Training Report oF BSNL

Acknowledgement

I acknowledge my gratitude and thank to all the well knowledge persons for giving me opportunity to avail all the best facilities available at this telecom centre through which I have gained knowledge thinking so as too just in the environment suitable for harmonic adjustment. I am grateful to the following persons for various help rendered by them during the training period.



Mr. A.K. Shukla JTO

Finally, a deep thanks to


Mr. B.N. Singh SDE

Last but not the least; I thank my teacher, friends and my family members for their constant encouragement.






PREFACE



Since time immemorial, a man has tried hard to bring the world as close to himself as possible. His thirst for information is hard to quench so he has continuously tried to develop new technologies, which have helped to reach the objective.
The world we see today is a result of the continuous research in the field of communication, which started with the invention of telephone by Grahm Bell to the current avtar as we see in the form INTERNET and mobile phones. All these technologies have come to existence because man continued its endeavor towards the objective.

This project report of mine, STUDY OF TRENDS TECHNOLOGIES IN COMMUNICATION AND NETWORKING has been a small effort in reviewing the trends technologies prevailing. For this purpose, no organization other than BAHRAT SANCHAR NIGAM LIMITED could have been a better choice.

Table of contents

1. Acknowledgement
2. Preface
3. Table of contents
4. Introduction
5. making a telephone call
6. About the exchange
a. computer unit
b. power plant
c. central air conditioner
d. main distribution frame
7. V-SAT network
a. Design aspects
b. Operational factors
8. Types of access V-SAT networks
a. fixed assignment time division multiple access
(F-TDMA)
b. Random access
c. Code division multiple access (CDMA)
9. The Internet
a. Introduction
b. Internet connectivity
c.OSI model
d. Communication b\w the layers
e. File transfer the internet
f. National internet backbone
10. Wireless in local loop
a. Technical aspects
b. Advantages
11. Global system for mobile communication (GSM)



BHARAT SANCHAR NIGAM LIMITED (BSNL)

An Introduction:-

Today, BSNL is the No. 1 telecommunication company and the largest public sector undertaking of India and its responsibilities includes improvement of the already impeccable quality of telecom services, expansion of telecom services in all villages and instilling confidence among its customers.

Apart from vast network expansions, especial emphasis has given for introducing latest technologies and new services like I-NET, INTERNET, ISDN (INTEGRATED SERVICES DIGITAL NETWORK), IN (INTELLIGENT NETWORK), GSM and WLL (WIRELESS IN LOCAL LOOP) services etc. Now BSNL has also entered in mobile communication. BSNL has all the new services send technological advantages, which are available with any well, developed Telecom network anywhere else in the country.
Full credit for all above achievement goes to the officers and staff of the BSNL. The administration is fully aware of the challenges lying ahead and quite committed to provide the latest and best telecom services by their continued support and active co-operation.

BSNL Services:-

When it comes connecting the four corners of the country , and much beyond , one solitary name lies embedded at the pinnacle- BSNL. A company that has gone past the number games and the quest to attain the position of the leader. It is working round the clock to take India in to the future by providing excellent telecom services for people of India.
Driven by the very best of telecom technology from global leaders, it connects each inch of India to the infinite corners of the globe, to enable you to step in to tomorrow.
The telecom services have been recognized the world over as an important tool for socio-economic development for a nation and hence telecom infrastructure is treated a crucial factor to realize the socio-economic objectives in India. Accordingly the Department of Telecom has been formulating developmental policies for the accelerated growth of the telecommunication services in various cities. The department is also responsible for frequency management in the field of radio connection in close coordination with the international bodies.


MAKING A TELEPHONE CALL


A telephone call starts when the caller lifts the handsets of the base. Once the dial tone is heard, the caller uses a rotary or a push button dial mounted either on the handset or on the base to enter a sequence of digits, the telephone number of called party. The switching equipment from the exchange removes the dial tone from the line after the first digit is received and after receiving the last digit, determines the called party is in the same exchange or a different ones. If the called is in the same exchange, burst of ringing current is applied to the called party’s line. Each telephone contains a ringer that responds to specific electric frequency. When the called party answers the telephone by pocking up the handset, steady start to flow in the called party’s line and is detected by the exchange. The exchange than stops applying ringing and sets up the connection between the caller and the called party. If the called party is in different exchange from the caller, the caller exchange set up the connection over the telephone network to the called party’s exchange. The called party then handles the process of ringing, detecting an answer, and notifying the calling and billing machinery when the call is completed. When conversation is over, one or both parties hang up by replacing their handset on the base, stopping the flow of current. The exchange when initiates the process of taking down the connection, including notifying billing equipment of the duration of the call if appropriate.




