GLOBAL SYSTEM FOR MOBILE COMMUNICATION
Report Submitted in Partial Fulfilment of the Requirements for the Evaluation of
CS440 Practical Training by
AMAN SINGH (11CSE003)
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY GOA MONTH 2014
Acknowledgement I would like to add a few heartfelt words for the people who were part of this training report in numerous ways, People who gave unending support right from the stage the training report idea were conceived. In particular I am extremely grateful to BHARAT SANCHAR NIGAM LIMITED for providing me with an excellent opportunity of undergoing summer training for the duration of six weeks. I express my effusive thanks to Mr. S. K. Pandey (S.D.E.) and the other technical staff members. With their expert guidance and kind help this training would have been a distant dream. I express my sincere gratitude to Mr. Kamal (J.T.O.) for providing me the required information for completion my job. Aman Singh 11CSE003
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Figure 1: Certificate of Internship at BSNL
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TABLE OF CONTENTS List of Figures
v
ABBREVIATIONS
vi
1
INTRODUCTION
vii
1.1
Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vii
1.2
About BSNL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vii
1.3
About GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
viii
1.3.1
The Goals of GSM . . . . . . . . . . . . . . . . . . . . . . . .
viii
1.3.2
Specifications and Characteristics of GSM . . . . . . . . . . . .
ix
2
3
Evoltion of GSM
x
2.1
History of GSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
x
2.2
GSM Around the World . . . . . . . . . . . . . . . . . . . . . . . . . .
x
2.3
GSM Statistics in India . . . . . . . . . . . . . . . . . . . . . . . . . .
x
Description
xii
3.1
GSM Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xii
3.2
HLR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xii
3.3
MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xii
3.4
AUC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xiv
3.5
MSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xiv
3.6
VLR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xiv
3.7
BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xv
3.8
BTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xv
3.9
BSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xv
3.10 SIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xvi
iii
3.11 OSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.12 Authentication and Encryption . . . . . . . . . . . . . . . . . . . . . . xviii 3.12.1 AUthentication . . . . . . . . . . . . . . . . . . . . . . . . . . xviii 3.12.2 Encryption . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii 3.12.3 Ciphering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii 3.12.4 Ki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii 3.12.5 RAND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
4
3.12.6 Signed Response . . . . . . . . . . . . . . . . . . . . . . . . .
xix
3.12.7 A3 Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.12.8 A8 Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.12.9 Kc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.13 Mobile subscriber identities in GSM . . . . . . . . . . . . . . . . . . .
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3.13.1 International Mobile Subscriber Identity (IMSI): . . . . . . . .
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3.13.2 Temporary Mobile Subscriber Identity (TMSI) . . . . . . . . .
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3.13.3 Mobile Station ISDN Number . . . . . . . . . . . . . . . . . .
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3.13.4 The Mobile Station Roaming Number (MSRN) . . . . . . . . .
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3.13.5 International Mobile Equipment Identity . . . . . . . . . . . . .
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3.14 GSM Frequency Bands . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.14.1 Dual-Band . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xxi
3.14.2 Tri-Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.14.3 Quad-Band . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xxi
3.15 Key Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.15.1 Increased Capacity . . . . . . . . . . . . . . . . . . . . . . . .
xxii
3.15.2 Frequency Reuse . . . . . . . . . . . . . . . . . . . . . . . . .
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3.16 Future Opportunities for GSM . . . . . . . . . . . . . . . . . . . . . .
xxii
Conclusion
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LIST OF FIGURES 1
Certificate of Internship at BSNL . . . . . . . . . . . . . . . . . . . . .
ii
2.1
Global Mobile Net Additions 1Q 2010 . . . . . . . . . . . . . . . . . .
xi
2.2
GSM Statistics in India . . . . . . . . . . . . . . . . . . . . . . . . . .
xi
3.1
GSM Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xiii
3.2
Mobile Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3.3
Base Station System . . . . . . . . . . . . . . . . . . . . . . . . . . .
xv
3.4
Base Transciever Station . . . . . . . . . . . . . . . . . . . . . . . . .
xvi
3.5
Base Station Controller . . . . . . . . . . . . . . . . . . . . . . . . . .
