GSM (Global System for Mobile Communications, originally Groupe
Spécial Mobile) is a standard developed by the European
Telecommunications Standards Institute (ETSI) to describe the
protocols for second-generation digital cellular networks used by
mobile devices such as tablets, first deployed in
Finland in December
1991. As of 2014[update], it has become the global standard for
mobile communications – with over 90% market share, operating in
over 193 countries and territories.
2G networks developed as a replacement for first generation (1G)
analog cellular networks, and the
GSM standard originally described as
a digital, circuit-switched network optimized for full duplex voice
telephony. This expanded over time to include data communications,
first by circuit-switched transport, then by packet data transport via
GPRS (General Packet Radio Services) and
EDGE (Enhanced Data rates for
GSM Evolution, or EGPRS).
3GPP developed third-generation (3G)
followed by fourth-generation (4G)
LTE Advanced standards, which do
not form part of the
"GSM" is a trademark owned by the
GSM Association. It may also refer
to the (initially) most common voice codec used, Full Rate.
2 Technical details
2.1 Network structure
Base station subsystem
GSM carrier frequencies
2.2.2 Voice codecs
Subscriber Identity Module
Subscriber Identity Module (SIM)
2.4 Phone locking
4 Standards information
GSM open-source software
5.1 Issues with patents and open source
6 See also
8 Further reading
9 External links
In 1983 work began to develop a European standard for digital cellular
voice telecommunications when the European Conference of Postal and
Telecommunications Administrations (CEPT) set up the Groupe Spécial
Mobile committee and later provided a permanent technical-support
group based in Paris. Five years later, in 1987, 15 representatives
from 13 European countries signed a memorandum of understanding in
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 very first agreed
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 (France), and Renzo Failli (Italy). In
1989 the Groupe Spécial Mobile committee was transferred from CEPT to
the European Telecommunications Standards Institute
Germany signed a joint development agreement in
1984 and were joined by
Italy and the UK in 1986. In 1986, the
European Commission proposed reserving the 900 MHz spectrum band
for GSM. The former Finnish prime minister
Harri Holkeri made the
GSM call on July 1, 1991, calling Kaarina Suonio (mayor
of the city of Tampere) using a network built by Telenokia and Siemens
and operated by Radiolinja. The following year saw the sending of
the first short messaging service (SMS or "text message") message, and
Vodafone UK and Telecom
Finland signed the first international roaming
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 became the first network operator to deploy a
outside Europe and the first practical hand-held
GSM mobile phone
In 1995 fax, data and SMS messaging services were launched
commercially, the first 1900 MHz
GSM network became operational
United States and
GSM subscribers worldwide exceeded 10
million. In the same year, the
GSM Association 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 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
Multimedia Messaging Service
Multimedia Messaging Service (MMS) was introduced and the first
GSM network in the 800 MHz frequency band became operational.
EDGE services first became operational in a network in 2003, and the
number of worldwide
GSM subscribers exceeded 1 billion in 2004.
GSM networks accounted for more than 75% of the worldwide
cellular network market, serving 1.5 billion subscribers. In 2005, the
first HSDPA-capable network also became operational. The first HSUPA
network launched in 2007. (High-Speed Packet Access (HSPA) and its
uplink and downlink versions are 3G technologies, not part of GSM.)
GSM subscribers exceeded three billion in 2008.
GSM Association estimated in 2010 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
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
Universal Mobile Telecommunications System (UMTS)
code division multiple access (CDMA) technology nor the 4G LTE
orthogonal frequency-division multiple access (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.
Australia shut down its 2G
GSM network on December 1, 2016,
the first mobile network operator to decommission a
The second mobile provider to shut down its
GSM network (on January 1,
2017) was AT&T Mobility from the United States.
Australia completed the shut down its 2G
GSM network on August 1,
2017, part of the
GSM network covering Western
Australia and the
Northern Territory had earlier in the year been shut down in April
Singapore shut down 2G services entirely in April 2017.
The structure of a
The network is structured into a number of discrete sections:
Base station subsystem
Base station subsystem – the base stations and their controllers
Network and Switching Subsystem – the part of the network most
similar to a fixed network, sometimes just called the "core network"
GPRS Core Network – the optional part which allows packet-based
Operations support system (OSS) – network maintenance
Base station subsystem
Base station subsystem
GSM cell site antennas in the Deutsches Museum, Munich, Germany
GSM is a cellular network, which means that cell phones connect to it
by searching for cells in the immediate vicinity. There are five
different cell sizes in a
GSM network—macro, micro, pico, femto, 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 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 used 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
the service provider’s network via a broadband internet connection.
