Question: What triggers the derivation of a fresh S-KeNB by the MeNB during an existing SeNB connection, aside from initial offload or modification requiring key update?
Option 1: Exhaustion of radio bearer identity space in the SeNB.
Option 2: Addition of a new User Equipment (UE) to the SeNB.
Option 3: Change in the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) configuration.
Option 4: Periodic security key refresh as per 3GPP specifications.
Explanation: When the MeNB cannot allocate an unused radio bearer identity for a new radio bearer in the SeNB due to radio bearer identity space exhaustion, it updates the SCG Counter and computes a fresh S-KeNB, ensuring continuous secure communication by updating encryption and integrity keys for affected radio bearers between the SeNB, UE, and MeNB.