Gsm Technology in Bangladesh

Student’s Name: Tanzana Rahman Student’s ID: 02201114 Supervisor’s Name: Ms. Sadia Hamid Kazi Thesis Title: GSM Technology & its application in Bangladesh Thesis Abstract: My thesis gives an overview about the GSM technology and its application in Bangladesh. GSM Technology is the most popular standard for mobile phones in the world. It allows the network operators to offer roaming services, which means that the subscribers can use their phones in many parts of the world This paper would describe how this GSM technology is being used worldwide and also how the telecom companies in our country are using it.

Supervisor Chairperson Department of Computer Science & Engineering X Chapter 1 Introduction 1. 1 What is GSM? GSM (Global System for Mobile communications), which originally stood for Groupe Speciale Mobile, the CEPT committee, which began the GSM standardization process. It is the most popular standard for mobile phones in the world. GSM service is used by over 2 billion people across more than 212 countries and territories. The ubiquity of the GSM standard makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world.

From the point of view of the consumers, the key advantage of GSM systems has been higher digital voice quality and low cost alternatives to making calls such as text messaging. The advantage for network operators has been the ability to deploy equipment from different vendors because the open standard allows easy inter-operability. Like other cellular standards GSM also allows network operators to offer roaming services, which means that subscribers can use their phones all over the world. As the GSM standard continued to develop, it retained backward compatibility with the original GSM phones.

For example, packet data capabilities were added in the Release ‘97 version of the standard, by means of GPRS. Higher speed data transmission has also been introduced with EDGE in the Release ’99 version of the standard. GSM is an open, digital cellular technology used for transmitting mobile voice and data services. GSM differs significantly from its predecessors in that both signaling and speech channels are Digital call quality, which means that it is considered as a second generation (2G) mobile phone system. This fact has also meant that data communication was built into the system from the Third Generation Partnership Project (3GPP).

This 2G digital technology was originally developed for Europe, which now has in excess of 71 per cent of the world XI market. Initially GSM was developed for operation in the 900MHz band and subsequently modified for the 850, 1800 and 1900MHz bands. GSM differs from the first generation wireless systems because it uses digital technology and time division multiple access transmission methods. GSM is a circuit-switched system that divides each 200kHz channel into eight 25kHz timeslots. GSM operates in the 900MHz and 1. 8GHz bands in Europe and the 1. 9GHz and 850MHz bands in the US.

The 850MHz band is also used for GSM and 3GSM in Australia, Canada and many South American countries. GSM supports data transfer speeds of up to 9. 6 kbit/s, allowing the transmission of basic data services such as SMS (Short Message Service). Another major benefit is its international roaming capability, allowing users to access the same services when traveling abroad as at home. This gives consumers seamless and same number connectivity in more than 210 countries. GSM satellite roaming has also extended service access to areas where terrestrial coverage is not available.

XII 1. 2 Date History of GSM Activity 1992-1985 ? Conference Europeenne des Postes et Telecomunication (CEPT) begin specifying a European digital telecommunications standard in the 900 MHz frequency band. This standard later became known as Global System for Mobile communication (GSM) 1986 ? Field tests held in Paris to select which digital transmission technology to use either Time Division Multiple Access (TDMA) or Frequency Division Multiple access. 1987 ? A combination of TDMA and FDMA selected as the transmission technology for GSM. ?

Operators from 12 countries sign a Memorandum of Understanding (MoU) committing to introduce GSM by 1991. 1988 ? CEPT begins producing GSM specifications for a phased implementation. ? 1989 ? Another five countries sign the MoU. European Telecommunication Standards Institute (ETSI) takes over responsibility for GSM specification. 1990 ? Phase 1 specification frozen to allow manufacturers to develop network equipment. 1991 ? ? The GSM 1800 standard was released. An addendum was added to the MoU allowing countries outside CEPT to sign. 1992 ? ? ? Phase 1 specifications are completed.

First commercial Phase 1 GSM networks launched. First international roaming agreement between Telecom Finland and Vodaphone in UK. 1993 ? ? Australia becomes the first non-European country to sign the MoU. The MoU now had a total of 70 signatories. The GSM networks launched in Norway, Austria, Ireland, Hong Kong and Australia. ? The number of GSM subscribers reaches one million. XIII ? 1994 ? ? ? 1995 ? The first commercial DCS 1800 system is launched in the UK. The MoU now has over100 signatories covering 60 countries. More GSM networks are launched. The total number of GSM subscribers exceeded 3 million.

The specification for the Personal Communications Services (PCS) developed in the U. S. A. this version of GSM operates at 1900 MHz. ? GSM growth trends continue steadily through 1995, with the number of GSM subscribers increasing at the rate of 10,000 per day and rising. ? In April 1995, there are 188 members of the MoU from 69 countries. 1996 ? The first GSM 1900 systems become available. These comply with the PCS 1900 standard. 1998 ? The MoU has a total of 253 members in over 100 countries and there are over 70 million GSM subscribers world-wide. GSM subscribers account for 31% of the world’s mobile market. 999 2002 ? ? GSM networks now exist in over 179 countries. Functionality of GSM extended to incorporate EDGE, AMR, and support for flexible positioning services. 2003 ? Total number of subscribers expected to soar to over 1 billion. Table 1. 1 GSM Milestones 1. 3 GSM Logo Figure 1. 1 GSM Logo Chapter 2 XIV GSM Services GSM services are a standard collection of applications and features available to mobile phone subscribers all over the world. The GSM standards are defined by the 3GPP collaboration and implemented in hardware and software by equipment manufacturers and mobile phone operators.

