Inplant Training Report 3g4i42

INPLANT TRAINING REPORT AT MAHANAGAR TELEPHONE NIGAM LIMITED (BKC)

SUBMITTED BY

ABHISHEK KUMAR PANDEY (6th, B.TECH)

ELECTRONICS & COMMUNICATION ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY, SRINAGAR FROM 27TH JANUARY 2009 TO 14TH MARCH 2009

CONTENTS

 ACKNOWLEDGEMENT  MTNL HISTORY  MOBILE TECHNOLOGY OVERVIEW  GSM NETWORK ARCHITECTURE  GPRS NETWORK ARCHITECTURE  ROAMING SERVICES IN GSM SYSTEM  CONCLUSION

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ACKNOWLEDGEMENT The industrial exposure that I have experienced as a trainee in MAHANAGAR TELEPHONE NIGAM LIMITED (BKC) has helped me a lot not only in improving my theoretical knowledge but also to understand the working of a large industry. I am sincerely grateful to the management of MAHANAGAR TELEPHONE NIGAM LIMITED (BKC) for giving me an opportunity to undergo six weeks Inplant Training in their organization & for providing homely atmosphere in their organization. I would like to express my deepest gratitude towards Mr. Sandeep Keshkar (Dy. General Manager, NSS-1, MS) for associating me in this training. I also express my sincere gratitude & thanks to my mentor Mr.Vikalp Maurya (Asst Manager) for making timely guidance and encouraging me at various stages during my training. He also helped me a lot on my personal front as far as my studies were concerned, by giving me tips to improve my performance. My experience with him as his subordinate is memorable. I am also thankful to Mrs. J.Wilson(SDE) and Mr. A.G.Pal(SDE) for their positive , coordination & guidance. And last but not the least I thank all the people of the department, for their kind cooperation and .

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MTNL HISTORY Mahanagar Telephone Nigam Limited is an Indian Government-owned telephone service provider in the cities of Mumbai, Thane, New Delhi, and Navi Mumbai in India. The company was a monopoly until 2000, when the telecom sector was thrown open to other service providers. MTNL provides fixed line telephones, cellular connection of both GSM — Dolphin (Postpaid) and Trump (prepaid) and WLL (CDMA) — Garuda-FW and Garuda-Mobile and internet services through dialup and DSL — Broadband internet TriBand. MTNL has also started Games on demand, video on demand and IPTV services in India through its Broadband Internet service called Triband. Phone numbers belonging to MTNL start with the prefix 2 infixed line telephones and WLL & in GSM Mobile services its start from 9869/9969/9868/9968/9757. MTNL also provides other services such as VPN, Internet Telephony- VOIP and leased lines through BSNL and VSNL.MTNL has been actively providing connections in both Mumbai and New Delhi areas and the efficiency of the company has drastically improved from the days when one had to wait years to get a phone connection to now when one can get a connection in even hours. Pre-activated Mobile connections are available at many places across both Metros. MTNL has also unveiled very cost-effective Broadband Internet access plans (TriBand) targeted at homes and small businesses. At present MTNL enjoys the largest of the market share of ISP services in Mumbai and Delhi. With the market opened to competition in 2001, MTNL has been facing rivalry for its share of the market and declining long-distance call rates. To diversify its revenue base, the cash rich company has expanded into GSM and CDMA cellular services and is developing its Internet related services, including ADSL, Intelligent Network services, call centers and IDCs. The company is expanding beyond its traditional areas to offer Internet services nationwide, and to provide basic services in Nepal. MTNL is considered a likely candidate for further divestment by the government.

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MOBILE TECHNOLOGY OVERVIEW

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Introduction One of the finest things that happened in 20th century is the use of radio channels for personal mobile communication systems. Considered to be a revolution of sorts in telecommunications, mobile communication is the fastest growing market segment and the field of intense research. Mobile communication today is, perhaps, the most powerful catalyst for change in lifestyle of the people all over the world. Mobile communication slowly, but surely is evolving as the backbone for business transactions, efficiency and success silently taking over the role of the elder cousin PSTN. Basic to the design of a mobile communication system is the ability of the to liberate himself from the confines of a wired line and therefore his freedom to move anywhere he wants. Mobile communication systems therefore are required to provide seamless service while the customers are on move transcending geographical and network borders. Provision of service under such environment throws a number of challenging issues and the way these issues are addressed and resolved makes each system different from all others. The first mobile telephone service started in 1946 in St. Louis, Missouri, USA as a manually operated system. Between 1950 and 1960, it evolved as an automatic system, but small subscriber base. Mobile telephony service in its useful form appeared in 1960s. The 1st generation mobile communication systems appeared in 1970s and remained till 1980s. They used analog transmission techniques for the radio link and confined its s to their respective system areas for which the mobile phone was designed. Capacity of the system was very limited and roaming between the coverage areas of the different systems was impossible. Apart from being very expensive, these systems provided poor QoS and ed only voice communication. The 2nd generation mobile communication systems grew out of the limitations of the 1st generation systems. They ed large subscriber base, carried both voice and data and have capability to design and deliver new value added services (VAS). The radio link became digital enabling use of versatile signaling capabilities and cross-network

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roaming. However, multiple standards made seamless roaming across all the networks impossible. GSM and CDMA emerged as the trend setting technologies. The domination of the 2G systems in the mobile communication market became apparent in second half of 1990s. The design objectives of the 3rd generation mobile systems are to provide high functionality with seamless global roaming. Apart from providing very high data rates, 3G systems seek to integrate the wire lines systems with mobile systems. 3G would provide s consistent voice, data, graphical, multi-media and video-based information service regardless of their location in the network (Cordless, Cellular, Satellite, Fixed/Wire line and so on….). The 3G system is an I.P. based system. 3G systems would also integrate the Intelligent Network (IN) capabilities into mobile systems.

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2G 2G (or 2-G) is short for second-generation wireless telephone technology. Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted, 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS text messages. After 2G was launched, the previous mobile telephone systems were retrospectively dubbed 1G. While radio signals on 1G networks are analog, and on 2G networks are digital, both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.

2G technologies 2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are: GSM (TDMA-based), originally from Europe but used in almost all countries on all six inhabited continents (Time Division Multiple Access). Today s for over 80% of all subscribers around the world. IS-95 aka cdmaOne, (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia. Today s for about 17% of all subscribers globally. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, Australia and South Korea. PDC (TDMA-based), used exclusively in Japan iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada IS-136 aka D-AMPS, (TDMA-based, simply TDMA in the US), was once prevalent in the Americas but most have migrated to GSM.

