An eUE initiates a TAU procedure in the following scenarios:
1) The TA of a registered eUE has changed. That is, after a cell reselection or handover, the new TA is not included In the TAI list.
2) The T3412 timer expires. (This scenario occurs only in the RRC IDLE state.)
3) The eUE's RRC connection is released due to the cause "load re-balancing TAU required."
4) The network capability or DRX parameters for the eUE have been changed.
5) A registered eUE moves to an uncovered area, and the local EPS bearer for the eUE is deactivated. The eUE then moves to a covered area.
6) The eUE performs an inter-RAT cell reselection, and the user-plane data is not buffered.