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[[Singapore]] shut down 2G services entirely in April 2017.<ref>{{cite web |url=https://www.m1.com.sg/AboutM1/NewsReleases/2017/2G%20services%20to%20cease%20on%201%20April%202017.aspx |title=Joint Media Release by IMDA, M1, Singtel & StarHub: 2G services to cease on 1 April 2017 |publisher=M1 |date=2017-03-27 |accessdate=2017-10-22}}</ref>
[[Singapore]] shut down 2G services entirely in April 2017.<ref>{{cite web |url=https://www.m1.com.sg/AboutM1/NewsReleases/2017/2G%20services%20to%20cease%20on%201%20April%202017.aspx |title=Joint Media Release by IMDA, M1, Singtel & StarHub: 2G services to cease on 1 April 2017 |publisher=M1 |date=2017-03-27 |accessdate=2017-10-22}}</ref>


== Technical details ==
[[File:Gsm structures.svg|thumb|upright=1.6|The structure of a GSM network]]
{{Main|GSM services}}

=== 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 ===
=== Base-station subsystem ===
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* [[femtocell|femto]], and
* [[femtocell|femto]], and
* umbrella cells
* 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|base-station]] [[antenna (electronics)|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 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|small-business]] environments and connect to a [[telecommunications service provider]]'s network via a [[broadband internet|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]], and [[propagation (disambiguation)|propagation]] conditions – from a couple of hundred meters to several tens of kilometers. The longest distance the GSM specification supports in practical use is {{convert|35|km|mi|0}}. There are also several implementations of the concept of an extended cell,<ref>[http://www.allbusiness.com/electronics/computer-electronics-manufacturing/6838169-1.html Motorola Demonstrates Long Range GSM Capability – 300% More Coverage With New Extended Cell]. {{webarchive |url= https://web.archive.org/web/20120219003334/http://www.allbusiness.com/electronics/computer-electronics-manufacturing/6838169-1.html |date= 19 February 2012 }}</ref> 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 [[Cellular repeater|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 ====
{{Main|GSM frequency bands}}
GSM networks operate in a number of different [[carrier frequency]] ranges (separated into [[GSM frequency ranges]] for 2G and [[UMTS frequency bands]] for 3G), with most [[2G]] GSM networks operating in the 900&nbsp;MHz or 1800&nbsp;MHz bands. Where these bands were already allocated, the 850&nbsp;MHz and 1900&nbsp;MHz bands were used instead (for example in Canada and the United States). In rare cases the 400 and 450&nbsp;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&nbsp;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 [[time-division multiplexing|timeslots]] for individual phones. This allows eight full-rate or sixteen half-rate speech channels per [[radio frequency]]. These eight radio timeslots (or [[burst transmission|burst]] periods) are grouped into a [[Time-division multiple access|TDMA]] frame. Half-rate channels use alternate frames in the same timeslot. The channel data rate for all {{nowrap|8 channels}} is {{nowrap|270.833 kbit/s,}} and the frame duration is {{nowrap|4.615 ms.}}<ref>{{Cite web |title=GSM Frame Structure: Multiframe Superframe Hyperframe » Electronics Notes |url=https://www.electronics-notes.com/articles/connectivity/2g-gsm/frame-structure-superframe-hyperframe-multiframe.php |access-date=2023-02-09 |website=www.electronics-notes.com}}</ref>

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

==== Voice codecs ====
GSM has used a variety of voice [[codec]]s to squeeze 3.1&nbsp;kHz audio into between 7 and 13&nbsp;kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called [[Half Rate]] (6.5&nbsp;kbit/s) and [[Full Rate]] (13&nbsp;kbit/s). These used a system based on [[linear predictive coding]] (LPC). In addition to being efficient with [[bitrate]]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<ref>
{{cite web
| url= http://www.3gpp.org/ftp/Specs/archive/06_series/06.51/0651-401.zip
| publisher= ETSI |title= GSM 06.51 version 4.0.1
| date = December 1997
| format= ZIP |accessdate= 5 September 2007
}}
</ref>
with the [[enhanced full rate]] (EFR) codec, a 12.2&nbsp;kbit/s codec that uses a full-rate channel. Finally, with the development of [[UMTS]], EFR was refactored into a variable-rate codec called [[Adaptive Multi-Rate|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.

Delivery departmentdelete

=== Phone locking ===
Sometimes [[mobile network operator]]s restrict handsets that they sell for exclusive use in their own network. This is called [[SIM lock]]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. [[Brazil]] and [[Germany]]) all phones are sold unlocked due to the abundance of dual-SIM handsets and operators.<ref name="German_Unlock">{{cite news|url=https://www.nytimes.com/2007/11/21/technology/21iphone.html|title=iPhone Must Be Offered Without Contract Restrictions, German Court Rules|accessdate=2 February 2011|newspaper=The New York Times|year=2007|author=Victoria Shannon}}</ref>


==GSM security==
==GSM security==

Revision as of 11:54, 24 April 2023

For other uses, see GSM (disambiguation).
GSM
Industrytelecommunication
FoundedDecember 1991
Successor3G Edit this on Wikidata
Productsdigital cellular networks
Websitewww.gsma.com

The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets. GSM is also a trade mark owned by the GSM Association.[2] GSM may also refer to the Full Rate voice codec.[3]

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 (1G) analog cellular networks. The GSM standard originally described 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 General Packet Radio Service (GPRS), and Enhanced Data Rates for GSM Evolution (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 <n>G mobile phone technologies evolved from it.

|archiveurl=https://web.archive.org/web/20110519093843/http://gsmworld.com/about-us/history.htm |archivedate=19 May 2011 |accessdate=5 May 2011 |quote=1982 Groupe Speciale Mobile (GSM) is formed by the Confederation of European Posts and Telecommunications (CEPT) to design a pan-European mobile technology. |url-status=dead}}</ref>[6]

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 Du </ref> 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.[7] Singapore shut down 2G services entirely in April 2017.[8]


Base-station subsystem

Main article: Base station subsystem
GSM cell site antennas in the Deutsches Museum, Munich, Germany

GSM utilizes a cellular network, meaning that cell phones connect to it by searching for cells in the immediate vicinity. There are five different cell sizes in a GSM network:

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.[9]

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 non-repudiation.

