Training Report- Rttc.doc

TRAINING REPORT On

STUDY OF BASICS OF TELECOMMUNICATION (16 July,12 to 24 Aug,12) At

REGIONAL TELECOM TRAINING CENTRE (BSNL), RAJPURA Submitted in partial fulfillment of requirement for the award of B.Tech degree In

Electronics and Communication Engineering Submitted by:

PRANIKA KAUR – 2310201

Submitted to:

Electronics and Communication Engineering Department Ambala College of Engineering And Applied Research Devasthali, Near Mithapur, Ambala Cantt (Affiliated to Kurukshetra University, Kurukshetra)

i

ACKNOWLEDGMENT

It’s a great pleasure to present this report of summer training in Telecommunication in partial fulfillment of B.Tech degree from Ambala College of Engineering and Applied Research, Ambala affiliated to Kurukshetra University, Kurukshetra. First of all i would like to thank almighty GOD who has given this wonderful gift of life to me. He is the one who is guiding me in right direction to follow noble path of humanity. At the outset, I would like to express my immense gratitude to my training guide Mr. Ajit Singh, Mr. A.S Sandhu and Mr. Rajesh Kumar Garg (SDE) for guiding me right from the inception till the successful completion of the training. I am falling short of words for expressing my feelings of gratitude towards them for extending their valuable guidance about market and support for literature, critical reviews of report and above all the moral support they had provided me with all stages of this training. I would also like to thank my friends and all my group members for their help and cooperation throughout the training.

Pranika (2310201)

ii

TABLE OF CONTENTS TITLE

PAGE NO.

TRAINING CERTIFICATE

i

ACKNOWLEDGMENT

ii

TABLE OF CONTENTS

iii

LIST OF FIGURES

viii

COMPANY PROFILE

1

Chapter 1- Overview of Telecommunication Networks

3-6

1.1- Introduction

3

1.2- Voice Signal Characteristics

4

1.3- Network Architecture

4

1.4- Access to an ISDN

6

Chapter 2- Overview Of Broadband Technology

7-10

2.1- Objectives

7

2.2- Introduction

7 iii

2.3- Definition of Broadband

8

2.4- Need of Broadband

8

Chapter 3- Digital Switching

11-16

3.1- Introduction

11

3.2- Time and Space Switching

11

3.3- Digital Space Switching

12

3.4- Practical Space Switch

13

3.5- Digital Time Switch

13

3.6- Output Associated Control

14

3.7- Input Associated Control

15

3.8- Time Delay Switching

16

3.9- Non Blocking Feature of a Time Switch

16

3.10- Two Dimensional switching

16

Chapter 4- PCM Principle

17-26

4.1- Introduction

17

4.2- Multiplexing Techniques

17 iv

4.2.1- Frequency Division Multiplexing

17

4.2.2- Time Division Multiplexing

18

4.3- Pulse Code Modulation

19

4.3.1- Sampling

19

4.3.2- Quantization

21

4.3.3- Encoding

23

4.4- Synchronization

24

4.5- Signalling in PCM Systems

25

4.6- Multiframe Structure

26

Chapter 5- Fiber Optics Communication

27-32

5.1- Fiber Optic Applications

27

5.2- Advantages of OFC

27

5.3- Fiber Optic System

28

5.4- Principle of Operation-Theory

28

5.5- Propagation of Light through Fiber

29

5.6- Geometry of Fiber

30 v

5.7- Fiber Types

31

5.7.1- Step Index Multimode Fiber

31

5.7.2- Graded Index Multimode Fiber

32

5.7.3- Single Mode Fiber

32

Chapter 6- GSM

33-41

6.1- The Cellular Structure

33

6.2- cluster

33

6.3- Architecture Of GSM Network

34

6.3.1- Mobile Station

34

6.3.2- The SIM

35

6.3.3- The Base Station Subsystem

35

6.3.4- The Operation and Support Subsystem

36

6.4- The GSM Functions

36

6.5- Operation, Administration & Maintenance

37

6.6- Frequency Hopping

38

6.7- Base Station Subsystem

38 vi

6.8- Mobile Evolution

40

6.8.1- First Generation

40

6.8.2- Second Generation

40

6.8.3- Third Generation

40

6.9- Enhanced Data Rates for GSM Evolution(EDGE)

41

Chapter 7- General Packet Radio Service

42-43

7.1- Introduction

42

7.2- What is General Packet Radio Service

42

Chapter 8- Present & Future Generations of Technology(3G/4G)

44-50

8.1- 3G Communication

44

8.2- Advantages of 3G

45

8.3- Disadvantages of 3G

45

8.4- Potential Killer Applications

46

8.5- 3G Network

46

8.6- Future Trends(3G to 4G onwards)

47

8.7- Operational Excellence

48 vi

8.8- Service Evolution

48

8.9- Multi-Technology Approach

49

ABBREVIATIONS

51

REFERENCES

52

vii

LIST OF FIGURES FIGURE NO.

PAGE NO.

3.1- Digital Switch

11

3.2- Serial Parallel Converter

13

3.3- Output associated with control switch

14

3.4- Input associated controlled time switch

15

4.1- Time division multiplexing

18

4.2- Sampling process

20

4.3- PAM output signals

21

4.4- Quantizing positive signal

22

4.5- 2.048 Mb/s PCM Multiframe

25

5.1- Principle of Fiber Optic Communication

28

5.2- Transmission of light between 2 mediums

29

5.3- Propagation of light through fiber

30

5.4- Geometric of fiber

30

5.5- Step –Index Multimode Fiber

32

5.6- Graded-Index Multimode Fiber

32

5.7- Single Mode Fiber

32

6.1- Architecture of the GSM network

34

6.2- BSS Configuration

39

8.1-The UMTS networks and domains

48

viii

COMPANY PROFILE The Regional Telecom Training Centre is one of the premier training institutes of BSNL, established on 1-12-1975.It imparts training in modern Telecommunication Engineering, Information Technology, and Management to BSNL Staff. This ISO 9001:2008 certified centre of excellence is equipped with state-of-the-art telecom technology laboratories, which include:OFC LAB MLLN LAB / RPR LAB NETWORKING LAB IPV6 LAB BROADBAND / MULTIPLAY LAB RPR LAB

PDH/SDH/DWDM LAB COMPUTER LABS GSM & CDMA LAB C-DOT LAB BATTERY & POWER PLANT LAB INTERNET NODE

The campus is situated away from the town’s hustle-bustle and has a beautiful ambience. Thishis his institute of the RTTC Complex is spread over 20 acres of lush green campus, havinges Aca academic /Administrative Block, Staff Quarters, 3 Hostels (Total capacity of 200 ),

o

and other facilities like Student Centre, health Club (GYM), Table Tennis, Badminton etc are ava .Fully furnished separate hostel for boys and girls with mess facilities and 24 hours lighttt , wateand security. Whole RTTC Campus is Wi-Fi enabled. There are 10 lecture halls,1Seminar& 1 & 1 Conference Hall –all fitted with overhead/DLP Projectors. The faculty members are llqualcertified technocrats and experienced professionals from among various Telecom specialties comcomprises of 35 staff members. Besides imparting all types of Telecom & Managementent relatcourses to the staff of BSNL, RTTC has also embarked upon to impart training to nonon BSNBSNL

aspirants.sts.

