Question: During an eNB handover with MME relocation in a 3GPP network, if the target MME supports a different set of NAS algorithms than the source MME, what action is taken regarding NAS keys and algorithm notification to the UE?
Option 1: The target MME continues using the existing NAS keys and algorithms without notifying the UE.
Option 2: The target MME re-derives the NAS keys from KASME using new NAS algorithm identities and sends a NAS Security Mode Command (SMC) to the UE, including an updated eKSI if applicable.
Option 3: The handover is cancelled, and the UE remains connected to the original eNB to maintain security integrity.
Option 4: The target MME uses default NAS algorithms predefined by the network manufacturer without re-deriving keys.
Explanation: This is the correct procedure for handling NAS algorithm changes during MME relocation. Re-deriving NAS keys from KASME with new algorithm identities ensures security continuity, and sending a NAS SMC with an updated eKSI (if AKA was run) notifies the UE of the changes, maintaining secure communication.