Location update results from two major causes in GSM system. One is when MS changes from old LAC to new LAC and the second is when the network notifies MS for periodic location update.
Network controls the location time interval and depends upon T3212 timer. Network broadcasts to all MSs in the cell by RIL3_RR SYSTEM INFORMATION TYPE3 message. T3212 timer is one of the system control parameters.
This parameter affects the overall service performance of the network and the utilization of the radio resource. For the area with higher traffic, the period could be bigger (for example 16 or 20 hours, even 25 hours); for the area with ordinary traffic, the value of T3212 could be smaller (for example 3 or 6 hours); for the area with extreme overload traffic, it is recommended to set T3212 as 0.