In aI In addition to in-house Training ,we are conducting Training program on :-

1 Industrial Training for Engineering /MBA(IT)/Diploma Graduates Students Summer / Vocational / Winter Industrial Training (4/ 6 Weeks) Summer / Vocational / Winter Industrial Training (6 months)

Project Work for Engineering Students ( 6 Months ) BSNL Certified program for Non BSNL Staff BSNL Certified Training Program on Mobile Communication. BSNL Certified Training Program on Optical Fiber Communication BSNL Certified Training Program on Transmission Systems BSNL Certified Training Program on Networking BSNL Certified Training Program on Telecom Industry Familiarization

BROADBAND LAB

COMPUTER LAB

SWITCHING LAB

2

CHAPTER-1 OVERVIEW OF TELECOMMUNICATION NETWORKS

1.1 Introduction: The telephone is a telecommunication device that is used to transmit and receive electronically or digitally encoded speech between two or more people conversing. It is one of the most common household appliances in the world today. Most telephones operate through transmission of electric signals over a complex telephone network which allows almost any phone user to communicate with almost any other user. With the appropriate attachments/equipments, they can be used to transmit dataTelecommunication networks carry information signals among entities, which are geographically far apart. An entity may be a computer or human being, a facsimile machine, a teleprinter, a data terminal and so on. The entities are involved in the process of information transfer that may be in the form of a telephone conversation (telephony) or a file transfer between two computers or message transfer between two terminals etc. With the rapidly growing traffic and untargeted growth of cyberspace, telecommunication becomes a fabric of our life. The future challenges are enormous as we anticipate rapid growth items of new services and number of users. What comes with the challenge is a genuine need for more advanced methodology supporting analysis and design of telecommunication architectures. Telecommunication has evaluated and growth at an explosive rate in recent years and will undoubtedly continue to do so. The communication switching system enables the universal connectivity. The universal connectivity is realized when any entity in one part of the world can communicate with any other entity in another part of the world. In many ways telecommunication will acts as a substitute for the increasingly expensive physical transportation. The telecommunication links and switching were mainly designed for voice communication. 3 1.2 Voice Signal Characteristics: Telecommunication is mainly concerned with the transmission of messages between two distant points. The signal that contains the messages is usually converted into electrical

waves before transmission. Our voice is an analog signal, which has amplitude and frequency characteristics. Voice frequencies: - The range of frequencies used by a communication device determines the communication channel, communicating devices, and bandwidth or information carrying capacity. The most commonly used parameter that characterizes an electrical signal is its bandwidth of analog signal or bit rate if it is a digital signal. In telephone system, the frequencies it passes are restricted to between 300 to 3400 Hz. In the field of telecommunications, a Telephone exchange or a Telephone switch is a system of electronic equipment including telephone switches

1.3 Network Architecture: When electronic devices were introduced in the switching systems, a new concept of switching evolved as a consequence of their extremely high operating speed compared to their former counter-parts, i.e., the Electro-mechanical systems, where relays, the logic elements in the electromechanical systems, have to operate and release several times which is roughly equal to the duration of telephone signals to maintain required accuracy. Research on electronic switching started soon after the Second World War, but commercial fully electronic exchange began to emerge only about 30 years later. However, electronic techniques proved economic for common control systems much earlier. In electromechanical exchanges, common control systems mainly used switches and relays, which were originally designed for use in switching networks. In common controls, they are operated frequently and so wear out earlier. In contrast, the life of an electronic device is almost independent of its frequency of operation.

4

In electromechanical switching, the various functions of the exchange are achieved by the operation and release of relays and switch (rotary or crossbar) contacts, under the direction of a Control Sub-System. These contracts are hard - wired in a predetermined way. When the data is to be modified, for introduction of a new service, or change in services already available to a subscriber, the hardware change ranging from inconvenient to near impossible, are involved. In an SPC exchange, a processor similar to a general-purpose computer is used to control the functions of the exchange. All the control functions, represented by a series of various instructions, are stored in the memory. e.g. for taking a decision according to class of service, the stored data is referred to, Hence, this concept of switching. This imparts and enormous flexibility in overall working of the exchange. Digital computers have the capability of handling many tens of thousands of instructions every second, Hence, in addition to controlling the switching functions the same processor can handle other functions also. The immediate effect of holding both the control program and the exchange data, in easily alterable memories, is that the administration can become much more responsive to subscriber requirements. both in terms of introducing new services and modifying general services, or in responding to the demands of individual subscriber. For example, to restore service on payment of an overdue bill or to permit change from a dial instrument to a multi frequency sender, simply the appropriate entries in the subscriber data-file are to be amended. Stored program control (SPC) has become the principal type of control for all types of new switching systems throughout the world, including private branch exchanges, data and Telex systems. Two types of data are stored in the memories of electronic switching systems. One type is the data associated with the progress of the call, such as the dialed address of the called line.

5 Examples include:-

1. Call barring (outgoing or incoming): The customer can prevent unauthorized calls being made and can prevent incoming calls when wishing to be left in peace. 2. Call waiting: The ‘Call waiting’ service notifies the already busy subscriber of a third party calling him. 3. Call Forwarding: The subscriber having such a feature can enable the incoming calls coming to his telephone to be transferred to another number during his absence. 4. Conference calls: Subscriber can set up connections to more than one subscriber and conduct telephone conferences under the provision of this facility. 5. Do Not Disturb: This facility enables the subscriber to free himself from attending his incoming calls. Using this facility the calls coming to the subscriber can be routed to an operator position or to an answering machine.

1.4 Access to an ISDN: 1. Basic-Rate Access (BRA) :- The customer’s line carries two 64 kbit/s “B” channels plus a 16 kbit/s “D” channel (a common signaling channel) in each direction. 2. Primary Rate Access (PRA):- The line carries a complete PCM frame at 2 Mbit/s in each direction. This gives the customer 30 circuits at 64 kbit/s plus a common signaling channel, also at 64 kbit

6

CHAPTER-2

OVERVIEW OF BROADBAND TECHNOLOGY

2.1 OBJECTIVES: The main objective of this chapter is to build up the following : i)

To understand what is Broadband

ii)

To understand the need of broadband

iii)

To familiarize with the various broadband technologies

iv)

To familiarize with Broadband Network

2.2 INTRODUCTION: With the evolution of computer networking and packet switching concept a new era of integrated communication has emerged in the telecom world. Rapid growth of data communication market and popularity of Internet, reflect the needs of enhanced infrastructure to optimize the demand of traffic. Integration of telecom and computer networking technology trend has further amplified the importance of telecommunications in the field of information communication. The demand for high-speed bandwidth is growing at a fast pace, driven mostly by growth in data volumes as the Internet and related networks become more central to business operations. The rapid growth of distributed business applications, e-commerce, and bandwidth-intensive applications (such as multimedia, videoconferencing, and video on demand) generate the demand for bandwidth and access network.

7 2.3 DEFINITION OF BROADBAND:

Broadband is the nonspecific term for high-speed digital Internet access. To state the obvious, ‘broadband’ indicates a means of connectivity at a high or ‘broad’ bandwidth. There are the various ways to define the broadband :i) Term for evolving digital technologies that provide customers a high-speed data network connection ii) Provides signal switched facility offering integrated access to voice, data, video, and interactive delivery services iii) The Federal Communications Commission (FCC) defines broadband as an advanced telecommunications capability “An ‘always-on’ data connection that is able to support interactive services including Internet access and has the capability of the minimum download speed of 256 kilo bits per second (kbps) to an individual subscriber from the Point Of Presence (POP) of the service provider intending to provide Broadband service where interactive services including the Internet through this POP. It reflects that: i)

One of the latest trends in enhancing communication systems involves broadband technology

ii)

Broadband refers to greater bandwidth-or transmission capacity of medium.

iii)

Broadband technology will allow for high-speed transmission of voice, video, and data over networks like the Internet

2.4 NEED OF BROADBAND: The concept of socio economy has an important role in the field of communication of data, audio, video, speech or any other kind of application. It is an era of CAPEX and OPEX. 8

The Internet, e-mail, web sites, software downloads, file transfers: they are all now part of the fabric of doing business. But until now, it has not been possible for businesses to fully take advantage of the benefits that technology can truly deliver. Kim Maxwell in his book-"Residential Broadband: An Insider's Guide to the Battle for the Last Mile" has grouped potential residential broadband applications into three general categories: "professional activities " (activities related to users' employment), "entertainment activities " (from game playing to movie watching), and "consumer activities " (all other non-employment and non-entertainment activities). as follows: Professional Activities: i)

