In Europe, GSM was originally designed to operate at a frequency of 900 Mhz. At this frequency, the frequency of its use uplinks 890-915 MHz frequency, while the frequency of 935-960 MHz frequency downlinksnya. Bandwidth used is 25 MHz (915-890 = 960-935 = 25 MHz), and width of the canal amounted to 200 Khz. Of the two, then got 125 channels, in which 124 channels are used for voice and one channel for the signal. In its development, 124 of the channel increasingly inadequate in meeting the needs caused by rapidly growing number of users. To meet the needs of more channels, then the GSM regulators in Europe attempt to use additional frequency bands for GSM at 1800 MHz frequency range with frequency as a frequency of 1710-1785 MHz 1805-1880 MHz frequency uplinks and downlinks as frequency. With the new GSM frequency bands was then known as GSM 1800, which provides a bandwidth of 75 MHz (1880-1805 = 1785-1710 = 75 Mhz). With the wide canal that remains the same ie 200 Khz same, when the GSM at 900 Mhz frequency, then the GSM will be available in 1800 as many as 375 canals. In Europe, the GSM standards and is also used for railway communication, which became known as GSM-R.
Source : http://id.wikipedia.org/wiki/GSM#Spesifikasi_teknis_GSM