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Capacity Using digital signals between the handsets and the towers increases system capacity in two key ways: 

Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various codecs, allowing more calls to be packed into the same amount of radio bandwidth.



The digital systems were designed to emit less radio power from the handsets. This meant that cells could be smaller, so more cells could be placed in the same amount of space. This was also made possible by cell towers and related equipment getting less expensive.

Advantages Digital systems were embraced by consumers for several reasons. 

The lower powered radio signals require less battery power, so phones last much longer between charges, and batteries can be smaller.



The digital voice encoding allowed digital error checking which could increase sound quality by increasing dynamic range and lowering the noise floor.



The lower power emissions helped address health concerns.



Going all-digital allowed introduction of digital data services, such as SMS and email.



Greatly reduced fraud. With analog systems it was possible to have two or more "cloned" handsets that had the same phone number.



Enhanced privacy. A key digital advantage not often mentioned is that digital cellular calls are much harder to eavesdrop on by use of radio scanners. While the security algorithms used have proved not to be as secure as initially d, 2G phones are immensely more private than 1G phones, which have no protection against eavesdropping.

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Disadvantages The downsides of 2G systems, not often well publicized, are: •

In less populous areas, the weaker digital signal may not be sufficient to reach a cell tower. This tends to be a particular problem on 2G systems deployed on higher frequencies, but is mostly not a problem on 2G systems deployed on lower frequencies. National regulations differ greatly among countries which dictate where 2G can be deployed.

•

Analog has a smooth decay curve, digital a jagged steppy one. This can be both an advantage and a disadvantage. Under good conditions, digital will sound better. Under slightly worse conditions, analog will experience static, while digital has occasional dropouts. As conditions worsen, though, digital will start to completely fail, by dropping calls or being unintelligible, while analog slowly gets worse, generally holding a call longer and allowing at least a few words to get through.

• While digital calls tend to be free of static and background noise, the lossy compression used by the codecs takes a toll; the range of sound that they convey is reduced. You'll hear less of the tonality of someone's voice talking on a digital cellphone, but you will hear it more clearly.

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GSM GSM (Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 80% of the global mobile market uses the standard. GSM is used by over 3 billion people across more than 212 countries and territories. Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signaling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system. The ubiquity of the GSM standard has been an advantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM). GSM also pioneered a low-cost (to the network carrier) alternative to voice calls, the Short message service (SMS, also called "text messaging"), which is now ed on other mobile standards as well. Another advantage is that the standard includes one worldwide Emergency telephone number, 112. This makes it easier for international travellers to connect to emergency services without knowing the local emergency number.

GSM security GSM was designed with a moderate level of security. The system was designed to authenticate the subscriber using a pre-shared key and challenge-response. Communications between the subscriber and the base station can be encrypted. GSM only authenticates the to the network (and not vice versa). The security model therefore offers confidentiality and authentication, but limited authorization capabilities, and no non-repudiation. GSM uses several cryptographic algorithms for

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security. The A5/1 and A5/2 stream ciphers are used for ensuring over-the-air voice privacy.

Advantages of GSM  GSM uses radio frequencies efficiently and, because of the digital radio path, the system tolerates more inter cell disturbances.  The average quality of speech achieved is better than that in existing analogue systems.  Data transmission is ed throughout the system.  Speech is encrypted and subscriber information security is guaranteed.  Due to ISDN compatibility, new services are offered as compared to the analogue systems.  International roaming is technically possible within all the countries concerned.  The large market toughens the competition and lowers the prices both for investments and usage.

GSM Frequencies GSM networks operate in a number of different frequency ranges (separated into GSM frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated. Most 3G GSM networks in Europe operate in the 2100 MHz frequency band GSM-900 uses 890–915 MHz to send information from the mobile station to the base station (uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is

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used. This band of frequencies may be allocated equally for up to 4 operators in a telecom circle. To achieve a high spectral efficiency in the cellular network a combination of FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) is used. The FDMA part involves the division by frequency of the 25 MHz bandwidth into 124 carrier frequencies spaced at 200 KHz for GSM-900. For GSM-18OO the frequency spectrum of the 75 MHz bandwidth is divided into 374 carrier frequencies spaced at 200 KHz. One or more frequencies are assigned to each BTS. Each of these carrier frequencies is then divided in time, using a TDMA scheme to increase the number of channels per carrier. Each carrier frequency channel carries eight time-division multiplexed physical channels.

FREQUENCY RANGE

GSM 900

GSM 1800

GSM 1900

Uplink Freq.

935-960 MHz

1710-1785 MHz

1850-1910 MHz

Downlink Freq.

935-960 MHz

1805-1880 MHz

1930-1990 MHz

Channel Spacing

200 KHz

200 KHz

200 KHz

No. of Channels

124

374

299

Duplex Spacing

45 MHz

95 MHz

80 MHz

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Evolution from 2G to 3G From 2G to 2.5G (GPRS)

The first major step in the evolution to 3G occurred

with the introduction of General Packet Radio Service (GPRS). So the cellular services combined with GPRS became 2.5G.GPRS could provide data rates from 56 Kbit/s up to 114 Kbit/s. It can be used for services such as Wireless Application Protocol (WAP) access, Short Message Service (SMS), Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access. GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the actually is utilizing the capacity or is in an idle state.

From 2.5G to 2.75G

GPRS

networks

evolved

to

EDGE

networks

with

introduction of 8PSK encoding. Enhanced Data rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC) is backward-compatible digital mobile phone technology that allows improved data transmission rates, as an extension on top of standard GSM. EDGE can be considered a 3G radio technology and is part of ITU's 3G definition, but is most frequently referred to as 2.75G. EDGE is standardized by 3GPP as part of the GSM family, and it is an upgrade that provides a potential three-fold increase in capacity of GSM/GPRS networks. The specification achieves higher data-rates by switching to more sophisticated methods of coding (8PSK), within existing GSM timeslots. EDGE can be used for any packet switched application, such as an Internet, video and other multimedia.

From 2.75G to 3G

From EDGE networks the introduction of UMTS networks

and technology is called pure 3G. 3G Bandwidth 5 MHz

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GSM NETWORK ARCHITECTURE

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Network structure The network behind the GSM seen by the customer is large and complicated in order to provide all of the services which are required. It is divided into a number of sections and these are each covered in separate articles. 

The Base Station Subsystem (the base stations and their controllers).



The Network and Switching Subsystem (the part of the network most similar to a fixed network). This is sometimes also just called the core network.



The GPRS Core Network (the optional part which allows packet based Internet connections).