Telecommuting (access to corporate networks and systems to support working at home on a regular basis)

ii)

Video conferencing (one-to-one or multi-person video telephone calls)

iii)

Home office (access to corporate networks and e-mail to supplement work at a primary office location)

Entertainment Activities: i)

Web surfing (as today, but at higher speeds with more video content)

ii)

Video-on-demand (movies and rerun or delayed television shows)

iii)

Video games (interactive multi-player games)

Consumer Activities: i)

Shopping (as today, but at higher speeds with more video content)

ii)

Telemedicine (including remote doctor visits and remote medical analyses by medical specialists)

iii)

Distance learning (including live and pre-recorded educational presentations)

iv)

Public services (including voting and electronic town hall meeting). 9

These applications have different bandwidth requirements, and some of them are still out of reach today. For example, all of the "professional" activities will likely be supported with less than 1.0 Mbps of bandwidth. Similarly, web surfing and home shopping will be supported with less than 1.0 Mbps of bandwidth. Movies and video, however, demand more bandwidth. Feature length movies can probably be delivered with 1.5 Mbps of bandwidth, but broadcast quality video will probably require more— perhaps as much as 6.0 Mbps. The Internet is poised to spin off thousands of specialized broadband services. The access network needs to provide the platform for delivery of these services. Following are the various applications or services, which are very popular in society and needs broadband connectivity: -

Virtual Networks: The private virtual networks (LAN/WAN) can be used in an ample variety of multimedia services, like bank accounts and central offices.

Education by distance: Education will not have any limits to reach from source to destination. Along with the traditional school a concept of remote leaning center is emerged out and popular for various courses. There is no limit of distance, area or location in such distance learning.

Telework: Organization firm workers that incorporate communication systems via satellite, can work remotely connecting directly to their head offices Internet by a high speed connection that permits users to work efficiently and comfortable.

Telemedicine: Doctors situated in different clinics can stay in contact and consult themselves directly to other regional medical centers, using videoconference and the exchange of high quality images, giving out test results and any type of information.

Electronic commerce: Electronic commerce is a system that permits users to pay goods and services by Internet. Thanks to this service, any person connected to the network can ad quire such services with independence from the place that he is situated and during the 24 hours, simply using a portable computer. 10

CHAPTER-3 DIGITAL SWITCHING 3.1 Introduction: A Digital switching system, in general, is one in which signals are switched in digital form. These signals may represent speech or data. The digital signals of several speech samples are time multiplexed on a common media before being switched through the system. To connect any two subscribers, it is necessary to interconnect the time-slots of the two speech samples which may be on same or different PCM highways. The digitalized speech samples are switched in two modes, viz., Time Switching and Space Switching.

3.2 Time and Space Switching: Generally, a digital switching system several time division multiplexed (PCM) samples. These PCM samples are conveyed on PCM highways (the common path over which many channels can pass with separation achieved by time division.). For example, PCM samples appearing in TS6 of I/C PCM HWY1 are transferred to TS18 of O/G PCM HWY2, via the digital switch, as shown in Fig 3.1.

Fig 3.1: Digital Switch

11

The interconnection of time-slots, i.e., switching of digital signals can be achieved using two different modes of operation. These modes are: - i) Space Switching ii) Time switching A sample, in a given time-slot, TSi of an I/C HWY, say HWY1, is switched to same timeslot, TSi of an O/G HWY, SAY HWY2. Obviously there is no delay in switching of the sample from one highway to another highway since the sample transfer takes place in the same time-slot of the PCM frame. Time Switching, on the other hand, involves the interconnection of different time-slots on the incoming and outgoing highways by reassigning the channel sequence.

3.3 Digital Space Switching: The Digital Space Switch consists of several input highways, X1, X2,...Xn and several output highways, Y1,Y2,.............Ym, inter connected by a crosspoint matrix of n rows and m columns. The individual crosspoint consists of electronic AND gates. The operation of an appropriate crosspoint connects any channel, a , of I/C PCM highway to the same channel, a, of O/G PCM highway. Each crosspoint column, associated with one O/G highway, is assigned a column of control memory. The control memory has as many words as there are time-slot per frame in the PCM signal. In practice, this number could range from 32 to 1024. Each crosspoint in the column is assigned a binary address, so that only one crosspoint per column is closed during each time-slot The binary addresses are stored in the control memory, in the order of time-slots. The word size of the control memory is x bits, so that 2x = n, where n is the number of cross points in each column . A new word is read from the control memory during each timeslot, in a cyclic order. Each word is read during its corresponding time-slot, i.e. Word 0 (corresponding to TS0), followed by word 1 (corresponding to TS1) and so on. The word contents are contained on the vertical address lines for the duration of the time-slot.

12

3.4 Practical Space Switch: In a practical switch, the digital bits are transmitted in parallel rather than serially, through the switching matrix. In a serial 32 time-slots PCM multiplex, 2048 Kb/s are carried on a single wire sequentially, i.e., all the bits of the various time-slots follow one another. This single wire stream of bits, when fed to Serial to Parallel Converter is converted into 8-wire parallel output. For example, all 8 bits corresponding to TS3 serial input are available simultaneously on eight output wires (one bit on each output wire), during just one bit period, as shown in fig.3.2. This parallel output on the eight wires is fed to the switching matrix.

Fig 3.2: Serial parallel converter It can be seen that during one full time-slot period, only one bit is carried on the each output line, whereas 8 bits are carried on the input line during this period. Therefore, bit rate on individual output wires, is reduced to 1/8th of input bit rate=2048/8=256Kb/s

3.5 Digital Time Switch: A Digital Time Switch consists of two memories, address memory to control the writing and reading of the samples in the buffer memory and directing them on to the appropriate time-slots. 13

Speech memory has as many storage locations as the number of time-slots in input PCM, e.g., 32 locations for 32 channel PCM system. The writing/reading operations in the speech memory are controlled by the Control Memory. It has same number of memory locations as for speech memory, i.e., 32 locations for 32 channel PCM system. Each location contains the address of one of the speech memory locations where the channel sample is either written or read during a time-slot.

3.6 Output associated control: In this mode of working, 2 samples of I/C PCM are written cyclically in the speech memory locations in the order of time-slots of I/C PCM, i.e., TS1 is written in location 1, TS2 is written in location 2. The contents of speech memory are read on output PCM in the order specified by control memory. Each location of control memory is rigidly associated with the corresponding time-slot of the O/G PCM and contains the address of the TS of incoming PCM to be connected to.

Fig. 3.3: Output associated with control switch

14

3.7 Input associated control: Here, the samples of I/C PCM are written in a controlled way, i.e., in the order specified by control memory, and read sequentially. Each location of control memory is rigidly associated with the corresponding TS of I/C PCM and contains the address of TS of O/G PCM to be connected to. The previous example with the same connection objective of connecting TS4 of I/C PCM to TS6 of O/G PCM may be considered for its restoration. The location 4 of the control memory is associated with incoming PCM TS4. Hence, it should contain the address of the location where the contents of TS4 of I/C PCM are to be written in speech memory. A CC writes the number of the destination TS, viz., 6 in this case, in location 4 of the control memory. The contents of TS4 are therefore, written in location of speech memory, as shown in fig3.4. The contents of speech memory are read in the O/G PCM in a sequential way, i.e., location 1 is read during TS1, location 2 is read during TS2, and so on. In this case, the contents of location 6 will appear in the output PCM at TS6. Thus the input PCM TS4 is switched to output PCM TS6. In this switch, there is sequential reading but controlled writing.

Fig 3.4: Input Associated Controlled Time Switch 15

3.8 Time Delay Switching: The writing and reading, of all time-slots in a frame, has to be completed within one frame time period (before the start of the next frame). A TS of incoming PCM may, therefore, get delayed by a time period ranging from 1 TS to 31 TS periods, before being transmitted on outgoing PCM.

