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The Global System for Mobile Communications (GSM) is a standard developed by the
European Telecommunications Standards Institute ETSI (European Telecommunications Standards Institute) is an independent, not-for-profit, standardization Standardization or standardisation is the process of implementing and developing s based on the consensus of different parties that in ...
(ETSI) to describe the protocols for second-generation (
2G
2G
) digital
cellular network A cellular network or mobile network is a communication network A telecommunications network is a group of nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may re ...
s used by mobile devices such as mobile phones and tablets. It was first deployed in
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the west, Russia to the east, Norway to the north, and is defined by the Gulf of B ...

Finland
in December 1991. By the mid-2010s, it became a global standard for mobile communications achieving over 90% market share, and operating in over 193 countries and territories. 2G networks developed as a replacement for first generation ( 1G) analog cellular networks. The GSM standard originally described a digital, circuit-switched network optimized for
full duplex A duplex communication system 400px, Communication system A communications system or communication system is a collection of individual telecommunications network A telecommunications network is a group of nodes interconnected by links ...
voice
telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
. This expanded over time to include data communications, first by circuit-switched transport, then by
packet Packet may refer to: * A small container or pouch ** Packet (container) A packet is a small bag or pouch, made from paper, Aluminium foil, foil, plastic film or another type of Packaging and labeling, packing material, often used to contain dis ...
data transport via
General Packet Radio Service General Packet Radio Service (GPRS) is a packet oriented Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation (DBA). In statistical multiplexing, a communication channel is divided into ...
(GPRS), and Enhanced Data Rates for GSM Evolution (EDGE). Subsequently, the
3GPP The 3rd Generation Partnership Project (3GPP) is an umbrella term for a number of standards organizations which develop protocols for mobile telecommunications. Its best known work is the development and maintenance of: * GSM and related 2G and 2. ...
developed third-generation (
3G
3G
)
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...

UMTS
standards, followed by the fourth-generation ( 4G) LTE Advanced and the fifth-generation 5G standards, which do not form part of the ETSI GSM standard. "GSM" is a
trade mark A trademark (also written trade mark or trade-markThe styling of ''trademark'' as a single word is predominantly used in the United States and Philippines only, while the two-word styling ''trade mark'' is used in many other countries around ...
owned by the
GSM Association The GSM Association (commonly referred to as 'the GSMA' or '' Global System for Mobile Communications'', originally ''Groupe Spécial Mobile'') is an industry organisation that represents the interests of mobile network operators worldwide. More ...
. It may also refer to the (initially) most common voice codec used,
Full Rate Full Rate (FR or GSM-FR or GSM 06.10 or sometimes simply GSM) was the first digital speech coding standard used in the GSM digital mobile phone system. It uses linear predictive coding (LPC). The bit rate of the codec is 13 kbit/s, or 1.625 bits/aud ...
. As a result of the network's widespread use across Europe, the acronym "GSM" was briefly used as a generic term for mobile phones in France, the Netherlands and in
Belgium Belgium ( nl, België ; french: Belgique ; german: Belgien ), officially the Kingdom of Belgium, is a country in Western Europe Western Europe is the western region of Europe. The region's countries and territories vary depending on cont ...

Belgium
. A great number of people in Belgium still use it to date. Many carriers (like Verizon) will shutdown GSM and
CDMA Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of channel access method, multiple access, where several transmitters can send information simultaneously over ...

CDMA
in 2022.


History


Initial development for GSM by Europeans

In 1983, work began to develop a European standard for digital cellular voice telecommunications when the
European Conference of Postal and Telecommunications Administrations The European Conference of Postal and Telecommunications Administrations (CEPT) was established on June 26, 1959 by nineteen European states in Montreux, Switzerland ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or ...

European Conference of Postal and Telecommunications Administrations
(CEPT) set up the ''Groupe Spécial Mobile'' (GSM) committee and later provided a permanent technical-support group based in
Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, most populous city of France, with an estimated population of 2,175,601 residents , in an area of more than . Since the 17th century, Paris ha ...

