1.) First of all mobile+SIM should be detected by mobile station. 2.) Then it passes the signal to BTS of the area, (which is occured in BSS). 3.) Then it passes to the neareast MSC by this it is connected to HLR,VLR,AUC & OMC, (which is occur in NSS). 4.) from this it is connected to PSTN,ISDN,DATA NETWORK(this all is occur in public network)