xvi
3.6
SIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xvii
v
ABBREVIATIONS
NITG
National Institute of Technology Goa
HLR
Home Location Register
MS
Mobile Station
AUC
Authentication Center
MSC
Mobile Services Switching Center
VLR
Visitor Location Register
BSS
Base Station System
BTS
Base Transceiver Station
BSC
Base Station Controller
SIM
Subscriber Identity Module
OSS
Operation and Support System
RAND
Random
SRES
Signed Response
ME
Mobile Equipment
IMSI
International Mobile Subscriber Identity
TMSI
Temporary Mobile Subscriber Identity
MSRN
Mobile Station Roaming Number
IMEI
International Mobile Equipment Identity
HSCSD
High Speed Circuit Switched Data
GSM
Global System for Mobile Communication
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CHAPTER 1
INTRODUCTION
1.1
Motivation
Practical exposure for doing things makes a person conversant to the technicalities involved in any job. In view of such benefits, imparting of vocational training has been made an integral part of any academic structure.
1.2
About BSNL
˘ Zs ´ 7th largest telecommuniBharat Sanchar Nigam Ltd. Formed in oct. 2000, is worldâA cations company providing comprehensive range of telecom services in India: wire line, CDMA mobile, GSM mobile, internet, broadband, carrier services. Within a span it has become the one of the largest public sector unit in India. BSNL is the only service provider, making focused efforts and planned initiatives to ˘ Surban bridge the rural âA ¸ digital divide ICT sector. In fact there is no telecom operator in the country to beat it reach with its wide network giving services I every nook corner of country and operates across India except Delhi Mumbai. BSNL cellular service cellone, has more than 20.7 million cellular customers, garnering 24 BSNL has set up a world class multi-gigabit, multi-protocol convergent IP infrastructure that provides convergent services like voice, data and video through the same Backbone and broadband access network. At present there are 0.6 million Data one broadband customers. The company has vast experience in Planning, Installation, network integration and Maintenance of Switching Transmission Networks and also has a world class ISO 9000 certified Telecom Training Institute. BSNL plans to expand its customer base from present 73 millions lines to 125 million lines and infrastructure investment plan to
the tune of Rs. 733 crores (US16.67million)inthenextthreeyears.T oday, BSN LisIndia0 slargestT 100 Billion. The company is planning an IPO with in 6 months to offload 10The turnover, nationwide coverage, reach, comprehensive range of the telecom services and the desire to excel has made BSNL the no. 1 telecom company of India.
1.3
About GSM
˘ GSM stands for âAŸGlobal Services for Mobile communication’ and is an open, digital cellular technology used for transmitting mobile voice and data services. GSM supports voice calls and data transfer speeds of up to 9.6 kbit/s, together with the transmission of SMS (Short Message Service). This technology is globally accepted and most popular among all countries. It is started in Europe to integrate all countries with wireless communication. Earlier each country in Europe has its own standard for wireless communication ,so due to this a person cannot use the same mobile in two different country and cannot even communicate with the same mobile in different countries, so due to this fragmentation problem occurred. So to overcome this problem European Union (EU) came with GSM technology that is accepted by whole continent and standardized by ITU-T. It is a 2 ˘ Zs ´ first cellular technology and it is most popular 2G technolG technology and worldâA ogy. Today GSM operator has largest customer base. In India total cellular operator have more than 550 million customers and GSM has more than 400 million customer bases alone. It is a second generation cellular standard developed to cater voice services and data delivery using digital modulation.
1.3.1
The Goals of GSM
• Improved spectrum efficiency • International roaming • Low-cost mobile sets and base stations • High-quality speech • Compatibility with ISDN and other telephone
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• Company services. • Support for new services
1.3.2
Specifications and Characteristics of GSM
˘ c Frequency band âA ˘ S¸ the frequency range specified for GSM is 1,850 to 1,990 • âA´ MHz (mobile station to base station). ˘ S¸ the duplex distance is 80 MHz. Duplex distance is the distance • Duplex distance âA between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart. ˘ S¸ the separation between adjacent carrier frequencies. In • Channel separation âA GSM, this is 200 kHz. ˘ S¸ Modulation is the process of sending a signal by changing the • Modulation âA characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK). ˘ S¸ GSM is a digital system with an over-the-air bit rate of 270 • Transmission rate âA kbps. ˘ S¸ GSM utilizes the time division multiple access (TDMA) con• Access method âA cept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot. ˘ S¸ GSM uses linear predictive coding (LPC). The purpose of LPC • Speech coder âA is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract.
