1Summer Training Report On Basic Telecom Submitted in partial fulfillment of the requirement for the award of the degree of Bachelor of Technology in Electronics and Communication By Subhash Chandra Tank Enrollment No. 11EC001351 Submitted to Department of Electronics and Communication Engineering Sir Padampat Singhania University Udaipur – 313601, Rajasthan India Under the supervision of Mr. PRAMOD TAILOR Junior Telecom Officer BSNL Nimbahera, Rajasthan 312601 2 CERTIFICATE This is to certify that the Internship in ‗BSNL’ being submitted by Subhash Chandra Tank , In fulfilment of the requirement for the award of degree of Bachelor of Technology in discipline of engineering, has been carried out under my supervision and guidance. The matter embodied in this thesis has not been submitted, in part or in full, to any other university or institute for the award of any degree, diploma or certificate. Dr. Achintya Choudhury Dean, School of Engineering Sir Padampat Singhania University Udaipur 313601 Rajasthan, India Prof. Udayprakash R. Singh Head of Department Department of Electronics and Communication Sir Padampat Singhania University Udaipur 313601 Rajasthan, India 3 ACKNOWLEDGEMENT “It is not possible to prepare a project report without the assistance & Encouragement of other people. This one is certainly no exception.” On the very outset of this report, I would like to extend my sincere & heartfelt obligation towards all the personages who have helped me in this endeavour. Without their active guidance, help, cooperation & encouragement, I would not have made headway in the project. I am ineffably indebted to Mr. PRAMOD TAILOR for conscientious guidance and Encouragement to accomplish this assignment. I am extremely thankful and pay my gratitude to department of BSNL for their Valuable guidance and support on completion of this project in its presently. I extend my gratitude to SPSU for giving me this opportunity. I also acknowledge with a deep sense of reverence, my gratitude towards my Parents and member of my family, who has always supported me morally as well as economically. At last but not least gratitude goes to all of my friends who directly or indirectly Helped me to complete this project report. Any omission in this brief acknowledgement does not mean lack of gratitude. Thanking You Subhash Chandra Tank 4 ABSTRACT Spending a period of four weeks with the Telecommunication Networking. The report on how the BSNL Basic Telecome Network work and how to exchange work and how the company work with telecommunication Network. This Report also contains the basic telecommunication that work with all team work of employees and the exchange work. I was in direct selling and, I realized that it is very difficult to understand the behaviour of customers. I am saying this because even though I was associated with a brand, sometimes it was difficult to convince the custom BSNL has a Quality telecommunication system which is demonstrated through its ability to consistently provide product and services that meets customer and applicable regulatory requirements. It aims to enhance customer satisfaction through its effective services. Previously electro mechanically exchange for use in India namely Strowger type exchange, cross bar exchange were there. These Manual telephone exchanges suffered from some disadvantages. To overcome these an automatic exchange was introduced in this system. In this system 1980‘s PITHROTHA LTD. Imtroduced ―C-DOT― exchange in India. Besides C-DOT exchange ILT exchange, E-10B exchange also proved of mild stone in Telecommunication Sector to replace electromechanical exchages, which were most sophisticated and modern latest techniques electronics exchanges. There after it was OCB-283 exchange which proved very important exchange in this series to replace electromechanical exchanges. Now it is ―WLL‖ & ―GSM‖ mobiles which is also proved a mild stone in telecommunication sector. It was 31 st march 2002 when BSNL started these GSM mobile and today it has provided almost 35 lacks mobiles in all over country. 