SUMMER TRAINING REPORT 15th June to 30th July

Submitted By:- Kunwar Digvijay Singh0921531038ECE-(7th sem)

ABOUT THE COMPANY

CORPORATE VISION :

“A world class integrated power major, powering India's growth with increasingglobal presence.”

CORE VALUES :

BCO

- - -

Business ethics Customer focus Organizational & professional pride

M - Mutual respect & trust IT

- -

Innovation & speed Total quality for excellence

NTPC Limited is the largest thermal power generating company of India,public sector company. It was incorporated in the year 1975 to accelerate power development in the country as a wholly owned company of the Government of India. At present, Government of India holds 89.5% of the total equity shares of the company and the balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within a span of 31 years, NTPC has emerged as a truly nationalpower company, with power generating facilities in all the major regions of the country.

Type

Industry

Founded

State-owned enterprise Public ( BSE : 532555 )

Electricity generation

1975

Headquarters Delhi , India

Source:

Wikipedia

Key people

Products

Revenue

Net income

Employees

Website

R S Sharma, Chairman& Managing Director

Electricity

▲ 50,188.52 crore( US$ 10.89 bil ion)(2009-10) [1]

▲ 8,837.65 crore( US$ 1.92 bil ion)(2009-10) [1]

25944 (2009)

www.ntpc.co.in

1975

1997

2004

2005

EVOLUTION OF NTPC

NTPC was set up in 1975 with 100% ownership by the Government of India. In the last 30 years, NTPC has grown into the largest power utility in India.

In 1997, Government of India granted NTPC status of “Navratna‟ being one of the nine jewels of India, enhancing the powers to the Board of Directors.

NTPC became a listed company with majorityGovernment ownership of 89.5%. NTPC becomes third largest by Market Capitalisation of listed companies

The company rechristened as NTPC Limited in line withits changing business portfolio and transform itself from a thermal power utility to an integrated power utility.

NTPC is the largest power utility in India, accounting for about 20% of India‟s installed capacity.

Sites of NTPC

NTPC Head Quarters

Sr. No. Head Quarter City 1 2 3 4 5 6

NCR HQ ER-I, HQ ER-II, HQ

NER SR HQ WR HQ

Delhi Patna

Bhubaneswar Lucknow

Hyderabad Mumbai

NTPC Project Sites:

1 Singrauli

2 Korba

Uttar Pradesh

Chhattisgarh

2,000

2,100

3 Ramagundam Andhra Pradesh 2,600

4 Farakka West Bengal 1,600

5 Vindhyachal Madhya Pradesh 3,260

6 Rihand

7 Kahalgaon

8 NCTPP, Dadri

9 Talcher Kaniha

10 Unchahar

11 Talcher Thermal

Uttar Pradesh

Bihar

Uttar Pradesh

Orissa

Uttar Pradesh

Orissa

2,000

2,340

1,330

3,000

1,050

460

12 Simhadri Andhra Pradesh 1,000

13 Tanda

14 Badarpur

15 Sipat-II

16 Sipat-I(erection phase)

Uttar Pradesh

Delhi

Chhattisgarh

Chhattisgarh

440

705

1000

1980

17 Bongaigaon(erection phase.) Assam

Total

750

24,835

Need for communication Among different sites

Enterprise Resource Planning (ERP) An ERP system can either reside on a centralized server or be distributed across modular hardware and software units that provide "services" and communicate on a local area network. The distributed design allows a business to assemble modules from different vendors without the need for the placement of multiple copies of complex and expensive computer systems in areas whichwill not use their full capacity

Manufacturing Engineering, bills of material, work orders, scheduling, capacity, workflow management, quality control, cost management, manufacturing process, manufacturing projects, manufacturing flow

Supply chain management Order to cash, inventory, order entry, purchasing, product configurator, supply chain planning, supplier scheduling, inspection of goods, claim processing, and commission calculation

Financials General ledger, cash management, accounts payable, accounts receivable, fixed assets

Project management Costing, billing, time and expense, performance units, activity management

Human resources Human resources, payroll, training, time and attendance, rostering, benefits

Customer relationship management Sales and marketing, commissions, service, customer contact, call-center support

Data services Various "self-service" interfaces for customers, suppliers and/or employees

Access control Management of user privileges for various processes

Types of networks used by NTPC

NTPC uses 3 different types of networks for the purpose of communicationamong its various sites. These are listed below:

MPLS Network ISDN Network VSAT Network

MPLS Network MPLS Network is the Multiple Protocol Level Shift Network. It provides a network speed of 2 mbps to 34 mbps. It is the primary network which is used by the NTPC sites.