All of the elements in the system combine to produce many GSM services such as voice calls and SMS.

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MOBILE STATION (MS) The MS consist of two parts, the Mobile Equipment (ME) and an electronic smart card called as Subscriber Identity Module (SIM). The ME is the hardware used by the subscriber to access the network. The hardware has an identity number associated with it, which is unique for that particular device and permanently stored in it. This identity number is called the International Mobile Equipment Identity (IMEI) and enables the network operator to identity mobile equipment which may be causing problems on the system. The SIM is a card which plugs into the ME. This card identifies the MS subscriber and also provides other information regarding the service that subscriber should receive. The subscriber is identified by an identity number called the International Mobile Subscriber Identity (IMSI). Mobile Equipment may be purchased from any store but the SIM must be obtained from the GSM network provider. Without the SIM inserted, the ME will only be able to make emergency calls. By making a distinction between the subscriber identity, GSM can route calls and perform billing based on the identity of the subscriber rather than the equipment or its location. 1. MOBILE EQUIPMENT (ME) The ME is the only part of the GSM network which the subscribers really see. There are three main type of ME, these are listed below: •

Vehicle Mounted: These devices are mounted in a vehicle and the antenna is physically mounted on the outside of the vehicle.

•

Portable Mobile Unit: This equipment can be handheld when in operation, but the antenna is not connected to the handset of the unit.

•

Hand portable Unit: This element comprises of a small telephone handset not much bigger than a calculator. The antenna is connected to the handset.

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The ME is capable of operating at a certain maximum power output dependent on its type and use. These mobile types have distinct features which must be known by the network, for example their maximum transmission power and the services they . The ME is therefore identified by means of classmark. The classmark is sent by the ME in its initial message.

2. SUBSCRIBER IDENTITY MODULE (SIM) The SIM as mentioned previously is a "Smart Card" which plugs into the ME and contains information about the MS subscriber hence the name subscriber Identity Module. Most of the data contained within the SIM is protected against reading (KI) or alternations (IMSI). Some of the parameters (LAI) will be continuously updated to reflect the current location of the subscriber. The SIM card and the high degree of inbuilt system security provide protection of the subscriber's information and protection of networks against fraudulent access. SIM cards are designed to be difficult to duplicate. The SIM can be protected by use of Personal Identity Number (PIN) , similar to bank/credit charge cards, to prevent unauthorized use of the card. The SIM is capable of storing additional such as accumulated call charges. This information will be accessible to the customer via handset/keyboard key entry. The SIM also executes the Authentication Algorithm. The SIM contains several pieces of information:  International Mobile Subscriber Identity (IMSI)  Temporary Mobile Subscriber Identity (TMSI)  Location Area Identity (LAI)  Mobile Station International Services Digital Network (MSISDN) 18

 Subscriber Authentication Key (Ki)  A3(Authentication Algorithm)  A8 (Cipher Key (Kc)  A5 (Encryption Algorithm)

Functions of MS The primary functions of MS are to transmit and receive voice and data over the air interface of the GSM system. MS performs the signal processing function of digitizing, encoding, error protecting, encrypting, and modulating the transmitted signals. It also performs the inverse functions on the received signals from the BS. In order to transmit voice and data signals, the mobile must be in synchronization with the system so that the messages are the transmitted and received by the mobile at the correct instant. To achieve this, the MS automatically tunes and synchronizes to the frequency and TDMA timeslot specified by the BSC. This message is received over a dedicated timeslot several times within a multi frame period of 51 frames. The exact synchronization will also include adjusting the timing advance to compensate for varying distance of the mobile from the BTS. MS keeps the GSM network informed of its location during both national and international roaming, even when it is inactive. This enables the System to page in its present LA. Finally, the MS can store and display short received alphanumeric messages on the liquid crystal display (LCD) that is used to show call dialing and status in formation. These messages are limited to 160 characters in length (varies from mobile to mobile).

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Mobile Station ISDN (MSISDN)

MSISDN Stands for Mobile Station international Subscriber Dialing Number. It is a Logical Identity. 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 istrated. MSISDN must be ed in the telephone directory. It is used by the calling party for dialing. It is used to Call routing to destination terminal or to the MSC/HLR of the called MS.

International Mobile Subscriber Identity (IMSI)

IMSI stands for International Mobile Subscriber Identity. It is the Software Identity. An IMSI is assigned to each authorized GSM . It consists of a mobile country code (MCC), mobile network code (MNC) (to identify the PLMN), and a PLMN unique mobile subscriber identification number (MSIN) and shall not exceed 15 digits. The IMSI is the only absolute identity that a subscriber has within the GSM system. It is used in the case of system-internal signaling transactions in order to identify a subscriber. The first two digits of the MSIN identify the HLR where the mobile subscriber is istrated.

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International Mobile Equipment Identity (IMEI) IMEI stands for International Mobile Equipment Identity. It is the Hardware 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 s are granted access to the system.

Temporary Mobile Subscriber Identity (TMSI) It is used for identification & addressing of the visiting MS. The VLR assigns a TMSI to each subscriber entering into VLR area. It is assigned only after successful subscriber authentication. The correlation of a TMSI to an IMSI only occurs during a mobile subscriber’s initial transaction with an MSC (for example, location updating). TMSI is stored in MS’s SIM and VLR and is not stored in HLR.

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 ed.

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BASE STATION SUBSYSTEM (BSS) The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone and the network switching subsystem. The BSS carries out transcoding of speech channels, allocation of radio channels to mobile phones, paging, quality management of transmission and reception over the air interface and many other tasks related to the radio network.

Base transceiver station (BTS):

The BTS contains the RF components that provide

the air interface for a particular cell. This is the part of the GSM network which communicates with the MS. The antenna is included as part of the BTS. Base station controller (BSC):

The BSC as its name implies provides the

control for the BSS. The BSC communicates directly with the MSC. The BSC may control single or multiple BTSs. Transcoder (XCDR):

The Transcoder is used to compact the signals from the MS

so that they are more efficiently sent over the terrestrial interfaces. Although the transcoder is considered to be a part of the BSS, it is very often located closer to the MSC. The transcoder is used to reduce the rate at which the traffic (voice/data) is transmitted over the air interface. Although the transcoder is part of the BSS, it is often found physically closer to the NSS to allow more efficient use of the terrestrial links.

