cluster. No frequencies are reused in a cluster.Features of Digital Cellular Systems:

• Small cells

• Frequency reuse

• Small, battery-powered handsets

• Performance of handovers

The spectrum allocated for a cellular network is limited. As a result there is a limit to the number of frequencies or channels that can be used. A cellular network can only provide service to a large number of subscribers, if the channels allocated to it can be reused. Channel reuse is

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implemented by using the same channels within cells located at different positions in the cellular network service area.Radio channels can be reused provided the separation between cells containing the same channel set is far enough apart so that co-channel interference can be kept below acceptable levels most of the time

GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM)

In wireless communication every region is divided into cells. Cell size is constant for whole system. GSM is a form of multiplexing, which divides the available bandwidth among the different channels. Most of the times the multiplexing used is either TDM (Time division multiplexing) or FDM (Frequency Division Multiplexing). SM differs from its predecessor technologies in that both signaling and speech channels are digital, and thus GSM is considered a second generation (2G) mobile phone system.

A GSM system is basically designed as a combination of three major subsystems: the network subsystem, the radio subsystem, and the operation support subsystem. In order to ensure that network operators will have several sources of cellular infrastructure equipment, GSM decided to specify not only the air interface, but also the main interfaces that identify different parts. There are three dominant interfaces, namely, an interface between MSC and the base Transceiver Station (BTS), and an Um interface between the BTS and MS.

GSM NETWORK STRUCTUREEvery telephone network needs a well-designed structure in order to route incoming called to the correct exchange and finally to the called subscriber. In a mobile network, this structure is of great importance because of the mobility of all its subscribers [1-4]. In the GSM system, the network is divided into the following partitioned areas.

• GSM service area;• PLMN service area;• MSC service area;• Location area;

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• Cells.

MAIN FEATURES OF GSM:

• Support for voice and data services• Better frequency efficiency, smaller cells and more customers per cell• High audio quality and reliability for wireless, uninterrupted phone

calls at higher speeds (e.g. from cars, trains) i.e. high transmission quality.

• Authentication via chip-card and PIN.• Worldwide connectivity.

GSM SUBSYSTEMS:

• BASE STATION SYSTEM (BSS)• NETWORK SWITCHING SUBSYSTEM (NSS)

RADIO SUBSYSTEM:

MOBILE STATION (MS):A mobile unit is a transmitter as well as receiver too. It has a SIM (Subscriber Identity Module) which gives a unique identity of a subscriber. Every mobile unit has a unique IMEI (International Mobile Equipment Identity) number.

BASE TRANSCEIVER STATION (BTS):• A base transceiver station or cell site (BTS) is a piece of equipment

that facilitates wireless communication between user equipment (UE) and a network.

• It encodes, encrypts, modulates and feeds the RF signal to antenna.

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• It produces time and frequency synchronization signals.• It does power control and frequency hopping too.

BASE STATION CONTROLLER (BSC):• Its main work is to control several transceivers.• Switching between BTSs• Managing of network resources• Mapping of radio channels

NETWORK AND SWITCHING SUBSYSTEM:

This subsystem does mainly switching, mobility management, interconnection to other networks, system control.

COMPONENTS:

1. MOBILE SERVICES SWITCHING CENTRE (MSC):

It controls all connections via a separated network to/from a mobile terminal within the domain of the MSC – several BSC can belong to a MSC. The basic switching function of performed by the MSC, whose main function is to coordinate setting up calls to and from GSM users.

FUNCTION OF MAIN SWITCHING CENTER (MSC):

• Manages communication between GSM and other network (PSTN, Data Network and GPRS).

• Call setup basic switching, call handling.• Location register• Billing for subscriber

2. DATABASES:

Home Location Register (HLR):The HLR is a database that permanently stores data related to a given set of subscribers. Various identification numbers and addresses as well as authentication parameters, services subscribed, and special routing information are stored.

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The HLR is responsible for storage and provision of SIM authentication and encryption parameters needed by the MSC where the MS-SIM is operating. It obtains these parameters from the AUC.The HLR maintains record of which supplementary service each user has subscribed to and provides permission control in granting services. Some data are mandatory, other data are optional. Both the HLR and the VLR can be implemented in the same equipment in an MSC (collocated). A PLMN may contain one or several HLRs.