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CHAPTER 2
Evoltion of GSM
2.1
History of GSM
In 1982, the European Conference of Postal and Telecommunications administrations (CEPT) created the Group Special Mobile (GSM) to develop a standard for a mobile telephone system that could be used across Europe. In 1987, a memorandum of understanding was signed by 13 countries to develop a common cellular telephone system across Europe. Finally the system created by SINTEF led by Torleiv Maseng was selected. In 1989, GSM responsibility was transferred to the European Telecommunications Standards Institute (ETSI) and phase I of the GSM specifications were published in 1990. The first GSM network was launched in 1991 by Radio linja in Finland with joint technical infrastructure maintenance from Ericsson. By the end of 1993, over a million subscribers were using GSM phone networks being operated by 70 carriers across 48 countries.
2.2
GSM Around the World
2.3
GSM Statistics in India
[scale=0 Figure 2.1: Global Mobile Net Additions 1Q 2010
Figure 2.2: GSM Statistics in India
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CHAPTER 3
Description
3.1
GSM Architecture
3.2
HLR
HLR is database, which holds very important information of subscribers. It is mostly known for storing and managing information of subscribers. It contains subscriber service profile, status of activities, information about locations and permanent data of all sorts. When new connections are purchased, these subscribers are registered in HLR of mobile phone companies.
3.3
MS
It consists of mobile equipment and SIM. At the time of manufacturing, an international mobile equipment number (IMEI) is programmed in ME.A SIM is required to activate the GSM services. A international mobile subscriber identification (IMEI) number is programmed along with security parameter and algorithm. The called number is not linked to ME but to SIM.A SIM has following data stored in it. MSISDN (mobile subscriber isdn) IMSI (international mobile subscriber identity) - 15 digit number. TMSI (temporary ˘ S¸ 4 octets, allocated by VLR, continuously changed.IMEI mobile subscriber identity) âA (international mobile equipment identity) unique, permanently assigned to MS.
Figure 3.1: GSM Architecture
Figure 3.2: Mobile Station
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3.4
AUC
AUC is small unit which handles the security end of the system. Its major task is to ˘ Zs ´ identification and hence authenticate and encrypt those parameters which verify userâA ˘ S¸ enables the confidentiality of each call made by subscriber. Authentication center âA AUC makes sure mobile operators are safe from different frauds most likely to happen when hackers are looking for even smallest loop wholes in systems.
3.5
MSC
MSC is also important part of SS, it handles technical end of telephony. It is build to ˘ Zs ´ most important task is to perform switching functionality of the entire system. ItâA control the calls to and from other telephones, which means it controls calls from same networks and calls from other networks. Toll ticketing, common channel signaling, network interfacing etc are other tasks which MSC is responsible for.
3.6
VLR
VLR performs very dynamic tasks; it is database which stores temporary data regarding subscribers which is needed by Mobile Services Switching Center-MSC VLR is directly connected to MSC, when subscribe moves to different MSC location, Visitor location ˘ S¸ VLR integrates to MSC of current location and requests the data about subregister âA ˘ SHLR. scriber or Mobile station (MS) from the Home Location Register âA ¸ When subscriber makes a call the Visitor location register-VLR will have required information for making call already and it will not required to connect to Home Register Location - HRL again.
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Figure 3.3: Base Station System
3.7
BSS
The base station system have very important role in mobile communication. BSS are basically outdoor units which consist of iron rods and are usually of high length. BSS are responsible for connecting subscribers (MS) to mobile networks. All the communication is made in Radio transmission. The Base station System is further divided in two systems. These two systems, they are BSC, and BTS.
3.8
BTS
Subscriber, MS (Mobile Station) or mobile phone connects to mobile network through BTS; it handles communication using radio transmission with mobile station. As name suggests, Base transceiver Station is the radio equipment which receive and transmit voice data at the same time. BSC control group of BTSs.
3.9
BSC
The Base Station normally controls many cells; it registers subscribers, responsible for MS handovers etc. It creates physical link between subscriber (MS) and BTS, then manage and controls functions of it. It performs the function of high quality switch by handover over the MS to next BSC when MS goes out of the current range of BTS, it helps in xv
Figure 3.4: Base Transciever Station
Figure 3.5: Base Station Controller connecting to next in range BTS to keep the connection alive within the network. It also performs functions like cell configuration data, control radio frequency in BTS.
