Project Report On Satellite Communication

Transcript

AMITY SCHOOL OF ENGINEERING & TECHNOLOGY, NOIDA UTTAR PRADESH PROJECT REPORT On SATELLITE COMMUNICATION AND LAN/WAN NETWORKING TECHNIQUES. PROGRAMME : B.TECH ECE (2007-2011) SEMESTER Faculty Guide: Mr. Devesh Kumar : SEVENTH Submitted by: ayeshna mehra A2305119228 CERTIFICATE This is to certify that the project entitled “SATELLITE COMMUNICATION AND LAN/WAN NETWORKING TECHNIQUES” is a bona fide record of the industrial training project under my supervision and guidance, guidance, in partial fulfillment fulfillment of the requirements requirements for the award of Degree Degree of Bachelor of Technology in Electronic and Communication Engineering from Amity School of Engineering and Technology, Noida, Sec-125 . Mr. DEVESH KUMAR (guide) Dept. of  Electronics & Communication Engineering ACKNOWLEDGEMENT Setting an endeavor may not always be an easy task; obstacles are bound to come in its way and when this happens, help is welcome and needless to say without help of those  people whom whom I am mentioning mentioning here, here, this endeavor endeavor would would not have been been successful. successful. The completion of any project brings with it a sense of satisfaction, but it is never  complete complete without thanking those people who made it possible possible and whose constant support has crowned our efforts with success. I would like to express my gratitude to Ms Ms Meena agarwal, DGM( IT) at NTPC for encouraging and inspiring me to carry out the project in the Central Satellite Earth Station, NTPC Station,  NTPC.. I would also like to thank all the staff members of NTPC for providing me with the required facilities and support towards the completion of the project .My sincere thanks to my faculty guide Mr. Devesh Kumar  for his constant support and guidance. Without his corporation the project would not have  been completed completed successfully. successfully. . I am extremely extremely happy to acknowledge acknowledge and express my sincere gratitude to my parents for their constant support and encouragement. ABSTRACT The project basically deals with the study of satellite communication and how it works. Organizations with many remote affiliates can create a private high-speed satellite intranet, which links the main office reliably with all local sites. Within and amongst institutions there is an ever-growing need to communicate and to enhance the existing networks. These networks need high speed, reliable and cost-effective communications. This is especially true when the locations are dispersed over remote regions , and barely connectable via a terrestrial network infrastructure. In this case, satellite communications are an effective way way to provid providee priva private te or secu secure re data data netwo network rks. s. There Therefor foree for for comm communi unica cati tion on and exchange of data between various sites a central satellite earth station has been installed at  NTPC Noida since it is the hub station station for communication communication with its various other sites. sites.  NTPC Satcom Network Network is working in STAR Configuration Configuration with this Hub Earth Station .NTPC has been assigned transponder number 3 in the recently launched satellite INSAT 3E. The project covers detailed detailed study of the ground segment of satellite satellite communication. communication. The transm transmiss ission ion and receive receive path which which include include various various sub compone components nts like MODEM MODEM,, up/down Converters etc have been studied and how they are connected practically.  NTPC has a LAN for exchange of information information within within the building and a WAN for  communication with various other sites so the project also covers a brief study of LAN and WAN networking techniques and basics of services like audio and video conferencing. Figure (1) - VSAT Star-shaped Network  TABLE OF CONTENTS CONTENTS Certificate Acknowledgement Abstract Chapter 1 : INTRODUCTION COMPANY NY PROFILE PROFILE Chapter 2 :  NTPC COMPA 2.1 Overview of organization Chapter 3 : INTRODUCTION TO NETWORKING 3.1 Introduction 3.2 Networking topologies 3.3 Types of network  3.4 Local area network  3.5 Wide area network  Chapter 4 : SATELLITE COMMUNICATION OVERVIEW 4.1 How it works 4.2 Types Types of satellite satellite 4.3 Types Types of orbits orbits 4.4 Frequency bands Chapter 5 : VERY SMALL APERTURE TERMINAL 5.1 VSAT system architecture 5.2 VSAT topologies 5.3 Hub station Chapter 6 : CENTRAL SATELLITE EARTH STATION NTPC NOIDA 6.1 Specifications 6.2 CSES block diagram 6.3 Functioning of CSES 6.4 Various subsystems 6.5 Multiple access schemes 6.6 Implementing VSAT Chapter 7 :  NTPC NETWO NETWORK RK TODAY TODAY Chapter 8 : CONCLUSION Chapter 9 : FUTURE IMPLICATIONS Chapter 10: REFERENCES CHAPTER 1 INTRODUCTION A satellite is an object that orbits or revolves around another object. Man-made satellites  placed around the earth for the purpose of communicatio communication n are called as communication communication satellites. satellites. They are highly specialized wireless receiver/transm receiver/transmitters itters that are launched by a rocket and placed in orbit around the Earth. There are hundreds of satellites currently in operation. Satellite communication is one particular example of wireless communication systems. Similar and maybe more familiar examples of wireless systems are radio and television broadcasting and mobile and cordless telephones. Satellite communication is very simply the communication of the satellite in space with large number of earth stations on the ground. Users are the ones who generate baseband signals, which is processed at the earth earth statio station n and then transm transmitt itted ed to the satell satellite ite throug through h dish dish antennas antennas.. The satell satellite ite receives the uplink frequency and the transponder present inside the satellite does the  processing  processing function function and frequency frequency down conversion conversion in order to transmit transmit the downlink  signal at different frequency. The earth station then receives the signal from the satellite through parabolic dish antenna and processes it to get back the baseband signal. There are two basic elements of satellite communication:1) Sp Spac acee seg segm ment ent 2) Gr Grou oun nd segm segment ent The space segment is primarily the satellite that is used for communication. The satellites used are exclusively in the Geo-stationary orbit, located on an arc 36,000 km above the equator. equator. This This segment segment is availab available le from from organiz organizati ations ons that have procure procured d satell satellites ites,, arranged launch and who operate these satellites on a commercial basis. In addition to internat international ional agencies, agencies, a number number of private private players players have emerged emerged who own or lease lease satellites which are used to carry their own or their customer’s data-traffic. The ground segment is primarily called the Earth terminal segment or the earth station. Earth stations are located either on the surface of the earth, or within earth’s atmosphere. It maintains maintains communication communication link between between earth and the satellite. satellite. . Major components of a earth station are generally grouped in two categories, ODU (outdoor unit) and IDU (indoor  unit). The indoor unit interfaces with the end user equipment like stand alone PCs, LANs, Telephones.  