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CELL PRINCIPLES Cellular networks have many advantages ewer the existing land telephones networks. A cellular telephone system links Mobile Station (MS) subscriber into the PSTN system on to another MS subscriber. MS and cellular networks uses radio communication, due to this MS is able to move around and become fully mobile. MS within the cellular network are located in "CELLS", these cells are provided by the BSS. Each BSS can provide one or more cells, dependent on the manufacturer’s equipment. The cells are normally represented by a hexagon, but in practice they are irregular in shape. This is as a result of the influence of the surrounding terrain, or of design by the network planners.

Frequency reuse The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission. If there is a single plain transmitter, only one transmission can be used on any given frequency. Unfortunately, there is inevitably some level of interference from the signal from the other cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a one cell gap between cells which reuse the same frequency. Depending on the size of the city, a taxi system may not have any frequency-reuse in its own city, but certainly in other nearby cities, the same frequency can be used. In a big city, on the other hand, frequency-reuse could certainly be in use.

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NETWORK SWITCHING SYSTEM (NSS) The network switching system includes

the

main

switching

functions of the GSM network. It also

contains

the

database

required for subscriber data and mobility management. It’s main function

is

to

manage

communication between the GSM network

and

other

telecommunication network. The components of network switching system are listed below: 1. Mobile Services Switching Centre (MSC) The MSC is included in the GSM system for call switching. Its overall purpose is the same as that of any telephone exchange. However, because of the addition complications involved in the control and security aspects of the GSM cellular system and the wide range of subscriber facilities that it offers, the MSC has to be capable of fulfilling many additional functions. The MSC will carry out several different functions depending upon its position in the network. When the MSC provides the interface between the PSTN and BSSs in the GSM network it will be known as a gateway MSC. In this position it will provide the switching required for all MS originated or terminated traffic. Each MSC provides service to MSs located within a defined geographic coverage area, the network typically contains more than one MSC. One MSC is capable of ing a regional capital with approximately one million inhabitants. An MSC of this size will be contained in about half a dozen racks.

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The functions carried out by the MSC are listed below: •

Call Processing

•

Operations and Maintenance

•

Internetwork Interworking

•

Billing

2. Home Location s (HLR) The HLR is the reference database for subscriber parameters. Various identification numbers and addresses are stored as well as authentication parameters. Thos information is entered into the database by the network provider when new subscriber added to the system. The parameters stored in the HLR are listed opposite: •

Subscriber ID ( IMSI and MSISDN)

•

Current subscriber VLR (current location)

•

Supplementary services subscribed to

•

Supplementary service information ( e.g. current forwarding number)

•

Subscriber status ( ed/deed)

•

Authentication key and AUC functionality

•

Mobile Subscriber Roaming Number

The HLR database contains the master database of all the subscribers to a GSM PLMN. The data it contains is remotely accessed by all the MSCs and the VLRs in the network and although the network may contain more than one HLR, there is only one database record per subscriber each HLR is therefore handling a portion of the total subscriber database. The subscriber data may be accessed by either the IMSI or the MSISDN Number. The data can also be accessed by MSC or a VLR in a different PLMN, to allow intersystem and inter country roaming.

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3. Visitor Locations (VLR) The VLR contains a copy of most of the data stored at the HLR. It is however temporary data which exists for only as long as the subscriber is “Active” in the particular area covered by VLR. The VLR database will therefore contain some duplicate data as well as more precise data relevant to the subscriber remaining within the VLR coverage. The VLR provides a local database for the subscriber wherever they are physically located within a PLMN; this may or may not be the home system. This function eliminates the need for excessive and time consuming reference to the "home" HLR database. The additional data stored in the VLR is listed below: •

Mobile status (busy. free, no answer etc)

•

Location Area Identity (LAI)

•

Temporary Mobile Subscriber Identity (TMSI)

•

Mobile Station Roaming Number

4. Equipment Identity s (EIR) The EIR contains A centralized database for validity the international mobile equipment identity (IMEI). This database is concerned solely with MS equipment and not with the subscriber who is using it to make or receive a call. The EIR database consists of lists of IMEIs (or ranges of IMEIs) organized as follows: 

White list: Contains those IMEIs which are known to have been assigned to valid MS equipment.



Black list: Contains IMEIs of MS which have been reported stolen or which are to be denied service for some other reason.



Grey list: Contains IMEIs of MS which have problems (for example, faulty software). These are not, however, sufficiently significant to warrant a "black listing".

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The EIR database is remotely accessed by the MSCs in the network and can also be accessed by an MSC in a different PLMN.As in the case of the HLR; a network may well contain more than one EIR with each EIR controlling certain blocks of IMIE numbers. The MSC contains a translation facility, which when given an IMEI, returns the address of the EIR controlling the appropriate section of the equipment database. 5. Authentication Center (AUC) The AUC is a processor system; it performs the "Authentication" function. It will be colocated with the Home Location (HLR) as it will be required to continuously access and update, as necessary, the system subscriber records. The AUC/HLR center can be co-located with the MSC or located remote from the MSC. The authentication process will be usually take place each time the subscriber "initializes" on the system. Authentication Procedure When a new subscription is ed in GSM, the mobile is given a subscriber authentication key (Ki) and a telephone number, or

international

mobile

subscriber identity (IMSI), which are used in the network to identify the mobile. The Ki and IMSI are stored both in the mobile and in a special network element called AUC. The AUC uses the Ki and IMSI to calculate an identification parameter called signal response (SRES). SRES is calculated as a function of Ki and a random number (RAND) generated by the AUC. RAND and SRES are then stored in the HLR for use in set-up procedures. Set-up or registration will not be accepted until authentication has been performed. Using the mobile's IMSI, the MSC fetches the corresponding RAND and SRES from the HLR. RAND is sent to the mobile, which uses its stored Ki value to calculate SRES. It then returns the calculated SRES to the MSC, where it is compared with the SRES value

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received from the HLR. If the values tally, the set-up is accepted; if not, set-up is rejected.

6. Gateway Mobile services Switching Centre (GMSC) The GMSC is responsible for the same tasks as the MSC, except for paging. It is needed in case of mobile terminated calls. In fixed networks, a call is established to the local exchange, to which the telephone is connected. But in GSM, the MSC, which is serving the MS, changes with the subscriber’s mobility. Therefore, in a mobile terminated call, the call is set up to a well defined exchange in the subscriber’s home PLMN. This exchange is called GMSC. The GMSC than interacts with a database called Home Location , which holds the information about the MSC, which is currently serving the MS. The process of requesting location information from the HLR is called HLR Interrogation. Given the information about the serving MSC, the GMSC then continues the call establishment process. In many real life implementations, the MSC functionality and the GMSC functionality are implemented in the same equipment, which is then just called MSC. Many operators use GMSCs for breakout to external networks such as PSTNs.