ISDN Network ISDN is the Integrated Service Digital Network. This Network is provided by operators like BSNL or VSNL, in the form of a leased line which is a dedicated line. The speed provided is up to 2 mbps.

VSAT Network VSAT or Very Small Aperture Network is a satellite based network. It is used as a backup network. The speed provided by VSAT is about 2 mbps.

Launch Date 28.09.2003

INSAT-3E is the fourth satellite launched in the INSAT-3 series. It is an exclusive

communication satellite to further augment the communication services that are

being provided by the INSAT System. Weighing 2775 kg at lift-off, INSAT-3E

carries 24 Normal C-band and 12 Extended C-band transponders.

Mission Communication

Spacecraft Mass 2,775 Kg (Mass at Lift-off)

Launch date

Launch site

1218 Kg (Dry mass)

September 28, 2003

French Guyana

Launch vehicle Ariane5-V162

Orbit Geostationary Orbit

VSAT Network

Definition:

A Very Small Aperture Terminal (VSAT), is a two-way satellite ground station with a dish antenna that is smaller than 3 meters (most VSAT antennas range from 75 cm to 1.2 m). VSAT data rates typically range from narrowband up to 4 Mbit/s. VSATs access satellites in geosynchronous orbit to relay data from small remote earth stations (terminals) to other terminals (in meshconfigurations) or master earth station "hubs" (in star configurations).

VSATs access satellites in geosynchronous orbit to relay data from smallremote earth stations (terminals) to other terminals (in mesh configurations) or master earth station "hubs" (in star configurations).

Technology:

VSAT was originally intended for sporadic store-and-forward data communications but has evolved into real-time internet services. VSAT uses existing satellite broadcasting technology with higher powered components and antennas manufactured with higher precision than conventional satellite television systems. The satellite antenna at the customer's location includes, inaddition to the receiver, a relatively high-powered transmitter that sends a signalback to the originating satellite. A very small portion of a transponder is used for each VSAT return path channel. Each VSAT terminal is assigned a frequency for the return path which it shares with other VSAT terminals using a shared transmission scheme such as time division multiple access.

An innovative feature of VSAT is that the technology has evolved to the point that something that previously could only be done with large, high-powered transmitting satellite dishes can now be done with a much smaller and vastly lower-powered antenna at the customer's premises. In addition, severalreturn-path channels can co-exist on a single satellite transponder, and each of these return-path channels is further subdivided using to serve multiple customers.

Now days, nearly all VSAT systems are now based on IP, with a very broadspectrum of applications.

History:

The first commercial VSATs were C band (6 GHz) receive-only systems byEquatorial Communications using spread spectrum technology. More than30,000 60 cm antenna systems were sold in the early 1980s. Equatorial later developed a C band (4/6 GHz) 2 way system using 1 m x 0.5 m antennas and sold about 10,000 units in 1984-85.

In 1985, Schlumberger Oilfield Research co-developed the world's first Kuband (12/14 GHz) VSATs with Hughes Aerospace to provide portable network connectivity for oil field drilling and exploration units. Ku Band VSATs make up the vast majority of sites in use today for data or telephony applications.

A recent breakthrough in the VSAT technology has enabled us to use Ka band frequency which further reduces the size of Antenna to 3 meters.

Configuration:

Most VSAT networks are configured in one of these topologies:

A star topology, using a central uplink site, such as a network operations center (NOC), to transport data back and forth to each VSAT terminal via satellite. A mesh topology, where each VSAT terminal relays data via satellite to another terminal by acting as a hub, minimizing the need for a centralized uplink site. A combination of both star and mesh topologies. Some VSAT networks are configured by having several centralized uplink sites (and VSAT terminals stemming from it) connected in a multi-star topology with each star (and each terminal in each star) connected to each other ina mesh topology. Others configured in only a single star topologysometimes will have each terminal connected to each other as well, resulting in each terminal acting as a central hub. These configurations are utilized to minimize the overall cost of the network, and to alleviate the amount of data that has to be relayed through a central uplink site (or sites) of a star or multi-star network.

Advantage of VSAT Network:

VSAT is a satellite based communication service that offers a flexible and reliable communication solution including Enterprise Wide Networkingwith high reliability and reach that extends even to remote sites.

A VSAT Network provides:

Reliability in transmission of data (data, voice, video) Allocation of resources to different users (bandwidth, amplificationpower) Fixed Network solution. Provide point-to-multipoint (broadcast), multipoint-to-point (Data Collection), point-to-point communication and broadband multimedia services. Provide communication to remote and inaccessible areas.