5 CONTENTS CHAPTER NO. PARTILULAR PAGE NO. Cover Page 1 Certificate 2 Acknowledgement 3 Abstract 4 Contents 5-6 List of Figures 7 Introduction to BSNL 8 Profile of the Company 9-10 Facilities / Departments Visited 11 Chapter-1 Telecome Network 12-16 1.1 Call Setup 12 1.2 Electronic Exchange 13 1.3 Carrier Room 13 1.3.1 Conventional Leased Line System 13 1.3.2 Managed Leased Line Network 14 1.4 Main Distribution Frame 14 1.4.1 Function of MDF 14 1.5 Power Plant 15 1.6 How a Telecom Exchange Work 15 1.7 Engine and Alternator 16 6 1.8 OMC 16 1.9 Switches 16 Chapter-2 Switching 17-20 2.1 C-DOT 18 Chapter-3 Mobile Communication 21-24 3.1 Generation Gap 21 3.2 How a call is connected 23 Chapter-4 CDMA 25-26 4.1 Advantage of CDMA 26 Chapter-5 GSM 27-30 5.1 GSM Subsystem 28 5.2 GSM Evoulation 29 5.3 Advantages for Operation 30 Chapter-6 Broadband 31-37 6.1 Feature of Broadband 32 6.2 Wire Line Broadband Technologies 32 6.2.1 ADSL 32 6.2.2 DSL 35 6.2.3 ISDN 35 6.2.4 Advantages 36 6.2.5 BPL 36 6.2.6 Applications of Broadband 37 Chapter-7 Conclusion 38 References 39 7 List of Figures FIGURE NO. Title of Figure Page No. FIG 1.1 How Line Reaches From Subscriber to Exchange 12 FIG 1.2 Main Distribution Frame 14 FIG 1.3 Block Diagram of Telephone Exchange 16 FIG 2.1 General Diagram of a Digital Switch 17 FIG 2.2 C-DOT Rax 19 FIG 2.3 The C-DOT DSS MAX Basic Architecture 20 FIG 3.1 Cell Phone and Base Station 22 FIG 4.1 Different b/w CDMA and Other Systems 26 FIG 5.1 GSM Network Architecture 29 FIG 5.2 Evalution of GSM 29 FIG 6.1 Broadband Connection 34 8 INTRODUCTION The telephone is a telecommunication device that is used to transmit and receive electronically or digitally encoded speech between two or more people conversing. It is one of the most common household appliances in the world today. Most telephone network which allows any phone user to communicate with almost any other user. Telecommunication networks carry information signals among entities, which are geographically far apart. The entities are involved in the process of information transfer that may be in the form of a telephone conversation or a file transfer between two computers or message transfer between two terminals etc. With the rapidelly growing traffic and untargerted growth of cyberspace, telecommunication becomes a fabric of our life. The future challenges are enormous as we anticipate rapid growth items of new services and number of user. Telecommunication has evaluated and growth at an explosive rate in recent years and will undoubtedly continue to do so. The telecommunication links and switching were mainly designed for voice communication. With the appropriate attachments/equipments, they can be used to transmit data. A modern society, therefore needs new facilities including very high bandwidth switched data networks, and large communication satellites with small, cheap earth antennas. 9 COMPANY PROFILE Company Name: Bharat Sanchar Nigam Ltd. Type: State-owned enterprise Founded: 15 September 2000 Headquarters: New Delhi, India Industry: Telecommunications Key people: R.K. Upadhyay (Chairman & MD) Services: Fixed line and mobile telephony, Internet services, digital television, IPTV Revenue : 271.28 billion (2013) 279.33 billion (2012) Operating Income: -79.55 billion (2013) -88.21 billion (2012) Net income: -78.84 billion (2013) -88.51 billion (2012) Total assets: 956.89 billion (2013) 1018.35 billion (2012) Total equity: 956.89 billion (2013) 1018.35 billion (2012) Owner(s): Government of India Employees: 2,44,891 Website: www.bsnl.co.in 10 Bharat Sanchar Nigam Limited is a state-owned telecommunications company headquartered in New Delhi, India. BSNL is one of the largest Indian cellular service providers, with over 87.1 million subscribers as of April 2011, and the largest land line telephone provider in India. BSNL is India‘s oldest and largest communication service provider (CSP). It had a customer base of 90 million as of June 2008. It has footprints throughout India except for the metropolitan cities of Mumbai and New Delhi, which are managed by Mahanagar Telephone Nigam Limited (MTNL). As of June 30, 2010, BSNL had a customer base of 27.45 million wire line and 72.69 million wireless subscribers. BSNL is the only service provider, making focused efforts and planned initiatives to bridge the Rural-Urban Digital Divide ICT sector. In fact there is no telecom operator in the country to beat its reach with its wide network giving services in every nook & corner of country and operates across India except Delhi & Mumbai. Whether it is inaccessible areas of Siachen glacier and North-eastern region of the country BSNL serves its customers with its wide bouquet of telecom services. BSNL is numerous operator of India in all services in its license area. The company offers wide ranging & most transparent tariff schemes designed to suite every customer. BSNL cellular service, Cell One, has 55,140, 282 2G cellular customers and 88,493 3G customers as on 30.11.2009. In basic services, BSNL is miles ahead, with 85 per cent share of the subscriber base and 92 percent share in revenue terms. BSNL has more than 2.5 million WLL subscribers and 2.5 million Internet Customers who access Internet through various modes. BSNL has been adjudged as the NUMBER ONE ISP in the country. BSNL has set up a world class multi-gigabit, multi-protocol convergent IP infrastructure that provides convergent services like voice, data and video through the same Backbone and Broadband Access Network. At present there are 0.6 Million broadband customers. The company has vast experience in Planning, Installation, network integration and Maintenance of Switching & Transmission Networks and also has a world class ISO 9000 certified Telecom Training Institute. 