3.9 Non-Blocking feature of a Time Switch: In a Time Switch, there are as many memory locations in the control and speech memories as there are time-slots in the incoming and outgoing PCM highways, i.e., corresponding to each time-slot in incoming highway, there is a definite memory location available in the speech and control memories. Similarly, corresponding to each time-slot in the outgoing highway there is a definite memory location available in the control and speech memories. This way, corresponding to free incoming and outgoing time-slots, there is always a free path available to interconnect them. In other words, there is no blocking in a time switch.

3.10 Two Dimensional Switching: Though the electronic cross points are not so expensive, the cost of accessing and selecting them from external pins in a Space Switch, becomes prohibitive as the switch size increases. Similarly, the memory location requirements rapidly go up as a Time Switch is expanded, making it uneconomical. Hence, it becomes necessary to employ a number of stages, using small switches as building blocks to build a large network. This would result in necessity of changing both the time-slot and highway in such a network. Hence, the network, usually, employs both types of switches viz., space switch and time switch and. therefore, is known as two dimensional network. These networks can have various combinations of the two types of switches and are denoted as TS, STS, TSST etc. Though to ensure full availability, it may be desirable to use only T stages.

16

CHAPTER-4 PCM PRINCIPLE

4.1 Introduction: A long distance or local telephone conversation between two persons could be provided by using a pair of open wire lines or underground cable as early as early as mid of 19th century. However, due to fast industrial development and increased telephone awareness, demand for trunk and local traffic went on increasing at a rapid rate. To cater to the increased demand of traffic between two stations or between two subscribers at the same station we resorted to the use of an increased number of pairs on either the open wire alignment, or in underground cable. This could solve the problem for some time only as there is a limit to the number of open wire pairs that can be installed on one alignment due to headway consideration and maintenance problems.

4.2 Multiplexing Techniques: There are basically two types of multiplexing techniques i) Frequency Division Multiplexing (FDM) ii) Time Division Multiplexing (TDM)

4.2.1 Frequency Division Multiplexing Techniques (FDM): The FDM technique is the process of translating individual speech circuits (300-3400 Hz) into pre-assigned frequency slots within the bandwidth of the transmission medium. The frequency translation is done by amplitude modulation of the audio frequency with an appropriate carrier frequency. At the output of the modulator a filter network is connected to select either a lower or an upper side band. 17

4.2.2 Time Division Multiplexing: Basically,

time

division

multiplexing

involves

nothing

more

than

sharing

a transmission medium by a number of circuits in time domain by establishing a sequence of time slots during which individual channels (circuits) can be transmitted. Thus the entire bandwidth is periodically available to each channel. Normally all time slots 1 are equal in length. Each channel is assigned a time slot with a specific common repetition period called a frame interval. This is illustrated in Fig. 4.1.

Fig. 4.1: Time Division Multiplexing Each channel is sampled at a specified rate and transmitted for a fixed duration. All channels are sampled one by one and the cycle is repeated again and again. The channels are connected to individual gates which are opened one by one in a fixed sequence. At the receiving end also similar gates are opened in unison with the gates at the transmitting end. The signal received at the receiving end will be in the form of discrete samples and these are combined to reproduce the original signal.

18

4.3 Pulse Code Modulation: PCM systems use TDM technique to provide a number of circuits on the same transmission medium viz open wire or underground cable pair or a channel provided by carrier, coaxial, microwave or satellite system. Basic Requirements for PCM System: To develop a PCM signal from several analogue signals, the following processing steps are required i)

Filtering

ii)

Sampling

iii)

Quantization

iv)

Encoding

v)

Line Coding

4.3.1 Sampling: It is the most basic requirement for TDM. Suppose we have an analogue signal Fig. 4.2(b), which is applied across a resistor R through a switch S as shown in Fig. 4.2(a) . Whenever switch S is closed, an output appears across R. The rate at which S is closed is called the sampling frequency because during the make periods of S, the samples of the analogue modulating signal appear across R. Fig.4.2(d) is a stream of samples of the input signal which appear across R. The amplitude of the sample depends upon the amplitude of the input signal at the instant of sampling.

19

Fig. 4.2: Sampling Process

Sampling Theorem: "If a band limited signal is sampled at regular intervals of time and at a rate equal to or more than twice the highest signal frequency in the band, then the sample contains all the information of the original signal." Mathematically, if fH is the highest frequency in the signal to be sampled then the sampling frequency Fs needs to be greater than 2 fH. i.e. Fs>2fH Let us say our voice signals are band limited to 4 KHz and let sampling frequency be 8 KHz. Time period of sampling Ts =

1 sec 8000

or Ts = 125 micro seconds In a 30 channel PCM system. TS i.e. 125 microseconds are divided into 32 parts. That is 30 time slots are used for 30 speech signals, one time slot for signalling of all the 30 chls, signals

and on

one the

time

slot for synchronization between Transmitter & Receiver. The

common

medium

(also

of a TDM system will consist of a series of pulses, 20

called

the

common

highway)

the amplitudes of which are proportional to the amplitudes of the individual channels at their respective sampling instants. This is illustrated in Fig. 4.3

Fig 4.3: PAM Output Signals

4.3.2 Quantization: In FDM systems we convey the speech signals in their analogue electrical form. But in PCM, we convey the speech in discrete form. The sampler selects a number of points on the analogue speech signal (by sampling process) and measures their instant values. The transmission of PAM signal will require linear amplifiers at trans and receive ends to recover distortion less signals. Therefore, in PCM systems, PAM signals are converted into digital form by using Quantization Principles. The process of measuring the numerical values of the samples and giving them a table value in a suitable scale is called "Quantizing". Of course, the scales and the number of points should be so chosen that the signal could be effectively reconstructed after demodulation. 21

Quantizing, in other words, can be defined as a process of breaking down a continuous amplitude range into a finite number of amplitude values or steps. A sampled signal exists only at discrete times but its amplitude is drawn from a continuous range of amplitudes of an analogue signal. On this basis, an infinite number of amplitude values are possible. A suitable finite number of discrete values can be used to get an. approximation of the infinite set. The discrete value of a sample is measured by comparing it with a scale having a finite number of intervals and identifying the interval in which the sample falls.

Quantizing Process: Suppose we have a signal as shown in Fig. 4.4 which is sampled at instants a, b, c, d and e. For the sake of explanation, let us suppose that the signal has maximum amplitude of 7 volts.In order to quantize these five samples taken of the signal, let us say the total amplitude is divided into eight ranges or intervals as shown in Fig. 4.4. Sample (a) lies in the 5th range. Accordingly, the quantizing process will assign a binary code corresponding to this i.e. 101, Similarly codes are assigned for other samples also. Here the quantizing intervals are of the same size. This is called Linear Quantizing.

Fig. 4.4: Quantizing-positive signal 22

Assigning an interval of 5 for sample 1, 7 for 2 etc. is the quantizing process. Giving, the assigned levels

of samples, the binary code are

called coding of the quantized samples.

Relation between Binary Codes and Number of levels: Because the quantized samples are coded in binary form, the quantization intervals will be in powers of 2. If we have a 4 bit code, then we can have 2" = 16 levels. Practical PCM systems use an eight bit code with the first bit as sign bit. It means we can have 2" = 256 (128 levels in the positive direction and 128 levels in the negative direction) intervals for quantizing.