VSAT Frequency Spectrum Allocation

Band Frequency Area Foot- Delivered Rainfall

Band C

Band Ku

Band Ka

GHz

3 to 7

10 to 18

18 to 31

print

Large

Medium

Small

Power

Low

Medium

High

effect

Minimum

Moderate

Severe

However, NTPC uses C Band frequency range (4GHz to 6 GHz). NTPC has been assigned Transponder No. 3 in the recently launched satellite INSAT 3E with uplink frequency range of 5.925 GHz to 6.425 GHz and downlink frequency range of 3.7 GHz to 4.2 GHz. The central frequency range used byNTPC to uplink and downlink its signals are 6025000Hz and 3800000 Hz respectively. The frequency at which satellite confirms its position by sending a signal is called the Beacon Signal, and in case of INSAT 3E it is 4197.51 MHz which is measured with a spectrum analyzer connected to antenna through the LNA.

A VSAT System can be broadly classified into two segments.

Space Segment. Earth Segment.

Earth Segment

Space Segment:

Space Segment

This 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 the organizations that have procured satellites, arranged launch and who operate these satellites on 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 customers‟ data traffic.

Ground Segment:

This is primarily called the Earth Terminal segment, The Earth terminal (or equipment at the customer‟s premises) can typically be divided into two parts

1. Outdoor unit 2. Indoor Unit

The outdoor unit is generally, ground or even wall mounted and the indoor unit, which is the size of a desktop computer, is normally located near existingcomputer equipment in your office.

Satellite communication concept

Note:

HPA – High Power Amplifier (Earth Station equipment that amplifies the transmit RF signal)

CPE – Customer Premises Equipment (eg. Telephone, PABX, Ethernet hub, host server etc.)

VSAT Specifications

Antenna diameter: 11 m

Traffic Capacity: 9.6 kbps – 2 mbps

Diagram

Frequency Bands:

C-Band (4/6 GHz)

Ku-Band (12/14 GHz)

Ka-Band (20/30 GHz)

Network: Point-to-Point

Configuration: Point-to-Multipoint

Equipment List:

Antenna; Outdoor Unit: HPA, LNA, SSPA(Solid State Power Amplifier) Indoor Unit : Chassis

Note:

Antenna size is used to describe the ability of antenna to amplify the signalstrength;

Outdoor unit (ODU) is connected through a low-loss coaxial cable to the indoor unit (IDU) called IFL (Inter-facility Link).

Typical VSAT System

Outdoor Unit:

The antenna system consists of a reflector, feed horn and a mount. The size of the antenna varies from 1.8 meters to 3-8 meters, 7.8 meters or 11 meters. The feed horn is mounted on the antenna frame at its focal point by support arms. The feed horn directs the transmitted power towards the antenna dish or collects the received power from it.

Antenna size is used to describe the ability of the antenna to amplify the signal strength.

Up converters and High Power Amplifiers (HPA) used for converting and amplifying the signal before transmitting to the feed horn. Extended C band, down converter receives the signal at 4.5 to 4.8 GHz and the up converter converts it to 6.725 to 7.025 GHz.

Antenna varies – antenna size is describe the ability of the antenna to amplify the signal strength feed-horns directs transmitted power to antenna dishor collects the received power from it.

Cassegrain Antenna System:

1. A Double reflector system 2. Works on the principle of cassegrain optical telescope. Employs a

parabolic contour for the sub dish. 3. Permits a reduction in the axial dimension of the antenna. 4. Greater flexibility in the design of the feed system. 5. Used for monopulse radar, satellite communication and eliminates the

need for long transmission lines.

Radio Frequency Terminal (RFT):

RFT is mounted on the antenna frame and interconnected to the feed horn + Low Noise Amplifier (LNA) + down-converters. LNA – minimize signal noise. Noise temperature is a parameter used to describe the performance of LNA.

Indoor Unit (IDU):

The IDU consists of modulators that superimpose the user traffic signal on a carrier signal. This is then sent to the RTF for up conversion, amplification and transmission. It also consists of demodulators which receive the signal fromthe RFT in the IF range and demodulates the same to segregate the user traffic signal from the carrier.

IDU also interfaces with various end user equipments, ranging fromstandalone computers, LANs, routers, multiplexes, telephone instruments, EPABX as per the requirement. It performs the necessary protocol conversionon the input data from the customer end equipment prior to modulation and transmission to RFT.

