GSM ( Global System for Mobile Communications ) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation mobile networks used by mobile devices such as tablets , was first used in Finland in December 1991. By 2014, it has become a global standard for mobile communications - with over 90% market share, operating in over 193 countries and territories.
The 2G network was developed as a replacement for the first generation (1G) analog cellular network, and the GSM standard was originally described as digital, circuit-switched networks optimized for full-duplex voice phones. It extends over time to enter data communications, first by circuit-switched transport, then by packet data transmission via GPRS (General Packet Radio Services) and EDGE (Enhanced Data rates for GSM Evolution, or EGPRS).
Furthermore, 3GPP is developing a third generation UMTS standard (3G), followed by fourth generation (4G) LTE Advanced standards, which do not form part of the GSM ETSI standard.
"GSM" is a trademark owned by the GSM Association. It can also refer to the most commonly used (initially) voice codec, Full Rate.
Video GSM
Histori
In 1983 work began to develop European standards for digital cellular voice telecommunications when the European Conference of Post and Telecommunications Administration (CEPT) established the Groupe Spà © cial Mobile committee and subsequently 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 regulations authorized to make GSM a compulsory standard. The decision to develop continental standards eventually resulted in a unified, open, standards-based network larger than that in the United States.
In February 1987 Europe produced the first GSM Technical Specifications agreed upon. Ministers from the four major EU nations strengthened their political support for GSM with the Bonn Declaration on Global Information Networks in May and the GSM MoU was submitted for signature in September. The MoU attracted mobile operators from across Europe to promise to invest in new GSM networks to an ambitious shared date.
In this brief 38-week period, all of Europe (countries and industries) have been brought behind the GSM in a rare unity and speed is guided by four public officials: Armin Silberhorn (Germany), Stephen Temple (UK), Philippe Dupuis (France) and Renzo Failli (Italy). In 1989, Groupe Spà © cial Mobile Committee was transferred from CEPT to the European Telecommunications Standards Institute (ETSI).
In parallel France and Germany signed a joint development agreement in 1984 and joined Italy and the UK in 1986. In 1986, the European Commission proposed the ordering of the 900 MHz spectrum band for GSM. Former Finnish Prime Minister Harri Holkeri made the world's first GSM call on July 1, 1991, calling Kaarina Suonio (the mayor of Tampere) using a network built by Telenokia and Siemens and operated by Radiolinja. The following year saw delivery of the first short message service (SMS or "text messaging"), and Vodafone UK and Telecom Finland signed the first international roaming agreement.
Work began in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network began operations in the UK in 1993, called DCS and 1800. Also that year, Telecom Australia became the first network operator to deploy GSM networks. outside Europe and the first practical GSM handset available.
In 1995 faxes, data and SMS messaging services were launched commercially, the first 1900 MHz GSM network became operational in the United States and GSM customers worldwide exceeded 10 million. In the same year, the GSM Association was formed. The pre-paid GSM SIM card was launched in 1996 and GSM customers worldwide graduated 100 million in 1998.
In 2000, the first commercial GPRS service was launched and the first compatible GPRS handset became available for sale. In 2001, the first UMTS (W-CDMA) network was launched, 3G technology that is not part of GSM. GSM customers worldwide exceed 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. The EDGE service first operated on the network in 2003, and the number of GSM subscribers worldwide exceeded 1 billion in 2004.
In 2005 the GSM network accounted for over 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 was launched in 2007. (High Speed ​​Package Access (HSPA) and uplink and downlink version are 3G technologies, not part of GSM.) GSM subscribers worldwide exceeded three billion in 2008.
The GSM Association estimates in 2010 that the technology set in the GSM standard serves 80% of the mobile market, spanning over 5 billion people in over 212 countries and regions, making GSM the most among many standards for mobile networks.
GSM is the second generation standard (2G) that uses time-sharing multi-access divisions (TDMA), issued by the European Telecommunications Standards Institute (ETSI). The GSM standard does not include 3G Mobile Universal Commun Telecommunications System (UMTS) dual access code sharing (CDMA) technology or 4G LTE orthogonal frequency-division double access (OFDMA) technology standard issued by 3GPP.
GSM, for the first time, sets a common standard for Europe for wireless networks. It was also adopted by many countries outside Europe. This allows customers to use other GSM networks that have roaming agreements with each other. Common standards reduce research and development costs, as hardware and software can be sold with little adjustment for local markets.
Telstra in Australia closed its 2G GSM network on December 1, 2016, the first mobile network operator to disable GSM networks. The second mobile provider to shut down its GSM network (on January 1, 2017) is AT & amp; T Mobility from the United States. Optus in Australia completed the closing of the GSM 2G network on August 1, 2017, part of the GSM Optus network covering Western Australia and the Northern Territory at the beginning of the year closed in April 2017. Singapore closed its 2G service entirely in April. 2017.