NTPC has a LAN for exchange of information information within within the building. building. A network network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers,  but often often link hundreds hundreds of computers computers used used by thousands thousands of people. people. Communication Communication to to other  sites takes place by a WAN via satellite. A Wide area networking combines multiple LANs that are geographically separate. CHAPTER 2 NATIONAL THERMAL POWER CORPORATION CORPORATION COMPANY PROFILE 2.1 Overview of Organization India’s largest largest power company, NTPC was set up in 1975 to accelerate accelerate power development in India. NTPC is emerging as a diversified power major with presence in the entire value chain of the power generation business. Apart from power generation, which is the mainstay of the company, NTPC has already ventured into consultancy, power trading, ash utilization and coal mining. NTPC ranked 317th in the ‘2009, Forbes Global 2000’ ranking of the World’s biggest companies. The total installed capacity of the company is 31,704 MW (including JVs) with 15 coal  based and 7 gas based stations, stations, located across across the country. In addition addition under JVs, 3 stations stations are coal based & another station uses naphtha/LNG naphtha/LNG as fuel. By 2017, the power generation generation  portfolio  portfolio is expected expected to have a diversified diversified fuel mix with coal based capacity of around 53000 MW, 10000 MW through gas, 9000 MW through Hydro generation, about 2000 MW from nuclear sources and around 1000 MW from Renewable Energy Sources (RES). NTPC has adopted a multi-pronged growth strategy which includes capacity addition through green field projects, expansion of existing stations, joint ventures, subsidiaries and takeover  of stations.  NTPC has been operating operating its plants at high efficiency efficiency levels. Although Although the company has 18.10% of the total national capacity it contributes 28.60% of total power generation due to its focus on high efficiency. In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of 5.25% as fresh issue and 5.25% as offer for sale by Government of India. NTPC thus became a listed company in November 2004 with the government holding 89.5% of the equity share capital. The rest is held by Institutional Investors and the Public. The issue was a resounding succ succes ess. s. NTPC NTPC is amon among g the the larg larges estt five five comp compan anie iess in Indi Indiaa in term termss of mark market et capitalization. At NTPC,  People before Plant Load Factor  is the mantra that guides all HR related  policies.  policies. NTPC has been awarded awarded No.1, Best Best Workplace Workplace in India India among large large organizations organizations and the best PSU for the year 2009, by the Great Places to Work Institute, Institute, India Chapter in collaboration with The Economic Times.  NTPC has integrated integrated Informatio Information n Technology Technology as a strategic tool in its manageme management nt systems and aligned Business & Process based on Enterprise Resource planning using SAP AG Product. Services covered include the following: German business business software software major SAP selecting selecting its entire 1)  NTPC Ltd has mandated German module and has pioneered as first organization in the country to implement all modules. ERP software package that has helped NTPC in for better control over a host host of busine business ss activi activitie tiess such such as produc producti tion, on, sales sales,, Mate Materi rial al manag managem ement ent,, Codif Codifica icati tion on of Item Items, s, Plant Plant & Oper Operat atio ion n Manag Managem ement ent,, Cust Custome omerr Relat Relation ion Manag Managem ement ent , C-Fo C-Folde lderr for recei receivin ving g draw drawing ings, s, Inspe Inspect ction ion manag managem ement ent,, eProcurement, Knowledge portal, etc. across the organizational structure. 2) Management Information Systems 3) Satellite Communication captive network of NTPC established since 1989 hiring 1/2 Transponders on INSAT series of Satellites. 4) Reviewed IT infrastructure for Network Strengthening in view of ERP, VideoConferencing, and other applications with retaining consultants from IIT-D . 5) Esta Establ blis ished hed Mult Multii Prot Protoco ocoll Label Label Swit Switchi ching ng (MPL (MPLS) S) Netw Network ork with with BSNL BSNL's 's Backbone for Wide area Network connectivity. IP packets to travel through WAN networks as well as to ease the routers' overhead by simplifying routing tables. CHAPTER 3 INTRODUCTION TO NETWORKING NETWORKING 3.1 INTRODUCTION Networking is the concept of sharing resources and services. A network of  computers is a group of interconnected systems sharing resources and interacting using a shared communications communications link. A network, network, therefore, therefore, is a set of interconnected interconnected systems systems with something to share. The shared resource can be data, a printer, a fax modem, or a service such as a database or an email system. The individual systems must be connected through a  pathway (called the transmissio transmission n medium) medium) that is used to transmit transmit the resource or service  between  between the computers. computers. All systems systems on the pathway must follow a set of common common communication rules for data to arrive at its intended destination and for the sending and receiving systems to understand each other. The rules governing computer communication are called protocols. In summary, all networks must have the following: 1. A resou resource rce to to share share (re (reso sour urce ce)) 2. A pathway pathway to to transfe transferr data (tran (transmi smissi ssion on medium medium)) 3. A set of rule ruless governi governing ng how to commu communica nicate te (protoc (protocols ols)) Figure(2) - Simplest form of a computer network  Having a transmission pathway does not always guarantee comm commun unic icat atio ion. n. When hen two two enti entiti ties es comm commun unic icat ate, e, they they do not not mere merely ly exch exchan ange ge information; rather, they must understand the information they receive from each other. The goal goal of comp comput uter er netwo networki rking ng,, ther theref efor ore, e, is not simp simply ly to excha exchange nge data data but to understand and use data received from other entities on the network. An analogy is people speaking, just because two people can speak, it does not mean they automatically can understand each other. These two people might speak different languages or interpret words differently. One person might use sign language, while the other uses spoken language. As in human communication, even though you have two entities who "speak," there is no guarantee guarantee they will be able to understand understand each other. Just because two computers are sharing resources, it does not necessarily mean they can communicate. Figure (3) - An analogy of a computer network  Because computers can be used in different ways and can be located at different distances from each other, enabling computers to communicate often can be a daunting task that draws on a wide variety of technologies. The two main reasons for using computer networking are to provide serv service icess and and to reduc reducee equip equipme ment nt costs costs.. Netw Networ orks ks enabl enablee comput computer erss to share share thei their  r  resources by offering services to other computers and users on a network. The following are specific reasons for networking PCs 1. Shari haring ng file filess 2. Sharing Sharing printer printerss and and othe otherr device devicess 3. Enablin Enabling g centraliz centralized ed administ administrat ration ion and security security of the resources resources within within the system. 4. Supporting network applications such as electronic mail and database services 5. Limi Limite ted d res resou ourc rces es 6. Desi Desire re to to share share the the reso resour urce cess 7. Cost Cost Reduc educti tion on Today, that's a limiting view, because the most important resource is information. Network lets us share information and Resource Sharing achieves the same.  