Mobile Global System for Communications

This page relates to standard GSM, for the homonymous apparatus to see Mobile phone or GSM (homonymy) . ----

The Mobile Global System for Communications or GSM (historically Mobile Special Group ) is a numerical standard of second generation for the Mobile telephony. It was established in 1982 by CEPT (Conference of the European Administrations of the Stations and Télécommunications).

It was developed by ETSI on frequency the band of the 900 MHz. An alternative called DIGITAL Communication System (DCS) uses the range of the 1800 MHz. This standard is particularly used in Europe, in Africa, with the the Middle East and in Asia. Two other alternatives in 850 MHz and 1900 MHz (GCV) are also used. The data protection is ensured by the encryption algorithms A5/1 and A5/2. A standard GSM-400, using the frequencies of 450 MHz or 480 MHz, is also being studied.

Such as it was conceived, network GSM is ideal for the communications of the type “voice”. The network being commutated, the resources are allocated only for the duration of the conversation, as during the use of fixed phone lines. The customers can either buy a prepaid card, or to take out a subscription.

It is it should be noted that in Belgium, the term GSM is used for mobile phone .

History

The cellular concept comes from the networks of first generation. Each point of cover was a radius of 50 kilometers with, in the center of each circle of cover, a relay and a basic station. These circles being assembled or not, without being concerned with any problem of Roaming. Each user being in the ray of cover had a static band allocated on his telephone, this with or without telephone call. Thus each station could provide channels of communication as many wavebands available. This system, not very reliable, was replaced by another system making it possible to allocate a waveband only if the user needed some, also making it possible to potentially increase the number of subscribers until a certain stage, on the assumption that all the subscribers do not telephone at the same time. The system of the GSM was with its stammerings. The antennas of the BTS then required rather important powers (up to 8 Watts in a current way) and the mobiles also. However, and in order to avoid the interferences, each circle of cover could not re-use the same frequencies thus reducing the frequential spectrum.

In 1987, the technological choices concerning the use of mobile telecommunications are fixed by group GSM. Thus the digital transmission, the coding of information and the temporal multiplexing of the channels radios will be used.

1991, first experimental communication made by group GSM. Initials GSM also change significance to become Global System for Mobile communications. The technical specifications are improved to be able to function in the band of the 1800 MHz.

GSM 850 and 1900

They are present at the the United States and the Canada. Certain countries use only standard GSM 850 (Ecuador, Panama…). The GSM 1900 is also called GCV 1900 ( Personal Communications Service ).

GSM 900 and 1800

One meets these two types of networks in Europe, in particular, in Belgium, Spain, France.

The GSM 900 uses the band 890-915 MHz for the sending of the data and the band 935-960 MHz for the reception of information.

The GSM 1800 uses the band 1710-1785 MHz for the sending of the data and the band 1805-1880 MHz for the reception of information.

The apparatuses which function so much into 900 than 1800 are called dual GSM band or simply dual band .

The GSM 1800 is also called DCS 1800 ( DIGITAL Communication Systems ).

GSM 400

The establishment of a network GSM in 900 MHz with a good cover is often difficult in much developing country. The extents to be covered are enormous, the very low population density by place and financial means to set up the infrastructure are reduced. The main issue in the little populated zones is the high number of basic stations to install. Even the industrialized countries are confronted with this problem of cover in the rural areas.

The use of less low frequencies would increase the range of the basic stations appreciably. Thus in 450 MHz, their range would be close to the double of what it would be in 900 MHz. Ericsson and Nokia works with the development of a standard GSM functioning in 450 MHz or 480 MHz.

In band 450, the frequencies used would be 450,4 to 457,6 MHz for the uplinks (GSM towards basic station) and 460,4 to 467,6 MHz for the downlinks.

In band 480, the frequencies would be 478,8 to 486 MHz in emission and 488,8 to 496 MHz in reception (bases towards mobile).

The countries which had an analogical mobile telephone network NMT-450 could re-use these frequencies for the GSM-400 (450 MHz)

With these frequencies, the cover could reach 120 km. It is particularly well adapted to the coastal areas, desert or rural, where the traffic is weak and the flat ground.