Maps GSM
Technical details
Network structure
This network is organized into separate sections:
- The base station subsystem - base station and their controllers explain
- Moving Networks and Subsystems - parts of networks that are most similar to fixed networks, sometimes simply called "core networks"
- GPRS Core Network - an optional part that enables packet-based Internet connections
- Operating support system (OSS) - network maintenance
Basic station subsystem
GSM is a mobile network, which means the phone is connected to it by searching for nearby cells. There are five different cell sizes in the 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 considered as cells in which a base station antenna is mounted on a pole or building above the average roof level. Micro cells are cells whose antenna height is below the average roof level; they are usually used in urban areas. Picnic cells are small cells with a diameter of a few dozen meters; they are mainly used indoors. Femtocells are cells that are designed to be used in residential or small business environments and connect to network service providers via broadband internet connections. The umbrella cell is used to cover the smaller shadow areas of the cell and fill the gap in coverage between the cells.
The cell's horizontal radius varies depending on the height of the antenna, the antenna gain, and the propagation conditions from several hundred meters to several tens of kilometers. The longest distance supported by GSM specifications in practical use is 35 kilometers (22 mi). There are also several implementations of the extended cell concept, in which the radius of a cell can be double or even more, depending on the antenna system, field type, and forward time.
Indoor coverage is also supported by GSM and can be achieved using an indoor picocell base station, or indoor repeater with a distributed indoor antenna that flows through power splitters, to transmit radio signals from outdoor antennas to separate distributed antenna systems. This is typically used when significant call capacity is needed indoors, such as in a shopping center or airport. However, this is not a prerequisite, since indoor coverage is also provided by the penetration of radio signals from within nearby cells.
GSM carrier frequency
The GSM network operates in a number of different carrier frequency ranges (separated into the GSM frequency range for the 2G and UMTS bands for 3G), with most GSM 2G networks operating in the 900Ã, MHz or 1800Ã, MHz bands. When these tapes have been allocated, the bands 850 MHz and 1900 MHz are used instead (eg in Canada and the United States). In rare cases, the bands 400 and 450 MHz are assigned in some countries because they were previously used for first generation systems.
By comparison, most 3G networks in Europe operate in the 2100 MHz frequency band. For more information on using GSM frequencies worldwide, refer to the GSM frequency band.
Regardless of the frequency chosen by the operator, this is divided into time slots for each phone. This allows eight full-or half-rate speech channels per radio frequency. These eight radio timeslots (or burst periods) are grouped into TDMA frames. Half-level channels use alternate frames in the same time slot. Channel data rate for all 8 channels is 270.833 kbit/s, and frame length 4,615 ms.
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 .
Sound codec
GSM has used various voice codecs to squeeze 3.1 kHz audio to between 6.5 and 13 kbit/s. Initially, two codecs, named after the type of data channel allocated, are used, called Half Rate (6.5 Kbit/s) and Full Rate (13 Kbit/s). It uses a system based on linear prediction coding (LPC). In addition to efficient bitrate, the codec also makes it easier to identify the more important audio parts, allowing the air interface layer to prioritize and better protect these signal parts. GSM was further upgraded in 1997 with an improved codec rate (EFR), a 12.2 kbit/s codec that uses full-rate channels. Finally, with the development of UMTS, EFR is reactorized into a variable-rate codec called AMR-Narrowband, which is of high quality and resilient to interference when used on full-speed channels, or less strong but still of relatively high quality when used in good condition. radio conditions on a half-tariff channel.
Subscriber Identity Module (SIM)
One of the main features of GSM is the Customer Identity Module, commonly known as SIM card . SIM is a removable smart card that contains user and phone subscription information. This allows the user to save the information after switching the handset. Alternatively, the user can change the carrier while maintaining the handset simply by changing the SIM. Some operators will block this by allowing the phone to use only one SIM, or only the SIM issued by them; this practice is known as SIM locking.
Phone lock
Sometimes mobile network operators limit the handsets they sell for use with their own networks. This is called locking and is implemented by the phone software feature. Customers can usually contact the provider to remove the key for a fee, utilize the personal service to remove the key, or use the software and website to unlock the handset itself. You can hack through a phone that is locked by the network operator.
In some countries (eg Bangladesh, Belgium, Brazil, Canada, Chile, Germany, Hong Kong, India, Iran, Lebanon, Malaysia, Nepal, Pakistan, Poland, Singapore, South Africa, Thailand) all phones are unlocked.
GSM Security
GSM is meant to be a secure wireless system. It has considered user authentication using pre-shared keys and challenge responses, and over-the-air encryption. However, GSM is vulnerable to various types of attacks, each intended for different parts of the network.