ABOUT THE EXCHANGE



All telephone subscribers are served by automatic exchanges, which perform the functions the human operator. The number being dialed is stored and then passed to the exchange’s central computer, which in turns operates the switching to complete the call or routes it a higher level switch for further processing. Today’s automatic exchanges uses a pair of computers, one running the program that provides services and the second monitoring the operation of the first, ready to take over in a few seconds in the event of equipment failure.

Various exchanges present in BSNL are:

E-10B
OCB283
EWSD


All exchange has some purposes and some basic structural units, which are:

1. subscribers connection unit
2. switching network (CX)
3. control unit
4. OMC

For smooth working of an exchange following unit are very important:-

1. Computer Unit: - it deals with additional services of the exchange to the customers with the help of computers.

2. Power Plant:- to feed proper power supply to exchange

3. AC Plant: - to maintain the continuous temperature + or – 2 degree Celsius to the digital switch (exchange).

4. MDF: - to connect switch (exchange) with the external environment (subscriber) i.e. it is the interface between subscribers and exchange.




Computer unit

As the name specified it is the main part of the exchange that deals with the all services provided by the exchange to the customers with the help of computer. It also provides the updated data to all other part of the exchange.

The customers are using the services of the exchange by using the internet also gets connected to the main server present this room via an internet room.

It mainly consists of the servers that are providing the different services. The main servers of this room are:-

IVRS is used for the change number services provided by the exchange.

CERS are provided by the exchange to avoid the problems that the users are facing the repairing of telephone. In this system when the user enters it’s complained it gets directly entered to the server and user is allotted with an id number.

LOCAL DIRECTORY ENQUIRY is another services provided by the exchange, by using this; subscribers calls the particular number and gets the directory enquiry. The server present in the main computer room provides this service.

INTERNET DIRECTORY ENQUIRY is the latest service by the exchange. In this type of service makes it enquiry using the internet, which gets connected to the main server at the internet room in the exchange and further to the main server in the computer room.



POWERPLANT

As we know that, the power is the main source or any organization. It is the case of E-10B exchange. That is the first requirement of any organization is the input.
The main source of this exchange is AC supply. However, as soon as the power supply is gone off, then what is source? No one think on this that the telephone is always plays its role in the human life. Even if the power supply gone off. Thus there must be adjustment source of power.
The main parts of the power room are:

Batteries: - these are the instant sources of the power as soon as power is gone off.

UPS (Uninterrupted Power Supply):- the UPS must give supply to the computer. As we know there is some equipment which can withstand any type of power supply, but there are also some instruments which cannot withstand with this type of power supply, even a microsecond delay will cause the loss of data.

Charging- Discharging Unit: - the batteries we are using in the power room need timely charging. As soon as the AC power supply is on, we make use of the charging unit present in the power room. The slowly charging of the batteries is known as the trickle charging. But sometimes we need the BOOSTER charging. In this type of charging awe take of the batteries from the load and charge separately, until it gets fully charged.
The main work of the discharging unit is to control the discharging of the batteries.

Inverter and Converter Unit: - the main use of this system is to change AC mains to DC and vice versa as required by the parts of exchange.

Engine Room:-we know that the batteries are the instant source of supply but we cannot use it for much larger time, thus for this, we have an engine to generate the power supply. They are of 885 KVA. Thus, this room controls the supply of the engine.





CENTRAL AIR CONDITIONER


For the function of electrical equipment, cooling system is basic requirement. The basic advantages of cooling systems are following-
It provides the thermal stability so that the temperature does not reach the tolerance limit of electronic equipment
It saves equipment from dust so to avoid malfunction of equipment’s.
It protects equipment from excess humidity which can caused rusting of equipment.

The basic unit of measurement used in the industry is known as “ton of refrigeration” (TR) which is equivalent to the heat extracted in 24 hours for converting thousands kg of liquid to ice at zero degree.
The compressor is the heart of the AC system and the costliest. It increases the pressure and temperature of the refrigerant gas coming from the evaporator coils by compressing it.
Compressor comes in various types. The most widely used is simple reciprocal type a cylinder and piston arrangement. For capacity more than 120 TR, centrifugal compressors are used. The condenser liquefies the refrigerant gas by a heat exchange process. The capillary tube or the expansion valve pressurizes liquid refrigerant and meters it flows to the evaporator.
The refrigerant then passes trough the evaporator coils, which extract heat out of the ambience.



