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 : SEVENTH

Faculty Guide: Submitted by:

Mr. Devesh Kumar 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, in partial fulfillment of the requirements for the

award of 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 I am mentioning here, this endeavor would not have been successful.

The completion of any project brings with it a sense of satisfaction, but it is

never complete without thanking those people who made it possible and whose

constant support has crowned our efforts with success. I would like to express my

gratitude to Ms Meena agarwal, DGM( IT) at NTPC for encouraging and inspiring me

to carry out the project in the Central Satellite Earth 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 successfully. . I am extremely happy to 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 to provide private or secure data networks. Therefore for communication and exchange of data between various sites a central satellite earth station has been installed at NTPC Noida since it is the hub station for communication

with its various other sites. NTPC Satcom Network is working in STAR Configuration with this Hub Earth Station .NTPC has been assigned transponder number 3 in therecently launched satellite INSAT 3E.The project covers detailed study of the ground segment of satellite communication. The transmission and receive path which include various sub components like MODEM, up/down Converters etc have been studied and how they are connected practically. NTPC has a LAN for exchange of information 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

Chapter 2 : NTPC COMPANY PROFILE

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 of satellite

4.3 Types of 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 NETWORK 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 communication are called as communication

satellites. They are highly specialized wireless receiver/transmitters 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 station and then transmitted to the satellite through dish antennas.

The satellite receives the uplink frequency and the transponder present inside the satellite

does the processing function and frequency down conversion in order to 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) Space segment

2) Ground segment

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. This segment is available from organizations that have procured

satellites, arranged launch and who operate these satellites on a commercial basis. In

addition to international agencies, a number of private players have emerged who own or

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 communication link between earth and the 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 within the building. A 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 link hundreds of computers used by thousands of people.

Communication 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

COMPANY PROFILE  

2.1 Overview of Organization

India’s largest power company, NTPC was set up in 1975 to 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, located across the country. In addition under JVs, 3

stations are coal based & another station uses naphtha/LNG as fuel. By 2017, the power

generation portfolio is expected to have a 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 its plants at high efficiency levels. 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 success. NTPC is among the largest five companies in India in terms of

market capitalization.

At NTPC, People before Plant Load Factor is the mantra that guides all HR related

policies. NTPC has been awarded No.1, Best Workplace in India among large

organizations and the best PSU for the year 2009, by the Great Places to Work Institute,

India Chapter in collaboration with The Economic Times.

NTPC has integrated Information Technology as a strategic tool in its management

systems and aligned Business & Process based on Enterprise Resource planning using

SAP AG Product.

Services covered include the following:

1) NTPC Ltd has mandated German business software major SAP selecting its entire

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 of business activities such as production, sales, Material management,

Codification of Items, Plant & Operation Management, Customer Relation

Management , C-Folder for receiving drawings, Inspection management, e-

Procurement, 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, Video-

Conferencing, and other applications with retaining consultants from IIT-D .

5) Established Multi Protocol Label Switching (MPLS) Network with BSNL'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

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 link. A network, therefore, is a set of interconnected 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 transmission medium) that is used to transmit the resource

or service between the computers. All systems on the pathway must follow a set of

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 resource to share (resource)

2. A pathway to transfer data (transmission medium)

3. A set of rules governing how to communicate (protocols)

Figure(2) - Simplest form of a computer network

Having a transmission pathway does not always guarantee

communication. When two entities communicate, they do not merely exchange

information; rather, they must understand the information they receive from each other.

The goal of computer networking, therefore, is not simply to exchange 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 they will be able to 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

services and to reduce equipment costs. Networks enable computers to share their

resources by offering services to other computers and users on a network. The following

are specific reasons for networking PCs

1. Sharing files

2. Sharing printers and other devices

3. Enabling centralized administration and security of the resources within the

system.

4. Supporting network applications such as electronic mail and database services

5. Limited resources

6. Desire to share the resources

7. Cost Reduction

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 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 enough to warrant access

via a network. The facilities accessible by networks are in fact becoming more interesting

at a rapid rate.

The remote computer may contain software that a user needs to employ. It may be

proprietary software kept at one location. It may require a larger machine than any at the

user's location. The distant computer may provide access to data that is stored and

maintained at its location. Sometimes the remote machine controls a large or special

printing facility. Sometimes the remote machine compiles programs that are used on

smaller peripheral machines.

Cost Reduction

There are various aspects of technology that are likely to force the price of

terminal usage drastically lower. This is important because almost all aspects of

telecommunications are characterized by high price elasticity. In other words, when the

price comes down, the usage goes up.

