Section: 10.2.1.3 UE in RM-REGISTERED state requests a PDU Session for IMS Emergency services
Content: The UE initiates the UE requested PDU session establishment procedure to receive emergency services as specified in clause 5.16.4 in TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. Since the UE already has a current 5G security context when it attempts to set up an IMS Emergency Session, the UE shall use this 5G security context to protect NAS, RRC and UP traffic. If the AMF successfully validates the PDU Session request for emergency bearer services using the current 5G security context, the AMF may accept this request and setup a PDU session. If the AMF attempts to re-authenticate the UE after receiving a correctly integrity protected request for emergency bearer services based on the current NAS security context and the authentication failed and if the serving network policy does not allow unauthenticated IMS Emergency Sessions, the UE and AMF shall proceed as for the initial registration error scenario as described in clause 6.1.3. If the AMF attempts to re-authenticate the UE after receiving a correctly integrity protected request for emergency bearer services based on the current NAS security context and the authentication failed and the serving network policy allows unauthenticated IMS Emergency Sessions, then the set up of the emergency bearers shall proceed in one of the two ways: a) The set-up proceeds according to clause 10.2.2. In this case, there is no need for the UE to re-attach, and the AMF requests the use of the NULL ciphering and integrity algorithms in the same way as described in clause 10.2.2.2 for the case of Emergency registration by UEs in limited service state. NOTE 1: If the authentication failure is detected in the AMF then the UE is not aware of the failure in the AMF, but still needs to be prepared, according to the conditions specified in TS 24.301[ Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 ] , to accept a NAS SMC from the AMF requesting the use of the NULL ciphering and integrity algorithms. NOTE 2: Regardless of if the authentication failed in the UE or in the AMF, the AMF can assume that the UE will accept that NULL integrity and ciphering algorithms are selected in the security mode control procedure b) The UE and the AMF continues using the current security context as described below for the case when primary authentication is executed while setting up a PDU session for emergency services. If primary authentication procedure is executed while setting up a PDU Session for emergency bearer services, the AMF and UE shall behave as follows: UE behavior: - Upon successful authentication verification in the UE, the UE shall continue using the current security context. - Alternatively, upon authentication verification failure in the UE, the UE shall send a failure message to the AMF and shall continue using the current security context. If the UE receives a NAS security mode command selecting NULL integrity and ciphering algorithms, the UE shall accept this as long as the IMS Emergency session progresses. AMF behavior: - If the serving network policy allows unauthenticated IMS Emergency Sessions, the AMF, after the unsuccessful authentication verification of the UE, should not send a reject an Authentication Reject message and continue using the current security context with the UE. - After receiving both, the EC Indication and the failure message from the UE, the AMF shall continue using the current security context with the UE for establishing an emergency bearer.