MAIN DISTRIBUTION FRAME


The primary function of MDF is:
The fault of telephone number is removed in the MDF; it is called as Fault Remove Section.
For removing the fault of telephone number, we use the testing
These testing are T.T.Y. testing, Group testing, etc.
For any type of testing firstly we need the vertical no. or the live tester, printer and computer test N.E. number of that particular telephone number.
The telephone numbers are also disconnected in the MDF because of some specific reason.







ORGANISATION OF THE MDF
PARTS OF THE MDF

Horizontal side
Vertical side

HORIZONTAL SIDE:

It is again subdivided in to two parts
Exchange side
Line side

Description of the horizontal side:-

RACK: - On the rack, the tags are situated. One rack is having eight tags. The courting is done from up (0) to down (7).

TAG: - Each rack consists of eight tags.
1 tag = 4 core
1 core = 4 bunch
1 bunch = 2 line

N.E.:- The word NE stands for the ‘NUMBER OF EQUIPMENT’.
It is a 128 pair cable. The EWSD and MDF connected by NE.

WEDGE:-If we want to disconnect any two numbers then we insert a wedge between subscriber side and exchange side. Here wedge works as insulator made of plastic.



VERTICAL SIDE:

The vertical aside connected to the underground cable. This cable is having 100 pairs.
These pair is distributed when we allot the telephone number to the subscriber.
Vertical side is again subdivided in two parts:

One part is connected with the horizontal side and another with the subscriber line by using 100 pair underground cable.

This is how the present day telephone system works. Different exchanges have different architectures of switching call routing and other features.

Now let us see how BSNL has kept up with the changing world and provided the subscribers with the latest facilities technologies, which include the V-SAT network, Internet, the WLL (wireless in local loop) and the GSM mobile.




V-SAT NETWORK


What is V-SAT?

It can be defined as a class of very small aperture Intelligent Satellite Earth Station suitable for easy on-premise installation, usually operating in conjugation with a large size HUB earth station. Capable of supporting a wide range of two ways integrated Telecom Services.
It has the following components:
Micro Earth Station
Mini Earth Station
Personal Earth Station
Roof Top Terminal
Customer Premises Terminal



ADVANTAGES OF V-SAT

Can be located in the user premises on roof top or backyard and hence eliminate last mile problem.
Superior quality satellite based data services.
Quick implementation time.
Reliable communication.
Broadcast feature on satellite communication.
Communication to different areas.
Flexibility for network and changes.
Service in distance insensitive.
Low cost.


REASON FOR V-SAT EVOLUTION

The main reason for V-SAT evolution is due to advances in following areas:
Packet transmission and switching.
Efficient multiple access protocol.
Powerful microprocessor.
KU and RF electronics.
Antennae miniaturization
Spread spectrum techniques.
Protocol standardization and implementation.
LSI based FEC codec has and modems.
Higher power satellites.

CLASSIFICATION OF V-SATs

V-SAT can be classified as following:
1. Modulation type
2. Application used for.
3. Transmission rate.
4. Cost.

CATEGORIES OF V-SATs

1. Broadcast/ point to multipoint
Types of services
a. Broadcast video
b. Program quality audio.
c. Packetised data.
In this mode of operation V-SATs transmit/receive data through a centralized HUB. This type of network is called star network.
2. Point to point
Types of services
a. Voice
b. Data
c. Image
In this mode of operation, V-SATs transmit/receive data without the help of hub station. This type of network is called a mesh network.
3. Two way interactive
Types of services
a. Voice
b. Data
c. Image
In this configuration, V-SATs can communicate both on star as well as mesh topology.







DESIGN FACTORS FOR V-SAT SYSTEMS

The capabilities of V-SAT system depend upon the following factors.
I. Satellite characteristics
II. Geographical and environmental factors.
III. Transmission link properties.
IV. Earth station characteristics.
V. Information encoding and modulation.
VI. Total system operation.



When evaluating V-SAT system each of the above attributes should be given attention. However, few of more important attributes are
Operational aspects
Frequency bands
Satellite access methods


OPERATIONAL ASPECTS

Considering a V-SAT system from its operational aspects, there are five broad functions that determines how the system works. These are:
Bandwidth allocation
Multiplexing
Network management
Protocol handling
Transmission



TYPE OF ACCESS FOR V-SAT DATA NETWORK

There are three types access available for V-SAT data networks. They are:

1. Fixed assignment time division multiple access (F-TDMA)
2. Random access
a. Pure aloha
b. Slotted aloha
c. Reservation
i. Implicit
ii. Explicit
3. code division multiple access (CDMA)




FIXED ASSIGNMENT TIME DIVISION MULTIPLE ACCESS (F-TDMA)


In a fixed assignment TDMA, each frame is divided in to slots of fixed time durations among stations of network. The assignment of stations to slots is permanent similar to TDMA system carrying digitalized voice except FTDMA does not have synchronization. Packets are sent asynchronously, with no frame sync signals.