Block Diagram of a VSAT System

Antenna Control Unit:

This unit works to receive and transmitting signals from the satellite usingantenna and tracks antenna when required.

1. Beacon Signal Receiver The satellite sends a self generated signal named beacon signal to the earth station so that the antenna can track the signal. This signal is 4197 MHz for NTPC. This receiver the 4197 MHz signal can convert it to 70 MHz signal for antenna tracking.

2. Antenna TrackerThis checks the voltage level of the signal and when reduced automatically moves the dish antenna to track the maximum strength.

Tracking modes (For checking):

a) Time mode – The antenna tracker checks for the voltage level after every10 sec, 20 sec or whatever time is.

b) Signal Mode – The antenna tracker tracks the antenna to obtain the maximum signal strength whenever there is a difference of 3dB.

c) Time and Signal mode – It is the combination of both the above modes. The antenna tracks the signal whenever the signal strength decreases.

Half Power Beam Width (HPBW) – It is a parameter to check the strength of the signal. The width of the beam when the there is a difference of 3 dB fromthe maximum point of the gain i.e. beam width at that point of half power.

Given by

HPBW = 70λ/DxD

λ=V/n

where λ = Wavelength

D = Diameter of antenna

V = Velocity of the wave

As the antenna size is decreased HPBW increases as D is inverselyproportional to HPBW. Hence tracking in small antennas is not required but incase of antennas with big diameter, tracking is essential.

Antenna Control Unit

High Power Amplifier:

These are also known as Vacuum Tubes (Valve) Amplifiers or Tube Amplifiers, while semiconductor amplifiers have largely displaced valve amplifiers for low power applications, valve amplifiers are much more cost effective in high power applications such as RADAR, countermeasures equipment, or communication equipment. etc.

Now we‟ll compare two types of HPA which were used in our training

TWT High Power Amplifier

1. Used where power required is less, 1. Used

Klystron II

for high power i.e. for less power rating around 100W, 400W, 750 W

2. No tuning required as the signal is wide band signal

3. Suitable for NTPC as power ratingis low

4.

requirements, eg. 1kW, 3kW

2. Needs tuning so that maximumgain is achieved at a particular frequency. Narrow band signal.

3. Also used. NTPC CSES has got both types of High Power Amplifiers.

Both run each at a time to avoid burnout. So to avoid heating up we use Klystron II & TWT HPAalternatively.

4.

Working of Travelling Wave Tube (TWT):

This device is an elongated vacuum tube with an electron gun (a heated cathode that emits electrons) at one end. A solenoid coil wrapped around the tube creates magnetic field which focuses the electrons into the beam, whichthen passes down the middle of a wire helix that stretches the length of the tube, finally striking a collector at the other end. (In Lower power devices, the solenoid coil can be replaced by permanent magnets)

A directional coupler, which can be either a waveguide or an electromagnetic coil, fed with low powered radio signal that is to be amplified, is positioned near the emitter, includes a current into the helix.

The helix acts as a delay line, in which the RF signal travels at the same speed along the tube as the electron beam. The electromagnetic field due to the current in the helix interacts with the electron beam, causing bunching of the electrons (an effect called velocity modulation), and the electromagnetic field due to the beam current then induces more current back into the helix (i.e. the current builds up and thus is amplified as it passes down).

A second directional coupler, positioned near the collector, receives anamplified version of the input signal from the far end of the helix. An attenuator prevents any reflected wave from travelling back to the cathode.

The bandwidth of a broadband TWT can be as high as one octave, althoughtuned (narrowband) versions exist, and operating frequencies range from300MHz to 50 GHz. The voltage gain of the tube can be of the order of 40 decibels.

A TWT integrated with a regulated power supply and protection circuits is referred to as a Travelling Wave Tube Amplifier (TWTA).

Working of a Klystron II Tube:

Klystrons are used as an oscillator or amplifier at microwave frequencies to produce both low power reference signals for super heterodyne radar receivers and to produce high power carrier waves for communications and the driving force for linear accelerators, It has the advantage (over the magnetron) of coherently amplifying the reference signal and so its output may be preciselycontrolled in amplitude, frequency and phase. Many Klystrons have a waveguide for coupling microwave energy into and out of the device, althoughit is quiet common for lower power and lower frequency klystrons to use coaxial couplings instead. In some cases a coupling probe is used to couple the microwave energy from a klystron into a separate external waveguide.