Visitor Location Register (VLR):The VLR is collocated with an MSC. A MS roaming in an MSC area is controlled by the VLR responsible for that area. When a MS appears in a LA, it starts a registration procedure. The MSC for that area notices this registration and transfers to the VLR the identity of the LA where the MS is situated. A VLR may be in charge of one or several MSC LA’s. The VLR constitutes the databases that support the MSC in the storage and retrieval of the data of subscribers present in its area. When an MS enters the MSC area borders, it signals its arrival to the MSC that stores its identify in the VLR. The information necessary to manage the MS is contained in the HLR and is transferred to the VLR so that they can be easily retrieved if so required. the data are present in the VLR only as long as the MS is registered in the area related to that VLR.

EQUIPMENT IDENTIFY REGISTEREIR is a database that stores the IMEI numbers for all registered ME units. The IMEI uniquely identifies all registered ME. There is generally one EIR per PLMN. The EIR keeps track of all ME units in the PLMN. It maintains various lists of message. There are three classes of ME that are stored in the database, and each group has different characteristics.

• White List: contains those IMEIs that are known to have been assigned to valid MS’s. This is the category of genuine equipment.

• Black List: contains IMEIs of mobiles that have been reported stolen.

• Gray List: contains IMEIs of mobiles that have problems (for example, faulty software, wrong make of the equipment). This list contains all MEs with faults not important enough for barring.

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AUTHENTICATION CENTERThe AUC stores information that is necessary to protect communication through the air interface against intrusions, to which the mobile is vulnerable. The legitimacy of the subscriber is established through authentication and ciphering, which protects the user information against unwanted disclosure. Authentication information and ciphering keys are stored in a database within the AUC, which protects the user information against unwanted disclosure and access.

PUBLIC SWITCH TELEPHONE NETWORKThe public switched telephone network (PSTN) is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telephone operators, providing infrastructure and services for public telecommunication. The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing any telephone in the world to communicate with any other.

OPERATION AND MAINTENANCE CENTERThe operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network..

FEATURES OF GSM:

• GSM is already used worldwide with over 450 million subscribers.• International roaming permits subscribers to use one phone

throughout Western Europe. CDMA will work in Asia, but not France, Germany, the U.K. and other popular European destinations.

• GSM is mature, having started in the mid-80s. This maturity means a more stable network with robust features. CDMA is still building its network.

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• The availability of Subscriber Identity Modules, which are smart cards that provide secure data encryption give GSM m-commerce advantages.

GENERAL PACKET RADIO SERVICE (GPRS)

General packet radio service (GPRS) is a packet oriented mobile data service available to users of the 2G cellular communication systems, global system for mobile communications (GSM), as well as in the 3G systems. In 2G systems, GPRS provides data rates of 56-114 kbps. It provides moderate speed data transfer, by using unused time division multiple access (TDMA) channels.

Its supported protocols are Internet Protocol (IP), Point to Point Protocol (PPP) and X.25.

GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is using the capacity or is in an idle state. GPRS is a best effort packet switched service, as opposed to circuit switching, where a certain Quality of service (QoS) is guaranteed during the connection for non-mobile users.

GPRS extends the GSM circuit switched data capabilities and makes the following services possible:

• “ Always on” Internet access• Multimedia messaging service (MMS)• Push to talk over cellular (PoC/PTT)• Instant messaging and presence – wireless village

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• Internet applications for smart devices through wireless application protocol (WAP)

• Point to Point (P2P) service: inter-networking with the internet (IP).

• Increase message sending speed 30 messages per minute approximately.

CODE DIVISION MULTIPLE ACCESS (CDMA)

Code Division Multiple Access (CDMA) consistently provides better capacity for voice and data communications that other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.CDMA is a spread spectrum technology, allowing many users to occupy the same time and frequency allocations in a given band/space. As it name implies, CDMA assigns unique codes to each communication to differentiate it from others in the same spectrum resources, CDMA enables many more people to share the airwaves at the same time than do alternative technologies.

ADVANTAGES OF CDMA:

• Increased cellular communications security.• Simultaneous conversations• Increased efficiency, meaning that the carrier can serve more

subscribers.• Smaller phones• Low power requirements and little cell-to-cell coordination needed

by operators.• Extended reach-beneficial to rural users situated far from cells.

DISADVANTAGES OF CDMA:

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• Due to its proprietary nature, all of CDMA’s flaws are not known to the engineering community.

• CDMA is relatively new, and the network is not as mature as GSM.

• CDMA cannot offer international roaming, a large GSM advantage.