Umbrella cells are used to cover shadowed regions of smaller cells and
fill in gaps in coverage between those cells.
Cell horizontal radius varies depending on antenna height, antenna
gain, and propagation conditions from a couple of hundred meters to
several tens of kilometres. The longest distance the
supports in practical use is 35 kilometres (22 mi). 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.
Indoor coverage is also supported by
GSM and may be achieved 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. These are typically deployed when
significant call capacity is needed indoors, like in shopping centers
or airports. However, this is not a prerequisite, since indoor
coverage is also provided by in-building penetration of the radio
signals from any nearby cell.
GSM carrier frequencies
GSM frequency bands
GSM networks operate in a number of different carrier frequency ranges
GSM frequency ranges for 2G and
UMTS frequency bands
for 3G), with most 2G
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 3G networks in Europe operate in the 2100 MHz
frequency band. For more information on worldwide
GSM frequency usage,
GSM frequency bands.
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. 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 8 channels is 270.833 kbit/s, and the frame
duration is 4.615 ms.
The transmission power in the handset is limited to a maximum of 2
GSM 850/900 and 1 watt in
GSM has used a variety of voice codecs to squeeze 3.1 kHz audio
into between 6.5 and 13 kbit/s. Originally, two codecs, named
after the types of data channel they were allocated, were used, called
Half Rate (6.5 kbit/s) and
Full Rate (13 kbit/s). These used
a system based on linear predictive coding (LPC). In addition to being
efficient with bitrates, 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.
further enhanced in 1997 with the enhanced full rate (EFR) codec,
a 12.2 kbit/s codec that uses a full-rate channel. Finally, with
the development of 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
Subscriber Identity Module
Subscriber Identity Module (SIM)
Main article: Subscriber Identity Module
One of the key features of
GSM is the Subscriber Identity Module,
commonly known as a SIM card. The SIM is a detachable smart card
containing the user's subscription information and phone book. This
allows the user to retain his or her information after switching
handsets. Alternatively, the user can change operators while retaining
the handset simply by changing the SIM. Some operators will block this
by allowing the phone to use only a single SIM, or only a SIM issued
by them; this practice is known as SIM locking.
Main article: SIM lock
Sometimes mobile network operators restrict handsets that they sell
for use with their own network. This is called locking 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 (e.g., Bangladesh, Belgium, Brazil, Canada, Chile,
Germany, Hong Kong, India, Iran, Lebanon, Malaysia, Nepal, Pakistan,
Poland, Singapore, South Africa, Thailand) all phones are sold
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 introduced an optional Universal Subscriber
Identity Module (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
GSM uses several cryptographic algorithms for security. The A5/1,
A5/3 stream ciphers are used for ensuring over-the-air voice
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
project with plans to use FPGAs that allow
A5/1 to be broken with a
rainbow table 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
A5/2 algorithms have been broken,
and their cryptanalysis has been revealed in the literature. As an
example, Karsten Nohl (de) developed a number of rainbow tables
(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
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
General Packet Radio Service
General Packet Radio Service (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
ciphers and published the open-source "gprsdecode" software for
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 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.
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
gsmd daemon by Openmoko
OpenBTS develops a Base transceiver station
GSM Software Project aims to build a
GSM analyzer for less than
OsmocomBB developers intend to replace the proprietary baseband GSM
stack with a free software implementation
YateBTS develops a
Base transceiver station
Base transceiver station 
Issues with patents and open source
Patents remain a problem for any open-source
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.
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. As of 2011, there have been no lawsuits
against users of
GSM use.
Enhanced Data Rates for GSM Evolution (EDGE)
Enhanced Network Selection (ENS)
GSM forwarding standard features codes – list of call forward codes
working with all operators and phones
GSM frequency bands
Multimedia Messaging Service
Multimedia Messaging Service (MMS)
NITZ Network Identity and Time Zone
Wireless Application Protocol
Wireless Application Protocol (WAP)
GSM USSD codes – Unstructured Supplementary Service Data: list of
GSM codes for network and SIM related functions
High-Speed Downlink Packet Access
High-Speed Downlink Packet Access (HSDPA)
International Mobile Subscriber Identity (IMSI)
Long Term Evolution (LTE)
MSISDN Mobile Subscriber ISDN Number
Nordic Mobile Telephone
Nordic Mobile Telephone (NMT)
Personal communications network (PCN)
RTP audio video profile
Comparison of mobile phone standards
GEO-Mobile Radio Interface
GSM 02.07 - Cellphone features
GSM 03.48 – Security mechanisms for the SIM application toolkit
RRLP – Radio Resource Location Protocol
Visitors Location Register (VLR)
^ Sauter, Martin (21 Nov 2013). "The
GSM Logo: The Mystery of the 4
Dots Solved". Retrieved 23 Nov 2013. [...] here's what [Yngve
Zetterstrom, rapporteur of the Maketing and Planning (MP) group of the
MoU (Memorandum of Understanding group, later to become the GSM
Association (GSMA)) in 1989] had to say to solve the mystery: '[The
dots symbolize] three [clients] in the home network and one roaming
client.' There you go, an answer from the prime source!
