Question: What is the mandatory mode for implementing IPsec on the eNB for protecting S1-U and X2-U interfaces?
Option 1: Transport Mode with optional IKEv2
Option 2: Tunnel Mode with optional IKEv2
Option 3: Tunnel Mode IPsec is mandatory to implement on the eNB for X2-U and S1-U
Option 4: Both Transport and Tunnel Modes are equally mandatory for implementation
Explanation: Tunnel Mode IPsec is explicitly stated as mandatory for implementation on the eNB to ensure confidentiality, integrity, and replay protection for backhaul links (S1 and X2 user plane), highlighting the importance of secure data transmission between network elements.