The Global System for Mobile communications (GSM) is a wireless telecommunications standard for digital cellular services. The original standard was optimized for voice communications and provided only circuit-switched data connections at a bit rate of 9.6 kbps and a short messages service (SMS). Later enhancements made higher bit rates and packet switched data possible. GSM is based on TDMA technology.
Although the roots of GSM are European, GSM is nowadays the biggest standard used for the 2nd generation of mobile communications. The success of GSM made roaming in big parts of the world possible.
GSM networks operate in different frequency ranges:
Besides these 3 bands the 850 MHz band and the 450 MHz band are used on a rather small scale.
A complete list of GSM bands is given in the table below.
|GSM400||GSM450||450,4 - 457,6||460,4 - 467,6|
|GSM480||478,8 - 486,0||488,8 - 496,0|
|GSM700||GSM750||777,0 - 792,0||747,0 - 762,0|
|GSM850||GSM850||824,0 - 849,0||869,0 - 894,0||Used in the Americas and Asia|
|GSM900||Primary GSM||890,0 - 915,0||935,0 - 960,0||The original GSM band.|
|Extended GSM||880,0 - 890,0||925,0 - 935,0||Extension of the primary band.|
|GSM Rail||876,0 - 880,0||921,0 - 925,0||Especially used for railways, for both safety related services and communications.|
|1 710 - 1 785||1 805 - 1 880|
|1 850 - 1 910||1 930 - 1 990||Mainly used in the Americas.|
See ARFCN for the exact frequencies of the radio channels.
The GSM network infrastructure consists of one or more Mobile Switching Centres (MSC) each connected to and controlling 2 or 3 Base Station Controllers (BSC). Each BSC is connected to and controlling a number of Base Transceiver Stations (BTS).