FEATURES

No inter modulation problems.
Transport utilization is better.
Burst from different stations must arrive at satellite exactly in allocated slots.
Throughput is 70% to 80%
Delay – medium is too high.
Complexity-medium.





RANDOM ACCESS


With TDMA schemes, signals are transmitted by earth stations in a burst mode. If no scheduling is provided b/w the transmitting station, this type of access is called time random multiple access. This simplest method for the stations to transmit burst without regard for other station.

Random access id of two types:
Pure aloha
Slotted aloha


PURE ALOHA

Pure aloha, also called unslotted aloha is the simplest form of random access schema.
In this form of access stations transmit packets\bursts randomly.
Packet from different stations may collide, thereby destroying information content.
Station transmits the packet until they are received correctly.
The aloha channel throughout can be analyzed in terms of traffic offered through the following relationship:
S=Ge-2g
Maximum throughput is 13% to 18%.
Delay- low
Complexity- very low




SLOTTED ALOHA

The maximum throughput of an unslotted aloha channel is limited to 18% due to collision.
To reduce probability of each collision time slots are introduced so that the transmission could only at the start of the slots.
The above network discipline reduces the rate of collision by half and hence increases the maximum throughput efficiency of the channel.
In S-Aloha, each station has 2 queues.
a. New packet queue
b. Retransmit packet queue.
Only if the retransmit packet queue is empty, a new packet queue is sent.
The analysis of slotted aloha channel shows that
S = Ge2g
Maximum channel throughput is 36%.
Delay- low.
Complexity- low- medium.


Reservation

The low bandwidth utilization of pure aloha and the slotted aloha has led to many proposals for increasing utilization by means of slot reservation schemes.
The object of slot reservation schemes is to receive a particular time slot for a given station. This ensures that no collision takes place.
This scheme has a higher throughput than either S- Aloha or F-TDMA depending on traffic.
This increase in channel utilization efficiency is obtained at some overhead either in terms of allocation of bandwidth for reservation purposes and\or increased complexity of the control mechanism in transmitting stations.
All reservation methods use some form of framing approach and the reservation scheme can be either implicit or explicit.
The implicit reservation method involves reservation by use. This is done whenever a station successfully transmit in a slot; all the stations internally assign that slot in sub-segment frames for exclusive use by the successful station. This is called R-Aloha. In this there is no way to prevent a station capturing most or all of the slots in a frame for an indefinite time.
The explicit reservation is a distinct and unique assignment of slots to a user by the network scheduler.







CODE DIVISION MULTIPLE ACCESS (CDMA)


With CDMA transmission from earth station are spread over the time frequency plane by a code transformation. These techniques are referred to as Spread Spectrum Systems. In addition to their multiple access capabilities, they are useful in combating jamming, and are for this reason principally used in military systems.



Features

All stations operate on the same transponder frequency using a large bandwidth than needed for the data rate.
Network needs no time for frequency coordination.
Provide anti jam capabilities or protection against interference.
Provide for a graceful degradation of network performance as the number of simultaneous users increases.
Low spectral density compared to conventional emissions.
It yields same capacity as FDMA.


Limitations of CDMA

Require large transponder ratio.
Due to imperfect code orthogonalities, expected simultaneous users may be limited.
Requires a highly central earth station called HUB using star configuration.
VSAT technology using SSMA is presently available only for low bit rate application.


VSAT NETWORK IN DOT

Department of telecommunication entered the VSAT era in 1991 by commissioning its first satellite based low bit rate network known as REMOTE AREA BUSINESS MESSAGE NETWORK (RABMN).
This has been engineered for users located in remote areas for stable and reliable data communication.
This service envisages installation of very small aperture terminals (VSAT) to work with satellite based pocket switched network.

It has 3 main components:-

A large master earth station (hub)
A satellite transponder located in geo stationary orbit
A small micro earth station located at user’s premises




SERVICES OFFERED BY RABM NETWORK:-


Data communication up to 1200 bps
Fax services.
Access to Public Telex Network
Access to international data network through VSNL gateway.