DIFFERENCE BETWEEN CDMA AND GSM:

• The GSM stands for global system for mobile communication and CDMA for code division multiple accesses.

• GSM is a form of multiplexing, which divides the available bandwidth among the different channels. Most of the times the multiplexing used are either TDM (Time Division Multiplexing) or FDM (Frequency Division Multiplexing). On the other hand CDMA is a type of multiple access scheme (which means allotting the given bandwidth to multiple users) and makes use of spread spectrum technique which is essentially increasing the size of spectrum.

• In CDMA each user is provided a unique code and all the conversations between 2 users are coded. This provides a greater level of security to CDMA users than the GSM ones.

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OPTICAL FIBRE

Optical Fiber is new medium, in which information (voice, Data or Video) is transmitted through a glass or plastic fiber, in the form of light, following the transmission sequence give below :

(1) Information is encoded into Electrical Signals.(2) Electrical Signals are converted into light Signals.(3) Light Travels down the Fiber.(4) A Detector Changes the Light Signals into Electrical Signals.(5) Electrical Signals are decoded into Information.

OPTICAL FIBER TRANSMISSION

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ARCHITECTURE OF FIBER:

The optical fiber has two concentric layers called the core and the cladding. The inner core is the light carrying part. The surrounding cladding provides the difference refractive index that allows total internal reflection of light through the core. The index of the cladding is less than 1%, lower than that of the core. Most fibers have an additional coating around the cladding. This buffer coating is a shock absorber and has no optical properties affecting the propagation of light within the fiber.

OPERATIONIn an optical fiber, a refracted ray is one that is refracted from the core into the cladding. Specifically a ray having direction such that where r is the radial distance from the fiber axis, φ(r) is the azimuthal angle of projection of the ray at r on the transverse plane, θ(r) is the angle the ray makes with the fiber axis, n (r) is the refractive index at r, n (a) is the refractive index at the core radius, a. Refracted rays correspond to radiation modes in the terminology of mode descriptors.For the fiber to guide the optical signal, the refractive index of the core must be slightly higher than that of the cladding. In different types of fibers, the core and core-cladding boundary function slightly differently in guiding the signal. Especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding.

The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances. However, some of the light signal degrades within the fiber, mostly due to impurities in the glass. The extent that the signal degrades depends on the purity of the glass and the wavelength of the transmitted light.

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Phenomena of Total internal reflection.

Jacket

CladdingCore

Cladding

Angle of reflection

Angle of incidence

Light at less thancritical angle isabsorbed in jacket

Jacket

Light is propagated by total internal reflection

Jacket

Cladding

Core

(n2)

(n2)

Fig. Total Internal Reflection in an optical Fibre

PROPAGATION OF LIGHT THROUGH FIBRE

CLASSIFICATION:

There are two types of fibers:

(I) Step Index fiber (Step Index fiber)

(II) Graded Index fiber (Graded Index fiber)

(I) STEP-INDEX FIBER: It has a large core, up to 100 microns in diameter. There is a step change between the core-cladding interface. As a result, some of the light rays that make up the digital pulse may travel a direct route, whereas others zigzag as they bounce off the cladding. This type of fiber is best suited for transmission over short distances, in an endoscope, for instance.

(II) GRADED-INDEX FIBER: It contains a core in which the refractive index diminishes gradually from the center axis out toward the cladding. There is gradual change between the core-cladding interface. The higher refractive index at the center makes the light rays moving down the axis advance more slowly than those near the cladding. A digital pulse suffers less dispersion.

11.4 ADVANTAGES OF FIBRE OPTICS:

• SPEED: Fiber optic networks operate at high speeds - up into the gigabits.• BANDWIDTH: large carrying capacity.

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• DISTANCE: Signals can be transmitted further without needing to be refreshed or strengthened.• RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables.• MAINTENANCE: Fiber optic cables costs much less to maintain

CONCLUSION

Engineering student will have to serve in the public and private sector industries and workshop based training and teaching in classroom has advantage but has its own limitation. Practical training is one of the major steps in this direction. I did my training from RTTC BSNL, Lucknow which is one of the best known communication service provider companies of India. The training helps me in gaining in depth knowledge of the working of telephone exchange, various technologies of BSNL GSM, GPRS, MLLN and optical fiber transmission etc.

In the end, I hereby conclude that I have successfully completed my industrial training Mobile Communication System.

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