3.10
SIM
One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM card. The SIM is a detachable smart card containing the user’s subscription information and phone book. This allows the user to retain his or her information after switching handsets. Alternatively, the user can also change operators while retaining the xvi
Figure 3.6: SIM handset simply by changing the SIM.
3.11
OSS
OMC- Operations and maintenance center is designed to connect to equipment of MSCMobile Switching Center and BSC-Base Station Controller. The implementation of OMC is called OSS-The Operations and Support System.OSS helps in mobile networks to monitor and control the complex systems. The basic reason for developing operation and support system is to provide customers a cost effective support and solutions. It helps in managing, centralizing, local and regional operational activities required for GMS networks.
xvii
3.12
Authentication and Encryption
3.12.1
AUthentication
Whenever a MS requests access to a network, the network must authenticate the MS. Authentication verifies the identity and validity of the SIM card to the network and ensures that the subscriber is authorized access to the network.
3.12.2
Encryption
In GSM, encryption refers to the process of creating authentication and ciphering crypto variables using a special key and an encryption algorithm.
3.12.3
Ciphering
3.12.4
Ki
The Ki is the individual subscriber authentication key. It is a 128-bit number that is paired with an IMSI when the SIM card is created. The Ki is only stored on the SIM card and at the Authentication Center (AuC). The Ki should never be transmitted across the network on any link.
3.12.5
RAND
The RAND is a random 128-bit number that is generated by the Auc when the network requests to authenticate a subscriber. The RAND is used to generate the Signed Response (SRES) and Kc crypto variables.
xviii
3.12.6
Signed Response
The SRES is a 32-bit crypto variable used in the authentication process. The MS is challenged by being given the RAND by the network; the SRES is the expected correct response. The SRES is never passed on the Um (Air) interface. It is kept at the MSC/VLR, which performs the authentication check.
3.12.7
A3 Algorithm
The A3 algorithm computes a 32-bit Signed Response (SRES). The Ki and RAND are inputted into the A3 algorithm and the result is the 32-bit SRES. The A3 algorithm resides on the SIM card and at the AuC.
3.12.8
A8 Algorithm
The A8 algorithm computes a 64-bit ciphering key (Kc). The Ki and the RAND are inputted into the A8 algorithm and the result is the 64-bit Kc. The A8 algorithm resides on the ISM card and at the AuC.
3.12.9
Kc
The Kc is the 64-bit ciphering key that is used in the A5 encryption algorithm to encipher and decipher the data that is being transmitted on the Um interface.
3.13
Mobile subscriber identities in GSM
3.13.1
International Mobile Subscriber Identity (IMSI):
An IMSI is assigned to each authorized GSM user. It consists of a mobile country code (MCC), mobile network code (MNC) (to identify the PLMN), and a PLMN unique mobile
xix
subscriber identification number (MSIN). The IMSI is the only absolute identity that a subscriber has within the GSM system. The IMSI consists of the MCC followed by the MNC and MSIN and shall not exceed 15 digits.
3.13.2
Temporary Mobile Subscriber Identity (TMSI)
A TMSI is a MSC-VLR specific alias that is designed to maintain user confidentiality. It is assigned only after successful subscriber authentication. The correlation of a TMSI to ˘ Zs ´ initial transaction with an MSC (for an IMSI only occurs during a mobile subscriberâA example, location updating). Under certain condition (such as traffic system disruption and malfunctioning of the system), the MSC can direct individual TMSIs to provide the MSC with their IMSI.
3.13.3
Mobile Station ISDN Number
The MS international number must be dialed after the international prefix in order to obtain a mobile subscriber in another country. The MSISDN numbers is composed of the country code (CC) followed by the National Destination Code (NDC), Subscriber Number (SN), which shall not exceed 15 digits. Here too the first two digits of the SN identify the HLR where the mobile subscriber is administrated.
3.13.4
The Mobile Station Roaming Number (MSRN)
The MSRN is allocated on temporary basis when the MS roams into another numbering area. The MSRN number is used by the HLR for rerouting calls to the MS. It is assigned upon demand by the HLR on a per-call basis. The MSRN for PSTN/ISDN routing shall have the same structure as international ISDN numbers in the area in which the MSRN is allocated. The HLR knows in what MSC/VLR service area the subscriber is located. At the reception of the MSRN, HLR sends it to the GMSC, which can now route the call to the MSC/VLR exchange where the called subscriber is currently registered.