Resource  Resource Sharing  The purpose of many computer networks is to permit a far-flung community of  users to share computer resources. Many such users now have their own microcomputers, so the shared resources have to be interesting interesting enough to warrant access via a networ n etwork. k. The facilities accessible by networks are in fact becoming more interesting at a rapid rate. The remot remotee comput computer er may may conta contain in soft softwa ware re that that a user user needs needs to emplo employ. y. It may may be  proprietary  proprietary software kept at one location. location. It may require a larger larger machine than any at the user's user's locat location ion.. The The dist distant ant comp comput uter er may may prov provide ide acces accesss to data data that that is stor stored ed and maintai maintained ned at its location. location. Someti Sometimes mes the remote remote machine machine controls controls a large large or special special  printing facility. facility. Sometimes Sometimes the remote remote machine compiles compiles programs programs that are used on smaller peripheral machines. Cost Reduction There are various aspects of technology that are likely to force the price of  term termina inall usage usage dras drasti tica call lly y lowe lower. r. This This is impor importa tant nt becau because se almo almost st all all aspe aspect ctss of  telecommunications are characterized by high price elasticity. In other words, when the  price comes comes down, down, the usage usage goes up. up. 3.2 NETWORK NETWORK TOPOLOGIE TOPOLOGIES S The term topology refers to the way a network is laid out, either physically or  logically. Two or more devices connect to a link; two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and linking linking devices devices (usuall (usually y called called nodes) nodes) to each each other. other. There There are five five basic basic topolog topologies ies  possible:  possible: mesh, mesh, star, tree, tree, bus, and ring. Figure(4) - Multipoint Line Configuration Figure (5) - Categories of Topologies These five labels describe how the devices in a network are interconnected rather  than their physical arrangement. For example, having a star topology does not mean that all of the computers in the network must be placed physically around a hub in a star shape. A consideration when choosing a topology is the relative status of the devices be linked. Two relationships are possible: peer-to-peer, where the devices share the link equally, and  primary-second  primary-secondary, ary, where one device controls traffic and the others must transmit through through it. Ring and mesh topologies are more convenient for peer-to-peer transmission, while star  and tree are more convenient for primary-secondary, bus topology is equally convenient for  either. •  Mesh In a mesh topology, topology, every device has a dedicated dedicated point-to-point point-to-point link to every other  device. The term dedicated means that the link carries traffic only between the two devices it connects. A fully connected mesh network therefore has n*(n - l)/2 physical channels to link n devices. To accommodate that many links, every device on the network must have 7 input/output (I/O) ports. Figure (6) - Fully Connected Mesh Mesh Topology A mesh offers several advantages over other network topologies. First, the use of  dedica dedicate ted d links links guar guarant antee eess that that each each conne connect ction ion can carry carry its its own own data data load, load, thus thus eliminating the traffic problems that can occur when links must be shared by multiple devices. Second, a mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system. Another advantage is privacy or security. When every message sent travels along dedicated line, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages. Finally Finally,, point-t point-to-po o-point int links links make fault fault identif identificat ication ion and fault fault isolat isolation ion easy. easy. Traffic can be routed to avoid links with suspected problems. This facility enables the network manager to discover the precise location of the fault and aids in finding its cause and solution. The main disadvantages of a mesh are related to the amount of cabling and the number of I/O ports required. First, because every device must be connected to ever other  device, installation and reconfiguration are difficult. Second, the sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate. And, finally, the hardware required connecting each link (I/O ports and cable can be  prohibitively  prohibitively expensive). expensive). For these reasons a mesh topology topology is usually implemented implemented in a limited fashion—for example, as a backbone connecting the main computers of a hybrid network that can include several other topologies. •  Star  In a star topology, each device has a dedicated point-to-point link only to a central controller, controller, usually called a hub. h ub. The devices are not directly directly linked to each other. Unlike a mesh topology, a star topology does not allow direct traffic between devices. The controller  acts as an exchange. If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device. Hub Figure (7) - Star topology A star topology is less expensive than a mesh topology. In a star, each device needs only one link and one I/O port to connect it to any number of others. This factor also makes it easy to install and reconfigure. Far less cabling needs to be housed, and additions, moves, and deletions involve only one connection: between that device and the hub. Other advantages include robustness. If one link fails, only that link is affected. All other links remain active. This factor also lends itself to easy fault identification and fault isolation. As long as the hub is working, it can be used to monitor link problems and  bypass defective defective links. links. However, although a star requires far less cable than a mesh, each node must be linked to a central hub. For this reason more cabling is required in a star than in some other  topologies (such as tree, ring, or bus). • Tree A tree topology is a variation of a star. As in a star, nodes in a tree are linked to a central hub that controls the traffic to the network. However, not every device plugs directly into the central hub. The majority of devices connect to a secondary hub that in turn is connected to the central hub. The central hub in the tree is an active hub. An active hub contains a repeater, which is a hardware device that regenerates the received bit patterns before sending them out. Repeating strengthens trans- missions and increases the distance a signal can travel. Figure (8) - Tree Topology The secondary hubs may be active or passive hubs. A passive hub provides a simple physical connection between the attached devices. The advantages and disadvantages of a tree topology are generally the same as those of a star. The addition of secondary hubs, however, brings two further advantages. First, it allows more devices to be attached to a single central hub and can therefore increase the distance a signal can travel between devices. Second, it allows the network to isola isolate te and priori prioriti tize ze comm communi unica cati tions ons from from diffe differe rent nt comput computer ers. s. For For exam example ple,, the the computers computers attached to one secondary hub can be given priority over computers attached to another secondary secondary hub. In this way, the network network designers and operator operator can guarantee guarantee that time-sensitive data will not have to wait for access to the network. A good example of tree topology can be seen in cable TV technology where the main cable from the main office is divided into main branches and each branch is divided into smaller branches and so on. The hubs are used when a cable is divided. •  Bus The preceding examples all describe point-to-point configurations. A bus topology, on the other hand, is multipoint. Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. As a signal travels along the backbone, some of its energy is transformed into heat. Therefore, it becomes weaker and weaker the farther it has to travel. For this reason there is a limit on the number of taps a bus can support and on the distance between those taps. Advantages of a bus topology include ease of installation. Backbone cable can be laid along the most efficient path, then connected to the nodes by drop lines of various lengths. In this way, a bus uses less cabling than mesh, star, or tree topologies. In a star, for  example, example, four network devices in the same room require four lengths of cable reaching all the way to the hub. In a bus, this redundancy is eliminated. Only the backbone cable stretches through the entire facility. Each drop line has to reach only as far as the nearest  point on the the backbone. backbone. Figure (9) - Bus Topology Disadvantages include difficult reconfiguration and fault isolation. A bus is usually designed to be optimally efficient at installation. It can therefore be difficult to add new devices. As mentioned above, signal reflection at the taps can cause degradation in quality. This This degr degrada adati tion on can be contr control olle led d by limi limiti ting ng the numbe numberr and and spaci spacing ng of devic devices es connec connecte ted d to a give given n lengt length h of cable cable.. Addi Adding ng new device devicess may may there therefor foree requi require re modification or replacement of the backbone. In addition, a fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. The damaged area reflects signals back in the direction of  origin, creating noise in both directions. •  Ring  In a ring topology, each device has a dedicated point-to-point line configuration only with the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. Each device in the ring incorporates a repeater. When a device receives a signal intended for another device, its repeater regenerates the bits and passes them along. A ring is relatively easy to install and reconfigure. Each device is linked only to its immediate neighbors (either physically or logically). To add or delete a device requires moving only two connections. The only constraints are media and traffic considerations (maximum ring length and number of devices). In addition, fault isolation is simplified. Generally in a ring, a signal is circulating at all times. If one device does not receive a signal signal within a specif specified ied period, period, it can issue issue an alarm. alarm. The alarm alarm alerts alerts the networ network  k  operator to the problem and its location. However, unidirectional traffic can be a disadvantage. In a simple ring, a break in the ring (such as a disabled station) can disable the entire network. This weakness can be solved by using a dual ring or a switch capable of closing off the break. Figure (10) - Ring Topology 3.3 TYPES OF NETWORK- LAN, WAN AND MAN Today when we speak of networks, we are generally referring to three primary categories: local area networks, metropolitan area networks, and wide area networks. Into which category a network its size, its ownership, the distance it covers, and its physical architecture determine falls. Figure(11) - Categories of networks  Local Area Network (LAN) A local area network (LAN) is usually privately owned and links the devices in a single office, building, building, or campus. campus. Depending on the needs of an organization organization and the type of technology used, a LAN can be as simple as two PCs and a printer in someone's home offic office, e, or it can extend extend thro throug ughou houtt a compa company ny and incl include ude voice voice,, sound, sound, and vide video o  peripherals.  peripherals. Currently, Currently, LAN LAN size is limited limited to a few kilometer kilometers. s. Figure(12) - LAN LANs are designed to allow resources to be shared between personal computers or  workstations. The resources to be shared can include hardware e.g., a printer, software e.g., an application program, or data. A common example of a LAN, found in many business environm environment ents, s, links links a work work group group of task-r task-relat elated ed compute computers, rs, for exampl example, e, enginee engineering ring workstations workstations or accounting PCs. One of the computers computers may be given a large-capacity disk  drive and become a server to the other clients. Software can be stored on this central server  and used as needed by the whole group. In this example, the size of the LAN may be determined by licensing restrictions on the number of users per copy of software, or by restrictions on the number of users licensed to access the operating system. In addition to size, LANs are distinguished from other types of networks by their  transmission media and topology. In general, a given LAN will use only one type of  transmission medium. The most common LAN topologies are bus, ring, and star. Traditionally, LANs have data rates in the 4 to 16 Mbps range. Today, however speeds are increasing and can reach 100 Mbps with gigabit systems in development.  Metropolitan Area Network (MAN   ) A metropolitan area network (MAN) is designed to extend over an entire city. It may be a single network such as a cable television network, or it may be a means of  connecting a number of LANs into a larger network so that resources may be shared LANto-LAN as well as device-to-device. For example, a company can use a MAN to connect the LANs in all of its offices throughout a city. Figure(13) - MAN A MAN may be wholly owned and operated by a private company, or it may be a service provided by a public company, such as a local telephone company. Many telephone companies provide a popular MAN service called Switched Multi-megabit Data Services (SMDS). Wide Area Network (WAN   ) A wide area network (WAN) provides long-distance transmission of data, voice, image, and video information over large geographical areas that may comprise a country, a continent, or even the whole world. Figure(14) - WAN In contrast to LANs (which depend on their own hardware for transmission), WANs WANs may may util utilize ize publi public, c, lease leased, d, or priva private te comm communi unica cati tion on devic devices es,, usual usually ly in combinations, and can therefore span an unlimited number of miles. A WAN that is wholly owned and used by a single company is often referred to as an enterprise network. 3.4 LOCAL AREA NETWORK NETWORK (LAN) Local area networks, networks, generally generally called LANs, are privately-owne privately-owned d networks networks within a single  building or campus of up to a few kilometres kilometres in size. They are widely used to connect  personal computers and workstations workstations in company offices and factories factories to share resources (e.g., printers) and exchange information. LANs are distinguished from other kinds of  networks by three characteristics: (1) their size, (2) their transmission technology, and (3) their topology. LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance. Knowing this bound makes it possible to use certain kinds of  designs that would not otherwise be possible. It also simplifies network management. LANs transmission technology consisting of a cable to which all the Desktops/Nodes are connected, similar to like telephones connected to an EPABX Exchange, however here the data and voice both are transmitted. Various topologies are possible and are implemented for LANs such as; Star, Bus, or Ring topology. 3.5 WIDE AREA NETWORK  NETWORK  A wide wide area area netwo network, rk, or WAN, WAN, spans spans a larg largee geog geogra raphi phica call area area,, often often a count country ry or  continent. It contains a collection of machines intended for running user (i.e., application)  programs.  programs. These machines are called hosts. The hosts are connected by a communication communication subnet. The hosts are owned by the customers (e.g., people's personal computers), whereas the communication subnet is typically owned and operated by a telephone company or  Internet Internet service provider. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener. Separation of the pure communication aspects of the network (the subnet) from the application aspects (the hosts), greatly simplifies the complete network design. In most wide area networks, the subnet consists of two distinct components: i. Transmission li lines and ii. Switching elements. Transmission lines move bits between machines. They can be made of copper wire, optical fibre, or even radio links whereas; Switchi Switching ng elemen elements ts are special specialized ized compute computers rs that that connect connect three three or more more transm transmiss ission ion lines. lines. When When data data arrive arrive on an incomi incoming ng line, line, the switching switching element element must must choose choose an outgoing line on which to forward them. Figure(15)- WAN CHAPTER 4 SATELLITE COMMUNICATION OVERVIEW 4.1 HOW IT WORKS The basic elements elements of satellite satellite communication communication are the earth stations, terrestrial terrestrial system and the users. The earth stations on the ground linked with a satellite in the space. The user is connected to the earth station through a terrestrial network and this terrestrial network may  be a telephone telephone switch switch or a dedicated dedicated link link to the earth earth station. station. The user user