11 Facilities/ Departments Visited Department/ Facility Duration of visit Major equipment/ Software available Name of official under whom training was carried out Frome To Working of Telecom network May 5 th May 10 th C-DOT , MDF, Telecom Network Mr. Pramod Tailor GSM, CDMA and Landline May 10 th May 16 th Sanchar Soft, KENAN FX, and C-DOT Mr. Pradeep Navlakha Broadband and Telecome May 16 th May 23 th Switch Room, OFC Room Mr. Mahesh Joshi Exchange Shifting May 24 th May 24 th Landline Exchange Mr. Mahesh Joshi Telecom network May 24 th May 30 th C-DOT, WLL Mr. Pramod Tailor & Mr. Mahesh Joshi 12 Chapter-1 TELECOM 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. 1.1 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. FIG 1.1 HOW LINE REACHES FROM SUBSCRIBER TO EXCHANGE 13 FUNCTION OF EXCHANGE: Exchange of information with subscriber lines with other exchange. This is done by two type of signaling: 1. Inchannel signaling 2. Common channel signaling Processing of signaling information and controlling the operation of signaling network. Charging and billing. 1.2: 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. 1.3: CARRIER ROOM: Leased line connectivity is provided in carrier room. This room has two parts: 1. Conventional leased line system 2. MLLN 1.3.1: 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. 14 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. 1.3.2: MANAGED LEASED LINE NETWORK: No open wiring. Route can be changed by the computer software In Agra Gate Exchange, we have 3 VMUX of type II. 1.4: 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. FIG 1.2 MDF (REF- 1.4.1) 1.4.1: 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. 15 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. 1.5: 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. 1.6: HOW A TELECOM EXCHANGE WORKS: It require -48 Vdc. A telephone exchange or telephone switch is a system of electronic compo nents that connects telephone calls. A central office is the physical building used to h ouse inside plant equipment including telephone switches, which make telephone calls ―work‖ in the sense of making connections and relaying the speech information. The basic block diagram for a telecom exchange is as follows- 16 Fig 1.3 : Block diagram of telephone exchange 1.7: Engine and Alternator It provides AC output in the event of commercial power supply failure. The diesel engine provides the prime mover to the alternator so that the alternating current is generated to support the exchange systems. 150 KV Generator with 6 Silinder, and it require 24 V DC for Starting System 1.8: OMC (Operation and Maintenance Control) It contains input-output processor terminals, visual display units, printers, cartridges, etc. It controls the entire operation of exchange data and billing data. The new connections, adding and removing of facilities to the subscriber is done in the OMC room. 1.9: Switch It provides the switching facility and connection to the outside of the exchange. The switch room contains actual telephone switching hardware such as cabinets, racks, slots and cards. Switching is the most important part of the exchange process. 17 Chapter-2 SWITCHING A switch is defined as establishing a temporary connection from the calling subscriber to the called subscriber. Switch is a device that makes the connection and breaks the connection. It is a device that channels incoming data from any of the multiple input ports to the specific input that will take the data toward its intended destination. A Digital switching system, in general, is one in which signals are switched in digital form. These signals may represent speech or data. The digital signals of several speech samples are time multiplexed on a common media before being switched through the system. To connect any two subscribers, it is necessary to interconnect the time-slots of the two speech samples which may be on same or different PCM highways. The digitalized speech samples are switched in two modes, viz., Time Switching and Space Switching. Fig 