Paris
. Five years later, in 1987, 15 representatives from 13 European countries signed a
memorandum of understanding A memorandum of understanding (MoU) is a type of agreement between two (bilateral Bilateral may refer to any concept including two sides, in particular: *Bilateria, bilateral animals *Bilateralism, the political and cultural relations between ...
in
Copenhagen Copenhagen ( da, København ) is the capital and most populous city of Denmark. As of 1 January 2021, the city had a population of 799,033 (638,117 in Copenhagen Municipality, 103,677 in Frederiksberg Municipality, 42,670 in Tårnby Municipal ...

Copenhagen
to develop and deploy a common cellular telephone system across Europe, and EU rules were passed to make GSM a mandatory standard. The decision to develop a continental standard eventually resulted in a unified, open, standard-based network which was larger than that in the United States. In February 1987 Europe produced the first agreed GSM Technical Specification. Ministers from the four big EU countries cemented their political support for GSM with the Bonn Declaration on Global Information Networks in May and the GSM MoU was tabled for signature in September. The MoU drew in mobile operators from across Europe to pledge to invest in new GSM networks to an ambitious common date. In this short 38-week period the whole of Europe (countries and industries) had been brought behind GSM in a rare unity and speed guided by four public officials: Armin Silberhorn (Germany), Stephen Temple (UK),
Philippe Dupuis Philippe Dupuis (born April 24, 1985) is a Canadians, Canadian former professional ice hockey player who played in the National Hockey League (NHL) with the Colorado Avalanche and the Toronto Maple Leafs. Playing career Dupuis was drafted 104th o ...
(France), and Renzo Failli (Italy). In 1989 the Groupe Spécial Mobile committee was transferred from CEPT to the
European Telecommunications Standards Institute ETSI (European Telecommunications Standards Institute) is an independent, not-for-profit, standardization Standardization or standardisation is the process of implementing and developing s based on the consensus of different parties that in ...
(ETSI). The IEEE/RSE awarded to
Thomas Haug Dr. Thomas Haug (born 1927 in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norwegian language Norwe ...

Thomas Haug
and
Philippe Dupuis Philippe Dupuis (born April 24, 1985) is a Canadians, Canadian former professional ice hockey player who played in the National Hockey League (NHL) with the Colorado Avalanche and the Toronto Maple Leafs. Playing career Dupuis was drafted 104th o ...
the 2018 James Clerk Maxwell medal for their "leadership in the development of the first international mobile communications standard with subsequent evolution into worldwide smartphone data communication". The GSM (2G) has evolved into 3G, 4G and 5G.


First networks

In parallel
France France (), officially the French Republic (french: link=no, République française), is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses ...

France
and
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...

Germany
signed a joint development agreement in 1984 and were joined by
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...

Italy
and the in 1986. In 1986, the
European Commission The European Commission (EC) is the executive branch The executive is the branch of government exercising authority in and holding Moral responsibility, responsibility for the governance of a State (polity), state. The executive executes a ...

European Commission
proposed reserving the 900 MHz spectrum band for GSM. The former
Finnish Finnish may refer to: * Something or someone from, or related to Finland * Finnish culture * Finnish people or Finns, the primary ethnic group in Finland * Finnish language, the national language of the Finnish people * Finnish cuisine See also

...

Finnish
prime minister
Harri Holkeri Harri Hermanni Holkeri () (6 January 1937 – 7 August 2011) was a Finns, Finnish statesman representing the National Coalition Party of Finland (Kokoomus / Samlingspartiet). He was the Prime Minister of Finland 1987–1991, speaker of the Unit ...

Harri Holkeri
made the world's first GSM call on 1 July 1991, calling (deputy mayor of the city of
Tampere Tampere ( , , ; sv, Tammerfors ; la, Tammerforsia) is a city in the Pirkanmaa Regions of Finland, region, located in the western part of Finland. Tampere is the most populous inland city in the Nordic countries; it has a population of 238,14 ...