4.3.3 Encoding: Conversion of quantized analogue levels to binary signal is called encoding. To represent 256 steps, 8 level code is required. The eight bit code is also called an eight bit "word". The 8 bit word appears in the form P Polarity bit ‘1’

ABC Segment Code

WXYZ Linear encoding

for + ve 'O' for - ve. in the segment The first bit gives the sign of the voltage to be coded. Next 3 bits gives the segment number. There are 8 segments for the positive voltages and 8 for negative voltages. Last 4 bits give the position in the segment. Each segment contains 16 positions. Referring to Fig. 4.6, voltage Vc will be encoded as 1 1 1 1 0101. The quantization and encoding are done by a circuit called coder. The coder converts PAM signals (i.e. after sampling) into an 8 bit binary signal. The coding is done as per Fig. 9 which shows a relationship between voltage V to be coded and equivalent binary number N. The function N = f(v) is not linear. 23

Concept of Frame: Since Ts is much larger as compared to St. a number of channels can be sampled each for a duration of St within the time Ts. The first sample of the first channel is taken by pulse 'a', encoded and is passed on the combiner. Then the first sample of the second channel is taken by pulse 'b' which is also encoded and passed on to the combiner, Likewise the remaining channels are also sampled sequentially and are encoded before being fed to the combiner. For a 30 chl PCM system, we have 32 time slots. Thus the time available per channel would be 3.9 microsecs. Thus for a 30 chl PCM system, Frame = 125 microseconds Time slot per channel = 3.9 microseconds.

Structure of Frame: A frame of 125 microseconds duration has 32 time slots. These slots are numbered Ts 0 to Ts 31. Information for providing synchronization between trans and receive ends is passed through a separate time slot. Usually the slot Ts 0 carries the synchronization signals. This slot is also called Frame alignment word (FAW). The signaling information is transmitted through time slot Ts 16. Ts 1 to Ts 15 are utilized for voltage signal of channels 1 to 15 respectively. Ts 17 to Ts 31 are utilized for voltage signal of channels 16 to 30 respectively.

4.4 Synchronization: The output of a PCM terminal will be a continuous stream of bits. At the receiving end, the receiver has to receive the incoming stream of bits and discriminate between frames and separate channels from these. That is, the receiver has to recognize the start of each frame correctly. 24

This operation is called frame alignment or Synchronization and is achieved by inserting a fixed digital pattern called a "Frame Alignment Word (FAW)" into the transmitted bit stream at regular intervals. The receiver looks for FAW and once it is detected, it knows that in next time slot, information for channel one will be there and so on. The FAW is transmitted in the Ts O of every alternate frame.Frame which do not contain the FAW, are used for transmitting supervisory and alarm signals. To distinguish the Ts 0 of frame carrying supervisory/alarm signals from those carrying the FAW, the B2 bit position of the former are fixed at T. The FAW and alarm signals are transmitted alternatively.

4.5 Signalling in PCM Systems: In a telephone network,-the signaling information is used for proper routing of a call between two subscribers, for providing certain status information like dial tone, busy tone, ring back. NU tone, metering pulses, trunk offering signal etc. All these functions are grouped under the

general

terms

"signaling"

in

PCM

systems.

The signaling information can be transmitted in the form of DC pulses (as in step by step exchange) or multi-frequency pulses (as in cross bar systems) etc.

Fig. 4.5: 2.048 Mb/s PCM Multi-frame

25

4.6 Multi-frame Structure: In the time slot 16 of FO, the first four bits (positions 1 to 4) contain the multi-frame alignment signal which enables the receiver to identify a multi-frame. The other four bits (no. 5 to 8) are spare. These may be used for carrying alarm signals. Time slots 16 of frames F1 to FT5 are used for carrying the signaling information. Each frame carries signaling, data for two VF channels. For instance, time slot Ts 16 of frame F1 carries the signal data for VF channel 1 in the first four bits. The next four bits are used for carrying signaling information for channel 16. Similarly, time slot Ts16 of F2 carries signalling data of chls 2 and 17.

26

CHAPTER-5 FIBER OPTICS COMMUNICATION

5.1 Fiber-Optic Applications: The use and demand for optical fiber has grown tremendously and optical-fiber applications are numerous. Telecommunication applications are widespread, ranging from global networks to desktop computers. These involve the transmission of voice, data, or video over distances of less than a meter to hundreds of kilometers, using one of a few standard fiber designs in one of several cable designs. Optical fiber is also used extensively for transmission of data. Multinational firms need secure, reliable systems to transfer data and financial information between buildings to the desktop terminals or computers and to transfer data around the world. Cable television companies also use fiber for delivery of digital video and data services. The high bandwidth provided by fiber makes it the perfect choice for transmitting broadband signals, such as high-definition television (HDTV) telecasts. Intelligent transportation systems, such as smart highways with intelligent traffic lights, automated tollbooths, and changeable message signs, also use fiber-optic-based telemetry systems.

5.2 Advantages of OFC: Fiber Optics has the following advantages :

i)

SPEED: Fiber optic networks operate at high speeds - up into the gigabit

ii)

BANDWIDTH: large carrying capacity

iii)

DISTANCE: Signals can be transmitted further without needing to be "refreshed" or strengthened.

iv)

RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables. 27

5.3 Fiber Optic System: Optical Fiber is new medium, in which information (voice, Data or Video) is transmitted through a glass or plastic fiber, in the form of light, following the transmission sequence give below: i)

Information is encoded into Electrical Signals.

ii)

Electrical Signals are converted into light Signals.

iii)

Light Travels down the Fiber.

iv)

A Detector Changes the Light Signals into Electrical Signals.

Fig. 5.1: Principle of Fiber optic transmission system

5.4 Principle of Operation – Theory: 

Total Internal Reflection - The Reflection that Occurs when a Light Ray Travelling in One Material Hits a Different Material and Reflects Back into the Original Material without any Loss of Light.

Speed of light is actually the velocity of electromagnetic energy in vacuum such as space. Light travels at slower velocities in other materials such as glass. Light travelling from one material to another changes speed, which results in light changing its direction of travel. This deflection of light is called Refraction. 28

Angle of incidence

ø1

ø1 n1 n2 ø2

Light is bent away from normal

n1 n2

ø1

Angle of reflection

ø2

n1 n2

ø2 Light does not enter second material

Fig. 5.2: Transmission of light between 2 mediums

As the angle of incidence increases, the angle of refraction approaches 90 o to the normal. The angle of incidence that yields an angle of refraction of 90 o is the critical angle. If the angle of incidence increases amore than the critical angle, the light is totally reflected back into the first material so that it does not enter the second material. The angle of incidence and reflection are equal and it is called Total Internal Reflection.

5.5 Propagation of light through fiber: The optical fiber has two concentric layers called the core and the cladding. The inner core is the light carrying part. The surrounding cladding provides the difference refractive index that allows total internal reflection of light through the core. The index of the cladding is less than 1%, lower than that of the core. Typical values for example are a core refractive index of 1.47 and a cladding index of 1.46. Fiber manufacturers control this difference to obtain desired optical fiber characteristics.

Most fibers have an

additional coating around the cladding. The light will continue zigzagging down the length of the fiber. Such total internal reflection forms the basis of light propagation through a optical fiber. This analysis consider only meridional rays- those that pass through the fiber axis each time, they are reflected.

29

The specific characteristics of light propagation through a fiber depends on many factors, including i) The size of the fiber. ii) The composition of the fiber. iii) The light injected into the fiber. Jacket

Jacket Cladding Core

Cladding

Cladding (n2)

Jacket

Core (n2)

Light at less than critical angle is absorbed in jacket

Angle of incidence

Angle of reflection

Light is propagated by total internal reflection

Fig. Total Internal Reflection in an optical Fibre

Fig. 5.3: Propagation of light through fiber 5.6 Geometry of Fiber: A hair-thin fiber consist of two concentric layers of high-purity silica glass the core and the cladding, which are enclosed by a protective sheath as shown in Fig. 5.4. Light rays modulated into digital pulses with a laser or a light-emitting diode moves along the core without penetrating the cladding.

Fig. 5.4: Geometry of fiber 30

The light stays confined to the core becausethe cladding has a lower refractive index—a measure of its ability to bend light. Refinements in optical fibers, along with the development of new lasers and diodes, may one day allow commercial fiber-optic networks to carry trillions of bits of data per second. Fiber sizes are usually expressed by first giving the core size followed by the cladding size. Thus 50/125 means a core diameter of 50m and a cladding diameter of 125m.

