Question: In 3GPP SAE networks, for interfaces between elements in the same security domain, what is the requirement for applying network layer security to secure signaling messages?
Option 1: Mandatory application of network layer security with IPsec protection
Option 2: Optional application of network layer security, dependent on additional security measures
Option 3: No mandate for protecting the interface with IPsec
Option 4: Always required in conjunction with certificate-based security
Explanation: When two entities are within the same security domain, network layer security does not require the protection of the interface using IPsec. This highlights different security handling for intra-domain vs. inter-domain communications.