Tampere
) using a network built by Nokia and Siemens and operated by
Radiolinja Radiolinja was a Finnish GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildh ...
. The following year saw the sending of the first
short messaging service SMS (short message service) is a text messaging service component of most telephone, Internet, and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text messages. An intermediary service ...
(SMS or "text message") message, and
Vodafone UK Vodafone Limited ( trading as Vodafone UK) is a British telecommunications services provider, and a part of the Vodafone Vodafone Group plc () is a British multinational telecommunication Telecommunication is the transmission of informati ...
and Telecom Finland signed the first international
roaming Roaming is a wireless Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points that do not use an electrical conductor In physics Physics (from grc, φυσικ ...

roaming
agreement.


Enhancements

Work began in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became operational in the UK by 1993, called and DCS 1800. Also that year,
Telecom Australia Telstra Corporation Limited is an Australian telecommunications Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and t ...

Telecom Australia
became the first network operator to deploy a GSM network outside Europe and the first practical hand-held GSM
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunication Telecommunication is the tra ...

mobile phone
became available. In 1995 fax, data and SMS messaging services were launched commercially, the first 1900 MHz GSM network became operational in the United States and GSM subscribers worldwide exceeded 10 million. In the same year, the
GSM Association The GSM Association (commonly referred to as 'the GSMA' or '' Global System for Mobile Communications'', originally ''Groupe Spécial Mobile'') is an industry organisation that represents the interests of mobile network operators worldwide. More ...
formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide GSM subscribers passed 100 million in 1998. In 2000 the first commercial
GPRS General Packet Radio Service (GPRS) is a packet oriented Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation (DBA). In statistical multiplexing, a communication channel is divided into ...
services were launched and the first GPRS-compatible handsets became available for sale. In 2001, the first UMTS (W-CDMA) network was launched, a 3G technology that is not part of GSM. Worldwide GSM subscribers exceeded 500 million. In 2002, the first
Multimedia Messaging Service Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia Multimedia is a form of communication that combines different content forms such as text, audio, images, animations, or video into a single presenta ...
(MMS) was introduced and the first GSM network in the 800 MHz frequency band became operational.
EDGE Edge or EDGE may refer to: Technology Computing * Edge computing Edge computing is a distributed computing paradigm that brings computation and data storage closer to the sources of data. This is expected to improve response times and save bandw ...

EDGE
services first became operational in a network in 2003, and the number of worldwide GSM subscribers exceeded 1 billion in 2004. By 2005 GSM networks accounted for more than 75% of the worldwide cellular network market, serving 1.5 billion subscribers. In 2005, the first
HSDPA High Speed Packet Access (HSPA) is an amalgamation of two mobile protocols Protocol may refer to: Sociology and politics * Protocol (politics)Protocol originally (in Late Middle English, c. 15th century) meant the minute or logbook taken at a ...
-capable network also became operational. The first
HSUPA High Speed Packet Access (HSPA) is an amalgamation of two mobile protocols Protocol may refer to: Sociology and politics * Protocol (politics)Protocol originally (in Late Middle English, c. 15th century) meant the minute or logbook taken at a ...
network launched in 2007. (High-Speed Packet Access (HSPA) and its uplink and downlink versions are 3G technologies, not part of GSM.) Worldwide GSM subscribers exceeded three billion in 2008.


Adoption

The
GSM Association The GSM Association (commonly referred to as 'the GSMA' or '' Global System for Mobile Communications'', originally ''Groupe Spécial Mobile'') is an industry organisation that represents the interests of mobile network operators worldwide. More ...
estimated in 2011 that technologies defined in the GSM standard served 80% of the mobile market, encompassing more than 5 billion people across more than 212 countries and territories, making GSM the most ubiquitous of the many standards for cellular networks. GSM is a second-generation (2G) standard employing time-division multiple-access (TDMA) spectrum-sharing, issued by the European Telecommunications Standards Institute (ETSI). The GSM standard does not include the 3G
Universal Mobile Telecommunications System The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the Int ...
(UMTS),
code-division multiple access Code-division multiple access (CDMA) is a channel access method In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminal (telecommunication), terminals connected to the same t ...
(CDMA) technology, nor the 4G LTE
orthogonal frequency-division multiple access Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) Modulation#Digital modulation methods, digital modulation scheme. Multiple access is achieved in OFDMA ...
(OFDMA) technology standards issued by the 3GPP. GSM, for the first time, set a common standard for Europe for wireless networks. It was also adopted by many countries outside Europe. This allowed subscribers to use other GSM networks that have roaming agreements with each other. The common standard reduced research and development costs, since hardware and software could be sold with only minor adaptations for the local market.