generates generates a baseband baseband signal that is processed through a terrestrial network and transmitted to a satellite. The satellite consists of a large number of repeaters in space, that receives the modulated RF carrier in its uplink frequency spectrum from all the earth stations in the network, amplifies these carriers and retransmits them back to the earth stations in the down link frequency spectrum. To avoid interference the downlink frequency spectrum should be different from the uplink frequency spectrum. spectrum. The signal at the receiving earth station is processed processed to get  back the baseband baseband signal, signal, it is sent to the user through a terrestrial terrestrial network. network. There are various frequency bands utilized by satellites but the most recognized of them is the uplink  frequency of 6 Ghz and the downlink frequency of 4 Ghz. Actually the uplink frequency  band is 5.725 5.725 to 7.075 7.075 Ghz and the actual actual downlink downlink frequency frequency band is is from 3.4 to 4.8 Ghz. Satellite communication is one particular example of wireless communication systems. Similar and maybe more familiar examples of wireless systems are radio and television  broadcasting  broadcasting and mobile mobile and cordless cordless telephones. telephones. 4.2 TYPES OF SATELL SATELLITE:ITE:- The satellite can be classified into two categories: • Active satellite • Passive satellite The major difference between these two is that weather the communication communication relay involves  passive reflect reflection ion or active active electronic electronic system system An active satellite is one which has transmitting transmitting equipment abroad such as a transponder. transponder. It is a device which receives a signal from earth, amplifies it and retransmits it back to earth. A passive satellite merely reflects or scatters the incident radiation from earth. Passive satellite relays would require surface transmitters of greater power than would active relay , however the active satellite relays must carry abroad receiving and transmitting equipment and the necessary power sources. 4.3 DIFFERENT TYPES OF ORBITS Geosynchronous Orbit (GEO): 35,786 km above the earth Figure(16) -GEO • Orbiting at the height of 22,282 miles above the equator (35,786 km), the satellite travels in the same direction and at the same speed as the Earth's rotation on its axis, taking 24 hours to complete a full trip around the globe. Thus, as long as a satellite is  positioned  positioned over the equator in an assigned assigned orbital location, it will appear to be "stationary" with respect to a specific location on the Earth. • A single geostationary satellite can view approximately one third of the Earth's surface. If three satellites are placed at the proper longitude, the height of this orbit allows almost all of the Earth's surface to be covered by the satellites. Medium Earth Orbit (MEO): 8,000-20,000 km above the earth Figure(17) - MEO • These orbits are primarily reserved for communications satellites that cover the  North and and South Pole Pole • Unlike the circular orbit of the geostationary satellites, MEO's are placed in an elliptical (oval-shaped) orbit Low Earth Orbit (LEO): 500-2,000 km above the earth Figure(18) -LEO • These orbits are much closer to the Earth, requiring satellites to travel at a very high speed in order to avoid being pulled out of orbit by Earth's gravity • At LEO, a satellite can circle the Earth in approximately one and a half hours GEO vs. MEO vs. LEO Most communications satellites in use today for commercial purposes are placed in the geostationary orbit, because of the following advantages: • One satellite can cover almost 1/3 of Earth's surface, offering a reach far more extensive than what any terrestrial network can achieve • Communications require the use of fixed antennas. Since geosynchronous satellites remain remain statio stationary nary over over the same same orbita orbitall locatio location, n, users users can point point their their satell satellite ite dish dishes es in the the righ rightt dire direct ctio ion, n, with withou outt cost costly ly trac tracki king ng acti activi viti ties es,, maki making ng communications reliable and secure • GEO satellites are proven, reliable and secure - with a lifespan of 10-15 years 4.4 FREQUENCY BANDS FOR SATELLITE SATELLITE COMMUNICATION COMMUNICATION Satellite communications, like any other means of communication (radio, TV, telephone, etc) etc),, use use frequ requeency ncy band bandss that hat are are par part of the the elect lectro roma magn gneetic tic spe spectru ctrum. m. The electromagnetic radiation spectrum starts with the longest waves (including those in the audible range) and extends through radio waves and the visible light, which is effectively a very small part of the spectrum, all the way to the extremely short wavelengths such as radi radioa oact ctiv ivee radi radiat atio ion. n. With Within in this this broa broad d rang rangee of freq freque uenc ncie ies, s, the the Inte Intern rnat atio iona nall Telecommunications Union (the United Nations institution that regulates worldwide use of  airwa airwave ves) s) has allo allocat cated ed parts parts of the spect spectru rum m that that are are suit suitabl ablee for and and dedicat dedicated ed to transm transmiss ission ion via satell satellite ite.. Some Some of these these bands bands are exclus exclusivel ively y dedicat dedicated ed to satell satellite ite transmission. Figure (19) Spectrum Band Downlink Uplink L/S 1.610 to 1.625 GHz 2.483 to 2.50 GHz C 3.7 to 4.2 GHz 5.924 to 6.425 GHz Ext C band 4.5 to 4.8 GHz 6.725 to 7.025 GHz Ku 11.7 to 12.2 GHz 14.0 to 14.5 GHz Ka 17.7 to 21.7 GHz 27.5 to 30.5 GHz Figure(20)- Various Bands The satellite transmission bands that are of interest to us are the C-, Ku- and Ka-bands. C-band is the oldest allocation and operates in the frequency range around 6 GHz for  tran transm smis issi sion on (upl (uplin ink) k) and and betw betwee een n 3.7 3.7 and and 4.2 4.2 GHz GHz for for rece recept ptio ion n (dow (downl nlin ink) k).. Ku-band is the most common transmission format in Europe for satellite TV and uses aro around und 14 GHz for upl uplink and and between 10.9 and 12.75 2.75 GHz for dow downli nlink. nk. Ka-band uses around 30 GHz up- and between 18 and 20 GHz downlink frequency. C-band and Ku-band are becoming congested by an increasing amount of users, so satellite service operators are more and more turning to the use of Ka-band. The selection of the band is not something that individual service providers decide, but is rather chosen by large satellite operators based on different factors: • Availa Availabili bility: ty: C-band C-band is still still the most most widely widely availab available le worldw worldwide. ide. Ku-band Ku-band is  becoming more available available recently recently in regions which were less covered in the past (South America, Asia, Africa) • C-band is more prone to interference from other transmission services that share the same frequencies (adjacent satellites or terrestrial transmissions) than the higher   bands • While the C-band technology is cheaper in itself, it requires larger dishes (1 to 3 m) than than Ku- and Ka-band Ka-band (0.6 to 1.8 m) and therefore therefore impose imposess relati relatively vely higher  (installation) costs on the end-user  • Ku- and especially Ka-band make better use of satellite capacity • Higher frequency bands (Ku- and especially Ka-) suffer significantly more from signal signal deteri deteriorat oration ion caused caused by rainfal rainfall: l: to ensure ensure availab availabilit ility y in bad weather  weather  conditions, the signal has to be much stronger. 0.1% of unavailability means in fact that the service will be interrupted for almost 9 hours over a 1-year period. 