A klystron makes use of speed-controlled streams of electrons that pass through a resonating cavity. Electrons in a klystron are accelerated to a controlled speed by the application of several hundred volts. As the electrons leave the heated cathode of the tube, they are directed through a narrow gap into a resonating chamber, where they are acted upon by a RF signal. The electrons bunch together and are directed into one or more additional chambers that are tuned at or near the tube‟s operating frequency. Strong RF fields are induced inthe chambers as the electron bunches give up energy. These fields are ultimatelycollected at the HPA alternatively.

NTPC CSES has got both types of HPAs. Both are run each at a time to avoid burnout. So to avoid heating up we use Klystron II & TWT HPAalternatively.

Low Noise Amplifier:

The Low Noise Amplifier (LNA) is a special type of electronic amplifier used in communication systems to amplify very weak signals captured byantenna. It is often located very close to antenna.

Using a LNA, the noise of all the subsequent stages is reduced by the gain of the LNA and the noise of the LNA is injected directly into the received signal. Thus, it is necessary for a LNA to boost the desired signal power while addingas little noise and distortion as possible in the later stages in the system.

LNA is rated with Noise Temperature Rating. Lower the noise temperature better the quality and more is the cost,

Here at CSES NTPC we have LNA of 37 K rating.

Other NTPC sites generally have LNA of 54 K rating.

Make : NEC

: Paradise make

Down Converter

UP/Down converter:

UP Converter

They are used to convert signals from low to high frequency or from a highto low frequency respectively. Up converter are used while transmitting, to increase the frequency, while down converter are used to decrease the frequencywhile reception.

The center frequency of up converter is 6025 MHz and Down converter is 3800 MHz. In C band, up converter converts 70 MHz frequency to 5.9-6.4 GHz and just the opposite occurs in down converter while reception.

Block diagram of up converter

Modem:

Modem is a combination of two words Modulation and Demodulation. This is a device which modulates the transmitting signal and demodulates the receiving signal. A communication device that converts one form of signal into another that is suitable for transmission over communication circuits, typically from digital to analog and then from analog to digital.

Modulation means superimposing the baseband signal on a carrier of high frequency so that it can be transmitted and demodulation is just vice versa of it i.e. it extracts the message signal from carrier wave at receiving end.

Modulation techniques used:

QPSK – Quadrature Phase Shift keying. QAM 16

Forward Error Correction (FEC) – this is a parameter determining the output of QPSK & BPSK. This is represented in fractions eg. ½, ¾, 7/8. etc.

Multiplexer: Multiplexer is a device that allows multiple logicalsignals to be transmitted simultaneously across a single channel.

Works in the following manner:

Quantization + Pulse Code Modulation (PCM) + Compressor.

Quantization – Quantizing refers to use of a finite set of amplitude levels anda selection of level nearest to a particular sample value of the message signal as the representation for it.

Multiplexer

Pulse Code Modulation – In PCM system, the message signal is sampled and the amplitude of each sample is rounded off to the nearest one of a finite set of allowable values, so both „time and amplitude‟ are quantized.

Compressor – It reduces the output frequency (compresses) to optimumlevel.

Block Diagram of MUX & Modem networking

Router:

A device or setup that finds the best route between any two networks, even if there are several networks to traverse, such a device is called router. Like bridges, remote sites can be connected using routers over dedicated or switched lines to create WANs. There are data ports in router known as DTE ports. It is a 25 pin data port. When two routers are connected i.e. same ports then there is a cross connection. But when different ports are connected like port of router with DCE port of MUX then there will be straight connection.

Router

Exchange:

Exchange

A workplace that serves as a telecommunication facility where lines fromtelephone can be connected together to permit communication is called Exchange. The voice signal from modem + mux is sent to exchange so that it candistribute it to its telephone subscribers. In NTPC 184 trunk lines are possible. Parameters: -

Route Number – It specifies NTPC site which has to receive data. Trunk number Transmission network Lens number – Combination of Module, unit, group (chord) & circuit number.

Communication between two Sites via VSAT:

CSES NOIDA

VSAT Topology:

STAR – the hub station controls and monitors can communicates with a large number of dispersed VSATs. Generally, the Data TerminalEquipment and 3 hub antenna is in the range of 6-11 m 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 inthe network without going through a central hub. A hub station in a meshnetwork 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 mesh topology, thereby accruing benefits of both the topologies.

TDMA (Time Division Multiple Access):

When numerous remote sites communicate with one central hub, this design is similar to packet switched networks. Because of competition with one another for access to the central hub, it restricts the maximum bandwidth in most cases to about 19.2 kbps. All VSATs share satellite sources on a time slot basis. Usually used in star topology as a transmission technique. Offered to domestic needs.