Discontinuation

Telstra Telstra Corporation Limited is an Australian telecommunications Telecommunication is the transmission of information by various types of technologies over , radio, , or other systems. It has its origin in the desire of humans for commun ...

Telstra
in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
shut down its 2G GSM network on 1 December 2016, the first mobile network operator to decommission a GSM network. The second mobile provider to shut down its GSM network (on 1 January 2017) was
AT&T Mobility AT&T Mobility LLC, also known as AT&T Wireless and Trade name, marketed as simply AT&T, is an American telecommunications company. It is a wholly owned subsidiary of AT&T, AT&T Inc. and provides wireless services in the United States, excluding ...

AT&T Mobility
from the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
.
Optus Singtel Optus Pty Limited (commonly referred to as Optus) is an Australian Telecommunications in Australia, telecommunications company headquartered in Macquarie Park, New South Wales, Australia. It is a wholly owned subsidiary of Singtel. Optu ...
in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
completed the shut down its 2G GSM network on 1 August 2017, part of the Optus GSM network covering
Western Australia Western Australia (abbreviated as WA) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspape ...

Western Australia
and the
Northern Territory The Northern Territory (NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, ...
had earlier in the year been shut down in April 2017.
Singapore Singapore (), officially the Republic of Singapore, is a sovereign state, sovereign island city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, bor ...

Singapore
shut down 2G services entirely in April 2017.


Technical details


Network structure

The network is structured into several discrete sections: *
Base station subsystem 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 A mobile phone, cellular phone, cell phone, cellphone, handphone, o ...
– the base stations and their controllers *
Network and Switching Subsystem Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out telephone exchange, call out and mobility management functions for mobile phones roaming on the Base Station subsystem, network of base sta ...
– the part of the network most similar to a fixed network, sometimes just called the "core network" *
GPRS Core Network The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet The Internet (Capitalization of Inte ...
– the optional part which allows packet-based Internet connections *
Operations support system Operations Support Systems (OSS), Operational Support Systems in British usage, or Operation System (OpS) in NTT, are computer systems used by telecommunications service providers to manage their networks (e.g., telephone networks). They support ...
(OSS) – network maintenance


Base-station subsystem

GSM utilizes a
cellular network A cellular network or mobile network is a communication network A telecommunications network is a group of nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may re ...
, meaning that
cell phone A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunication Telecommunication is the tra ...

cell phone
s connect to it by searching for cells in the immediate vicinity. There are five different cell sizes in a GSM network: *
macro Macro (or MACRO) may refer to: Science and technology * Macroscopic The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the o ...
*
micro Micro may refer to: Measurement * micro- (μ), a prefix in the SI and other systems of units denoting a factor of 10−6 (one millionth) Places * Micro, North Carolina, town in U.S. People * DJ Micro, (born Michael Marsicano) an American trance ...
*
pico Pico may refer to: Places The Moon * Mons Pico, a lunar mountain in the northern part of the Mare Imbrium basin Portugal *Pico, a civil parish in the municipality of Vila Verde Vila Verde () is a List of municipalities of Portugal, municipali ...
*
femto ''Femto'' (symbol f) is a unit prefix A unit prefix is a specifier or mnemonic that is prepended to units of measurement A unit of measurement is a definite magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity ...
, and * umbrella cells The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base-station
antenna Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two col ...
is installed on a mast or a building above average rooftop level. Micro cells are cells whose antenna height is under average rooftop level; they are typically deployed in urban areas. Picocells are small cells whose coverage diameter is a few dozen meters; they are mainly used indoors. Femtocells are cells designed for use in residential or small-business environments and connect to a
telecommunications service provider A telecommunications service provider (TSP) is a type of communications service provider A telecommunications service provider (TSP) is a type of communications service provider that has traditionally provided telephone A telephone is ...
's network via a broadband-internet connection. Umbrella cells are used to cover shadowed regions of smaller cells and to fill in gaps in coverage between those cells. Cell horizontal radius varies – depending on antenna height,
antenna gain In electromagnetics Electromagnetism is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matt ...
, and propagation conditions – from a couple of hundred meters to several tens of kilometers. The longest distance the GSM specification supports in practical use is . There are also several implementations of the concept of an extended cell, where the cell radius could be double or even more, depending on the antenna system, the type of terrain, and the timing advance. GSM supports indoor coverage – achievable by using an indoor picocell base station, or an indoor repeater with distributed indoor antennas fed through power splitters – to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. Picocells are typically deployed when significant call capacity is needed indoors, as in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of radio signals from any nearby cell.


