Question: For a Relay Node (RN) to enroll a device certificate prior to attaching to a Donor eNB (DeNB), which of the following is a valid method for establishing the required IP connectivity, assuming no secure channel on the Un interface has been established?
Option 1: Utilize an existing secure tunnel from a neighboring RN to access the Registration Authority (RA).
Option 2: Attach to an eNB like a normal User Equipment (UE) using a different Universal Subscriber Identity Module (USIM), known as USIM-INI, without requiring a secure channel between the RN and USIM-INI.
Option 3: Leverage the DeNB's existing IP connectivity by temporarily acting as a UE to access the RA directly.
Option 4: Employ a satellite uplink to connect directly to the RA for certificate enrollment.
Explanation: According to the security architecture, an RN can establish IP connectivity for certificate enrollment by attaching to an eNB as if it were a normal UE using a USIM-INI (different from the USIM-RN), without needing a secure channel between the RN and USIM-INI, allowing controlled access through APN restrictions based on the USIM-INI subscription profile.