The role of the Network Exposure Function (NEF) in the 5GASP Project

The landscape of 5G technology is witnessing a transformative era. One of the 5G Network Function propelling it, is the Network Exposure Function (NEF). This key element provides interfaces that make it possible for a Network Application to interact with the 5G network, and even request specific network configurations. Therefore, it paves the way for groundbreaking applications in the 5G domain.

This blogpost explores the NEF, its APIs, and its pivotal role of the 5GASP project, where we harness the power of NEFSim, an innovation by EVOLVED-5G, to validate and certify 5G Network Applications.

NEF’s Key Benefits

NEF offers several significant advantages:

  • Elevated Network Customization: NEF allows for the integration of network features with external service providers, promoting a network ecosystem that is both open and customizable.
  • Assured API Security: It ensures the secure exposure of 5G network functionalities and services.
  • Adaptability and Alignment: NEF guarantees adaptability and alignment with the 5G Core, enabling seamless interactions across various network functionalities.
  • Varied Application Spectrum: NEF can be relied upon by a plethora of applications, ranging from throughput-centric services to specialized industry applications, such as the automotive ones, showcasing its versatility.

NEF’s API Suite:

NEF introduces a suite of APIs, each designed for specific functions. Bellow, we briefly present some of these APIs.

  • EventMonitoring: Delivers insights into the connectivity, availability, and location status of User Equipment (UE).
  • MoLcsNotify: Alerts applications regarding the UE’s geographical position.
  • AsSessionWithQoS: Enables session establishment with predefined Quality of Service parameters.
  • ChargeableParty: Enables applications to notify the network about traffic flow sponsorship.
  • PfdManagement: Allows applications to contribute Packet Flow Descriptors for traffic identification and policy implementation.
  • ResourceManagementOfBdt: Assists external applications in conveying data transfer prerequisites to the 5G network for policy creation.


NEFSim [1] is an open-source simulator that allows for developers to experiment with 5G’s Network Exposure Function (NEF). It bridges the gap between mobile operators and service providers, offering a platform for testing 5G network capabilities. Its key features include an interactive environment for creating network scenarios, support for monitoring events and session management with QoS, and user authentication. This simulator was developed under the EVOLVED-5G project ( and later extended in the scope of the 5GASP project, where it is currently employed in 5GASP’s Network Application testing and certification processes. The recent developments in the 5GASP project resulted in the addition of several northbound APIs. Currently, the last version of NEFSim offers the following northbound APIS:

Northbound APIStandardSTUB vs Relies on Simulation Layer
Events Monitoring29.122 – 17.8.0Relies on simulation layer
Session establishment with Quality of Service (QoS)29.122 – 17.8.0May rely on simulation layer
Resource Management of Background Data Transfer (BDT)29.122 – 17.8.0STUB
Chargeable Party29.122 – 17.8.0STUB
Network Status Reporting29.122 – 17.8.0May rely on simulation layer
Communication Patterns (CP) Parameters Provisioning29.122 – 17.8.0STUB
Network Parameter Configuration29.122 – 17.8.0STUB
RACS (Radio Capability Signaling) Parameter Provisioning29.122 – 17.8.0STUB
Traffic Influence29.122 – 17.8.0STUB
Analytics Exposure29.122 – 17.8.0May rely on simulation layer

5GASP’s Integration with NEFSim

The 5GASP project relies on NEFSim to validate the interaction of Network Applications with the NEF. This is made possible since:

  • NEFSim replicates real-world NEF responses, offering an authentic test environment.
  • NEFSim can be relied upon to evaluate the capability of Network Applications to engage with NEF APIs, verifying accurate endpoint communication.
  • NEFSim aids in creating NEF response models, contributing to the validation process of Network Applications.

To monitor the interaction of Network Applications with NEFSim, an additional component was developed by 5GASP: the Report API. The Report API enables the monitoring and recording of all operations invoked in NEFSim and produces a detailed report listing them. This report can be later evaluated to verify if a Network Application is able to correctly interact with a 5G NEF. The flow of this testing and certification process can be observed in the diagram below.

5GASP’s NEF-related Tests

As previously stated, 5GASP evaluates the capability of a Network Application to interact with a 5G NEF. To this end, a collection of NEF-related tests is currently being developed by 5GASP. Among these tests, we may highlight the following:

Test CaseTest Description
Authentication with 5GSThis test validatea the authentication and authorization of a Network Application to use 5GS resources (NEF)
Acquisition of UE locationThis test validates that a Network Application is able to retrieve an indicative UE location
Acquisition of UE handover eventThis test validates that a Network Application is able to subscribe and eventually retrieve information about an indicative UE handover event (servicing cell switch)
Acquisition of UE Received Signal Strength Indicator (RSSI) informationThis test validates that a Network Application is able to retrieve indicative information about RSSI
Acquisition of UE path lossThis test validates that a Network Application is able to retrieve indicative information about the UE RSSI subtracted from the respective radio node transmitted (path loss)


[1] D. Fragkos, G. Makropoulos, A. Gogos, H. Koumaras and A. Kaloxylos, “NEFSim: An open experimentation framework utilizing 3GPP’s exposure services,” 2022 Joint European Conference on Networks and Communications & 6G Summit (EuCNC/6G Summit), Grenoble, France, 2022, pp. 303-308, doi: 10.1109/EuCNC/6GSummit54941.2022.9815829.