NB entity. The mobile sends the eNB entity the measurements in the RRC MeasurementReport message. Measurements carried out on the serving cell and neighboring cells are used for the selection of the cell and for the handover. Intra-frequency measurement, essential for mobility, is configured when connecting. 40 VoLTE and ViLTE Inter-frequency and inter-radio access technology (RAT) measurement can also be configured when connecting. As the mobile does not generally have several radio receivers, the inter- frequency and inter-RAT measurement should be performed at intervals arranged in the frame. The configuration of measurements to be performed by the mobile is triggered by the eNB entity in RRC ConnectionSetup, Connection Reconfiguration, ConnectionReestablishment messages. The measurement configurations to perform define the following parameters: - the object that identifies the radio channel; - the event triggering the measurement report; - the combination of objects and events; - the measurement of filtering parameters; - the periodicity of measurements. 2.3. S1-AP protocol The S1-AP protocol is the signaling exchanged between the eNB and MME entities over the S1-MME interface. The S1-AP protocol performs the following functions: - activation of the context of the mobile by the MME entity; establishment, modification and release of the EPS radio access bearer (E-RAB); - handover management; - paging. This procedure tells the eNB entity that the message needs to be broadcast in the cell; - transport of the NAS signaling exchanged between the mobile and the MME entity; - establishment of the S1-MME interface. Signaling Protocols Table 2.4 summarizes the S1-AP messages sent to paging, context management, bearer management, mobility management, management of the S1-MME interface and NAS messages transport. Function Request Response INITIAL CONTEXT INITIAL CONTEXT SETUP RESPONSE or SETUP REQUEST INITIAL CONTEXT Context management SETUP FAILURE UE CONTEXT RELEASE UE CONTEXT RELEASE COMMAND COMPLETE Function Request