Question: For DRBs (Data Radio Bearers) between a DeNB (Donor eNodeB) and an RN (Relay Node), what is the requirement for integrity protection for those carrying S1AP and/or X2AP signalling?
Option 1: Mandatory for all DRBs, regardless of the type of signaling they carry.
Option 2: Required for DRBs carrying S1AP and/or X2AP signalling, but optional for other DRBs.
Option 3: Optional for all DRBs, with the choice dependent on the specific implementation.
Option 4: Not required for any DRB between a DeNB and an RN.
Explanation: This is correct because integrity protection is specifically mandated for DRBs carrying S1AP and/or X2AP signalling to ensure security of control plane signals. For other DRBs, which may carry user plane data, integrity protection is not strictly required but can be implemented optionally, depending on the network's security policies.