mme finds the originally registered sgsn according to the p tmsi and rai and acquires ue context from the sgsn in this step an isr may be established between the sgsn and the mme s 514 the mme finds the corresponding msc vlr according to the globally unique temporary ue identity guti and the current location information included in the tracking area update message and initiates a cs update process to the msc vlr s 516 after registration the msc vlr returns an mme cs update response including location information lai and the temporary ue identify tmsi distributed by the msc vlr to the mme s 518 after update the mme returns to the ue a combined ta la update response including location information lai and tmsi registered in the msc vlr and location information tai list and temporary ue identification guti registered in the mme and flag of isr as activated through steps from s 510 to s 518 the ue implements registration in the mme a sgs association is established between the msc vlr and the mme and the isr function is activated s 520 ue accesses from the gsm umts network again due to movement of the user and because the isr has been activated and the current routing area has been registered the rau process will not be initiated s 522 because currently the e utran periodic tau timer in the ue still runs the timer will expire after a period of time herein it should be noted.