The VSAT Hub communicates with all dispersed VSATs (typically a 1.8 mdiameter parabolic shaped dish) on an outgoing channel of up to 512 kbps based on the TDM scheme. The incoming or return channel from the dispersedVSATs uses the TDMA channel technology that enables a large number of respective VSATs to share this single return channel. The incoming routes typically operate at 128kbps, and can go up to a maximum bandwidth of 256 kbps.

Petrol stations, information providers, retail chains, financial institutions and many large corporation that requires transfer of low to medium rate data applications between its head office and, local and outstation branch offices. Example of Point of Sales (POS transactions), Credit Card Verification, Reservations Systems Financial and Banking Applications (tellers, loans, ATM) etc.

SCPC (Single Carrier Per Channel) SCPC-based design provides a point to point technology, making VSAT equivalent to conventional leased lines. Dedicated Bandwidth up to 2 Mbps Usually using an international VSAT service in Asia Pacific.

SCPC overview

In the Hub-to-Remote configuration, one end of the VSAT link (normally the customer‟s HQ) is connected to the 11m VSAT Hub (Earth Station) via a terrestrial leased line. A VSAT antenna at the remote end or the distant end (normally the branch office) of the VSAT link is then interconnected to the VSAT hub via the satellite.

VSAT links with a Remote to Remote configuration bypass the VSAT Hub and has a stand-alone VSAT antenna at both ends of the link. Typical VSAT antenna size ranges from 1.8m to 2.4m.

FDMA (Frequency Division Multiple Access)

Oldest method of channel allocation. The satellite channel bandwidth is broken into frequency bands for different earth station. The earth stations must be carefully power controlled to prevent the microwave power spilling into the bands for the other channels. Here, allVSATs share the satellite resource on the frequency domain only.

3 Types:

PAMA (Pre Assigned Multiple Access) DAMA (Demand Assigned Multiple Access) CDMA (Code Division Multiple Access)

PAMA (Pre-Assigned Multiple Access)

The VSATs are pre-allocated a designated frequency. Equivalent of the terrestrial (Land Based) Leased line solutions.

PAMA solutions use the satellite resources constantly. Therefore, no call-up delays in the interactive data applications or high traffic volumes. PAMA connects high data traffic sites within an organization

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. Since the satellite resource is used only in proportion to the active circuits and their holding times, this is ideally suited for voice traffic and data traffic in batch mode. DAMA offers point-to-point voice, fax, and data requirements and supports video-conferencing. Satellite connections are established and dropped only when traffic demands them.

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. The data signal is combined with a high bit rate code signal which is independent of the data, Reception at the end of the link is accomplished by mixing the incomingcomposite data/code signal with a locally generated and correctlysynchronized replica of the code. Since this network requires that the central network management system co-ordinates code management and clock synchronization of all remote VSATs, STAR topology is the best one. Mainly used for interference rejection or for security reasons in militarysystems.

VSAT Characteristics and Advantages:

Reliability: Reliable satellite transmission of data, voice and video between an unlimited number of geographically dispersed sites or from these sites to headquarters.

Flexibility: The VSAT networks offer enormous expansion capabilities; On the other hand, VSATs offer unrestricted and unlimited reach. Additional VSATs can be rapidly installed to support the network expansion to any site, no matter however remote. Network Management: Network Monitoring and control of the entire VSAT network is much simpler than a network of leased lines, easilyintegrates end-to-end monitoring and configuration control of all network subsystems. A low mean-time to repair: Few hours, compared to leased lines whichextend up to a few days. Essentially, lesser elements imply lower MTTR. Up time of up to 99.5 % is achievable on a VSAT network. This is significantly higher than the typical leased line uptime of approximately80-85%. Cost: VSAT network offers significant savings over 2-3 years timeframe. The service charged depends on the bandwidth which is allocated to the network in the line with customer requirements. Link Budgets: RF equipment would cater to the requirements of the network topology and satellite modems in use. The link budget estimates the ground station and satellite EIRP (Effective Isotropic Radiated Power) required.

