N3IWF Architecture

General Concepts to Support Non-3GPP Access

To enable connectivity of user equipment (UE) through non-3GPP access networks, such as WLAN access networks, the 5G Core Network provides support.

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We have taken advantage of 5G allowing multi-access technology to be adopted, mainly categorized as below:
• Non-3GPP wireless access networks
• Wireline access networks

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These non-3GPP access networks are deployed outside the Next-Generation Radio Access Network (NG-RAN).

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The 5G Core Network supports both non-3GPP access networks and 3GPP access networks (RANs).

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A Non-3GPP access network is connected to the 5G Core Network through a Non-3GPP InterWorking Function (N3IWF). N3IWF interface with the 5G Core Network CP (Control Plane) and UP (User Plane) functions via the N2 and N3 interfaces, respectively.

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A non-3GPP access network can advertise the Public Land Mobile Networks (PLMNs) or Selected Non-Public Networks (SNPNs) for which it supports connectivity, specifying the type of supported connectivity, such as “5G connectivity.”

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The decision to utilize non-3GPP access for connecting to a 5G PLMN is made by the UE through procedures specified by Cientra (API).

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When a UE opts for untrusted non-3GPP access to connect with a 5G Core Network in a PLMN, the following sequence is followed:

• The UE first selects a PLMN/SNPN.

• Then, the UE selects a non-3GPP access network that supports connectivity to the chosen PLMN. In this case, the selection of the non-3GPP access network is done by IoT.

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For a UE accessing the 5G Core Network over non-3GPP access, we support NAS (Non-Access Stratum) signaling with the 5G Core Network control-plane functions using the N1 reference point after UE registration.

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If a UE is registered with a PLMN over non-3GPP access, the UE performs PLMN selection for the 3GPP access regardless of this particular PLMN.

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Even after all the PDU Sessions for a UE over non-3GPP access have been released, it is possible to maintain the UE NAS signaling connection with the AMF over the non-3GPP access.

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The differentiation of user plane Quality of Service (QoS) between the IoT and N3IWF is supported.