3.2 NETWORK TOPOLOGIES

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 devices (usually called nodes) to each other. There are five basic topologies

possible: mesh, star, 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-secondary, where one device controls traffic and the others must

transmit 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, every device has a dedicated 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 Topology

A mesh offers several advantages over other network topologies. First, the use of

dedicated links guarantees that each connection can carry its own data load, 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, point-to-point links make fault identification and fault isolation 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 expensive). For these reasons a mesh topology is usually 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, usually called a hub. The devices are not 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.

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 links.

Hub

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

isolate and prioritize communications from different computers. For example, the

computers attached to one secondary hub can be given priority over computers attached

to another secondary hub. In this way, the network designers and operator can 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 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, 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 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 degradation can be controlled by limiting the number and spacing of

devices connected to a given length of cable. Adding new devices may therefore require

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 within a specified period, it can issue an alarm. The alarm alerts the

network 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, or campus. Depending on the needs of an organization and the

type of technology used, a LAN can be as simple as two PCs and a printer in someone's

home office, or it can extend throughout a company and include voice, sound, and video

peripherals. Currently, LAN size is limited to a few kilometers.

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 environments, links a work group of task-related computers, for example,

engineering workstations or accounting PCs. One of the 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

LAN-to-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 may utilize public, leased, or private communication devices, usually 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 (LAN)

Local area networks, generally called LANs, are privately-owned networks within a

single building or campus of up to a few kilometres in size. They are widely used to

connect personal computers and workstations in company offices and 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

A wide area network, or WAN, spans a large geographical area, often a country or

continent. It contains a collection of machines intended for running user (i.e., application)

programs. These machines are called hosts. The hosts are connected by a 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 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 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;

Switching elements are specialized computers that connect three or more transmission

lines. When data arrive on an incoming line, the switching element must 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 of satellite communication are the earth stations, 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 switch or a dedicated link to the earth station. The user

generates a 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. The signal

at the receiving earth station is processed to get back the baseband signal, it is sent to the

user through a terrestrial 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 to 7.075 Ghz and the

actual downlink frequency band 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 and mobile and cordless telephones.

4.2 TYPES OF SATELLITE:-

The satellite can be classified into two categories:

Active satellite

Passive satellite

The major difference between these two is that weather the communication relay involves

passive reflection or active electronic system

An active satellite is one which has transmitting equipment abroad such as a 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 over the equator in an 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 South 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 stationary over the same orbital location, users can point their

satellite dishes in the right direction, without costly tracking activities, making

communications reliable and secure

GEO satellites are proven, reliable and secure - with a lifespan of 10-15 years

4.4 FREQUENCY BANDS FOR SATELLITE COMMUNICATION

Satellite communications, like any other means of communication (radio, TV, telephone,

etc), use frequency bands that are part of the electromagnetic spectrum. 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

radioactive radiation. Within this broad range of frequencies, the International

Telecommunications Union (the United Nations institution that regulates worldwide use

of airwaves) has allocated parts of the spectrum that are suitable for and dedicated to

transmission via satellite. Some of these bands are exclusively dedicated to satellite

transmission.

Figure (19) Spectrum

Band Downlink Uplink

L/S 1.610 to 1.625 GHz 2.483 to 2.50 GHz

C

Ext C band

3.7 to 4.2 GHz

4.5 to 4.8 GHz

5.924 to 6.425 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

transmission (uplink) and between 3.7 and 4.2 GHz for reception (downlink).

Ku-band is the most common transmission format in Europe for satellite TV and uses

around 14 GHz for uplink and between 10.9 and 12.75 GHz for downlink.

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:

Availability: C-band is still the most widely available worldwide. Ku-band is

becoming more available 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 Ku- and Ka-band (0.6 to 1.8 m) and therefore imposes relatively 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 deterioration caused by rainfall: to ensure availability in bad 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 using VSAT (Very Small Aperture 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 communications service that offers businesses and government agencies

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 ground stations by transmitting to and receiving from satellite

spacecraft. 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 geo-synchronous satellite suitable for supporting a variety

of two – 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

signals via the satellite to other VSATs in the network. Depending on the access

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 and control. In addition, the star topology allows VSATs to use 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 6-

11m 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.

The satellite communication network of NTPC is operating in star 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 manages the network, including an outdoor antenna, for the transmission

and reception of signals. Hub stations are quite expensive and consist of several main

subsystems; except for the antenna these are usually fully redundant with automatic

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 implementation can be adopted. 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. In contrast to the hub station, the remote 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 0.5 seconds and makes the

technology highly synchronized.