5.7 Fiber types: The refractive Index profile describes the relation between the indices of the core and cladding. Two main relationships exist: i) Step Index ii) Graded Index The step index fiber has a core with uniform index throughout. The profile shows a sharp step at the junction of the core and cladding. In contrast, the graded index has a nonuniform core. The Index is highest at the center and gradually decreases until it matches with that of the cladding. There is no sharp break in indices between the core and the cladding. By this classification there are three types of fibers: i) Multimode Step Index fiber (Step Index fiber) ii)Multimode graded Index fiber (Graded Index fiber) iii) Single- Mode Step Index fiber (Single Mode Fiber)

5.7.1 Step Index Multimode Fiber:- has a large core, up to 100 microns in diameter. As a result, some of the light rays that make up the digital pulse may travel a direct route, whereas others zigzag as they bounce off the cladding.

31

These alternative pathways cause the different groupings of light rays, referred to as modes,

to

arrive

separately

at

a

receiving

point..

Fig. 5.5: Step-Index Multimode Fiber

5.7.2 Graded Index Multimode Fiber:- contains a core in which the refractive index diminishes gradually from the center axis out toward the cladding. The higher refractive index at the center makes the light rays moving down the axis advance more slowly than those near the cladding. Also, rather than zigzagging off the cladding, light in the core curves helically because of the graded index, reducing its travel distance.

Fig.5.6: Graded index multimode fiber

5.7.3 Single Mode Fiber:- has a narrow core (eight microns or less), and the index of refraction between the core and the cladding changes less than it does for multimode fibers. Light thus travels parallel to the axis, creating little pulse dispersion. Telephone and cable television networks install millions of kilometers of this fiber every year.

Fig. 5.7: Single Mode Fiber

32

CHAPTER-6 GSM The Global System for Mobile communications is a digital cellular communications system. It was developed in order to create a common European mobile telephone standard but it has been rapidly accepted worldwide. GSM was designed to be compatible with ISDN services.

6.1 The Cellular Structure: In a cellular system, the covering area of an operator is divided into cells. A cell corresponds to the covering area of one transmitter or a small collection of transmitters. The size of a cell is determined by the transmitter's power. The frequency band allocated to a cellular mobile radio system is distributed over a group of cells and this distribution is repeated in all the covering area of an operator. The whole number of radio channels available can then be used in each group of cells that form the covering area of an operator. Frequencies used in a cell will be reused several cells away. The distance between the cells using the same frequency must be sufficient to avoid interference. The frequency reuse will increase considerably the capacity in number of users.

6.2 Cluster: The cells are grouped into clusters. The number of cells in a cluster must be determined so that the cluster can be repeated continuously within the covering area of an operator. The typical clusters contain 4, 7, 12 or 21 cells. The number of cells in each cluster is very important. The smaller the number of cells per cluster is, the bigger the number of channels per cell will be. The capacity of each cell will be therefore increased. 33

6.3 ARCHITECTURE OF THE GSM NETWORK: The GSM technical specifications define the different entities that form the GSM network by defining their functions and interface requirements. The GSM network can be divided into four main parts: The

architecture

of

the

GSM

network

is

presented

in

figure

6.1.

Other G OMC

VLR B

BSS

A

VLRs D

C

BSC

BTS

MS

MSCs

HLR

MSC

AUC

Abis

Un

F

E Other MSCs

Other Networks

EIR

Fig. 6.1: Architecture of the GSM network

6.3.1 Mobile Station: A Mobile Station consists of two main elements: The Terminal: There are different types of terminals distinguished principally by their power and application: i) The `fixed' terminals are the ones installed in cars. Their maximum allowed output power is 20 W. ii) The GSM portable terminals can also be installed in vehicles. Their maximum allowed output power is 8W. 34

iii) The handheld terminals have experienced the biggest success thanks to the weight and volume, which are continuously decreasing. These terminals can emit up to 2 W. The evolution of technologies allows decreasing the maximum allowed power to 0.8 W.

6.3.2 The SIM: The SIM is a smart card that identifies the terminal. By inserting the SIM card into the terminal, the user can have access to all the subscribed services. Without the SIM card, the terminal is not operational. The SIM card is protected by a four-digit Personal Identification Number (PIN). In order to identify the subscriber to the system, the SIM card contains some parameters of the user such as its International Mobile Subscriber Identity (IMSI). Another advantage of the SIM card is the mobility of the users. In fact, the only element that personalizes a terminal is the SIM card. Therefore, the user can have access to its subscribed services in any terminal using its SIM card.

6.3.3 The Base Station Subsystem: The BSS connects the Mobile Station and the NSS. It is in charge of the transmission and reception. The BSS can be divided into two parts: The Base Transceiver Station: The BTS corresponds to the transceivers and antennas used in each cell of the network. A BTS is usually placed in the center of a cell. Its transmitting power defines the size of a cell. Each BTS has between one and sixteen transceivers depending on the density of users in the cell. 35

The Base Station Controller: The BSC controls a group of BTS and manages their radio resources. A BSC is principally in charge of handovers, frequency hopping, exchange functions and control of the radio frequency power levels of the BTS.

6.3.4 The Operation and Support Subsystem (OSS): The OSS is connected to the different components of the NSS and to the BSC, in order to control and monitor the GSM system. It is also in charge of controlling the traffic load of the BSS. However, the increasing number of base stations, due to the development of cellular radio networks, has provoked that some of the maintenance tasks are transferred to the BTS. This transfer decreases considerably the costs of the maintenance of the system.

6.4 THE GSM FUNCTIONS: In this paragraph, the description of the GSM network is focused on the different functions to fulfill by the network and not on its physical components. In GSM, five main functions can be defined: Transmission: The transmission function includes two sub-functions: i) The first one is related to the means needed for the transmission of user information. ii) The second one is related to the means needed for the transmission of signaling information. Not all the components of the GSM network are strongly related with the transmission functions. 36

The MS, the BTS and the BSC, among others, are deeply concerned with transmission. But other components, such as the registers HLR, VLR or EIR, are only concerned with the transmission for their signaling needs with other components of the GSM network. Some of the most important aspects of the transmission are described. Radio Resources management (RR): The role of the RR function is to establish, maintain and release communication links between mobile stations and the MSC. The elements that are mainly concerned with the RR function are the mobile station and the base station. However, as the RR function is also in charge of maintaining a connection even if the user moves from one cell to another, the MSC, in charge of handovers, is also concerned with the RR functions. Some of the main RR procedures that assure its responsibilities are: i) Channel assignment, change and release. ii) Handover. iii) Frequency hopping. iv) Power-level control. v) Discontinuous transmission and reception. vi) Timing advance. Some of these procedures are described. In this paragraph only the handover, which represents one of the most important responsibilities of the RR, is described.

6.5 Operation, Administration and Maintenance (OAM): The OAM function allows the operator to monitor and control the system as well as to modify the configuration of the elements of the system. 37

Not only the OSS is part of the OAM, also the BSS and NSS participate in its functions as it is shown in the following examples: i) The components of the BSS and NSS provide the operator with all the information it needs. This information is then passed to the OSS which is in charge of analyzing it and control the network. ii) The self test tasks, usually incorporated in the components of the BSS and NSS, also contribute to the OAM functions. iii) The BSC, in charge of controlling several BTSs, is another example of an OAM function performed outside the OSS.

6.6 Frequency hopping: The propagation conditions and therefore the multipath fading depend on the radio frequency. In order to avoid important differences in the quality of the channels, the slow frequency hopping is introduced. The slow frequency hopping changes the frequency with every TDMA frame. A fast frequency hopping changes the frequency many times per frame but it is not used in GSM. The frequency hopping also reduces the effects of co-channel interference. There are different types of frequency hopping algorithms. The algorithm selected is sent through the Broadcast Control Channels.

