Question: When does the network initiate the paging procedure for an incoming mobile terminating SMS to a UE that is attached for EPS services with CIoT EPS optimization and has requested "SMS only"?
Option 1: Only when the UE is in NB-S1 mode and there is no NAS signalling connection.
Option 2: When the UE is in any mode, as long as there is no NAS signalling connection.
Option 3: When the UE is in NB-S1 mode, there is no NAS signalling connection, and no paging restriction is applied in the network.
Option 4: Only when the UE is not using eDRX.
Explanation: According to the specification, for a UE attached for EPS services with CIoT EPS optimization and requesting "SMS only", the network initiates the paging procedure when the UE is in NB-S1 mode, there is no NAS signalling connection, and no paging restriction is applied in the network. This ensures that the UE can receive the SMS even if it's not actively connected to the network.