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GSM TELECOMMUNICATION SERVICES The ETSI Standards define the telecommunication services. With D900/D1800 the GSM telecommunication services offered to the GSM subscriber are subdivided as follows: •

Bearer services (for data only)

•

Tele-services (for voice and data)

•

Supplementary services

Bearer services and tele-services are also called basic telecommunication services. The use of GSM telecommunication services is subject to subscription. A basic subscription permits participation in those GSM telecommunication services that are generally available. If a GSM subscriber roams out of the entitled area there is no possibility of establishing communication (roaming not allowed), except the use of the tele-service emergency call. Bearer Services

Bearer services are telecommunication services providing the

capability of transmission of signals between access points. The bearer services describe what the network can offer (e.g. speech, data and fax).

The bearer services are pure transport services for data. Some of the transmission modes and rates already used in modern data networks are implemented; others are planned. The following, already implemented, bearer services provide unrestricted information transfer between the reference points in the mobile stations.

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•

Data CDA (circuit duplex asynchronous) + basic PAD (packet assembler Disassembler)

•

Data CDS (circuit duplex synchronous)

•

PAD CDA (dedicated PAD access)

•

Alternate speech/data CDA (circuit duplex asynchronous)

•

Speech followed by data CDA (circuit duplex asynchronous)

•

Data compression on the GSM radio interface

Tele-services

Teleservices are telecommunication services including terminal

equipment functions, which provide communication between s according to protocols established by agreement between network operators. The teleservices are end-to-end services (e.g. emergency call and short message service).

Tele-services use both low layer and high layer functions for the control of communication from terminal to terminal. The following tele- services have already been realized: •

Telephony

•

Emergency call

•

Short message service (SMS)

•

Short message cell broadcast

•

Automatic facsimile (group 3)

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Supplementary Services

Supplementary Services modify or supplement a basic

telecommunication service. Consequently, they cannot be offered to a customer as a stand-alone service. They must be offered together or in association with a basic telecommunication service. The same supplementary service may be applicable to a number of telecommunication services. Most supplementary services are directly inherited from a fixed network, with minor modifications (when needed) to adapt to mobility. Supplementary services extend beyond the normal bearer services and teleservices (basic telecommunication services) and can be subscribed to separately. In the following a supplementary service is called simply service, in contrast to basic telecommunication service. •

•

•

• • •

Number Identification Services ♦ Calling line identification presentation (CLIP) ♦ Calling line identification restriction (CLIR) Call Offering Services ♦ Call forwarding unconditional (CFU) ♦ Call forwarding on mobile subscriber busy (CFB) ♦ Call forwarding on no reply (CFNRy) ♦ Call forwarding on mobile subscriber not reachable (CFNRc) Call Completion Services ♦ Call hold ♦ Call waiting (CW) Multi-Party Service Charging Services ♦ Advice of charge (AOC) Call Restriction Services ♦ Barring of all outgoing calls (BAOC) ♦ Barring of all outgoing international calls (BOIC) ♦ Barring of all outgoing international calls except to home PLMN country (BOICexHC) ♦ Barring of all incoming calls (BAIC) ♦ Barring of all incoming calls when roaming outside home PLMN country (BIC Roam) ♦ Closed Group (CUG)

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ACCESSING A GSM NETWORK In order to gain access to GSM services, a needs three things: 

A subscription with a mobile phone operator. This is usually either a Pay As You Go arrangement, where all GSM services are paid for in advance (commercially called "prepaid"), or a Pay Monthly option where a bill is issued each month for line rental, normally paid for a month in advance, and for services used in the previous month (commercially called "postpaid").



A mobile phone which is GSM compliant and operates at the same frequency as the operator. Most phone companies sell phones from third-party manufacturers.



A SIM ("Subscriber Identity Module") card which is activated by the operator once the subscription is granted. After activation the card is then programmed with the subscriber's MSISDN ("Mobile Subscriber Integrated Services Digital Network Number") (the telephone number). Personal information such as numbers of friends and family can also be stored on the SIM by the subscriber.

After subscribers sign up, information about their identity (telephone number) and what services they are allowed to access are stored in a "SIM record" in the Home Location (HLR). Once the SIM card is loaded into the phone and the phone is powered on, it will search for the nearest mobile phone mast, also called a Base Transceiver Station or BTS. If a mast can be successfully ed, then there is said to be coverage in the area. The key feature of a mobile phone is the ability to receive and make calls in any area where coverage is available. This is generally called roaming from a customer perspective, but also called visiting when describing the underlying technical process. Each geographic area has a database called the Visitor Location (VLR) which contains details of all the mobiles currently in that area. Whenever a phone attaches, or visits, a new area, the Visitor Location must the Home Location to obtain the details for that phone. The current cellular location of the phone (i.e.

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which BTS it is at) is entered into the VLR record and will be used during a process called paging when the GSM network wishes to locate the mobile phone. Every SIM card contains a secret key, called the Ki, which is used to provide authentication and encryption services. This is useful to prevent theft of service, and also to prevent "over the air" snooping of a s activity. The network does this by utilizing the Authentication Center and is accomplished without transmitting the key directly. Every GSM phone contains a unique identifier (different from the phone number), called the International Mobile Equipment Identity (IMEI). This can be found by dialing " *#06# ". When a phone s the network, its IMEI may be checked against the Equipment Identity to locate stolen phones and facilitate monitoring.

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VOICE CALLS How outgoing calls are made from a mobile Once a mobile phone has successfully attached to a GSM network as described above, calls may be made from the phone to any other phone on the global Public Switched Telephone Network. The s dials the telephone number, presses the send or talk key, and the mobile phone sends a call setup request message to the mobile phone network via the nearest mobile phone mast (BTS). The call setup request message is handled next by the Mobile Switching Center, which checks the subscriber's record held in the Visitor Location to see if the outgoing call is allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in a fixed network. If the subscriber is on a Pay As You Go tariff (sometimes known as Prepaid (for example, in Australia and India)), then an additional check is made to see if the subscriber has enough credit to proceed. If not, the call is rejected. If the call is allowed to continue, then it is continually monitored and the appropriate amount is decremented from the subscriber's . When the credit reaches zero, the call is cut off by the network. The systems that monitor and provide the prepaid services are not part of the GSM standard services, but instead an example of intelligent network services that a mobile phone operator may decide to implement in addition to the standard GSM ones.