CHAPTER 6

Central satellite earth station- NTPC Noida

6.1 SPECIFICATIONS

1)NTPC has been assigned transponder number 3 in ISRO's communication 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 allotted only 27 MHz bandwidth. The Ku-Band is internationally popular

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, Indian service providers hire a space segment only on the INSAT series

and operate in C band only.

CSES NOIDA is the hub station for NTPC Satcom network providing

facilities to:-

28 power stations.

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.

Generation data from power projects to CC control room on high speed data

(WAN)

Online packages of stores, finance, contracts & generation through 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 BLOCK DIAGRAM

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 interfaces with various end user equipment, ranging from stand alone

computers, LAN's, routers, multiplexes, telephone instruments as per the requirement.

6.3 FUNCTIONING OF CSES NTPC

NTPC has a local area network (LAN) for exchange of data and information. 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 communication, voice communication is also

taking place. for voice communication, earlier they were using a multiplexer in

which multiplexing of data and voice was done. But now they are using another

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 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 to the antenna which transmits the data out to the 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 of the centralized earth station NTPC will be 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 SUBSYSTEMS:-

6.4.1 MODEM

A modem (modulator-demodulator) is a device that modulates an analog carrier signal to

encode digital information, and also demodulates such a carrier signal to decode the

transmitted information. The goal is to produce a signal that can be transmitted easily and

decoded to reproduce the original 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 are transferred to a modem from Data terminal equipment (e.g. a

computer). The modem usually has Intermediate frequency (IF) output (that is, 50-

200 MHz). At NTPC the modems has an output of IF that ranges from 70±18 MHz .This

frequency has to be converted using an up .converter before amplification and

transmission. Similarly, a signal received from a satellite is firstly down converted then

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 using four types of 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 so the bandwidth is allocated to each site according to the site traffic and the

requirement. So the

27 Hz bandwidth is allocated accordingly.

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 from a lower frequency to a higher 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 HIGH POWER AMPLIFIER (HPA)

The high power amplifier (HPA) is an earth station facility that provides the RF carrier

power to the input terminals of the antenna. The output power typically may few watts

for a single data channel, around a hundred watts or less for a low capacity system, or

several kilowatts for high capacity traffic. An RF power amplifier is a type of

electronic amplifier used to convert a low power radio frequency signal into a larger

signal of significant power, typically for driving the antenna of a transmitter. It is usually

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 and control systems.

6.4.4 LOW NOISE AMPLIFIER

The low-noise amplifier (LNA) is a special type of electronic amplifier or 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.

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.

6.4.5 ANTENNA SUBSYSTEM

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 MULTIPLE ACCESS SCHEMES

The primary objective of the VSAT networks is to maximize the use of common satellite

and other resources amongst all VSAT sites. The methods by which these networks

optimize the use of satellite capacity, and spectrum utilization in a flexible and cost-

effective 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, the available satellite channel bandwidth is broken into frequency bands for

different earth stations. This means that guard bands are needed to provide separation

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 enabling multiple VSATs to transmit simultaneously and share a common

frequency band. Although this is best applicable for very large networks with low data

requirements, there are practical restrictions in the use of spread spectrum. It is

employed mainly for interference rejection or for security reasons in military systems.

VSAT Accessing Schemes

TDMA

Time-division

Multiple Access

TDMA

Time-division

Multiple Access

FDMA

FrequencFrequency y

Division Division

Multiple Multiple AccessAccess

FDMA

FrequencFrequency y

Division Division

Multiple Multiple AccessAccess

SCPC

Single-Single-carrier carrier

per per ChannelChannel

SCPC

Single-Single-carrier carrier

per per ChannelChannel

VSAT

TECHNOL-0GY

VSAT

TECHNOL-0GY

DAMDAMAA

CDMCDMAA

PAMAPAMA

FDMA

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 Network connects all its Projects, Regional HQ’s, and Regional

Inspection Offices & Commercial Offices to Corporate Centers at SCOPE and at EOC

NOIDA for Voice and Data Communication via Satellite, MPLS & Leased Lines. The

data network supports all applications like Internet, Email, etc.

NTPC Satcom Network working in STAR 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 at the data rate of 34 Mbps for Data Center Noida,2 Mbps for power

plants & RHQ’s and 256 Kbps lines for RIO’s & Commercial offices. For running ERP

24 *7 a Back up router in case of failure of main router at Data Centre NOIDA, is to be

installed which shall be exact replica of Main Data Centre router but work in 1+1 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: 29 (22 POWER PROJECTS, 5 RHQS TO CC & EOC 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

CHAPTER 8

CONCLUSION

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 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 communication but in future I would like to 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-satellite-communications.htm

http://www.britannica.com/EBchecked/topic/524891/satellite-communication

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