GSM

GSM

Telecommunication
Founded	December 1991; 32 years ago (December 1991)
Successor	3G
Products	Digital cellular networks
Website	www.gsma.com

The Global System for Mobile Communications (GSM) is a standard developed by the

It was first implemented in Finland in December 1991.^[4] 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.^[5]

2G networks developed as a replacement for first generation (

(EDGE).

Subsequently, the 3GPP developed third-generation (3G) 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.

Beginning in the late 2010s, various carriers worldwide started to shut down their GSM networks. Nevertheless, as a result of the network's widespread use, the acronym "GSM" is still used as a generic term for the plethora of G mobile phone technologies evolved from it.

History

Initial European development

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 (GSM) 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.^[6] 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.^{[7][8][9][10]}

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),

The IEEE/RSE awarded to Thomas Haug and Philippe Dupuis 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".^[12] The GSM (2G) has evolved into 3G, 4G and 5G.

First networks

In parallel

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, Telstra became the first network operator to deploy a GSM network outside Europe and the first practical hand-held GSM 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

In 2000 the first commercial General Packet Radio Service (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 first Multimedia Messaging Service (MMS) was introduced and the first GSM network in the 800 MHz frequency band became operational. Enhanced Data rates for GSM Evolution (EDGE) services first became operational in a network in 2003, and the number of worldwide GSM subscribers exceeded 1 billion in 2004.^[9]

By 2005 GSM networks accounted for more than 75% of the worldwide cellular network market, serving 1.5 billion subscribers. In 2005, the first

Adoption

The

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

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.[17]

Discontinuation

Telstra in Australia shut down its 2G GSM network on 1 December 2016, the first mobile network operator to decommission a GSM network.^[18] The second mobile provider to shut down its GSM network (on 1 January 2017) was AT&T Mobility from the United States.^[19] Optus in Australia completed the shut down of its 2G GSM network on 1 August 2017, part of the Optus GSM network covering Western Australia and the Northern Territory had earlier in the year been shut down in April 2017.^[20] Singapore shut down 2G services entirely in April 2017.^[21]

Technical details

Network structure

The network is structured into several discrete sections:

• 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 Internet connections
• Operations support system (OSS) – network maintenance

Base-station subsystem

GSM utilizes a

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

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,

.

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

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, see 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.^[23] TDMA noise is interference that can be heard on speakers near a GSM phone using TDMA.^[24]

The transmission power in the handset is limited to a maximum of 2 watts in GSM 850/900 and 1 watt in GSM 1800/1900.

Voice codecs

GSM has used a variety of voice

with the

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

containing a user's subscription information and phone book. This allows users to retain their information after switching handsets. Alternatively, users can change networks or network identities without switching handsets - simply by changing the SIM.

Phone locking

Sometimes mobile network operators restrict handsets that they sell for exclusive use in their own network. This is called SIM 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 and regions (e.g. Brazil and Germany) all phones are sold unlocked due to the abundance of dual-SIM handsets and operators.^[26]

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.^[27]

Research findings indicate that GSM faces susceptibility to hacking by script kiddies, a term referring to inexperienced individuals utilizing readily available hardware and software. The vulnerability arises from the accessibility of tools such as a DVB-T TV tuner, posing a threat to both mobile and network users. Despite the term "script kiddies" implying a lack of sophisticated skills, the consequences of their attacks on GSM can be severe, impacting the functionality of cellular networks. Given that GSM continues to be the main source of cellular technology in numerous countries, its susceptibility to potential threats from malicious attacks is one that needs to be addressed.^[28]

The development of

.

GSM uses several cryptographic algorithms for security. The

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

GSM uses General Packet Radio Service (GPRS) for data transmissions like browsing the web. The most commonly deployed GPRS ciphers were publicly broken in 2011.^[33]

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

, 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 was not intentional. This may have been done in order to satisfy European controls on export of cryptographic programs.[34]^[35][36]

Standards information

The GSM systems and services are described in a set of standards governed by ETSI, where a full list is maintained.^[37]

GSM open-source software

Several open-source software projects exist that provide certain GSM features:^[38]

• gsmd daemon by Openmoko^[39]
• OpenBTS develops a Base transceiver station
• The GSM Software Project aims to build a GSM analyzer for less than $1,000^[40]
• OsmocomBB developers intend to replace the proprietary baseband GSM stack with a free software implementation^[41]
• YateBTS develops a Base transceiver station^[42]

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.^{[citation needed]}

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. As of 2011^[update], there have been no lawsuits against users of OpenBTS over GSM use.^{[citation needed]}

See also

References

Further reading

• Redl, Siegmund M.; Weber, Matthias K.; Oliphant, Malcolm W (February 1995). An Introduction to GSM. Artech House.
  ISBN 978-0-89006-785-7
  .
• Redl, Siegmund M.; Weber, Matthias K.; Oliphant, Malcolm W (April 1998). GSM and Personal Communications Handbook. Artech House Mobile Communications Library. Artech House.
  ISBN 978-0-89006-957-8
  .
• Hillebrand, Friedhelm, ed. (December 2001). GSM and UMTS, The Creation of Global Mobile Communications. John Wiley & Sons.
  ISBN 978-0-470-84322-2
  .
• Mouly, Michel; Pautet, Marie-Bernardette (June 2002). The GSM System for Mobile Communications. Telecom Publishing.
  ISBN 978-0-945592-15-0
  .
• Salgues, Salgues B. (April 1997). Les télécoms mobiles GSM DCS. Hermes (2nd ed.). Hermes Sciences Publications.
  ISBN 978-2866016067
  .

External links

Wikimedia Commons has media related to GSM Standard.

• 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