Question: What modifications are made to the procedure for untrusted non-3GPP access when applying it to trusted non-3GPP access?
Option 1: The UE is substituted by a TNAP, and the PDU Session is activated in step 1.
Option 2: The N3IWF is substituted by the TNGF, but no other modifications are made.
Option 3: The untrusted non-3GPP access point is retained, but the PDU Session is activated in step 3.
Option 4: The untrusted non-3GPP access is substituted by a TNAP, and the N3IWF is substituted by the TNGF, with the PDU Session activated in step 2.
Explanation: According to the text, when applying the procedure for untrusted non-3GPP access to trusted non-3GPP access, two modifications are made. Firstly, the untrusted non-3GPP access is substituted by a TNAP (Trusted Non-3GPP Access Point). Secondly, the N3IWF (Non-3GPP Interworking Function) is substituted by the TNGF (Trusted Non-3GPP Gateway Function), and the PDU Session is activated in step 2 as specified in clause 4.12a.5.