Question: When can a UE initiate a registration procedure for mobility and periodic registration update to request WUS assistance information?
Option 1: After the UE has an emergency PDU session established.
Option 2: During a registration procedure for initial registration for emergency services.
Option 3: When the UE is in the state 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE and has an emergency PDU session established.
Option 4: After the emergency PDU session is released over 3GPP access, if a UE supporting WUS assistance information did not receive the Negotiated WUS assistance information IE during the last registration procedure due to an active emergency PDU session over 3GPP access.
Explanation: According to the text, if a UE supporting WUS assistance information did not receive the Negotiated WUS assistance information IE during the last registration procedure due to an active emergency PDU session over 3GPP access, the UE shall initiate a registration procedure for mobility and periodic registration update to request WUS assistance information after the emergency PDU session is released over 3GPP access.