GSM carrier frequencies

GSM networks operate in a number of different
carrier frequency In telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, Optical system, optical, or other Electromagnetism, electromagnetic systems. It has its origin in the desire of hu ...
ranges (separated into
GSM frequency ranges GSM frequency bands or frequency ranges are the cellular frequencies Cellular frequencies are the sets of frequency ranges within the ultra high frequency Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range b ...
for 2G and
UMTS frequency bands The UMTS frequency bands are radio frequency, radio frequencies used by 3G, third generation (3G) wireless Universal Mobile Telecommunications System networks. They were allocated by delegates to the World Administrative Radio Conference (WARC-92) ...
for 3G), with most GSM networks operating in the 900 MHz or 1800 MHz bands. Where these bands were already allocated, the 850 MHz and 1900 MHz bands were used instead (for example in Canada and the United States). In rare cases the 400 and 450 MHz frequency bands are assigned in some countries because they were previously used for first-generation systems. For comparison, most networks in Europe operate in the 2100 MHz frequency band. For more information on worldwide GSM frequency usage, see
GSM frequency bands GSM frequency bands or frequency ranges are the cellular frequencies designated by the International Telecommunication Union, ITU for the operation of GSM mobile phones and other mobile devices. Frequency bands GSM frequency usage around th ...
. Regardless of the frequency selected by an operator, it is divided into timeslots for individual phones. This allows eight full-rate or sixteen half-rate speech channels per
radio frequency Radio frequency (RF) is the oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparently irreversible p ...
. These eight radio timeslots (or burst periods) are grouped into a TDMA frame. Half-rate channels use alternate frames in the same timeslot. The channel data rate for all is and the frame duration is The transmission power in the handset is limited to a maximum of 2 watts in and in .


Voice codecs

GSM has used a variety of voice
codec A codec is a device or computer program In imperative programming, a computer program is a sequence of instructions in a programming language that a computer can execute or interpret. In declarative programming, a ''computer program'' is a Set ...
s to squeeze 3.1 kHz audio into between 7 and 13 kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called
Half Rate Half Rate (HR or GSM-HR or GSM 06.20) is a speech coding system for GSM, developed in the early 1990s. Since the codec, operating at 5.6 kbit/s, requires half the Bandwidth (computing), bandwidth of the Full Rate codec, network capacity for voice t ...
(6.5 kbit/s) and
Full Rate Full Rate (FR or GSM-FR or GSM 06.10 or sometimes simply GSM) was the first digital speech coding standard used in the GSM digital mobile phone system. It uses linear predictive coding (LPC). The bit rate of the codec is 13 kbit/s, or 1.625 bits/aud ...
(13 kbit/s). These used a system based on
linear predictive coding Linear predictive coding (LPC) is a method used mostly in audio signal processing and speech processing for representing the spectral envelope of a Digital data, digital signal (information theory), signal of Speech communication, speech in data co ...
(LPC). In addition to being efficient with
bitrate In telecommunications Telecommunication is the transmission of information by various types of technologies over , radio, , or other systems. It has its origin in the desire of humans for communication over a distance greater than that ...
s, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal. GSM was further enhanced in 1997 with the
enhanced full rate Enhanced Full Rate or EFR or GSM-EFR or GSM 06.60 is a speech coding Speech coding is an application of data compression of digital audio Digital audio is a representation of sound recorded in, or converted into, Digital signal (signal proces ...
(EFR) codec, a 12.2 kbit/s codec that uses a full-rate channel. Finally, with the development of
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...