Tariff and billing:-

A RABMN customer availabling VSAT has to pay the following charges:-
Registration charge Rs. 5000 per terminal
Cost of each VSAT Rs. 5.2 lakhs
Cost of each installation Rs. 15,000 per terminal
License fees Rs. 100 per terminal
Maintenance charges Rs. 25,000 per terminal annually
Satellite access charges Rs. 5000 per month per terminal
Traffic charges Rs. 50 per kilo segment of data




Network users:

Some of the probable users are

Banking network
Civil aviation
Airlines\railways
Public\private sector industries
Meteorological department
Police department



RABMN NETWORK

Introduction

Satellite communication plays a vital role in long distance communication.
Satellite medium offers high bandwidth making it suitable for data communication and computer networking.
Satellite communication is of distance and cost effective.
Multi access nature of satellites.
Provides two way communications.
Dynamic assignment of channels between geographically dispersed users.
Satellite network provides point to point and point to multipoint communication needs.





Frequency division multiple access (FDMA):-


Bandwidth is split in to narrow frequency bands with multiple users each allocated a frequency range within the larger bandwidth.

Time division multiple access (TDMA):-


Each terminal is allotted a short time slot in which to transmit on a sequential basis. This time slot is usually a fraction of a second.






Code division multiple access (CDMA)


Each terminal is allotted a unique encryption code. The transmitted signals are encoded and only the terminal intended to receive it, can decode it. This is also known as Spread Spectrum Multiple Access.





Statistical time division multiplexing (STDM):-

In TDM, time slots are allotted to the multiplexed lines even if they have no data transmit. In STDM, a time slot is allotted to the multiplexed line only if there is data to be sent. The multiplexed circuit is used more efficiently.




VSAT (very small aperture terminal)

It is also called Micro Earth Station or Personal Earth Station.

Its main features are as follows:-

Independent of terrain can be installed in hilly regions, islands and remote places.
Flexible service carrying data, Telex.
No last mile problems of cable pair\overhead lines.
Interference immunity.
Data security


The main services offered by VSAT are as follows:-

Interactive data communication.
Connection to public telex network.
Connection to Packet Switched Data Network – INET.
Connection to international gateway packet switch.



The different technologies used in VSAT are-

Satellite based
Spread spectrum
Packet switching



Tariffs:-



Cost of VSAT : about Rs. 7,00,000
Installation cost : Rs. 15,000
Maintenance cost : Rs. 25,000
Satellite access charge : Rs. 5,000 per month

Charges for using VSAT are as follows:

Ø National : Rs. 50 per kilo segment of data
: Rs. 10 per min in addition to vol. of telex
Ø International : Rs.200 per Kilo segment of data
: Rs. 240 per hour duration.


Dialing codes for VSAT are as follows:

Within RABMN:
o 12 digit code
o 4041xxxxxxxx


to other data networks:
o I-NET
o 4043xxxxxxxx
o international networks
o DNICxxxxxxxx

To telex networks
NATIONAL
Q008/area code/telex number

INTERNATIONAL
0009/country code/telex number

TELEX TO RABMIN
09841xxxxx (last 5 digits of telex number)


Specifications for master earth station:

There are two types of master earth stations:

Outbound
Inbound






Outbound:

Each VSAT and host computer is allotted an HCL port
NPG polls HCL ports and generates a 153.6 Kbps demand based STDM data stream
Data stream contains variable length packets of data addressed to various VSAT’s
Outmux chips the data @1:16 resulting in 2.4576 MB stream.
BPSK modulator produced 5 MHz of spectrum
Upconvertor converts to 5GHz RF
Mes transmits 153.6KBps STDM/BPSK/SS carriers
NPG provides FEC encoding for outbound data




Inbound:

Inbound signals originates from VSAT’s
VSAT has a unique PN code
Data spread by its PN code and transmitted to satellite in 6 GHz band
MES resolves the signal in 4 GHz band, converts to 70 MHz IF and sends to Demod section
Demod cards compare the pattern of the to other PN code for its associated VSAT. When the correct pattern is detected, the original signal is extracted from the IF signal and transmitted to INMUX
NPG polls INMUX for I\C data packets and transmits the packets to HCL








VSAT specifications


Antennae module

Ø Reflector : 1.2M X 1.8M
Ø Weight : 60 KGs
Ø Tracking : fixed
Ø Amb. Temp : -40 to +50 deg. Cel.
Ø Wind speed : operating 100 kmph

Controller module

Ø Size : 15 cm(h) x 43 cm(w) x 55 cm (d)
Ø Weight : 15 kgs
Ø Power supply : 220V\60Hz, 300 watts
Ø Oper. Temp. : -5 to 50 deg. Cel.
Ø Humidity : up to 95%



Controller module :

Ø INPUT\OUTPUT PROCESOR
· Converts raw data to packets
· Customer protocol to network protocol

Ø NETWORK PROCESSOR
TRANS SIDE:
· generates BFEC & FCS
· Retains packets in buffer until ACK’s receives and transmits if required.