1% unavailability represents 90 hours or almost 4 full days CHAPTER 5 VERY SMALL APERTURE TERMINAL NETWORKS (VSAT) Satellite Communication Communication using VSAT (Very (Very Small Aperture Aperture Terminal) Terminal) since the science fiction on radio transmission through space using geo-synchronous earth satellite, provider  has progressed significantly in the field of satellite communications. VSAT is a satellite based communicatio communications ns service that offers offers businesses businesses and government government agencies flexible flexible and reliable communications solutions, both nationally and internationally, on land and at sea. VSAT is a term widely used in the satellite industry to describe an earth station that is installed on the ground to receive communications from a satellite or to communicate with other other ground ground statio stations ns by transm transmitt itting ing to and receiving receiving from from satell satellite ite spacecr spacecraft. aft. The antenna size being restricted to 3.8m.. Terminals installed at distant sites are connected to a central hub via satellite using small diameter antenna dishes. It is an earth station connected to the the geogeo-sy sync nchr hron onou ouss sate satell llit itee suit suitab able le for for supp suppor orti ting ng a vari variet ety y of two two – way way telecommunication and information, services like voice, data and video. 5.1 VSAT SYSTEM ARCHITECTURE A VSAT system consists of a satellite transponder, central hub or a master earth station, and remote VSATs. The VSAT terminal has the capability to receive as well as transmit signal signalss via via the the sate satell llite ite to other other VSAT VSATss in the the netw networ ork. k. Depen Dependi ding ng on the the acces accesss technology used the signals are either sent via satellite to a central hub, which is also a monitoring centre, or the signals are sent directly to VSATs with the hub being used for  monitoring monitoring and control. control. In addi additio tion, n, the star topo topolog logy y all allows ows VSATs to use smaller  smaller  antennas and lower power transmitters, since they’re communicating only with the large hub antenna. National thermal power corporation limited has a VSAT network or a SATCOM network for communication and exchange of data and information amongst various sites. NTPC Noida is the central hub and also the monitoring centre. 5.2 VSAT TOPOLOGIES • Star The hub station controls and monitors can communicate with a large number of dispersed VSATs. Generally, the Data Terminal Equipment and 3 hub antenna is in the range of 611m in diameter. Since all VSATs communicate with the central hub station only, this network is more suitable for centralized data applications. • Mesh A group of VSATs communicate directly with any other VSAT in the network without going through a central hub. A hub station in a mesh network performs only the monitoring and control functions. These networks are more suitable for telephony applications. • Hybrid Network  In practice usually using hybrid networks, where a part of the network operates on a star  topology while some sites operate on a mesh topology, thereby accruing benefits of both topologies. topologies. The satellite communic communicatio ation n network network of NTPC NTPC is operating operating in star topology topology with NTPC Noida being the Hub station. So a central satellite earth station (CSES) is installed at NTPC Noida (The study of which is the core aim of the project). One major  advantage of this configuration is that there is virtually no limit on the number of remote VSATs that can be connected to the hub. 5.3 HUB STATION The hub station is usually a relatively large, high performance earth station with an antenna diameter of anything between 6 and 9m or 11. The hub consists of a control centre which which manage managess the networ  networ k, includi including ng an outdoor outdoor antenna, antenna, for the transmi transmissi ssion on and rece recepti ption on of signa signals ls.. Hub Hub stat station ionss are are quite quite expen expensiv sivee and and consi consist st of sever several al main main subsyst subsystems ems;; except except for the antenna antenna these these are usually usually fully fully redunda redundant nt with with automat automatic ic switchover in the event of failure. Hub stations can be shared between several networks, resulting in a sharing of costs. Two  principal options for network network implementati implementation on can be adopted. adopted. Firstly, Firstly, some very large users will wish to purchase their own dedicated VSAT networks including a hub. Other  users will choose to buy or lease the user terminals and to lease access to a hub which will  be owned by the system operator. operator. In contrast contrast to the hub station, station, the remote terminals terminals are much simpler. To minimise total system costs, VSAT networks are designed to have a single expensive hub and a large number of much smaller remote terminals. The actual communication between remote sites is through hub and happens in two steps  because, of which there is a time delay of approximately approximately 0.5 seconds and makes the technology highly synchronized. CHAPTER 6 Central satellite earth station- NTPC Noida 6.1 SPECIFICATIONS 1)  NTPC has has been assigned assigned transponde transponderr number 3 in ISRO's ISRO's communicat communication ion satellite satellite INSAT 3E. 2) INSAT-3E, was successfully launched on September 28, 2003 by the Ariane-5 launch vehicle of Arianespace. 3) INSAT-3E is positioned at 55 deg East longitude in the geosynchronous orbit. 4) INSAT-3E is being tracked, monitored and controlled from the Master Control Facility (MCF) at Hassan in Karnataka 5) The INSAT series of satellites have typically 12/18 transponders in various frequency bands; the bandwidth of each transponder is typically 40 MHz but the usable bandwidth is only 36 MHz. Out of this 36 MHz bandwidth NTPC is Ku-Band d is interna internatio tionall nally y popular  popular  allott allotted ed only only 27 MHz MHz bandw bandwidt idth. h. The Ku-Ban frequency band. This Ku-Band because of its higher frequency can support traffic with smaller antenna sizes in comparison to C/Ext – C band. However it can be affected by rain which makes it unsuitable for use in Southern regions. 6) Presently, Presently, Indian Indian service provider providerss hire a space space segment segment only on the INSAT INSAT series series and operate in C band only. CSE SES S NOIDA is the hub facilities to:• 28 power stations. stati tation on for for NTP NTPC Satc Satcom om netw etwork provi rovidi din ng • 5 regional offices & NCPS, DADRI. • Two corporate centre’s at New Delhi. Using transponder no. 3 of satellite INSAT 3E with allotted bandwidth of 27 MHz. Services provided by CSES • Telephone & fax services among all sites & with CC. • Connecting about 1000 users through transit switch at SCN. • Generat Generation ion data data from power power proje projects cts to CC contro controll room room on high speed speed data data (WAN) • Online Online packag packages es of stor stores es,, finan finance ce,, contr contrac acts ts & gener generat ation ion throug through h WAN WAN connectivity (256 -512 kbps) provided by multiport router at SCN, Noida . • Internet services to all sites through multiport router  • Round the clock technical support to sites. 6.2 CSES NTPC NTPC BLOCK BLOCK DIAGRA DIAGRAM M 6.2.1 Transmission path Figure(21) -transmission path block diagram. 6.2.2 Receive path Figure (22)- receive path block diagram The hub station consists of several main subsystems:6.2.3 TRANSMISSION PATH SUBSYSTEMS:- • Modem • Up converters • High power amplifier (HPA) • Antenna 6.2.4 RECEIVE PATH SUBSYSTEMS:• Low noise amplifier (LNA) • Down converters • Modem The modem modem interf interface acess with with vario various us end user user equip equipme ment, nt, rangi ranging ng from from stan stand d alone alone computers, LAN's, routers, multiplexes, telephone instruments as per the requirement. 