Section: 5.6.1.6A Service request procedure for an emergency services fallback not accepted by the network
Content: If the service request for initiating an emergency services fallback cannot be accepted by the network, the UE shall perform the procedures as described in subclause 5.6.1.5, if the service request for initiating an emergency services fallback fails due to receiving the AUTHENTICATION REJECT message, the UE shall perform the procedures as described in subclauses 5.4.1.2.2.11, 5.4.1.2.3.1, 5.4.1.2.3A.1 or 5.4.1.3.5, and if the UE does not attempt to select an E-UTRA cell connected to EPC or 5GCN as described in subclause 5.6.1.5 and is camped on NR or E-UTRA cell connected to 5GCN in the same PLMN where the last service request was attempted, the UE shall inform the upper layers of the failure of the procedure. NOTE 1: This can result in the upper layers requesting another emergency call attempt using domain selection as specified in 3GPP TS 23.167[ IP Multimedia Subsystem (IMS) emergency sessions ]  [6]. If the service request for initiating an emergency services fallback fails due to abnormal cases a) in subclause 5.6.1.7, the UE shall inform the upper layers of the failure of the emergency services fallback. NOTE 2: This can result in the upper layers requesting another emergency call attempt using domain selection as specified in 3GPP TS 23.167[ IP Multimedia Subsystem (IMS) emergency sessions ]  [6]. If the service request procedure for initiating an emergency services fallback fails due to abnormal cases other than a) in subclause 5.6.1.7, the UE may abort the service request procedure, if not aborted already and attempt to select an E-UTRA cell connected to EPC or 5GCN according to the domain priority and selection rules specified in 3GPP TS 23.167[ IP Multimedia Subsystem (IMS) emergency sessions ]  [6]. If the UE finds a suitable E-UTRA cell, it then proceeds with the appropriate EMM or 5GMM procedures. If the UE operating in single-registration mode has changed to S1 mode, it shall disable the N1 mode capability for 3GPP access.