^ Anton A. Huurdeman, The Worldwide History of Telecommunications,
John Wiley & Sons, 31 juli 2003, page 529
GSM Global system for Mobile Communications". 4G Americas. Archived
from the original on 8 February 2014. Retrieved 2014-03-22.
^ EU Seeks To End Mandatory
GSM for 900Mhz - Source
^ Leader (7 September 2007). "Happy 20th Birthday, GSM". zdnet.co.uk.
CBS Interactive. Archived from the original on 5 May 2011. Retrieved 5
May 2011. Before GSM, Europe had a disastrous mishmash of national
analogue standards in phones and TV, designed to protect national
industries but instead creating fragmented markets vulnerable to big
guns from abroad.
^ a b "GSM". etsi.org. European Telecommunications Standards
Institute. 2011. Archived from the original on 5 May 2011. Retrieved 5
GSM was designed principally for voice telephony, but a
range of bearer services was defined...allowing circuit-switched data
connections at up to 9600 bits/s.
^ a b c d e f "History". gsmworld.com.
GSM Association. 2001. Archived
from the original on 5 May 2011. Retrieved 5 May 2011. 1982 Groupe
Speciale Mobile (GSM) is formed by the Confederation of European Posts
and Telecommunications (CEPT) to design a pan-European mobile
^ a b "Cellular History". etsi.org. European Telecommunications
Standards Institute. 2011. Archived from the original on 5 May 2011.
Retrieved 5 May 2011. The task was entrusted to a committee known as
Groupe Spécial Mobile (GSMTM), aided by a "permanent nucleus" of
technical support personnel, based in Paris.
^ "Who created GSM?". Stephen Temple. Retrieved 7 April 2013. Before
GSM, Europe had a disastrous mishmash of national analogue standards
in phones and TV, designed to protect national industries but instead
creating fragmented markets vulnerable to big guns from abroad.
^ "Maailman ensimmäinen GSM-puhelu" [World's first
GSM call]. yle.fi.
Yelisradio OY. 22 February 2008. Archived from the original on 5 May
2011. Retrieved 5 May 2011.
Harri Holkeri made the first call on the
Radiolinja (Elisa's subsidiary) network, at the opening ceremony in
Helsinki on 07.01.1991.
GSM World statistics". gsmworld.com.
GSM Association. 2010.
Archived from the original on 21 May 2010. Retrieved 8 June
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^ Martin Sauter (23 June 2014). From
GSM to LTE-Advanced : An
Introduction to Mobile Networks and Mobile Broadband (Second ed.).
John Wiley & Sons, Incorporated. ISBN 9781118861929.
Telstra switches off
GSM network". TeleGeography. 2016-12-02.
^ bmobile in
Trinidad and Tobago
Trinidad and Tobago shut down it's 2G
GSM network in
December 2017. "2G Sunset" (PDF). ATT Mobility. Retrieved 10 August
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^ "Joint Media Release by IMDA, M1, Singtel & StarHub: 2G services
to cease on 1 April 2017". M1. 2017-03-27. Retrieved 2017-10-22.
Motorola Demonstrates Long Range
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^ Victoria Shannon (2007). "iPhone Must Be Offered Without Contract
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^ Solutions to the
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Services, and Technologies (NGMAST2008), pp.576–581, Cardiff, UK,
September 2008, arXiv:1002.3175
^ Steve. "The
A5/1 Cracking Project". scribd.com. Retrieved 3 November
^ Kevin J. O'Brien (28 December 2009). "Cellphone Encryption Code Is
Divulged". New York Times.
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^ Owano, Nancy (27 December 2011). "
GSM phones -- call them unsafe,
says security expert". Archived from the original on 28 December 2011.
Retrieved 27 Dec 2011. Nohl said that he was able to intercept voice
and text conversations by impersonating another user to listen to
their voice mails or make calls or send text messages. Even more
troubling was that he was able to pull this off using a seven-year-old
Motorola cellphone and decryption software available free off the
^ "Codebreaker Karsten Nohl: Why Your Phone Is Insecure By Design".
Forbes.com. 12 August 2011. Retrieved 13 August 2011.
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