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3.13.5
International Mobile Equipment Identity
The IMEI is the unique identity of the equipment used by a subscriber by each PLMN and is used to determine authorized (white), unauthorized (black), and malfunctioning (gray) GSM hardware. In conjunction with the IMSI, it is used to ensure that only authorized users are granted access to the system.
3.14
GSM Frequency Bands
There are three different frequency bands on which mobile phones are usually operates and these are Dual Band, Tri-Band and Quad Band.
3.14.1
Dual-Band
Dual frequency band operates on 900MHz and 1800 MHz, that means mobile phone that supports dual band can be operated anywhere in the world where 900 MHz and 1800 MHz frequencies are used. Dual Band GSM networks usually found in all continents Europe, Asia, Africa, Australia and South America.
3.14.2
Tri-Band
Three frequencies are supported in Tri Band, these frequencies are 900 MHz, 1800MHz and 1900 MHz Tri band is also supported all around the world these days.
3.14.3
Quad-Band
Quad Band supports four frequencies which are 850 MHz, 900 MHz, 1800 MHz , 1900 MHz Quad band also enables GSM phones to road almost anywhere in the world. All countries support GSM networks hence make communication possible.
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3.15
Key Features
3.15.1
Increased Capacity
It provides better channel capacity than analog system. It provides 25KHZ per user, that means eight conversation per 200KHZ channel pair(a channel pair consists of a forward channel and a reverse channel). Channel coding and modulation provided to enhance the channel capacity and from this 12 DB is achieved as a channel to interference ratio(C/I ration), as compare to 18db of analog system.
3.15.2
Frequency Reuse
GSM has a advantage of frequency reuse pattern from which same frequency can be used in different cells. Normally 124 carriers are provided by the GSM system and if we multiply it with the 7 time slots used for traffic than we get 868 numbers of calls can be made and that is very less in number. so to overcome this problem same RF carrier is used for several conversation in different cells and for this there is regular pattern is defined. The pattern to be used depends on the traffic requirement and spectrum availability. Some typical patter are 4/12 , 7/21 etc.
3.16
Future Opportunities for GSM
• 2nd Generation • GSM -9.6 Kbps (data rate) • 2.5 Generation ( Future of GSM) • HSCSD (High Speed ckt Switched data) • Data rate : 76.8 Kbps (9.6 x 8 kbps) • GPRS (General Packet Radio service) • Data rate: 14.4 - 115.2 Kbps • EDGE (Enhanced data rate for GSM Evolution) xxii
• Data rate: 547.2 Kbps (max) • 3 Generation • WCDMA(Wide band CDMA) ˘ S¸ 2.0 Mbps • Data rate : 0.348 âA
xxiii
CHAPTER 4
Conclusion During the period of Evolution of mobile communication technologies various systems were introduced and deployed to achieve standardization in mobile industry, but all the efforts were failed. Multiple issues were sustained like incompatibility of systems, development of digital radio frequency. That is, when GSM (Global System for Mobile Communication) Technology was introduced and problems like standardization, incompatibility etc were overcame. TDMA solution was chosen in 1987, it is narrowband system and TDMA standards for Time Division Multiple access. In 1991 in Finland. GSM based mobile phones are operated on TDMA Systems, in TDMA single radio frequency is offered to users with any interference. After all these years, GSM is now the largest mobile communication technology worldwide, all manufacturers of Mobile phones develop their products based on GSM, and all mobile companies provide their subscribers GSM networks. GSM technology facilitates with high speed integrated data, voice data, fax, mail, voice mail and mostly used SMS feature. GSM also make sure that all the communication made between networks are secured and protected from intruders and frauds. .SM actually brought the concept of being Mobile way beyond the limits. It enabled us to communicate across the continents. GSM supports multiple frequency levels like 900 MHz, 1800 MHz, 1900 MHz 1900MHz frequency is used in North America where as 1800MHz is used in other parts of the world. Different frequency bands are used by different mobile phone operators. Moreover, there are over 700 GSM networks available in the world operating in their respective countries and providing international roaming services courtesy GSM technology. There are over 2 billion GSM subscribers in the world. Countries which are using GSM networks on larger scales are Russia, United States, India. Giver the above facts and very good voice quality, support useful services and standards, delivered by GSM, it is expected that GSM shall remain the prominent technology for offering the mobile telephony.
REFERENCES [1] www.gsmworld.com [2] www.gsacom.com [3] www.whytelecom.com [4] www.wikipedia.com
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