Identification of the apparatuses

The mobile phones contain a chart SIM which makes it possible to identify the user and sometimes to store a certain number of phone numbers. Each apparatus is identified, whatever its mark, by a number IMEI which one obtains, while entering on the keyboard, the sequence: *#06#. It is advisable to note this number and to announce it to its operator, in case of theft, in order to carry out its blocking. This identifier should not be confused with IMSI contained in SIM.

However on a cellular network, an apparatus is identified via a TMSI (Temporary Mobile Station To identify). Thanks to this system of IMSI/TMSI, a cellphone does not see its call number revealed on the network, which allows the confidentiality of the calls: as the TMSI often change and are sometimes allotted to several apparatuses at the same time, a person intercepting the traffic has very little chance to associate a phone number with a TMSI.

Structure network and protocol

The specific network for the GSM is called PLMN (Public Mobile Land Network), each operator having to it his clean. It is connected to the Public Phone network Commutated (RTCP).

By not taking account of extensions GPRS, such a network is composed of 4 great entities:

• a Mobile station called Mobile Station ( ms ): it is usually a mobile phone, but in a general way, that can be any apparatus having of an adequate transmitter and a chart SIM.
• the radio operator part of the network, called Base Station Subsystem ( BSS ): it is made up of a grid of basic stations ( BTS ) and of their stations of control ( BSC ). With that the Transcoder is added ( Transcoder and Rate Adaptation Links , TRAU ) which takes care of compression/decompression of the voice.
• the part Routing, called Network Subsystem ( NSS ) or Core Network Subsystem , charged with conveying the communication between two users of the network or towards outside (network fixes for example): it made up of Mobile Switching Center S ( MSC ) is connected between them which carry out the routing of the communications. To each MSC a Visitor Location Register is attached ( VLR ) which manages information of the subscribers being in the zone managed by the MSC. A single database, the Home Hiring Register ( HLR ) manages the list of the subscribers of the operator of the network. To connect itself to other external networks, there is a dedicated footbridge, the Commutateur network Gateway Mobile Switching Center ( GMSC ). AuC (Authentication Center) takes care of the Authentification of the users.

• the Operation part and Maintenance, managed by the Operation and Maintenance Center ( OMC ), which is charged to set up and to take care of the good performance of the various elements of the network.

Communication enters the basic mobile phone and station

The AMRT (multiple Access to distribution in time) and the AMRF (multiple access to distribution in frequency) are used to make it possible more users to be connected without saturating the network.

Characteristics of the radio interface

The GSM uses two wavebands, one for the up line, the other for the down line. The band 890-915  MHz is used for the up line, while the band 935-960  MHz is used for the down line. Each one of these bands includes/understands 124 carrying ( channels ) 200 Khz each one. The modulation used on these carrying is the GMSK, which makes it possible to avoid the overlappings of the carrying ones.

Each carrying comprises eight time slot S (TS). They last approximately 577 μs. The physical channels are these slots.

Each carrying has a rough flow of 271  kbit/s, while the physical channels thus have a rough flow of 33,8  kbit/s. the productive flow is as for him of 24,7  kbit/s.

Services

Network GSM allows several services:

• the voice;

• the data (WAP, the Fax or like a traditional telegraphic modem);
• short written messages or SMS;
• the Concealment Broadcast (diffusion in the cells), which makes it possible to send the same SMS to all the subscribers inside an geographical area;
• the additional services (call forwardings, presentation of the number…) ;
• services with added-value such as for example the services of localization (Hiring Based Services), of information to the request (weather, horoscope), of bank (consultation of account, reloads of account prepaid).

The GSM in the world

Networks GSM (Total system communication) are not very present on the American continent (via some operators like Cingular Wireless and T-Mobile), whereas they are used everywhere in Europe.

In Belgium, there exist three operators: Base, Mobistar, Proximus. GSM is also the expression usually used to indicate as well a Cellphone in Belgium, French-speaking as Dutch-speaking.

• Proximus is a company belonging to Belgacom, the historical operator (Vodafone had a participation of 25%, but this one was repurchased by Belgacom in August 2006). Proximus holds the greatest number of customers for mobile telephony: : 4,200,000 in December 2004, is 52% of the market shares. It had started to offer services for the 900 MHz then for the 1800 MHz.
• Mobistar is a company created in 1995 by France Telecom with the Belgian group Telinfo, it also started to offer services for the 900 MHz before also proposing the 1800 MHz.
• Base (had partly by Royal KPN), in the past called Orange is the last operator to be appeared on the Belgian market. It has as of the beginning suggested the 1800 MHz but without allowing the 900 MHz.

In France, there exist three operators:

• Orange France is a subsidiary company via Orange SA of France Telecom, the historical operator of French fixed telephony. It was called formerly France Telecom Mobile, and operated under the three marks Itinéris, Ola and Mobicarte. (22,5 million mobile subscribers in 2006)
• SFR (SFR-Cegetel group) is an private operator of mobile telephony who belongs to Vivendi Universal and with Vodafone.
• Bouygues Telecom is a subsidiary company of the group Bouygues, which is owner in particular of the television channel TF1.

The three networks propose an access to services 900 MHz and 1800 MHz, now supplemented by more recent technology known as UMTS for Orange, SFR and Bouygues Telecom.

In Italy, there exist four operators:

• Mobile Tim Telecom Italia
• Tre initials which means figure 3
• Vodafone
• Wind company founded in 1997 by groups ENEL, France Telecom E Deutsche Telekom, but to 100% Italian since 2003, third Italian operator (approximately 19% of the market hold).

Tre belongs to the Mobile Company Media of the Group Hutchison Whampoa of mobile telephony working in Italy, not - quoted on the stock exchange, and which has its head office just as its seat of exploitation in Milan. Tre was the first operator required in Italy the telephone services mobile to standard UMTS (W-CDMA); the company is owner of network UMTS, while for the not directly served zones, she concluded an agreement from Roaming with network GSM/GPRS of TIM. Tre Italia is the first Italian operator and European for the number of customers UMTS/HSDPA/DVB-H

The Swiss account four operators of mobiles:

• Mobile Swisscom
• Sunrise
• Orange
• Télé2

There exist still many other countries equipped well in Europe!

With the Morocco, there exist two operators:

• Maroc Telecom, oldest. 11,3 million subscribers GSM.
• Meditel, entered on the market in 2000. 5 million subscribers GSM.

In Algeria, there are three operators:

• Mobilis, oldest of the three. Subsidiary company of the historical operator Algeria Telecom (7,3 million subscribers)
• Djezzy, held by the Egyptian Orascom (10 million subscribers)
• Nedjma, held by the group Watanyia (3 million subscribers)

In Tunisia, there are two operators:

• Tunisiana : single private operator GSM, extremely moreover: 2.7 million subscribers (2006), held by the group Orascom Telecom
• Tunisia Telecom: strong historical operator in Tunisia of 3,5 million subscribers GSM (2005).

In Mauritania, there exist two operators:

• Mattel, theTunisian one of Telecommunications; the first private operator who settled in the country in the month of October 2000 and who counts about: 400,000 subscribers (a sixth of the population).
• Mobile Mauritel, an operator of which the State Mauritanian holds half; subsidiary company of Maroc Telecom and which counts: 500,000 subscribers (a fifth of the population).

The Burkina Faso account three operators:

• Telmob, subsidiary of the National office of Telecommunications (ONATEL), the historical operator.
• Celtel Burkina (Subsidiary company of International Celtel).
• Telecel Faso (Subsidiary company of the Atlantic Telecom).

With the Mali, there exist two operators:

• Malitel : First mobile telephone operator GSM with the Mali, subsidiary of the Company of Telecommunications of Mali (SOTELMA).
• Orange Mali: Named Ikatel beforehand, Orange Mali covers more than 700 localities to the Mali. It offers GSM/GPRS/EDGE.

There exist also virtual operators who do not have an infrastructure but which uses in hiring the networks of the other operators (MVNO).

List mobile operators

List names of the mobile operators and their identifier network MCC-MNC (see IMSI) :

Ref., ref.

References

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