Pushing the Boundaries of Scalable 5G Core Networks: Cloud-Native NEF and CAPIF Interplay

The advent of Cloud-Native principles and architectures stands as a beacon of innovation in the design of the next generation of 5G/6G, promising a transition from initial (disaggregated) 5G Service-Based Architectures (SBA) implemen-tations capable of running on the cloud to a truly distributed and scalable Cloud-Native 6G. However, the incumbent components and interfaces of the 5G core (5GC) pose barriers to the seamless integration of microservices. Challenges range from intricate Network Functions (NF) interdependencies to interface constraints and the absence of an event-driven architecture, which might jeopardise efficient microservice communication. This paper discusses the interplay between the Network Exposure Function (NEF) and the Common API Framework (CAPIF), defined by 3GPP, to standardize how network APIs are discovered, exposed, and consumed. First, we propose a novel microservice and eventdriven Network Exposure Function (MNEF) built upon the NEF standard, featuring CAPIF support and various purpose-built microservices. Then, we evaluate its interoperability with reference implementations of 5GC (Open5GS) and CAPIF (OpenCAPIF) and its performance and scalability for handling large-scale request scenarios. The results attest to the MNEF's benefits and interoperability with compliant 5GC implementations. Despite an additional (expected) overhead in communications, MNEF fulfils its purpose as defined in the 5G architecture, acting as an interface between external parties and 5G core NFs. Moreover, the proposed MNEF presents itself as a design solution that pushes the scalable 5G communication boundaries.