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How incoming calls are made to a mobile Step One: the Gateway MSC When someone places a call to a mobile phone, they dial the telephone number (also called a MSISDN) associated with the phone and the call is routed to the mobile phone operator's Gateway Mobile Switching Centre. The Gateway MSC, as the name suggests, acts as the "entrance" from exterior portions of the Public Switched Telephone Network onto the provider's network. As noted above, the phone is free to roam anywhere in the operator's network or on the networks of roaming partners, including in other countries. So the first job of the Gateway MSC is to determine the current location of the mobile phone in order to connect the call. It does this by consulting the Home Location (HLR), which, as described above, knows which Visitor Location (VLR) the phone is associated with, if any. Step Two: Determine how to route the call When the HLR receives this query message, it determines whether the call should be routed to another number (called a divert), or if it is to be routed directly to the mobile. If the owner of the phone has previously requested that all incoming calls be diverted to another number, known as the Call Forward Unconditional (CFU) Number, then this number is stored in the Home Location . If that is the case, then the CFU number is returned to the Gateway MSC for immediate routing to that destination. If the mobile phone is not currently associated with a Visited Location (because the phone has been turned off) then the Home Location returns a number known as the Call Forward Not Reachable (CFNRc) number to the Gateway MSC, and the call is forwarded there. Many operators may set this value automatically to the phone's voice mail number, so that callers may leave a message. The mobile phone may sometimes override the default setting. Finally, if the Home Location knows that the phone is roaming in a particular Visited Location area, then it will request a temporary number (called an MSRN) 35

from that VLR. This number is relayed back to the Gateway MSC, and then used to route the call to the MSC where the called phone is roaming. Step Three: Ringing the phone When the call arrives at the Visiting MSC, the MSRN is used to determine which phone is being called. The MSC then pages all the mobile phone masts in the area in order to inform the phone that there is an incoming call for it. If the subscriber answers, a speech path is created through the Visiting MSC and Gateway MSC back to the network of the person making the call, and a normal telephone call follows. It is also possible that the phone call is not answered. If the subscriber is busy on another call (and call waiting is not being used) the Visited MSC routes the call to a predetermined Call Forward Busy (CFB) number. Similarly, if the subscriber does not answer the call after a period of time (typically 30 seconds) then the Visited MSC routes the call to a pre-determined Call Forward No Reply (CFNRy) number. Once again, the operator may decide to set this value by default to the voice mail of the mobile so that callers can leave a message.

HOW SPEECH IS ENCODED DURING MOBILE PHONE CALLS During a GSM call, speech is converted from analogue sound waves to digital data by the phone itself, and transmitted through the mobile phone network by digital means. (Though older parts of the fixed Public Switched Telephone Network may use analog transmission.) The digital algorithm used to encode speech signals is called a codec. The speech codec used in GSM are called Half-Rate (HR), Full-Rate (FR), Enhanced Full-Rate (EFR) and Adaptive Multirate (AMR). All codec except AMR operate with a fixed data rate and error correction level.

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VOICE CHARGES Mobile networks in Europe, Asia, Australia & Argentina only charge their subscribers for outgoing calls. Incoming calls are free to the mobile subscriber; however, callers typically pay a higher rate when calling mobile phones. Special prefixes are used to designate mobile numbers so that callers are aware they are calling a mobile phone and therefore will be charged a higher rate. In the United States and Canada, callers pay the cost of connecting to the Gateway MSC of the subscriber's phone company, regardless of the actual location of the phone. As mobile numbers are given standard geographic numbers according to the North American Numbering Plan, callers pay the same to reach fixed phones and mobile phones in a given geographic area. Mobile subscribers pay for the connection time (typically using in-plan or prepaid minutes) for both incoming and outgoing calls. For outgoing calls, any long distance charges are billed as if they originate at the GMSC, even though it is the Visiting MSC which completes the connection to the PSTN. Plans that include nationwide long distance and/or nationwide roaming at no additional charge over "local" outgoing calls are popular. From the caller's point of view, it does not matter where the mobile subscriber is, as the technical process of connecting the call is the same. If a subscriber is roaming on a different company's network, the subscriber, instead of the caller, may pay a surcharge for the connection time. International roaming calls are often quite expensive, and as a result some companies require subscribers to grant explicit permission to receive calls while roaming to certain countries. When a subscriber is roaming internationally and a call is forwarded to his or her voice mail, such as when his or her phone is off, busy, or not answered, he or she may actually be charged for two simultaneous international phone calls—the first to get from the GMSC to the VMSC and the second to get from the VMSC to the Call Forward Busy or Call Forward No Reply number (typically the voice mailbox) in the subscriber's country.

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Network Management Subsystem (NMS) The Network Management Subsystem (NMS) is the third subsystem of the GSM network in addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS), which we have already discussed. The purpose of the NMS is to monitor various functions and elements of the network.

The functions of the NMS can be divided into three categories: • Fault management • Configuration management • Performance management These functions cover the whole of the GSM network elements from the level of individual BTSs, up to MSCs and HLRs.

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1. Fault management The purpose of fault management is to ensure the smooth operation of the network and rapid correction of any kind of problems that are detected. Fault management provides the network operator with information about the current status of alarm events and maintains a history database of alarms. The alarms are stored in the NMS database and this database can be searched according to criteria specified by the network operator. 2. Configuration management The purpose of configuration management is to maintain up-to-date information about the operation and configuration status of network elements. Specific configuration functions include the management of the radio network, software and hardware management of the network elements, time synchronization, and security operations. 3. Performance management In performance management, the NMS collects measurement data from individual network elements and stores it in a database. On the basis of these data, the network operator is able to compare the actual performance of the network with the planned performance and detect both good and bad performance areas within the network.

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GPRS NETWORK ARCHITECTURE

40

INTRODUCTION The General Packet Radio Service (GPRS) is a packet-switched data transmission protocol which was incorporated into the GSM standard in 1997. It is backwardscompatible with systems that use pre-1997 versions of the standard. GPRS does this by sending packets to the local mobile phone mast (BTS) on channels not being used by circuit-switched voice calls or data connections. Multiple GPRS s can share a single unused channel because each of them uses it only for occasional short bursts. The advantage of packet-switched connections is that bandwidth is only used when there is actually data to transmit. This type of connection is thus generally billed by the kilobyte instead of by the second, and is usually a cheaper alternative for applications that only need to send and receive data sporadically, like instant messaging. GPRS provides mobile s access to value-added WAP services and different external packet switched networks. These networks can be, for example, the Internet or corporate intranets. The GSM-BSS provides the radio interface, and the GPRS core network handles mobility and access to external packet networks and services.