6.7 Base Station System (BSS): BSS comprises of BTS (Base Transceiver Station) and BSC (Base Station Controller). Characteristics of the Base Station System (BSS) are: i) The BSS is responsible for communicating with mobile stations in cell areas ii) One BSC controls one or more BTSs and can perform inter-BTS and intra- BTS handover. 38

iii) The BTS serves one or more cells in the cellular network and contains one or more TRXs (Transceivers or radio units).

Fig. 6.2: BSS Configuration BSS types are differentiated by the following characteristics: The BSS can be an integrated (Intg) BSS or a distributed (Dist) BSS. An integrated BSS is a BSS, which has the BSC, and BTS functionality located in the same physical unit. In a distributed BSS, the BTS and BSC are physically separated. The BSS can have internally (Int) or externally (Ext) located speech transcoding. Speech transcoding to 64 kbit/s takes place either in the BSC for BSS types 1, 4 and 5, or external to the BSS (i.e. the transcoder is co-located with the MSC) for BSS types 2, 6 and 7. For BSS type 3 transcoding takes place in the BTS. The Abis interface uses multiplexing (Mult) or rate adaptation (RA) on its links.

39

6.8 Mobile Evolution: 6.8.1 First Generation: In the early 1980s the First Generation were the Worlds first public mobile telephone services such as AMPS (US), TACS (UK) and NMT (Scandinavia). These systems were analogue, provided national coverage (though from complete in most cases) and offered limited services. 6.8.2 Second Generation: GSM is by far the World’s primary Second-Generation system. Designed by a joint effort from manufacturers, regulators and service suppliers from many (European) countries, GSM became a European and then a global standard. CDMA systems now under the collective term of cdmaOne are the other major Second-Generation technology. Globally, arguments about which was superior became largely academic because GSM was deployed first (early 1990s) and rapidly gained universal acceptance (with the exception of the US and Japan). CDMA has been launched more recently (mid 1990s) and has shown remarkable uptake and growth. In late 1998 there are an estimated 12 million CDMA users and over a 100 million GSM users.

Second Generation Systems offer: i) Open standards (arguable for CDMA) ii) Digital technology iii) (near) National coverage and roaming iv) Voice and data (limited rates) v) Supplementary Services 6.8.3 Third Generation: The World’s leading telecommunication authorities such as the International Telecommunications Union (ITU), ETSI and others are formulating specifications for the 40

next generation of mobile telecommunication devices and networks. Within ETSI this network is known as the Universal Mobile Telecommunication System – UMTS and is data focused.

6.9 Enhanced Data Rates for GSM Evolution (EDGE): Enhanced Data Rates for GSM Evolution (EDGE) is a proposed modification to the modulation scheme utilized by GSM (i.e. Gaussian Minimum Shift Keying). This change will drastically increase the bit rates available to end users for the purpose of data transfer. It is envisaged that the enhanced modulation techniques will make it possible to maintain a good quality link by automatically adapting to the radio interference conditions and thereby provide the highest possible rate. The exact implementation and technical details are still being discussed in various ETSI feasibility studies but there are certain factors that one can almost assume to be near completion. Wherever possible, EDGE adopts the GSM standards so as to minimize the changes required by manufactures and operators who wish to support this new technology. This includes maintaining the same frequency plan, meaning that 200kHz will still separate carriers. The feasibility study carried out by ETSI on EDGE proposes that it will be able to support both circuit switched services: transparent and non–transparent in addition to the packet based GPRS. These three new services will be called: ECSD T Enhanced Circuit Switched Data – Transparent. ECSD NT Enhanced Circuit Switched Data – Non–transparent. EGPRS Enhanced General Packet Radio Service.

41

CHAPTER - 7 GENERAL PACKET RADIO SERVICE (GPRS)

7.1 INTRODUCTION: General Packet Radio Services (GPRS) has been specified to optimize the way data is carried over GSM networks with new requirements for features, network capacity and bearer services. This chapter gives an overview of a General Packet Radio Services (GPRS) network and other Data Networks in Europe and throughout the world. This section also lists the history of GPRS. The services provided and the main benefits. 7.2 WHAT IS GENERAL PACKET RADIO SERVICE (GPRS)? GPRS is a data service for GSM, the European standard digital cellular service. It is a packet-switched mobile data service, a wireless packet based network. GPRS, further enhancing GSM networks to carry data, is also an important component in the GSM evolution entitled GSM+. High-speed mobile data usage is enabled with GPRS. IF GPRS is compared to GSM data services, the following applies: In GSM all the data that has to be sent, is sent via a circuit switched connection. This means, that a link has to be established and is used and maintained from setup until release. The data is sent via one physical timeslot and has a maximum data rate of 9.6 kbps. In GPRS all the data that has to be sent, is split into several smaller data packets first. Those packets are then sent individually across the GPRS network and each of those packets can travel on a different route. The packets arrive at the right destination address and could be reassembled in the right order, because every single packet contains the destination address and information about the sequencing of the different packets. 42

In GPRS, one user can occupy more than one timeslot or more than one user can be on a single timeslot. Depending on different aspects, a maximum data rate of 171.2 kbps could be achieved. For GPRS the ETSI Standard introduces two new elements, the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN) (Shown in the diagram below as shadowed objects) is introduced to create an end-to-end packet transfer mode. The HLR is enhanced with GPRS subscriber data and routing information. Two services are provided; i) Point -To-Point (PTP) ii) Point-To-Multipoint (PTM) (not yet specified by the Standards) The European Telecommunications Standards Institute (ETSI) has specified GPRS as an overlay to the existing GSM network to provide packet data services. In order to operate a GPRS service over a GSM network, new functionality has to be introduced into existing GSM network elements and new network elements have to be integrated into the existing operators GSM networks. The Base Station Subsystem (BSS) of GSM has to be upgraded to support GPRS. The BSS works with the GPRS Support Node (GSN) to provide GPRS service in a similar manner to its interaction with the Switching subsystem for the circuit switched services. A new logical network node called the GPRS Support Node (GSN) supports independent packet routing and transfer within the Public Land Mobile Network (PLMN). The Gateway GPRS support Node (GGSN) acts as a logical interface to external packet data networks. The Serving GPRS Support Node (SGSN) is responsible for the delivery of packets to the MSs within its service area. Within the GPRS network, Protocol Data Units (PDUs) are encapsulated at the originating GSN and decapsulated at the destination GSN, In between the originating GSN, Internet Protocol (IP) is used as the backbone to transfer PDUs.

43

CHAPTER-8 PRESENT & FUTURE GENERATIONS OF TECHNOLOGY (3G/4G)

8.1 3G Communication: The emergence of the Third Generation Mobile Technology (Commonly known as 3G), has been the latest innovation in the field of communication. In fact, in the European market few years back the operators have taken license to operate 3G services at quite high cost. After initial teething troubles, the technology is finally taking shape. The architecture and the specification are in place. The products and the network roll outs have started and customer base is growing. This can give the customers Internet access at 2 Mbps, while he/she is on the move. Although practically, the bit rate is likely to be lower at least in the initial phase. 3G is the next generation of wireless network technology that provides high speed bandwidth (high data transfer rates) to handheld devices. The high data transfer rates will allow 3G networks to offer multimedia services combining voice and data. Specifically, 3G wireless networks support the following maximum data transfer rates: i) 2.05 Mbits/second to stationary devices. ii) 384 Kbits/ second for slowly moving devices, such as a handset carried by a walking user. iii) 128 Kbits/second for fast moving devices, such as handset in moving vehicles. These data rates are the absolute maximum numbers. For example, in the stationary case, the 2.05 Mb/second rate is for one user hogging the entire capacity of the base station. This data rate will be far lower if there is voice traffic (the actual data rate would depend upon the number of calls in progress). The maximum data rate of 128 Kbits/second for moving devices is about ten times faster than that available with the current 2G wireless networks. Unlike 3G networks, 2G networks were designed to carry voice but not data. 3G wireless networks have the bandwidth to provide converged voice and data services. 44

i) Always-on connectivity. 3G networks use IP connectivity, which is packet based. ii) Multi-media service with streaming audio and video. iii) Email with full-fledged attachments such as Power Point files. iv) Instant messaging with video/audio clips. v) Fast downloads of large files such as faxes and Power Point files. vi) Access to corporate applications.