2.1 : General Diagram of a Digital Switch 18 AU : Subscriber rack for feeding current and other functionalities Interface: Interface between main exchange and subscribers/Trunks Switch: Main switching network and other exchange equipment MDD: Magnetic Disk Drive for storing data MTD: Magnetic Tape Drive for backup and regeneration of the exchange OMT: Operation and Maintenance terminal to issue various commands. Control: Processor to control peripherals and interfacing Main Exchange. Printer: To get hard copy for all the reports. Different types of Electronic Switches are – (1) C-DOT : Indian Made (2) E10B : France Made (3) OCB : France Made (4) EWSD : Germany Made Of these, the most important ones include C-DOT and EWSD. Which are mostly used now a days. 2.1 : C-DOT The Centre for Development of Telematics (C-DOT) was established in August 1984 as an autonomous body. Its goal was to develop telecommunication technology to meet the needs of the Indian telecommunication network. In the initial years, a telecom revolution in rural India that was responsible for all-round socio-economic development from global connectivity. As part of its development process, C-DOT spawned equipment manufacturers and component vendors. Research and development facilities were located at its Delhi and Bangalore campuses. 19 Within a very short time, telecom switching products suited to Indian conditions appeared in the form of small rural automatic exchanges (RAXs) and medium size switches as SBMs for towns. This was followed by higher capacity digital switches known as main automatic exchanges (MAXs). C-DOT technology spread across the country through its licensed manufacturers.. Beginning with digital switching systems, C-DOT developed products for optical, satellite and wireless communication from circuit switching technology, ATM and next generation networks. From a purely hardware development centre, it diversified into development of telecom software like IN, NMS, Data Clearing House and from a protected environment of closed market to an open and competitive market. While developing the RAX/MAX digital switches, C-DOT also evolved processes and procedures for manufacturing the switches in Indian factories which set up an Indian manufacturing vendor base. Later, C-DOT projects included central monitoring systems for telecom security, for the Indian government. Fig 2.2 : C-DOT Rax 20 Block diagram :C-DOT DSS MAX exchange can be configured using four basic modules Base Module Central Module Administrative Module Input Output Module Fig 2.3: The C-DOT DSS MAX Basic Architecture 21 Chapter-3 MOBILE COMMUNICATION A mobile phone, cell phone or hand phone is an electronic device used to make mobile telephone calls across a wide geographic area, served by many public cells, allowing the user to be mobile. By contrast, a cordless telephone is used only within the range of a single, private base station, for example within a home or an office. A mobile phone can make and receive telephone calls to and from the public telephone network which includes other mobiles and fixed-line phones across the world. It does this by connecting to a cellular network provided by a mobile network operator. In addition to telephony, modern mobile phones also support a wide variety of other services such as text messaging, MMS, email, Internet access, sh ort range wireless communications (infrared, Bluetooth), business applications, gaming and photography. Mobile phones that offer these more general computing capabilities are referred to as smart phones. 3.1: Generation Gap Generation#1 Analog [routines for sending voice] All systems are incompatible No international roaming Generation#2 Digital [voice encoding] Increased capacity More security Compatibility Can use TDMA or CDMA for increasing capacity 22 Generation#2.5 Packet-switching Connection to the internet is paid by packets and not by connection time. Connection to internet is cheaper and faster [up to 56KBps] Generation#3 The present future Permanent web connection at 2Mbps Internet, phone and media: 3 in 1 The standard based on GSM is called UMTS. The EDGE standard is the development of GSM towards 3G. The genius of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a city, so that millions of people can use cell phones simultaneously. In a typical analog cell-phone system, the cell-phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10squaremiles (26 square 22ilometres). Cells are normally thought of as hexagons on a big hexagonal grid, like this: Fig 3.1: Cell Phones and base Stations 23 3.2 : HOW A CALL IS CONNECTED When you first power up the phone, it listens for an SID on the control channel. The control channel is a special frequency that the phone and base station use to talk to one another about things like call set-up and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range and displays a ―no service‖ message. When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs match, the phone knows that the cell it is communicating with is part of its home system. Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone‘s location in a database — this way, the MTSO knows which cell you are in when it wants to ring your phone. The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in. The MTSO picks a frequency pair that your phone will use in that cell to take the call. The MTSO communicates with your phone over the control channel to tell it which frequencies to use, and once your phone and the tower switch on those frequencies, the call is connected. Now, you are talking by two-way radio to a friend. As you move toward the edge of your cell, your cell‘s base station notes that your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) sees 24 your phone‘s signal strength increasing. The two base stations coordinate with each other through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell. Let‘s say you‘re on the phone and you move from one cell to another — but the cell you move into is covered by another service provider, not yours. Instead of dropping the call, it‘ll actually be handed off to the other service provider. If the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database to confirm that the SID of the phone you are using is valid. Your home system verify your phone to the local MTSO, which then tracks your phone as you move through its cells. And the amazing thing is that all of this happens within seconds. 25 Chapter- 4 CDMA One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a band of frequencies. This concept is called multiple access. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physicalchannel. By contrast, time division multiple access (TDMA) divides access by time,w hile frequency-division multiple access(FDMA) divides it by frequency. CDMA is a form of spreadspectrumsignalling, since the modulated coded signal has a much higher data bandwidth than the data being communicated. FDMA - Different users use different frequency TDMA - Different user use different time slotof one frequency CDMA - Different user use same frequency at the same time, but with different spreading code CDMA is a spread spectrum multiple access technique. A spread spectrum technique spreading the bandwidth of the data uniformly for the same transmitted power. Spreading code is a pseudo-random code that has a narrow Ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined via bitwise XOR(exclusive OR) with the faster code. Each user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. The best performance will occur when there is good separation between the signal of a desired user and the 26 signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user‘s code then the correlation function will be high and the system can extract that signal. If the desired user‘s code has nothing in common with the signal the correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross correlation. If the code is correlated with the signal at any time offset other than zero, the correlation should be as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference. 4.1: Advantages of CDMA Frequency reuse factor is 1. Network design and expanding become much easier. Large Coverage, almost 2 times than GSM, saves money for operators. High spectrum capacity 8—10 times than AMPS, 4²6 times than GSM. High privacy, hard to wiretapping. Perfect Power Control and voice activation make the MS power low, healthy for body green mobile phone. Use soft handoff, decreases call-drop rate. CDMA – ―make before break‖---soft handoff Other systems – ―make after break‖---hard handoff Fig 4.1: Differences b/w CDMA and other systems 27 Chapter-5 GSM GSM (Global System for Mobile Communications) is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe technologies for second generation (or ―2G‖) digital cellular networks. Developed as a replacement for first generation analog cellular networks, the GSM standard originally described a digital, circuit switched network optimized for full duplex voice telephony. The standard was expanded over time to include first circuit switched data transport, then packet data transport via GPRS. Packet data transmission speeds were later increased via EDGE. The GSM standard is succeeded by the third generation (or ―3G‖)UMTS standard developed by the 3GPP. GSM networks will evolve further as they begin to incorporate fourth generation (or ―4G‖) LTE Advanced standards.