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

N3IWF Architecture

The Cientra IoT Gateway is like N3IWF and many more features added to it. The core interfacing N2/N3 follows the architecture of the 5G System, which operates based on a service-oriented architecture. The interaction between network functions is represented in two distinct ways.

Firstly, there is a service-based representation where network functions, such as AMF (Access and Mobility Management Function), provide access to their services for other authorized network functions within the Control Plane. This representation includes the use of point-to-point reference points whenever necessary.

Secondly, User plane NF (Network Function – UPF) services within the network functions with control nodes. N11 connects AMF and SMF. Network functions within the 5GC Control Plane exclusively employ service-based interfaces for their interactions, as depicted in the 3GPP diagram depicted below.

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Figure: Non-Roaming 5G System Architecture

Support of non-3GPP access

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 advantages 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) pertaining to 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