UMTS development introduces an optional Universal Idential Identity Module (USIM), which uses longer authentication keys to provide greater security, and authenticate networks and users, while GSM only authenticates users to the network (and not vice versa). Therefore, the security model offers confidentiality and authentication, but the authorization capabilities are limited, and there is no refusal.
GSM uses several cryptographic algorithms for security. The A5/1, A5/2, and A5/3 stream ciphers are used to ensure over-the-air sound privacy. A5/1 developed first and is a more powerful algorithm used in Europe and the United States; A5/2 is weaker and is used in other countries. A serious drawback has been found in both algorithms: it is possible to solve A5/2 in real-time with ciphertext-only attacks, and in January 2007, The Hacker's Choice initiated the A5/1 crack project with plans to use FPGAs that allow A5/1 to be broken with a rainbow table attack. This system supports several algorithms so that the operator can replace the cipher with a more powerful.
Since 2000 various attempts have been made to solve the A5 encryption algorithm. Both A5/1 and A5/2 algorithms have been damaged, and their cryptanalysis has been revealed in the literature. For example, Karsten Nohl developed a number of rainbow tables (static values ​​that reduce the time required for an attack) and have found new sources for famous text attacks. He said that it is possible to build "complete GSM interceptor... from open source components" but they do not do so because of legal issues. Nohl claims that he is able to bypass voice and text conversations by emulating other users to listen to voicemail, make calls, or send text messages using Motorola phones and the seven-year-old decryption software available online for free.
GSM uses General Packet Radio Service (GPRS) for data transmission such as surfing the web. The most commonly used GPRS Ciphers were publicly damaged in 2011.
The researchers revealed the deficiencies in the commonly used GEA/1 and GEA/2 ciphers and published the open source gprsdecode software to sniff out the GPRS network. They also note that some operators do not encrypt data (that is, using GEA/0) to detect the use of traffic or protocols that they do not like (eg, Skype), leaving customers unprotected. GEA/3 seems relatively difficult to solve and is said to be used on some of the more modern networks. If used with USIM to prevent connections to counterfeit base stations and downgrade attacks, users will be protected in the medium term, although a 128-bit GEA/4 migration is still recommended.
Default information
GSM systems and services are described in a set of standards set by ETSI, where the complete list is maintained.
GSM open source software
Some open source software projects exist that provide certain GSM features:
- gsmd daemon by Openmoko
- OpenBTS develops Base transceiver stations
- GSM Software Project aims to build a GSM analyzer of less than $ 1,000
- OsmocomBB developers intend to replace baseband GSM stack with free software implementation
- YateBTS developed Base transceiver station
Problems with patents and open source
Patents remain an issue for open-source GSM implementations, as it is not possible for GNU or other free software distributors to secure immunity from all patent lawsuits against the user. Furthermore, new features are added to the standard all the time which means they have patent protection for several years.
The original GSM implementation from 1991 can now be completely free of the patent freeze, but patent freedom is uncertain because the "first to create" United States system existed until 2012. The "first to find" system, plus "Patent adjustment" can extend the age of the US patent far exceeds 20 years from its priority date. It is unclear at this time whether OpenBTS will be able to implement unlimited initial feature specifications. However, once the patent expires, the features can be added to the open-source version. In 2011, there was no lawsuit against OpenBTS users through the use of GSM.
See also
References
Further reading
- Redl, Siegmund M.; Weber, Matthias K.; Oliphant, Malcolm W (February 1995). Introduction to GSM . Artech House. ISBN: 978-0-89006-785-7. Ã,
- Redl, Siegmund M.; Weber, Matthias K.; Oliphant, Malcolm W (April 1998). GSM and Personal Communication Handbook . Mobile Communication Library Artech House. Artech House. ISBN: 978-0-89006-957-8.
- Hillebrand, Friedhelm, ed. (December 2001). GSM and UMTS, Creation of Global Mobile Communications . John Wiley & amp; Children. ISBN 978-0-470-84322-2.
- Mouly, Michel; Pautet, Marie-Bernardette (June 2002). GSM System for Mobile Communications . Telecommunication Issuance. ISBN 978-0-945592-15-0.
- Salgues, Salgues B. (April 1997). Les tÃÆ'Â © lÃÆ' Â © coms GSM DCS phone . Hermes (2nd ed.). Publications of Hermes Sciences. ISBN: 2866016068.
External links
- GSM Association - Official industry trade group representing GSM network operators worldwide
- 3GPP - 3G GSM standard development group
- LTE-3GPP.info: GSM online message decoder fully supports all 3GPP releases from initial GSM up to the latest 5G
Source of the article : Wikipedia
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