‖GSM‖ is a trademark owned by the GSM Association. GSM is a cellular network, which means that mobile phones connect to it by searching for cells in the immediate vicinity. There are five different cell sizes in a GSM network² macro, micro, pico, femto and umbrella cells. The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average roof top level. Micro cells are cells whose antenna height is under average roof top level; they are typically used in urban areas. Pico cells are small cells whose coverage diameter is a few dozen metres; they are mainly used indoors. Femto cells are cells designed for use in residential or small business environments and connect to the service provider‘s network via a broadband internet connection. Umbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells. 28 Cell horizontal radius varies depending on antenna height, antenna gain and propagation conditions from a couple of hundred meters to several tens of kilometres. The longest distance the GSM specification supports in practical use is 35 kilometres (22 mi). There are also several implementations of the concept of an extended cell, where the cell radius could be double or even more, depending on the antenna system, the type of terrain and the timing advance. Indoor coverage is also supported by GSM and may be achieved by using an indoor microcell base station, or an indoor repeater with distributed indoor antennas fed through power splitters, to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. These are typically deployed when a lot of call capacity is needed indoors; for example, in shopping centres or airports. However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of the radio signals from any nearby cell. The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first smoothened with a Gaussian low-pass filter prior to being fed to a frequency modulator, which greatly reduces the interference to neighbouring channels (adjacent-channel interference). 5.1: GSM subsystems Network Subsystem: includes the equipments and functions related to end-to-end call. Radio Subsystem: includes the equipments and functions related to the management of the connections on the radio path. Operations and Maintenance subsystem: includes the operation and maintenance of GSM equipment for the radio and network interface. - 29 Fig 5.1: GSM Network Architecture 5.2: GSM Evolution Fig 5.2.: Evolution of GSM 30 5.3: Advantages for Operators More revenue : By providing more than a mobile connection. Also operator can charge on the basis of type and amount of content accessed. Huge Potential Market for Data Services: Mobile Phone and Internet, both are fastest growing technologies and GPRS is the merger of two. Fast Roll-out and Continuous Network Expansion: GPRS is an integral part of GSM. GPRS uses excess voice capacity for data: GPRS Packets are transmitted in short, free periods between busy hour calls. 31 Chapter-6 BROADBAND An ―always-on‖ data connection that is able to support interactive services including Internet access and has the capability of the minimum download speed of 256 kilo bits per second (kbps) to an individual subscriber from the Point Of Presence (POP) of the service provider is called Broadband. Data rates are defined in terms of maximum download because network and server conditions significantly affect the maximum speeds that can be achieved and because common consumer broadband technologies such as ADSL are ―asymmetric‖ supporting much lower maximum upload data rate than download. In practice, the advertised maximum bandwidth is not always reliably available to the customer; physical Link quality can vary, and ISPs usually allow a greater number of subscribers than their backbone connection or neighb ourhood accessnetwork can handle, under the assumption that most users will not be using their full connection capacity very frequently. This aggregation strategy (known as a contended service) works more often than not, so users can typically burst to their full bandwidth most of the time however, peer-to-peer (P2P) filesharing systems, often requiring extended durations of high bandwidth usage, violate these assumptions, and can cause major problems for ISPs. In some cases the contention ratio, or a download cap, is agreed in the contract, and businesses and other customers, who need a lower contention ratio or even an uncondensed service, are typically charged more. When traffic is particularly heavy, the ISP can deliberately throttle back user traffic, or just some kinds of traffic. This is known as traffic shaping. Careful use of traffics happing by the network provider can ensure quality of service for time critical services even one extremely busy networks, but overuse can lead to 32 concerns about network neutrality if certain types of traffic are severely or completely blocked. 