The common standard makes it possible to use the same phones with different companies’ services, or even roam into different countries. GSM is the world’s most dominant mobile phone standard. The design of the service is moderately complex because it must be able to locate a moving phone anywhere in the world, and accommodate the relatively short battery life, limited input/output capabilities, and weak radio transmitters on mobile devices 2. 1 Data transmission The Public Switched Telephone Network (PSTN) is essentially a collection of interconnected systems for taking an audio signal from one place and delivering it to another.

Older analogue phone networks simply converted sound waves into electrical pulses and back again. The modern phone system digitally encodes audio signals so that they can be combined and transmitted long distances over fiber optic cables and other means, without losing signal quality in the process. When someone uses a computer with a traditional modem, they are encoding a (relatively slow) data stream into a series of audio chirps, which are then relayed by the PSTN in the same way as regular voice calls.

This means that computer data is being encoded as phone audio, which is then being re-encoded as phone system data, and then back to phone quality audio, which is finally converted back to computer data at the destination. XV GSM voice calls are essentially an extension of the PSTN, dealing only with audio signals. Behind the scenes, we know these audio channels happen to be transmitted as digital radio signals. The GSM standard also provides separate facilities for transmitting digital data directly, without any of the inefficient conversions back and forth to audio form.

This allows a mobile “phone” to act like any other computer on the Internet, sending and receiving data via the Internet Protocol or X. 25. The mobile may also be connected to a desktop computer, laptop, or PDA, for use as a network interface. (Like a modem or Ethernet card, but using a GSMcompatible data protocol instead of a PSTN-compatible audio channel or an ethernet link to transmit data. ) Newer GSM phones can be controlled by a standardised Hayes AT command set through a serial cable or a wireless link (using IrDA or Bluetooth).

The AT commands can control anything from ring tones to data compression algorithms. In addition to general Internet access, other special services may be provided by the mobile phone operator, such as SMS. 2. 2 ACCESSING A GSM NETWORK In order to gain access to GSM services, a user needs three things: 1. A subscription with a mobile phone operator. 2. A mobile phone, which is GSM compliant and operates at the same frequency as the operator. 3. A SIM card, which is issued by the operator once the subscription is granted. The SIM card comes pre-programmed with the subscriber’s

XVI phone “identity” and will be used to store personal information (like contact numbers of friends and family). After subscribers sign up, information about their phone’s identity and what services they are allowed to access are stored in a “SIM record” in the Home Location Register (HLR). The Home Location Register is a database maintained by the “home” phone company for all of its subscribers. Once the SIM card is loaded into the phone and it 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 contacted, then there is said to be coverage in the area. Stationary phones are always connected to the same part of the phone network, but mobile phones can “visit” any part of the network, whether across town or in another country via a foreign provider. Each geographic area has a database called the Visitors Location Register (VLR) which contains details of all the local mobiles. Whenever a phone attaches, or visits, a new area, the Visitors Location Register must contact the Home Location Register.

The Visitors Location Register will tell the Home Location Register where the phone is connected to the network (which VLR), and will ask it for a copy of the SIM record (which includes, for example, what services the phone is allowed to access). The current cellular location of the phone (i. e. 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 it uses to prove its identity to the phone network (to prevent theft of services) upon first contact.

The network does this by consulting the Authentication Center of the “home” phone company, which also has a copy of the secret key. XVII Every phone contains a unique identifier (different from the phone number, which is associated at the HLR with the removable SIM card), called the International Mobile Equipment Identity (IMEI). When a phone contacts the network, its IMEI is supposed to be checked against the global Equipment Identity Register to locate stolen phones and facilitate monitoring. 2. 3 Voice Services 2. 3. 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 assuming the subscriber has an arrangement with their “home” phone company to allow the call. The user 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 mobile phone mast (BTS) it is in contact with.

The element in the mobile phone network that handles the call request is the Visited Mobile Switching Center (Visited MSC). The MSC will check against the subscriber’s temporary record held in the Visitor Location Register 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. XVIII Figure 2. 1 GSM Outgoing Calls If the subscriber is on a Pay As You Go tariff, 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 account. 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. 2. 3. 2 How incoming calls are made to a mobile XIX Step One: Contact 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 user 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 Register (HLR), which, as described above, knows which Visitor Location Register (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 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 Register.

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 Register (because the phone has been turned off or is not in range) then the Home Location Register 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 XX 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 Register knows that the phone is in the jurisdiction of a particular Visited Location Register, then it will request a temporary number (called an MSRN) from that VLR. This number is relayed to the Gateway MSC, which uses it to route the call to another Mobile Switching Center, called the Visiting MSC. Figure 2. 2 GSM Outgoing Calls Step Three: Ringing the phone When the call is received by the Visiting MSC, the MSRN is used to find the phone’s record in the Visited Location Register. This record identifies the phone’s location area. Paging occurs to all mobile phone masts in that area.

When the subscriber’s mobile responds, the exact location of the mobile is returned to the Visited MSC. The VMSC then forwards the call to the appropriate phone mast, XXI and the phone rings. 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 pre-determined Call Forward Busy (CFB) number.