UMTS
, EFR was refactored into a variable-rate codec called AMR-Narrowband, which is high quality and robust against interference when used on full-rate channels, or less robust but still relatively high quality when used in good radio conditions on half-rate channel.


Subscriber Identity Module (SIM)

One of the key features of GSM is the
Subscriber Identity Module A GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM London, a higher education provider * Guildhall School of Music and Drama The Guildhall School of Music an ...
, commonly known as a SIM card. The SIM is a detachable
smart card A smart card, chip card, or integrated circuit card (ICC or IC card) is a physical electronic authorization device, used to control access to a resource. It is typically a plastic credit card #REDIRECT Credit card A credit card is a paym ...
containing the user's subscription information and phone book. This allows the user to retain their information after switching handsets. Alternatively, the user can change operators while retaining the handset simply by changing the SIM.


Phone locking

Sometimes
mobile network operator A mobile network operator (MNO), also known as a wireless service provider, wireless carrier, cellular company, or mobile network carrier, is a provider of wireless communications Wireless communication (or just wireless, when the context all ...
s restrict handsets that they sell for exclusive use in their own network. This is called
SIM lock A SIM lock, simlock, network lock, carrier lock or (master) subsidy lock is a technical restriction built into GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Education * GSM L ...
ing and is implemented by a software feature of the phone. A subscriber may usually contact the provider to remove the lock for a fee, utilize private services to remove the lock, or use software and websites to unlock the handset themselves. It is possible to hack past a phone locked by a network operator. In some countries and regions (e.g.,
Bangladesh Bangladesh (, bn, বাংলাদেশ, ), officially the People's Republic of Bangladesh, is a country in South Asia South Asia is the southern region of Asia, which is defined in both geography, geographical and culture, ethno-c ...

Bangladesh
,
Belgium Belgium ( nl, België ; french: Belgique ; german: Belgien ), officially the Kingdom of Belgium, is a country in Western Europe Western Europe is the western region of Europe. The region's countries and territories vary depending on cont ...

Belgium
,
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
,
Canada Canada is a country in the northern part of North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...

Canada
,
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern ...

Chile
,
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...

Germany
,
Hong Kong Hong Kong (; , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (HKSAR), is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Pe ...

Hong Kong
,
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

India
,
Iran Iran ( fa, ایران ), also called Persia, and officially the Islamic Republic of Iran, is a country in Western Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion A subregion is a part of a larger regio ...

Iran
,
Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon or the Lebanese Republic, is a country in Western Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion A subregion is a part ...

Lebanon
,
Malaysia Malaysia ( ; ) is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical southeastern subregion of Asia, consisting of the regions ...

Malaysia
,
Nepal Nepal (; ne, नेपाल ), officially the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in South Asia. It is ma ...

Nepal
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Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norwegian language Norwegian (Norwegian: ''norsk'') is a Nort ...

Norway
,
Pakistan Pakistan, . Pronounced variably in English as , , , and . officially the Islamic Republic of Pakistan, is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a popul ...

Pakistan
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Poland Poland, officially the Republic of Poland, is a country located in Central Europe. It is divided into 16 Voivodeships of Poland, administrative provinces, covering an area of , and has a largely Temperate climate, temperate seasonal cli ...

Poland
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Singapore Singapore (), officially the Republic of Singapore, is a sovereign state, sovereign island city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, bor ...

Singapore
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South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. With over 60 million people, it is the world's 23rd-most populous nation and covers an area of . South Africa has three capital citie ...

South Africa
,
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකාව, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon, and officially the Democratic Socialist Republic of Sri Lanka, is ...

Sri Lanka
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Thailand Thailand ( th, ประเทศไทย), historically known as Siam, () officially the Kingdom of Thailand, is a country in Southeast Asia. It is located at the centre of the Mainland Southeast Asia, Indochinese Peninsula, spanning , wi ...