RECIEVER SIDE:
· checks BFEC & FCS
· ACK’s the packets and requests retransmission of missing packets

Ø SPACE PROCESSOR
TRANS SIDE
· Encodes the packets with PN sequence to 2.45MBps stream
· BPSK modulation of IF


RECIEVER SIDE
· Demodulates IF signal to 2.45MBps
· Dispreads to 153.6KBps stream
· Checks destination link address in the header
· Discards packets addressed to other links.

Micro earth station transmits 1.2KBps\9.6KBps BPSK/CDMA carrier’s bursts in absolutely random access mode in the same frequency.










INTERNET

Introduction:

The Internet is not a program, not software, not hardware or a big system. It is a group of various co-operating computers worldwide interconnected by computer based on TCP\IP communication protocols. People use it to get information over a standard communication link. The hundreds or thousands or millions of computer network are connected to each other for exchanging the information which is based on the unique identity and set of procedures. Internet is a series of interconnected networks providing global link to information.

GIAS: BSNL launched the Gateway Internet Access Service (GAIS) through dial up/leased/ISDN network. Users can access GAIS from 99 cities in India by this means.




INTERNET CONNECTIVITY


INTERNET TECHNOLOGY


The basic function of Internet can be summarized as under-

Interconnecting of computers to form a network.
Interconnecting of computers to form a network of networks.
To establish a communication link between two computers within as network.
To provide alternate communication link among the networks, even if one network is not working. These are based on TCP/IP communications protocol.



Transfer of a file through Internet:-


Suppose a file is to be transmitted on Internet from one computer to other ones

Break the file in to small packets
Attached destination and source address in o packets
Multiplexed and transmit these packets
At destination de-multiplex the packets
Remove address bits from the packets and assemble the data in to the original file
Make source bits as destination address and send the acknowledgement in to the source

Therefore, it is clear that network hardware sends the packets to specified destination and network software reassembles of communications, the computer network performs the following functions-

Addressing and routing
Fragmentation and error correction
Data error checking
Connectivity control
Multiplexing and de-multiplexing
Data flow control
End users interface etc.
The data handling


A single module cannot handle the entire process. One that adopted as a standard is an open system interconnection (OSI) model.


OSI NETWORKING MODEL: The open systems interconnection model defines all the methods and protocols needed to connect one computer to any other over a network.

The OSI model separates the methods and protocols needed for a network connection in to seven different layers. Each higher layer relies on services provided by a lower level layer.

The OSI model is sometimes called “the seven layer model”. It was developed by the International Standards Organization (ISO) in 1983 and is documented as standard 7498.

Layers are:


Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer




PHYSICAL LAYER:

The physical layer defines the properties of the physical medium used to make a network connection. It includes a network cable that can transmit a stream of bits between nodes on the physical network. The physical connection can be either point to point or multipoint, and it can consist of either half duplex (one direction at a time) or full duplex (both directions simultaneously) transmissions. Moreover, the bits can be transmitted either in series or in parallel (most network use a serial stream of bits, but the standard allows for both serial and parallel transmission). The specification for the physical layer also defines the cable used, the voltages carried on the cable, the timing of the electrical signals, the distance that can be run, and so on. For example, a NIC network interface network) is part of the physical layer.


DATA LINK LAYER: the data link layer, layer 2, defines standard that assign meaning to the bits carried by the physical layer. It establishes a reliable protocol through the physical layer, so the network layer (layer 3) can transmit its data. The data link layer typically includes error detection and correction to ensure a reliable data stream. The data elements carried by the data link layer are called frames.
Examples of frame types include x.25 and 802.x (802.x includes both Ethernet and Token Ring networks).

The data link layer is usually subdivided in to two sub layers, called the Logical link control (LLC) and Media Access Control (MAC) sub layers. The LLC sub layer performs tasks such as call set up and termination and data transfer. The MAC sub layer handles frame assembly and disassembly, error detection and correction, and addressing. The two most common MAC protocols are 802.3 Ethernet and 802.5 Token ring .Other MAC protocols include 802.12 100 Base VBG, 802.11 Wireless, and 802.7 Broadband.



