Question: In which substate does a UE enter when the registration procedure for mobility and periodic registration update fails due to a missing response from the network?
Option 1: 5GMM-DEREGISTERED
Option 2: 5GMM-REGISTERED.ATTEMPTING-REGISTRATION
Option 3: 5GMM-IDLE
Option 4: 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE
Explanation: The UE enters the substate 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE when the registration procedure for mobility and periodic registration update fails due to a missing response from the network, as specified in the 3GPP TS 24.501 standard. This substate is chosen by the UE under these specific circumstances, indicating that the UE will attempt to re-register with the network.