VSAT Services

Interactive real time application: o Point of sale/retail/banking (eg. ATM) o Corporate data

Telephony o Rural: individual subscriber o Corporate Telephony

Intranet, Internet and IP infrastructure o Multimedia delivery (eg. Video streaming) o Interactive Distant Learning/ Training

Direct-to-Home o Broadband internet access for consumers and businesses

Opportunities in VSAT Technology:

Voice over IP (VoIP) via satellite Frame Relay via Satellite ATM via Satellite

Video-on-Demand via satellite Multimedia Application

o Internet/e-mail connection o Telemedicine o Distance Learning

LAN/WAN:

A computer network that spans a relatively small area is called LAN. MostLANs are confined to a single building or a group of buildings. However one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a Wide-Area-Network (WAN). Most LANs are connected workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it is also able to access data and devices anywhere on LAN. This means that many users can share expensive devices such as Laser Printers, as well as data. Users can also use the LAN to communicate with each other, bysending emails or engaging in chat sessions.

LAN

Leased Circuits:

WAN

A leased circuit is a dedicated link provided between two fixed locations for the exclusive use of the customer. A Leased circuit may be speech may be speech circuit, a data circuit or telegraph circuit. Leased Line charges are uniform in all cases and are same as applicable to point to point leased circuit. In addition to above installation charges are also leviable.

Minimum hiring period for all regular leased circuit is one year.

Leased Line Circuit

E-mail:

Shorter for electronic mail, the transmission of messages over communication networks is called e-mail. The message can be notes entered from the keyboard or the electronic files stored on the disk. Most mainframes, minicomputers, and computer network have an e-mail system. Some e-mail systems are confined to single computer systems or network, but others have gateways to other computer systems, enabling the users to send electronic mails anywhere in the world. Companies that are fully computerized make extensive use of e-mail because it is fast, flexible and reliable.

Proxy Server:

A server that sits between a client application, such as web browser, and a real server is called Proxy Server. It intercepts all real requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the realserver.

Proxy Server

Hubs:

A common connection point for the devices in a network is called hub. Hubs are commonly used to connect the segment of LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all the packets. A passive hub serves simply acts as a conduit for the data, enabling it to go from one device (or segment) to another. So called intelligent hubs include additional features that enables an administrator to monitor the traffic passingthrough the hub and to configure each port in the hub. Intelligent hubs are also called manageable hubs. A third type of hub, called a switching hub, actually reads the destinationaddress of each packet and then forwards the packet to the correct port.

A Diagram showing Hub connecting nodes

Switches:

In networks, a device that filters and forwards packets between LAN segments is known as switch. Switches operate at the data link layer (Layer 2) and sometimes the network layer (Layer 3) of the OSI Reference Model and therefore supports any packet protocol. LANs that use switches to join segments are called switched LANs or incase of Ethernet networks, Switched Ethernet LANs.

Switch

Routers:

A device that forwards data packet along with networks is called Router. Arouter is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP‟s network. Routers are located at gateways, the places where two or more network connect.

Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best routes between any two hosts. Very little filtering of data is done through routers.

Router

Mobile Communication:

In a mobile communication system at least one of the transceivers is mobile. It may be on board a vehicle that can move at high speeds, or it may be a handheld unit by a pedestrian.

Mobile communication

Wireless Network:

In networking terminology, wireless is the term used to describe anycomputer network where there is no physical wired connection between sender and receiver, but rather the network is connected by radio waves and/or microwaves to maintain communications. Wireless networking utilizes specific equipments such as NICs, APs and routers in place of wires (copper or opticalfiber) for connectivity.

Radio Paging Overview: On site Pagers provide a fast and flexible means of communication betweenfixed installations and mobile packet pagers. They can be used to transmit tones, text message and alarm conditions and, unlike public systems, no call charges are incurred once the system has been installed.

Radio paging

Applications of Radio Paging:

Industrial Site Paging Alarm Monitoring Security Systems Warehousing Hotels and Restaurants Medical Facilities Environmental monitoring Retail Checkouts

Local Area Network (LAN):

The Local Area Network (LAN) is by far most common type of data network. As the name suggests, a LAN serves a local area (typically the area of the floor of a building, but in some cases spanning a distance of several kilometers). Typically installations are in industrial plants, office buildings, college or university campuses, or similar locations. In these locations, it is feasible for the

owning Organization to install high quality, high-speed communication links interconnecting nodes. Typical data transmission speeds are one to 100 megabytes per second. A wide variety of LANs have been built and installed, but a few types have more recently become dominant. The most widely used LAN system is Ethernet system developed by Xerox Corp. Intermediate nodes (i.e. repeaters, bridges and switches) allow LANs to be connected together to form larger LANs. A LAN may also be connected to another LAN or WANs and MANs using a “router”.

