Content for  TS 23.501  Word version:  18.3.0

This clause describe the specific aspects for untrusted non-3GPP access, trusted non-3GPP access and W-5GAN access.

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.

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.

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. The UE mentioned in this clause corresponds to the 5G-RG in the case of W-5GAN and 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. A UE that successfully establishes a Non-3GPP Access Connection to the 5GC over a Non-3GPP access transitions to CM-CONNECTED state for the Non-3GPP access. In the case of Untrusted Non-3GPP access to 5GC, the Non-3GPP Access Connection corresponds to an NWu connection. In the case of Trusted access to 5GC, the Non-3GPP Access Connection corresponds to an NWt connection. In the case of N5CW devices access 5GC via trusted WLAN access networks, the Non-3GPP Access Connection corresponds to an Yt' connection. In the case of Wireline access to 5GC, the Non-3GPP Access Connection corresponds to a Y4 connection and to Y5 connection. A UE does not establish multiple simultaneous Non-3GPP Access Connection to the 5GC. The Non-3GPP Access Connection is released either as a result of an Explicit Deregistration procedure or an AN Release procedure. In the case of Untrusted Non-3GPP access, Trusted Non-3GPP access and W-5GAN access to 5GC, the N3IWF, TNGF, TWIF and W-AGF may in addition explicitly release the NWu, NWt, Yt', Y4 and Y5 signalling connection due to NWu, NWt, Yt', Y4 and Y5 connection failure, respectively. In the case of NWu and NWt, the release may be determined by the "dead peer detection" mechanism in IKEv2 defined in RFC 7296. In the case of Y4 and Y5 the release may be detected for example by lost of synchronisation of physical link, lost of PPPoE session, etc. Further details on how NWu, NWt, Yt', Y4 and Y5 connection failure is detected is out of scope of 3GPP specifications. For W-5GCAN, the W-AGF explicitly releases the N2 connection due to Y4 or Y5 connection failure, as determined by the "dead peer detection" mechanism in DOCSIS MULPI [89]. The release of the Non-3GPP Access Connection between the UE and the N3IWF, TNGF, TWIF or W-AGF shall be interpreted as follows:

• By the N3IWF, TNGF, TWIF and W-AGF as a criterion to release the N2 connection.
• By the UE as a criterion for the UE to transition to CM-IDLE. A UE registered over non-3GPP access remains in RM-REGISTERED state, unless the Non-3GPP Access Connection release occurs as part of a Deregistration procedure over non-3GPP access in which case the UE enters the RM-DEREGISTERED state. When the UE in RM-REGISTERED transitions to CM-IDLE, the UE non-3GPP Deregistration timer starts running in the UE. The UE non-3GPP Deregistration timer stops when the UE moves to CM-CONNECTED state or to the RM-DEREGISTERED state.

In the case of Non-3GPP access, when the AMF releases the N2 interface, the N3IWF, TNGF, TWIF and W-AGF shall release all the resources associated with the UE including the Non-3GPP Access Connection with the UE and its corresponding N3 resources. A release of the N2 connection by the AMF shall set the CM state for the UE in the AMF to CM-IDLE. An UE cannot be paged on Non-3GPP access network. When a UE registered simultaneously over a 3GPP access and a non-3GPP access moves all the PDU Sessions to one of the accesses, whether the UE initiates a Deregistration procedure in the access that has no PDU Sessions is up to the UE implementation. Release of PDU Sessions over the non-3GPP access does not imply the release of N2 connection. When the UE has PDU Sessions routed over the non-3GPP access and the UE state becomes CM-IDLE for the non-3GPP access, these PDU Sessions are not released to enable the UE to move the PDU Sessions over the 3GPP access based on UE policies. The core network maintains the PDU Sessions but deactivates the N3 user plane connection for such PDU Sessions.