Thailand
) all phones are sold unlocked due to the abundance of dual SIM handsets and operators.


GSM security

GSM was intended to be a secure wireless system. It has considered the user authentication using a pre-shared key and challenge-response, and over-the-air encryption. However, GSM is vulnerable to different types of attack, each of them aimed at a different part of the network. The development of
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM GSM (Global System for Mobile communications) is a European standard for mobile devices. GSM may also refer to: Edu ...
introduced an optional
Universal Subscriber Identity Module A SIM card, also known as subscriber identity module or subscriber identification module (SIM), is an integrated circuit running a card operating system (COS) that is intended to encryption, securely store the international mobile subscriber ...
(USIM), that uses a longer authentication key to give greater security, as well as mutually authenticating the network and the user, whereas GSM only authenticates the user to the network (and not vice versa). The security model therefore offers confidentiality and authentication, but limited authorization capabilities, and no
non-repudiationNon-repudiation refers to a situation where a statement's author cannot successfully dispute its authorship or the validity of an associated contract A contract is a legally binding document between at least two parties that defines and governs th ...
. GSM uses several cryptographic algorithms for security. The
A5/1A5/1 is a stream cipher used to provide over-the-air communication privacy in the Global System for Mobile Communications, GSM Cell phone, cellular telephone standard. It is one of seven algorithms which were specified for GSM use. It was initially ...
,
A5/2 A5/2 is a stream cipher generator in A5/1, an LFSR-based stream cipher used to encrypt mobile phone conversations. A stream cipher is a symmetric key algorithm, symmetric key cipher where plaintext digits are combined with a pseudorandom cipher d ...
, and A5/3
stream cipher generator in A5/1A5/1 is a stream cipher used to provide over-the-air communication privacy in the Global System for Mobile Communications, GSM Cell phone, cellular telephone standard. It is one of seven algorithms which were specified for GSM us ...

stream cipher
s are used for ensuring over-the-air voice privacy. A5/1 was developed first and is a stronger algorithm used within Europe and the United States; A5/2 is weaker and used in other countries. Serious weaknesses have been found in both algorithms: it is possible to break A5/2 in real-time with a ciphertext-only attack, and in January 2007, The Hacker's Choice started the A5/1 cracking project with plans to use
FPGA A field-programmable gate array (FPGA) is an integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a pr ...
s that allow A5/1 to be broken with a
rainbow table A rainbow table is a precomputed table for caching the output of cryptographic hash functions, usually for cracking password hashes. Tables are usually used in recovering a key derivation function (or credit card numbers, etc.) up to a certain ...
attack. The system supports multiple algorithms so operators may replace that cipher with a stronger one. Since 2000, different efforts have been made in order to crack the A5 encryption algorithms. Both A5/1 and A5/2 algorithms have been broken, and their cryptanalysis has been revealed in the literature. As an example, developed a number of
rainbow table A rainbow table is a precomputed table for caching the output of cryptographic hash functions, usually for cracking password hashes. Tables are usually used in recovering a key derivation function (or credit card numbers, etc.) up to a certain ...
s (static values which reduce the time needed to carry out an attack) and have found new sources for known plaintext attacks. He said that it is possible to build "a full GSM interceptor...from open-source components" but that they had not done so because of legal concerns. Nohl claimed that he was able to intercept voice and text conversations by impersonating another user to listen to voicemail, make calls, or send text messages using a seven-year-old Motorola cellphone and decryption software available for free online. GSM uses
General Packet Radio Service General Packet Radio Service (GPRS) is a packet oriented Statistical multiplexing is a type of communication link sharing, very similar to dynamic bandwidth allocation (DBA). In statistical multiplexing, a communication channel is divided into ...
(GPRS) for data transmissions like browsing the web. The most commonly deployed GPRS ciphers were publicly broken in 2011. The researchers revealed flaws in the commonly used GEA/1 and GEA/2 (standing for GPRS Encryption Algorithms 1 and 2) ciphers and published the open-source "gprsdecode" software for Packet analyzer, sniffing GPRS networks. They also noted that some carriers do not encrypt the data (i.e., using GEA/0) in order to detect the use of traffic or protocols they do not like (e.g., Skype), leaving customers unprotected. GEA/3 seems to remain relatively hard to break and is said to be in use on some more modern networks. If used with Subscriber Identity Module, USIM to prevent connections to fake base stations and downgrade attacks, users will be protected in the medium term, though migration to 128-bit GEA/4 is still recommended. The first public cryptanalysis of GEA/1 and GEA/2 (also written GEA-1 and GEA-2) was done in 2021. It concluded that although using a 64-bit key, the GEA-1 algorithm actually provides only 40 bits of security, due to a relationship between two parts of the algorithm. The researchers found that this relationship was very unlikely to have happened if it wasn't intentional. This may have been done in order to satisfy European controls on export of cryptographic programs.


