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N3IWF- A brief introduction

3GPP is a global collaboration of telecommunications standards organizations that develops the technical specifications for mobile networks, including:

3G (UMTS)
4G (LTE)
5G (5G NR, 5G Core)
Now working on 6G concepts (as of 2025)

3GPP has defined many functions and standard for 5G communications. One of them is N3IWF.

N3IWF stands for Non-3GPP Interworking Function, it is officially part of the 5G standard.

1. Major components in a 5G and where 5G-Core lies

A 5G mobile system can be broken in following three major components:

1. UE (e.g. A phhone)
2. gNB: Basestaion with antenna that provides connectivity to UE
3. 5G Core: A backend system that provides actualy functionality e.g.
user-authentication, internet access, communication among users etc.

An anology: 

UE (Your phone) = A car
gNB (5G tower) = The on-ramp to the highway
5G Core = The traffic control center that:
    authenticates: Checks who you are
    routes your data: Allows you onto the highway, and routes you to the right destination
    security: keeps your data private and secure

2. What are 5G-Core functions

A 5G Core is an important part of 5G infrastructure which: 

- Handles connections and movement between towers
- Stores your subscriber info and identity information
- Actually moves your data (like video, messages) across the network
- Keeps your data private and secure (encryption)
It implements major 5G functions and protocols such as AMF, SMF, UPF, N3IWF, etc.

Where does N3IWF fit

N3IWF function of 5G lies AFTER gNB, hence it is part of 5G-Core components. In order to be able to use it, the 5G-core implementaiton must support N3IWF functionality.

3. Connection without N3IWF (Traditional)

A user equipement (UE) such as a mobile phone is connected to the core network through a basestation. This requires antennas and necessary equipment on the UE itself. Without N3IWF

4. Connection through N3IWF Gateway (bypass gNB)

In a N3IWF-based system, a UE device connects to 5G core THROUGH A GATEWAY (called N3IWF) , without involving gNB.

In this case, a device such as a laptop is connected to the core mobile network through a gateway, which provides connections and necessary protocol conversion.

N3IWF is a gateway between untrusted non-Mobile networks (like public WiFi) and the 5G core.

N3IWF

5. Goals and benefits of N3IWF

There are several reasons for using N3IWF gateway.

  • Enhanced Security: 5G communication is inherently more secure than Wifi (or other Non-3GPP) technologies. This way we can add SECURITY to untrusted networks like WiFi.

  • Low Avialbility of of Mobile Network: Many environments—like homes, offices, factories, rural areas—don’t have great cellular coverage, but Wi-Fi, fixed broadband, or satellite are available.

  • Cost Reduction and Offloading: Cellular spectrum is expensive and limited. Offloading to Wi-Fi saves capacity for users who truly need cellular bandwidth.

  • No Radio Connction Needed: Some devices — such as laptops, tablets, or IoT devices — don’t have cellular radios or SIM modules, so they can’t connect directly to 5G NR (New Radio).

  • Seamless Handover and Mobility: A user walking from outdoors (cellular) into a building (Wi-Fi) should experience no service drop.

6. "Real" vs "Simulated UE" modes

In N3IWF, a device can be connected in either of two modes:

  • Real mode: In real mode, a physical device (phone, tablet, or PC) with proper support acts as the UE, and it connects to the 5G-Core through N3IWF over Wi-Fi.

  • Simulation mode: you don’t need a real phone or device. The software itself pretends to be the UE and tests how it would behave when connecting to a N3IWF gateway. As long as N3IWF gateway is reachable (even without Wifi), we can reach 5G-Core and do experiemnts with 5G-core functions.

N3IWF Real Mode

N3IWF Simulated UE Mode

7. Open5GCore and N3IWF

Open5GCore is a software implementation of the 5G Core network, developed by the Fraunhofer Institute in Germany, which:

- follows 3GPP standards (the official rules of how 5G works)
- implements major 5G Core network functions (like AMF, SMF, UPF, etc.)
- can be used in universities, private networks, or companies testing 5G tech
- Useful in non-3GPP access testing, such as:
    Secure enterprise Wi-Fi + 5G integration
- Open5GCore software includes an N3IWF implementation that supports both simulated UE mode and real UE mode.

  • Open5GCore does not support seamless handover between Wi-Fi (N3IWF) and 5G gNB as a built-in, production-ready feature. Open5GCore does not support seamless handover from simulated UE (N3IWF over Wi-Fi) to a real gNB.

  • We can test the following connections to Open5GCore separately:

    • Connect to Open5GCore over Wi-Fi (N3IWF) — real or simulated UE
    • Connect to Open5GCore over 5G gNB
    • Switch manually between Wi-Fi and 5G (disconnect Wi-Fi, then connect to 5G) — but the IP address will be reset, and the session will not be seamless

8. Summary

  • A 5G network has three major components: UE, gNB, and 5G-Core
  • N3IWF is an alternate method to bypass gNB and connect a UE to 5G-Core using a gateway called N3IWF.
  • The benefits of N3IWF include: Security, availablity of 5G even when signals are not available everywhere (i.e ubiquity), Isolated testing of 5G Core, cost reduction, seamless handover during indoor and outdoors mobility.

  • N3IWF implementations support two modes (either or both)

    • In simulated UE mode, the UE is virtual and runs inside the computer, using a simulated Wi-Fi environment — no real Wi-Fi or physical device is involved. This mode is mainly for easy testing and development.
    • In real UE mode, a real device can connect over actual Wi-Fi by establishing an IPSec tunnel to the N3IWF server, enabling real UE registration and session establishment via Wi-Fi. However, this requires additional setup of IPSec/IKEv2/EAP and proper SIM authentication.

  • Open5GCore is an open-source implementaiton of 5G-Core, that includes N3IWF function as well (alongwith other 5G-Core functions such as AMF, SMF, UPF,...)

  • Open5GCore does not support seamless inter-access handover between Wi-Fi (N3IWF) and 5G gNBaccess as a built-in, production-ready feature. Open5GCore does not support seamless handover from simulated UE (N3IWF over Wi-Fi) to a real gNB.