Question: During an RRC connection resume to the same eNB, what action does the MME take if its local policy indicates a new NH (Next Hop) derivation is needed after receiving the S1-AP UE Context Resume Request message?
Option 1: The MME keeps its NCC (Next Hop Chain Counter) value unchanged and reuses the existing NH.
Option 2: The MME increases its locally kept NCC value by one and computes a fresh NH from its stored data, then sends this new pair to the eNB.
Option 3: The MME requests additional UE context information from the eNB before making a decision on NH derivation.
Option 4: The MME ignores the local policy check for NH derivation during an RRC connection resume to the same eNB.
Explanation: When resuming an RRC connection to the same eNB and the MME's local policy requires a new Next Hop (NH) derivation, the MME must update its security context. This involves incrementing the NCC (Next Hop Chain Counter) by one and calculating a fresh NH based on stored data, as defined in Annex A.4 of the relevant 3GPP specification. The updated {NH, NCC} pair is then communicated to the eNB for storage and potential use in future suspend/resume or X2-handover procedures, ensuring security context freshness even when resuming within the same cell.