5G Non-3GPP Access

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The 5G Core Network supports the connectivity of the UE via non-3GPP access networks, e.g. WLAN access.

Only the support of non-3GPP access networks deployed outside the NG-RAN (referred to as "standalone" non-3GPP accesses) is described in this clause.

In this Release of the specification, 5G Core Network only supports untrusted non-3GPP accesses.

Non-3GPP access networks shall be connected to the 5G Core Network via a Non-3GPP InterWorking Function (N3IWF). The N3IWF interfaces the 5G Core Network CP and UP functions via N2 and N3 interfaces, respectively.

The N2 and N3 reference points are used to connect standalone non-3GPP accesses to 5G Core Network control-plane and user-plane functions respectively.

A UE that accesses the 5G Core Network over a standalone non-3GPP access shall, after UE attachment, support NAS signalling with 5G Core Network control-plane functions using the N1 reference point.

When a UE is connected via a NG-RAN and via a standalone non-3GPP access, multiple N1 instances shall exist for the UE i.e. there shall be one N1 instance over NG-RAN and one N1 instance over non-3GPP access.

A UE simultaneously connected to the same 5G Core Network of a PLMN over a 3GPP access and a non-3GPP access shall be served by a single AMF if the selected N3IWF is located in the same PLMN as the 3GPP access.

When a UE is connected to a 3GPP access of a PLMN, if the UE selects the N3IWF and the N3IWF is located in a PLMN different from the PLMN of the 3GPP access, e.g. in a different VPLMN or in the HPLMN, the UE is served separately by the two PLMNs. The UE is registered with two separate AMFs. PDU Sessions over the 3GPP access are served by V-SMFs different from the V-SMF serving the PDU Sessions over the non-3GPP access.

The PLMN selection for the 3GPP access does not depend on the N3IWF selection. If a UE is registered over a non-3GPP, the UE performs PLMN selection for the 3GPP access independently of the PLMN to which the N3IWF belongs.

A UE shall establish an IPSec tunnel with the N3IWF to attach to the 5G Core Network over untrusted non-3GPP access. The UE shall be authenticated by and attached to the 5G Core Network during the IPSec tunnel establishment procedure. Further details for UE attachment to 5G Core Network over untrusted non-3GPP access

It shall be possible to maintain the UE NAS signalling connection with the AMF over the non-3GPP access after all the PDU Sessions for the UE over that access have been released or handed over to 3GPP access.

N1 NAS signalling over standalone non-3GPP accesses shall be protected with the same security mechanism applied for N1 over a 3GPP access.

User plane QoS differentiation between UE and N3IWF is supported as described