GSM uses several cryptographic algorithms for security. The A5/1, A5/2, and A5/3 stream ciphers 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 FPGAs that allow A5/1 to be broken with a rainbow table attack.[10] 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, Karsten Nohl 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.[11] 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.[12] 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.[13]

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.[14]

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 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 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.[15][16][17]

Standards information

The GSM systems and services are described in a set of standards governed by ETSI, where a full list is maintained.[18]

GSM open-source software

Several open-source software projects exist that provide certain GSM features:[19]

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, there have been no lawsuits against users of OpenBTS over GSM use.[citation needed]

See also

References

  1. ^ Sauter, Martin (21 November 2013). "The GSM Logo: The Mystery of the 4 Dots Solved". Archived from the original on 4 March 2016. Retrieved 23 November 2013. [...] here's what [Yngve Zetterstrom, rapporteur of the Marketing 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!
  2. ^ "GSM BRANDS Trademark of GSM Sales LLC - Registration Number 5523328 - Serial Number 87703883 :: Justia Trademarks". trademarks.justia.com. Retrieved 9 February 2023.
  3. ^ "GSM Audio Codec: Vocoder: AMR, CELP etc .. » Electronics Notes". www.electronics-notes.com. Retrieved 9 February 2023.
  4. ^ Anton A. Huurdeman, The Worldwide History of Telecommunications, John Wiley & Sons, 31 July 2003, page 529
  5. ^ "GSM Global system for Mobile Communications". 4G Americas. Archived from the original on 8 February 2014. Retrieved 22 March 2014.
  6. ^ "Cellular History". etsi.org. European Telecommunications Standards Institute. 2011. Archived from the original on 17 February 2012. 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.
  7. ^ "Optus to complete 2G network turn off". Optus. 1 August 2017. Retrieved 20 November 2020.{{cite web}}: CS1 maint: url-status (link)
  8. ^ "Joint Media Release by IMDA, M1, Singtel & StarHub: 2G services to cease on 1 April 2017". M1. 27 March 2017. Retrieved 22 October 2017.
  9. ^ Solutions to the GSM Security Weaknesses, Proceedings of the 2nd IEEE International Conference on Next Generation Mobile Applications, Services, and Technologies (NGMAST2008), pp.576–581, Cardiff, UK, September 2008, arXiv:1002.3175
  10. ^ Steve. "The A5/1 Cracking Project". Retrieved 3 November 2011 – via Scribd.
  11. ^ Kevin J. O'Brien (28 December 2009). "Cellphone Encryption Code Is Divulged". The New York Times.
  12. ^ "A5/1 Cracking Project". Archived from the original on 25 December 2009. Retrieved 30 December 2009.
  13. ^ Owano, Nancy (27 December 2011). "GSM phones -- call them unsafe, says security expert". Archived from the original on 3 January 2012. Retrieved 27 December 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 Internet.
  14. ^ "Codebreaker Karsten Nohl: Why Your Phone Is Insecure By Design". Forbes.com. 12 August 2011. Retrieved 13 August 2011.
  15. ^ Lorenzo Franceschi-Bicchierai (12 June 2021). "Bombshell Report Finds Phone Network Encryption Was Deliberately Weakened". www.vice.com.
  16. ^ Christof Beierle; et al. (18 June 2021). "Cryptanalysis of the GPRS EncryptionAlgorithms GEA-1 and GEA-2" (PDF). Annual International Conference on the Theory and Applications of Cryptographic Techniques. Lecture Notes in Computer Science. 12697: 155–183. doi:10.1007/978-3-030-77886-6_6. ISBN 978-3-030-77885-9. S2CID 235452714. Archived (PDF) from the original on 16 June 2021.
  17. ^ Matthew Sparks (17 June 2021). "Flaw in old mobile phone encryption code could be used for snooping". New Scientist.
  18. ^ "GSM UMTS 3GPP Numbering Cross Reference". ETSI. Retrieved 30 December 2009.
  19. ^ Donald, Ene; Favour, Osagie Nosa (October 2016). "Analysing GSM Insecurity". International Journal of Research & Scientific Innovation. 3 (10): 10. ISSN 2321-2705. S2CID 212468467.
  20. ^ "Gsmd – Openmoko". Wiki.openmoko.org. 8 February 2010. Retrieved 22 April 2010.
  21. ^ "The Hacker's Choice Wiki". Archived from the original on 15 August 2010. Retrieved 30 August 2010.
  22. ^ "OsmocomBB". Bb.osmocom.org. Archived from the original on 26 February 2011. Retrieved 22 April 2010.
  23. ^ "YateBTS". Legba Inc. Retrieved 30 October 2014.

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.
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