Network Layer: The network layer, Layer-3, is where a lot of action goes on for most networks. The network layer defines how data packets get from one point to another on network. The Network layer is also known as packet layer, it defines different packet protocols, such as Internet Protocol (IP) and Internet Protocol Exchange (IPX). These packet protocols include source and destination routing information. The routing information in each packet tells the network where to send the packets to reach its destination and tells the receiving computer from where the packet originated.

Transport Layer: The Transport Layer, layer-4, manages the flow of information from one network node to another. It identifies each computer or node on a network uniquely. It ensures that the packets are decoded in the proper sequence and that all packets are received. Transport layer protocols include Transmission Control Protocol (TCP) and Sequenced Packet Exchange (SPX).Each is used in concert with IP and IPX respectively.


Session layer: The session layer, layer-5, defines the connection from a user to a network server, or from a peer on a network to another peer. These virtual connections are referred to as sessions. They include negotiation between the client and the host, or peer and peer, on matters of flow and control, transaction- processing, transfer of user information, and authentication to the network.


Presentation Layer: The presentation layer, layer-6, takes the data supplied by the lower level layer and transform so it can be presented to the system. The Presentation layer can include data compression and decompression as well as data encryption and decryption.

Application Layer: The Application layer, layer 7, controls how the operating system and its application interact with network.
As mentioned earlier, data flows from an application program or the operating system, and then goes through the protocols and devices that make up the seven layers of the OSI model one by one until the data arrives at the physical layer and is transmitted over the network connection. The computer at the receiving end reverses this process. At each stage of the OSI model, the data is “wrapped” with new control information related to the work done at the particular layer. This control information is different for each layer, but it includes headers, trailers pre-ambles, and post-ambles.
Therefore, for example, when the data goes into the networking software and components making up the OSI model, it starts at the application layer and includes an application header and application data. Next, at the presentation layer, a presentation header is wrapped around the data and it is passed to the session layer, where a session header is wrapped around all the data, and so on, until it reaches the physical layer. At the receiving computer this process is reversed.





COMMON TERMINOLOGY USED IN INTERNET:

WWW:

World Wide Web (WWW) is a wide area hypermedia information retrieval aiming to give universal access to a large universe of documents.

HTTP:

Hyper text transmission Protocol (HTTP) is the communication protocol used to transfer documents from the server to client over the WWW (http:// www).

HTML:


Hyper Text Markup Language (HTML) is a system of marking or tagging the various parts of web documents to tell the browser software how to display the document text, link graphics and link media.

ISDN:

Integrated Service Digital Network (ISDN) is a digital phone connection technology that provides both voice and data services over the same connection.

ISP:

Internet Service Provider (ISP) is an agency that provides Internet access and other net related services.




NATIONAL INTERNET BACKBONE (NIB)


Networking is a key component of any Internet Services Provider (ISP) operations. The networking equipments like access servers, routers and modems are critical to the successful functioning of ISP.
An ISP node where subscribers enter internet, consists of a set of equipments as given below.
Access server
Router
Modem bank
LAN (Local Area Network) components
Security server
Rack, console & power supply
Network management agent.
Help desk





WIRELESS IN LOCAL LOOP (WLL) MOBILE

WLL is a communication system that connects customers to the Public Switch Telephone Network (PSTN) using radio frequency signals as substitutes of conventional wires for all part of connection between the subscribers and the telephone exchange. It works on CDMA technique. The local loop is access part of telecommunication network i.e. the part between PSTN switch and subscribers. WLL network application involves uses of radio to replace of the wire link between PSTN switch and subscriber. The radio technology is able to provide same quality of services as that provided by the wires line. Application of wireless loop technology has just been started in the worldwide. There is no standard for this so far. However, a number of national and international air interface standards for digital cellular mobile telephone system are available.


TECHNICAL ASPECTS:

WLL is based on CDMA technique and is entirely different from GSM. The system for WLL services can be divided in to following parts:-

BSC (Base Switching Centre):- It provides links between BTS & BSM; it consists of different processors, in BSNL it is of SUN Polaris of LG Company. In LG 1 BSC can have 48 BTS? In BSNL we have two types of BSC:-


V-5.2:- This type of BSC cannot switch by itself so it is dependent on local exchange / PSTN for switching and keeping records of billing etc. BSNL uses this type of BSC for rural areas.


CCS-7 / R2:- These types of BSC are totally automatic it doesn’t depend on local exchange for its functions, it is complete in itself. BSNL uses this type of BSC for urban areas.