The GPRS network acts in parallel with the GSM network, providing packet switched connections to the external networks. The requirements of a GPRS network are the following:

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

The GPRS network must use as much of the existing GSM infrastructure with the smallest number of modifications to it.



Since a GPRS may be on more than one data session, GPRS should be able to one or more packet switched connections.



To the budgets of various GPRS s, it must be able to different Quality of Service (QoS) subscriptions of the .



The GPRS network architecture has to be compatible with future 3rd and 4th generation mobile communication systems.



Able to both point-to-point and point-to-multipoint data connections.



It should provide secure access to external networks.

A GPRS network must provide all of the functionality of a GSM network for packet switched networks and more. The GPRS is expected to perform the functions of a traditional mobile communication network and a traditional packet switched computer network.

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Network elements The GPRS system brings some new network elements to an existing GSM network. Not all of the network elements are compulsory for every GPRS network. These elements are: 

Packet Control Unit (PCU)



Serving GPRS Node (SGSN): the MSC of the GPRS network



Gateway GPRS Node (GGSN): gateway to external networks



Border Gateway (BG): a gateway to other PLMN



Intra-PLMN backbone: an IP based network inter-connecting all the GPRS elements



Charging Gateway (CG)



Legal Interception Gateway (LIG)



Domain Name System (DNS)



Firewalls: used wherever a connection to an external network is required.

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Packet Control Unit (PCU)

The PCU separates the circuit switched and packet

switched traffic from the and sends them to the GSM and GPRS networks respectively. It also performs most of the radio resource management functions of the GPRS network. The PCU can be either located in the BTS, BSC, or some other point between the MS and the MSC. There will be at least one PCU that serves a cell in which GPRS services will be available. Frame Relay technology is being used at present to interconnect the PCU to the GPRS core. Channel Codec Unit (CCU)

The CCU is realized in the BTS to perform the Channel

Coding (including the coding scheme algorithms), power control and timing advance procedures. Serving GPRS Node (SGSN)

The SGSN is the most important element of

the GPRS network. The SGSN of the GPRS network is equivalent to the MSC of the GSM network. There must at least one SGSN in a GPRS network. There is a coverage area associated with a SGSN. As the network expands and the number of subscribers increases, there may be more than one SGSN in a network. The SGSN has the following functions: •

Ciphering of GPRS data between the MS and SGSN

•

Data compression is used to minimise the size of transmitted data units

•

Authentication of GPRS s. Protocol conversion (for example IP to FR)

•

Mobility management as the subscriber moves from one area to another, and possibly one SGSN to another

•

Routing of data to the relevant GGSN when a connection to an external network is required

•

Interaction with the NSS (that is, MSC/VLR, HLR, EIR) via the SS7 network in order to retrieve subscription information

•

Collection of charging data pertaining to the use of GPRS s

•

Traffic statistics collections for network management purposes.

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Gateway GPRS Node (GGSN)

The GGSN is the gateway to external

networks. Every connection to a fixed external data network has to go through a GGSN. The GGSN acts as the anchor point in a GPRS data connection even when the subscriber moves to another SGSN during roaming. The GGSN may accept connection request from SGSN that is in another PLMN. Hence, the concept of coverage area does not apply to GGSN. There are usually two or more GGSNs in a network for redundancy purposes, and they back up each other up in case of failure. The functions of a GGSN are given below: •

Routing mobile-destined packets coming from external networks to the relevant SGSN

•

Routing packets originating from a mobile to the correct external network

•

Interfaces to external IP networks and deals with security issues

•

Collects charging data and traffic statistics

•

Allocates dynamic or static IP addresses to mobiles either by itself or with the help of a DH or a RADIUS server

•

Involved in the establishment of tunnels with the SGSN and with other external networks and VPN.

From the external network's point of view, the GGSN is simply a router to an IP subnetwork. This is shown below. When the GGSN receives data addressed to a specific in the mobile network, it first checks if the address is active. If it is, the GGSN forwards the data to the SGSN serving the mobile. If the address is inactive, the data is discarded. The GGSN also routes mobile originated packets to the correct external network.

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GPRS MS

Different GPRS MS classes were introduced to cope with the different

needs of future subscribers. The mobiles differ in their capabilities.

Domain Name Servers

These devices convert IP names into IP addresses, for

example, server.nokia.com to 133.44.15.5. There is a primary DNS server and a secondary DNS server. In the specifications, the DNS functionality is included in the SGSN. However, the main vendors have chosen to separate the DNS functions from the SGSN.

Firewalls

A firewall protects an IP network against external attack (for example,

hackers from the mobile s or from the Internet). In the case of GPRS, the firewall might be configured to reject all packets that are not part of a GPRS subscriber-initiated connection. The firewall can also include NAT (Network Address Translation), see the Introduction to T/IP module. In the specifications for GPRS, the firewalls are not 46

included. It is however included here due to the fact that operators usually need to implement firewalls in their GPRS network (for security reasons). Border Gateway

The Border Gateway (BG) is a router that can provide a direct

GPRS tunnel between different operators' GPRS networks. This is referred to as an interPLMN data network. It is more secure to transfer data between two operators' PLMN networks through a direct connection rather than via the public Internet. The Border Gateway will commence operation once the GPRS roaming agreements between various operators have been signed. It will essentially allow a roaming subscriber to connect to company intranet through the Home Charging Gateway

GPRS s have to be charged for the use of the network. In a

GSM network, charging is based on the destination, duration, and time of call. However, GPRS offers connectionless service to s, so it not possible to charge subscribers on the connection duration. Charging has to be based on the volume, destination, QoS, and other parameters of a connectionless data transfer. These GPRS charging data are generated by all the SGSNs and GGSNs in the network. This data is referred to as Charging Data Records or CDRs. One data session may generate a number of CDRs, so these needs to be collected and processed. The Charging Gateway (CG) collects all of these records, sorts them, processes it, and es it on to the Billing System. Here the GPRS subscriber is billed for the data transaction. All CDRs contain unique subscriber and connection identifiers to distinguish it. A protocol called GTP' (pronounced GTP prime) is used for the transfer of data records between GSNs and the Charging Gateway.

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ROAMING SERVICES IN GSM SYSTEM

48

ROAMING “Roaming is defined as the ability for wireless customers to automatically make and receive voice calls, send and receive data, or access other services when travelling outside the geographical coverage area of their own home network, by means of using a visited network.” (International) Roaming enables the clients of one network operator to use the services of another operator where both networks have a commercial agreement in place to permit this, once all testing and technical implementation are completed. The roaming process is split into two main phases where different activities are carried out. In the pre-commercial phase the agreement is negotiated plus the network and IT elements are implemented and tested. When these activities are successfully completed, then commercial roaming can begin and customers can use each other’s networks. While in most cases roaming involves bi lateral, two-way roaming, in some cases, unilateral or one way roaming takes place either for technical or commercial reasons.

