GSM

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 2^nd generation of mobile communications. The success of GSM made roaming in big parts of the world possible.

GSM networks operate in different frequency ranges:

900 MHz,
the core band that is extended later (E-GSM);
1800 MHz,
1900 MHz,
used in South and North America.

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.

Band	Name	Uplink (MHz)	Downlink (MHz)	Remarks
GSM400	GSM450	450,4 - 457,6	460,4 - 467,6
GSM400	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.
GSM1800	GSM1800 (DCS1800)	1 710 - 1 785	1 805 - 1 880
GSM1900	GSM1900 (PCS1900)	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).