Standards information

The GSM systems and services are described in a set of standards governed by ETSI, where a full list is maintained.


GSM open-source software

Several open source software projects exist that provide certain GSM features: *gsmd daemon by Openmoko *OpenBTS develops a Base transceiver station *''The GSM Software Project'' aims to build a GSM analyzer for less than $1,000 *''OsmocomBB'' developers intend to replace the proprietary baseband GSM stack with a free software implementation *YateBTS develops a Base transceiver station


Issues with patents and open source

Patents remain a problem for any open-source GSM implementation, because it is not possible for GNU or any other free software distributor to guarantee immunity from all lawsuits by the patent holders against the users. Furthermore, new features are being added to the standard all the time which means they have patent protection for a number of years. The original GSM implementations from 1991 may now be entirely free of patent encumbrances, however patent freedom is not certain due to the United States' "first to invent" system that was in place until 2012. The "first to invent" system, coupled with "patent term adjustment" can extend the life of a U.S. patent far beyond 20 years from its priority date. It is unclear at this time whether OpenBTS will be able to implement features of that initial specification without limit. As patents subsequently expire, however, those features can be added into the open-source version. , there have been no lawsuits against users of OpenBTS over GSM use.


See also

* Cellular network * Enhanced Data Rates for GSM Evolution (EDGE) * Enhanced Network Selection (ENS) * Call forwarding#Mobile .28cell.29 phones, GSM forwarding standard features codes – list of call forward codes working with all operators and phones *
GSM frequency bands GSM frequency bands or frequency ranges are the cellular frequencies designated by the International Telecommunication Union, ITU for the operation of GSM mobile phones and other mobile devices. Frequency bands GSM frequency usage around th ...
* GSM modem * GSM services ** Cell Broadcast ** GSM localization **
Multimedia Messaging Service Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia Multimedia is a form of communication that combines different content forms such as text, audio, images, animations, or video into a single presenta ...
(MMS) ** NITZ Network Identity and Time Zone ** Wireless Application Protocol (WAP) * GSM-R (GSM-Railway) *Unstructured Supplementary Service Data, GSM USSD codes – Unstructured Supplementary Service Data: list of all standard GSM codes for network and SIM related functions * Handoff * High-Speed Downlink Packet Access (HSDPA) * International Mobile Equipment Identity (IMEI) * International Mobile Subscriber Identity (IMSI) * LTE (telecommunication), Long Term Evolution (LTE) * MSISDN Mobile Subscriber ISDN Number * Nordic Mobile Telephone (NMT) * ORFS * Personal communications network (PCN) * RTP audio video profile * Network simulation, Simulation of GSM networks * Standards ** Comparison of mobile phone standards ** GEO-Mobile Radio Interface ** GSM 02.07 – Cellphone features ** GSM 03.48 – Security mechanisms for the SIM application toolkit ** Intelligent Network ** Parlay X ** RRLP – Radio Resource Location Protocol * Um interface * Visitors Location Register (VLR)


References


Further reading

* * * * *


External links


GSM Association
Official industry trade group representing GSM network operators worldwide
3GPP
3G GSM standards development group
LTE-3GPP.info: online GSM messages decoder fully supporting all 3GPP releases from early GSM to latest 5G
{{DEFAULTSORT:Gsm Telecommunications-related introductions in 1991 GSM standard