6.3 FUNCTIONING OF CSES NTPC •  NTPC has a local local area network network (LAN) for exchange exchange of data and informat information. ion. So all the computers are connected by a switch. But in order to communicate with various other sites (stations) i.e. a wide area network (WAN) a router is required. Therefore the switch is connected to the router in order to establish a Wide area network. At  NTPC along with data communicatio communication, n, voice communication communication is also taking place. for for voic voicee comm commun unic icat atio ion, n, earl earlie ierr they hey were were usin using g a mult multip iple lexe xerr in which hich mult multip iple lexi xing ng of data data and and voic voicee was was done done.. But But now now they they are are usin using g anot anothe her  r  technology called VOIP for voice communication. VOIP is basically voice over  internet protocol. It is a technology in which the telephone is connected to VOIP which converts voice signal into a digital signal. The output of VOIP is given to the switch to which all the PC’s are connected. This forms the complete LAN at NTPC. The switch is connected to the router for WAN. •  Now the modem interfaces with the end user equipment which is the router router here. Since NTPC is the hub station working in star topology. There are around 28 sites located in various regions of the country. So for every site there is a modem. Now for the transmission of voice/data to a remote site the router output is given to every modem. The modulator part of the modem modulates an analog carrier  signal to encode digital information. The modem has IF( intermediate frequency) output that is 70 ± 18 MHz • The output of modem is given to the up converter which translates or converts this IF frequency to RF (radio frequency) – 6GHz. Finally the up converter output is given to HPA for amplification the output of  which is transmitted transmitted to the antenna which transmits transmits the data out to the satellite satellite and eventually to other ground stations. • The receive subsystem consisting of a Low Noise Amplifier (LNA) which removes the noise present in the signal. The frequency of the signal received is 4 GHz. • The LNA output is given to the down converter which converts this RF frequency to IF frequency i.e. 70 MHz • The output of down converter is given to the modem for the demodulation process in order to extract the baseband signal. And finally the modem interfaces with the router and the information or data reaches the user.  Now each subcomponent subcomponent of of the centralized centralized earth station station NTPC will will be discussed discussed in a little more detail. The router and the LAN part will be discussed in the networking  part to follow. 6.4 THE VARIOUS VARIOUS SUBSYSTEMS:SUBSYSTEMS:- 6.4.1 MODEM A modem (modulator-demodulator ) is a device that modulates an analog carrier signal to encode encode digital digital informat information, ion, and also also demodul demodulate atess such such a carrie carrierr signal signal to decode decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded decoded to reprodu reproduce ce the original original digital digital data. A satellite modem or  sat modem is a modem used to establish data transfers using a communications satellite as a relay. Data to  be transmitted transmitted are transferr transferred ed to a modem from Data Data terminal terminal equipment equipment (e.g. a computer). computer). The modem usually has Intermediate frequency (IF) output (that is, 50-200 MHz). At  NTPC the modems modems has an an output of IF that that ranges ranges from 70±18 70±18 MHz .This .This frequency frequency has to  be converted converted using an up .converter .converter before amplificatio amplification n and transmission. transmission. Similarly, Similarly, a signal received received from a satellite satellite is firstly down converted converted then demodulated demodulated by a modem, and at last handled by data terminal equipment. Popular modulation types being used for satellite communications: a) Binary phase shift keying (BPSK);  b) Quadrature phase shift keying (QPSK); c) Orthogonal quadrature phase shift keying (OQPSK); d) 8PSK; e) Quadrature amplitude modulation (QAM), especially 16QAM. The modulation techniques used at NTPC are mainly QPSK and 16QAM. MODEMS USED AT NTPC:-  NTPC is currently currently using four types types of modems: modems:-a) UMOD  b) SSE c) Datum d) DMD 20 DMD 20 is the latest modem used here. The main features of this modem are:• Frequency- 50-90 MHz At NTPC 70±18 MHz • Data rate- 2.4 Kbps-20Mbps At NTPC 6Mbps • Modulation At NTPC QPSK, 16QAM The various options available in it are:- • Monitor  • Modulation • Demodulation • Test • Interface etc The various configurations done in the DMD 20 are:- • Frequency • Modulation • Data rate • FEC rate etc 16QAM is the latest modulation technique used at NTPC. The main advantage of this technique is that it saves the bandwidth. Since there are around 28 sites to which service is  provided  provided so the bandwidth bandwidth is allocated allocated to each site according according to the site traffic traffic and the requirement. So the 27 Hz bandwidt bandwidth h is allocated allocated accordi accordingly ngly.. 6.4.2 UP/DOWN CONVERTER  An up converter works in the transmitting side whereas the down converter functions in the receive path. The main function of the up converter is that it converts or translates the intermediate frequency (which is the output of the modem) to the radio frequency (RF) which is 6GHz. The up converter used at NTPC is a block up converter which converts a  band (or "block") of frequencies frequencies from a lower frequency frequency to a higher frequency. frequency. Just the opposite work is done by the down converter that is it takes the radio frequency and converts it to an intermediate frequency before giving to the modem. 6.4.3 6.4.3 HIGH HIGH POWE POWER R AMPL AMPLIFI IFIER ER (H (HPA PA)) The high power amplifier (HPA) is an earth station facility that provides the RF carrier   power to the input terminals terminals of the antenna. antenna. The output power typically typically may few watts watts for  a single data channel, around a hundred watts or less for a low capacity system, or several kilowatts kilowatts for high capacity traffic. An RF power amplifier amplifier is a type of electronic electronic amplifier  used to convert a low power radio frequency signal into a larger signal of significant  power, typically typically for driving the antenna of a transmitter. transmitter. It is usually usually optimized optimized to have high efficiency, high output power compression, good return loss on the input and output, good gain, and optimum heat dissipation. C-band high power amplifiers offer output powers of 50, 100, 150 or 200 watts Built for reliable, trouble-free service, the amplifiers incorporate microprocessor based monitor monitor and and control control systems. systems. 6.4. 6.4.4 4 LOW LO W NO NOISE ISE AMP AMPLI LIFI FIE ER  The low-noise amplifier amplifier (LNA) is a special type of electronic amplifier amplifier or amplifier amplifier used in communication systems to amplify very weak signals captured by an antenna. It is often located very close to the antenna, so that losses in the feed line become less critical. critical. Using an LNA, the noise of all the subsequent stages is reduced by the gain of the LNA, while the noise of the LNA itself is injected directly into the received signal. 6.4. 6.4.5 5 ANTEN NTENNA NA SU SUBS BSY YST STEM EM The antenna subsystem consisting of a large antenna (6 to 9 m or 11m in diameter) on a mount with a tracking system which allows the antenna to follow the satellite as it moves very slightly in the sky. A feed horn is fitted at the focus of the dish to collect the received signals from the antenna and to feed the transmit signals to it.  Software configuration (in NTPC):  IF frequency: 70+-18 MHz  Threshold level (at the Rx side): -70 dB  Power range (at the Tx side): -25 dB to 0dB  Signal to noise ratio (at the Rx side): 9dB  Type of modulation: BPSK, QPSK, 16-QAM  Data rate: 512 Kbps 6.5 MULT MULTIPL IPLE E ACC ACCES ESS S SCHE SCHEME MES S The primary objective of the VSAT networks is to maximize the use of common satellite and other other resour resources ces amongs amongstt all VSAT sites. sites. The methods methods by which which these these networ networks ks optimize the use of satellite capacity, and spectrum utilization in a flexible and costeffective manner are referred to as satellite access schemes. . Good network efficiency depends very much on the multiple accessing schemes. There are many different access techniques tailored to match customer applications. The VSAT services are primarily based on one of two technologies: i.Single-carrier per channel (SCPC) and ii. Time-division multiple access (TDMA). 6.5.1 SCPC (Single-Carrier Per Channel) SCPC-based design provides a point-to-point technology, making it the VSAT equivalent to conventional leased lines. 