5.5.1 Registration Management

This clause applies to Non-3GPP access network corresponding to the Untrusted Non-3GPP access network, to the Trusted Non-3GPP access network and to the W-5GAN. In the case of W-5GAN the UE mentioned in this clause corresponds to 5G-RG or to the W-AGF in the case of FN-RG. In the case of N5CW devices access 5GC via trusted WLAN access networks, the UE mentioned in this clause corresponds to TWIF.

The UE shall enter RM-DEREGISTERED state and the AMF shall enter RM-DEREGISTERED state for the UE on non-3GPP access as follows:

• at the UE and at the AMF, after performing an Explicit Deregistration procedure;
• at the AMF, after the Network non-3GPP Implicit Deregistration timer has expired.
• at the UE, after the UE non-3GPP Deregistration timer has expired.

NOTE: This is assumed to leave sufficient time to allow the UE to re-activate UP connections for the established PDU Sessions over 3GPP or non-3GPP access.

Whenever a UE registered over non-3GPP access enters CM-IDLE state for the non-3GPP access, it starts the UE non-3GPP Deregistration timer according to the value received from the AMF during a Registration procedure.

Over non-3GPP access, the AMF runs the Network non-3GPP Implicit Deregistration timer. The Network non-3GPP Implicit Deregistration timer is started with a value longer than the UE's non-3GPP Deregistration timer, whenever the CM state for the UE registered over non-3GPP access changes to CM-IDLE for the non-3GPP access.

For a UE that is registered over Non-3GPP access, a change of the point of attachment (e.g. change of WLAN AP) shall not lead the UE to perform a Registration procedure.

A UE that is registered over non-3GPP access may trigger a Mobility Registration Update procedure via a new non-3GPP AN node (i.e. N3IWF or TNGF) to switch traffic from an old non-3GPP access to a new non-3GPP access.

Traffic switching from an old non-3GPP access to and from a wireline access is not supported in this Release.

Traffic switching from an old non-3GPP access to new non-3GPP access is supported only when PLMN of the new non-3GPP access is the same PLMN of the old non-3GPP access.

A UE shall not provide 3GPP-specific parameters (e.g. indicate a preference for MICO mode) during registration over a non-3GPP access.

During registration procedure the AMF may determine whether the serving N3IWF/TNGF is appropriate based on the slices supported by the N3IWFs/TNGFs as specified in clause 6.3.6 and clause 6.3.12 respectively.