Network-initiated Service Request Procedure
The network-initiated service request procedure is used when the peer network needs to communicate (for example, User Plane connection activation for PDU sessions to deliver mobile terminating user data) with a UE. If the UE is in CM-IDLE state or CM-CONNECTED state in 3GPP access, the network initiates a Network Triggered Service Request procedure. If the UE is in CM-IDLE state, and asynchronous type communication is not activated, the network sends a Paging Request to (R)AN or UE. The Paging Request triggers the UE Triggered Service Request procedure in the UE. If asynchronous type communication is activated, the network stores the received message and forwards the message to the (R)AN and/or the UE (that is, it synchronizes the context with the (R)AN and/or the UE) when the UE enters CM-CONNECTED state.