6.1: FEATURES OF BROADBAND Fast connection to the Internet Access to the services which would otherwise be impossible on a slower dial up connection. These include facilities such as downloading music or video footage, listening to your favourite radio station or downloading (or sending) large attached files with emails. “Always-on” connection Means that you are permanently connected to the internet; hence no need to dial up connection every time you want to surf the web, send email, etc. Flat-rate billing If you choose an uncapped rate there will be no additional charges for the time you are online. You can use it as much or as little as you would like, for a fixed fee. Some connections are available at a lower cost, but limit you to the amount of data being downloaded (known as ‗capped rate‘). Dedicated connection Simultaneous use of both telephone & data line. 6.2: WIRE LINE BROADBAND TECHNOLOGIES : 6.2.1: ADSL (A symmetric Digital Subscriber Line) ADSL exploits the copper wires which have a much greater bandwidth or range of frequencies than that demanded for voice without disturbing the line‘s ability to carry phone conversations. The A stands for asymmetric, meaning that data transmission rate is not the same in both directions i.e., more bandwidth, or data-carrying capacity, is devoted to data travelling downstream-from the Internet to your PC-than to upstream data travelling 33 from your PC to the Internet. The reason for the imbalance is that, generally upstream traffic is very limited to a few words at a time, like for example ±an URL request and downstream traffic, carrying graphics, multimedia, and shareware program downloads needs the extra capacity. An ADSL circuit connects an ADSL modem on each end of a twisted pair telephone line, creating three information channels 1. A high speed downstream channel 2. A medium speed duplex channel 3. A basic telephone service channel The basic telephone service channel is split off from the digital modem by filters, thus guaranteeing uninterrupted basic telephone service, even if ADSL fails. 6.2.1.1: Features of ADSL Allows simultaneous access to the line by the telephone and the computer In case of power/ADSL failure, data transmission is lost but basic telephone service will be operational ADSL Provides 16-1000 kbps upstream and 1.5-24 Mbps downstream. It can work up to a distance of 3.7 to 5.5 km depending upon the speed required. 6.2.1.2: Advantages of ADSL You can leave your Internet connection open and still use the phone line for voice calls. The speed is much higher than a regular modem DSL doesn‘t necessarily require new wiring; it can use the phone line you already have. In BSNL, Broadband Access Network, there has to be an ADSL modem on either end of the telephone line. One end of the line, terminated at Subscriber‘s premises is first connected to the splitter which filter out the low 34 frequency voice to be connected to the telephone instrument. The higher frequency, which carries the data is connected to the modem. The connectivity is shown in the figure 1 given below. Fig 6.1: Broadband Connections The other end is terminated at service providers end which also has similar arrangement. But at service providers point, numerous ADSL lines are terminated and there has to be equal number of splitters and ADSL modems. So instead of separate splitters & modems, it is aggregated into single nit called Digital Subscriber Line Access Multiplexer (DSLAM). So one side of the DSLAM interfaces the subscriber lines and the other side interfaces to the core network through several LAN switches. Before being given access to the subscriber, subscriber is authenticated based on username and password by the BRAS. After authentication(verification of username & password), subscriber is authorised to access the Providers core network and in turn is connected to whatever service or content the subscriber demands and accounting is initiated based on either time based or volume based billing. The LAN Switch collocated with the Core router is termed as Tier ± 1 Switch and all other LAN switches which 35 aggregate the DSLAM are called Tier -2 switches. DSLAMs can also be aggregated to Tier -1switch. The various components in the Broadband Access