Section: 4.6.3.2 ECM-CONNECTED
Content: The UE location is known in the MME with an accuracy of a serving eNodeB ID. The mobility of UE is handled by the handover procedure, except for when the NB-IoT is being used, in which case there are no handover procedures. The UE performs the tracking area update procedure when the TAI in the EMM system information is not in the list of TA's that the UE registered with the network, or when the UE handovers to an E-UTRAN cell and the UE's TIN indicates "P-TMSI". For a UE in the ECM-CONNECTED state, there exists a signalling connection between the UE and the MME. The signalling connection is made up of two parts: an RRC connection and an S1_MME connection. The UE shall enter the ECM-IDLE state when its signalling connection to the MME has been released or broken. This release or failure is explicitly indicated by the eNodeB to the UE or detected by the UE. The S1 release procedure or, if the UE is enabled to use User Plane CIoT EPS Optimisation the S1 Connection Suspend procedure (clause 5.3.4A) changes the state at both UE and MME from ECM-CONNECTED to ECM-IDLE. NOTE 1: The UE may not receive the indication for the S1 release, e.g. due to radio link error or out of coverage. In this case, there can be temporal mismatch between the ECM-state in the UE and the ECM-state in the MME. After a signalling procedure, the MME may decide to release the signalling connection to the UE, after which the state at both the UE and the MME is changed to ECM-IDLE. NOTE 2: There are some abnormal cases where the UE transitions to ECM-IDLE. When a UE changes to ECM-CONNECTED state and the network initiates establishment of data radio bearers, then if a data radio bearer cannot be established, or the UE cannot maintain a data radio bearer in the ECM-CONNECTED state during handovers, the corresponding EPS bearer is deactivated. An exception to this is when the UE has been informed by the MME that a specific EPS bearer will never use a data radio bearer (e.g. because that EPS bearer is for a connection to the SCEF).