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The Global System for Mobile Communications (GSM) is a second generation (2G) standard for mobile networks.
In the early 1980s, a group was formed by the European Telecommunications Standards Institute (ETSI) to develop a digital mobile communication system. Aptly named Groupe Speciale Mobile (GSM), its main task was to develop a single, consistent network for all of Europe and come up with a better and more efficient technical solution for wireless communication.
The GSM standard operates on three different carrier frequencies: the 900 MHz band, which was used by the original GSM system; the 1800 MHz band, which was added to support the swelling number of subscribers and the 1900 MHz frequency, which is used mainly in the U.S.
Although GSM is based on the time division multiple access (TDMA) system, its technology uses digital signaling and speech channels and is considered a second generation (2G) mobile phone system.
The GSM standard has given birth to wireless services like General Packet Radio Service (GPRS) and Enhanced Data Rates for GSM Evolution (EDGE). Its end users were the first to take advantage of an inexpensive implementation of SMS (short message system), which is more popularly known as texting.
Being a cellular network, GSM makes use of cells to provide wireless communication to subscribers who are in the vicinity of these cells. The four main cells that make up a GSM network are called macro, micro, pico and femto. Outdoor coverage is typically provided by macro and micro cells, while indoor coverage is usually provided by the pico and femto cells.
GSM phones may be identified by the presence of a Subscriber Identity Module (SIM). This tiny object, which is about as wide as a finger, is a removable smart card that contains a user’s subscription information, as well as some contact entries. This SIM card allows a user to switch from one GSM phone to another. In some countries, especially those in Asia, GSM phones are locked to a specific carrier. However, if a user manages to unlock a phone, he can insert any SIM from any carrier into the same phone.
One of the main advantages of the GSM standard is the ability to roam and switch carriers by using individual mobile units (if partner networks are located in their destination).