Network are Customer Premises Equipment(CPE) (ADSL Modem & Splitter) Digital Subscriber Line Access Multiplexer (DSLAM) LAN Switches: for aggregating DSLAM (Tier -1 & Tier -2 Switch) Broadband Remote Access Server (BRAS) 6.2.2: DSL DSL is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term Digital Subscriber Line is widely understood to mean Asymmetric Digital Subscriber Line (ADSL), the most commonly installed technical variety of DSL. DSL service is delivered simultaneously with regular telephone on the same telephone line. This is possible because DSL uses a higher frequency. These frequency bands are subsequently separated by filtering. The data throughput of consumer DSL services typically ranges from 256 Kb/s to 20 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and service-level implementation. In ADSL, the data throughput in the upstream direction, (i.e. in the direction to the service provider) is lower, hence the designation of asymmetric service. In Symmetric Digital Subscriber Line (SDSL) service, the downstream and upstream data rates are equal. 6.2.3: ISDN Integrated Service Digital Network (ISDN) is one of the oldest broadband digital access methods for consumers and businesses to connect to the Internet. It is a telephone data service standard. A basic rate ISDN line 36 (known as ISDN-BRI) is an ISDN line with 2 data ―bearer‖ channels (DS0 -64 Kbit/s each). Using ISDN terminal adapters (erroneously called modems), it is possible to bond together 2 or more separate ISDN-BRI lines to reach bandwidths of 256 Kbit/s or more. The ISDN channel bonding technology has been used for video conference applications and broadband data transmission. 6.2.4: Advantages: Constant data rate at 64 Kbit/s for each DS0 channel. Two way broadband symmetric data transmission, unlike ADSL. One of the data channels can be used for phone conversation without disturbing the data transmission through the other data channel. When a phone call is ended, the bearer channel can immediately dial and re-connect itself to the data call. Call setup is very quick. Low latency ISDN Voice clarity is unmatched by other phone services. Caller ID is almost always available for no additional fee. Maximum distance from the central office is much greater than it is for DSL. 6.2.5: BPL Broadband over power lines (BPL), also known as power-line Internet or power band, is the use of PLC technology to provide broadband Internet access through ordinary power lines. A computer (or any other device) would need only to plug a BPL ―modem‖ into any outlet in an equipped building to have high-speed Internet-access. BPL my offer benefits over regular cable or DSL connections: the extensiv e infrastructurealready available appears to allow people in remote locations to access the Internet with relatively little equipment investment by 37 the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up. Cost of running wires such as Ethernet in many buildings can be prohibitive; Relying on wireless has number of predictable problems including security, limited maximum throughput and inability to power devices efficiently. 6.2.6: APPLICATIONS OF BROADBAND Basic WWW browsing and Email access Run Servers (Web / FTP) Business tariff, can depend on company Some technologies are asymmetric (cable, ADSL) Video On Demand (VOD) Audio Streams (Internet Radio) Fast File Transfers (Possibility of downloading large files in short period of time) 38 Chapter-7 CONCLUSION Bharat Sanchar Nigam Ltd. Formed in October 2000 is the world‘s 7 th largest Telecommunications company providing comprehensive range of telecom services in India: Wired-line, CDMA mobile, GSM mobile, Internet, Broadband, Carrier Service, MPLS-VPN,VSAT, VoIP services, IN services, etc. Presently it is one of the largest and leading public sector unit in India. The training was aimed at providing the students with basic knowledge about telecommunications and the working of telecom exchanges. The various aspects regarding the working of telecommunications, the various modules in the telecom exchange and their importance in the exchange process was explained. Both wired and wireless (mobile) communication aspects were dealed with. Mobile communication ± both CDMA and GSM ± was extensively covered. Also, information about broadband internet and its requirements was provided. Along with technical lecture sessions, practical sessions were also conducted where the telecom exchanges and their equipment were shown and explained. 39 REFERENCES BSNL In-plant training material www.bsnl.co.in www. .wikipedia.org Telecommunication system engineering by Roger L Freeman