asurement object, one or several reporting configurations can be defined (a reporting configuration defines the reporting criteria). Three reporting criteria are used: (1) event-triggered reporting, (2) periodic reporting, and (3) event-triggered periodic reporting. The associa- tion between a measurement object and a reporting configuration is created by a New Radio Access Layer 2/3 Aspects and System Operation 259 measurement identity (a measurement identity associates one measurement object and one reporting configuration of the same RAT). By using several measurement identities (one for each measurement object, reporting configuration pair), it is possible to associ- ate several reporting configurations to one measurement object and to associate one reporting configuration to several measurement objects [8]. The measurements identity is used when reporting results of the measurements. Measurement quantities are considered separately for each RAT. Measurement commands are used by NG-RAN to instruct the UE to start, modify, or stop measurements. Handover can be performed within the same RAT and/or CN, or it can involve a change of the RAT and/or CN. Inter-system fallback toward LTE RAN is performed for load balancing when 5GC does not support emergency ser- vices or voice services. Depending on certain criteria such as CN interface availabil- ity, network configuration, and radio conditions, the fallback procedure results in either connected-state mobility (handover procedure) or idle state mobility (redirec- tion) [8]. 2.5.1 Network-Controlled Mobility The mobility of the UEs in RRC_CONNECTED state is controlled by the network (net- work-controlled mobility), which is classified into two types of mobility, namely, cell-level mobility and beam-level mobility. The cell-level mobility requires explicit RRC signaling in order to be triggered, which results in handover. The main steps of the inter-gNB handover signaling procedures are illustrated in Fig. 2.27. The inter-gNB handover comprises the fol- lowing steps 