LTE:EPC
User Identifiers - IMSI and GUTI
IMSI A globle id that unique identifies a subscribe.It composed two parts : PLMN and MSIN , Also you know there is two part of PLMN: MCC and MNC , which is mobile country codes and mobile network (operators?) codes . why do operators need IMSI to unique identifies their subscribers? reasons have three: first is operator can tell wether allow one access in their network;second is choose what Qos to the subscriber and the Third, charging it according the services rendered to the subscriber.