Question: What signaling protocol is used to release the user plane between the UE and N3IWF during CN-initiated selective deactivation of UP connection for an established PDU Session associated with non-3GPP Access?
Option 1: RRC signalling
Option 2: S1AP signalling
Option 3: IKEv2 signalling
Option 4: Diameter signalling
Explanation: During CN-initiated selective deactivation of UP connection for an established PDU Session associated with non-3GPP Access, the user plane between the UE and N3IWF is released using IKEv2 signalling. This is specified in clause 4.12.7 and is an exception to the general procedure described in clause 4.3.7.