Question: When must the User Equipment (UE) include the Additional GUTI Information Element (IE)?
Option 1: Only when the UE is in idle mode.
Option 2: If the Temporary Identity used in Next Generation Network (TIN) indicates "P-TMSI" and the UE holds a valid Globally Unique Temporary Identifier (GUTI), P-TMSI, and Routing Area Identifier (RAI); or if the UE performs an N1 mode to S1 mode inter-system change and the UE holds a valid GUTI.
Option 3: When the UE is in connected mode and has ongoing sessions.
Option 4: Only during initial attach procedures.
Explanation: The UE must include the Additional GUTI IE under specific conditions, which are when the TIN indicates "P-TMSI" and the UE holds a valid GUTI, P-TMSI, and RAI; or if the UE performs an N1 mode to S1 mode inter-system change and the UE holds a valid GUTI. This ensures that the network can properly identify and manage the UE's context during mobility and session management procedures.