In this chapter, we discuss the mobility management procedures that the network uses to keep track of the mobile's location.
The choice of mobility management procedures depends on the state that the mobile is in. Mobiles in RRC_IDLE use a mobile-triggered procedure known as cell reselection, whose objective is to maximize the mobile's battery life and minimize the load on the network. In contrast, mobiles in RRC_CONNECTED use the network-triggered procedures of measurements and handover, to give the base station the control it requires over mobiles that are actively transmitting and receiving. We begin the chapter by covering the procedures that switch a mobile between these states in response to changes in the user's activity, namely S1 release, paging and service requests, and continue by describing the mobility management procedures themselves.
Several specifications are relevant for this chapter. TS 36.304  defines the mobility management procedures that the mobile should follow in RRC_IDLE, while TS 23.401  and TS 36.300  describe the signalling procedures in RRC_CONNECTED and the procedures that switch the mobile between states. As usual, the relevant stage 3 specifications [4–8] define the details of the individual signalling messages. Another specification  defines the measurements that the mobile has to make in both RRC states and the corresponding performance requirements.