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The Cientra Advantage

Non-3GPP Interworking Function (N3IWF) for 5G

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.

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

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

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

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.

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.”

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

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.

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.

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.

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.

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


The functionality of N3IWF, in non-3GPP access encompasses the following aspects:

  • Handling the termination of N2 and N3 interfaces to the 5G Core Network for control-plane and user-plane operations, respectively.

  • Transmitting uplink and downlink control-plane NAS (N1) signaling between the UE and AMF.

  • Managing N2 signaling from SMF (relayed by AMF) about PDU Sessions and QoS.

  • Enforcing QoS corresponding to N3 packet marking, while considering the associated QoS requirements received over N2.

  • Implementing N3 user-plane packet marking in the uplink.

  • Supporting AMF selection

Figure: Non-roaming architecture for 5G Core Network with untrusted non-3GPP access

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