BTS (Base Transreceiver System):- As it is clear from its name it transmits as well as receive signal, it works as an amplifier (router) to overcome the loss in signal in transmission.


BSM (Base Station Management):- It controls and manages the WLL services. It can troubleshoot the problem; add new users as well as capable to block service given to user. It is basically a computer system, which manages the whole process of WLL service. In BSNL BSM are two UNIX based computer system.


CODE DIVISION MULTIPLE ACCESS (CDMA):

CONCEPT OF MULTIPLE ACCESSES: - Multiple access system allows a large number of users to share a common pool of radio telephone circuits, like sharing of trunked radio facility. Multiple access radio has similarity to the LAN in which the common channel is available to all users. The circuits are demands assigned i.e. assigned on demand first-cum-first-served basis. The provision of access to the radio circuits methods of multiple accesses are:

CDMA: - Where large number of transmission are combined on the same channel at the same time and separated by the codes.


FDMA (Frequency Division Multiple Access):- Where individual transmission separated by each other by the time.

WHAT IS CDMA?

CDMA, a cellular technology originally known as IS-95, competes with GSM technology for dominance in the cellular world.
There are now different variations, but the original CDMA is known as CdmaOne.

Latest CDMA global subscriber & operators numbers
As of December 2002, there were 120 millions users worldwide, with 55 million of these in the USA.
See other cellular technology in the world.

We now have CDMA2000 and its variant like 1X EV, 1XEV-DO and MC 3X. The refer of variant of usage of a 1.25 MHz channel. 3X uses a 5 MHz channel. Wide band CDMA forms that the basis of UMTS 3G networks, developed originally by Qualcomm, high capacity and small cell radius, employing spread-spectrum technology and special coding scheme characterized by CDMA.

The Telecommunication Industry Association (TIA) in 1993 adopted CDMA. May 2001 there were 35 million subscribers on cdmaOne system worldwide. Over 35 countries have either commercial or trial activity ongoing. There were already 43 WLL systems in 22 countries using cdmaOne technology.
Enhancing today’s data capabilities is the 1XRTT CDMA standard this next evolutionary step for cdmaOne operators will provide data rates up to 300 kbps, significant capacity increases as well as extended batteries life for handsets.
Worldwide resources are being devoted to roll out third generation CDMA technology, including multi-carrier (cdmaOne2000 1xMC and HDR in 1.25 MHz bandwidth and 3xMC in 5 MHz bandwidth) and direct spread (WCDMA in 5 MHz bandwidth).
This first phase of cdmaOne2000 variously called 1XRTT, 3G1X or just plain 1X is designed to double current voce capacity and support always on data transmission speed 10 times faster than typically available today, some 153.6 kbps on both the forward and reverse links.



ADVANTAGES OF WLL:

Country wide induction of WLL underway of areas than are non-feasible for the normal network
Helping relieves congestion of connections in the normal cable / wire based network in urban areas
Limited the mobility without any airtime charges
It has improved signal and reducing the interference
Greater capacity than mobile
Provides ease of operation, administration & maintenance at lower cost.
The telecommunication is the biggest factor in influencing the speed of life in the modern age. Today we can get connection with any corner of world through the push button of computer; with the small mobile phone we can send not only the messages but also the secret document. As we know that there is positive view behind any mention that it should be helpful in the development of society. But humans have diverted mentality some of them of positive view and some of them of negative view. Where use any invention for the welfare of society but some uses for the satisfaction their disturbed mentality and to earn more and more money whether it may be harmful for the society. They infringe the norms of society and their behavior is condemned as antisocial, immoral and sinful.


CELLULAR MOBILE SERVICES:

Cellular is one of the fastest growing and most demanding telecommunication applications. Today, it represents a continuously increasing percentage of all new telephone subscriptions around the world. Currently there are more than 45 million subscribers in worldwide and nearly 50% of those subscribers are located in USA. It is forecasted that cellular system using a digital technology will become the universal method of telecommunications. By the year 2005, forecasters predict that there will be more than 100 million cellular subscribers worldwide.


GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM)

The GSM Association is a unique organization, with a truly global reach, offering a full range of business and technical services to its members. Now as the wireless family unfolds the association is deriving forward its vision of seamless, limitless, world of wireless communication.
Throughout the evolution of cellular telecommunications, various systems have been developed without the benefit of standardized specifications. This presented many problems directly related to compatibility, especially with the development of digital radio technology. The GSM standard is intended to address these problems.
Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulae the specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many country outside of Europe will join the GSM partnership.