1 GSM Principles and Call Flow

1.1 GSM Frequency Band Allocation
GSM cellular system can be divided into GSM900M and DCS1800M according to frequency band, with carrier frequency interval of 200 KHz and up and down frequencies as follows:

Table 1-1 GSM frequency allocation
Frequency band(MHz), Bandwidth(MHz), Frequency number, Carrier frequency number (pair)
GSM900 Up 890–915 Down 935–960, 25, 1–124, 124
DCS1800 Up 1710–1785 Down 1805–1880, 75, 512–885, 374

“Up” and “down” are classified according to base station. Base station transmitting - mobile station receiving is “down”; mobile station transmitting - base station receiving is up.
With the expanding services, GSM protocol adds EGSM(expanded GSM frequency band) and RGSM (expanded GSM frequency band including railway service) to the original GSM900 frequency band. The frequency band allocation is as follows:

Table 1-2 EGSM/RGSM frequency allocation
Frequency band(MHz), Bandwidth (MHz), Frequency number, Carrier frequency number (pair) EGSM Up 880–915 Down 925–960, 35, 0–124 , 975–1023, 174
RGSM Up 876–915 Down 921–960, 40, 0–124, 955–1023, 199