RRC layer maintains two states, RRC-IDLE and RRC-CONNECTED. Similarly, MME maintains following states.
Once UE releases RRC connection with eNodeB it RRC state move to RRC-IDLE and at the same time, connection state moves from ECM-CONNECTED to ECM-IDLE at MME. In ECM-IDLE state, when downlink data arrives at SGW, it sends indication to MME. As result , MME initiates paging for UE.