Section: 4.4.3.2 Replay protection
Content: Replay protection shall be supported for received NAS messages both in the AMF and the UE. However, since the realization of replay protection does not affect the interoperability between nodes, no specific mechanism is required for implementation. Replay protection assures that one and the same NAS message is not accepted twice by the receiver. Specifically, for a given 5G NAS security context, a given NAS COUNT value shall be accepted at most one time and only if message integrity verifies correctly. Replay protection is not applicable when 5G-IA0 is used.