5G interworking

Non-3GPP Interworking Function (N3IWF)

N3IWF allows devices to connect to the 5G core network with access technologies that do not exist in 3GPP standards.

Examples of accessing the 5G core include:

• Trusted non-3GPP networks: Such as Wi-Fi, where operators can define security settings; access to the 5G core is facilitated through the trusted non-3GPP access network (TNAN).
• Untrusted non-3GPP networks: Such as Wi-Fi, where operators lack control over security settings; access is facilitated through the non-3GPP interworking function (N3IWF). This category also encompasses land mobile radio (LMR) technologies (e.g., TETRA or P25) for mission-critical communications (MCX) and DVB-S2X for television broadcasting.
• Wireline networks: Such as DSL or fiber optic, which represent the underlying technologies in fixed mobile convergence (FMC).

Wi-Fi has the advantage of simplicity, particularly in terms of network access. 5G, on the other hand, is very flexible, especially when it comes to scheduling, security credentials and QoS. The primary goal of non-3GPP access is to combine the advantages of Wi-Fi with those of 5G:

• Wider range of services and use cases
• Efficient traffic offloading for bandwidth-intensive applications
• Seamless mobility and QoS management for enhanced user experience

In the architectural design of 5G networks, devices can connect to the 5G core network functions through a Non-3GPP Interworking Function (N3IWF) or a Trusted Non-3GPP Access Network (TNAN). These functions enable secure access. For example, they can utilize secure IP tunnels for non-access stratum control messages and user plane data. Additionally, signaling procedures are in place to manage access, authentication and mobility scenarios across both access networks, while also leveraging QoS flow control for user plane data.

Access traffic steering, switching and splitting (ATSSS)

ATSSS leverages multi-path connectivity and provides sophisticated mechanisms to support higher and lower layer steering functionalities and modes, which are used in simultaneous connectivity for 3GPP and non-3GPP access.

• Steering: An access network is selected for new dataflow, and the traffic of this data flow is transferred over the selected access network.
• Switching: All ongoing data traffic from one access network is moved to another access network in such a way that the continuity of data flow is maintained.
• Splitting: Data traffic is split across multiple access networks to benefit from access with the purpose of either link aggregation or redundancy

ATSSS can be realized above the IP layer by using the multipath transmission control protocol (MPTCP) or multipath user datagram protocol (MPQUIC). It can also be realized below the IP layer, using the new ATSSS lower layer function for traffic steering, enabling multi-access PDUs. The ATSSS control is handled by the policy control function (PCF) based on the operator-defined ATSSS rules (multi-access rules MAR) and a performance measurement function (PMF) at user equipment (UE) and network side.

Your cellular and Wi-Fi interworking testing challenges

Key test challenges for successful interworking between 3GPP and non-3GPP networks include:

• Testing radio access technologies in signaling mode
• Testing interworking and mobility functions
• Application test of relevant audio and video services
• Testing device functionalities under different aspects, such as functional compliance, quality of experience (QoE) or power consumption
• Performance testing, i.e., evaluation of key performance indicators (KPI)
• Enhanced troubleshooting, i.e., detailed analysis of signaling flow and layer 3 message exchanges between UE and network

This requires a test setup that supports the full range of radio access technologies.

High-performance solutions for cellular and Wi-Fi interworking testing

For decades, Rohde & Schwarz has offered test solutions for Wi-Fi and cellular convergence. An example of this is our well-established WLAN traffic offload in LTE test solution.

Our cellular and WLAN interworking test solution was initially based on the R&S®CMW500 mobile radio tester. With the advent of 5G and Wi-Fi 7, the solution is now fully supported by the R&S®CMX500 5G one-box signaling tester.

The R&S®CMX500 supports an inbuilt fading module and allows user-specific configuration of IP impairments, such as data loss or data disordering. With its sophisticated message analyzer view, users can enter signaling flow details and user tools like filters, breakpoints or layered views for deep dive troubleshooting. This one-box tester simultaneously supports WLAN and 5G for sophisticated protocol procedure analysis and RF testing. It also includes a data application until for end-to-end data application testing.

The test setup offers an integrated N3IWF function for testing seamless connectivity transfer between Wi-Fi and 5G. For enhanced application and quality of service (QoS) analysis, the throughput can be measured in the IP layer. An integrated management system (IMS) server enables the transfer from voice over NR (VoNR) to Wi-Fi voice call. It also performs audio quality analysis with the PoLQA algorithm.