4.9.3 Disabling and re-enabling of UE's N1 mode capability for non-3GPP access

When the UE disables the N1 mode capability for non-3GPP access, the UE NAS layer shall not initiate any 5GS NAS procedures towards the network over non-3GPP access.

When the UE supporting both N1 mode and S1 mode needs to stay in non-3GPP access connected to EPC (e.g. due to the domain selection for UE originating sessions as specified in clause 4.3.2), in order to prevent unintentional selection of a non-3GPP access network connected to 5GCN, the UE operating in single-registration mode shall not transfer any PDN connection to a non-3GPP access network connected to the 5GCN.

If the disabling of N1 mode capability for non-3GPP access was due to IMS voice is not available over non-3GPP access in 5GS and the UE's usage setting is "voice centric", the UE shall re-enable the N1 mode capability for non-3GPP access when the UE's usage setting is changed from "voice centric" to "data centric" as specified in clauses 4.3.3.

The UE shall re-enable the N1 mode capability for non-3GPP access when a new PLMN or SNPN is selected over non-3GPP access.

The UE may disable the N1 mode capability for the current PLMN or SNPN over non-3GPP access if no network slice is available for the current PLMN or SNPN.

As an implementation option, the UE may start a timer for re-enabling the N1 mode capability for non-3GPP access, after the N1 mode capability for non-3GPP access was disabled. On the expiry of this timer, the UE should re-enable the N1 mode capability for non-3GPP access.