In summary, a LAN is a communication network which is:

Local (i.e. one building or groups of buildings) Controlled by one administrative authority Assumes other users of LAN are trusted Usually high speed and is always shared

LANs allow users to share resources on computer within an organization, and may be used to provide a (shared) access to remote organizations through a router connected to a Metropolitan Area Network (MAN) or a Wide Area Network (WAN).

The photograph shows some of the networking equipment at the center of the LAN used by the Communication Group in the Department of Engineering. Unshielded Twisted Pair cabling (UTP) enters the rack from the five suchlaboratories and is terminated on the patch panel (housed in the bottom box). Each outlet is connected via a colored patch lead to either 10 or 100 Mbps Ethernet Switch (blue, above the patch panels). Access to the remainder of the campus network is controlled via a TCP/IP Internet Router (blue, with cables connected at the rear). A second switch/router may be used to connect other equipment (white) forming separate experimentaltest LANs. The two smaller boxes on the top are Ethernet Hubs for connectinggroups of workstations, similar hubs also provide connection for the fiber optic links to other parts of the work area.

Wireless Network Topologies

Topology: The physical (real) or logical (virtual) arrangement of elements. In our case, this refers to the arrangement of nodes (i.e. computers, network printers, servers, etc.) in which the network is connected. There are five major topologies used today in wired networks: Bus, Star, Ring, Tree, and Mesh, but only two make sense in a wireless environment. These include the star and meshtopologies. The Star topology, which happens to be in widest use today, describes a network in which there is one central base station or Access Point (AP) for communication. The information packets transmitted by the originating node and are received by the central station and routed to the proper wireless destination node.

This station can be a bridge to a wired LAN giving access to other wired clients, the Internet, other network devices, and etc. From our review system, Complex‟s SoftBridge program provides a “software bridge” to wired clients and services without specialized hardware or AP. With this software, any computer that is connected to the wired network has a wireless Network Interface Card (NIC) can act as bridge.

The mesh topology is a slightly different type of network architecture thanthe star topology, except that there is no centralized base station. Each node that is in range of one another can communicate freely.

Advantages of Networking:

Sharing Resources

#Software The ability to share both a software application and the files it creates amongst all of your computers is the primary reason for setting up a network. Not only will you see an increase in your employees‟ productivity, but anincrease in the organization of their computer files as well. No longer will youhave to copy files to floppies and carry them from another computer to yours for processing. Opening files on a computer across your office will be as simple if they were stored on their own machine.

#Printers Sometimes the printer connected to your machine doesn‟t have the capabilities of another printer of your office. ; i.e. color or laser quality. To print on another printer in a non networked situation, you have two options.

First, you can disconnect your printer and install the new printer on your computer. Second, you could copy the file to a floppy disc and load it into the computer with connected printer. In a networked situation it is easy to select the printer in the network.

#Internet Most of the employees in the office can increase their productivity withaccess to internet. Using a technology such as Roadrunner and a cable/DSL router combined with a network allows multiple computers to share the same account.

#Logging Every time something happens on your network, an entry to the server‟s logis added. Some examples include:

1. Logging in or out of workstation. 2. Opening or closing a file. 3. Creating or deleting a directory. 4. Copying a file or files. 5. Errors or problems on the server or network. 6. Files printed and by whom. 7. Virus Scan results.

These log files can be then analyzed and to detect and solve the problems and weaknesses in your network.

#Security Windows NT uses a file system called NTFS, which has an ability to permit or deny the use of a file, folder, or drive based on the user‟s access level.

#Centralization A Server-based design which increases the organization of the network inmany important ways, including:

#Dedicated File Server Throughout a business day, your employees produce many electronic documents. A server is built with enough storage space to save all of your company‟s important files at one location. The job of the server is to give or “serve” these files to whatever user, with the proper security requests them.

#Redundancy All Networks, Inc servers are built with mirrored storage for increased up time. If there is a network problem accessing a drive, the information that is needed will be accessed from the mirrored drive without any interruption to the user.

#Disaster Recovery The server provides a central location for saving files and thus a centrallocation for backing them up. Daily or Weekly backup tapes of the entire server can be produced and placed in a fireproof save or take off-site as a precaution

for a natural disaster or theft. If a user accidentally deletes a file, the file can be replaced by using the copy on the latest backup.

#Virus Scanning Every computer should have a virus scanner installed. When dealing withmore than one computer in an office environment, the task of stopping viruses and updating virus patterns can waste a lot of human and computer time. Avirus scanner on the server can be setup to scan and repair all the files on the server regularly, and watch for new viruses on the network. When the user tries to open any new file, the server scans the file and can actually restrict access to an infected file and alert the administrator with a popup message.