Glossary definition of Global System for Mobile Communication

Also known as: GSM

GSM (Global System for Mobile Communications) is a second generation, cellular, digital mobile phone system, and it is one of the world's main 2G wireless standards, having become widely established in Europe and many other countries of the world. GSM operates in the three main frequency bands of 900 MHz, 1800 MHz, and 1900 MHz, which are known respectively as GSM 900, GSM 1800 and GSM 1900. In the USA, GSM is also known as PCS (Personal Communication Service), and it operates in the 1900 MHz frequency band, although GSM is not as common in North America as it is in Europe. For historical reasons the 1800 MHz band is also sometimes referred to as PCN (Personal Communication Network).

In order to make the most efficient use of its available frequency bands, and to provide maximum traffic-carrying capacity, GSM networks employ a combination of FDMA (frequency division multiple access) and TDMA (time division multiple access). Although GSM was primarily developed as a voice communication system, with a reliance on circuit switching techniques, there is also a limited data handling capability available through the Short Message Service (SMS), allowing the phone-user to send and receive text messages. Another characteristic of GSM, that is not evident to the user, is that it employs a slow frequency-hopping feature.

Many of the GSM network operators have set up roaming agreements with foreign operators, which enables subscribers to travel abroad and use their own mobile phones on the foreign networks. To help support seamless roaming, a common solution is the readily available dual-band and tri-band phones that automatically switch the phone standards as it moves from one network to the next.

The architecture within a GSM network consists of several basic elements, which each deal with the various communication stages and the routing of calls. These elements are the Base Transceiver Station (in each cell), Base Station Controller, Mobile Switching Centre and the Gateways, which act as interfaces between the mobile network and other parts of the public telephone system.

When handling calls, GSM networks also rely on a sophisticated process for authentication and security, including a number of other basic operating units such as the Home Location Register, Visitor Location Register, Equipment Identity Register and Authentication Centre, which together enable the network to perform checks on the identity and status of the subscriber and the phone. The SIM (Subscriber Identification Module) card is another essential element in the GSM operating system, and this card stores important data relevant to the phone and the user.

The abbreviation GSM originally stood for Groupe Spciale Mobile, which was the name of the sub-organisation of CEPT (French acronym for European Conference of Posts and Telecommunications) responsible for starting the standardisation process for GSM. Later the responsibility for GSM standards was transferred to the ETSI. The change in the meaning of the abbreviation reflects the international importance of this originally European mobile phone technology.

The GSM Association is responsible for the further development of the GSM standard, and they have a website at: