Question: During an inter-RAT handover to E-UTRA initiated by another RAT or E-UTRA connected to a different Core Network (CN) type, what action does E-UTRAN take regarding security if it was not already activated in the source RAT or CN?
Option 1: Activate ciphering, possibly using NULL algorithm.
Option 2: Deactivate all existing ciphering algorithms for seamless handover.
Option 3: Request UE to change its security protocol before proceeding.
Option 4: Ignore security activation until the handover is complete.
Explanation: During an inter-RAT handover to E-UTRA, ensuring continuity and security of the connection is crucial. Activating ciphering (even with a NULL algorithm as a placeholder or for specific scenarios) is a step to secure the new connection if it wasn't already secured in the previous setup, thus maintaining or initiating a level of encryption for the ongoing communication. This action aligns with standard practices in telecommunications for handover procedures, prioritizing security.