Communications Engineering. The commercial start of GSM 900 with the aim to replace the analog first generation of mobile communications systems was in 1992. Short time thereafter, the technology and the standardization of GSM 1800 began. Due to the lesser knife-edge diffraction and the higher output power of GSM 900 terminals, greater ranges are feasible with the GSM 900 technology. Frequencies from 890 - 915 MHz are used for the uplink and frequencies from 925 - 960 MHz for the downlink.