Roaming Functions The following functions are common within operators who have launched Roaming. 1. Roaming – Commercial and Operational

Function can be organized in several

ways. In many companies, the functions of Roaming and Interconnection are contained in the same department. Usually you within the Roaming department find a “Roaming Manager” who is in charge of Agreements, overall coordination between various functions and strategy. The responsibility of producing the company Inter Operator Tariff (IOT) is most likely to be placed here. The Roaming Department may also have responsibility for managing outbound roaming which may include pricing, marketing, and promotion. Increasingly, companies are recognizing the value of roaming to their business and that roaming is no

49

longer simply an implementation and management function. Increasingly, companies are splitting the work between “operational” roaming and “Commercial” roaming. Typically one group will look after the implementation and ongoing management whilst the other will focus on strategy, pricing, commercial inter-operator activities etc. Sometimes, both are within the same group, other times they are divided between different departments. The second role you are most likely to find in this department is the “Roaming Assistant”. This is the person who has most of the day-to-day with the Roaming partners. As a result this person is the one most likely to collate the IOT information of the Roaming partners. This information is then published within the company. As the roaming department often has to interface with every department within the company and have overall visibility of the status of Roaming, it is often compared to the spider in the centre of the web. 2. Marketing The role of the Marketing team within Roaming is to design effective promotional initiatives for your customers travelling outside their home country. 3. Test SIM Card

The person responsible for the test SIM cards is

usually a representative from Customer Services or Network Department; however, it can often be the responsibility of the Roaming department itself. The role requires providing all Roaming partners with their requested amount of test SIM (Subscriber Identity Module) cards, and upon confirmation of receipt of the test SIMs will activate them accordingly. 4. IREG (Inter-Working, Roaming Expert Group)

This function is performing the

actual Roaming tests, and trouble shooting for network problems. They will be responsible for ordering the signalling links and opening the network to testing, and later to commercial Roaming. This function also undertakes periodical roaming tests and troubleshooting after the commercial Roaming is in place. Signaling is a prerequisite to testing, as it is the basis for the communication between the two networks. This function is normally an outsourced service provided by a third party.

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5. TADIG (Transferred Data Interchange Group)

This function will (on the

basis of the data produced when performing the technical roaming testing) perform billing tests. They will be responsible for TAP (Transferred Procedure) formats, liaison with Data Clearing House (if used) and managing the TAP file flows between networks on a daily basis. 6. Finance

The functions of the Finance department can be divided into two when it

comes to Roaming. •

One part is to produce invoices (based on TAP file data) for any traffic generated in your network by the customer of a Roaming partner.

•

The other part is to ensure that you receive invoices from your roaming partners for any traffic your customers have generated in their network.

The final responsibility will be to ensure payment and collection for all the invoices. Many operators use the services of a Financial Clearing House for parts or all of this process. 7. Fraud

This function assumes responsibility for the creation and management of

High Usage Reports. They are responsible for supplying data in the event of an actual fraud case. Many operators contract a Data Clearing House for parts, or all of this process. All email addresses deployed as part of the High Usage Reports process must be on company (operator or clearing house) domains. Domains like yahoo.com; hotmail.com etc may not be used. This email address must be exclusively used for receiving HURs, to enable automated processing of the incoming HUR emails. This will ensure that all emails are processed as potential fraud alerts rather than personal emails. The Fraud department also supplies IMEIs (International Mobile Equipment Identity) to either to their own national EIR (Equipment Identity ) or to the CEIR (Central Equipment Identity ), preferably both.

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8. Roaming Customer Care

This function can be divided in two parts, one responsible

for assisting inter operator issues and the second one responsible for assisting in Roaming Customer Queries.

CAMEL CAMEL (Customized Application for Mobile network Enhanced Logic) is a network solution, which allows the functionality of IN services for roamers. It thus compensates for restrictions met by mobile operators willing to offer IN-based services while roaming. Emancipation from proprietary solution, real-time call supervision and building operator specific service for roamers are among the advantages. Moreover, roaming subscribers using CAMEL based services are offered a Virtual Home Environment enabling service usage as if they were in their home network. The importance of CAMEL grew during the last few years, as many operators decided to offer IN-based Pre-paid services abroad, abandoning the old call-back platform (e.g. USSD based) and launching a more elegant solution which allows direct connection towards the home network, with real-time billing. The above described service is just one component contained in the different features offered with CAMEL phase 1 and 2. Further CAMEL phases will enable for example services like GPRS Roaming and UMTS Roaming. CAMEL can also be used to the above mentioned value added services to Post-Paid subscribers. By the implementation of CAMEL phase 1 and 2, many operators encountered major inter-compatibility problems, mostly due to the matter of fact that vendors enclose different features in their packages. And we haven’t reached an acceptable quality of implementation. Further complications are represented by the fact that operators are using different documents for agreeing commercially about the launch of CAMEL services. In addition, being no comprehensive information about this topic, it is rather difficult for non-technical personnel to understand from scratch how to set-up CAMEL Roaming.

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Services The main reason to incorporate Camel services within your existing Roaming Portfolio is indicated below. There are number of key benefits: Prepaid Roaming

Using a CAMEL platform Prepaid customers can roam in a similar

way to postpaid, and via CAMEL the home network can qualify the action the customer does. Home Routing Roaming

Using Camel it’s possible for Pre-Paid or Post-Paid

customers to set-up a call that is then routed to the home network, and then routed onwards. VPN roaming / short codes

The Pre-paid or Post-paid customer dials the short code,

and via CAMEL, the home network is requested to tell the long code associated. This can be as detailed as per IMSI, thus allowing VPN to be used when roaming.

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CONCLUSION It has been a great opportunity for me to work in one of the most illustrious telephone company existing in India. This not only help me to bridge the gap between engineering & industry, but also aids me in having a few of an industry, it's environment & functioning of various departments for achievements of the company objective. Since I was placed in MAHANAGAR TELEPHONE NIGAM LIMITED (BKC), I learned the importance of teamwork. I also had experience about how to analyze a problem & solve it. This training offered an exposure to industrial environment, which cannot be simulated in engineering college. We understood the scope function job responsibilities of an engineering organization. We have to touch the right chords of the people & get the work done without hurting their feelings. I was able to learn some of these skills during our training. Thus I can confidentially conclude that this training is memorable and a fruitful one for me.

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