6.5.2 TDMA (Time-division multiple access) In a TDMA network, all VSATs share satellite resource on a time-slot basis. Remote VSATs use TDMA channels or inroutes for communicating with the hub. There could be several inroutes associated with one outroute. Several VSATs share one inroute hence sharing the bandwidth. Typical inroutes operate at 64 or 128 Kbit/s. 6.5.3 FDMA (Frequency Division Multiple Access) It is the oldest and still one of the most common methods for channel allocation. In this scheme, scheme, the availabl availablee satell satellite ite channel channel bandwid bandwidth th is broken broken into into freque frequency ncy bands bands for  different earth stations. This means that guard bands are needed to provide separation  between  between the bands. i. PAMA (Pre-Assigned Multiple Acceess) It implies that the VSATs are pre-allocated a designated frequency. Equivalent of the terrestrial leased line solutions, PAMA solutions use the satellite resources constantly. Consequently, there is no call-up delay what makes them most suited for interactive data applications or high traffic volumes. As such, PAMA connects high data traffic sites within an organization. SCPC (Single Channel Per Carrier) refers to the usage of a single satellite carrier for  carrying a single channel of user traffic. The frequency is allocated on a pre-assigned basis in case of SCPC VSAT which is also synonymously known as PAMA VSAT. ii. DAMA (Demand Assigned Multiple Access) The network uses a pool of satellite channels, which are available for use by any station in that network. On demand, a pair of available channels is assigned so that a call can be established. Once the call is completed, the channels are returned to the pool for an assignment to another call. . DAMA systems allow the number of channels at any time be less than the number of potential users. Satellite connections are established and dropped only when traffic demands them. iii. CDMA (Code Division Multiple Access) Under this, a central network monitoring system allocates a unique code to each of the VSATs VSATs enab enablin ling g multi multiple ple VSAT VSATs s to trans transmit mit simul simultan taneou eously sly and and share share a commo common n frequency band. Although this is best applicable for very large networks with low data requir requirem emen ents ts,, ther there e are prac practic tical al restr restrict iction ions s in the the use use of sprea spread d spec spectru trum. m. It is employed mainly for interference rejection or for security reasons in military systems. VSAT Accessing Schemes 6.6 IMPLEMENTING VSAT The Pros: • Provides an integrated solution for Voice, data and video communication. • Better Reach- Installable in difficult terrain, remote areas. • Reliability – uptime of up to 99.5 % is achievable in VSAT network compared to lease line (in Indian conditions). • Maintenance - A single point contact with the service provider – lesser elements involved and hence easy fault finding. • Better Network Management. • Quick establishment of new sites. • Wide geographic coverage. The Cons: • Very high Initial Cost of Implementation. • High Propagation delay CHAPTER 7 NTPC NETWORK TODAY  NTPC Communication Communication Network Network connects all its Projects, Projects, Regional Regional HQ’s, and Regional Regional Inspection Inspection Offices Offices & Commercial Commercial Offices to Corporate Corporate Centers Centers at SCOPE and at EOC  NOIDA  NOIDA for Voice Voice and Data Data Communicati Communication on via Satellite Satellite,, MPLS & Leased Leased Lines. Lines. The data network supports all applications like Internet, Email, etc.  NTPC Satcom Network Network working in STAR Configuration Configuration with the Hub Earth Station located at EOC Noida (U.P.). These are working in C Band on leased capacity on the INSAT satellite. Data Links are working at the data rate of 1024/512kbps on PAMA to form WAN connectivity using Multiport Router at hub earth station. Internet, Mail & GDAMS are working on Satcom Network. Telephony is through DAMA/VOIP in most location.NTPC has implemented MPLS Network hired from supplier for ERP and other  online applications applications at the data rate of 34 Mbps for Data Center Center Noida,2 Mbps for power  power   plants & RHQ’s RHQ’s and and 256 Kbps lines lines for RIO’s RIO’s & Commer Commercial cial offices. offices. For running running ERP 24 *7 a Back Back up router router in case of failure failure of main router router at Data Data Centre NOIDA NOIDA,, is to be installed installed which shall shall be exact replica of Main Main Data Centre router router but work in 1+1 with with mail router. Satellite Communication Network  Network Features SATELLITE C-BAND LEASED TRANSPONDER (3/4th) CAPACITY ON INSAT 3E. HUB: INSAT TYPE ‘A’ WITH 11m Ø ANTENNA SATELLITE EARTH STATION Phase I: 5 NOS. INSAT TYPE ‘B’ WITH 7.5 m Ø ANTENNA WITH MCPC 512 Kbps DATA RATE Phase II: 6 NOS. 3.8 m Ø ANTENNA WITH MCPC 512 Kbps DATA RATE. Phase III: 8 NOS. 3.8 m Ø ANTENNA WITH 256 Kbps DATA RATE Phase IV: 3 NOS. 3.8 m Ø ANTENNA WITH 256 Kbps DATA RATE MICROWAVE LINKS: 2 GHz 2/8 MBPS DIGITAL RADIO SYSTEM.  NODES CONNECTED CONNECTED:: 29 (22 POWER POWER PROJECTS, PROJECTS, 5 RHQS RHQS TO CC & EOC EOC NOIDA) NOIDA) NTPC – Business Reach COAL BASED SITES - 15 No’s SINGRAULI, RIHAND, DADRI, UNCHAHAR, BADARPUR  TANDA NR / NCR FARAKKA, KAHALGAON, TALCHER,TTPS ER   KORBA, VINDHYACHAL, SIPAT WR   RAMAGUNDAM, SIMHADRI SR   COMBINED CYCLE - 7 No’s (6+1) DADRI**, AURIYA, ANTA, FARIDABAD NCR  KAWAS, GANDHAR WR   KAYAMKULAM SR HYDRO KOLDAM CC HEAD QUARTER / REGIONAL HQ. 8 No’s (3 + 5 No s) SCOPE, EOC, PMI, NOIDA LUCKNOW, PATNA, MUMBAI, HYDERABAD ** CO - LOCATED WITH DADRI THERMAL NTPC VSAT NETWORK       N T P C N E T W O R K  Central Network H ub/ K o ld a m D a t a c e n t e r L o c a t io io n a t N O I D A NEW DELHI Noida F a r id a b ad D ad ri B ad ar p u r LUCKNOW T an d a A ura iyaU nc hBa arh ha Pr A T N A S ing rau li K a h a lg a o n A nt a R ih a nd V i n d h y a c h al F ara k k a K o rb a G an d h ar K aw as S ip a t MUM BAI R a m a g u nd a m H y d e ra b adS im h a d ri K a y a m k u la m CHAPTER 8 CONCLUSION T a lc h Se ru p e r T alc h Te rhe rm a l Hence we have seen the NTPC’s communication network and learnt about the satellite link, satellite bandwidth what we are using, and about the main equipments and their technical specifications. I have also learnt the basics of networking and the LAN/WAN networking techniques. Since the central satellite earth station that has been installed at NTPC Noida is the hub station for various other sites therefore it needs a continuous supervision so that the requests requests and the traffic from various other sites is efficiently handled and managed. I have learnt how satellite communication practically works and the functioning of a VSAT hub station. Latest technologies keep coming in the market and NTPC also tries to update itself  so that it is able to manage the increasing traffic and utilize the bandwidth allotted to it efficiently. CHAPTER 9 FUTURE IMPLICATIONS In future if I get an opportunity to work on the same project then I would like to learn more about the networking in NTPC. Now in the new era of ERP the communication facilities have to very rugged and they should provide communication with zero down time. NTPC has introduced new services like ERP. Due to time limitation our main focus was on the satellite satellite communication communication but in future I would like to research research and study further about how the video conferencing works in NTPC and the latest services that are being introduced in its IT department. I would also like to understand how link budget calculations are done. CHAPTER 10 REFERENCES • http://en.wikipedia.org/wiki/Communications_satellite • http://www.tutorialsweb.com/satcom/fundamentals-of-satellitecommunications.htm • http://www.britannica.com/EBchecked/topic/524891/satellitecommunication • http://www.gatewayforindia.com/technology/satellite.htm • http://www.wtec.org/loyola/satcom/toc.htm • http://en.wikipedia.org/wiki/Earth_station • http://en.wikipedia.org/wiki/Very_small_aperture_terminal • http://www.angelfire.com/electronic/vikram/tech/vsattut.html • http://hubpages.com/hub/How-the-VSAT-Technology-Works • http://www.crystalcommunications.net/satellite/vsat/about_vsat.htm • http://www.gilat.com/Content.aspx? Page=how_to_communicate_across_satellite_networks