8.2 Advantages of 3G: 3G networks offer the users advantages such as: i) New radio spectrum to relieve overcrowding in existing systems. ii) More bandwidth, security and reliability. iii) Asymmetric data rates. iv) Backward compatibility of devices with existing networks. v) Always-online devices, 3G will use IP connectivity. IP is packet based (not circuit based). vi) Rich multimedia services.

8.3 Disadvantages of 3G: There are some issues in deploying 3G: i) The cost of upgrading base station and cellular infrastructure to 3G is likely to be very high. ii) Requires different handsets and there is the issue of handset availability. 3G handsets will be a complex product. Roaming and making both data/voice works has not yet been fully and seamlessly operational.

45

8.4 Potential Killer Applications: Not withstanding the disadvantage mentioned above, telecom industry still perceive that there a big potential market for 3G services, Perhaps that is the reason that many operators, specially in Europe have paid heavy license fee to acquire 3G licenses. The high bandwidth of 3G networks will lead to the creation of new services, some of which we have no idea at this time. The big question is what services will be big revenue markets for the wireless service providers. In 2G networks, the big winners have been short text messaging in GSM networks (In Europe and countries other that USA) and image downloads. Some of the services likely to be big winners in 3G networks are: i) video conferencing ii) video messaging iii) Mobile Games

The first application is more form business application. The other two are targeted towards the younger generation. MMS (Multi Media Services) are likely to grow very fast. Similarly, as per some estimation, it is felt that gaming industry could be as big as $20-25 billion in near future. In fact, the optimist predict that it will be bigger than Hollywood box office collection. The trend is not restricted to US but is likely to be followed by Asian countries. Presently India and China are perceived as bid market for Mobile Growth (Including 3G).

8.5 3G Network: UMTS (universal Mobile Telecommunication System) is amalgamations of both packet are circuit switched technologies. It has simultaneously been designed to have the upgradeability features of earlier mobile systems such as GSM and GPRS. In addition, it is expected that, IP multimedia will be and integral part of the UMTS standards. 46

Signaling Signaling & User Data IP Multimedia

WLAN Evolved GPRS

EDGE Iu WCDMA

IP Network

Backbone Evolved GSM

PSTN

Backbone

Fig 8.1: The UMTS networks and domains The circles to the left show three different radio access networks, which are attached to the backbone networks in the middle via the Iu interface. A Wireless LAN (WLAN) need not be connected to the GPRS backbone but could also be linked directly to an IP Network. The upper circle to the right depicts the SIP based and access independent IP Multimedia subsystem. To the far right are legacy PSTNs and an external IP network (e.g. the Internet).

8.6 Future Trends (3G to 4G Onwards): New data services, interactive TV and evolving Internet behavior will influence mobile data usage. Long sessions in always-on mode will force a re-think of radio access technology to achieve the required but not easy to attain capacity (Gbit/s/km) at low cost. The ideas presented in this article can increase capacity by a factor of 500 with regard to expected cellular deployments. Coverage will be based on large umbrella cells (3G, WiMAX) and numerous Pico cells interconnected to provide the user with seamless high data rate (several Mbs) sessions. Scalable and progressive deployments are possible while protecting the operator’s long-term investment. The 4G infrastructure operator will mix several technologies, each of which has its optimal usage.

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The connection to one of them will result in a real-time trade-off which will offer the user the best possible service. Some tools that genuinely improve the user’s multimedia quality of experience (availability, response time, definition, etc) are also presented in this article.

8.7 OPERATIONAL EXCELLENCE: Voice was the driver for second generation mobile and has been a considerable success. Today, video and TV services are driving forward third generation (3G) deployment and in the future, low cost, high speed data will drive forward the fourth generation (4G) as short-range communication emerges. Service and application ubiquity, with a high degree of personalization and synchronization between various user appliances, will be another driver. At the same time, it is probable that the radio access network will evolve from a centralized architecture to a distributed one.

8.8 SERVICE EVOLUTION: The evolution from 3G to 4G will be driven by services that offer better quality (e.g. video and sound) thanks to greater bandwidth, more sophistication in the association of a large quantity of information, and improved personalization. Convergence with other network (enterprise, fixed) services will come about through the high session data rate. It will require an always-on connection and a revenue model based on a fixed monthly fee. The impact on network capacity is expected to be significant. Machine-to-machine transmission will involve two basic equipment types: sensors (which measure parameters) and tags (which are generally read/write equipment). It is expected that users will require high data rates, similar to those on fixed networks, for data and streaming applications. Mobile terminal usage (laptops, Personal digital assistants, hand-held) is expected to grow rapidly as they become more user friendly.

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Fluid high quality video and network reactivity are important user requirements. Key infrastructure design requirements include: fast response, high session rate, high capacity, low user charges, rapid return on investment for operators, investment that is in line with the growth in demand, and simple autonomous terminals. The infrastructure will be much more distributed than in current deployments, facilitating the introduction of a new source of local traffic: machine-to-machine.

8.9 MULTI-TECHNOLOGY APPROACH: Many technologies are competing on the road to 4G, as can be seen in Figure 3. Three paths are possible, even if they are more or less specialized. The first is the 3G-centric path, in which Code Division Multiple Access (CDMA) will be progressively pushed to the point at which terminal manufacturers will give up. When this point is reached, another technology will be needed to realize the requi-red increases in capacity and data rates. The second path is the radio LAN one. Wide-spread deployment of WiFi is expected to start in 2005 for PCs, laptops and PDAs. In enterprises, voice may start to be carried by Voice over Wireless LAN (Vo WLAN). However, it is not clear what the next successful technology will be. Reaching a consensus on a 200 Mb it/s (and more) technology will be a lengthy task, with too many proprietary solutions on offer. A third path is IEEE 802.16e and 802.20, which are simpler than 3G for the equivalent performance. A core network evolution towards a broadband Next Generation Network (NGN) will facilitate the introduction of new access network technologies through standard access gateways, based on ETSI-TISPAN, ITU-T, 3GPP, China Communication Standards Association (CCSA) and other standards. How can an operator provide a large number of users with high session data rates using its existing infrastructure?

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At least two technologies are needed. The first (called “parent coverage”) is dedicated to large coverage and real-time services. Legacy technologies, such as 2G/3G and their evolutions will be complemented by WiFi and WiMAX. A second set of technologies is needed to increase capacity, and can be designed without any constraints on coverage continuity. This is known as picocell coverage. Only the use of both technologies can achieve both targets. Handover between parent coverage and pico cell coverage is different from a classical roaming process, but similar to classical handover. Parent coverage can also be used as a back-up when service delivery in the pico cell becomes too difficult.

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ABBREVIATIONS

ABBREVIATIONS

DESCRIPTION

GSM

Global System For mobile

GPRS

General Packet Radio Service

EDGE

Enhanced Data Rates for Global Evolution

LAI

Location Area Identifier

ME

Mobile Equipment

BSS

Base Station Subsystem

BTC

Base Transceiver Station

BSC

Base Switching Center

MSC

Mobile Switching Center

PLMN

Public Land Mobile Network

PUK

Pin Unblocking Key

EIR

Equipment Identity Register

IMEI

International Mobile Equipment Identity

PSTN

Public Switched Telephone Network

PIN

Personal Identification Number

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REFERENCES

[1]

http://www.3ginindia.com/index.php/2010/01/11/benefits-of-3g-to-

information-technology. [2]

GSM Networks: Protocols, Terminology ,and Implementation by

Gunnar Hein [3]

http://en.wikipedia.org/wiki/High_Speed_Packet_Access

[4]

http://en.wikipedia.org/wiki/3G

[5]

http://en.wikipedia.org/wiki/File:BSNL_Logo.svg

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